MICROBIAL DYNAMICS IN SALT AFFECTED SOILSprr.hec.gov.pk/jspui/bitstream/123456789/1289/1/2039S.pdfmicrobial dynamics in salt affected soils by syed asif shah doctor of philosophy (ph.d)

MICROBIAL DYNAMICS IN SALT AFFECTED SOILS

BY

SYED ASIF SHAH

DOCTOR OF PHILOSOPHY (Ph.D) IN AGRICULTURE (SOIL & ENVIRONMENTAL SCIENCES)

DEPARTMENT OF SOIL AND ENVIRONMENTAL SCIENCES, FACULTY OF CROP PRODUCTION SCIENCES,

THE UNIVERSITY OF AGRICULTURE, PESHAWAR, PAKISTAN

NOVEMBER, 2013

MICROBIAL DYNAMICS IN SALT AFFECTED SOILS

BY

SYED ASIF SHAH

A Thesis Submitted to The University of Agriculture, Peshawar in Partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY (Ph.D) IN AGRICULTURE (SOIL & ENVIRONMENTAL SCIENCES)

APPROVED BY: _________________________________ Prof. Dr. Zahir Shah Dept. of Soil and Environmental Sciences

Chairman Supervisory Committee

_________________________________ Prof. Dr. Muhammad Jamal Khan Dept. of Soil and Environmental Sciences

Member (Major)

_________________________________ Prof. Dr. Muhammad Tariq Jan Dept. of Agronomy

Member (Minor)

_________________________________ Prof. Dr. Zahir Shah Dept. of Soil and Environmental Sciences

Convener Board of Studies

_________________________________ Prof. Dr. Zahoor Ahmed Swati

Dean, Faculty of Crop Production Sciences

_________________________________ Prof. Dr. Farhatullah

Director Advanced Studies and Research

DEPARTMENT OF SOIL AND ENVIRONMENTAL SCIENCES FACULTY OF CROP PRODUCTION SCIENCES,

THE UNIVERSITY OF AGRICULTURE, PESHAWAR, PAKISTAN NOVEMBER, 2013

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TABLE OF CONTENTS

No. Title Page #

LIST OF TABLES .................................................................................................. VI

LIST OF FIGURES .................................................................................................. X

ABSTRACT ......................................................................................................... XIII

1 GENERAL INTRODUCTION ........................................................................ 1

2 OBJECTIVES .................................................................................................... 4

2.1 MAIN OBJECTIVE .............................................................................................. 4

2.2 SPECIFIC OBJECTIVES ........................................................................................ 4

3 REVIEW OF LITERATURE ........................................................................... 5

3.1 SALT AFFECTED SOILS ..................................................................................... 5

3.2 EXTENT OF SALINITY ........................................................................................ 5

3.3 CATEGORIES OF SALT-AFFECTED SOILS ........................................................... 6

3.4 EFFECT OF SALTS ON SOILS .............................................................................. 8

3.5 EFFECT OF SALTS ON PLANTS ........................................................................... 9

3.6 SALT-AFFECTED SOILS RECLAMATION ........................................................... 10

3.6.1 Pressmud ............................................................................................... 11

3.6.2 Gypsum .................................................................................................. 12

3.6.3 Farmyard manure .................................................................................. 13

3.7 EFFECT OF SALTS ON SOIL MICROBIAL PROPERTIES ....................................... 13

3.8 MICROBIAL INOCULATION .............................................................................. 14

3.9 ROLE OF MICROBES IN RECLAMATION OF SALT-AFFECTED SOIL .................... 15

4 MATERIALS AND METHODS .................................................................... 17

4.1 SITE CHARACTERISTICS .................................................................................. 17

4.2 SOIL SAMPLING AND PROCESSING .................................................................. 22

4.3 PROPOSED EXPERIMENTS ............................................................................... 22

4.3.1 Microbiological properties of native salt affected soils ........................ 23

4.3.2 Effect of NaCl induced salinity on CO2 evolution and N mineralization

in silty clay loam soil ......................................................................................... 23

ii

4.3.3 Effect of MgCl2 induced salinity on CO2 evolution and N mineralization

in a silty clay loam soil ...................................................................................... 24

4.3.4 Comparative effect of pressmud, gypsum, farmyard manure and

microbial inoculations on soil microbial biomass and activity in saline sodic

soil 25

4.4 LABORATORY ANALYSIS ................................................................................ 25

4.4.1 Microbial biomass C and N ................................................................... 26

4.4.1.1 Fumigation ..................................................................................... 26

4.4.1.2 Inoculations ................................................................................... 26

4.4.1.3 Measurements of CO2 evolution ................................................... 26

4.4.1.4 Calculation of biomass C ............................................................... 27

4.4.1.5 Calculation of biomass N .............................................................. 27

4.4.2 Determination of total mineral N .......................................................... 28

4.4.3 Mineralizable N (mg N kg-1 soil) ........................................................... 28

4.4.4 Total N ................................................................................................... 28

4.4.5 Preparation of microbial inoculants of salt tolerant microorganisms .. 29

4.4.5.1 Isolation and culture of salt tolerant microorganisms ................... 29

4.4.5.2 Inoculation of soil with desired number of salt tolerant

microorganisms ............................................................................................. 29

4.4.5.3 Preparation of nutrient agar media ................................................ 30

4.4.5.4 Preparation of peptone glucose acid agar media ........................... 30

4.4.6 Measurement of gypsum requirements .................................................. 30

4.4.7 Saturation moisture percentage/saturation extracts ............................. 31

4.4.8 Sodium ................................................................................................... 31

4.4.9 Calcium and magnesium ....................................................................... 31

4.4.10 Carbonates and bicarbonates ............................................................ 31

4.4.11 Chloride ............................................................................................. 32

4.4.12 Sodium adsorption ratio (SAR) ......................................................... 32

4.4.13 Exchangeable sodium percentage ..................................................... 32

4.4.14 pH ...................................................................................................... 33

4.4.15 Electrical conductivity ....................................................................... 33

4.4.16 Lime content ...................................................................................... 33

4.4.17 Organic matter .................................................................................. 33

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4.4.18 Soil texture ......................................................................................... 34

4.5 STATISTICAL ANALYSIS .................................................................................. 34

5 RESULTS AND DISCUSSION ...................................................................... 35

5.1 MICROBIAL BIOMASS AND ACTIVITY IN NATIVE SALT AFFECTED

SOIL ...................................................................................................................... 35

5.1.1 Soil chemical characteristics ................................................................. 35

5.1.2 Soil microbial characteristics ................................................................ 37

5.1.2.1 Effect of soil EC on microbiological parameters .......................... 37

5.1.2.1.1 Microbial biomass carbon ........................................................ 37

5.1.2.1.2 Microbial biomass nitrogen ..................................................... 38

5.1.2.1.3 Microbial biomass C/N ratio ................................................... 38

5.1.2.1.4 Nitrogen mineralization ........................................................... 41

5.1.2.1.5 Nitrification .............................................................................. 43

5.1.2.1.6 Rate of soil respiration ............................................................. 43

5.1.2.1.7 Cumulative CO2 production .................................................... 45

5.1.2.2 Effect of soil pH on microbial indices ........................................... 48

5.1.2.2.1 Microbial biomass carbon ........................................................ 48

5.1.2.2.2 Microbial biomass nitrogen ..................................................... 48

5.1.2.2.3 Microbial biomass C/N ratio ................................................... 50

5.1.2.2.4 Nitrogen mineralization ........................................................... 52

5.1.2.2.5 Nitrification .............................................................................. 52

5.1.2.2.6 Rate of soil respiration ............................................................. 54

5.1.2.2.7 Cumulative CO2 production .................................................... 54

5.1.2.3 Correlation coefficient of microbial indices with sodium ............. 58

5.1.2.4 Correlation coefficient of microbial indices with sodium

adsorption ratio .............................................................................................. 66

5.1.2.5 Correlation coefficient of microbial indices with soluble salts of

calcium and magnesium ................................................................................ 74

5.1.2.6 Correlation coefficient of microbial indices with soil carbonates . 81

5.1.2.7 Correlation coefficient of microbial indices with soil bicarbonates

88

5.1.2.8 Correlation coefficient of microbial indices with soil chloride ..... 95

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5.2 EFFECT OF NACL INDUCED SALINITY ON CO2 EVOLUTION AND N

MINERALIZATION IN A SILTY CLAY LOAM SOIL .................................... 103

5.2.1 Introduction ......................................................................................... 103

5.2.2 Materials and methods ........................................................................ 103

5.2.2.1 Experimental site ......................................................................... 104

5.2.2.2 Soil sampling and processing ...................................................... 104

5.2.2.3 Treatment arrangements .............................................................. 104

5.2.2.4 Incubation experiment ................................................................. 104

5.2.3 Soil chemical characteristics ............................................................... 105

5.2.4 Results and Discussion ........................................................................ 105

5.2.4.1 Rate of soil respiration ................................................................. 105

5.2.4.2 Cumulative CO2 evolution .......................................................... 106

5.2.4.3 Nitrogen mineralization ............................................................... 108

5.3 EFFECT OF MGCL2 INDUCED SALINITY ON CO2EVOLUTION AND N

MINERALIZATION IN A SILTY LOAM SOIL................................................ 112

5.3.1 Introduction ......................................................................................... 112


5.3.2.1 Site characteristics ....................................................................... 113



5.3.2.4 Treatment arrangements .............................................................. 113


5.3.3 Results and Discussions....................................................................... 114


5.3.3.2 Cumulative CO2 production ........................................................ 117

5.3.3.3 Nitrogen mineralization ............................................................... 119

5.4 COMPARATIVE EFFECT OF PRESSMUD, GYPSUM, FARMYARD

MANURE AND MICROBIAL INOCULATIONS ON SOIL MICROBIAL

BIOMASS AND ACTIVITY IN SALINE SODIC SOIL .................................... 122

5.4.1 Introduction ......................................................................................... 122




v

5.4.2.3 Treatments and experimental design ........................................... 123


5.4.3 Results and Discussion ........................................................................ 124


5.4.3.2 Microbial biomass C .................................................................... 125

5.4.3.3 Microbial biomass N ................................................................... 126

5.4.3.4 Microbial biomass C/N ratio ....................................................... 127

5.4.3.5 Ammonification ........................................................................... 128

5.4.3.6 Nitrification ................................................................................. 128

5.4.3.7 Net N mineralization ................................................................... 130

5.4.3.8 Crop response to amendments ..................................................... 131

6 SUMMARY .................................................................................................... 133

7 CONCLUSIONS AND RECOMMENDATIONS ...................................... 136

8 LITERATURE CITED ................................................................................. 137

9 APPENDICES ................................................................................................ 157

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List of Tables

No. Title Page #

Table 4.1: Meteorological data of Peshawar during 1973-2002. 21

Table 5.1: Chemical characteristics of soils (0-20cm) used in the study 36

Table 5.2: Correlation coefficient of soil EC with MBC, MBN, MB C/N ratio and

Nitrification 39

Table 5.3: Microbiological properties of soils (0-20cm) as affected by EC levels 39

Table 5.4: Rate of soil respiration in response to varying salinity levels during

different incubation periods 44

Table 5.5: Cumulative CO2 production in response to varying salinity levels during


Table 5.6: Correlation coefficient of soil pH with MBC, MBN, MB C/N ratio and

Nitrification 49

Table 5.7: Microbial biomass C, N, Microbial biomass C/N ratio, N-mineralization

and Nitrification as affected by soil pH 49

Table 5.8: Effect of soil pH on soil respiration rate at different incubation periods 55

Table 5.9: Effect of soil pH on cumulative CO2 production 57

Table 5.10: Correlation coefficient of Na with MBC, MBN, MB C/N ratio and

Nitrification 59

Table 5.11: Microbial biomass C, N, N-mineralization, Microbial biomass C/N ratio

and Nitrification as influenced by soluble Na 59

Table 5.12: Effect of soil Na concentration on rate of respiration during different

incubation periods 63

Table 5.13: Cumulative CO2 production as influenced by soluble Na content 65

Table 5.14: Correlation coefficient of SAR with MBC, MBN, MB C/N ratio and

Nitrification 67

Table 5.15: Microbial biomass C, N, Microbial biomass C/N ratio, N-Mineralization

and Nitrification as influenced by soil SAR 67

Table 5.16: Rate of soil respiration as affected by SAR during different incubation

periods 71

Table 5.17: Cumulative CO2 production as affected by soil SAR 73

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Table 5.18: Correlation coefficient of Ca+Mg with MBC, MBN, MB C/N ratio,

nitrification and CO2 production 75

Table 5.19: Microbial biomass C, N, Microbial biomass C/N ratio, N-miniralizaion

and Nitrification with different soil Ca+Mg contents 75

Table 5.20: Rate of soil respiration as affected by soluble calcium and magnesium

content during different incubation periods 79

Table 5.21: Cumulative CO2 productions (mg kg-1) as influenced by soluble Ca+Mg

contents 80

Table 5.22: Correlation coefficient of MBC, MBN, MB C/N ratio, Nitrification and

CO2 production with soil carbonates content 82

Table 5.23: Microbial biomass C, N, N-Mineralization, Microbial biomass C/N ratio

and Nitrification as influenced with soluble carbonates 82

Table 5.24: Rate of soil respiration influenced by soluble carbonates during different


Table 5.25: Cumulative CO2 production as influenced by soluble carbonates content

87


CO2 production with soil bicarbonates content 89

Table 5.27: Microbiological properties of soils as affected by soluble HCO3- content

89

Table 5.28: Rate of soil respiration influenced with bi-carbonate contents during


Table 5.29: Cumulative CO2 production as influenced with bicarbonates content

during different incubation periods 94


CO2 production with soil chloride content 96

Table 5.31: Microbiological properties of soils as affected by soil chloride content 96

Table 5.32: Rate of soil respiration in response to varying chloride concentrations

during different incubation periods 100

Table 5.33: Cumulative CO2 production as influenced by chloride contents during


Table 5.34: Some properties of the soil (0-20 cm) used in the experiment 105

viii

Table 5.35: Rate of soil respiration as influenced by NaCl induced salinity during


Table 5.36: Cumulative CO2 production during 40 days of incubation periods as

influenced by NaCl induced salinity 109

Table 5.37: N-mineralization as influenced by NaCl induced salinity during different


Table 5.38: Some properties of the soil (0-20 cm) used in the experiment 113

Table 5.39: Rate of soil respiration in induced MgCl2 treated soils during different


Table 5.40: Cumulative CO2 production (mg kg-1) during different incubation

periods as influenced by MgCl2 induced salinity 118

Table 5.41: N-mineralization during different incubation periods as influenced by

MgCl2 induced salinity 121

Table 5.42: Chemical characteristics of Pressmud collected from Khazana Sugar

Mill, Peshawar 124

Table 5.43: Chemical Characteristics of Farmyard manure collected from University

of Agriculture KPK Research Farm. 124

Table 5.44: Microbial activity (CO2 evolution), MBC, MBN, Microbial biomass

C/N, Ammonification, Nitrification and N mineralization in silt loam saline

sodic soil treated with G, PM and FYM alone or in various combinations 129

Table 5.45: Percent change in microbial indices with different amendments 129

Table 9.1: ANOVA [CR design] showing F values for rate of soil respiration in

response to NaCl induced salinity during different incubation periods 157

Table 9.2: 2-factors ANOVA [CR design] showing F values for Cumulative CO2

production during 40 days of incubation in response to various levels of

NaCl induced salinity 157

Table 9.3: ANOVA [CR design] showing F values for N-mineralization during 40

days of incubation period with induced NaCl salinity 157

Table 9.4: ANOVA [CR design] showing F values for rate of soil respiration in

induced MgCl2 treated soils during different incubation periods 157

Table 9.5: ANOVA [CR design] showing F values for Cumulative CO2 production

in soil with induced MgCl2 salt 157

ix

Table 9.6: 2-factors ANOVA [CR design] showing F values for N-mineralization

during different incubation periods in MgCl2 induced salinity 158

Table 9.7: ANOVA [CR design] showing F values for CO2 evolution, MBC, MBN,

Microbial biomass C/N, Ammonification, Nitrification and N mineralization

in silt loam saline sodic soil treated with G, PM and FYM alone or in various

combinations 158

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List of Figures

No. Title Page # Figure 4.1 Map of district Charsadda and Mardan, showing the sampling area for

salt-affected soils. .......................................................................................... 19

Figure 4.2 Map of district Peshawar, showing Agricultural University Peshawar

Research Farm Malkandher. .......................................................................... 20

Figure 4.3: Meteorological data of Peshawar, Charsadda and Mardan districts during

1973-2002. ..................................................................................................... 21


1973-2002. ..................................................................................................... 21

Figure 5.1: Polynomial Regression of soil MBC with electrical conductivity .......... 40

Figure 5.2: Polynomial Regression of soil MBN with electrical conductivity ......... 40

Figure 5.3: Polynomial Regression of soil MB C/N ratio with electrical conductivity

....................................................................................................................... 42

Figure 5.4: Polynomial Regression of soil N mineralization with electrical

conductivity ................................................................................................... 42

Figure 5.5: Polynomial Regression of soil nitrification with electrical conductivity 42

Figure 5.6: Influence of salinity on soil respiration during 10 days of incubation

period ............................................................................................................. 44

Figure 5.7: Salinity effect on cumulative CO2 production during 10 days of

incubation period ........................................................................................... 47

Figure 5.8: Simple Regression of MBC with soil pH ............................................... 51

Figure 5.9: Simple Regression of MBN with soil pH ............................................... 51

Figure 5.10: Simple Regression of MB C/N ratio with soil pH ................................ 53

Figure 5.11: Simple Regression of N mineralization with soil pH ........................... 53

Figure 5.12: Simple Regression of Nitrification with soil pH ................................... 53

Figure 5.13: Effect of soil pH on soil respiration rate measured during 10 days of

incubation period ........................................................................................... 55

Figure 5.14: Effect of soil pH on cumulative CO2 production .................................. 57

Figure 5.15: Simple Regression of Na content on MBC ........................................... 60

Figure 5.16: Polynomial Regression of Na content on MBN ................................... 60

Figure 5.17: Simple Regression of Na content on microbial biomass C/N ratio ...... 62

xi

Figure 5.18: Simple Regression of Na content on N mineralization ......................... 62

Figure 5.19: Polynomial Regression of Na content on nitrification .......................... 62

Figure 5.20: Effect of soluble Na on rate of soil respiration during different

incubation periods ......................................................................................... 63

Figure 5.21: Soluble Na effect on cumulative CO2 production during different


Figure 5.22: Simple Regression of MBC with soil SAR ........................................... 67

Figure 5.23: Polynomial Regression of MBN with soil SAR ................................... 68

Figure 5.24: Polynomial Regression of MB C/N ratio with soil SAR ...................... 68

Figure 5.25: Polynomial Regression of N mineralization with soil SAR ................. 70

Figure 5.26: Polynomial Regression of Nitrification with soil SAR ......................... 70

Figure 5.27: Effect of SAR on soil respiration rate measured during different


Figure 5.28: SAR effect on cumulative CO2 production during different incubation

periods ........................................................................................................... 73

Figure 5.29: Simple Regression of MBC with soluble salts of Ca+Mg .................... 75

Figure 5.30: Simple Regression of MBN with soluble salts of Ca+Mg .................... 76

Figure 5.31: Simple Regression of MB C/N ratio with soluble salts of Ca+Mg ....... 76

Figure 5.32: Simple Regression of N mineralization with soluble salts of Ca+Mg .. 78

Figure 5.33: Simple Regression of nitrification with soluble salts of Ca+Mg .......... 78

Figure 5.34: Relationship of soil respiration rate with soluble salts of Ca+Mg during

different incubation periods ........................................................................... 79

Figure 5.35: Relationship of cumulative CO2 production with soluble salts of

Ca+Mg during different incubation periods .................................................. 80

Figure 5.36: Simple Regression of soil carbonates content on MBC ........................ 83

Figure 5.37: Simple Regression of soil carbonates content on MBN ....................... 83

Figure 5.38: Simple Regression t of soil carbonates content on MB C/N ratio ........ 85

Figure 5.39: Simple Regression of soil carbonates content on N mineralization ..... 85

Figure 5.40: Simple Regression of soil carbonates content on nitrification .............. 85

Figure 5.41: Effect of soil carbonates content on rate of soil respiration .................. 86

Figure 5.42: Effect of soil carbonates content on cumulative CO2 production ......... 87

Figure 5.43: Simple Regression of soil bicarbonates content on MBC .................... 90

Figure 5.44: Polynomial Regression of soil bicarbonates content on MBN ............. 90

xii

Figure 5.45: Simple Regression of soil bicarbonates content on MB C/N ratio ....... 92

Figure 5.46: Simple Regression of soil bicarbonates content on N mineralization .. 92

Figure 5.47: Simple Regression of soil bicarbonates content on nitrification .......... 92

Figure 5.48: Effect of soil bicarbonates content on rate of soil respiration .............. 93

Figure 5.49: Effect of soil bicarbonates content on cumulative CO2 production ...... 94

Figure 5.50: Simple Regression of soil chloride content on MBC ............................ 97

Figure 5.51: Polynomial Regression of soil chloride content on MBN .................... 97

Figure 5.52: Simple Regression of soil chloride content on MB C/N ratio .............. 99

Figure 5.53: Polynomial Regression of soil chloride content on N mineralization .. 99

Figure 5.54: Simple Regression of soil chloride content on nitrification .................. 99

Figure 5.55: Effect of soil chloride content on rate of soil respiration .................... 100

Figure 5.56: Effect of soil chloride content on cumulative CO2 production ........... 101

Figure 5.57: Rate of CO2 evolution as influenced by NaCl induced salinity .......... 107

Figure 5.58: Cumulative CO2 production as influenced by induced NaCl salinity . 109

Figure 5.59: N mineralization (mg kg-1) as influenced by induced NaCl salinity .. 111

Figure 5.60: Rate of soil respiration as influenced by MgCl2 induced salinity ....... 116

Figure 5.61: Cumulative CO2 production as influenced by MgCl2 induced salinity

..................................................................................................................... 118

Figure 5.62: N mineralization as influenced by MgCl2 induced salinity ................ 121

Figure 5.63: CO2 evolution as affected by different soil amendments in saline sodic

soil ............................................................................................................... 132

Figure 5.64: MBC as affected by different soil amendments in saline sodic soil ... 132

Figure 5.65: MBN, MB C/N ratio, Ammonification, Nitrification and net N

mineralization as affected by different soil amendments in saline sodic soil

..................................................................................................................... 132

xiii

Microbial Dynamics in Salt Affected Soils Syed Asif Shah and Zahir Shah

Department of Soil and Environmental Sciences, The University of Agriculture, Peshawar

Abstract

Soil salinity is a worldwide problem which not only influences the physical and

chemical properties of soil but may also seriously affect the microbiological

properties of soil. This project was undertaken to assess the behavior of various

microbiological properties of soil in relation to salinity in a series of incubation and

pot experiments during 2009-12. Initially the soil microbiological properties of

thirty naturally occurring diverse salt affected soils were determined. Based on the

results of preliminary experiments, further experiments were conducted to evaluate

the effect of NaCl and MgCl2 induced salinity on N dynamics and soil microbial

activity in soil. Finally, a pot experiment was conducted to assess the effect of

important amendments such as pressmud, gypsum and farmyard manure, which are

normally used for the reclamation of salt affected soils, on growth of wheat and

maize and on various microbial attributes in a highly saline-sodic soil (EC 20.3 dS

m-1). In addition, some bacteria and fungi were isolated from a highly saline-sodic

soil, and the effects of same organisms were also tested in the above experiment.

For experiment 1, soil samples at 0-20 cm were collected from various salt affected

soils ranged in salinity from EC < 4.0 to 32 dS m-1 in November 2009. The samples

were analyzed for soil microbiological (such as microbial biomass-C, microbial

biomass-N, N mineralization, nitrification, rate of soil respiration) and chemical

properties (such as pH, EC, soluble Ca+Mg, soluble Na, SAR (sodium adsorption

ratio), ESP (exchangeable sodium percentage), carbonates, bicarbonates, chloride).

The results showed that almost all microbial indices including microbial biomass-C

(MBC), microbial biomass-N (MBN), basal soil respiration, nitrification and net N

mineralization were negatively correlated with increasing salinity (r = -0.89, -0.74, -

0.79, -0.64 and -0.57 respectively). The results further showed that the depressive

effects of SAR and ESP on various soil microbial indices were much stronger than

that of carbonates and bicarbonates. Both NaCl and MgCl2 induced salinity

significantly reduced the rate of CO2 evolution and N mineralization during all

xiv

incubation periods. The depressive effects increased with increase in salts level. The

NaCl induced salinity depressed cumulative CO2 production by about 80% and N

mineralization by 50% during 40 days of incubation. Whereas MgCl2 induced

salinity decreased cumulative CO2 production by 95% and N mineralization by 81%

during 30 days of incubation. These results suggested that the impact of MgCl2

salinity on microbial indices was stronger than that of NaCl.

The amendment of saline-sodic soil with pressmud, gypsum and farmyard manure

(FYM) significantly improved the rate of CO2 evolution, N mineralization,

microbial biomass-C and microbial biomass-N. The effects were more pronounced

with combined application of pressmud with farmyard manure or gypsum. It was

also evident that the effect of pressmud + FYM was further improved with microbial

inoculation of microbial isolation from highly salt affected soil. Organic matter

decomposition generally increases the production of CO2 and liberation of H+ ions.

The H+ ion enhance the dissolution of CaCO3 and releases more Ca to replace Na

from clay particles and thus helps in the reclamation of saline-sodic soils. Both

wheat and maize seeds failed to germinate under the prevailing saline-sodic

conditions despite repeated re-seeding and thus no data was generated in this

respect. These results suggested that all microbial indices decreased significantly

with increasing salinity levels indicating that soil microorganisms were sensitive to

different types of salinity. Thus, salinity is a stress factor and can reduce microbial

diversity and control microbial abundance, composition and functions. Although,

amendments of saline-sodic soil with organic sources (such as FYM, pressmud)

substantially improved microbial attributes they did not enable the germination and

survival of wheat and maize sown in the soil. Nevertheless the evidence suggests

that organic matter may play significant role in the amelioration of saline-sodic or

sodic soils.

1

1 GENERAL INTRODUCTION

Salt-affected soils include saline soils, sodic soils or both saline-sodic soils that

interfere with the growth of normal plants. Approximately 10% of the total land

surface (954 million hectares) in the world is affected with different types of salinity

(Alam et al., 2000). In Pakistan nearly 5.7 m ha of land is salt affected, mainly in

Indus plain, where about 4.2 m ha of land is affected by water-logging and salinity,

0.12 m ha falling in the canal commanded area, while 4.45 m ha outside it. Of all the

salinized lands 1.9 m ha are saline, 2.91 m ha are saline-sodic and 0.028 m ha sodic

(Mujtaba et al., 2003).

Salt-affected soils are mostly found in arid landscapes where, most of the year

evapotranspiration exceeds precipitation (Jurinak, 1990). Generally, high

evapotranspiration in semi-arid and arid zones like in Pakistan is the basic cause for

salt accumulation. In Pakistan, the temperature reaches 40°C during summer and is

as low as 2°C to 5°C in winter. The annual precipitation varies from 100-700 mm

throughout the country. The high temperature and low precipitation plus shallow

ground water depth, enhances the accumulation of salts in the upper soil surface.

Other conditions that enhance salt concentration in soil includes improper irrigation

practices and lack of drainage which adds about 120 million tons of salts in canal

irrigated land and brackish underground water in which only 20% salt finds its ways

to the sea.

The presence of excess salts in soils influence crop growth through adverse

physiological effects (Osmotic stress or ion toxicity) and high sodium degrades its

physical structure (decreased adsorption of essential nutrients) (Richards, 1954;

Lauchli and Epstein, 1990; Rhoades, 1990; Shainberg, 1990). The excess amounts

of salts adversely affect soil biological processes including soil enzymes activity, N

mineralization, soil microbial biomass carbon and nitrogen (Frankenberger and

Bingham, 1982; McClung and Frankenberger, 1985; Sarig and Steinberger, 1994).

Salinity and sodicity has detrimental effect on soil microbial activity. Many studies

have shown a decrease in soil respiration with elevated salinity (Sardinha et al.,

2003; Wichern et al., 2006; Yuan et al., 2007). In another study Sardinha et al.

2

(2003) found that the combined effects of salinity and acidity depressed microbial

communities more than those of heavy-metal pollution in acidic conditions. They

attributed this to the possibility that a decline in vegetation reduces the root and litter

debris, which is an important energy resource for microbial organisms.

The rate of mineralization from added straw decreased with salinity and sodicity

early in the incubation Abdou et al. (1975). Salinity influenced soil mineralization

negatively (Wichern et al., 2006). Laura (1974) and Carter (1986) respectively

examined that soil respiration and microbial biomass both reduced with salinity.

Similar depressive effect on soil microbial activity due to saline irrigation was found

by Sarig et al. (1993). Negative effects on soils biological and biochemical fertility

were found by the addition of saline solution by Garcia and Hernandez, (1996).

Similar results were found in literature (Singh et al., 1969; Agarwal et al., 1971Ryan

and Sims, 1974;). Increases in salinity decrease the rate of soil respiration and the

soil microbial biomass (Laura 1973; Laura 1976; Pathak and Rao, 1998). Batra and

Manna (1997) stated that salt stress reduces microbial population due to osmotic

potential changes. Increasing sodicity levels showed depressive effect on C

mineralization (Nelson et al., 1997) and causes a decrease for biomass C (Chander

et al., 1994).

The salt affected soils can be reclaimed through physical, chemical and biological

methods (Ahmad and Qadir, 1995; Qadir et al., 2007). The salt affected soil can also

be reclaimed through biological means. Increasing microbial population of exo-

polysaccharides producing bacteria reduces the availability of Na+ for plant uptake

by binding the sodium ion, and thus help in reducing salt stress under saline

conditions. Selected exo-polysaccharides producing bacteria could be used for

salinity stress reduction in saline soils (Ashraf et al., 2004). Fungal inoculation can

cause water stable aggregates to form and thereby open up air spaces that contribute

to improve soil structure. As a result of these amendments, over time the soil tilth

will be improved as will the root system. Roots will penetrate and explore more of

the soil profile, and have the necessary air to be healthy and functional. Some of the

microbes provide relief from the toxic effects of salinity or heavy metals. Microbial

amendments may reduce soil salinity by creating better drainage so salts can be

leached down the soil profile. The mobility of phosphorus is very low in alkali soil,

3

making the phosphorus totally unavailable or available in limited quantities.

Phosphorus solubility is enhanced by addition of phosphorus solubilizing bacteria

(PSB) and phosphorus mobilizing fungi. Alkali soil is nitrogen deficient due to high

losses by volatilization process. Nitrogen fixing bacteria improves nitrogen content

of the soil by fixing atmospheric nitrogen into the soil. Shao et al., (2001) studied

that secondary salinization can be controlled using effective microbes.

Soil biological properties in relation to amendments and plant growth are poorly

understood for salt affected soils. The present analysis was planned to study the

microbial dynamics in salt affected soils and assess the effect of salt tolerant

microorganisms on reclamation of salt affected soils.

4

2 OBJECTIVES

2.1 Main objective

The main objective of this research was to improve our understanding regarding the

microbial dynamics in salt affected soils.

2.2 Specific objectives

Specific objectives were:

1. To evaluate salt-affected soils for various soil microbial characteristics and

determine their relationship with important soil properties.

2. To assess the effect of Na and Mg salinity on important soil microbiological

properties (rate of soil respiration and N mineralization).

3. To study the effect of different chemical amendments including pressmud,

gypsum and farmyard manure on soil microbiological properties.

4. To assess the influence of salt tolerant microbial inoculation on

improvement of salt affected soils.

5

3 REVIEW OF LITERATURE

3.1 Salt Affected Soils

Salt-affected is a general term which includes soils that are saline, sodic and saline-

sodic. Mostz occur in arid and semiarid regions of the world where

evapotranspiration is greater than annual precipitation. In addition, salt-affected soils

can also occur in humid and sub humid regions of the world under conditions

favorable to their development. One of the major causes of reduced crop production

is the salt accumulation in the root zone. Most crops have their threshold level up to

which they can tolerate salinity (Sharma, 1997; Kafi and Goldani, 2001).

3.2 Extent of Salinity

The distribution of salt-affected lands has a close relation with the environmental

factors, particularly in arid and semi-arid climatic conditions. In agriculture the

increasing salinity rate in arid and semi-arid lands has become a problem of great

concern. According to some recent estimates the total area of salt affected soils is

some 9.5 million km2 on a world-wide (Szabolcs, 1989) results an enormous loss of

agricultural production. The belief is, that about 7% of the earth crust is salt affected

and 10% of the world’s (7 × 109 hectare) arable land surface is saline or sodic

(Francois and Maas, 1994). Of the total 1.5 × 109 hectare cultivated lands, 23% are

saline and 37% sodic. It is estimated that 1/2 of all irrigated lands (about 2.5 × 108

hectare) are affected by waterlogging or salinity (Rhoades and Loveday, 1990).

Salinity is considered to be one of the major stresses to crops, and affecting about 950

× 106 hectare of land world-wide (Flowers and Yeo, 1995).

Salts that accumulate insitu through the weathering of parent material act as a source

of primary salinization, or through water causing secondary salinization. The soils of

Pakistan have both the process of salinization causing 6.3 x 106 hectare saline, of

which 60% is sodic or saline-sodic (Muhammad, 1983; Ghafoor et al., 1990; Qadir et

al., 2007).

In addition, the uses of unsuitable procedures for reclamation of salt-affected soils and

unscientific water management practices have been adding to the threat over the

passage of time (Reeve and Fireman, 1967; Bohn et al., 2001). Reports showed that

6

on the whole basis world is losing about 10 ha of arable land every minute, including

5 hectare because of soil erosion, 3 hectares due to soil salinization and 1 hectare due

to soil degradation processes (Abrol et al., 1988).

3.3 Categories of Salt-affected Soils

Topography, climate, geology, soil and cultural conditions influence the natural and

secondary processes, which actuate the nature and extent of saline soils (Fitzpatrick et al.,

1995). The ions that is dominant in the soil affects pH changes that in turn determine the

development of saline soil, the type of clay and how much precipitation the soil

receives. The main source of salts accumulation in the soil is weathering (US

Salinity Staff, 1954; Brady and Weil, 1999). Because of high precipitation these

salts are passed beyond the root zone in humid and sub humid areas. These salts

accumulate over time on the crust of the earth in arid and semiarid areas as the

leaching is restricted, to deteriorate soil physical, chemical and biological properties

(Rengasamy et al., 1984) and reduces crop productivity. Atmospheric precipitation

or deposition and fossil salts are two other natural sources of soil salinity (Bresler et

al., 1982; Bohn et al., 2001).

Elements that comprise salt affected soils includes Ca, Mg, Na, K, in major amounts

and CO3, NO3, Cl, SO4, HCO3, and B in minor amounts (US Salinity Staff, 1954;

Barber, 1984; Abrol et al., 1988; Ghafoor et al., 2004). The pH of a soil solution

determines the relative amount of HCO3 and CO3 in the soil (Lindsay, 1979; Bresler

et al., 1982). Only at pH values of 9.5 appreciable amount of CO3 can be present

with higher nitrate in some salt affected soils (Kelley, 1951; US Salinity Staff,

1954). The presence of white salt crusts on the surface is an indication of saline soil.

The saline soils also known as white alkali (US Salinity Staff, 1954) and in urdu

these soils are called “Thur” or “Kallar and “Khora” in Pashto. The sodic soils are

called “black alkali” in Russian and “Bara” in Urdu.

The main source of salt includes mineral weathering (Gunn and Richardson, 1979;

Lindsay, 1979; Macumber, 1991), rainfall (Rengasamy and Olsson, 1993),

groundwater (Macumber, 1991), various surface waters including irrigation

(Mehanni and Chalmers, 1986; Rengasamy and Olsson, 1993; Spore, 1995). Under

high evapotranspiration in arid climatic conditions, saline soil is formed due to the

7

upward movement of saline ground water (Isabelo and Jack, 1993), with highest

levels of salinity in areas of low water tables. However, physico-chemical

characteristics of the soil determine the extent of salinity like texture, hydraulic

conductivity, soil permeability, clay mineralogy and salt retention capacity

(Shainberg et al., 2001).

The amounts and kinds of salts determine the chemical characteristics of saline soils.

Soil Na is not usually adsorbed to any significant extent because it seldom

comprises more than half of the soluble cations (US Salinity Staff, 1954; Sposito,

1989; Bohn et al., 2001) and has a low affinity for cation exchange sites compared

with Ca and Mg. In the presence of excess soluble salts, saline soils are generally

flocculated and their permeability is increased or equals to that of non-saline soils.

Salts of MgCl2 and CaCl2 increase the darkness of the soil surface than non-saline

soil due to hygroscopic nature (FAO/UNESCO, 1973) hence the term black alkali

soils.

In proportion to Na the relative concentrations of other cations on exchange complex

and in soil solution deeply affect the behavior of saline-sodic soils. The soil turns

into sodic soil when Ca is exchanged by Na on exchange sites. The three cations i.e.

Ca, Na and Mg are exchangeable with each other and their exchange depends on

their relative concentrations and chemical affinity. Salts of Ca and Mg are

precipitate due to the evaporation process, whenever, due to evaporation excess salt

are accumulated or concentrated and Na becomes the predominant cation. As

because of precipitation of Ca and Mg, Na becomes excessively available at the

exchange complex, and soil become sodic or saline-sodic. But as soil affinity for Ca

and Mg is more than that of Na (Lindsay, 1979; Sposito, 1989) and thus the amounts

of Mg and Ca adsorbed much higher than that of Na. Generally, Na must be half or

more of the soluble cations at the exchange complex before significant amounts are

adsorbed (US Salinity Staff, 1954). The cations, NH4 and K can be fixed at certain

positions on clay particles so that they occur as exchangeable and fixed cations

(Mengel and Kirkby, 1987).

Frequently saline soils can turn into saline-sodic or sodic soils when irrigated with

water that contains high amounts of salt. The change occurs as soluble salts, are

8

leached and exchangeable Na+ remains in the soil but at concentration insufficient to

cause clay flocculation (Naidu and Rengasamy, 1993; SalCon, 1997).

3.4 Effect of Salts on Soils

Due to intense evaporation in semi-arid zones salts accumulate in the upper soil

profile instead of downward movement with water (Isabelo and Jack, 1993). With

increase in soil electrical conductivity the soil physico-chemical properties are

deteriorated (Rengasamy et al., 1984; Yasin et al., 1987). Use of saline sodic water

increases soil bulk density and compaction while, soil infiltration capacity and porosity is

reduced (Gupta and Gupta, 1997; Al-Nabulsi, 2001). Growth and yield of most crops is

affected with the imbalanced ionic concentrations of soil solution with high salt

concentration and poor soil properties (Sumner 1993; Curtin and Naidu, 1998; Grattan

and Grieve, 1999; Bohn et al., 2001).

Saline soils contain, relatively large amounts of neutral soluble salts (Abrol et al.,

1988), which can be present in soils in form of chlorides and sulphates of Mg2+, Ca2+

and Na+ and sometimes in the form of nitrate (NO3-) (SalCon, 1997; Anzecc, 2000;

Fitzpatrick et al., 2001). The concentration and nature of salts in the soil solution

determine soil pH.

The effects of elevated soluble salt concentrations are such that they prevent soil

colloids from dispersing and promote flocculation of soil particles. For example

exchangeable Ca2+ has the ability to flocculate or clump individual clay particles and

as a consequence creating larger pore spaces in the soil, which facilitates root

growth and better movement of water and air through the soil (Bell, 1993). Plant

growth in saline soil is generally not constrained by poor infiltration, aggregate

stability and aeration, but instead by high salt levels which are detrimental to plants

(Abrol et al., 1988; Brady and Weil, 2002; Warrence et al., 2002).

Saline soils can turn into saline-sodic or sodic soils when irrigated with low quality

water, due to the accumulation of exchangeable Na+ ions relative to Ca2+ and Mg2+

ions in soil and water (SalCon, 1997; Anzecc, 2000). For example, if irrigation

water has a high exchangeable sodium percentage (ESP) and is low in soluble salts,

the exchangeable Na will replace the soluble salts present at the cation-exchange

sites, and thus saturating the soil with exchangeable Na+ ions (Fetter, 2001). The soil

9

structure is destroyed as Na+ weakens the bonds between the clay particles

(Rengasamy and Walters, 1994; SalCon, 1997; Fetter, 2001). These small clay

particles, as they move down through the soil profile, are able to clog pore spaces,

thus reducing water infiltration and, consequently, causing temporary waterlogging

(Naidu and Rengasamy, 1993; Sumner, 1995; Qadir et al., 2001; Warrence et al.,

2002). Over time the soluble salts accumulate in the subsoil if they cannot be

dissolved, and leached (Rengasamy and Olsson, 1991), resulting in the upper soil

layer becoming sodic and the subsoil becoming saline (Rengasamy, 2002).

Saline or salt affected soils will often not show symptoms of sodicity, even when

excess Na+ is present (Rengasamy and Walters, 1994), as excess salt can prevent

clay particles from dispersing. Only if these soils are leached of the salt will the

symptoms of sodicity start to appear (Rengasamy and Walters, 1994). Even a small

amount of adsorbed Na+ (about 6%) at the exchange sites is enough to cause the

decline in soil structure (Naidu and Rengasamy, 1993). Accumulation of Na+ can be

a predominant feature in the heavy cracking clays (Vertosols) that swell upon

wetting, thus preventing deep penetration of irrigation water (Rengasamy and

Olsson, 1991). Repeated wetting and drying solidifies sodic soils over time,

producing cement like soil with little or no structure (Sumner, 1995; Warrence et al.,

2002). A relatively thin (up to 10 mm thick) but very dense crust can form upon

wetting, which then acts as a natural barrier for emerging seedlings. Another

important factor is the low organic matter level in sodic soils. The high levels of

Na+, low biological activity and low or high pH found in sodic soils are responsible

for low mineralization rate and low organic matter accumulation (Naidu and

Rengasamy, 1993; Peineman et al., 2005).

3.5 Effect of Salts on Plants

Apart from adverse effects of salinity and /or sodicity on soil physical conditions, it

also affects crop growth includes osmotic potential, specific ion effects like that of

toxic concentrations of Na, B and Cl, and interaction with the nutrient elements that

reduce the nutrients bio availabilities (US Salinity Staff, 1954; Muhammad, 1996;

Bonn et al., 2001; Yamaguchi and Blumwald, 2005). Due to salinity and /or sodicity

plant metabolism is affected with imbalance in plant nutrient concentration (Kramer,

10

1983; Garg and Gupta, 1997). These changes under saline conditions directly affect

and decrease crop growth and yield (Mer et al., 2000; Qadir et al., 2001; Qadir et

al., 2006), and excessive salts concentrations make the soil toxic for the plant

growth (Donahue et al., 1983). The salinity results in reduced crop growth and yield

along with stunned root’s growth by causing reduction in leaf area and reduce

photosynthesis rate (Garg and Gupta, 1997)

The responses of plant to salinity depend upon the (1) duration of plant’s exposure

to such conditions, (2) type of salts present, (3) on the time of the day, (3)

developmental stage of the plant, and many other factors (Maas and Hoffman, 1977;

Cramer et al., 2001). Salinity reduces plant growth by interacting with the plant’s

nutrients or by making the soil toxic due to high concentration of the cations (Garg and

Gupta, 1997; Mer et al., 2000) and with excessive salts concentrations plants fails

completely (Donahue et al., 1983). In case of salinity above threshold level, saline

tolerant crop growth is retarded (Maas and Hoffman, 1977). Ramoliya et al.

(2004) reported that under increasing salinity stress the acacia seedling show

shorter stems and roots with reduced emergence and stunted biomass. These

adverse conditions of salinity could be mitigated through effective reclamation

measures.

3.6 Salt-affected Soils Reclamation

The adequate physico-chemical properties of soil in saline or sodic environments

could be accomplished by using good quality water, appropriate drainage and

cultural practices, with suitable soil chemical amendments (Grattan and Oster,

2003). These includes the development of the most appropriate reclamation method

or a combination of methods necessary to optimize farm management to increase

crop yields in a sodic soil. The most effective method for removal of soluble salts

from the rhizo-sphere is proved to be the leaching process (Abrol et al., 1988). In

this process the high quality fresh water is intensely irrigated onto the soil surface

and allowed to flow the soluble salts down from the surface of the soil by mean of

infiltration, and is mostly incorporated with an effective drainage system (Jury et al.,

1979). On the other hand, application of chemical amendments necessitates removal

of exchangeable sodium from the soil’s cation exchange sites and replacement of Ca

11

(Sahin et al., 2002). Due to its availability at low cost and effectiveness gypsum

(CaSO4.2H2O) is the most commonly used amendment. The amelioration of saline-

sodic soils, thus, requires both leaching and application of gypsum (Abrol et al.,

1988). Various organic amendments such as organic mulch, manures, and compost

have been investigated for their effective reclamation of saline-sodic soils (Diez and

Krauss 1997; Wahid et al., 1998). In general, alone organic amendments application

has a very little effect on improving soil salinity (Madejon et al., 2001). But it can

improve many soil properties (Cheny and Swift, 1984; Uson and Cook, 1995;

Giusquiani et al., 1995; Gao and Chang, 1996; Prihar et al., 1996; Singh and Singh,

1996; Entry et al., 1997; Ibrahim and Shindo, 1999; Mamo et al., 2000; Naeni and

Cook, 2000).

Reclamations include all those strategic measures that are employed to reduce the

soil salinity (Abrol et al., 1988). These methods of reclamation can be of chemical,

physical or biological that can be used alone or in combination. Amendments are

materials that directly or indirectly furnish divalent cations (usually Ca2+) through

chemical or microbial action for replacement of exchangeable Na+ (Muhammad,

1996; Qadir et al., 2001). Many saline-sodic soils contains large amounts of Ca, as

(CaCO3) (Kovda et al., 1973) but it is less effective in ameliorating processes

because of its extremely low solubility (Qadir et al., 2007).

The salt affected soils characteristics includes high pH, level of ESP, desired rate

and extent of replacing exchangeable Na and presence of CaCO3 and MgCO3, soil

type and the cost and availability of the amendment. All chemical amendments

supply soluble Ca that replaces Na on exchange sites when applied under

appropriate soil conditions (Keren and Miyamoto, 1990; Nadler et al., 1996; Bohn et

al., 2001). Some of amendments used in reclamation are reviewed in the following

sections.

3.6.1 Pressmud

Pressmud (PM), sugar mills by-product, does the same job as any organic and

inorganic fertilizers can that is why it can be used for saline-sodic soil reclamation

(Patel and Singh, 1993; Zerega et al., 1995; Rai et al., 1999; Yaduvanshi and

Swarup, 2005). Although PM contains Ca of low solubility, but it produces desirable

12

effects in saline-sodic and sodic soils due to its higher organic contents and other

nutrients especially in low organic matter soils. Pressmud was used by many

researchers, to test its effectiveness on crop yield and soil conditions under

examination. The pressmud was found effective under percolated conditions in

removing leachable Ca, Mg and Na (Patel and Singh, 1993). Application of

pressmud can help in the retention of inorganic fertilizers, it improves the physical

condition of the soil and supplies trace nutrients (Singh et al., 1991; Yadav et al.,

1995). With PM addition soil’s biological properties can improve. In a study the root

zone microbial population were increased after 30 days of the application of the

pressmud especially bacteria and actinomycetes (Gaikwad et al., 1996).

3.6.2 Gypsum

Research showed that gypsum is very useful for sodic and saline sodic soils reclamation

(Shainberg et al., 1982; Elshout and Kamphorst 1990; Bohn et al., 2001; Qadir et al.,

2006; 2007). The constant dissolution of gypsum is considered an additional advantage

to sustain long term availability of Ca (Doneen, 1975). The application of gypsum in

standing water shows much better result than surface application (Chaudhry et al., 1986).

Similarly, gypsum, when used in powder form show more efficiency in the reclamation

of sodic soils (Dutt et al., 1971; Chaudhry et al., 1986; Ghafoor et al., 1989; Chaudhry

and Ihsanullah, 1989; Chaudhry, 2001). According to the estimation 20 to 28 inches

water is needed to dissolve 17 to 24 Mg ha-1 gypsum on surface soil application. While,

under sodic soil conditions the solubility of gypsum increases by 10 folds. Moreover, the

exchange process tends to be much speedy when the mixing of gypsum is accompanied

with the removal of Na from the soil solution (Frenkel et al., 1989). Ilyas et al. (1997)

observed that when gypsum is applied in the soil with poor permeability the soil will

show higher Na, Ca+, Mg, and EC values. Under such soil conditions deep spiking

facilitates the process of reclamation to allow leaching of salts mainly of Na.

The application of Gypsum improves soil physical and chemical properties (Ayers and

Westcot, 1985), increases empty spaces in the soil (soil porosity) (Oster, 1982; Gal et al.,

1984; Shainberg et al., 1989) and improves soil hydraulic conductivity (Scotter, 1985;

Greene et al., 1988). When treated with surface applied phospogypsum a noticeable

decrease in bulk density of soil was observed (Southard et al., 1988). Dramatic

13

increase in wheat grain yield was reported with application of gypsum (Ghafoor et

al., 1985).

3.6.3 Farmyard manure

Soil fertility improves with the application of organic materials (Tang et al., 1999;

Tang and Yu, 1999; Grace et al., 2006; Flavel and Murphy, 2006; Ferreras et al.,

2006) and brings favorable effects to the soil’s biological and physic-chemical

properties as well (Clark et al., 2007; Abbas and Fares, 2009). With the increased

number of soil macro pores due to structural stability indicated an improvement in

pore size distribution (Marinari et al., 2000). Because of improvement of soil

aggregation, organic materials influence root development, seedling emergence and

plant growth (Marinari et al., 2000; Ferreras et al., 2000). The sugar beet yield was

increased with increase in farmyard manure application rate up to 42% in salt-

affected soils of Mardan, Charsadda and Swabi district, KPK, Pakistan as compared

with control (Haq, 2005).

Upon decomposition organic matter releases essential plant nutrients. However, the

literature shows that salinity may reduce C and N mineralization rate (Malik and

Haider, 1977; Wichern et al., 2006) or it increases with salinity (Laura, 1973; Laura,

1976) depending upon the nature of organic matter and C/N ratio. Abdou et al.

(1975) found that the rate of mineralization from added straw is decreased by

salinity and sodicity. Mineralization and salinity has a negative correlation (Wichern

et al., 2006). The decomposition of organic matter depends on percentage of clay,

clay mineral type, the soil structure and presence of divalent cations, which directly

or indirectly affect microbial activity and the availability of water and soil aeration

(Baldock and Skjemstad, 2000; Von-Lutzow et al., 2006).

3.7 Effect of Salts on Soil Microbial Properties

The soil’s microbes are essential for plants as they release and mobilize minerals

and nutrients in the soil; and take oxygen, carbon dioxide and also may fix nitrogen

from the atmosphere and make it available to plants. Saline and sodic soils exhibit

soil structural problems, due to changes in physico-chemical properties (Qadir et al.,

2007). Presence of excess sodium in salt affected soil leads to the development of

poor physical conditions by dispersing the soil aggregates.

14

The soil microbial biomass is an ever changing organic matter pool that constitutes 1

to 3% of total organic matter in soil (Jenkinson and Ladd, 1981). It regulates the

functioning of the soil system by acting as a source and sink of nutrients for the

plant (Singh et al., 1991). The chemistry of the soil is influenced by physical

problems such as waterlogging and compaction, which can lead to changes in the

nutrient ion formation, rendering them unavailable to plants (Naidu and Rengasamy,

1993). Osmotic stress and high levels of Na+ can cause imbalances in plant nutrition,

causing ion deficiencies or toxicities (Sheldon et al., 2004; Qadir et al., 2007). These

physical and chemical changes reduce the activity of plant roots and crop growth as

well as of soil microbes (Rietz and Haynes, 2003). Furthermore, low SOM

combined with high salt concentrations and high or low pH, will generally also show

low biological activity (Naidu and Rengasamy, 1993; Sardinha et al., 2003).

Salinity and sodicity in soils has a detrimental effect on the microbial activity

including reduce microbial biomass, which in turn are then less efficient in using

available C resources and consequently showing a decrease in soil respiration (Rietz

and Haynes, 2003; Sardinha et al., 2003; Wichern et al., 2006; Yuan et al., 2007).

Yuan et al., (2007) found that in soils with highest salinity, the organic C content

was lowest. Rietz and Haynes (2003) reported declines in soil C due to lower OM

inputs, as plant growth was greatly reduced in these soils.

Soil respiration rate and salinity are inversely proportion as increases in salinity have

been shown to decrease soil microbial biomass and soil respiration rates (Laura,

1973; Laura, 1976; Pathak and Rao, 1998) changes in osmotic potential due to

salinity places stress on the microbial population (Batra & Manna, 1997).

Conversely, increased solubilization of organic matter with increasing sodicity is

possibly due to increased C mineralization (Nelson et al., 1997).

3.8 Microbial Inoculation

Microbial inoculants are amendments that use beneficial microbes to help and foster

plant health. Microbial inoculants are used to promote plant growth by stimulating

plant hormone production and to improve plant nutrition as well (Bashan and

Holguin, 1997; Sullivan, 2001). Most of the microbes follow mutualism, a form of

symbiotic relationship, with the target crops where both parties get the benefit. The

15

use of beneficial and effective microorganisms in agriculture as microbial inoculants

is a new technique (Shao et al., 2001). The use of microbial inoculants has been

shown to raise the growth yield and quality of crops by improving soil health and

quality (Li et al., 1999). Mycorrhizosphere development process by the inoculation

of mycorrhiza has been reported to modify the abundance and quality of

rhizospheric microflora and alter overall rhizosphere microbial activity which may

be responsible for the bioremediation in the contaminated soil (Khan, 2006).

Moreover, they influence the physiology of their host plant making them less

vulnerable to pathogens, soil pollution, salinity, drought and a number of other

environmental stress factors.

The combination of different strains of plant-growth promoting rhizobacteria

(PGPR) has been said to benefit barley (Belimov et al., 1995a) and rice (Nguyen et

al., 2002). Increased plant nutrient uptake in soils and also from fertilizer is the main

benefit of using combination of strains of PGPR (Belimov et al., 1995a; Bashan et

al., 2004). Interestingly, even if only one strain is diazotrophic in many strained

inoculants the increased total nitrogenase activity is noticed as compared to single

strain inoculants (Lippi et al., 1992; Khammas & Kaiser, 1992; Belimov et al.,

1995a). In nutrient poor soil, combination of PGPR and arbuscular mycorrhizae

(AM) can be useful in increasing crop growth (Singh and Kapoor, 1999) and for

improving nitrogen-extraction from the fertilized soils (Galal et al., 2003). The

beneficial effects of AM inoculation with Azospirillum brasilense associated with

Vicia faba plants were found by Rabie and Almadini (2005).

3.9 Role of Microbes in Reclamation of Salt-affected Soil

Increasing exo-polysaccharides producing bacteria population density in the root

zone decreases Na+ cations available for plant uptake. Fungal inoculation can cause

water stable aggregates to form and thereby open up air spaces that contribute to

improved soil structure. As a result of these amendments, over time the soil tilth

will be improved as will the root system. Roots will penetrate and explore more of

the soil profile, and have the necessary air to be healthy and functional. Some of the

microbes provide relief from the toxic effects of salinity or heavy metals. Microbial

amendments may reduce soil salinity by creating better drainage so salts can be

leached down the soil profile. The mobility of phosphorus is very low in alkali soil,

making the phosphorus totally unavailable or available in limited quantities.

16

Phosphorus solubility is enhanced by addition of phosphorus solubilizing bacteria

(PSB) and phosphorus mobilizing fungi. Alkali soil is nitrogen deficient due to high

losses by volatilization process. Nitrogen fixing bacteria improves nitrogen content

of the soil by fixing atmospheric nitrogen into the soil. Shao et al. (2001) studied

that secondary salinization can be controlled using effective microbes.

17

4 MATERIALS AND METHODS

Various experiments were conducted to assess the influence of salts on soil

microbiological properties in the Khyber Pakhtunkhwa Agricultural University

Peshawar Pakistan during 2009-2011. In the first study, soil microbiological

properties were assessed in 30 different salt affected soils collected from Charsadda

and Mardan districts. In the second study, the effect of NaCl induced salinity in soil

with native EC of 0.65 dS m-1 on soil microbial activity and N mineralization were

evaluated. In third experiment, the effects of MgCl2 induced salinity in soil with

native EC of 0.63 dS m-1 on soil microbiological parameters were assessed. In the

fourth experiment, saline-sodic soil (with pH = 10.47 and EC = 20.3 dS m-1) was

amended with pressmud, gypsum, farmyard manure and microbial inoculums and

their effects on soil microbial biomass C and N, ammonification, nitrification, CO2

evolution and N mineralization were evaluated during lab experiments. The details

on site characteristics and experimental procedures are given as under:

4.1 Site Characteristics

The soils of districts Charsadda, Mardan and Peshawar of Khyber Pakhtunkhwa

province of Pakistan were used in this study (Figure 4.1 and Figure 4.2). The

Charsadda district covering an area of 996 km2 is situated between 71°28’ and

71°35’ E and 34°03’ and 34°38’ N surrounded by Malakand agency on the north,

Mardan district on the east, Nowshera and Peshawar district on the south and the

Mohmand agency of the Federally Administrated Tribal Area on the west. Total

population of the area is about 1022,000 with most of them are agriculturist and

cultivating mainly tobacco, sugarcane, sugar beet and rice crops. Most of the area

was waterlogged and saline or saline-sodic before the establishment of tile drainage

system by the Salinity Control and Reclamation Project (SCARP) in 1983-92.

Although waterlogging and salinity problems have been eradicated in areas where

drainage system are installed, the problem of salinity/waterlogging still exist in areas

with no drainage system. The area lacking drainage system include Majoke,

Faqirabad, Nazo Kali and Bajovro Kali in district Charsadda are faced with

problems of shallow water-table, restricted leaching and poor drainage. During the

moon-soon rains soils become flooded and water logged (Soil Survey of Pak.,

18

2007b). The climatic characteristics of districts Peshawar which closely resembles

the Charsadda and Mardan districts are given in Table 4.1. In summer (May-August)

the temperature reached to 45°C, minimum 25°C and average is 32°C. The mean

maximum temperature is 20°C in winter (December to February) with average 5.3°C

and minimum 4.1°C. Mean annual precipitation in the area is 430 mm.

The Mardan district is situated between 71°48’ to 72°25’ E and 34°05’ to 34°32’ N

covering an area of 1632 km2 and is surrounded in the north by Buner district and

Malakand protected area, on the south by Nowshera district, on the east by Swabi

and Buner districts and on the west by Charsadda district and Malakand protected

area. The total population was 1.46 million with population density of 895 persons

per square kilometer (1998 census). A steep rise in temperature occurs from May

and stays highest in June to September. The temperature reaches its maximum in

June (41.5 °C). Most of the area was waterlogged and saline or saline-sodic before

the establishment of tile drainage system by the Salinity Control and Reclamation

Project (SCARP) in 1989-03. Although waterlogging and salinity problems have

been overcome in areas where drainage system have been installed, the problem of

salinity/waterlogging still exist in areas with no drainage system. The area lacking

drainage system include Ahmed village and Sherzaman kali in Mardan. Having poor

drainage, restricted leaching and shallow water table problems. The area is humid

due to intensive cultivation and artificial irrigation. A rapid fall of temperature

occurs from October onwards. December and January are the coldest months. The

mean minimum temperature is 2.1 °C recorded in January. Most of the rainfall

occurs in July to August and December to January. Maximum rainfall was126 mm

recorded in August. The relative humidity is quite high throughout the year while

maximum humidity has been recorded 73% in December.

19

Figure 4.1 Map of district Charsadda and Mardan, showing the sampling area for salt-affected soils.

20

Figure 4.2 Map of district Peshawar, showing Agricultural University Peshawar Research Farm Malkandher.

21

Table 4.1: Meteorological data of Peshawar during 1973-2002.

Parameters --------------------------------------Monthly means---------------------------------------- Annual

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Precipitation (mm)

29.5 46 84 46.6 23 14.5 46.6 74 21.7 18.8 12.1 16.6 433.2

Max. Temp.(°C)

18.5 20 23.8 30.6 36.9 40.2 37.7 35.9 35.2 31.5 26.1 20.7 29.8

Min. Temp. 4.0 6.4 11.0 16.8 21.8 25.3 26.7 25.9 22.6 16.1 9.7 5.4 16.1

Mean Temp. 11.4 13.1 17.1 23.6 29.3 33 32 30.9 29 23.8 18 13 23

Mean RH (%) 48 41 42 38 29 29 48 56 50 46 52 5 50

RH: Relative Humidity


1973-2002.

Figure 4.4: Meteorological data of Peshawar, Charsadda and Mardan districts during 1973-2002.

05

1015202530354045


Tem

pera

ture

(°C)

Month of the year

Temp(Max)Temp(Min)

0

20

40

60

80

100


Prec

ipita

tion

(mm

)

Month of the year

Precipitation

22

Along with the other sites of the Khyber Pakhtunkhwa, Peshawar lies mainly on the

Iranian plateau and is situated near the eastern end of the Khyber Pass. Peshawar

was historically part of the Silk Road. Peshawar is situated between 34° 0' 28"

North, and 71° 34' 24" East with 329 meters elevation above the sea level. Peshawar

has a semi-arid, sub-tropical, warm to hot, continental climate with 360 mm average

annual rainfall. Temperature increases in summer (May to September) and reached

to a maximum 46°C with a mean minimum temperature of 25°C. The winter rainfall

is higher than that of summer on average basis. The mean minimum temperature is

4°C in winter (December to March) with a maximum temperature of 20°C. The

highest rainfall occurs in winter (February and March) and in summer (July and

August).

4.2 Soil Sampling and Processing

Soil samples were collected from 30 different locations in districts Charsadda and

Mardan. All the soil samples were taken from the surface 20 cm, with varying salt

concentrations (i.e. ECe of < 4.0 to 32 dS m-1) in the month of March, 2009. Fields

were either under wheat crops or fallow at the time of sampling. Soon after

collection the samples were transferred to the Lab of Soil and Environmental

Science Department in cool box and processed immediately for measurements of

microbial activities and other soil properties. The samples in its moist condition

were broken and passed through < 4.0 mm sieve. The samples were kept in

refrigerator if unable to run immediately for microbial analysis.

Samples required for measurements of microbiological characteristics were kept

moist and cool. However, part of soil samples were air-dried, ground and passed

through < 2.0 mm sieve, and analyzed for soil characteristics such as soil pH, EC

(Electrical conductivity), soluble calcium plus magnesium, soluble sodium, ESP

(exchangeable sodium percentage), SAR (sodium adsorption ratio), carbonates,

bicarbonates and chloride.

4.3 Proposed Experiments

The following experiments were conducted in the study.

a. Microbiological properties of native salt affected soils

23

b. Effect of NaCl induced salinity on CO2 evolution and N

mineralization in a silty loam soil

c. Effect of MgCl2 induced salinity on CO2 evolution and N

mineralization in a silty loam soil

d. Comparative effect of pressmud, gypsum farmyard manure and

microbial inoculations on soil microbial biomass and activity in

saline sodic soil

The detail of each experiment is given below:

4.3.1 Microbiological properties of native salt affected soils

Soil microbiological properties were determined on moist samples of the 30 soils

(see 4.2 for soil preparation).

The soil microbial properties determined in salt affected soils include microbial

biomass N, microbial biomass C, microbial activity, N mineralization, nitrification

and C/N ratio of the microbial biomass. After air drying part of soil samples were

ground and passed through < 2.0 mm sieve, and analyzed for soil characteristics

such as soil pH, EC, soluble calcium plus magnesium, soluble sodium, SAR, ESP,

carbonates, bicarbonates and chloride.

4.3.2 Effect of NaCl induced salinity on CO2 evolution and N mineralization in silty clay loam soil

The induced NaCl effect was studied in a lab experiment during November, 2009.

Soil used for this experiment was collected. A bulk soil sample of about 9.0 kg was

collected from the research farm of Agricultural University Peshawar. Soil was

collected from the upper 20 cm recently cultivated wheat field. Soon after collection

the sample was transferred to the Lab of Soil and Environmental Sciences

Department in cool box and processed immediately for measurements of microbial

activities and other soil properties. The sample was broken down by hand and

passed through < 4.0 mm sieve whilst still moist. Sample required for measurements

of microbiological characteristics was kept moist and cool. However, part of soil

24

sample was analyzed for EC, pH, CaCO3, total N, organic matter and soil texture

after air-drying and passing through < 2.0 mm sieve.

Eight treatments with EC levels of 0.65, 4, 8, 12, 16, 20, 30 and 40 dS m-1 were

arranged in a Completely Randomized Design with three replications. The soil was

amended with NaCl salt at 0, 4.87, 11.11, 18.86, 24.44, 32.44, 55.55 and 78.22 mg

g-1 soil to get the desired EC levels, respectively. For each treatment, moist soil

sample of 300 g in triplicate was taken in a clean plastic pot and amended with the

desired level of NaCl salt solution. The required amount of NaCl salt was dissolved

in 30 mL water and spread uniformly over the surface of soil (300 g) in each

incubation pot. After amendments, the pots were incubated at 28°C. The CO2

evolution was measured at 10 days of interval to 40 days of incubation period, while

N mineralization was measured at day 0 to day 40 at 10 days of interval.

4.3.3 Effect of MgCl2 induced salinity on CO2 evolution and N mineralization in a silty clay loam soil

A laboratory incubation experiment was conducted to evaluate the effect of MgCl2

induced salinity on microbial activity and N mineralization in a slity clay loam soil

collected from the research farm of Khyber Pakhtunkhwa Agricultural University

Peshawar in March, 2010. Eight treatments with EC levels of 0.63, 4, 8, 12, 16, 20,

30 and 40 dSm-1 were arranged in a Completely Randomized Design with three

replications. The soil was amended with MgCl2 salt at 0, 6.5, 17.5, 29.0, 44.0, 66.5,

132.75 and 200 mg g-1 soil to get the desired EC levels, respectively.

For each treatment, moist soil sample of 300 g in triplicate was taken in clean plastic

pot and amended with the desired level of MgCl2 salt solution. The required amount

of MgCl2 salt was dissolved in 30 mL water and spread uniformly over the surface

of soil (300 g) in each incubation pot. Peptone was added at 200 µg N g-1 soil for N

mineralization determination only. After amendments, the pots were incubated at

28°C. The CO2 evolution was measured at 10, 20 and 30 days of incubation period,

while N mineralization was measured at 0, 10, 20 and 30 days of incubation period.

25

4.3.4 Comparative effect of pressmud, gypsum, farmyard manure and microbial inoculations on soil microbial biomass and activity in saline sodic soil

An experiment was performed to evaluate the comparative effect of gypsum,

pressmud and farmyard manure on soil microbial biomass and activity in a saline

sodic soil collected from Majoke in District Charsadda. The soils were collected

from Khati Khel soil series with silt loam or vary fine sandy loam texture that

comprises 5970 ha area in Khyber Pakhtunkhwa dominated by saline sodic soil

(Khan, 1993). The sampling soil was strongly saline sodic having EC value of 20

mS cm-1, pH 10.0 with silt loam texture comprising redeposit loess material.

Gypsum was collected from Agricultural Research Station Tarnab Peshawar.

Pressmud was collected from Khazana Sugar Mill Peshawar and analyzed for pH,

EC, Na, SAR, lime, total N and organic matter. FYM was collected from

Agricultural Research Station Malakandher and analyzed for total N (0.65 g 100 g-1).

The treatments arranged for this experiment were; control, gypsum (G), pressmud

(PM), farmyard manure (FYM), G+FYM, G+PM, PM+FYM and PM+FYM +

microbial inoculation. Each treatment was repeated three times in a CR (completely

randomized) design. For each treatment 6 kg soil of saline sodic soil (pH = 10.4 and

EC= 20.3 dSm-1) was taken in clean plastic pot and amended with the required

amount of the desired amendment. Gypsum and pressmud were applied on the basis

of 100% gypsum requirement equal to 20 Mg ha-1. FYM alone or in combination

with chemical amendments, was applied at the rate of 17 Mg ha-1. Inoculum was

applied @ 100-120 million microbes per pot.

4.4 Laboratory Analysis

The important soil microbiological and chemical properties including microbial

biomass C and N, basal soil respiration, microbial biomass C/N ratio,

ammonificaton, nitrification, total mineral N, total N, nitrogen mineralization,

microbial inoculums preparation, gypsum requirement, saturation extracts, soluble

Na, soluble Ca+Mg, sodium adsorption ratio, exchangeable Na percentage, chloride,

carbonates and bicarbonates, organic matter, lime content, texture, pH and EC were

measured as follows:

26

4.4.1 Microbial biomass C and N

Microbial biomass carbon and nitrogen were determined by chloroform fumigation

incubation method Brookes et al. (1985) and Vance et al. (1987) as described in

Horwath and Paul (1994). In this method, 50 g soil sample was fumigated with

chloroform. After re-inoculation, the fumigated soil samples were run for measuring

CO2 evolution during incubation using the alkali trapping technique. The un-

fumigated soil samples were also run for CO2 measurement in similar manner.

Microbial biomass was calculated from the difference of CO2 evolved between the

fumigated and un-fumigated soil samples. The chloroform fumigation incubation

consists of the following steps:

4.4.1.1 Fumigation

For fumigation, 50 g moist soil samples were taken in 100 ml beaker and kept in

desiccator lined with moist tissue papers. Another tall beaker containing about 50 ml

chloroform and few anti-bumping granules was kept in the center of desiccator

along with the soil samples. The desiccator was properly air-tightened and

connected to the vacuum pump. The air from desiccator was evacuated 3 times; each

time for about 1 minute after chloroform began boiling. After the last evacuation,

the desiccator was kept in dark under vacuum for 24 hrs. The unfumigated samples

were also kept in desiccator (without vacuum and chloroform) and placed in dark for

the same period. After incubation in the dark, chloroform was carefully removed

from desiccator. The residual effect of chloroform was evacuated with the help of

vacuum pump.

4.4.1.2 Inoculations

The fumigated samples were then removed from desiccator and inoculated with 1 g

of respective fresh unfumigated soil samples and thoroughly mixed.

4.4.1.3 Measurements of CO2 evolution

The CO2 evolution was measured in both fumigated and un-fumigated soil samples

as follows:

27

Each soil sample was transferred to a 500 ml conical flask. A vial containing 5 ml of

0.3 M NaOH was suspended in the flask and properly air-tightened with a rubber

bung, and then incubated at 28°C for 2, 5, and 10 days. At each incubation period,

the NaOH solution of the vial was treated with 10 ml of 1 M BaCl2 solution in the

presence of 3 to 4 drops of phenolphthalein following titration against 0.1 N HCl till

the disappearance of pink color.

The vial was re-filled with fresh NaOH solution (same amount and strength) and

suspended in the same flask. The sample was re-incubated to measure CO2 evolution

at 5th and 10th day of incubation period. The amount of CO2 evolution was calculated

from the amount of HCl used in titration and expressed in mg CO2 kg-1 soil d-1.

After measurement of CO2 evolution at day 10, both the fumigated and un-

fumigated soil samples were analyzed for total mineral N.

4.4.1.4 Calculation of biomass C

Soil microbial biomass C was calculated from the amount of CO2-C produced in

fumigation and un-fumigated samples using the following expression:

Biomass C = (Fc – Ufc) / Kc

Where: KC = constant value i.e. 0.45 (Jenkinson and Ladd, 1981)

FC = CO2 flush from fumigated soil sample

Ufc = CO2 flush from un-fumigated soil sample

4.4.1.5 Calculation of biomass N

Soil microbial biomass N was calculated from the amount of mineral N produced in

the fumigated and un-fumigated soil samples using the following equation:

Biomass N = (Fn – Ufn) / Kn

Where: Kn = constant i.e. 0.54 (Jenkinson, 1981)

Fn = flush of NH4-Nfrom fumigated soil sample

Ufn = flush of NH4-N from un-fumigated soil sample

28

4.4.2 Determination of total mineral N

Total mineral N was determined in soil samples by the steam distillation procedure

(Mulvaney, 1996). Taking 20 g soil sample and shaking with 100 ml of 1 M KCl for

1 hr. The sample was filtered and NH4-N was recovered with MgO in 20 ml of

extract and both NH4+ and NO3

- nitrogen with MgO plus devarda’s alloy, titrated

against 0.005 M HCl in a 5 ml boric acid mixed indicator solution. A blank was also

run simultaneously. Mineral N was calculated using the following expression:

Mineral N (mg N kg-1 soil) = 20(g) soil ofweight

1001000014.0005.0)(

BlankSample

Nitrate N was determined by difference as follows:

Nitrate N (mg N kg-1 soil) = Total mineral N (mg N kg-1 soil) – NH4-N (mg N kg-1

soil)

4.4.3 Mineralizable N (mg N kg-1 soil)

Mineralizable N was calculated from total mineral N as follows:

Mineralizable N = Total mineral N at day 10 – Total mineral N at day 0.

Ammonification = Ammonium N at day 10 – Ammonium N at day 0.

Nitrification = Nitrate N at day 10 – Nitrate N at day 0.

4.4.4 Total N

Total N was determined by the Kjeldhal method of Bremner (1996). The method

includes digestion of 0.2 g soil sample with concentrated 3 ml of H2SO4 in the

presence of 1.1 g digestion mixture containing K2SO4, H2SO4 and Se in 100:10:1

ratio. The digest was cooled and distilled in a 5 ml boric acid mixed indicator

solution with 20 ml of 40% NaOH solution following titration against 0.005 N HCl.

The amount of N was calculated as 1 ml of 0.005 N HCl equals 70 µg N.

29

4.4.5 Preparation of microbial inoculants of salt tolerant microorganisms

The preparation of microbial inoculants of salt tolerant microorganisms was consist

of the following steps:

4.4.5.1 Isolation and culture of salt tolerant microorganisms

Salt tolerant microbes (bacteria and fungi) were isolated from salt affected soils. The

microorganisms present in salt-affected soil were grown on nutrient agar media for

bacteria or peptone-glucose-acid agar media for fungi using the dilution plate

technique as described in Wollum II (1982). In this method, 1 g fresh saline-sodic

soil (pH 10.5, EC 20.3) sample was shaken in 25 ml bottle in the presence of few

glass beads for 10 minutes in 9.5 ml diluents. Transferred 1 ml of the suspension to a

2nd bottle containing 9 ml of sterilized water for further dilutions. The same process

was repeated until reached to the desired dilutions. The bacterial (Nutrient Agar

Media) and fungal (Peptone Glucose Acid Agar Media) plates were inoculated form

the desired dilutions and incubated at 28°C for 1 wk. Any bacteria and fungi

appeared on these plates were considered as salt tolerant. Clear colonies of bacteria

and fungi on these plates were selected and multiplied further on relevant media.

4.4.5.2 Inoculation of soil salt tolerant microorganisms

In order to inoculate the soil with the desired number of microorganisms, the

following procedure was used:

A series of dilutions were prepared by transferring a loop of bacterial or fungal

colonies from salt tolerant microorganisms cultured as above to a test tube

containing 10 mL sterilized water. After shaking, 1 mL suspension from this tube

was transferred to another test tube containing 9 mL diluents, and then 1 mL from

this to another tube until the required dilutions were obtained. From each of the 3 or

4 last dilutions, 0.1 mL suspension was transferred to bacterial or fungal plates and

incubated at 28°C for about a week and counted the number of colonies appeared on

each plate. The number of microbial cells was then calculated per mL in each

dilution. Based on these calculations, the required amount of aliquot/suspension

from selected dilutions was transferred to achieve the targeted population of 100

30

million microorganisms in each sample. After transferring, the inoculums were

thoroughly mixed in the soil.

4.4.5.3 Preparation of nutrient agar media

Nutrient agar media was prepared by dissolving 3 g beef extract, 5 g peptone, one g

yeast extract and 15 g agar powder in 1000 mL distilled water. The media was

autoclaved at 121°C for 20 min. After cooling to a pouring temperature of 48°C,

about 15 mL media was distributed evenly into each sterilized petri dish and allowed

to solidify. The plates were inverted and cured for 2 days before inoculation.

4.4.5.4 Preparation of peptone glucose acid agar media

Peptone glucose acid agar media was prepared by dissolving 5 g peptone, 10 g

glucose, 1 g KH2PO4, 0.5 g MgSO4.7H2O and 20 g agar powder dissolved in 1 L

distilled water. The media was autoclaved and plated as nutrient agar media except

that 1 mL of 0.5 N sulfuric acid (H2SO4) per 100 mL of media was added just before

plating.

4.4.6 Measurement of gypsum requirements

Gypsum requirement to reclaim a sodic or saline-sodic soil was determined by the

method of Richards (1954). An air dried 5.0 g of soil was shaken with 100 mL of

saturated gypsum solution (28 meq Ca L-1). After shaking for 30 minutes on a

mechanical shaker, the suspension was filtered. For Ca+Mg measurements in the

solution, 5 mL of the filtrate was taken and added with 10 drops of Erichrom Black-

T indicator in China dish. The solution was then titrated against 0.01 N EDTA when

the color changed from wine red to blue or green. Gypsum requirement (GR) was

calculated from the following expression:

GR(mgg-1) =

224

Ca meq 1

0).2HCaSO mg (86

(g) sample ofweight

filt.)in MgCa meq - sol.in MgCa (meq

GR (Mg ha-1) = area ha 1

cm) 15-(0 soil kg 102

kg 10

Mg 1

mg 10

soil 1kg

soil g

mg GR 6

36

31

4.4.7 Saturation moisture percentage/saturation extracts

Saturation moisture percentage in soil sample (saturation extract) was determined as

described by Gardner (1986). Distilled water was added to 250 g air dried soil till

paste had the characteristic to flow off from the spatula easily while stirring with a

spatula. The saturation moisture percentage was calculated as follows:

% Saturation = dry wt.Oven

dry wt. - wet wt.

The extract was collected from the saturation paste after kept overnight in labeled

plastic bottles and analyzed for sodium, Ca+Mg, carbonates, bicarbonates, chloride,

pH and electrical conductivity as follows:

4.4.8 Sodium

Sodium (Na) concentration in the soil saturation extract was read on flame

photometer (Jenway PFP-7). The machine was calibrated with Na standards before

running the samples.

4.4.9 Calcium and magnesium

Calcium and Mg concentration in the soil saturation extract were measured by the

versinate method as described in Richards (1954). In this method, one ml of soil

saturation extract was treated with of ammonium chloride plus ammonium hydro

oxide solution (10 drops) and 2-3 drops of Eriochrome Black-T in China dish. The

sample was titrated with EDTA (0.01N) until the color changed to blue or green.

The amount of Ca+Mg was calculated from the following expression:

Ca+Mg (meq L-1) = aliquot of ml

1000 EDTA of (ml EDTAof

4.4.10 Carbonates and bicarbonates

Carbonates and bicarbonates in the saturation extract were determined by the

titration method as described in Richards (1954). Briefly, one ml of soil saturation

extract was added with few drops of solution in a China dish. The appearance of

pink color shows the presence of CO3. The extract is then titrated with H2SO4 (0.01

32

N) up to disappearance of the pink color. Note the burette reading as y. If the extract

did not changed color at first time with phenolphthalein or after the disappearance of

color with H2SO4, methyl orange (2-3 drops) was added to the sample solution and

titrated against H2SO4 (0.01 N) to the appearance of orange color and note the

burette reading as z. Both CO3 and HCO3 were calculated with the following

expressions:

CO3 (meq L-1) = aliquot of ml

1000 SOH of N (2y 42

HCO3 (meq L-1) = aliquot of ml

1000 SOH of N 2y -(z 42

4.4.11 Chloride

Chloride concentration in the saturation extract was determined with silver nitrate

titration method as described in Richards (1954). Briefly, one mL of sample was

added with 4 drops of 5% potassium chromate solution taken in a China dish and

titrated under bright light with 0.005 N AgNO3 to the appearance of permanent

reddish brown color. The amount of Cl was calculated from the following

expression:

Cl (meq L-1) = aliquot of ml

blank)for AgNO -samplefor AgNO of (ml 33

4.4.12 Sodium adsorption ratio (SAR)

The SAR was calculated from the amount of Na and Ca+Mg in soil saturation

extract using the following expression (Richards, 1954):

SAR=

2

MgCa

Na

4.4.13 Exchangeable sodium percentage

The exchangeable sodium percentage (ESP) was calculated from the SAR value

using the following formula (Richards, 1954):

33

ESP= )01475.00126.0(1

)01475.00126.0(100

SAR

SAR

4.4.14 pH

The soil saturation extract was read for pH with the help of pH meter (InoLab,

WTW, Germany).

4.4.15 Electrical conductivity

The EC was read on EC meter (WTW, Germany) in saturation extract. The EC

meter was calibrated against KCl (0.1 N and 0.01 N) solutions before analyzing soil

sample.

4.4.16 Lime content

Acid-neutralization method was used for the determination of lime in soil (Richards,

1954). In this method, 5 g soil sample was treated with 50 mL of 0.5 M HCl. The

suspension was heated for five minutes and after cooling filtered through Whatman

No. 42. The filtrate was titrated against 0.25 N NaOH in the presence of few drops

of phenolphthalein as indicator till the appearance of pink color. The amount of lime

(CaCO3) was calculated from the following expression:

% CaCO3 =

meq = milli equivalent

4.4.17 Organic matter

Organic matter in soil samples was determined by the K2Cr2O7 method of Walkley-

Black as described by Nelson and Sommers (1996). In this method, 1 g soil sample

was treated with 10 ml of 1 N K2Cr2O7 solution and 20 ml of concentrated H2SO4.

After cooling 200 ml of distilled water was added, filtered and titrated against 0.5 N

FeSO4 solution until color changed from green to dark brown using

organophenophthaline as indicator. At the same time a blank was also run. The

following formula is used to calculate soil organic matter:

Organic matter (%) = sample ofwt

C.F.(0.69)O).7HFeSO of meq OCrK of (meq 24722

gramsin sample ofWt

100 3CaCO meq on)in titrati used NaOH meq - added HCl (meq

34

4.4.18 Soil texture

The soil texture was determined by the bouyoucos hydrometer method as described

in Gee and Bauder (1986). In this method, 50 g soil sample was treated with 10 mL

of 1N Na2CO3 and dispersed mechanically for 10 minutes. After transfer to 1000 mL

cylinder, hydrometer was placed in the suspension and read its reading once after 40

sec for silt+clay and second after 2 hrs for clay. Temperature of the suspension was

also record with each hydrometer reading and corrected the readings accordingly.

Sand was calculated by subtracting silt and clay contents from the total weight of

soil. Soil texture class was determined using USDA textural triangle.

4.5 Statistical Analysis

The results are presented in the tables are arithmetic means of three replications.

Correlations between soil microbial parameters and various soil chemical properties

were studied using Pearson correlation (Pearson, 1896). Analysis of variance was

determined using a Completely Randomized Design (Steel and Torrie, 1980). Means

significant at the 5% level were tested using LSD (Least significant difference) test.

The statistical analyses were performed by using Win Stat computer program.

35

5 RESULTS AND DISCUSSION

Salts affect soils chemically, physically and biologically. Biological effects are the

changes in osmotic pressure and alteration of protoplasmic action in plants and the

microorganisms. The effect of salts on microorganisms depends on nature of salinity

(type and extent of salt concentrations, Na hazards), soil physico-chemical

properties (soil structure, texture, sodium adsorption ratio, soil reaction and organic

matter content) and climatic condition of the area. In the present investigation the

effect of different salinity levels were evaluated on soil microbial properties both in

induced and natural salt affected soils. The results obtained are presented and

discussed as follows:

5.1 MICROBIAL BIOMASS AND ACTIVITY IN NATIVE SALT AFFECTED SOIL

5.1.1 Soil chemical characteristics

Soils collected from thirty different locations in Charsadda and Mardan districts

were analyzed for different chemical properties including electrical conductivity

(EC), pH, soluble Ca+Mg, soluble Na, sodium adsorption ratio (SAR), exchangeable

sodium percentage (ESP), carbonates, bicarbonates and chloride. Results showed

that salinity varied considerably among all the thirty soils (Table 5.1). The soil EC

ranged from 0.63-32.3 dSm-1. The EC of seventeen soils was < 4.0 dSm-1, of three

soils (S17, S18 and S19) between 4.0-8.0 dSm-1, four soils (S2, S5, S11 and S13)

between 8.0-12.0 dSm-1, and six soils >12.0 dSm-1. All the thirty samples were

alkaline in reaction with pH > 7.0. The pH of five soils (S16, S17, S20, S22, and S30)

was below 8.0, thirteen soils between 8.0-9.0, eight soils between 9.0-10.0, and four

soils (S11, S13, S14 and S25) > 10.0. Soluble salts (Ca + Mg) varied from 2.5 to 29.5

meq L-1 in the corresponding soils. The soluble salts (Ca+Mg) of 25 soils were

below 10.0 meq L-1, and of five soils (S10, S15, S17, S18, and S19) >10.0 meq L-1. The

soluble Na ranged from 0.93-395 meq L-1, with seven soils > 10.0 meq L-1, twelve

soils between 10.0-100.0 meq L-1, seven soils between 100.0-200.0 meq L-1, and

four soils had >200.0 meq L-1.

36

Table 5.1: Chemical characteristics of soils (0-20cm) used in the study

Parameter Unit Range Category No. of soils

EC dS m-1 0.63-32.3

<4.0 17 4-8 3

8-12 4 >12 6

pH -- 7.85-10.47

<8 5 8-9 13

9-10 8 >10 4

Ca+Mg meq L-1 2.5-29.5 0-10 25

>10 5

Na meq L-1 0.9-395.1

<10 7 10-100 12

100-200 7 >200 4

SAR -- 0.5-255.0 <13 12

13-100 10 >100 8

ESP -- 2.0-79.1 <15 11

15-50 9 >50 10

CO3-2 meq L-1 0-196.0

<1 10 1-5 7

5-10 8 >10 5

HCO3- meq L-1 3.5-54.5

<5 8 5-10 9

10-20 6 >20 7

Cl- meq L-1 41.7-3183.3

<50 6 50-100 11

100-200 4 >200 9

37

The sodium adsorption ratio (SAR) ranged between 0.5-255.0 with more than 50%

had >150.0, twelve soils <13.0, ten soils between 13.0-100.0, and eight soils >100.0.

Exchangeable sodium percentage (ESP) ranged from 2.01 to 79.1, with eleven soils

had <15.0, nine soils between 15.0-50.0, and ten soils >50.0. Carbonate content

ranged from 0-196.0 meq L-1, with ten soils <1.0 meq L-1, seven soils between

1.0-5.0 meq L-1, eight soils between 5.0-10.0 meq L-1, and five soils >10.0 meq L-1.

Bicarbonates contents ranged from 3.5 to 54.5 meq L-1, with eight soils <5.0 meq

L-1, nine soils between 5.0-10.0, six soils between 10.0-20.0 meq L-1, and seven soils

>20.0 meq L-1. Chloride content ranged from 41.7 to 3183 meq L-1, with six soils

<50.0 meq L-1, eleven soils between 50.0-100.0 meq L-1, four soils between

100.0-200.0 meq L-1, and nine soils >200.0 meq L-1.

5.1.2 Soil microbial characteristics

Various soil microbial attributes were measured in soils of varying salinity levels. A

depressive effect of salinity parameters were observed for all microbial indices

including microbial biomass carbon (MBC), microbial biomass nitrogen (MBN),

biomass C/N ratio, N-mineralization and nitrification (Table 5.2).

5.1.2.1 Effect of soil EC on microbiological parameters

5.1.2.1.1 Microbial biomass carbon

The results showed that soil microbial biomass carbon ranged from 147 to 516 mg

kg-1 for all the thirty soils analyzed (Table 5.3). We observed that the level of soil

microbial biomass C was lowest in soils with highest EC. The microbial biomass

ranged from 317 to 516 mg kg-1 in soils with EC of <4.0 dS m-1, 313 to 391 mg in

soils with EC between 4.0-8.0 dS m-1, 264 to 310 mg in soils with EC between

8.0-12.0 dS m-1 and 147 to 275 mg in soils with EC of greater than 12.0 dS m-1.

These results indicated that salinity had negative effect on MBC of soil. Microbial

biomass C decreased proportionally with increasing salinity (Figure 5.1). Pearson

correlation coefficient between soil electrical conductivity (EC) and microbial

biomass carbon was found negative (r = -0.89, p = 0.05, n = 30). Rietz and Haynes

(2003) found exponential negative relationship of microbial biomass carbon with

soil EC. Reports in the literature showed that in non-saline soils MBC content

ranged from 101 to 603 mg kg-1 (Powlson et al., 1987; Sparling, 1997; Anderson,

38

2003) and in saline soils 120 to 443 mg kg-1 (Tripathi et al., 2006). Our results are in

line with these findings. Tripathi et al. (2006) found significant decrease in MBC

content in coastal saline soils with higher ECe (upto 16 dS m-1).

5.1.2.1.2 Microbial biomass nitrogen

The results showed that soil MBN content varied significantly with soil EC , and

ranged from 19.0-170.2 mg kg-1 (average 79.8 mg) for all the soils under study. We

observed that the level of soil microbial biomass N was lowest in soils with highest

EC. The microbial biomass N ranged from 46.7 to 170.2 mg kg-1 in soils with EC of

<4.0 dS m-1, 38.1 to 66.4 mg in soils with EC between 4.0-8.0 dS m-1, 22.8 to 51.5

mg in soils with EC between 8.0-12.0 dS m-1 and 19 to 34.9 mg in soils with EC of

greater than 12.0 dS m-1. It was observed that soil MBN decreased proportionally

with increasing salinity (Figure 5.2). There was a significant negative exponential

relationship between EC and MBN (r = -0.74, p =0.05, n = 30). A strong negative

correlation value (r = -0.82, p =0.05, n = 30) between MBN and soil EC was found

by Yuan et al. (2007). Similar results were found by Rietz and Haynes (2003) and

Sardinha et al. (2003). Low average soil MBN content (11.0 mg kg-1) was found by

Muhammad et al. (2006) in saline and alkaline soils. Microbial biomass decreased

with increasing level of salinity, underlying the detrimental effect of salinity on soil

microorganisms (Rajab, 1993).

5.1.2.1.3 Microbial biomass C/N ratio

Our results showed that C/N ratio in microbial biomass increased with increasing

salinity, unlike the other soil microbial parameters which showed a depressive effect

with increasing salinity. We found that C/N ratio in microbial biomass ranged from

2.5 to 8.9 in soils with EC <4.0 dS m-1, 2.5 to 8.9 in soils with EC between 4.0-8.0

dS m-1, 5.8 to 11.9 in soils with EC between 8.0-12.0 dS m-1 and 4.9 to 15.1 in soils

with EC value of >12.0 dS m-1. Microbial biomass C/N ratio showed positive

relationship with soil EC (r = 0.61, p =0.05, n =30) (Figure 5.3).

39

Table 5.2: Correlation coefficient of soil EC with MBC, MBN, MB C/N ratio and Nitrification

Parameter Correlation coefficient (r) Microbial biomass carbon -0.89**

Microbial biomass nitrogen -0.74**

N-mineralization -0.57**

Microbial biomass C/N ratio 0.61**

Nitrification -0.64**

Cumulative CO2 production -0.79**

**, significant at P < 0.01

Table 5.3: Microbiological properties of soils (0-20cm) as affected by EC levels

EC (dS m-1)

No. of soils in the category

MBC (mg kg-1)

MBN (mg kg-1)

MB C/N

N-Mineralization (mg kg-1)

Nitrification (mg kg-1)

≤4.0 17

min 317.3 46.7 2.5 10.3 -2.7 max 516.3 170.2 8.9 63.1 73.7 mean 391.0 113.8 4.2 32.9 31.3 CV 42.6 32.4 1.2 14.3 20.6

4.0-8.0 3

min 313.3 38.1 5.2 13.9 7.9 max 390.8 66.4 8.9 22.9 23.9 mean 340.5 55.6 6.6 18.4 15.4 CV 33.6 11.7 1.5 3.0 5.7

8.0-12.0 4

min 263.9 22.8 5.8 5.2 -11.3 max 301.5 51.5 11.9 19.9 19.2 mean 276.3 36.8 8.1 11.8 1.2 CV 12.6 8.2 1.9 4.1 9.0

>12.0 6

min 146.8 19.0 4.9 1.9 -19.2 max 274.9 34.9 15.1 26.3 10.1 mean 208.7 24.8 10.5 10.7 -5.4 CV 32.8 4.6 3.1 9.2 8.2

40

Figure 5.1: Polynomial Regression of soil MBC with electrical conductivity

Figure 5.2: Polynomial Regression of soil MBN with electrical conductivity

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35

MBC

(mg

kg-1

)

EC (dS m-1)

r2 = 0.84

Data Y = 431.656 - 17.9667*X + 0.303157*X^2

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30 35

MBN

(mg

kg-1

)

EC (dS m-1)

r2 =0.77

Data Y = 140.49 - 13.3276*X + 0.326514*X^2

41

A low microbial biomass C/N ratio (4.36-7.67) was found by Yaun et al. (2007).

Low N availability in combination with high C availability has been shown to

increase microbial biomass C/N ratio in pure cultures of soil fungi and soil bacteria

(Anderson and Domsch, 1980). For example, strongly increased microbial biomass

C/N ratio has been observed in a German soil after glucose addition (Chander and

Joergensen, 2007), and Rasul et al. (2008) found that average C/N of the microbial

biomass was 18.0 in the sugar filter cake and biogenic waste compost treated soils.

5.1.2.1.4 Nitrogen mineralization

The results indicated that N mineralization varied considerably with salinity.

Nitrogen mineralization ranged from 10.3 to 63.1 mg kg-1 in soils with EC of <4.0

dS m-1, 13.9 to 22.9 mg in soils with EC between 4.0-8.0 dS m-1, 5.2 to 19.9 mg in

soils with EC between 8.0-12.0 dS m-1 and 1.9 to 26.3 mg in soils with EC of greater

than 12.0 dS m-1. These results suggested that nitrogen mineralization showed

negative relationship with salinity and decreased proportionally with increasing

salinity (Figure 5.4). Potentially mineralizable N is describing as a sensitive measure

of the active soil organic N pool, which is the fraction accessible to soil organisms

and enzymes (Yuan et al., 2007). Our results demonstrated that soil N

mineralization was negatively affected by salinity. The Spearman correlation

coefficient (r =-0.57, p=0.05, n = 30) calculated between EC and N mineralization

showed that N mineralization decreased with increasing salinity. As salinity

provides a stressful environment for the microbial growth and activity therefore, it

directly influence the organic matter decomposition as the primary decomposer of

organic matter. Soil microbial biomass is mainly responsible for soil organic

substrate mineralization and its turnover (Killham, 1994), and increased salinity has

been shown to decrease soil microbial biomass and rate of soil respiration (Laura,

1973; Laura, 1976; Pathak and Rao, 1998). The decrease in microbial population

with increasing salinity is due to the stress placed by osmotic potential changes in

saline soil (Batra and Manna, 1997). Under osmotic stress, microorganisms enhance

their survival by channeling the consumed C and N into biomass production and

thus decreases rate of C and N mineralization (Killham et al., 1990).

42

Figure 5.3: Polynomial Regression of soil MB C/N ratio with electrical conductivity

Figure 5.4: Polynomial Regression of soil N mineralization with electrical conductivity

Figure 5.5: Polynomial Regression of soil nitrification with electrical conductivity

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35

MB

C/N

EC (dS m-1)

r2=0.52

Data Y = 2.66382 + 0.781424*X - 0.0193463*X^2

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Net

N-M

inira

lizat

ion

(mg

kg-1

)

EC (dS m-1)

r2=0.45

Data Y = 40.5249 - 3.56584*X + 0.0865111*X^2

-40

-20

0

20

40

60

80

0 5 10 15 20 25 30 35

Net

Nitr

ifica

tion

(mg

kg-1

)

EC (dS m-1)

r2=0.55

Data Y = 44.4482 - 5.65716*X + 0.135481*X^2

43

Sarig et al. (1993) also found that increasing rate of C and N accumulation for the

microbial biomass decrease the C and N mineralization rate irrigated with saline

water (EC = 5 dS m-1). The soil microbial biomass itself is a source of easily

mineralizable organic N in soils (Bonde et al., 1988), and due to saline environment

low microbial biomass N may be related to low potentially mineralizable N.

Furthermore, species comprehension of soil microorganisms affects N

mineralization by degrading various organic compounds. Of concern is that in saline

soils complex organic material decomposition is inhibited (Badran, 1994).

5.1.2.1.5 Nitrification

Nitrification process in soil correlates negatively with soil salinity. The results

demonstrate that soil nitrification ranged from -2.7 to 74 mg kg-1 in soils with EC of

<4.0 dS m-1, 7.9 to 23.9 mg in soils with EC between 4.0-8.0 dS m-1, -11.3 to 19.2

mg in soils with EC between 8.0-12.0 dS m-1 and -19.2 to 10.1 mg in soils with EC

of greater than 12.0 dS m-1 (Table 5.3). The rate of NO3-N formation decreased

proportionally with increasing salinity (Figure 5.5). Pearson correlation coefficient

for nitrification (the oxidation of NH4-N to NO3-N) with salinity (r = -0.64, p =0.05,

n =30) showed that nitrification was significantly reduced by increasing salinity. The

literature showed that both nitrification and N mineralization were inhibited by high

salinity levels (Laura, 1976; Pathak and Rao, 1998). Increasing salinity inhibit soil

nitrification rate while ammonification rate increased in such soils (Quanzhong and

Guanhua, 2009). Similar results were found in literature (Westerman and Tucker,

1974; McCormick and Wolf, 1980; Martikainen, 1985; McClung and

Frankenberger, 1985).

5.1.2.1.6 Rate of soil respiration

The data obtained on rate of soil respiration during 2, 5, 7 and 10 days of incubation

periods are presented in Table 5.4. The results showed that the rate of CO2 evolution

decreased with increasing salinity levels. The effect of salinity on rate of CO2

evolution was more pronounced during the first two days of incubation period.

44

Figure 5.6: Influence of salinity on soil respiration during 10 days of incubation period

Table 5.4: Rate of soil respiration in response to varying salinity levels during

different incubation periods

EC (dSm-1)

No. of soils in the category

CO2 evolution (mg kg-1 d-1) Incubation period (days)

2 5 7 10

≤4.0 17

min 10.0 5.0 8.1 2.7 max 25.1 16.5 18.0 9.0 mean 18.3 9.5 13.1 6.1 CV 3.7 2.5 3.5 1.6

4.0-8.0 3

min 13.2 5.1 7.6 5.9 max 17.8 7.9 9.4 7.6 mean 14.9 6.6 8.4 6.6 CV 2.0 1.0 0.6 0.7

8.0-12.0 4

min 8.8 7.0 6.5 4.0 max 10.6 8.2 9.4 5.7 mean 9.8 7.5 7.6 4.8 CV 0.7 0.5 1.0 0.6

>12.0 6

min 1.8 1.8 4.3 2.0 max 14.1 10.4 7.0 5.7 mean 7.0 5.1 5.6 3.7 CV 3.3 2.8 0.7 1.3

0

2

4

6

8

10

12

14

16

18

20

2 5 7 10

CO

2(m

g k

g-1

soil

d-1

)

Incubation period (days)

EC <4.0

4-8

8-12

>12

45

However, differences between soils with different salinity levels become narrower

as incubations advanced to 10 days. During first 2 days, the rate of CO2 evolution

ranged from 10.0-25.1 mg kg-1 soil d-1 (average 18.3 mg) for soils with EC value of

<4.0 dS m-1, 13.2-17.8 mg (average 14.9 mg) in soils with EC between 4.0-8.0 dS

m-1, 8.8-10.6 mg (average 9.8 mg) in soils with EC between 8.0-12.0 dS m-1 and

1.8-14.1 mg (average 7.0 mg) for soils having EC >12.0 dS m-1. During the 5th day,

the rate of CO2 evolution was 5.0-16.5 mg (average 9.5 mg) for soils with EC value

of <4.0 dS m-1, 5.1-7.9 mg (average 6.6 mg) in soils with EC between 4.0-8.0 dS

m-1, 7.0-8.2 mg (average 7.5 mg) in soils with EC between 8.0-12.0 dS m-1 and

1.8-10.4 mg (average 5.1 mg) for soils having EC >12.0 dS m-1.

During the 7th day, the rate of CO2 evolution measured was 8.1-18.0 mg (average

13.1 mg) for soils with EC value of <4.0 dS m-1, 7.6-9.4 mg (average 8.4 mg) in

soils with EC between 4.0-8.0 dS m-1, 6.5-9.4 mg (average 7.6 mg) in soils with EC

between 8.0-12.0 dS m-1 and 4.3-7.0 mg (average 5.6 mg) for soils having EC >12.0

dS m-1. However, the rate of CO2 evolution measured at 10th day of incubation

period ranged from 2.7-9.0 mg (average 6.1 mg) for soils with EC value of <4.0 dS

m-1, 5.9-7.6 mg (average 6.6 mg) for soils with EC between 4.0-8.0 dS m-1, 4.0-5.7

mg (average 4.8 mg) for soils with EC between 8.0-12.0 dS m-1 and 2.0-5.7 mg

(average 3.7 mg) for soils with EC >12.0 dS m-1. The experiment indicates that

salinity influenced rate of soil respiration negatively (Figure 5.6). It is further

concluded that early days of incubation showed more response to salinity as

compared to increasing incubations because of exhaustion of the reserve of easily

decomposable C during early days of incubation.

5.1.2.1.7 Cumulative CO2 production

The results obtained on cumulative CO2 production in salt affected soils during 2, 5,

7 and 10 days of incubation period with varying salinity are presented inTable 5.5. It

was observed that cumulative CO2 production during 2 days of incubation period

ranged from 20.0-50.2 mg kg-1soil (average 36.5 mg) in soils with EC value of <4.0

dS m-1, 26.4-35.7 mg (average 29.8 mg) in soils with EC from 4.0-8.0 dS m-1,

17.6-21.2 mg (average 19.6 mg) in soils with EC between 8.0-12.0 dS m-1 and

3.6-28.1 mg (average 14.0 mg) in soils with EC >12.0 dS m-1.

46

The average CO2 production during 5 days of incubation period was 65.0 mg in soils

with EC value of <4.0 dS m-1, 49.5 mg in soils with EC between 4.0-8.0 dS m-1, 42.3

mg in soils with EC between 8.0-12.0 dS m-1, and 29.2 mg in soils with EC of >12.0

dS m-1. Similarly, the mean cumulative CO2 production during 7 days was 91 mg in

soils with EC of <4.0 dS m-1, 66.3 mg in soils with EC between 4.0-8.0 dS m-1, 58

mg in soils with EC between 8.0-12.0 dS m-1 and 40.3 mg in soils with EC value of

>12.0 dS m-1. During 10 days of incubation period the corresponding values for

cumulative CO2 production were 113 mg in soils with EC values of <4.0 dS m-1,

86.1 mg in soils with EC between 4.0-8.0 dS m-1, 72.0 mg in soils with EC between

8.0-12.0 dS m-1 and 52.8 mg in soils with EC of >12.0 dS m-1. These results

demonstrated that cumulative CO2 production in soils showed depressing trend with

increasing salinity (Figure 5.7).

It is evident from these results that cumulative CO2 production decreased with

increasing salinity. An increase in EC from 4.0-8.0 dS m-1 caused a reduction of

4.96% in CO2 production. A significant and negative Pearson correlation coefficient

was found between cumulative CO2 production and soil EC (r =-0.79, p =0.05, n =

30). Vanessa et al. (2008) found higher rate of soil respiration (56-80 mg kg-1soil) in

low salinity treatments (0.5 dS m-1) and low rate of soil respiration (1-5 mg kg-1 soil)

were observed in the mid salinity treatments (10 dS m-1). Laura (1974) also reported

that increasing salinity generally inhibit microbial activity. Similar results were

found by Trapathi et al. (2006). Rietz et al. (2001) found that the size and activity of

the soil microbial community decreased with irrigation-induced salinity. Zahran

(1997) showed that taxonomically diverse microbial groups in saline environments

can exhibit modified structural and physiological characteristics. Pankhurst et al.

(2001) found that induced salinity due to agriculture caused a shift towards a less

active, less functionally diverse, bacterial dominated community. According to

Trapathi et al. (2006) a decrease in MBC and microbial activities with a rise in

salinity is probably one of the reasons for poor crop growth in coastal saline soils.

47

Table 5.5: Cumulative CO2 production in response to varying salinity levels during different incubation periods

EC (dS m-1)

No. of soils in this category

Cumulative CO2 production (mg kg-1) Incubation period (days)

2 5 7 10

≤4.0 17

min 20.0 39.9 58.2 80.0 max 50.2 92.3 127.8 153.7 mean 36.5 65.0 91.2 112.5 CV 7.4 14.2 20.5 21.4

4.0-8.0 3

min 26.4 41.7 60.5 81.4 max 35.7 59.5 74.7 93.4 mean 29.8 49.5 66.3 86.1 CV 3.9 6.7 5.6 4.9

8.0-12.0 4

min 17.6 38.6 52.1 65.9max 21.2 45.9 63.5 80.5 mean 19.6 42.3 57.5 72.0 CV 1.5 3.1 5.1 5.1

>12.0 6

min 3.6 10.7 21.4 28.6 max 28.1 59.2 73.3 90.3 mean 14.0 29.2 40.3 52.8 CV 6.6 15.0 15.8 18.3

Figure 5.7: Salinity effect on cumulative CO2 production during 10 days of incubation period

0

20

40

60

80

100

120

2 5 7 10

CO

2(m

g k

g-1so

il)

Incubation priod (days)

EC <4.0 4.0-8.0 8.0-12.0 >12.0

48

5.1.2.2 Effect of soil pH on microbial indices

5.1.2.2.1 Microbial biomass carbon

The effect of soil pH on soil microbial properties (i.e. microbial biomass C,

microbial biomass N, microbial biomass C/N, N mineralization and nitrification)

was also assessed. We found that most of the microbial indices were affected

negatively with soil pH (Table 5.6). The results showed that the soil microbial

biomass C ranged from 313 to 516 mg kg-1 with pH <8.0, 215-462 mg with pH

8.0-9.0, 147-385 mg with pH 9.0-10.0 and 172-302 mg with pH >10.0. The

reduction in soil microbial biomass C with increasing soil pH can be observed in

Figure 5.8.

The data suggest that soil MBC was influenced negatively with increasing soil pH.

With increase in soil pH form 8 to 9, caused 10% reduction in MBC and with further

increase in pH from 9 to 10, caused 20% reduction in soil MBC. A linear negative

Pearson correlation coefficient was found for MBC with soil pH (r =-0.62, p =0.05,

n =30). Kaur et al. (2008) found that soil pH significantly influenced MBC (r

= -0.42**, n = 60) but explained only 56 and 44% variation in MBC in the

un-amended and organically amended sodic water treatment respectively. Wardle

(1992) concluded that in influencing the size of the microbial biomass soil pH is as

important as soil carbon and nitrogen concentrations.

5.1.2.2.2 Microbial biomass nitrogen

The results showed that the soil microbial biomass N was negatively influenced with

increasing soil pH (Table 5.6). Soil microbial biomass N ranged from 62.4-170.2 mg

kg-1 in soil with pH <8.0, 19.0-160.9 mg in soil with pH 8.0-9.0, 21.2-86.4 mg in soil

with pH 9.0-10.0 and 22.6-51.5 mg in soil with pH >10.0. A depressive trend of

microbial biomass N with increasing soil pH was represented in Figure 5.9.

In arid and semi-arid climate, salinity is usually combined with high soil pH due to

CaCO3 enrichment in the upper most soil layer. High pH value is principally the

results of nodules of carbonates being present in the soil profile (Yuan et al., 2007).

49

Table 5.6: Correlation coefficient of soil pH with MBC, MBN, MB C/N ratio and

Nitrification








Table 5.7: Microbial biomass C, N, Microbial biomass C/N ratio, N-mineralization and Nitrification as affected by soil pH

Soil pH No of soils in this category

MBC (mg kg-1)

MBN (mg kg-1)

MB C/N

N-mineralization (mg kg-1)


<8.0 5

min 313.3 62.4 2.7 12.1 7.9 max 516.3 170.2 5.2 62.2 66.9 mean 404.0 112.0 4.0 35.2 34.3 CV 63.5 44.8 0.9 19.2 22.9

8.0-9.0 13

min 215.4 19.0 2.5 2.4 -19.2 max 462.4 160.9 13.0 63.1 73.7 mean 363.9 100.5 5.4 26.6 23.3 CV 52.0 40.5 2.7 13.1 21.3

9.0-10.0

8

min 146.8 21.2 4.4 2.1 -13.2 max 385.2 86.4 15.1 42.2 43.2 mean 290.7 48.5 8.1 19.3 6.4 CV 65.4 27.3 3.0 11.1 16.7

>10.0 4

min 172.3 22.6 4.9 1.9 -3.2 max 301.5 51.5 12.8 22.6 19.2 mean 237.6 35.8 7.8 12.4 6.5 CV 45.1 7.8 2.5 8.9 8.1

50

It is evident from our data that soil MBN decreased with increasing soil pH. Soil

MBN showed a significantly negative Pearson correlation coefficient with soil pH (r

=-0.60, P = 0.05, n = 30). Similar negative relationship of microbial biomass with

soil pH was also reported by Kaur et al. (2008). The effect of pH on soil microbial

biomass and activities were also observed by Rietz and Haynes (2003) and Sardinha

et al. (2003). Zahran (1997) reported that high soil pH may inhibit microbial growth.

Soil pH controls biotic factors such as the biomass composition of fungi and bacteria

(Fierer and Jackson, 2006) both in forest (Frostegard et al., 1993; Blagodatskaya and

Anderson, 1998; Baath and Anderson, 2003) and agricultural soils (Arao, 1999;

Bardgett et al., 2001).

5.1.2.2.3 Microbial biomass C/N ratio

The results showed that microbial biomass C/N ratio was the only microbial

property which showed positive response to increasing soil pH (Table 5.6). We

found that microbial biomass C/N ratio ranged from 2.7-5.2 with soil pH < 8.0,

2.5-13.0 with soil pH between 8.0-9.0, 4.4-15.1 with soil pH between 9.0-10.0 and

4.9-12.8 with pH > 10.0. The trend of microbial biomass C/N ratio in response to

increasing soil pH is represented in Figure 5.10.

Microbial biomass C/N ratio increased with increasing soil pH. A significantly

positive Pearson correlation coefficient between soil pH and soil microbial biomass

C/N ratio was found (r =0.46, p =0.05, n=30). Wolters and Joergensen (1991)

reported that microbial biomass C/N ratio tends to be higher with low soil pH. The

availability of biologically toxic aluminum is increased in low soil pH (Flis et al.,

1993). Wardle (1992) concluded that the size of the microbial biomass is influenced

with soil pH similar to that of C and N concentrations. It can also affect organic C

solubility (Andersson et al., 2000), which in turn, affects microbial community

structure (Blagodatskaya and Anderson, 1998; Zelles, 1999; Marstorp et al., 2000)

and brought significant changes in soil microbial activity (Baath and Anderson,

2003).

51

Figure 5.8: Simple Regression of MBC with soil pH

Figure 5.9: Simple Regression of MBN with soil pH

y = -68.038x + 937.26r² = 0.3791

0

100

200

300

400

500

600

7 8 9 10 11

MB

C (

mg

kg-1

soil

)

Soil pH

y = -37.201x + 409.65r² = 0.3644

0

20

40

60

80

100

120

140

160

180

7 8 9 10 11

MB

N (

mg

kg-1

soil

)

Soil pH

52

5.1.2.2.4 Nitrogen mineralization

The results showed that nitrogen mineralization also varied considerably with

change in soil pH (Table 5.7). The results showed that nitrogen mineralization

ranged from 12.1-62.2 mg kg-1 in soil with pH < 8.0, 2.4-63.1 mg in soil with pH

8.0-9.0, 2.1-42.2 mg in soil with pH 9.0-10.0 and 1.9-22.6 mg in soil with pH >10.0.

The results presented in Figure 5.11 showed that nitrogen mineralization was

decreased considerably with increasing soil pH. Our results suggested that high soil

pH negatively influenced N mineralization in soil. A significantly negative Pearson

correlation coefficient (r =-0.43, p =0.05, n=30) was found between soil N

mineralization and soil pH. Mineralization of organic N is also reduces with low soil

pH (Thompson et al., 1954).

5.1.2.2.5 Nitrification

The effect of soil pH on nitrification has been represented graphically in Figure 5.12

and in Table 5.7. The results showed that the rate of soil nitrification decreased

significantly with increasing soil pH. The rate of nitrification ranged from 7.9-66.9

mg kg-1 in soil with pH <8.0, -19.2-73.7 mg in soil with pH 8.0-9.0, -13.2-43.2 mg in

soil with pH 9.0-10.0 and -3.2-19.2 mg in soil with pH > 10.0 during 10 days of

incubation period. Pearson correlation coefficient between soil pH and soil

nitrification was negative (r =-0.46, p =0.05, n=30). Robertson (1982) also reported

that soil nitrification was affected negatively with increasing soil pH. Similar results

were found by Tietema et al. (1992) and Nugroho et al. (2007). The effect of pH on

soil nitrification has been the subject of many investigations (Meiklejohn, 1954;

Broadbent et al., 1957; Morrill and Dawson, 1967; Prakasam and Loehr, 1972).

According to Morrill and Dawson (1967) the patterns of nitrification observed in

soil could be related to numbers and proliferation characteristics of nitrifying

bacteria, which in turn are controlled by factors such as pH. Nyborg and Hoyt

(1978) found that rate of soil nitrification is decreased with soil pH but increasing

concentrations of toxic elements (Fe, Al, and Mn) and base saturation did not affect

nitrification rate. Similar results were found by Harmsen and vanSchreven (1955).

53

Figure 5.10: Simple Regression of MB C/N ratio with soil pH

Figure 5.11: Simple Regression of N mineralization with soil pH

Figure 5.12: Simple Regression of Nitrification with soil pH

y = 2.0079x - 11.605r² = 0.2159

0

2

4

6

8

10

12

14

16

7 8 9 10 11

MB

C/N

rat

io

Soil pH

y = -9.4878x + 108.32r² = 0.1889

0

10

20

30

40

50

60

70

7 8 9 10 11

N m

iner

aliz

atio

n (m

g kg

-

1so

il)

Soil pH

y = -14.525x + 147.12r² = 0.2096

-40

-20

0

20

40

60

80

7 8 9 10 11

Nit

rifi

cati

on (

mg

kg-1

soil

)

Soil pH

54

5.1.2.2.6 Rate of soil respiration

The results obtained on the influence of soil pH on basal soil respiration (BSR)

measured at 2, 5, 7 and 10th days of incubation period are presented in Table 5.8.

The results showed that BSR decreased with increasing soil pH. The rate of CO2

evolution measured at 2nd day of incubation period ranged from 16.0-25.1 mg kg-1

soil d-1 (average 19.4 mg) for soil with pH value <8.0, 2.3-25.1 mg (average 16.2

mg) for soil with pH between 8.0-9.0, 1.8-24.1 mg (average 11.5 mg) for soil with

pH between 9.0-10.0 and 7.0-10.6 mg (average 9.0 mg) for soil with pH >10.0.

The rate of CO2 evolution measured at 5th day of incubation period ranged from

5.6-16.5 mg kg-1 soil d-1 (average 10.2 mg) for soil with pH <8.0, 2.5-12.3 mg

(average 8.3 mg) for soil with pH value between 8.0-9.0, 2.4-10.4 mg (average 7.5

mg) for soil with pH between 9.0-10.0 and 1.8-8.2 mg (average 5.5 mg) for soil with

pH >10.0. The rate of CO2 evolution measured at 7th day of incubation period

ranged from 7.6-17.7 mg kg-1 soil d-1 (average 12.5 mg) for soil with pH <8.0,

5.9-18.0 mg (average 12.3 mg) for soil with pH between 8.0-9.0, 5.4-14.9 mg

(average 8.3 mg) for soil with pH between 9.0-10.0 and 4.3-7.8 mg (average 5.9 mg)

for soil with pH >10.0. The rate of CO2 evolution measured at 10th day of incubation

period ranged from 3.4-9.0 mg kg-1 soil d-1 (average 6.3 mg) for soil with pH <8.0,

2.7-8.3 mg (average 5.9 mg) for soil with pH between 8.0-9.0, 2.4-8.3 mg (average

5.4 mg) for soil with pH between 9.0-10.0 and 2.0-4.4 mg (average 3.5 mg) for soil

with pH >10.0. Our results suggested that basal soil respiration decreased with

increasing soil pH as evident in Figure 5.13.

5.1.2.2.7 Cumulative CO2 production

The results obtained on cumulative CO2 production measured at 2, 5, 7 and 10 days

of incubation, in response to soil pH are presented in Table 5.9. The results showed

that cumulative basal soil respiration also decreased with increasing soil pH.

Cumulative CO2 production during 2 days of incubation period ranged from

32.0-50.2 mg kg-1 (average 38.8 mg) for soil with pH <8.0, 4.7-50.2 mg (average

32.5 mg) for soil with pH 8.0-9.0, 6-48 mg (average 23.0 mg) for soil with pH

9.0-10.0 and 14.0-21.2 mg (average 18.0 mg) for soil with pH >10.0.

55

Table 5.8: Effect of soil pH on soil respiration rate at different incubation periods

pH No. of soils in this category

Carbon dioxide evolution (mg kg-1 d-1) Incubation period (days)

2 5 7 10

<8.0 5

min 16.0 5.6 7.6 3.4 max 25.1 16.5 17.7 9.0 mean 19.4 10.2 12.5 6.3 CV 3.1 4.0 4.1 1.6

8.0-9.0 13

min 2.3 2.5 5.9 2.7 max 25.1 12.3 18.0 8.3 mean 16.2 8.3 12.3 5.9 CV 4.0 2.6 3.7 1.5

9.0-10.0 8

min 1.8 2.4 5.4 2.4 max 24.1 10.4 14.9 8.3 mean 11.5 7.5 8.3 5.4 CV 4.7 1.7 2.1 1.3

>10.0 4

min 7.0 1.8 4.3 2.0 max 10.6 8.2 7.9 4.4 mean 9.0 5.5 5.9 3.5 CV 1.0 2.1 1.3 0.7

Figure 5.13: Effect of soil pH on soil respiration rate measured during 10 days of incubation period

0

5

10

15

20

25

2 5 7 10

CO

2(m

g kg

-1so

il d-1

)


pH <8.0

8-9

9-10

>10

56

The cumulative CO2 production during 5 days of incubation period ranged from


57.5 mg) for soil with pH 8.0-9.0, 10.7-79.2 mg (average 45.6 mg) for soil with pH

9.0-10.0, and 19.4-45.9 mg (average 34.5 mg) for soil with pH >10.0. The

cumulative CO2 production during 7 days of incubation period ranged from


82 mg) for soil with pH 8.0-9.0, 21.4-109.1 mg (average 62.3 mg) for soil with pH

9.0-10.0 and 28.0-61.8 mg (average 46.4 mg) for soil with pH >10.0.

The cumulative CO2 production during 10 days of incubation period ranged from

86.5-153.7 mg kg-1 (average 115.9 mg) for soil with pH <8.0, 32.9-139.0 mg

(average 101.6 mg) for soil with pH 8.0-9.0, 28.6-129.2 mg (average 80.1 mg) for

soil with pH 9.0-10.0 and 42.0-73.7 mg (average 58.8 mg) for soil with pH >10.0.

Our results suggested that cumulative CO2 production decreased with increasing

alkalinity of the soil as evident in Figure 5.14.

A significantly negative correlation (r =-0.54, p =0.05, n = 30) was found between

cumulative CO2 production and soil pH in the natural saline soils. In this

investigation we noticed 12.84% reduction in cumulative CO2 production with

increase in soil pH from 8.0 to 9.0, and a further reduction of 27.72% was noticed

with increase in soil pH above 9.0. Xiao et al. (2005) reported that soil

dehydrogenase activity and CO2 evolution is decreased with increasing soil pH with

KOH. Increasing soil pH alters the diversity of the soil microbial community by

decreasing proliferation of microbial species (Dick et al., 2000). Rietz and Haynes

(2003) also reported that adverse pH conditions inhibit microbial growth, and thus

soil respiration tends to reduce with increasing alkalinity of the soil.

57

Table 5.9: Effect of soil pH on cumulative CO2 production

Soil pH No. of Soils in this category


2 5 7 10

<8.0 5

min 32.0 48.9 70.8 86.5 max 50.2 92.3 127.8 153.7 mean 38.8 69.5 94.4 115.9 CV 6.1 18.1 26.2 29.3

8.0-9.0 13

min 4.7 12.3 24.1 32.9 max 50.2 83.3 114.2 139.0 mean 32.5 57.5 82.0 101.6 CV 8.0 14.1 21.4 23.0

9.0-10.0 8

min 3.6 10.7 21.4 28.6 max 48.2 79.2 109.1 129.2 mean 23.0 45.6 62.3 80.1 CV 9.4 13.5 16.3 18.6

>10.0 4

min 14.0 19.4 28.0 42.0 max 21.2 45.9 61.8 73.7 mean 18.0 34.5 46.4 58.8 CV 2.0 8.3 10.9 11.0

Figure 5.14: Effect of soil pH on cumulative CO2 production

0

20

40

60

80

100

120

140

2 5 7 10

CO

2(m

g kg

-1so

il)


pH <8.0 8.0-9.0 9.0-10.0 >10.0

58

5.1.2.3 Correlation coefficient of microbial indices with sodium

The correlation coefficient of soil microbial indices (microbial biomass C, microbial

biomass N, microbial biomass C/N ratio, N mineralization and nitrification) with

sodium are presented (Table 5.10) and discussed below:

The soil microbial biomass C (MBC) ranged from 327-516 mg kg-1 (average 434 mg

kg-1) for soil with Na content of <10.0 meq L-1 to 147-231 mg (average 191 mg)

with Na content of > 200 meq L-1. A significantly negative Pearson correlation

coefficient was found (r =-0.87, p =0.05, n = 30) between MBC and soluble Na.

These results suggested that MBC in soils decreased with increasing concentration

of soluble Na. The microbial biomass N (MBN) exhibited similar trend as that of

microbial biomass C with respect to soluble Na. The soil with lowest concentration

of soluble Na contained greatest amount of MBN and vice versa (Table 5.11, Figure

5.16). The result showed that soil MBN ranged from 125.7-170.2 mg kg-1 (average

149 mg) for soil with Na content of <10.0 meq L-1 to 19.0-34.9 mg (average 26 mg)

with soluble Na content of >200 meq L-1. A significantly negative Pearson

correlation coefficient (r =-0.71, p =0.05, n = 30) was found for soil MBN and

soluble Na. The results for C/N ratio in soil microbial biomass with respect to

different concentration of Na in soil are presented in Table 5.11 and Figure 5.17.

The results showed that C/N ratio of microbial biomass became wider with

increasing concentration of soluble Na. The C/N ratio of MB ranged from 2.5-8.9

(average 3.8) for soil with soluble Na content of <10.0 meq L-1 to 4.9-13 (average

8.8) for soil with soluble Na content of >200 meq L-1. A Significantly positive

Pearson correlation coefficient (r =0.52, p =0.05, n=30) was observed between C/N

ratio of microbial biomass and Na concentration in soil. The results further showed

that nitrogen mineralization decreased considerably with increasing concentrations

of soluble Na (Table 5.11 and Figure 5.18). Nitrogen mineralization in soil ranged

from 22.6-63.1 mg kg-1 (average 47.5 mg) for soil with soluble Na content of <10

meq L-1 to 2.1-26.3 mg (average 13.4 mg) with soluble Na content of >200 meq L-1.

Significantly negative Pearson correlation coefficient (r = -0.51, p =0.05, n=30) was

found for soil N mineralization and soil Na content. Our results further showed that

soil nitrification was significantly lowered in soils with increasing concentration of

soluble Na (Table 5.11).

59

Table 5.10: Correlation coefficient of Na with MBC, MBN, MB C/N ratio and Nitrification








Table 5.11: Microbial biomass C, N, N-mineralization, Microbial biomass C/N ratio and Nitrification as influenced by soluble Na

Na (meqL-1)


MBC (mg kg-1)

MBN (mg kg-1)

N-Mineralization (mg kg-1)

MB C/N


<10.0 7

Min 326.8 125.7 22.6 2.5 28.3 max 516.3 170.2 63.1 8.9 73.7 mean 433.6 148.7 47.5 3.8 54.2 CV 41.2 14.5 14.1 1.5 14.7

10.0-100.0 12

Min 313.3 38.1 10.3 2.6 -2.7 max 390.8 131.7 42.2 8.9 43.2 mean 359.7 82.6 21.6 4.9 15.2 CV 24.1 20.1 7.0 1.3 10.8

100.0-200.0 7

Min 212.5 22.3 1.9 4.7 -11.3 max 317.3 69.0 23.5 15.1 19.2 mean 272.9 37.3 11.6 9.3 1.5 CV 21.5 13.5 5.8 3.4 9.5

>200.0 4

Min 146.8 19.0 2.1 4.9 -19.2 max 230.6 34.9 26.3 13.0 10.1 mean 191.3 25.9 13.4 8.8 -5.2 CV 31.7 5.8 11.1 2.1 11.0

60

Figure 5.15: Simple Regression of Na content on MBC

Figure 5.16: Polynomial Regression of Na content on MBN

y = -0.7415x + 401.47r² = 0.7646

0

100

200

300

400

500

600

0 50 100 150 200 250 300 350 400

MB

C (

mg

kg-1

soil

)

Na (meq L-1)

0

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300 350 400 450

Biom

ass-

N (m

g kg

-1)

Soluble Na (meq l-1)

r2=0.68

Data Y = 129.014 - 0.894937*X + 0.00171649*X^2

61

Soil nitrification ranged from 28.3-73.7 mg kg-1 (average 54.2 mg) in soil with

soluble Na content of <10 meq L-1 to -19.2-10.1 mg (average -5.2 mg) in soil with

soluble Na content of >200 meq L-1. High soil soluble Na content showed a strong

depressive effect on soil nitrification rate (Figure 5.19). A significantly negative

Pearson correlation coefficient (r =-0.66, p =0.05, n=30) was found between

nitrification rate and soluble Na contents in soil.

The results showed that rate of soil respiration decreased with increasing

concentrations of soluble Na in soil (Table 5.12). The basal soil respiration

measured at 2nd day ranged from 12.8-25.1 mg kg-1 (average 18.8 mg) in soil with

soluble Na content of <10.0 meq L-1 to 1.8-14.1 mg (average 6.3 mg) in soil with

soluble Na content of >200 meq L-1. Similarly, the soil respiration at 5th day ranged

from 7.7-16.5 mg kg-1 (average 11.5 mg) in soil with soluble Na content of <10 meq

L-1 to 1.8-10.4 mg (average 4.3 mg) in soil with soluble Na content of >200 meq L-1.

At day 7, the soil respiration ranged from 8.9-17.7 mg kg-1 (average 14.9 mg) in soil

with soluble Na content of <10 meq L-1 to 4.3-7.0 mg (average 5.6 mg) in soil with

soluble Na content of >200 meq L-1. Similarly, at day 10, the soil respiration ranged

from 3.0-9.0 mg kg-1 (average 6.3 mg) in soil with soluble Na content of <10 meq

L-1 to 2.0-5.7 mg (average 3.2 mg) in soil with soluble Na content of >200 meq L-1.

Soluble Na content showed a depressive effect on basal soil respiration as presented

in Figure 5.20. Similarly the cumulative CO2 production decreased significantly

with increasing soil soluble Na content (Table 5.13). Cumulative CO2 production

after 2 days ranged from 25.6-50.2 mg kg-1 (average 37.6 mg) in soil with soluble

Na content of <10 meq L-1 to 3.8-28.1 mg (average 12.6 mg) in soil with soluble Na

content of >200.0 meq L-1. After 5 days, cumulative CO2 production ranged from

53.9-92.3 mg kg-1 (average 72.1 mg) in soil with soluble Na content of <10 meq L-1

to 10.7-59.2 mg (average 25.4 mg) in soil with soluble Na content of >200.0 meq

L-1. Similarly, after 7 days, cumulative CO2 production ranged from 71.6-127.8 mg

kg-1 (average 102 mg) in soil with soluble Na content of <10 meq L-1 to 21.4-73.3

mg (average 36.7 mg) in soil with soluble Na content of >200.0 meq L-1. After 10

days cumulative CO2 production ranged from 92.7-153.7 mg kg-1 (average 124.6) in

soil with soluble Na content of <10 meq L-1 to 28.6-90.3 mg (average 48.4 mg) in

soil with soluble Na content of >200.0 meq L-1.

62

Figure 5.17: Simple Regression of Na content on microbial biomass C/N ratio

Figure 5.18: Simple Regression of Na content on N mineralization

Figure 5.19: Polynomial Regression of Na content on nitrification

y = 0.0173x + 4.6265r² = 0.2709

0

5

10

15

20

0 50 100 150 200 250 300 350 400

MB

C/N

rat

io

Na (meq L-1)

y = -0.0859x + 32.016r² = 0.2631

-20

0

20

40

60

80

0 50 100 150 200 250 300 350 400N m

iner

aliz

atio

n (m

g kg

-1

soil

)

Na (meq L-1)

-40

-20

0

20

40

60

80

0 50 100 150 200 250 300 350 400 450

Net

Nitr

ifica

tion(

mg

kg-1

)

Soluble Na (meq l-1)

r2=0.5

Data Y = 40.0814 - 0.402779*X + 0.000793586*X^2

63

Table 5.12: Effect of soil Na concentration on rate of respiration during different incubation periods

Na (meqL-1)


Rate of soil respiration (mg kg-1 d-1) Incubation period (days)

2 5 7 10

<10 7

min 12.8 7.7 8.9 3.0 max 25.1 16.5 17.7 9.0 mean 18.8 11.5 14.9 6.3 CV 3.8 2.3 2.6 2.0

10-100 12

min 10.0 5.0 7.6 2.7 max 25.1 11.6 18.0 8.3 mean 17.2 7.9 11.2 6.2 CV 3.5 1.9 3.1 1.3

100-200 7

min 7.7 5.0 4.9 3.5 max 17.7 8.2 9.5 5.8 mean 10.5 7.1 7.3 4.9 CV 2.1 0.9 1.4 0.8

>200 4

min 1.8 1.8 4.3 2.0 max 14.1 10.4 7.0 5.7 mean 6.3 4.3 5.6 3.2 CV 4.2 3.0 0.8 1.2

Figure 5.20: Effect of soluble Na on rate of soil respiration during different incubation periods

0

2

4

6

8

10

12

14

16

18

20

2 5 7 10

CO

2(m

g kg

-1so

il d-1

)


Na <1010-100100-200>200

64

The depressive effect of soluble Na content on cumulative basal soil respiration rate

can be best described in Figure 5.21. A significant negative Pearson correlation

coefficient (r = -0.74, p =0.05, n=30) was found between cumulative CO2

production and soluble Na concentration in soil.

The decrease in various microbial attributes due to soluble Na concentration in soil

could be due to specific ion toxicities caused by Na and Cl- and might have inhibited

microbial growth in salt affected soil (Zahran, 1999). Sodium salts deteriorate

physical properties of soil including permeability and aeration because of swelling

and dispersion of clay particles and increase soil pH, EC, and ESP (Ayers and

Westcot, 1985; Minhas et al., 2007), and thus might have resulted in reduced

microbial biomass and activities in soil (Rietz and Haynes, 2003). Microbial growth

and activity are usually limited by osmotic stress in saline soils, while under sodic

condition, microbial growth and activities are inhibited by ion toxicities and adverse

pH conditions (Rietz and Haynes, 2003). The C/N ratio of microbial biomass tends

to be wider due to decrease in C and N mineralization with increasing salinity.

Decreased mineralizations of C and N with salinity have also been observed

elsewhere (Laura, 1974; McClung and Frankenberger, 1987; Nelson et al., 1996;

Pathak and Rao, 1998). McCormic and Wolf (1980), Pathak and Rao (1998) and

Quanzhong and Guanhua (2009), also found significant inhibition in mineralization

for EC = 61.63 dS m-1 and 96.54 dS m-1. Our results with respect to the influences of

Na salt on nitrification are similar to the findings of Sindhu and Cornfield, (1967),

Laura, (1974), Laura, (1977) where nitrification was inhibited with Na salt (NaCl) at

concentration ranging from 0.5-1.0%. These results suggest that soil microbial

processes and activity are adversely affected with high amount of sodium salt.

65

Table 5.13: Cumulative CO2 production as influenced by soluble Na content

Na (meq L-1)



2 5 7 10

<10 7

min 25.6 53.9 71.6 92.7 max 50.2 92.3 127.8 153.7 mean 37.6 72.1 102.0 124.6 CV 7.6 14.6 17.8 20.1

10-100 12

min 20.0 39.9 58.2 80.0 max 50.2 83.1 112.6 135.1 mean 34.3 57.9 80.2 100.8 CV 6.9 12.7 18.7 18.7

100-200 7

min 15.5 33.2 43.1 53.6 max 35.5 53.8 72.7 90.0 mean 21.1 42.3 56.9 71.6 CV 4.2 5.0 7.8 8.5

>200 4

min 3.6 10.7 21.4 28.6 max 28.1 59.2 73.3 90.3 mean 12.6 25.4 36.7 48.4 CV 8.5 16.9 18.3 20.9

Figure 5.21: Soluble Na effect on cumulative CO2 production during different incubation periods

0

50

100

150

2 5 7 10

CO

2(m

g kg

-1so

il)


Na <10 10-100 100-200 >200

66

5.1.2.4 Correlation coefficient of microbial indices with sodium adsorption ratio


biomass N, microbial biomass C/N ratio, N mineralization and nitrification) with

SAR are presented (Table 5.14) and discussed below:

The soil microbial biomass C (MBC) ranged from 313-516 mg kg-1 (average 400

mg) in soil with SAR <13.0 to 147-275 mg kg-1 (average 224 mg) in soil with SAR

> 100. A significantly negative Pearson correlation coefficient (r = -0.86**, n = 90)

was found for MBC with SAR. Microbial biomass nitrogen (MBN) decreased

significantly with increasing SAR during the incubation experiment (Table 5.15,

Figure 5.22). Soil MBN ranged from 38.1-170.2 mg kg-1 (average 119.6 mg) in soil

with SAR <13.0 to 19-38.6 mg (average 26.2 mg) in soil with SAR >100. The

influence of SAR on soil MBN is also presented in Figure 5.23. A significant

negative Pearson correlation coefficient was found between soil MBN and SAR (r

=-0.72, p =0.05, n=30).

The effect of SAR on soil microbial biomass C/N ratio can be best described in

Figure 5.24. A significant positive Pearson correlation coefficient was found

between soil microbial biomass C/N ratio and soil SAR (r =0.53, p =0.05, n =30).

Microbial biomass C/N ratio was the only microbial property which showed positive

relationship with increasing SAR. Our results showed that microbial biomass C/N

ratio ranged from 2.5-8.9 (average 4.4) with SAR <13.0 to 4.9-15.1 (average 10.2)

with SAR >100. The results further showed that N-mineralization decreased

substantially with the increasing SAR. However, N mineralization varied

considerably with increasing SAR and ranged from 10.3-63.1 mg kg-1 (average 34.9

mg) in soil with SAR <13.0 to 1.9-26.3 mg kg-1 (average 10.8 mg) in soil with SAR

>100. The average N mineralization was 34.9 mg in soil with SAR <13.0, 22.1 mg

in soil with SAR between 13 and 100 and 10.8 mg in soil with SAR >100. These

results suggested that increasing sodicity caused a depressive effect on soil N

mineralization as presented in Figure 5.25. A significant negative Pearson

correlation coefficient (r =-0.49, p =0.05, n=30) was found between soil N

mineralization and SAR. Nitrification showed similar response to elevated SAR. It

ranged from -2.7-73.7 mg kg-1 (average 36.4 mg) in soil with SAR <13 to -19.2-10.1

mg (average 16.1 mg) in soil with SAR >100 (Table 5.15).

67

Table 5.14: Correlation coefficient of SAR with MBC, MBN, MB C/N ratio and Nitrification








Table 5.15: Microbial biomass C, N, Microbial biomass C/N ratio, N-Mineralization and Nitrification as influenced by soil SAR

SAR No. of soils in this category

MBC (mg kg-1)

MBN (mg kg-1)


MB C/N


≤13 12

min 313.3 38.1 10.3 2.5 -2.7 max 516.3 170.2 63.1 8.9 73.7 mean 399.5 119.6 34.9 4.4 36.4 CV 52.4 36.0 17.1 1.7 22.2

13-100 10

min 263.9 34.3 5.2 2.6 -1.3 max 390.8 127.2 42.2 7.7 43.2 mean 344.0 75.3 22.1 5.1 16.1 CV 32.4 21.7 6.2 1.3 10.4

>100 8

min 146.8 19.0 1.9 4.9 -19.2 max 274.9 38.6 26.3 15.1 10.1 mean 224.0 26.2 10.8 10.2 -5.8 CV 37.3 5.8 7.1 3.0 7.2

Figure 5.22: Simple Regression of MBC with soil SAR

y = -1.1785x + 400.57r² = 0.734

0

100

200

300

400

500

600

0 40 80 120 160 200 240 280

MB

C (

mg

kg-1

soil

)

SAR

68

Figure 5.23: Polynomial Regression of MBN with soil SAR

Figure 5.24: Polynomial Regression of MB C/N ratio with soil SAR

0

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300

MBN

(mg

kg-1

)

SAR

r2=0.66

Data Y = 126.096 - 1.30321*X + 0.00380645*X^2

0

2

4

6

8

10

12

14

16

0 50 100 150 200 250 300

Mic

robi

al B

iom

ass C

/N

SAR

r2=0.5

Data Y = 3.27647 + 0.0936225*X - 0.000329681*X^2

69

The depressive effect of SAR on soil nitrification is also evident in Figure 5.26. A

significantly negative Pearson correlation coefficient (r =-0.58, p =0.05, n=30) was

found between SAR and soil nitrification rate.

Soil microbial activity as measured by the rate of soil respiration decreased

significantly with increasing SAR (Table 5.16). The soil respiration rate measured at

2nd day of incubation period ranged from 12.8-25.1 mg CO2 kg-1 (average 17.7 mg)

in soil with SAR <13.0 to 1.8-14.1 mg CO2 (average 7.7 mg) in soil with SAR >100.

Similarly, at day 5 soil respiration rate ranged from 5.1-16.5 mg CO2 (average 9.8

mg) in soil with SAR <13.0 to 1.8-10.4 mg CO2 (average 5.7 mg) in soil with SAR

>100. At day 7, soil respiration rate ranged from 7.6-18.0 mg CO2 (average 13.3

mg) in soil with SAR <13.0 to 4.3-9.4 mg CO2 (average 6.2 mg) in soil with SAR

>100. Similarly, at day 10, soil respiration rate ranged from 3.0-9.0 mg CO2

(average 6.4 mg) in soil with SAR <13.0 to 2.0-5.7 mg CO2 (average 4.1 mg) in soil

with SAR >100. The depressive effect of SAR on the rate of soil respiration is also

presented in Figure 5.27. The results obtained on cumulative CO2 production are

presented in Table 5.17.

A significantly negative Pearson correlation coefficient (r = -0.73, p =0.05, n=30)

was found between cumulative CO2 production and SAR. It was observed that

cumulative CO2 production during the first two days of incubation period ranged

from 25.6-50.2 mg kg-1 (average 35.4 mg) in soil with SAR <13.0 to 3.3-28.1 mg

(average 15.3 mg) in soil with SAR >100. After 5 days, cumulative CO2 production

ranged from 41.7-92.3 mg in soil with SAR <13.0 to 10.7-59.2 mg (average 32.7

mg) in soil with SAR >100. Similarly, after 7 days, cumulative CO2 production

ranged from 60.5-127.8 mg (average 91.9 mg) in soil with SAR <13.0 to 21.4-73.3

mg (average 44.7 mg) in soil with SAR >100. After 10 days, cumulative CO2

production ranged from 83.4-153.7 mg (average 112.8 mg) in soil with SAR <13.0

to 28.6-90.3 mg (average 58.1 mg) in soil with SAR >100. The depressive effect of

SAR on cumulative CO2 production can is also presented in Figure 5.28.

70

Figure 5.25: Polynomial Regression of N mineralization with soil SAR

Figure 5.26: Polynomial Regression of Nitrification with soil SAR

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300

Net

N-M

inira

lizat

ion

SAR

r2=0.4

Data Y = 37.2777 - 0.407004*X + 0.00137973*X^2

-40

-20

0

20

40

60

80

0 50 100 150 200 250 300

Net

Nitr

ifica

tion(

mg

kg-1

)

SAR

r2=0.51

Data Y = 39.6437 - 0.640249*X + 0.00206887*X^2

71

Table 5.16: Rate of soil respiration as affected by SAR during different incubation periods

SAR No. of soils in this

category


2 5 7 10

≤13 12

min 12.8 5.1 7.6 3.0 max 25.1 16.5 18.0 9.0 mean 17.7 9.8 13.3 6.4 CV 2.8 2.7 3.7 1.5

13-100 10

min 9.4 5.0 6.5 2.7 max 25.1 11.0 15.9 8.3 mean 16.2 7.8 10.3 5.6 CV 4.8 1.6 2.9 1.6

>100 8

min 1.8 1.8 4.3 2.0 max 14.1 10.4 9.4 5.7 mean 7.7 5.7 6.2 4.1 CV 3.0 2.7 1.1 1.4

Figure 5.27: Effect of SAR on soil respiration rate measured during different incubation periods

0

2

4

6

8

10

12

14

16

18

20

2 5 7 10

CO

2(m

g kg

-1so

il d-1

)


SAR <13

13-100

>100

72

The depressive effect of SAR on soil microbial attributes has also been reported in

other studies. In a long term sodic water irrigation study, Kaur et al. (2008) found

that MBC decreased from 132.5 to 44.6 mg kg-1 soil in the upper 75 mm soil layer

and from 49.0 to 17.3 mg kg-1 soil in the 75–150 mm soil layer, and found a linear

negative relationship of MBC with SAR (r = -0.57, n = 60). Similar negative

relationship of SAR with soil microbial biomass C was also found by Rietz and

Haynes (2003). Batra et al. (1997) found lower MBC content (57 mg kg-1 soil) in a

sodic soil. Both C and N mineralization were negatively correlated with increasing

soil sodicity (Nelson et al., 1997), and caused a decrease in the amount of soil

microbial biomass (Chander et al., 1994). The lower microbial attributes in salt

affected soils could be due to reduced microbial activity caused by high salt

concentration. The lower microbial activity reduces organic matter decomposition.

The decreasing effects of salinity and sodicity on the decomposition rate were

reported elsewhere (Zahran et al., 1992; Sarig and Steinberger, 1994; Sarig et al.,

1996; Batra and Manna, 1997; Zahran, 1997; Rietz and Haynes, 2003; Sardinha et

al., 2003; Mamilov et al., 2004). Microbial biomass C to N ratio became wider with

increasing salt concentrations. This could be associated with the low mineralization

rate in high sodic soil. Nelson et al. (1997) found that plant straw mineralization

were lower in soils with high sodicity and in high clay content. Similar low

mineralization rate in high sodic soils were found by Tisdall and Oades, (1982);

Shainberg and Letely, (1984) and Nelson et al. (1996). Our results also showed that

soil nitrification was inhibited with high salt concentrations. The reduction in

nitrification in salt affected soils could be attributed to the toxic effect of high salt

concentrations. Significant inhibitions of nitrification at relatively low salt

concentration, i.e. EC of 17.15 dS m-1 were found by Quanzhong and Guanhua

(2009). Similar results were found by Westerman and Tucker, 1974; McCormick

and Wolf, 1980; Martikainen, 1985; McClung and Frankenberger, 1985;, who

reported that nitrification is more sensitive to salt than mineralization.

73

Table 5.17: Cumulative CO2 production as affected by soil SAR

SAR No. of soils in this

category


2 5 7 10

≤13 12

min 25.6 41.7 60.5 83.4 max 50.2 92.3 127.8 153.7 mean 35.4 64.9 91.5 112.8 CV 5.6 13.3 19.7 21.1

13-100 10

min 18.7 39.7 52.7 65.9 max 50.2 83.1 112.6 135.1 mean 32.5 56.0 76.6 95.7 CV 9.6 13.7 19.6 20.8

>100 8

min 3.6 10.7 21.4 28.6 max 28.1 59.2 73.3 90.3 mean 15.3 32.3 44.7 58.1 CV 5.9 13.6 15.5 18.9

Figure 5.28: SAR effect on cumulative CO2 production during different incubation periods

0

50

100

150

2 5 7 10

CO

2(m

g kg

-1so

il)


SAR <13.0

13-100

>100

74

5.1.2.5 Correlation coefficient of microbial indices with soluble salts of calcium and magnesium

The effect of soluble salts of calcium and magnesium (Ca+Mg) content on soil

microbial properties (i.e. microbial biomass C, microbial biomass N, microbial

biomass C/N, N mineralization, nitrification, rate of soil respiration and cumulative

CO2 production) is presented in Table 5.19.

The results showed that soil microbial biomass C ranged from 172-462 mg kg-1

(average 359 mg) with soluble salt (Ca+Mg) content of <4.0 meq L-1 to 147-390 mg

kg-1 (average 306 mg) with soluble salt (Ca+Mg) content of >8.0 meq L-1. The effect

of increasing Ca+Mg content on soil microbial biomass C is also described in Figure

5.29. Pearson correlation coefficient revealed that soluble salts of Ca and Mg had no

significant effect (r = -0.04, n = 30) on microbial biomass C. The response of soil

microbial N to Ca+Mg was almost the same as of SMC. It ranged from 23-166 mg

kg-1 (average 98 mg) with Ca+Mg content of <4.0 meq L-1 to 21-82 mg kg-1 (average

59 mg) with Ca+Mg content of >8.0 meq L-1. The effect of Ca+Mg on soil microbial

biomass N is also described in Figure 5.30. A negatively non-significant Pearson

correlation was found between soil MBN and Ca+Mg (r =-0.16, p =0.05, n = 30).

Variation in C/N ratio of microbial biomass with changing soluble salts of Ca+Mg is

presented in Table 5.19. Our data showed that microbial biomass C/N ratio was not

significantly affected by Ca+Mg. The average C/N ratio of MB ranged from 5.4

with Ca+Mg content of <4.0 meq L-1 to 6.1 with Ca+Mg content of > 8.0 meq L-1.

A positive but non-significant Pearson correlation coefficient (r =-0.03, p =0.05,

n=30) was found between soil microbial biomass C/N ratio and soil Ca+Mg content.

The N mineralization was generally lower for soil containing high concentrations of

Ca+Mg (Figure 5.32). On average, N mineralization ranged from 32.9 mg kg-1 soil

with Ca+Mg content of <4.0 meq L-1 to 17.0 mg with Ca+Mg content of >8.0 meq

L-1. Although the correlation between N mineralization and Ca+Mg was negative (r

=-0.18, p =0.05, n=30) but it was statistically non-significant. The pattern of

nitrification in response to Ca+Mg concentration was the same as that of N

mineralization. The rate of nitrification was lowered at high concentration of

Ca+Mg.

75

Table 5.18: Correlation coefficient of Ca+Mg with MBC, MBN, MB C/N ratio, nitrification and CO2 production

Parameter Correlation coefficient (r) Microbial biomass carbon -0.04 ns

Microbial biomass nitrogen -0.16 ns

N-mineralization -0.18 ns

Microbial biomass C/N ratio -0.03 ns

Nitrification -0.12 ns

Cumulative CO2 production -0.08 ns ns, non-significant at (P < 0.05)

Table 5.19: Microbial biomass C, N, Microbial biomass C/N ratio, N-miniralizaion and Nitrification with different soil Ca+Mg contents

Ca+Mg (meq L-1)


MBC (mg kg-1)

MBN (mg kg-1)

MB C/N



<4.0 11

min 172.3 22.8 2.6 10.2 -11.3 max 462.4 165.8 11.9 63.1 73.7 mean 359.1 97.6 5.4 32.9 28.3 CV 71.5 45.8 2.2 16.3 25.1

4.0-8.0 13

min 212.5 19.0 2.5 1.9 -19.2 max 516.3 170.2 15.1 56.1 58.8 mean 326.3 74.8 6.9 20.3 13.5 CV 70.6 45.9 3.5 12.1 19.1

>8.0 6

min 146.8 21.2 4.4 2.1 -13.2 max 389.6 82.0 8.9 31.8 29.2 mean 305.7 58.7 6.1 17.0 10.7 CV 53.0 19.4 1.8 7.6 9.6

Figure 5.29: Simple Regression of MBC with soluble salts of Ca+Mg

NS

0

100

200

300

400

500

600

0 5 10 15 20 25 30

MB

C (

mg

kg-1

soil

)

Ca+Mg (meq L-1)

76

Figure 5.30: Simple Regression of MBN with soluble salts of Ca+Mg

Figure 5.31: Simple Regression of MB C/N ratio with soluble salts of Ca+Mg

NS

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30

MB

N (

mg

kg-1

soil

)

Ca+Mg (meq L-1)

NS

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30

MB

C/N

rat

io

Ca+Mg (meq L-1)

77

The average nitrification ranged from 28.3 mg kg-1 soil with Ca+Mg content of <4.0

meq L-1 to 10.7 mg with Ca+Mg content of > 8.0 meq L-1. The effect of calcium and

magnesium salts on soil nitrification rate is also described in Figure 5.33. Like in N

mineralization, the Pearson correlation coefficient between soil nitrification and

soluble salts of Ca+Mg was negative (r = -0.12, p =0.05, n=30).

The results on basal soil respiration were presented in (Table 5.20). The results

showed that the basal respiration was almost similar for soils with varying

concentrations of Ca+Mg. The average basal respiration at day 2 was 15 mg kg-1 soil

d-1 with Ca+Mg content of <4.0 meq L-1 to 13.9 mg with Ca+Mg content of >8.0

meq L-1. The corresponding values were 8.9 and 7.9 mg kg-1 soil d-1, 11.1 and 11.0

mg kg-1 soil d-1 at day 7 and 5.9 and 5.8 mg kg-1 soil d-1 respectively at day 10. It was

evident from the data that basal respiration generally decreased with time. The effect

of Ca+Mg content on basal soil respiration is also described in Figure 5.34. The

response of cumulative CO2 production to Ca+Mg concentration was almost similar

to that of basal respiration. Although the cumulative CO2 production was

consistently lower in soil with high concentration of Ca+Mg, differences were

statistically non-significant. The average cumulative CO2 production ranged from

100 mg kg-1 soil with Ca+Mg content of <4.0 meq L-1 to 79 mg mg kg-1 soil with

Ca+Mg content of >8.0 meq L-1. The effect of soluble salts content on cumulative

CO2 production is also presented in Figure 5.35. The Pearson correlation coefficient

(r = -0.08, n = 30) found between cumulative CO2 production and concentration of

Ca+Mg were negative but statistically non-significant.

In our study we found that it is not Ca and Mg salts that influenced soil

microbiological properties but it is the Na-salt which affect the microbiological

properties negatively, either physically by deteriorating soil properties or by its toxic

effect. Therefore, soil microbial biomass and their activity are expected to respond

differently in a sodic environment than in saline environment (Kaur et al., 2008).

Although literature showed that Mg2+ behaves similar characteristics like that of Na.

Hinrich et al. (2001) found that higher exchangeable Mg2+ is associated with low

water permeability, soil crusting, and high pH, similar to characteristic conditions of

sodic (Na+ rich) soils.

78

Figure 5.32: Simple Regression of N mineralization with soluble salts of Ca+Mg

Figure 5.33: Simple Regression of nitrification with soluble salts of Ca+Mg

NS

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

N m

iner

aliz

atio

n (m

g kg

-1so

il)

Ca+Mg (meq L-1)

NS

-40

-20

0

20

40

60

80

0 5 10 15 20 25 30

Nit

rifi

cati

on (

mg

kg-1

soil

)

Ca+Mg (meq L-1)

79

Table 5.20: Rate of soil respiration as affected by soluble calcium and magnesium content during different incubation periods

Ca+Mg (meq L-1)



2 5 7 10

<4.0 11

min 7.0 1.8 4.3 2.0 max 25.1 16.5 17.7 8.3 mean 15.0 8.9 11.1 5.9 CV 5.0 2.9 3.7 1.7

4.0-8.0 13

min 2.3 2.5 4.9 2.7 max 25.1 13.9 18.0 9.0 mean 14.4 8.4 10.7 5.1 CV 5.1 2.3 4.6 1.6

>8.0 6

min 1.8 2.4 5.4 2.4 max 17.8 7.9 11.0 7.6 mean 13.9 5.7 8.6 5.8 CV 4.3 1.3 1.4 1.3

Figure 5.34: Relationship of soil respiration rate with soluble salts of Ca+Mg during different incubation periods

0

2

4

6

8

10

12

14

16

2 5 7 10

CO

2(m

g kg

-1so

il d-1

)


Ca+Mg <4.0

4.0-8.0

>8.0

80

Table 5.21: Cumulative CO2 productions (mg kg-1) as influenced by soluble Ca+Mg contents

Ca+Mg (meq L-1)



2 5 7 10

<4.0 11

min 14.0 19.4 28.0 42.0 max 50.2 92.3 127.8 151.4 mean 30.1 56.9 79.0 99.7 CV 10.0 18.0 25.4 27.5

4.0-8.0 13

min 4.7 12.3 24.1 32.9 max 50.2 92.0 126.7 153.7 mean 28.9 54.0 75.4 92.5 CV 10.3 16.8 25.2 28.0

>8.0 6

min 3.6 10.7 21.4 28.6 max 35.7 59.5 74.7 94.4 mean 27.8 44.9 62.0 79.4 CV 8.5 12.4 14.1 16.9

Figure 5.35: Relationship of cumulative CO2 production with soluble salts of Ca+Mg during different incubation periods

0

50

100

150

2 5 7 10

CO

2(m

g k

g-1so

il)


Ca+Mg <4

4.0-8.0

>8.0

81

Our results for non-significant effect of Ca+Mg on soil microbiological properties

were not in line with the findings of Yuan et al. (2007), they concluded that salinity

and Mg2+ alkalinity altered both the size and composition of the microbial biomass,

as also suggested by Walley et al. (1996).

5.1.2.6 Correlation coefficient of microbial indices with soil carbonates


biomass N, microbial biomass C/N ratio, N mineralization, nitrification, rate of soil

respiration and cumulative CO2 production) with soil CO32- content are presented

(Table 5.22) and discussed below:

The soil microbial biomass C (MBC) ranged from 313-516 mg kg-1 (average 396

mg) with CO32- content of <1.0 meq L-1 to 172-352 mg kg-1 (average 261 mg) with

CO32- content of > 10.0 meq L-1. The depressive effect of soluble CO3

2- content on

soil microbial biomass C is also presented in Figure 5.36. A significantly negative

Pearson correlation coefficient was found (r =-0.49, p =0.05, n = 30) between MBC

and soluble carbonates content. The microbial biomass N exhibited similar trend like

that of microbial biomass C with soluble CO32- content and ranged from 38-170 mg

kg-1 (average 103 mg) with CO32- content of <1.0 meq L-1 to 23-52 mg kg-1 (average

38 mg) with soluble CO32- content of >10.0 meq L-1. The effect of soil CO3

2- content

on microbial biomass N is also presented in Figure 5.37. A significantly negative

Pearson correlation coefficient (r = -0.34, p = 0.05, n = 30) was found between soil

MBN and soluble carbonates.

The effect of CO3 on C/N ratio in soil microbial biomass is presented in Table 5.23

and Figure 5.38. The results showed that C/N ratio of microbial biomass became

wider with increasing carbonates concentration in soil. The C/N ratio of MB ranged

from 2.7-8.9 (average 4.6) with soluble CO32- content of <1.0 meq L-1 to 4.9-12.8

(average 7.7) with soluble CO32- content of >10.0 meq L-1. However, correlation

coefficient (r =0.16, p =0.05, n=30) between soil microbial biomass C/N ratio and

soil carbonates content were non-significant. The results further showed that

nitrogen mineralization decreased considerably with increasing concentrations of

soil carbonates content (Table 5.23 and Figure 5.39).

82

Table 5.22: Correlation coefficient of MBC, MBN, MB C/N ratio, Nitrification and CO2 production with soil carbonates content


Microbial biomass nitrogen -0.34*

N-mineralization -0.21

Microbial biomass C/N ratio 0.16

Nitrification -0.19


*, **, significant at P < 0.05 and 0.01 respectively

Table 5.23: Microbial biomass C, N, N-Mineralization, Microbial biomass C/N ratio and Nitrification as influenced with soluble carbonates

CO3-2

(meq L-1) No. of soils in this category

MBC (mg kg-1)

MBN (mg kg-1)


MB C/N


<1.0 10

min 313.3 38.1 12.1 2.7 7.9 max 516.3 170.2 63.1 8.9 73.7 mean 395.6 103.2 34.2 4.6 34.2 CV 59.0 44.3 16.5 1.3 20.8

1.0-5.0 7

min 215.4 19.0 2.4 2.5 -19.2 max 388.6 132.5 42.2 13.0 43.2 mean 325.5 88.2 20.5 5.3 10.4 CV 47.8 36.3 10.8 2.7 19.4

5.0-10.0 8

min 146.8 21.2 2.1 3.4 -13.2 max 434.5 148.2 58.0 15.1 68.9 mean 311.1 69.8 21.6 8.1 12.2 CV 80.2 46.1 12.3 3.2 22.4

>10.0 5

min 172.3 22.6 1.9 4.9 -3.2 max 352.2 51.5 22.6 12.8 19.2 mean 260.5 38.0 13.7 7.7 7.9 CV 54.4 8.9 8.1 2.0 7.6

83

Figure 5.36: Simple Regression of soil carbonates content on MBC

Figure 5.37: Simple Regression of soil carbonates content on MBN

y = -1.0587x + 351.28r² = 0.2444

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160 180 200

MB

C (

mg

kg-1

soil

)

Soil carbonates (meq L-1)

y = -0.4027x + 86.409r² = 0.1137

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160 180 200

MB

N (

mg

kg-1

soil

)


84

Nitrogen mineralization in soil ranged from 12-63 mg kg-1 (average 34 mg) with

soluble CO32- content of <1.0 meq L-1 to 1.9-23 mg kg-1 (average 14 mg) with

soluble CO32- content of >10.0 meq L-1. A non-significant negative Pearson

correlation coefficient was found (r = -0.21, p =0.05, n=30) between soil N

mineralization and carbonates content. Our results further showed that soil

nitrification was significantly lowered in soils with increasing concentration of

soluble Na (Table 5.23). Soil nitrification ranged from 7.9-74 mg kg-1 (average 34

mg) with soluble CO32- content of <1.0 meq L-1 to -3.2-19 mg kg-1 (average 7.9 mg)

with soluble CO32- content of >10.0 meq L-1. The depressive effect of soluble CO3

2-

on soil nitrification can be best described in Figure 5.40.

A non-significantly negative Pearson correlation coefficient (r = -0.19, p =0.05,

n=30) was found between soil nitrification rate with soluble CO32- content. The

results showed that rate of soil respiration decreased with increasing concentrations

of soluble carbonates content in soil (Table 5.24). The rate of soil respiration

measured at 2nd day ranged from 12.8-25.1 mg kg-1 d-1 (average 17.8 mg) with

soluble CO32- content of <1.0 meq L-1 to 7.0-14.7 mg kg-1 d-1 (average 10.1 mg) with

soluble CO32- content of >10.0 meq L-1. Similarly, at day 5, rate of soil respiration

ranged from 5.1-16.5 mg kg-1 d-1 (average 9.2 mg) with soluble CO32- content of

<1.0 meq L-1 1.8-8.2 mg kg-1 d-1 (average 5.4 mg) with soluble CO32- content of

>10.0 meq L-1. At day 7, rate of soil respiration ranged from 7.6-17.7 mg kg-1 d-1

(average 11.7 mg) with soluble CO32- content of <1.0 meq L-1 to 4.3-8.3 mg kg-1 d-1

(average 6.4 mg) with soluble CO32- content of >10.0 meq L-1. Similarly, at day 10,

rate of soil respiration ranged from 3.4-9.0 mg kg-1 d-1 (average 6.6 mg) with soluble

CO32- content of <1.0 meq L-1 to 2.0-4.4 mg kg-1 d-1 (average 3.3 mg) with soluble

CO32- content of >10.0 meq L-1. Soluble CO3

2- content showed a depressive effect

on basal soil respiration as described in Figure 5.41. Similarly the cumulative CO2

production decreased significantly with increasing soil carbonates content (Table

5.25). Our results showed that cumulative CO2 production after 2 days ranged from

25.6-50.2 mg kg-1 (average 35.5 mg) with soluble CO32- content of <1.0 meq L-1 to

14.0-29.3 mg kg-1 (average 20.3 mg) with soluble CO32- content of >10.0 meq L-1.

Similarly, after 5 days, cumulative CO2 production ranged from 42-92 mg kg-1

(average 63 mg) with soluble CO32- content of <1.0 meq L-1 to 19.4-46 mg kg-1

(average 37 mg) with soluble CO32- content of >10.0 meq L-1.

85

Figure 5.38: Simple Regression t of soil carbonates content on MB C/N ratio

Figure 5.39: Simple Regression of soil carbonates content on N mineralization

Figure 5.40: Simple Regression of soil carbonates content on nitrification

NS

02468

10121416

0 20 40 60 80 100 120 140 160 180 200

MB

C/N

rat

io


NS

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140 160 180 200

N m

iner

aliz

atio

n (m

g kg

-1)

soil

)


NS

-40

-20

0

20

40

60

80

0 20 40 60 80 100 120 140 160 180 200

Nit

rifi

cati

on (

mg

kg-1

soil

)


86

Table 5.24: Rate of soil respiration influenced by soluble carbonates during different incubation periods

CO3-2

(meq L-1) No. of soils in this

category


2 5 7 10

<1.0 10

min 12.8 5.1 7.6 3.4 max 25.1 16.5 17.7 9.0 mean 17.8 9.2 11.7 6.6 CV 3.3 3.3 3.1 1.3

1.0-5.0 7

min 2.3 2.5 5.9 2.9 max 25.1 11.6 18.0 8.3 mean 15.0 8.5 12.8 6.1 CV 6.4 2.4 4.0 1.2

5.0-10.0 8

min 1.8 2.4 5.4 2.4 max 22.1 10.5 16.0 8.0 mean 12.8 7.9 9.2 5.1 CV 5.1 1.8 3.3 1.6

>10.0 5

min 7.0 1.8 4.3 2.0 max 14.7 8.2 8.3 4.4 mean 10.1 5.4 6.4 3.3 CV 2.0 1.8 1.4 0.8

Figure 5.41: Effect of soil carbonates content on rate of soil respiration

0

2

4

6

8

10

12

14

16

18

20

2 5 7 10

CO

2(m

g kg

-1so

il d-

1)


Carbonates <1.0

1.0-5.0

5.0-10.0

>10.0

87

Table 5.25: Cumulative CO2 production as influenced by soluble carbonates content

CO32-


category


2 5 7 10

<1.0 10

min 25.6 41.7 60.5 81.4 max 50.2 92.3 127.8 153.7 mean 35.5 63.1 86.4 107.5 CV 6.6 15.7 21.9 24.3

1.0-5.0 7

min 4.7 12.3 24.1 32.9 max 50.2 83.1 112.6 135.1 mean 30.0 55.4 81.0 99.3 CV 12.7 19.8 27.7 29.0

5.0-10.0 8

min 3.6 10.7 21.4 28.6 max 44.1 74.1 105.9 127.1 mean 25.7 49.5 68.0 86.3 CV 10.1 14.8 19.6 23.3

>10.0 5

min 14.0 19.4 28.0 42.0 max 29.3 45.9 61.8 80.0 mean 20.3 36.5 49.3 63.1 CV 4.0 8.2 11.0 12.2

Figure 5.42: Effect of soil carbonates content on cumulative CO2 production

0

50

100

150

2 5 7 10

CO

2(m

g kg

-1so

il)


Carbonates <1.01.0-5.05.0-10.0>10.0

88

After 7 days, cumulative CO2 production ranged from 61-128 mg kg-1 (average 86

mg) with soluble CO32- content of <1.0 meq L-1 to 28-62 mg kg-1 (average 49 mg)

with soluble CO32- content of >10.0 meq L-1. Similarly after 10 days, cumulative

CO2 production ranged from 81-154 mg kg-1 (average 108 mg) with soluble CO32-

content of <1.0 meq L-1 to 42-80 mg kg-1 (average 63 mg) with soluble CO32-

content of >10.0 meq L-1. The effect of soluble CO32- content on cumulative CO2

production can be best presented in Figure 5.42. A significantly negative Pearson

correlation coefficient (r = -0.43, p =0.05, n=30) was found for cumulative CO2

production with soluble carbonates content. Kara and Bolat, (2007) found that

microbial biomass carbon correlated negatively with CaCO3 content (r = -0.52**,

p<0.05). Lorenz et al. (2001) reported that liming of soil decrease soil microbial

biomass. Zahran (1997) found that carbonates and bicarbonates along with high pH

inhibit microbial growth. Black (1968) found that despite altered composition of the

soil microbial population, after liming, a portion of the soil organic matter becomes

more susceptible to mineralization; but after this portion has been decomposed,

mineralization returns to near its original level.

5.1.2.7 Correlation coefficient of microbial indices with soil bicarbonates

High bicarbonates concentrations were found among the analyzed soils (Table 5.1).

The effect of bicarbonates concentrations on soil microbiological properties are

presented in Table 5.27 and discussed below:

The average soil microbial biomass C ranged from 350 mg kg-1 with HCO3- content

of <5.0 meq L-1 to 264 mg with HCO3- content of > 20.0 meq L-1. The depressive

effect of soluble HCO3- content on soil microbial biomass C can also be observed in

Figure 5.43. A significantly negative Pearson correlation coefficient (r = -0.57, p

=0.05, n = 30) was found between MBC and soluble HCO3- content. Microbial

biomass N showed similar trend like that of microbial biomass C with soluble

HCO3- content. Soil microbial biomass N ranged from 102 mg kg-1 with HCO3

-

content of <5.0 meq L-1 to 37 mg with soluble HCO3- content of >20.0 meq L-1. Soil

microbial biomass N was significantly reduced with higher soil HCO3- content as

observed in Figure 5.44. A significantly negative Pearson correlation coefficient (r =

-0.53, p =0.05, n = 30) was found between MBN and soluble HCO3- content.

89

Table 5.26: Correlation coefficient of MBC, MBN, MB C/N ratio, Nitrification and CO2 production with soil bicarbonates content


Microbial biomass nitrogen -0.53*

N-mineralization -0.37*

Microbial biomass C/N ratio 0.38*

Nitrification -0.34*


*, **, significant at 0.05 and 0.01 respectively

Table 5.27: Microbiological properties of soils as affected by soluble HCO3- content

CO3-2

(meq L-1) No. of soils in this category

MBC (mg kg-1)

MBN (mg kg-1)


MB C/N


<1.0 10

min 313.3 38.1 12.1 2.7 7.9 max 516.3 170.2 63.1 8.9 73.7 mean 395.6 103.2 34.2 4.6 34.2 CV 59.0 44.3 16.5 1.3 20.8

1.0-5.0 7

min 215.4 19.0 2.4 2.5 -19.2 max 388.6 132.5 42.2 13.0 43.2 mean 325.5 88.2 20.5 5.3 10.4 CV 47.8 36.3 10.8 2.7 19.4

5.0-10.0 8

min 146.8 21.2 2.1 3.4 -13.2 max 434.5 148.2 58.0 15.1 68.9 mean 311.1 69.8 21.6 8.1 12.2 CV 80.2 46.1 12.3 3.2 22.4

>10.0 5

min 172.3 22.6 1.9 4.9 -3.2 max 352.2 51.5 22.6 12.8 19.2 mean 260.5 38.0 13.7 7.7 7.9 CV 54.4 8.9 8.1 2.0 7.6

90

Figure 5.43: Simple Regression of soil bicarbonates content on MBC

Figure 5.44: Polynomial Regression of soil bicarbonates content on MBN

y = -3.9164x + 386.28r² = 0.3225

0

100

200

300

400

500

600

0 10 20 30 40 50

MB

C (

mg

kg-1

soil

)

Soil bicarbonates (meq L-1)

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50 60

MBN

(mg

kg-1

)

HCO3- (meq l-1)

r2=0.38

Data Y = 135.567 - 6.31845*X + 0.0846785*X^2

91

While, the C/N ratio of microbial biomass increased with increasing HCO3- content.

Our data showed that soil microbial biomass C/N ratio ranged from 5.0 with soluble

HCO3- content of <5.0 meq L-1 to 9.4 with soluble HCO3

- content of >20.0 meq L-1.

The effect of soluble HCO3- content on microbial biomass C/N ratio can also be

presented in Figure 5.45. Unlike microbial biomass C and N, the Pearson correlation

coefficient between soil microbial biomass C/N ratio and HCO3- content was

significant and positive (r = 0.38, p =0.05, n=30). Nitrogen mineralization in soil

ranged from 30 mg kg-1 with HCO3- content of <5.0 meq L-1 to 13 mg with HCO3

-

content of >20 meq L-1. A significantly negative Pearson correlation coefficient (r =-

0.37, p =0.05, n=30) was found between soil N mineralization and bicarbonates. Our

results further showed that soil nitrification was significantly low in soils with

increasing concentration of soluble bicarbonates (Table 5.27, Figure 5.47). Soil

nitrification ranged from 24 mg kg-1 with soil HCO3- content of <5.0 meq L-1 to 2.8

mg with HCO3- content of >20.0 meq L-1. A significantly negative Pearson

correlation coefficient (r = -0.34, p =0.05, n=30) was found between soil

nitrification and soil soluble HCO3- content.

The results on basal soil respiration were presented in Table 5.28. The results

showed that basal soil respiration was much lower for soils with high bicarbonates

content. The average basal soil respiration at day 2 was 18.4 mg kg-1 d-1 with soluble

HCO3- content of <5.0 meq L-1 to 9.6 mg kg-1 d-1 with soluble HCO3

- content of

>20.0 meq L-1. Similarly, at day 5, the corresponding basal soil respiration was 8.6

and 6.0 mg kg-1 d-1, 12.3 to 6.4 mg kg-1 d-1 and 7.1 to 3.9 mg kg-1 d-1 respectively at

day 10. The depressive effect of soluble HCO3- content on soil respiration rate is

also presented in Figure 5.48. Similar depressive effect of bicarbonates was

observed on cumulative CO2 production during different incubation days (Table

5.29). The average cumulative CO2 production ranged from 109 mg CO2 kg-1 in soil

with HCO3- content of <5.0 meq L-1 to 65 mg CO2 kg-1 with HCO3

- content of >20.0

meq L-1. The effect of soluble HCO3- content on cumulative CO2 production is also

observed in Figure 5.49. A significantly negative Pearson correlation coefficient (r =

-0.56, p=0.05, n=30) was found between cumulative CO2 production and HCO3-

content.

92

Figure 5.45: Simple Regression of soil bicarbonates content on MB C/N ratio

Figure 5.46: Simple Regression of soil bicarbonates content on N mineralization

Figure 5.47: Simple Regression of soil bicarbonates content on nitrification

y = 0.1036x + 4.8148r² = 0.1475

02468

10121416

0 10 20 30 40 50

MB

C/N

rat

io


y = -0.5037x + 30.918r² = 0.1367

0

10

20

30

40

50

60

70

0 10 20 30 40 50

N m

iner

aliz

atio

n (m

g kg

-1)

soil

)


y = -0.6823x + 27.45r² = 0.1187

-40

-20

0

20

40

60

80

0 10 20 30 40 50

Nit

rifi

cati

on (

mg

kg-1

soil

)


93

Table 5.28: Rate of soil respiration influenced with bi-carbonate contents during different incubation periods

HCO3-


category


2 5 7 10

<1.0 10

min 12.8 5.1 7.6 3.4 max 25.1 16.5 17.7 9.0 mean 17.8 9.2 11.7 6.6 CV 3.3 3.3 3.1 1.3

1.0-5.0 7

min 2.3 2.5 5.9 2.9 max 25.1 11.6 18.0 8.3 mean 15.0 8.5 12.8 6.1 CV 6.4 2.4 4.0 1.2

5.0-10.0 8

min 1.8 2.4 5.4 2.4 max 22.1 10.5 16.0 8.0 mean 12.8 7.9 9.2 5.1 CV 5.1 1.8 3.3 1.6

>10.0 5

min 7.0 1.8 4.3 2.0 max 14.7 8.2 8.3 4.4 mean 10.1 5.4 6.4 3.3 CV 2.0 1.8 1.4 0.8

Figure 5.48: Effect of soil bicarbonates content on rate of soil respiration

0

2

4

6

8

10

12

14

16

18

20

2 5 7 10

CO

2(m

g kg

-1so

il d-

1 )


bi-arbonates <5.05.0-10.010.0-20.0>20.0

94

Table 5.29: Cumulative CO2 production as influenced with bicarbonates content during different incubation periods

HCO3-


category


2 5 7 10

<5.0 10

min 25.6 41.7 60.5 81.4 max 50.2 92.3 127.8 153.7 mean 35.5 63.1 86.4 107.5 CV 6.6 15.7 21.9 24.3

1.0-5.0 7

min 4.7 12.3 24.1 32.9 max 50.2 83.1 112.6 135.1 mean 30.0 55.4 81.0 99.3 CV 12.7 19.8 27.7 29.0

5.0-10.0 8

min 3.6 10.7 21.4 28.6 max 44.1 74.1 105.9 127.1 mean 25.7 49.5 68.0 86.3 CV 10.1 14.8 19.6 23.3

>10.0 5

min 14.0 19.4 28.0 42.0 max 29.3 45.9 61.8 80.0 mean 20.3 36.5 49.3 63.1 CV 4.0 8.2 11.0 12.2

Figure 5.49: Effect of soil bicarbonates content on cumulative CO2 production

0

50

100

150

2 5 7 10

CO2

(mg

kg-1

soil)


bi-carbonates <5.05.0-10.010.0-20.0>20.0

95

Our results showed that most of the microbial properties were depressed with high

concentrations of bicarbonates content. These negative effects on soil microbes

could be attributed to the increase in soil pH and deterioration of soil physical

properties with toxic bicarbonates concentrations. Decrease in soil microbial

properties with increasing soil pH is found by Zahran (1997) and Lorenz et al.

(2001).

5.1.2.8 Correlation coefficient of microbial indices with soil chloride

The correlation coefficient of soil chloride content on microbial properties (i.e.

microbial biomass C, microbial biomass N, microbial biomass C/N ratio, N

mineralization, nitrification, rate of soil respiration and cumulative CO2 production)

is presented in Table 5.30. The results showed that average soil microbial biomass C

ranged from 403 mg kg-1 with chloride content of <50.0 meq L-1 to 233 mg kg-1 with

chloride content of >200 meq L-1. The effect of chloride concentrations on MBC can

also be presented in Figure 5.50. Pearson correlation coefficient revealed that effect

of soil chloride on MBC was negative and significant (r = -0.68, p=0.05, n=30).

Microbial biomass N behaves similar trend like that of MBC with soil chloride. The

average soil microbial biomass N ranged from 118 mg kg-1 with chloride content of

<50.0 meq L-1 to 29 mg kg-1 with chloride content of >200 meq L-1. A significantly

negative Pearson correlation coefficient (r = -0.54, p =0.05, n=30) was found

between soil MBN and soluble chloride content.

Variation in microbial biomass C/N ratio with changing soil chloride content is

presented in Table 5.31. The results showed that microbial biomass C/N ratio

increased with increasing soil chloride content. The average soil microbial biomass

C/N ratio ranged from 4.8 with chloride content of <50.0 meq L-1 to 9.7 with

chloride content of >200 meq L-1. The effect of chloride content on soil microbial

biomass C/N ratio can also be observed in Figure 5.52. A positive and significant

Pearson correlation coefficient (r =0.53, p =0.05, n=30) was found between soil

microbial biomass C/N ratio and soil chloride. Nitrogen mineralization was

generally lower where soil chloride concentration was higher. On average nitrogen

mineralization ranged from 39 mg kg-1 with chloride concentrations of <50.0 meq L-

1 to 12 mg kg-1 with chloride concentration of >200 meq L-1.

96

Table 5.30: Correlation coefficient of MBC, MBN, MB C/N ratio, Nitrification and CO2 production with soil chloride content








Table 5.31: Microbiological properties of soils as affected by soil chloride content

Cl- (meqL-1)


MBC (mg kg-1)

MBN (mg kg-1)


MB C/N


≤50 6

min 313.3 62.4 12.1 2.7 7.9 max 516.3 170.2 62.2 8.9 68.9 mean 402.6 118.1 39.0 4.8 40.0 CV 53.8 43.4 19.8 1.5 24.8

50-100 11

min 263.9 34.3 5.2 2.5 -1.3 max 462.4 160.9 63.1 8.9 73.7 mean 362.6 96.5 26.0 4.7 23.7 CV 51.0 37.8 10.5 1.8 17.4

100-200 4

min 373.3 66.4 10.3 3.0 -2.7 max 390.8 131.7 42.2 5.9 43.2 mean 382.0 91.6 25.0 4.4 19.6 CV 7.7 20.1 8.6 0.7 14.0

>200 9

min 146.8 19.0 1.9 4.9 -19.2 max 301.5 51.5 26.3 15.1 19.2 mean 232.7 29.0 11.8 9.7 -3.1 CV 41.3 8.4 7.5 3.1 8.9

97

Figure 5.50: Simple Regression of soil chloride content on MBC

Figure 5.51: Polynomial Regression of soil chloride content on MBN

y = -0.0833x + 368.31r² = 0.465

0

100

200

300

400

500

600

0 400 800 1200 1600 2000 2400 2800 3200

MB

C (

mg

kg-1

soil

)

Cl (meq L-1)

-20

0

20

40

60

80

100

120

140

160

180

0 500 1000 1500 2000 2500 3000 3500

MBN

(mg

kg-1

)

Cl- (meq l-1)

r2=0.43

Data Y = 106.96 - 0.112687*X + 2.84122e-05*X^2

98

The Pearson correlation coefficient between soil chloride content and N

mineralization was found negative (r = -0.42, p =0.05, n=30). The pattern of

nitrification in response to chloride concentrations was same as that of N

mineralization (Table 5.31). The average nitrification ranged from 40 mg kg-1 with

chloride concentrations of <50.0 meq L-1 to –3.1 mg kg-1 with chloride

concentrations of >200 meq L-1. The depressive effect of soil chloride content on

soil nitrification rate can also be described in Figure 5.54. A Significantly negative

Pearson correlation coefficient (r = -0.52, p =0.05, n=30) was found between rate of

soil nitrification and chloride concentrations.

The results on basal soil respiration were presented in (Table 5.32). The results

showed that the basal respiration was decreased with varying soil chloride

concentrations. The average basal respiration at day 2 was 19.2 mg kg-1 soil d-1 with

chloride concentrations of <50 meq L-1 to 7.8 mg kg-1 soil d-1 with chloride

concentrations of >200 meq L-1. The corresponding values were 10.3 and 5.8 mg kg-

1 soil d-1, 13.1 and 6.2 mg kg-1 soil d-1 at day 7 and 6.6 and 4.2 mg kg-1 soil d-1

respectively at day 10. It was evident from the data that basal respiration generally

decreased with time. The effect of chloride concentrations on basal soil respiration is

also described in Figure 5.55. The response of cumulative CO2 production to

chloride concentration was almost similar to that of basal respiration. Although the

cumulative CO2 production was consistently lower in soil with high chloride

concentrations, with significant statistical differences. The average cumulative CO2

production ranged from 117.1 mg kg-1 soil with chloride concentrations of <50 meq

L-1 to 59 mg mg kg-1 soil with chloride concentrations of >200 meq L-1. The effect of

chloride concentrations on cumulative CO2 production is also presented in Figure

5.56. The Pearson correlation coefficient (r = -0.62, n = 30) found between

cumulative CO2 production and chloride concentrations were negative and

significant.

99

Figure 5.52: Simple Regression of soil chloride content on MB C/N ratio

Figure 5.53: Polynomial Regression of soil chloride content on N mineralization

Figure 5.54: Simple Regression of soil chloride content on nitrification

y = 0.0025x + 5.1521r² = 0.2829

0

2

4

6

8

10

12

14

16

0 400 800 1200 1600 2000 2400 2800 3200

MB

C/N

rat

io

Cl (meq L-1)

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500Net

N-M

inira

lizat

ion

Cl- (meq l-1)

r2=21

Data Y = 30.2807 - 0.0221865*X + 4.5002e-06*X^2

y = -0.0183x + 25.865r² = 0.2719

-40

-20

0

20

40

60

80

0 400 800 1200 1600 2000 2400 2800 3200

Nit

rifi

cati

on (

mg

kg-1

soil

)

Cl (meq L-1)

100

Table 5.32: Rate of soil respiration in response to varying chloride concentrations during different incubation periods

Cl- (meqL-1)



2 5 7 10

≤50 6

min 16.0 5.6 7.6 3.4 max 25.1 16.5 17.7 9.0 mean 19.2 10.3 13.1 6.6 CV 2.7 3.4 4.0 1.6

50-100 11

min 10.6 5.0 7.9 2.7 max 25.1 12.3 17.4 8.3 mean 16.9 8.4 11.6 5.6 CV 3.8 2.0 3.2 1.7

100-200 4

min 10.0 6.6 8.3 5.9 max 24.1 11.6 18.0 8.3 mean 16.3 8.8 12.6 6.7 CV 4.5 2.2 3.9 0.8

>200 9

min 1.8 1.8 4.3 2.0 max 14.1 10.4 9.4 5.7 mean 7.8 5.8 6.2 4.2 CV 2.8 2.5 1.0 1.3

Figure 5.55: Effect of soil chloride content on rate of soil respiration

0

5

10

15

20

25

2 5 7 10

CO

2(m

g kg

-1so

il d-

1 )


Cl <5050-100100-200>200

101

Table 5.33: Cumulative CO2 production as influenced by chloride contents during different incubation periods

Cl- (meqL-1)



2 5 7 10

≤50 6

min 32.0 48.9 70.8 86.5 max 50.2 92.3 127.8 153.7 mean 38.3 69.1 95.2 117.1 CV 5.4 15.4 22.7 25.6

50-100 11

min 21.2 41.7 60.5 73.7 max 50.2 83.3 114.2 139.0 mean 33.7 59.0 82.1 102.3 CV 7.5 11.6 17.8 18.7

100-200 4

min 20.0 39.9 58.2 81.4 max 48.2 79.2 109.1 129.2 mean 32.6 59.0 84.1 104.4 CV 8.9 15.4 23.1 22.1

>200 9

min 3.6 10.7 21.4 28.6 max 28.1 59.2 73.3 90.3 mean 15.7 33.1 45.6 59.0 CV 5.6 12.6 14.6 17.5

Figure 5.56: Effect of soil chloride content on cumulative CO2 production

0

50

100

150

2 5 7 10

CO

2(m

g kg

-1so

il)


Cl <50.050-100100-200>200

102

The depressive effect of chloride concentrations on soil microbial properties might

be due to specific ion effect or osmotic stress. In saline conditions the inhibition of

microbial activity is by osmotic stress, while under sodic condition, ion toxicities

and adverse pH conditions inhibit microbial growth (Rietz and Haynes, 2003).

Similar results were found by Galinski, 1995 and Oren, 1999. High chloride slats

negatively influenced the size and activity of soil microbial biomass and

biochemical processes essential for maintenance of soil organic matter (Rietz and

Haynes, 2003; Tripathi et al., 2006). Literature shows that soil microbial activity are

inhibited with increasing salt concentrations (Batra and Manna, 1997; Rietz and

Haynes, 2003). Sardinha et al. (2003) reported that as compared to heavy-metal

pollution, salinization has stronger effects on soil microbial properties (Chander et

al., 2001), causing a more stress environmental conditions for microbial

proliferation and growth in soil.

Like other microbial properties soil nitrification was also negatively affected with

high chloride concentrations. Quanzhong and Guanhua (2009) reported that the

reduction of nitrification especially in high salt concentration is due to high NaCl

salt concentrations may become toxic to organisms and the microbial activity will be

retarded. Similar results were found by McCormick and Wolf, 1980; McClung and

Frnkenberger, 1985; Pathak and Rao, 1998. Nitrification is inhibited with NaCl at

concentration ranging from 0.5-1.0% (Sindhu and Cornfield, 1967; Laura, 1974;

Laura, 1977).

103

5.2 EFFECT OF NaCl INDUCED SALINITY ON CO2 EVOLUTION AND N MINERALIZATION IN A SILTY CLAY LOAM SOIL

5.2.1 Introduction

The salt accumulation may seriously affect the physical, chemical and biological

processes as well as the N dynamics in the soils and make negative influence on

crop growth. The influence of salt on nitrogen dynamics in soils varies with salinity

levels (Laura, 1974; Westerman and Tucker, 1974; Laura, 1976; McCormic and

Wolf, 1980; McClung and Frankenberger, 1985; Pathak and Rao, 1998;). Low

salinity levels can stimulate nitrogen mineralization and nitrification (Laura, 1974;

Pathak and Rao, 1998; Chandra et al., 2002), while both processes are inhibited by

high salinity levels (Laura, 1976; McCormic and Wolf, 1980; McClung and

Frankenberger, 1985; Pathak and Rao, 1998). Salinity has been found to negatively

influence the activity and size of soil microbial biomass and biochemical processes

essential for maintenance of soil organic matter (Rietz and Haynes, 2003; Tripathi et

al., 2006). The additions of salts to soils have been shown to result in decreased

microbial activity (Johnson and Guenzi, 1963; Singh et al., 1969; Agarwal et al.,

1971; Ryan and Sims, 1974; Laura, 1974, 1976, 1977). The adverse effect of excess

salts on soil microbial community is due to changes in osmotic pressure and

alteration of protoplasmic action in plants and the microorganisms (Smedema and

Rycroft, 1983).

The objective of present research was to assess the influence of NaCl induced

salinity on rate of CO2 evolution and N mineralization in silty loam soil. The

hypothesis were: (1) increasing NaCl induced salinity have depressive effect on

microbial activity (CO2 evolution) and (2) increasing NaCl induced salinity

influence N mineralization negatively and thus low N availability could be expected

in saline soils.

5.2.2 Materials and methods

A laboratory incubation experiment was conducted to evaluate the effect of NaCl

induced salinity on microbial activity and N mineralization in soil collected from the

Agricultural Research Farm of Khyber Pakhtunkhwa Agricultural University,

Peshawar, Pakistan in November, 2009. The soil and climatic condition of the area

104

and analytical procedure used to measure microbiological and other soil

characteristics are as follows:

5.2.2.1 Experimental site

The soil was collected from Malakandher (Research Farm of Agricultural University

Peshawar). The characteristics of the experimental sites are given earlier in section

4.1. The physico-chemical properties of the experimental site are given in Table

5.34.

5.2.2.2 Soil sampling and processing

A composite soil sample (9.0 kg) was collected from upper 20 cm soil from

Malakandher Farm in November, 2009. The sample field was cultivated with wheat.

Soon after collection the sample was transferred to the laboratory of Soil and

Environmental Sciences Department in cool box and processed immediately for

measurements of microbial activities and other soil properties. The samples were

broken down by hand and passed through < 4.0 mm sieve whilst still moist. Samples

required for measurements of microbiological characteristics were kept moist and

cool. However, part of soil samples were air-dried, ground and passed through < 2.0

mm sieve, and analyzed for ECe (Electrical conductivity of the saturation extract),

pH, CaCO3, total N, organic matter and soil texture.

5.2.2.3 Treatment arrangements


arranged in Completely Randomized Design. The soil was amended with NaCl salt

at 0, 4.87, 11.11, 18.86, 24.44, 32.44, 55.55 and 78.22 mg g-1 soil to get the desired

EC levels, respectively. The required amount of NaCl salt was dissolved in 30 mL

water and spread uniformly over the surface of 300 g soil in each incubation pot.

Peptone was not added during N mineralization.

5.2.2.4 Incubation experiment

For each treatment, moist soil sample 300 g in triplicate was taken in a clean plastic

pot and amended with the desired level of NaCl salt solution. After amendments, the

pots were incubated at 28°C. The CO2 evolution was measured at 10, 20, 30 and 40

105

days of incubation period, while N mineralization was measured at 0, 10, 20, 30 and

40 days of incubation period.

5.2.3 Soil chemical characteristics

The soil was non-saline, alkaline and low in organic matter (Table 5.34).

Table 5.34: Some properties of the soil (0-20 cm) used in the experiment

Parameter Unit Value Sand % 9 Silt % 51 Clay % 40 Textural class - Silty clay loam Organic matter % 0.8 Total N % 0.09 CaCO3 % 14.4 pHse - 7.5 Electrical Conductivityse dS m-1 0.65

se: Saturation extract

5.2.4 Results and Discussion

5.2.4.1 Rate of soil respiration

Analysis of variance based on 2-Factor (ANOVA) CRD (completely randomized

design) showed that NaCl amendments at all concentrations significantly (P<0.01)

reduced CO2 evolution during all incubation periods compared to un-amended

control treatment (Table 9.1). The maximum CO2 evolution was measured in the

control treatment during all incubation periods (Table 5.35). The results showed that

with increasing salt concentrations, the rate of CO2 evolution decreased

proportionally. Highly significant reduction in CO2 evolution occurred in soils

receiving NaCl solution at 11.11 mg g-1 soil. However, the highest reduction in CO2

evolution occurred in treatment receiving the highest amount of NaCl salt (78.22 mg

g-1 soil). We found that the lowest rate of CO2 evolution (6.1 mg kg-1d-1) occurred in

soils receiving the highest concentration of NaCl salt (78.22 mg g-1 soil). The

depressive effect of NaCl on rate of soil respiration is also presented in Figure 5.57.

During the 1st 10 days of incubation period, NaCl amendment at 4.0 dS m-1 reduced

CO2 evolution by 10.1% compared with the control treatment. The corresponding

decrease in CO2 evolution was 30.4% at 8, 48.2% at 12, 57% at 16, 62.4% at 20,

106

67.8% at 30, and 89.3% at 40 dS m-1 compared with the control treatment. During

the following 10 days of incubation period, the reduction in CO2 evolution ranged

from 21.6% at 4 dS m-1 to 89.9% at 40 dS m-1compared with the control treatment.

Similarly during the next 10 days of incubation period, the corresponding decrease

in CO2 evolution ranged from 20.8% at 4 dS m-1 to 80.4% at 40 dS m-1compared

with the control treatment, finally during the last 10 days of incubation period, the

corresponding reduction in CO2 evolution ranged from 17.5% at 4 dS m-1 to 83.3%

at 40 dS m-1 as compared the control treatment.

The depressive effect of NaCl on CO2 evolution could be due to the specific ion

toxicities (e.g. those of Na+ and Cl-) which tend to inhibit microbial activities in

saline soils (Zahran, 1999). Rietz and Haynes (2003) also reported that microbial

growth was inhibited by ion toxicities and high soil pH under sodic conditions. High

salts accumulation also deteriorate physical properties of soil such as soil

permeability and soil aeration due to swelling and dispersion of clay particles and

increase in soil EC, ESP, and pH (Ayers and Westcot, 1985; Minhas et al., 2007)

which adversely affect microbial biomass and activities in soil (Rietz and Haynes,

2003). Other reason for the reduced activity of soil microorganisms in salt affected

soils could be the osmotic stress which is caused by large concentrations of salts in

soil solution (Galinski, 1995; Oren, 1999).

5.2.4.2 Cumulative CO2 evolution

Analysis of variance based on 2-factor (ANOVA) CR design showed that

cumulative CO2 evolution decreased significantly (P<0.01) during 40 days of

incubation period (Table 9.2). The maximum cumulative CO2 of 327.6 mg kg-1 soil

was produced in the control treatment.

However the production of cumulative CO2 decreased gradually with increasing salt

concentration. The results showed that cumulative CO2 production decreased from

328 mg at EC of < 4 dSm-1 to 45 mg kg-1 soil at EC 40 dSm-1 during 40 days of

incubation period (Table 5.36). The decreasing trend in cumulative CO2 production

in NaCl amended treatments are also depicted in Figure 5.58.

107

Table 5.35: Rate of soil respiration as influenced by NaCl induced salinity during different incubation periods

Treatments

Amount of NaCl added (mg g-1)

Target EC

(dS m-1)

Incubation period (days) 0-10 10-20 20-30 30-40

CO2 evolution (mg kg-1 soil d-1)

% Reduction

%

Reduction

% Reduction

%

ReductionT1 0.00 0.65 126.3 --- 60.5 --- 63.7 --- 77.0 ---

T2 4.87 4.00 113.5 10.1 47.5 21.6 50.5 20.8 63.6 17.5

T3 11.11 8.00 87.8 30.4 47.1 22.1 42.6 33.2 46.7 39.4

T4 18.67 12.00 65.5 48.2 34.9 42.4 32.6 48.8 36.4 52.7

T5 24.44 16.00 54.3 57.0 28.8 52.4 30.2 52.7 37.4 51.4

T6 32.44 20.00 47.4 62.4 24.6 59.3 20.1 68.5 28.7 62.7

T7 55.55 30.00 40.7 67.8 16.4 72.9 22.6 64.5 25.8 66.5

T8 78.22 40.00 13.5 89.3 6.1 89.9 12.5 80.4 12.9 83.3

LSD --- 14.96 10.76 11.27 15.65

% Reduction in CO2 production = [(control – treatment)/control] x 100

Figure 5.57: Rate of CO2 evolution as influenced by NaCl induced salinity

y = 133.47e-0.052x

R² = 0.944

y = 66.924e-0.054x

R² = 0.965

y = 57.021e-0.038x

R² = 0.9202

y = 70.588e-0.041x

R² = 0.9482

0

20

40

60

80

100

120

140

0 4 8 12 16 20 24 28 32 36 40

CO

2ev

olu

tion

(mg

kg-

1 )

EC (dSm-1)

days 0-10

10-20

20-30

30-40

108


increasing salinity. There was a sharp decrease in CO2 evolution when the NaCl

concentration increased above 11.11 mg NaCl g-1. Similar trend were observed by

McCormick and Wolf (1980). Laura, (1974) found that total microbial activity (as

measured by CO2 evolution) was generally depressed as soil salinity increased.

Similar results were found by Tripathi et al. (2006). Wong et al. (2008) reported that

soil respiration was highest (56-80 mg kg-1soil) in the low salinity treatments and

lowest (1-5 mg kg-1 soil) in the mid salinity treatments. Rietz et al. (2001) found that

irrigation induced salinity decreased the size and activity of the soil microbial

community. Zahran, (1997) showed that saline soil environments harbor

taxonomically diverse microbial groups, which exhibit modified physiological and

structural characteristics under saline conditions. Increasing salinity has shown to

decrease soil respiration rates and soil microbial biomass (Laura, 1973; Laura, 1976;

Pathak and Rao, 1998) and was attributed to stress placed on the microbial

population due to change in osmotic potential (Batra and Manna, 1997).

5.2.4.3 Nitrogen mineralization

The results showed that during 40 days of incubation period (Figure 5.59) the NaCl

amendments significantly (P<0.01) reduced N mineralization in soil. The highest

reduction in N mineralization occurred in soil receiving NaCl at >50 mg g-1 soil (EC

> 30 dSm-1) (see Table 5.37). The results demonstrated that during 10 days of

incubation period, increasing salinity to only 4 dSm-1 reduced N mineralization by

16.2%. The corresponding decrease in N mineralization with further salt (NaCl)

concentration was 8.6% at 8 dS m-1, 18% at 12.0 dS m-1, 44.9% at 16 dS m-1, 45.8%

at 20 dS m-1, 60.9% at 30 dS m-1, and 55% at 40 dS m-1 compared with the control

treatment during 10 days of incubation period. Due to NaCl salinity during 20, 30

and 40 days of incubation the extent of reduction in mineralization was almost

similar to that during the first 10 days of incubation. The decreasing trend in N

mineralization with increasing NaCl concentration is also demonstrated in Figure

5.59.

109

Table 5.36: Cumulative CO2 production during 40 days of incubation periods as influenced by NaCl induced salinity

Treat

ments

Amount

of NaCl

added

(mg g-1)

Target

EC

(dS m-1)


10 20 30 40

Cumulative CO2 production (mg kg-1)

% Red % Red % Red % Red

T1 0.00 0.65 126.2 --- 186.80 --- 250.53 --- 327.55 ---

T2 4.87 4.00 113.5 10.1 160.97 13.8 211.43 15.6 274.99 16.0

T3 11.11 8.00 87.84 30.4 134.99 27.7 177.56 29.1 224.22 31.5

T4 18.67 12.00 65.46 48.2 100.34 46.3 132.94 46.9 169.38 48.3

T5 24.44 16.00 54.28 57.0 83.07 55.5 113.23 54.8 150.68 54.0

T6 32.44 20.00 47.42 62.4 72.05 61.4 92.14 63.2 120.86 63.1

T7 55.55 30.00 40.70 67.8 57.12 69.4 79.72 68.2 105.55 67.8

T8 78.22 40.00 13.50 89.3 19.64 89.5 32.13 87.2 44.99 86.3

LSD --- 14.97 --- 17.97 --- 21.87 --- 25.7 ---

% Red. Reduction in CO2 production = [(control – treatment)/control] x 100

Figure 5.58: Cumulative CO2 production as influenced by induced NaCl salinity

0

50

100

150

200

250

300

350

10 20 30 40

CO

2ev

olut

ion

(mg

kg-1

)


t1

t2

t3

t4

t5

t6

t7

t8

110

The reduction in N mineralization with NaCl salinity demonstrates the detrimental

effect of NaCl salt on soil microbial activity. McClung and Frankenberger (1985)

reported that excessive amounts of salts have an adverse effect on biological activity

including soil enzyme activity and N mineralization. Okur et al. (2001) reported that

soil N-mineralization was more sensitive than C-mineralization to salinity. Sarig et

al (1993) reported that irrigation with saline water (EC = 5 dS m-1) increased the

accumulation of C and N in the microbial biomass, but decreased the rate of C and

N mineralization. An important pool of readily mineralizable organic N in soils is

soil microbial biomass (Bonde et al., 1988) and due to saline environment low

potentially mineralizable N may be linked to low microbial biomass N. Furthermore,

as species differ in their ability to degrade various organic compounds, N

mineralization may be affected by species composition of soil microorganisms. In

saline soils the salinity induced bacterial dominance may inhibit the decomposition

of complex organic materials (Badran, 1994). Under osmotic stress microorganisms

prefer a survival strategy in which they channel the consumed C and N to biomass

production or cell proliferation naturally results with a decline in the rate of C and N

mineralization (Killham et al., 1990). The effect of sodicity and salinity on the

decomposition of soil organic matter can be direct: by influencing microbial

organisms which form the soil microbial biomass, the size of the microbial

population and the amount of substrate available; or, indirect via the dispersion or

flocculation of inorganic colloids which can influence the availability of substrate.

Killham (1994) reported that soil microbial biomass controls turnover and

mineralization rate of organic substrate in the soil. Our results further demonstrated

that reduced rate of N mineralization with increasing NaCl salt concentration have

reduced microbial activity and in turn N mineralization in soil.

111

Table 5.37: N-mineralization as influenced by NaCl induced salinity during different incubation periods

Treatme

nts

Amount of

NaCl

added

(mg g-1)

Target

EC

(dS m-1)


10 20 30 40

N mineralization (mg kg-1 soil)

% Red % Red % Red % Red

T1 0.00 0.65 38.29 --- 70.40 --- 106.82 --- 129.56 ---

T2 4.87 4.00 32.08 16.2 56.10 20.3 85.01 20.4 114.78 11.4

T3 11.11 8.00 34.98 8.6 57.83 17.9 81.26 23.9 111.18 14.2

T4 18.67 12.00 31.41 18.0 58.22 17.3 76.96 28.0 93.93 27.5

T5 24.44 16.00 21.08 44.9 42.70 39.4 67.71 36.6 86.51 33.2

T6 32.44 20.00 20.74 45.8 38.86 44.8 65.48 38.7 77.72 40.0

T7 55.55 30.00 14.98 60.9 31.75 54.9 44.80 58.1 57.79 55.4

T8 78.22 40.00 17.22 55.0 35.31 49.8 48.69 54.4 63.15 51.3

LSD --- 7.9 --- 6.33 --- 9.07 --- 9.55 ---

Red, % Reduction in N mineralization = [(control – treatment)/control] x 100

Figure 5.59: N mineralization (mg kg-1) as influenced by induced NaCl salinity

0

30

60

90

120

150

10 20 30 40

N m

iner

aliz

atio

n (m

g kg

-1)


t1 t2 t3 t4 t5 t6 t7 t8

112

5.3 EFFECT OF MgCl2 INDUCED SALINITY ON CO2EVOLUTION AND N MINERALIZATION IN A SILTY LOAM SOIL

5.3.1 Introduction

Soil salinity and sodicity is an increasing problem worldwide. Salt affected soils

covers nearly 1 billion hectares, equal to 10% of the earth crust (Ghassemi et al.,

1995; Pessarakli and Szabolics, 1999). In Pakistan nearly 5.7 m ha of land is salt

affected. The salt affected land situated mainly in Indus plain, where about 4.2 m ha

of land is affected by salinity and water-logging, 0.12 m ha falling in the canal

commanded area, while 4.45 m ha outside it. Of all the salinized lands 1.9 m ha are

saline, 2.91 m ha are saline-sodic and 0.028 m ha sodic (Mujtaba et al., 2003). High

salts content not only affect physical and chemical properties of soil but also affect

soil microbiological properties. Osmotic stress, caused by high salinity usually limits

microbial activity and growth in saline soil, while under sodic condition, adverse pH

conditions and ion toxicities suppress biological activities (Rietz and Haynes, 2003).

The depressive effects of salinity and/or sodicity on soil biological activities

including CO2 evolution and mineralization of organic compounds have been

reported in many studies (Zahran et al., 1992; Sarig and Steinberger, 1994; Sarig et

al., 1996; Zahran, 1997; Batra and Manna, 1997; Sardinha et al., 2003; Rietz and

Haynes, 2003; Mamilov et al., 2004), but the effect of Mg2+ alkalinity is less well

understood. Unlike Ca2+ which improves soil physical properties through ionic

bonding with soil organic matter and clay particles, Mg2+ increases clay dispersion

and reduces soil aggregate stability (Zhang and Norton, 2002). The magnesium

domination process has large implications on soil deterioration and thus affects soil

microbial properties.

The present research was conducted to analyze the interactions between increasing

MgCl2 salinity and soil biological properties (CO2 evolution and N mineralization)

in silty loam soil. The hypotheses were: (1) increasing Magnesium chloride (MgCl2)

induced salinity has depressive effect on microbial activity (CO2 evolution) and (2)

increasing MgCl2 induced salinity influences N mineralization negatively and thus

low N availability could be expected in saline soils.

113


5.3.2.1 Site characteristics

A laboratory incubation experiment was conducted to evaluate microbial activity

and N mineralization in induced MgCl2 salinity in soil collected from Khyber

Pakhtunkhwa Agricultural University Peshawar Research Farm in March, 2010. The

soil and climatic condition of the area and analytical procedure used to measure

microbiological and other soil characteristics are as follows:


The soils were collected from Malakandher (Research Farm of Agricultural

University Peshawar). The physico-chemical properties of the experimental site are

given in Table 5.38.

Table 5.38: Some properties of the soil (0-20 cm) used in the experiment

Parameter Unit Sampling Soil Sand % 9.0 Silt % 49.8 Clay % 41.2 Textural class - Slity clay loam Organic matter % 1.034 Total N % 0.084 CaCO3 % 15.3 pH - 7.4 Electrical Conductivity dS m-1 0.63


Same as described in section 5.2.2.2.

5.3.2.4 Treatment arrangements


arranged in Completely Randomized Design. The soil was amended with MgCl2 salt

at 0, 6.5, 17.5, 29.0, 44.0, 66.5, 132.75 and 200 mg g-1 soil to get the desired EC

levels, respectively. The required amount of MgCl2 salt was dissolved in 30 mL

water and spread uniformly over the surface of 300 g soil.

Peptone was added at 200 µg N g-1 soil for N mineralization determination only.

114


For each treatment, moist soil sample of 300 g in triplicate was taken in clean plastic

pot and amended with the desired level of MgCl2 salt solution. After amendments,

the pots were incubated at 28°C. The CO2 evolution was measured at 10, 20 and 30

days of incubation period, while N mineralization was measured at 0, 10, 20 and 30

days of incubation period.

5.3.3 Results and Discussions


Analysis of variance based on 2-Factor (ANOVA) CRD (Completely randomized

design) showed that all treatments of MgCl2 addition significantly (P<0.01) reduced

CO2 evolution during all incubation periods (Table 9.4 and Table 5.39). A more

pronounced and significant reduction in CO2 evolution was observed for soils

receiving MgCl2 ≥ 6.5 mg g-1 soil and the highest reduction in CO2 evolution was

observed with the highest MgCl2 treatment (200 mg g-1 soil). The addition of even

the smallest amount of MgCl2 (6.5 mg g-1 soil) reduced the CO2 evolution, however

more pronounced and significant reduction in CO2 evolution occurred with MgCl2

amended at > 6.5 mg g-1 soil. The lowest CO2 evolution (4.4 mg kg-1 d-1) was

observed for soils receiving the highest concentration of MgCl2 salt (200 mg g-1

soil).

During the 1st 10 days of incubation period, MgCl2 at the rate of 6.5 mg g-1 soil

increased soil EC from 0.63 to 4.0 dS m-1 reduced CO2 evolution by 4.2%, further

increase in soil EC from 4.0 to 8.0 dS m-1 caused 22.8% reduction in CO2 evolution.

Increasing soil EC to 12.0 dS m-1 caused 42.2% reduction CO2 evolution, while soil

EC of 16.0 dS m-1 caused 59.3% reduction in CO2 evolution. Further increase in soil

EC with MgCl2 addition to 20.0 dS m-1 caused 68.6% reduction CO2 evolution and

EC of 30.0 dS m-1 caused 86.4% reduction CO2 evolution. Salt amended at the

highest concentration 200 mg MgCl2 g-1 soil increased soil EC to 40.0 dS m-1 and

caused 96.2% reduction in CO2 evolution.

During the 10-20th days of incubation period, MgCl2 at the rate of 6.5 mg g-1 soil

increased soil EC from 0.63 to 4.0 dS m-1 reduced CO2 evolution by 2.7%, further

115




EC with MgCl2 addition to 20.0 dS m-1 caused 40% reduction CO2 evolution and EC

of 30.0 dS m-1 caused 71% reduction CO2 evolution. Salt amended at the highest

concentration 200 mg MgCl2 g-1 soil increased soil EC to 40.0 dS m-1 and caused

92% reduction in CO2 evolution. During the 20-30th days of incubation period,

MgCl2 at the rate of 6.5 mg g-1 soil reduced CO2 evolution by 13.6%, further




EC with MgCl2 addition to 20.0 dS m-1 caused 46% reduction CO2 evolution and EC

of 30.0 dS m-1 caused 74% reduction CO2 evolution. Salt amended at the highest

concentration 200 mg MgCl2 g-1 soil increased soil EC to 40.0 dS m-1 and caused

96% reduction in CO2 evolution. The depressive effect of MgCl2 on rate of soil

respiration can be observed in Figure 5.60.

High Mg2+ in soil competes with Ca2+ for plant uptake, and thus reduces its

availability to plants. High Mg2+ is also associated with low soil crusting,

permeability and high pH, similar to the sodic soils characteristic conditions

(Hinrich et al., 2001).

Calcium improve soil structure, inhibit clay dispersion and helps in aggregate

stability by replacing Mg2+ and Na+ in clay (Armstrong and Tanton, 1992). By

increasing clay dispersion Mg2+ may have a deleterious effect on soil aggregate

stability as compared to Ca2+ (Zhang and Norton, 2002). And by expanding clays

resulting in disruption of aggregates, Mg2+ may also result in high swelling. Thus it

can be concluded that increasing salinity and Mg2+ alkalinity becoming detrimental

to soil microorganisms and this was demonstrated by the decline in microbial

activities.

116

Table 5.39: Rate of soil respiration in induced MgCl2 treated soils during different incubation periods

Amount of

MgCl2 added

(mg g-1)

Target EC

(dS m-1)


0-10 10-20 20-30

CO2 evolution (mg kg-1)

% Reduct % Reduct %

Reduct

0.00 0.65 114.92 --- 59.98 --- 59.91 ---

6.50 4.00 110.15 4.2 58.34 2.7 51.76 13.6

17.50 8.00 88.77 22.8 56.71 5.5 47.40 20.9

29.00 12.00 66.47 42.2 49.07 18.2 43.62 27.2

44.00 16.00 46.74 59.3 38.17 36.4 34.31 42.7

66.50 20.00 36.14 68.6 35.99 40.0 32.28 46.1

132.75 30.00 15.58 86.4 17.45 70.9 15.41 74.3

200.00 40.00 4.36 96.2 4.91 91.8 2.62 95.6

LSD --- 8.1 --- 3.11 --- 2.9 ---

% Reduct = Reduction in CO2 evolution with each increment

Figure 5.60: Rate of soil respiration as influenced by MgCl2 induced salinity

y = 111.49e-0.08x

R² = 0.9917

y = 68.13e-0.06x

R² = 0.9694

y = -1.3321x + 52.449R² = 0.9533

0

20

40

60

80

100

120

140

0 4 8 12 16 20 24 28 32 36 40

CO

2ev

olut

ion

(mg

kg-1

)

EC (dS m-1)

Incubation Periiod (0-10 days)

10-20 days

20-30 days

117

5.3.3.2 Cumulative CO2 production

Analysis of variance based on 2-factor (ANOVA) CR design showed that

cumulative CO2 evolution decreased significantly (P<0.01) during 30 days of

incubation period with all MgCl2 treatments. The lowest CO2 evolution (8.1 mg kg-

1) was observed for soils receiving the highest concentration of MgCl2 salt (Table

9.5, Table 5.40). A more pronounced and significant reduction in CO2 evolution was

observed for soils receiving MgCl2 ≥ 17.5 mg g-1 soil and the highest reduction in

CO2 evolution was observed with the highest MgCl2 treatment (200 mg g-1 soil). The

addition of even the smallest amount of MgCl2 (6.5 mg g-1 soil) reduced the CO2

evolution, however more pronounced and significant reduction in CO2 evolution

occurred with NaCl amended at ≥ 17.5 mg g-1 soil.

Increasing soil EC from 0.65 to 4.0 dS m-1 through MgCl2 amendment caused 6.2%

reduction in soil microbial activities (measured as CO2 evolution) compared to un-

amended control soil. Further increase in soil EC from 4.0 to 8.0 dS m-1 caused 18%

reduction in CO2 evolution. Increasing soil EC from 20 dS m-1 with MgCl2 addition

(66.5 mg g-1 soil) cause >50% reduction in cumulative CO2 evolution, while EC of

30 dS m-1 caused 60% reduction in CO2 evolution as compared to control and goes

to 95% reduction as soil EC increased to 40 dS m-1 with the highest MgCl2

treatments. The reduction in CO2 evolution indicates that the microorganisms are

stressed by the saline conditions. The depressive effect of MgCl2 on cumulative CO2

evolution can be observed in Figure 5.61. The lowest CO2 evolution (8.1 mg kg-1)

was observed for soils receiving the highest concentration of MgCl2 salt.

118

Table 5.40: Cumulative CO2 production (mg kg-1) during different incubation periods as influenced by MgCl2 induced salinity

Amount of MgCl2

added (mg g-1)

Targeted

EC

(dS m-1)


10 20 30

Cumulative CO2 production (mg kg-1)

--- %Red --- %Red --- %Red

0.00 0.65 114.92 --- 174.90 --- 234.81 ---

6.50 4.00 110.15 4.2 168.49 3.7 220.25 6.2

17.50 8.00 88.77 22.8 145.47 16.8 192.87 17.9

29.00 12.00 66.47 42.2 115.54 33.9 159.16 32.2

44.00 16.00 46.74 59.3 84.90 51.5 119.22 49.2

66.50 20.00 36.14 68.6 72.13 58.8 104.41 55.5

132.75 30.00 15.58 86.4 33.03 81.1 48.44 79.4

200.00 40.00 4.36 96.2 9.27 94.7 11.89 94.9

LSD --- 8.1 --- 9.5 --- 9.78 ---

% Red = Reduction in CO2 evolution with each increment

Figure 5.61: Cumulative CO2 production as influenced by MgCl2 induced salinity

0

50

100

150

200

250

10 20 30

Cum

ulat

ive

CO

2ev

olut

ion

(mg

kg-1

soil)


T1 T2 T3 T4 T5 T6 T7 T8

119


increasing MgCl2 salinity. When the MgCl2 concentration increased above 6.5 mg

MgCl2 g-1, there was a sharp decrease in CO2 evolution, similar trend was observed

by Yuan et al. (2007), Ronald et al. (1979). In another experiment Laura, (1974)

found that total microbial activity (as measured by CO2 evolution) was usually

depressed with the increase in soil salinity. Similar results were found by Trapathi et

al. (2006). Vanessa et al. (2008) reported that soil respiration was lowest (1-5 mg

kg-1 soil) in the mid salinity treatments and highest (56-80 mg kg-1soil) in the low

salinity treatments. Rietz et al. (2001) showed that size and activity of the soil

microbial community decreased with irrigation induced salinity. Zahran, (1997)

found that under saline environments microbial growth and structure are

taxonomically modified which perform different physiological characteristics under

such conditions.

5.3.3.3 Nitrogen mineralization

Analysis of variance based on 8 treatments and 3 replications (CR design) showed

that all treatments had significantly (P<0.01) and negatively affect soil N

mineralization during 30 days of incubation period. The initial values at control

treatment showed that soil N mineralization was normal (Figure 5.62, Table 9.6 &

Table 5.41). N mineralization was reduced with MgCl2 treatments >4.0 dS m-1,

while the highest reduction in N mineralization was observed for soil receiving

MgCl2 in amount >50 mg g-1 soil.

During the 1st 10 days of incubation period N mineralization reduced from 93.3 to

18.4 mg kg-1 soil with control and highest MgCl2 treated soil respectively and

caused a net 80% reduction in N mineralization. During the 20 days of incubation

period N mineralization was 145.1 mg kg-1 for control and reduced to 26.2 mg kg-1

with the highest MgCl2 treatment (200 mg g-1 soil) which caused 82% reduction in

N mineralization. N mineralization measured after 30 days of incubation period was

185.4 mg kg-1 and 34.5 mg kg-1 for control and highest MgCl2 treated soil

respectively, which caused a net reduction of 81% in N mineralization. N

mineralization was reduced with all MgCl2 treatments, while significant reduction in

N mineralization was observed for soil receiving MgCl2 in amount >6.5 mg g-1 soil,

120

but no significant effect in N mineralization was observed for soils receiving MgCl2

<6.5 mg g-1 soil.

Application of MgCl2 at the lowest rate (6.5 mg g-1 soil) not significantly reduced N

mineralization by 10% during 1st 10 days of incubation period, 7.4% during 20 days

of incubation period and 6% during 30 days of incubation period. An abrupt

decrease in N mineralization was observed with the addition of > 17.5 mg MgCl2 g-1

soil during all incubation periods. The exponential decline in microbial activities

with MgCl2 salinity demonstrates the extremely detrimental effect of small increase

in salinity. Thus it can be concluded that soil N-mineralization affected negatively

with salinity. The depressive effect of MgCl2 on N mineralization rate can be

observed in Figure 5.62.

The increased EC with increasing MgCl2, result in higher osmotic pressure that

could result in cell lyses (Killham et al., 1990). By inhibiting microbial growth and

activities, salinity and Mg2+ alkalinity may directly decrease organic matter

decomposition. Reduction in soil microbial activities due to increased Mg2+

alkalinity and salinity caused an exponential decline in potentially mineralizable N.

Different species are involved in N mineralization, therefore species composition

may also effect N mineralization. The salinity-induced reduction of fungi may

reduce the decomposition of complex organic material in saline-soils (Badran,

1994). In a research Bandyopadhyay and Bandyopadhyay, (1983) found that

mineralization and immobilization of N were decreased with increasing salinity. The

microbial biomass of soil controls organic matter mineralization and turnover rate

(Killham, 1994). Increasing in salinity produced considerable reduction both in soil

microbial biomass and soil respiration rates (Laura, 1973; Laura, 1976; Pathak and

Rao, 1998) and microbial population is reduced with increasing osmotic potential in

soils (Batra and Manna, 1997).

121

Table 5.41: N-mineralization during different incubation periods as influenced by MgCl2 induced salinity

MgCl2

added

(mg g-1)

Targeted

EC

(dS m-1)


10 20 30

N mineralization (mg kg-1)

--- %Reduct --- %Reduct --- %Reduct

0.00 0.65 93.32 --- 145.08 --- 185.40 ---

6.50 4.00 84.09 9.9 134.32 7.4 174.24 6.0

17.50 8.00 71.22 23.7 108.55 25.2 144.63 22.0

29.00 12.00 54.69 41.4 80.67 44.4 105.70 43.0

44.00 16.00 42.42 54.5 63.43 56.3 80.11 56.8

66.50 20.00 33.94 63.6 45.77 68.5 57.61 68.9

132.75 30.00 22.91 75.4 32.05 77.9 40.88 78.0

200.00 40.00 18.40 80.3 26.24 81.9 34.45 81.4

LSD --- 9.7 --- 12.2 --- 14.8 ---

% Reduct = Reduction in CO2 evolution with each increment

Figure 5.62: N mineralization as influenced by MgCl2 induced salinity

0

40

80

120

160

200

10 20 30

N m

iner

aliz

atio

n (m

g kg

-1so

il )


T1 T2 T3 T4 T5 T6 T7 T8

122

5.4 COMPARATIVE EFFECT OF PRESSMUD, GYPSUM, FARMYARD MANURE AND MICROBIAL INOCULATIONS ON SOIL MICROBIAL BIOMASS AND ACTIVITY IN SALINE SODIC SOIL

5.4.1 Introduction

Gypsum, pressmud and FYM have been successfully used for amelioration of

saline-sodic and sodic soils. Pressmud (the byproduct of sugar mills) as a fertilizer

has been used as an ameliorant in sodic and saline-sodic soils (Raman et al., 1999;

Barry et al., 2001; Qureshi et al., 2001; Rangaraj et al., 2007; Elsayed et al., 2008).

In Pakistan sugar is extracted from the sugarcane juice by carbonation (Lime or

addition of CO2) and thus contains high amount of lime. The pressmud contains 2-

3% sugar, 15-20% organic matter, and approximately 70% lime as CaCO3

(Muhammad and Khaliq, 1975; Khattak and Khan, 2004). The organic matter is

highly soluble and readily available to the soil and so to the microbial activity. More

CO2 is produced due to the microbial activity that may increases the solubility of

lime and hence its effectiveness in reclaiming saline sodic soils (Qadir et al., 2006;

Robbins, 1986a).

However alone application of organic matter is quite a slow process for the

reclamation of saline soil (Muhammad and Khaliq, 1975; Chaudhry et al., 1982;

Chand et al., 1997), therefore, combination of different chemical amendments along

with organic matter is advised by many researchers for more efficient amelioration

of saline sodic soils (Hussain et al., 2001; Chaudhry, 2001; Qadir et al., 2007; Clark

et al., 2007).

In this study an attempt was made to evaluate the effect of pressmud (PM), farmyard

manure (FYM) and gypsum (G) either applied alone or in different combinations in

strongly saline-sodic silt loam soil to assess soid microbial activity (soil respiration)

and microbial biomass over a period of time.

The objectives of the study were to:

• To assess the microbiological properties of native salt affected soils.

123

• To study the effect of different amendments used in reclamation of salt

affected soil on plant growth and soil microbiological properties.



A laboratory incubation experiment was conducted to evaluate the comparative

effect of gypsum, farmyard manure, pressmud, and microbial inoculation on soil

microbial biomass and activity in saline sodic soil collected from Majoke (Khati

Khel soil series), Charsadda. The sampling site was situated near Charsadda Paper

Mill. The site (District Charsadda) characteristics are earlier discussed in section 4.1.

The soil was strongly saline sodic having EC value of 20 dS m-1, pH 10.0 with silt

loam texture.


A composite soil sample (100 kg) was collected from 0-20 cm uncultivated barren

soil layer from Majoke in April, 2010. Soon after collection the samples were

transferred to the Lab of Soil and Environmental Sciences Department, broken down

by hand and passed through < 4.0 mm sieve whilst still moist. Samples required for

amendments were kept in clean plastic buckets in glass house. However, part of soil

samples were air-dried, ground and passed through < 2.0 mm sieve, and analyzed for

ECe (Electrical conductivity of the saturation extract) and soil pH.

5.4.2.3 Treatments and experimental design

Plastic buckets were used with 6.0 kg soil for each treatment under study. The

treatments were arranged in CR design with three replications. Treatments included

(1) control, (2) gypsum (G), (3) pressmud (PM), (4) farmyard manure (FYM), (5)

G+FYM, (6) G+PM, (7) PM+FYM and (8) PM + FYN + microbial inoculum.

Gypsum and pressmud were applied on the basis of 100% gypsum requirement

equal to 20 Mg ha-1. FYM alone or in combination with chemical amendments, was

applied at the rate of 17 Mg ha-1. Inoculum was applied @ 100-120 million microbes

per pot.

124

Table 5.42: Chemical characteristics of Pressmud collected from Khazana Sugar Mill, Peshawar

Parameter Unit Value pH - 9.2 EC dS m-1 3.7 Na meq L-1 1.23

SAR - 1.4 Lime % 80.3

Organic Matter g kg-1 163.4 Total N g kg-1 4.1

Table 5.43: Chemical Characteristics of Farmyard manure collected from University of Agriculture KPK Research Farm.

Parameter Unit Value Total Nitrogen % 0.81

Total Solid % 38.3 Ammonical Nitrogen % 0.01

Organic Carbon % 21.2 C/N ratio 15.2


Respective treatments were applied on July 3, 2010 and incubated for two months in

glass house of Khyber Pakhtunkhwa Agricultural University Peshawar at natural

environmental conditions. Each soil sample was irrigated to maintain its moisture

capacity to 60%. After two months of incubation period all the soil samples were

tested for their microbial properties by taking 300g soil from each pot.

5.4.3 Results and Discussion


Analysis of variance showed that almost all soil amendments significantly (P<0.01)

increased the CO2 evolution under saline-sodic soil conditions (Table 9.7). The

highest CO2 evolution of 503 mg kg-1 was recorded in soil amended with microbial

inoculums followed by 458 mg kg-1 in soil amended with gypsum + pressmud, and

448 mg kg-1 in soil amended with PM+FYM. The lowest CO2 evolution was

obtained in the un-amended soil (Table 5.44). As compared to control, G, PM and

FYM increased CO2 evolution by 27, 29 and 28% respectively when applied alone

and by 39, 63 and 60% when applied in combinations as G+FYM, G+PM and

125

PM+FYM respectively. The increase in CO2 evolution with PM application could be

its increasing effect on soil microorganisms. After 30 days of pressmud application

the population of rhizosphere microbes especially actinomycetes and bacteria were

increased (Gaikwad et al., 1996). In another study Tompe and More (1996a), found

highest actinomycetes population with combined application of pressmud with

fertilizer and alone application of pressmud slightly increased the azotobacter,

bacterial and fungal population. Rangaraj et al. (2007) found that compared to the

same level of FYM, application of 12.5 Mg ha-1 pressmud to soil resulted in more

number of colonies of bacteria, fungi and actinomycetes.

The data demonstrated that addition of microorganisms as inoculums promoted CO2

evolution by 80%. Engelking et al. (2007) found that addition of organic amendment

increased the rate of CO2 evolution by 100% during a four week study. Rasul et al.

(2006) found that soil amended with pressmud increase microbial activity in saline

soil. In another study Linkins et al. (1990) and Kautz et al. (2004) found that

addition of organic material to soil increase soil microbial activity by 69% as

compared to the unfertilized control. In the present highly saline soil the increasing

CO2 production in response to microbial inoculums and organic amendments in this

study indicated that soil microorganisms are capable to perform their metabolic

functions and survive under salt stress conditions (Luna-Guido and Dendooven,

2001; Conde et al., 2005). As reported for ryegrass in comparison with glucose, the

addition of sugarcane filter cake seems to add new microbial micro-sites for survival

in soil (Wu et al., 1993). A strong increase in microbial activity was observed after

filter cake (PM) amendment (Rasul et al., 2006) and a small increase in microbial

activity after organic material amendment (Muhammad et al., 2006). Mathew and

Varughese (2007) reported that the integrated use of pressmud @ 5 t ha-1 along with

mineral nutrition of NPK at recommended dosed had appreciably enhanced the

activity of phosphatase and population of actinomycetes under sugarcane

cultivation.

5.4.3.2 Microbial biomass C

The application of amendments alone or in combinations and of microbial

inoculum’s significantly (P < 0.01) increased the microbial biomass carbon (MBC)

126

under saline-sodic soil conditions. The highest MBC of 248 mg kg-1 was recorded in

soil amended with PM+FYM, followed by 236 mg kg-1 in soil amended with

G+FYM. The application of inoculums also have higher CO2 evolution as compared

to alone treatments of G, PM and FYM (Table 5.44). As compared to control, FYM,

G+FYM, G+PM and PM+FYM significantly increased MBC by 139, 205, 51 and

102% respectively while application of PM alone showed no significant effect on

MBC. The data demonstrate that addition of microorganisms as inoculums increased

MBC by 179% and addition of G alone showed 11% reduction in MBC. Application

of FYM increased MBC more as compared to PM addition. Similar results were

found by Rasul et al. (2006) who finds that microbial biomass C reached

considerably higher values with dhancha leaves than with filter cake amendments.

Microbial biomass C was increased in proportionate with the addition of the amount

of C added by PM and FYM. These results are in agreement with the findings of

Witter and Kanal (1998) who reported that an increased microbial biomass C is

caused by increasing ratio of substrate C. The linear increase in microbial biomass C

indicates that sugarcane filter cake and compost added new micro-sites for the

microbial colonization of soil (Wu et al., 1993), independently of the autochthonous

microbial community (Flessa et al., 2002). Similar results were found by Rasul et al.

(2006) who finds that addition of PM led to an immediate increase in microbial

biomass C, contrasting the results of Dee et al. (2003). Goyal et al. (2006), Masto et

al. (2006) and Manna et al. (2007) concluded that microbial activity increased

significantly with application of FYM. Tejada et al. (2009) found that plant residues

had a positive effect on soil biological properties (biomass C and the enzymatic

activities).

5.4.3.3 Microbial biomass N

Analysis of variance showed that all treatments significantly (P<0.01) effect

microbial biomass nitrogen (MBN) under saline-sodic soil conditions. The highest

increase in MBN was recorded in soil amended with microbial inoculums (21.4 mg

kg-1), followed by PM+FYM (16.4 mg kg-1). As compared to control, G, PM and

FYM significantly increased MBN by 80, 18 and 63% respectively when applied

alone and by 77, 78 and 102% when applied in combination as G+FYM, G+PM and

127

PM+FYM respectively. The data demonstrate that addition of microorganisms as

inoculums promote MBN by 163% which is the highest increase in MBN as

compared to other treatments alone or in different combinations. PM alone or in

combination with other soil amendment increased immobilization of N. Although it

contains high content of extractable N and total N, the results are in agreement with

those of Rasul et al. (2006). Similar results were obtained by Wichern et al. (2004)

investigating the mineralization of FYM, having a similar low C/N ratio to the

present PM. PM has a specific feature of high concentration of extractable organic

C. As the biological decomposition proceeded, the concentration of this extractable

oraganic C is decreased. For the immobilization of N the importance of extractable

organic C has been shown repeatedly for immature or fresh FYM (Martin-Olmedo

and Rees, 1999; Wichern et al., 2004).

5.4.3.4 Microbial biomass C/N ratio

The application of chemical amendments alone or with different combination and

microbial inoculums significantly affected microbial biomass C/N ratio. Analysis of

variance showed that all treatments significantly (P<0.01) effect microbial biomass

C/N ratio. Microbial biomass C/N ratio ranged from 4.7-16.5 for all treatments. The

highest C/N ratio (16.5) was recorded for soil amended with G+FYM, while the

lowest C/N ratio (4.7) was found for soil amended with G alone. FYM alone or with

different combinations increase the microbial biomass C/N ratio, while microbial

inoculums showed no significant effect on microbial biomass C/N ratio. The highest

reduction (50 %) in microbial biomass C/N ratio was observed with G alone, while

PM and G+PM showed 14 and 15% reduction. The application of other amendments

i.e. FYM and PM+FYM increase the ratio of microbial biomass C/N by 47 and 57%

respectively. Similar results were found by Rasul et al., (2006 who found that

addition of sugar cane filter cake increased the microbial C/N ratio as compared to

the soil C/N ratio. However, in a German soil after glucose addition, strongly

increased microbial biomass C/N ratios have also been observed (Chander and

Joergensen, 2007).

128

5.4.3.5 Ammonification

Analysis of variance showed that most of the treatment significantly affect net

ammonification rate. The highest increase (200%) in net ammonification rate was

observed for soils treated with microbial inoculums as compared to control

treatment. Application of G, G+FYM and PM+FYM at the rate of 20, 20+17 and

20+17 Mg ha-1 brought no significant effect in net ammonification rate, while

application of pressmud alone or in combination with G cause > 70% increase in net

ammonification rate.

Application of FYM alone at the rate of 17 Mg ha-1 increases soil ammonification

rate by 71%. These results are in line with the findings of Rasul el al. (2006) who

finds that 50% of the N added to the soil is lost through NH4-N.

5.4.3.6 Nitrification

The results for net nitrification rate with different soil amendments presented in

Table 5.44 & Table 5.45. Alone application of G, PM and FYM brought no

significant changes in soil nitrification rate. Collective application of G+FYM

caused 10% reduction in soil nitrification rate. More significant increase in soil

nitrification was noticed with G+PM and PM+FYM, while more than 100% increase

was found with amendment of microbial inoculums. Darrah et al. (1987) and Pathak

and Rao (1998) found complete inhibition or reduction of nitrification at high salt

concentrations. Oren (1999) stated that the energy burden of saline environments for

the ammonia or nitrite-oxidizing autotrophic microorganisms might be too great. In

a saline acidic German soil, complete inhibition of nitrification was also reported by

Rasul et al. (2006). However, in accordance with Luna-Guido et al. (2000) this was

not observed in the saline soil used in the present study.

129

Table 5.44: Microbial activity (CO2 evolution), MBC, MBN, Microbial biomass C/N, Ammonification, Nitrification and N mineralization in silt loam saline sodic soil treated with G, PM and FYM alone or in various combinations

Treatments CO2

Evolution

MBC MBN C/N Ammoni

fication

Nitrification N

Mineralization

---mg kg-1--- --- ---mg kg-1---

Control 280d 78e 8.1f 9.6c 1.1c 7.9cd 8.6c

Gypsum (G) 356c 69e 14.6c 4.7d 1.2c 8.6c 9.2c

PM 362c 78e 9.6e 8.2c 1.8b 8.0cd 9.1c

FYM 358c 185c 13.3d 14.1b 1.8b 8.0cd 9.7c

G+FYM 391c 236a 14.4cd 16.5a 0.9c 7.0d 8.4c

G+PM 458b 117d 14.5c 8.1c 1.9b 12.4b 14.6b

FYM+PM 448b 248a 16.4b 15.1ab 1.0c 12.6b 13.3b

PM+FYM+

inoculum

503a 216b 21.4a 10.1c 3.5a 17.7a 22.0a

LSD (P <0.05) 44.76 18.87 1.34 2.0 0.33 1.35 1.56

*means followed by similar letter (s) in a column do not differ significantly (P <0.05)

#FYM = Farmyard manure; PM = Pressmud

Table 5.45: Percent change in microbial indices with different amendments

Treatments CO2

evolution

MBC MBN MB

C/N

Ammoni

fication

Nitrification N

mineralization

Control --

G 26.87 -11.20 79.92 -50.90 9.52 8.90 7.39

PM 29.13 0.71 18.44 -14.45 74.60 1.27 5.84

FYM 27.82 139.05 63.11 47.00 71.43 2.12 12.84

G+FYM 39.36 205.05 77.05 72.35 -12.70 -11.44 -2.33

G+PM 63.26 51.28 78.28 -15.31 77.78 57.20 70.04

PM+FYM 59.93 219.33 102.05 57.62 -9.52 60.17 55.64

PM+FYM

+Inoculum79.55 178.82 163.11 5.57 234.92 125.00 156.81

Negative values indicate percent decrease as compared to control

130

5.4.3.7 Net N mineralization

Analysis of variance showed that most of the treatments significantly (P<0.01) effect

nitrogen mineralization rate. The highest mineralization rate 22 mg kg-1 was

observed for soil treated with microbial inoculums followed by combined

application of G+PM and PM+FYM. Microbes including bacteria, fungi and

actinomycetes are the principal decomposers of organic matter in soil. The role of

soil microorganisms in sustainable productivity has been reviewed (Lee and

Pankhurst, 1992; Lata et al., 2000). No significant effect in N mineralization was

found for soil treated with G, PM, FYM alone or in combination of G+FYM.

Increase in mineralization of C and N can be attributed to a positive effect caused by

incorporation of FYM in the soil, which improves moisture conservation in the soil

stimulating microbial activity of the soil as well as addition of exogenous

microorganisms. The content of inorganic nitrogen released is related to the natural

mineralization potency of soil and is influenced by the simultaneous course of

mineralization and immobilization processed (Bizik, 1989, Bielek, 1998). The main

agent of both types of the processes is soil organisms, especially microorganisms,

which are besides abiotic factors affected by substrate resources.

The role of soil microorganisms in sustainable productivity has been reviewed (Lee

and Pankhurst, 1992; Lata et al., 2000). Microbes including bacteria, fungi and

actinomycetes are the principal decomposers of organic matter in soil. According to

the results of Vanek et al. (1997a), the amounts of mineral and mineralizable

nitrogen reached values of 30 to 50 ppm in soils unfertilized organically for a long

time. After fertilization with farmyard manure together with mineral fertilizers and

with pea as the previous crop, the values increased to 80 ppm in arable soil layer.

The decisive part of nitrogen available for plants comes from microbial biomass

mineralization (Novak, 1993). The turnover of nitrogen from dead microbial cells is

approximately 5 times quicker than the turnover of other soil nitrogen. This is

affected not only by abiotic factors but also by the input of substrate resources

whose quality and quantity are important from the viewpoint of net nitrogen

mineralization (Bielek, 1998).

131

5.4.3.8 Crop response to amendments

Wheat and maize were used to test the effect of different treatments used in

reclamation of saline sodic soil. Wheat was sown in October, 2009 while maize was

tested in March, 2010. Due to the adverse saline sodic condition of the soil (EC >20

dSm-1, pH=10.0) the test crops were unable to germinate. It might be due to the crust

formation or high alkalinity.

0

100

200

300

400

500

600

Control G PM FYM G+FYM G+PM PM+FYMInoculum

CO

2ev

olut

ion

(mg

kg-1

)

Soil amendments

132

Figure 5.63: CO2 evolution as affected by different soil amendments in saline sodic soil

Figure 5.64: MBC as affected by different soil amendments in saline sodic soil

Figure 5.65: MBN, MB C/N ratio, Ammonification, Nitrification and net N mineralization as affected by different soil amendments in saline sodic soil

0

50

100

150

200

250

300

Control G PM FYM G+FYM G+PM PM+FYMInoculum

MB

C (

mg

kg-1

)

Soil amendments

0

5

10

15

20

25

Control G PM FYM G+FYM G+PM PM+FYM Inoculum

Soil amendments

MBN (mg kg-1)

C:N

Ammonification (mgkg-1)

133

6 SUMMARY

Soil salinity is a worldwide problem which not only influences the physical and

chemical properties of soil but may also seriously affect the microbiological

properties of soil. This project was undertaken with the objective to assess the

behavior of various microbiological properties of soil in relation to salinity during

2009-2012. In this connection, a series of incubation experiments were conducted to

evaluate the effect of salts on soil microbiological properties. In first experiment,

soil microbiological properties were measured in relation to various salinity

parameters in naturally occurring salt affected soils. In next experiments, the effect

of NaCl and MgCl2 induced salinity on N dynamics and soil microbial activity were

evaluated. Finally, the effect of pressmud, gypsum, farmyard manure and microbial

inoculation were assessed on various soil microbiological properties including soil

microbial biomass C and N, ammonification, nitrification, CO2 evolution and N

mineralization in a saline-sodic soil.

For experiment 1, soil samples (0-20 cm) were collected from salt affected soils with

EC ranged from < 4.0 to 32 dS m-1 in November 2009. The samples were analyzed

for soil microbiological properties (such as microbial biomass C, and N, microbial

biomass C/N ratio, N mineralization, nitrification and rate of soil respiration) and

soil chemical properties (such as pH, EC, soluble Ca+Mg, soluble sodium, SAR

(sodium adsorption ratio), ESP (exchangeable sodium percentage), carbonates,

bicarbonates and chloride). The results showed that almost all microbial indices

including MBC, MBN, basal soil respiration, nitrification and net N mineralization

were negatively correlated with increasing salinity (r = -0.89, -0.74, -0.79, -0.64 and

-0.57 respectively) except microbial biomass C/N ratio which showed positive

response to increasing soil salinity (0.61). The effect of salinity on rate of CO2

evolution (soil respiration) was more pronounced during the first two days of

incubation period. However, differences between soils with different salinity levels

become narrower as incubations advanced to 10 days. MBC, MBN, basal soil

respiration net nitrification and net N mineralization strongly affected with SAR and

ESP and the relationship is depressive. Carbonates and bicarbonate of all the soils

analyzed showed little response to any of the analyzed biological parameters. It is

134

concluded from the correlation data that all biological parameter, except soil

microbial biomass C/N ratio decreased with increasing salinity.

In experiment 2, the effect of NaCl induced salinity were measured on microbial

activity and N mineralization in a silty clay loam non-saline soil (EC = 0.65 dS m-1)

during lab incubation experiment. The results showed that all treatments

significantly reduced CO2 evolution during all incubation periods. A more

pronounced and significant reduction in CO2 evolution was observed for soils with

EC of 8 dSm-1 and the highest reduction in CO2 evolution was observed with the

highest EC of 40 dSm-1. The greatest reduction in CO2 evolution (90%) was

occurred during the 1st 10 days of incubation period and 80% during 20-40 days of

incubation period. Similar depressive effect of NaCl induced salinity was observed

for N mineralization. The lowest N mineralization was observed for soils with EC

40 dSm-1, even with the lowest EC level reduced N mineralization by 10% during 1st

10 days of incubation period. These results suggested that NaCl induced salinity

substantially reduced both the microbial activity and N mineralization in soil.

Another experiment was conducted to assess the influences of MgCl2 induced

salinity on microbial activity and N mineralization and compare its results with that

obtained with the NaCl experiment. The results showed that all treatments reduced

CO2 evolution but more pronounced and significant reduction in CO2 evolution was

found for soils with EC of 4 dSm-1 and the highest reduction in CO2 evolution was

observed with EC of 40 dSm-1. Similarly, reduction in N mineralization was

observed with all treatments and the highest reduction (80%) was observed for soil

receiving MgCl2 in amount >50 mg g-1 soil during the 1st 10 days of incubation

period. N mineralization was reduced to 26.2 mg kg-1 from 145.1 mg kg-1 (82%)

with the highest MgCl2 addition (200 mg g-1 soil) during the next 10 days of

incubation period.

Finally in experiment 4, the effect of pressmud, gypsum, farmyard manure and

microbial inoculation were measured on maize growth and on soil microbiological

properties in a saline sodic soil (pH >10.0 and EC > 20 dSm-1) in pot experiment.

Treatments were; control, gypsum (G), pressmud (PM), farmyard manure (FYM),

G+FYM, G+PM, PM+FYM and PM + FYM + microbial inoculation arranged in a

135

CR design with 3 replications. Respective treatments were applied on July 3, 2010

and incubated for two months in the glass house at ambient temperature. The pots

were irrigated to maintain soil moisture capacity at around 60%. After two months

of incubation period all the soil samples were run to measure microbial activity and

N mineralization. The results showed that almost all soil amendments significantly

increased the CO2 evolution under saline-sodic soil conditions. The highest CO2

evolution of 503 mg kg-1 was recorded in soil amended with PM + FYM + microbial

inoculums this was followed by G + PM, and PM+FYM treatments. The lowest CO2

evolution was obtained in the un-amended soil. As compared to control, PM + FYM

increased CO2 evolution by 60%. The effect was further enhanced to 80% when

microbial inoculum was combined with PM + FYM. The measured rate of CO2

production can greatly help in the amelioration of sodic or saline-sodic soils. The

CO2 after reacting with H+ can help in the dissolution of calcium carbonate and

released Ca++ which replaces Na+ from clay particles. These results suggested that

soil microorganisms were capable to survive and perform to a large extent their

metabolic functions under the salt stress conditions and providing energy sources (in

the form of FYM or PM) further improved their metabolic activity.

Other microbial attributes (such as microbial biomass C and N, microbial biomass

C/N ratio, ammonification, nitrification, and N mineralization) exhibited almost

similar pattern of response to amended treatments. As for CO2 evolution, the PM +

FYM + inoculation treatment produced the greatest MB-C & N, ammonification,

nitrification and N mineralization. These treatments increased the MB-C by 179%,

MB-N by 163%, ammonification by 235%, N mineralization by 157% and

nitrification by 125% compared with the control un-amended treatment.

Wheat and maize were used to test the effect of different treatments used in

reclamation of saline sodic soil. Wheat was sown in October, 2010 while maize was

tested in March, 2011. Due to the adverse saline sodic condition of the soil (EC >20

dSm-1, pH=10.0) the test crops were unable to germinate.

136

7 CONCLUSIONS AND RECOMMENDATIONS

Increasing soil salinity, combined with high soil pH, showed negative effect

on all microbial indices including MBC, MBN, basal soil respiration,

nitrification and net nitrogen mineralization.

All analyzed biological parameters were little affected by the levels of

carbonates and bicarbonates.

Both CO2 evolution and N mineralization decreased significantly with

increasing NaCl salinity, and the reduction was proportional to the NaCl

levels.

The results showed that increasing NaCl salinity from 0.64 to 40 dS m-1

decreased cumulative CO2 production by 80% and N mineralization by 50%

during 40 days of incubation.

Induced MgCl2 salinity from 0.64 to 40 dS m-1 decreased cumulative CO2

production by 95% and N mineralization by 81% during 30 days of

incubation.

These results demonstrated that soil microorganisms were highly sensitive to

NaCl salinity indicating that salinity is a stress factor and can reduce

microbial diversity and control microbial abundance, composition and

functions.

The results suggested that amendments of saline-sodic soil with organic

sources substantially improved the microbial attributes in soil and thus can

play significant role in the amelioration of saline sodic or sodic soils.

Organic matter decomposition increases the production of CO2 and liberation

of H+ ions. The H+ ions enhance the dissolution of CaCO3 and release more

Ca to replace Na from clay particles and thus can help in the reclamation of

saline sodic soils.

Soil amendments plus proper salinity management practices are required for

the amelioration of adverse effect of saline-sodic soil. Apply farmyard

manure and crop residues once every three to four years to saline areas. This

will provide additional organic matter to the soil.

137

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9 APPENDICES

Table 9.1: ANOVA [CR design] showing F values for rate of soil respiration in response to NaCl induced salinity during different incubation periods

SOV D.F. Rate of soil respiration (mg kg-1 soil)

Incubation periods (days) 0-10 10-20 20-30 30-40

Replications 2 3.06ns 1.71ns 1.46ns 2.99ns Treatments 7 58.42** 25.01** 20.5** 15.95**

**, ns significant at P < 0.01 and non-significant respectively

Table 9.2: 2-factors ANOVA [CR design] showing F values for Cumulative CO2 production during 40 days of incubation in response to various levels of NaCl induced salinity

SOV D.F. Cumulative CO2 production (mg kg-1)

Incubation periods (days) 10 20 30 40

Replications 2 3.06ns 3.29ns 2.12ns 3.15ns Treatments 7 58.42** 86.73** 99.2** 118.3**

**, ns significant at P < 0.01and non-significant respectively

Table 9.3: ANOVA [CR design] showing F values for N-mineralization during 40 days of incubation period with induced NaCl salinity

SOV D.F. N mineralization (mg kg-1) Incubation periods (days)

10 20 30 40Replications 2 0.9ns 3.0ns 3.42ns 5.43*Treatments 7 11.12** 51.96** 57.64** 99.18**

** significant at P<0.01; ns: non-significant

Table 9.4: ANOVA [CR design] showing F values for rate of soil respiration in induced MgCl2 treated soils during different incubation periods

SOV D.F. Rate of soil respiration (mg kg-1)

Incubation period (days) 0-10 10-20 20-30

Replications 2 4.3ns 2.6ns 0.13ns Treatments 7 336.7** 454.8** 346.8**

**, ns significant at P < 0.01 and non-significant respectively

Table 9.5: ANOVA [CR design] showing F values for Cumulative CO2 production in soil with induced MgCl2 salt

SOV D.F. Cumulative CO2 production (mg kg-1)

Incubation period (days) 10 20 30

Replications 2 2.2ns 6.8ns 5.1ns Treatments 7 65.5** 95.7** 137.0**

**, ns, significant at P < 0.01 and not significant respectively

158

Table 9.6: 2-factors ANOVA [CR design] showing F values for N-mineralization during different incubation periods in MgCl2 induced salinity

SOV D.F. N-mineralization (mg kg-1) Incubation period (days)

10 20 30 Replications 2 10.9** 13.4** 9.7** Treatments 7 313.6** 495.6** 397.4**

** Significant at P < 0.01 Table 9.7: ANOVA [CR design] showing F values for CO2 evolution, MBC, MBN,

Microbial biomass C/N, Ammonification, Nitrification and N mineralization in silt loam saline sodic soil treated with G, PM and FYM alone or in various combinations

SOV D.F CO2 Evolution

MBC MBN MB C/N

Ammonification

Nitrification N mineralization

Treatments 7 22.85** 146.44** 82.55** 36.9** 62.66** 66.59** 80.18** Replications 2 2.03ns 1.21ns 0.89ns 0.35ns 1.10ns 0.49ns 2.42ns

MICROBIAL DYNAMICS IN SALT AFFECTED SOILSprr.hec.gov.pk/jspui/bitstream/123456789/1289/1/2039S.pdfmicrobial dynamics in salt affected soils by syed asif shah doctor of philosophy (ph.d)

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