mukiibi edward - Effect of Saw Dust on Soil Physical and Chemical Properties in Ntenjeru Sub County, Mukono District, Uganda

Effect of Saw Dust on Soil Physical and Chemical Properties in Ntenjeru Sub

county, Mukono District. Under Graduate Special Project Thesis

Mukiibi Edward

05/U/339

A Special project report submitted to the Department of Soil Science in partial fulfillment of the requirements of the award of a

Bachelor of Science Degree in Agricultural Land Use and Management of Makerere University, Kampala Uganda.

June 2008

PROFESSIONAL SOCIETY FOR AGRICULTURAL LAND MANAGERS UGANDA

Dedication

This study report is dedicated to the family of Mr. Wali Christopher Magala of Ntenjeru sub

county, Mukono district; you are my life time gift and source of inspiration. No body knows

better.

ediemukiibi ‘08 i

Acknowledgements

This study was entirely sponsored by my parents to whom am so grateful for their

contribution towards the success of this work up to this stage. I would also like to extend my

appreciation to the staff of Soil Science Department for providing the laboratory space and

other related logistics and support during the period of study. Special thanks go to Mr.

Balikuddembe Bonny of Soil Science Analytical Laboratories of the Soil Science

Department for your kind help to me at no monetary cost during laboratory analysis through

out the study period.

I would also like to express my sincere thanks to Professor Moses M. Tenywa for your

advice and guidance through out the study period. Your methods of work and constructive

criticisms indeed helped me to discover the science of organizing field generated figures and

numbers into a well organized and sought out scientific document like this. From you I learnt

to be thorough in what ever I do.

Lastly my immeasurable appreciation goes to Dr. Twaha Ateenyi of Soil Science Department

for your encouragement during hard times through the study. I pray that God the almighty

reward you accordingly.

ediemukiibi ‘08 ii

Table of contents

Dedication.................................................................................................................................. i

Acknowledgements................................................................................................................... ii

List of tables ............................................................................................................................. v

List of figures........................................................................................................................... vi

Acronyms................................................................................................................................ vii

Abstract..............................................................................................................................viiviii

CHAPTER ONE 1 1.0 Background and setting ................................................................................................ 1

1.1 Problem statement ........................................................................................................ 2

1.2 Objectives ..................................................................................................................... 3

1.3 Significance of the Study.............................................................................................. 3

CHAPTER TWO 4 2.1 Over view of Soil degradation in Sub Saharan Africa ................................................. 4

2.2 Soil productivity and soil degradation in Uganda ........................................................ 5

2.3 Enhancing Soil Productivity for Increased Agricultural Production............................ 5

2.4 Organic Soil Amendments and Soil Productivity Management................................... 6

2.5 Role of mulches in soil productivity management ....................................................... 8

CHAPTER THREE 10 3.1 Study area ................................................................................................................... 10

3.2 Experimental design and treatment ............................................................................ 10

3.3 Data analysis ............................................................................................................... 11

3.3.1 Soil analysis ................................................................................................................ 11

3.3.2 Plant analysis .............................................................................................................. 11

3.3.3 Statistical analysis....................................................................................................... 12

CHAPTER FOUR 13 4.1 Effects of saw dust Application on soil properties ..................................................... 13

4.1.1 Soil pH........................................................................................................................ 13

4.1.2 Soil Organic matter..................................................................................................... 14

ediemukiibi ‘08 iii

4.1.3 Soil Nitrogen............................................................................................................... 15

4.1.4 Available Phosphorus ................................................................................................. 16

4.1.5 Soil Exchangeable bases (K and Ca) .......................................................................... 17

4.1.6 Soil aggregation .......................................................................................................... 17

4.2 Maize Crop response to Saw Dust Application.......................................................... 18

4.2.1 Effect of saw dust application on maize plant height (cm). ....................................... 19

4.2.2 Effect of saw dust application on maize leaf width (cm) and number of leaves ........ 20

4.3 Relationship between maize plant height (cm) and number of leaves, soil pH, Organic

matter and soil nitrogen. ......................................................................................................... 21

CHAPTER FIVE 24 5.1 Conclusion .................................................................................................................. 24

5.2 Recommendations....................................................................................................... 24

References............................................................................................................................... 26

Appendices ............................................................................................................................. 32

ediemukiibi ‘08 iv

List of tables

Table 1: Soil properties before planting and application of saw dust in the first season-------13

Table 2: Soil response to application of saw dust in the first growing season-------------------18

Table 3: Soil response to application of saw dust in the second growing season---------------18

Table 4: effect of saw dust application on maize plant height (cm) ------------------------------19

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List of figures

Figure 1: Response of Maize Leaf Width to Saw Dust Application ------------------------ 20

Figure 2: Relationship between Maize Plant Height (Cm) and the Number of Leaves -- 21

Figure 3: Maize Plant Height (Cm) – Soil pH Relationship---------------------------------- 22

Figure 4: Maize Plant Height (Cm) – Organic Matter Relationship ------------------------ 23

Figure 5: Maize Plant Height (Cm) – Soil Nitrogen (%) --------------------------------------23

ediemukiibi ‘08 vi

Acronyms

SOM: Soil Organic Matter

SSA: Sub Saharan Africa

UEEF: Uganda Environmental Education Foundation

CIAT: International Center for Tropical Agriculture

CRBD: Completely Randomized Block Design

NGOs: Non Governmental Organizations

LSD: List Significant Difference

MWD: Mean Weight Diameter

ediemukiibi ‘08 vii

Abstract

In their transition to certified organic agricultural production, farmers in Ntenjeru sub county

use saw dust as an organic soil amendment. The use of saw dust has been reported to cause

problems like nitrogen immobilization and pH variations due to the high C/N ratio associated

with saw dust which also affects plant growth. So the major objective of the study was to

improve on the understanding of the effects of saw dust on soil conditions. The study was

carried out for two maize growing seasons on farm trials established at Kisoga village,

Ntenjeru Sub County in Mukono district from September 2007 to June 2008. The treatments

were; mulching with saw dust, Incorporation of saw dust into the soil and the control plot (no

saw dust) in a completely randomized block design with maize as a test crop.

Treatments where saw dust was applied as mulch significantly reduced soil nitrogen level

and soil pH. This also had a significant reduction in the growth of maize characteristics like

Height, leaf number and width. Incorporation of saw dust also inhibited the spply of soil

nitrogen but unlike in mulching, incorporation of saw dust significantly increased the supply

of calcium, potassium, which significantly increased the soil pH and hence favoured the

growth of maize as compared to the mulched plots. Soil organic matter levels were

significantly higher in saw dust applied treatments than in the control plots but the

application of saw dust did not have any significant influence on the soil phosphorus levels

and soil aggregation through out the study period.

This study concluded that in Ntenjeru Sub County it is better to use saw dust incorporated

into the soil than applying it on the surface as mulch. Samples of saw dust should be sent to

soil testing laboratory to analyze the C/N ratio and nutrient contents prior to its application as

a soil amendment by farmers.

ediemukiibi ‘08 viii

CHAPTER ONE INTRODUCTION

1.0 Background and setting

Agriculture as the main source of livelihood and food security in the Sub Saharan Africa

(SSA) region, and in Uganda specifically, is facing a challenge of matching food, fodder,

fuel and fibre production with population growth. For the period 1994 to 1998, 70% of SSA

population lived in areas where the average population growth rate exceeded the average

growth rate in per capita food production (FAO, 1999), Uganda inclusive. Although by the

year 2003, Uganda’s average annual growth rate in food production and population stood at

4.1 and 3.0%, respectively (FAO, 2006), it is important to note that the country’s arable land

area is limited, yet qualitatively diminishing under the forces of widespread soil degradation

(Lufafa et al., 2003). It is imperative therefore that resource productivity be increased in

order to bridge the gap between per capita food production and population growth. This calls

for increased use of inputs such as clean irrigation water, organic manures fertilizers and

crop protection techniques, which impact on the economics of agricultural production,

environmental quality as well as Soil fertility.

The fertility of soils is central to the sustainability of both natural and managed ecosystems.

(Wasswa et al, 2003). This is because it is the medium from which terrestrial production

emanates (Scholes et al 1994. soil organic matter (SOM) plays an important role in

maintaining soil texture, water holding capacity, the micro biomass and in nutrient cycling

among others (Angers and Caron 1998). It also helps in improving the drainage and aeration

properties of the root zone and acts as a great source of nutrients to the growing plants

(Starbuck, 1994).

The decline of Soil Organic Matter with cropping is a major factor affecting sustainability of

many cropping systems in sub Saharan Africa (Buyanovzky et al 1984). Nutrients have been

depleted by crop harvest removals, leaching, volatilization and soil erosion to the extent to

which soil fertility replenishment has been recommended by Izac, (1997) as a necessary

investment in natural resource capital. Studies also indicate that soil physical, biological and

ediemukiibi ‘08 1

chemical properties can sustainably be improved through the improvement of SOM (Paul

1984). This can be done through practices like mulching and addition of organic manures

(Unger 2001). One of such important soil amendments is Sawdust mulch. That is currently

used in Ntenjeru Sub County. Saw dust is mainly surface applied mulch used in ginger and

garlic organic gardens. According to Unger (2001), surface applied mulches serve to reduce

soil water evaporation thus enhancing the potential for increased soil water conservation.

This is highly important for improving crop production in tropical rain fed agriculture. (Jacks

et al 1955). The use of these inputs in agricultural production needs to be optimized in

relation to economic and environmental quality considerations. This necessitates thorough

understanding of the system response to applications of such inputs, which can only come

from long-term experiments with the inputs in the farming system.

1.1 Problem statement

In their transition to certified organic agricultural production, farmers in Ntenjeru sub county

use saw dust as an organic soil amendment. The use of sawdust has been reported to perform

poorly when used in different environments. (Starbuck, 1994). McDonald (1953) found out

that if used under uncontrolled conditions, sawdust whether used as mulch or incorporated

into the soil, could result into problems like soil nitrogen immobilization. Also Starbuck

(1994) justified that saw dust contains 50% carbon, 6% hydrogen, 44% oxygen and perhaps

0.1% nitrogen. This is generally because soil microbes use nitrogen to break down the

complex materials in sawdust since it is composed of about 70% carbohydrates (cellulose

and hemicellulose) and 27% lignin (Starbuck 1994, Mc Donald 1953). This utilization of

nitrogen by the microbes leads to a quick depletion of the entire supply of nitrogen in the soil

(White et al 1934). Hence it is important to assess the effects sawdust imparts to the soil

physical and chemical properties prior to its application in an area. So optimizing of the use

of saw dust as a soil amendment in Ntenjeru Sub County is dependent on predicting the

efficiency of transfer of nutrients and the subsequent effects to the plants and the soil system

in the area. Although there is substantial literature on the response of soil and crops to such

ediemukiibi ‘08 2

organic soil amendments (Swift 1994), there are very few studies that separate the variety of

effects involved.

1.2 Objectives

The general objective of this study is to improve on the understanding of the effects of

sawdust on soil conditions. The specific objectives are;

a) To find out the effects of sawdust on soil nutrients like N, P, K, and Ca

b) To establish the influence of sawdust on soil pH, soil aggregation, and soil

organic matter

1.3 Significance of the Study

As stated by Kirsch (1959), the value of saw dust and other wood wastes as mulches or soil

amendment has received considerable study. How ever a need exists for more complete

information to farmers regarding the effects of these materials on both physical and chemical

properties of soils to which they are added. (Kirsch, 1959). There fore since the major

obstacle hindering the efficient utilization of saw dust by the farmers is the lack of adequate

understanding on the effects of this soil amendment on the nature of resultant soil organic

matter and other soil properties. This study is important to farmers and decision makers in

soil management to understand and evaluate the changes in selected soil physical and

chemical properties as influenced by the application of saw dust either as mulch on the

surface or incorporated into the soil.

ediemukiibi ‘08 3

CHAPTER TWO LITERATURE REVIEW

2.1 Over view of Soil degradation in Sub Saharan Africa

Soil degradation is a major problem and wide spread in Sub Saharan Africa. Agriculture

lands are especially prone to erosion and nutrient depletion (Sara 1999). Reported yield

losses range from modest levels (2% decline one several decades) to catastrophic greater

than 50% depending on the soil type, crop, climate and production systems (Sara, 1999)

Dragne (1990) reported that 33 countries found compelling evidence of serious soil

degradation in sub regions of 13 countries, Uganda inclusive. It was also estimated by

Dragne and Chou (1992) that over 73% of the dry lands in SSA were degraded and 51%

hosting severely degraded soil. In Africa, Oldeman et al (1991) concluded that 65% of soil

on agricultural land has become degraded since the middle of the 20th century as had 31% of

permanent pastures and 19% of woodlands and forests. Soil degradation in SSA mainly

affects dry land soils and agricultural land with 72% and 19% respectively (Sara, 1999).

Among the most prominent causes of soil degradation in SSA include water erosion,

followed by wind erosion, chemical degradation (nutrient depletion and salinization) and

physical degradation and human activities like over grazing, agricultural crop production,

deforestation and over exploitation of soil resources (Sara, 1999).

Soil degradation among other factors has the largest impact on agricultural productivity in

Sub-Saharan Africa. According to Oldeman, (1998), the productivity loss in Africa from soil

degradation since Second War World has been estimated at 25% for cropland and 8-14% for

crop land and pasture together. Similarly, Dragne (1990) estimated that irreversible soil

productivity losses of at least 20% were due to soil erosion which occurred over the past

century in parts of twelve S.S.A countries including Uganda. It is worrying to see that in

originally fertile lands, under continuous cropping without nutrient inputs and better soil

management, cereal grain yields declined from 2 to 4 tons ha-1 to under one ton ha-1 (Sanchez

et al, 1997). The effect of soil degradation was best reviewed by Lal (1995) who emphasized

that in the absence of such causes and components of soil degradation, 3.6 millions tons

ediemukiibi ‘08 4

more of cereal, 6.5 million tones more of root tubers and 0.4 million tons more of pulses

would have been produced in 1989.

2.2 Soil productivity and soil degradation in Uganda

Like in many developing countries, the loss of soil productivity and one of the major causes

of soil degradation in Uganda is largely due to poor tillage methods, over grazing, burning,

lack of recycling, leaching ad nutrient using through harvesting, Zake (1993). Although the

problem of soil degradation in Uganda has not been quantified, it is clearly observable

(Semana 1994). There is a lot of nutrient removal as a result of crop harvesting for example

annual crops like maize, cassava and tobacco remove a lot of nutrients if grown every year

without replenishment (Semana, 1994). This problem is also accelerated by the high rates of

population growth. Kabera et al (1989) asserted that the rapid population growth affects

attainment of fundamental goals which undermines the country’s ability to alleviate rural

poverty through agricultural incomes. This has affected a number of districts especially in the

South Western Uganda in the Kigezi area where the rhetoric on soil degradation in the

highlands almost invariably paints an image of imminent disaster, and has done so since the first

colonial agricultural officers arrived in the 1940s (Simon Bolwig, 2002)

To combat soil degradation and improve soil productivity, Semana (1994) points out the role

played by some farmer but other stake holders like politicians have put in very little effort in

solving this problem. This is due to constitutional, cultural or social economic and technical

constraints in most cases.

2.3 Enhancing Soil Productivity for Increased Agricultural Production

Sustained agricultural production and controlled soil degradation can be achieved through

investment in soil productivity enhancement (Bunting 1992). This is important especially

when we want to overcome hunger and poverty amongst the smallholder farmers who are the

majority amongst all the stakeholders in agricultural production in S.S.A (Micheni, 1996).

Enhancing soil productivity in Sub-Saharan Africa is limited by a number of factors.

According to Rubaihayo (1990), soil productivity enhancement is mainly challenged by the

ediemukiibi ‘08 5

lack of capital by smallholder farmers to purchase soil amendments and other inputs

including fertilizers and coffee husks or hire labour to spread mulching materials. On the

other hand Zake et al. (1994) indicated that some farmers who adopt some sustainable soil

management practices such as use of organic manures and mulches of various types realized

high levels of production.

The use of mineral fertilizers and synthetic soil amendments has been recommended for long

and popularized by farmers but the adoption of these external inputs based technologies for

soil productivity enhancement is mainly constrained by high costs, relative to the low farm

returns and the inaccessibility of such inputs to the resource poor farmers in SSA (Micheni

1996, Micheni et al, 2004). Most farmers apply insufficient or no soil productivity

enhancement inputs to refurnish the degraded soil (DAREP, 1995). However, a number of

farmers in SSA have adopted, through indigenous knowledge, a number of low cost

sustainable soil productivity management practices and in some places these are operational.

2.4 Organic Soil Amendments and Soil Productivity Management

Most soil scientists agree that organic matter plays a key role in tropical soil management.

This is true even of production systems using high external inputs. (Karl and Johannes,

1997). Young et al (1976) reveals that the significance of organic mass in tropical soils is

greater than any other soil characteristic with an exception of soil moisture. (Sanchez 1976),

also emphasized that the maintenance of organic matter through crop residues is of a

fundamental importance to the productivity of tropical soils. In practical terms, this means

that the proper management of tropical soils which have only recently come under

cultivation must aim to maintain both the structure as well as the content of organic matter in

soils that have been cultivated beyond their capacity.(Ignantieff and Emos, 1963). The aim

should de to improve on the management of plant residues from crops and trees to improve

the soil structure and the organic matter content. Zake (1993); Agboola and Corey (1973);

and Unger (2001), reviewed similar statements on the importance of organic residue

management on typical weathered tropical soils.

ediemukiibi ‘08 6

Farmers in Africa utilize a wide range of locally derived organic and inorganic material for

soil productivity management (Swift 1994). These include crop residues, saw dust, litter and

prunings from trees, green – cut herbage, green manures, farm yard manures, House hold and

industrial wastes and many others (Lles and Dosman 1999).

The use organic soil amendments such as farming and manure, compost and plant residues

are known to improve soil fertility in many cropping system (Verma and Bhagat 1992,

Sharma et al 1995). These help improve soil productivity through building up of soil organic

matter (Micheni et al, 2004; Lles and Dosman, 1999; Wasswa et al, 2003). The organic

nutrient sources may be alternative to mineral fertilizers but it is preferred that are used

jointly with chemical fertilizers formation benefits as far as soil productivity enhancement is

concerned.

To effectively improve the level of SOM in degraded and over used soil, De Ridder and Van

Keulen (1990), recommend that large quantities of the organic inputs are continuously

applied on erosion free cultivated fields. These materials are readily available in quantities

that can be of great importance to farmers and easy to apply (Verma and Sharma, 2000).

They can either be incorporated into the soil or applied on the surface as mulch. Whether

used as mulch or incorporated into the soil organic amendments provide a number of benefits

as far as soil productivity is concerned (Wasswa et al 2003; Verma and Sharma 2000)

However the choice for method of application significantly depends on the C/N ratio of the

material (Karl and Johannes, 1992; white et al 1934) and even the environment where it is

applied (Thomas, 1975).

On that note, Jagnow (1967) therefore recommend that for most parts, materials having a

high C/N ratio for example saw dust with more than 500:1 (Starbuck 1994) should be used as

mulch in humid tropics. The C/N ratio of organic materials has a great effect on their rate of

decomposition. Materials with a low C/N ratio decompose relatively quicker than the ones

with a higher C/N ratio. So in case nutrient release is urgent in some farming systems with

short growing seasons, the latter should be incorporated into the soil (Sanders 1953). The

time of application of the organic soil amendments also vary from one amendment to

ediemukiibi ‘08 7

another, but Lal (1975) recommends that whenever possible, organic materials whether

applied as mulch or incorporated into soil be applied before or at the beginning of the first

heavy rains. This is because numerous experiments in various climatic zones of SSA have

demonstrated that organic materials especially mulches are considerably more effective when

applied at this time (Ramaswami, 1979).

2.5 Role of mulches in soil productivity management

Mulching plays a considerably great role in enhancement of soil productivity Zake (1993).

Surface applied organic amendments reduce soil water evaporation (Unger 2001) thus

enhancing the potential for increased soil water conservation which is highly important for

improving soil productivity in SSA. Lal (1975) also showed that mulching with organic

residues prevented excessive high temperatures, decreased soil runoff and soil erosion. Also

other researchers like Salou et al, (1987); Bhattacharyya and Madhava, (1989), noted an

increase in crop yields especially in bananas

However, according to studies by Pereira (1953), mulching is far more effective in

promoting infiltration than it is in reducing evaporation. Ali and Prassad (1975) also found

out from their long term experiments in India that the effect was practically non-existent on

plots where organic residues were applied to prevent evaporation in the dry period. Pain and

Pain (1977) also reveal that, plants are well established under organic amendments especially

when semi rotted mulch rich in lignin was removed temporarily for planting and then

covered the soil again completely once. There fore, in the long term, soil coverage should be

as permanent as possible, since only then are the beneficial effects of mulch fully expressed.

(Karl and Johannes 1997)

As emphasized earlier on, soil organic inputs can effectively act as alternatives to mineral

fertilizers, however, the low quality high labour requirements and low production levels are

the major constraints to the use of these valuable nutrient sources (Kihanda, 1998). Zake et al

(1994) also adds that on being bulky, mulching and other organic materials may harbour

pests and diseases which may be part of the ecology to be conserved. Other limitations

ediemukiibi ‘08 8

include bulkiness, alternative uses like feeds and beddings to livestock and sources of

energy. These materials are required in tones per hectare for example large quantities 5-10

tons ha-1 of farm yard manure are required to provide fraction of what would be needed to

maintain soil productivity at a desired level (Kihanda 1998, Micheni et al 2004).

.

ediemukiibi ‘08 9

CHAPTER THREE MATERIALS AND METHODS

3.1 Study area

A field experiment was conducted at Kisoga central village, Ntenjeru Sub County, Mukono

district for two planting seasons (September-December 2007 and March-June 2008.)

Ntenjeru Sub County is located in the southern part of Mukono district near the lake shores

of Lake Victoria. The climate is influenced by Mabira forest reserve and Lake Victoria. The

sub county has two rainy seasons (March - June and august -December) and two dry seasons

(June – July and January) which greatly influence the activities in the farming system.

Ntenjeru sub-county lies in a banana – coffee vanilla intensive farming system. Towards the

shores of Lake Victoria at Katosi landing site, fishing is an important component of the

system. This farming system in Ntenjeru has been reached by many secondary stakeholders

who included individuals, NGOs like CIAT and UEEF, government departments,

cooperative societies like Kisoga savings and cooperative society and traders.

3.2 Experimental design and treatment

The experimental design was a completely randomized block design (CRBD) with three

treatments namely mulching with saw dust, incorporation of saw dust and the control where

no amendment was applied. Each treatment was replicated three times on experimental plots

of units measuring 6 by 2 meters. Before planting and introduction of saw dust treatments, all

plots were tilled equally and the control plots were maintained as bare ground. (Jeffery and

Michael, 1999)

In the first season (September 2007), fresh fine saw dust from the near by saw mill (same

source with farmers) was applied to the plots and the next day an early maturing maize

variety longe 6H obtained from Ntenjeru sub county department of agriculture was planted at

a spacing of 60 x 30cm (one seed per hill). Weeding was done manually by uprooting the

weeds as they appeared.

ediemukiibi ‘08 10

The soil was sampled in the field covering all plots (0-15cm deep) for the pre-planting soil

properties prior to application of the treatments. The same plots were maintained throughout

the trial duration. For the second season, planting of maize was done without applying more

saw dust to the field as recommended by Starbuck (1994).

Twenty plants out of 44 from each of the 9 experimental plots were selected for data

collection in the trial. For the second season, recordings of the plant growth parameters were

taken twice that is at 2 weeks and 10 weeks (during anthesis) after germination and

application of treatment.

3.3 Data analysis

3.3.1 Soil analysis

Surface (0-15cm) composite soil samples collected on experimental plot basis by a soil auger

in December 2007 (1st growing season) and June 2008 (2nd growing season) were air dried in

the lower soils laboratory of Makerere University soil science department, sieved under

impact test series for the determination of mean weight diameter and then crashed and sieved

through a 2mm sieve for chemical property analysis.

The soil pH was determined using the glass colomed electrode pH meter; Nitrogen was

determined by the Kjedahl approach, available Phosphorus by Bray 1 Extraction Method,

Organic Matter by Walkey-black oxidation method and the aggregate size distribution by dry

sieving using the mean weight diameter approach. The exchangeable potassium and Calcium

were extracted using the ammonium acetate and then determined on a flame photometer in

the soil science East laboratory.

3.3.2 Plant analysis

Plant height, leaf width and number of leaves, data were collected two times in a growing

season that is; two weeks after germination and at the stage of anthesis. The plant height and

leaf width were measured using a tape measure as stated by (Mulanax, 2005) while the leaf


number was obtained by manual counting of leaves on each plants starting with the first to

the last leaf.

3.3.3 Statistical analysis

Maize growth data, and soil physical and chemical analysis data obtained from the laboratory

tests collected at a treatment and replicate basis was entered into Microsoft excel spread

sheet and were then subjected to analysis of variance and their means compared using the

least significance difference (LSD) at 5% level of probability under Genstat (Genwin 32)

window based computer package for experimental research.


CHAPTER FOUR RESULTS AND DISCUSSIONS

The pre planting soil tests are presented in table 1 above. The values of soil PH, % organic

matter, Ca, Phosphorus, nitrogen and potassium were all adequate for plant growth

(Kparmwang et al, 2004) because they were above the critical values indicated in table 1 as

presented by Okalebo et al 1993). This suggests that the favourable parameters could favour

maize growth in all the experimental units.

Table 1: Soil properties before planting and application of saw dust in the first season

Soil parameters tested K Ca

pH % OM % N P

(mg/kg) Me/100g MWD

Mean values

5.8

3.22

0.205

65.687

0.695

6.619

2.126

Critical values

5.5

3.0

0.2

15.00

0.4

0.8

2.0

4.1 Effects of saw dust Application on soil properties

Table 2 shows the soil chemical and physical properties influenced by saw dust application

after the first growing season. The data for soil parameters in the second growing season of

maize crop were obtained at the stage of Anthesis in June 2008 and the results are also

summarized in Table 3. In the second season, saw dust application greatly influenced the

levels of soil parameters.

4.1.1 Soil pH

In the first growing season, the plots in which saw dust was incorporated, the soil pH was

significantly higher (P<0.05) than the control and mulched plot (Table 2). This is in

agreement with findings by Owolabi et al (2003), where saw dust enhanced soil pH and

nutrient status of the soils in South West Nigeria. Generally saw dust application led to a

significant increase in soil Ph after the growing season. This increase in soil alkalinity with

the application of saw dust indicate an increasing supply of basic cations especially Calcium


and potassium (Awodun 2007). Also the elevated pH in plots treated with saw dust could

have resulted from the immobilization of ammonium from the decomposing organic matter

(Obi and Ekiperigin 2001). This is usually a short term pH effect because the pH will

decrease as ammonia is oxidized to nitrate by nitrifying bacteria in the soil in subsequent

growing seasons. (Awodun et al 2007)

Un like in the first season, saw dust application as mulch in the second season resulted into a

significant (p<0.05) reduction in the soil pH to 5.4 below the critical levels given in table 1.

The results presented in Table 3, show that the soil pH in mulched plots was significantly

lower than where saw dust was incorporated into the soil and in the control plots which did

not receive any saw dust (p<0.05). The soil pH was highest under the plots where saw dust

was incorporated into the soil, followed by the control plots and lowest in the mulched plots.

The difference among all treatments was highly significant (LSD=0.2). The highest pH level

in the incorporated plots in the second season could have resulted from the increased supply

of basic cations and exchangeable bases like potassium and calcium more than in the first

season. This finding implies that saw dust incorporated into the soil in humid tropics where

the rate of decomposition is high has a liming effect as explained by Owolabi et al (2003).

Comparing with results of the first season (Table 2), this result indicates that with time saw

dust application as a mulch to the soil induced soil acidity. This similar finding was also

reported by Lles and Dosman (1999) where mulching with wood wastes like saw dust and

bark led to a significant reduction in the soil pH. This saw dust mulch induced pH reduction

below the critical level could have resulted from addition or retention of high levels of

organic matter with organic acids produced from the decomposition of wood derived

materials which accumulates or leach into the soil as found out by Himelick and Watson

(1990)

4.1.2 Soil Organic matter

The results for the first season (Table 2) also show that the application of saw dust resulted

into significant increase in soil organic matter (Awodun 2007, Starbuck 1994). The mulched

plots had significantly higher soil organic matter content than the rest of the treatments.


While the control plots and incorporated plots averaged from 3.24% and 3.97% respectively,

the mulched plots averaged 4.035% which is significantly (p<0.005) higher than the rest of

the plots (LSD= 0.4). This was also true with the second season findings (Table 3) where the

soil organic matter content in mulched plots averaged 3.62% significantly higher than the

control plots (2.13%) but not significantly different (p>0.05) from the incorporated plots

(3.41%). The findings are consistent with Kirsch (1959). However, comparing with the

results in the first season, the results indicate that the level of soil organic matter in all

treatments dropped in the second season. This could be as a result of the increase

mineralization and decomposition of the organic matter common in tropical warm

environments which results into a decline in soil organic matter levels over time without

subsequent additions (Micheni et al 2004). In both seasons, the soil organic matter level was

highest in mulched plots as compared to other treatments. This could be due to the reduced

rates of organic matter mineralization by micro organisms when applied on surface (White et

al 1934) as compared to increased mineralization rates that occur when residues are

incorporated into the soil (Sanders 1953). The overall results indicate that the application of

saw dust as a soil amendment significantly improved the level of organic matter in the soil

which is an incentive to crop production.

4.1.3 Soil Nitrogen

In the first growing season, soil total nitrogen was significantly higher in control plots (LSD=

0.09) (Starbuck, 1994). The control plots recorded highest nitrogen levels (0.223%) followed

by incorporated plots (0.178) and the least nitrogen levels were recorded in plots mulched

with dust (0.176). These two plots had less than the minimum recommended level of 0.2%N

(Kparmwang et al, 2004). The difference in the level of available nitrogen between the

mulched and incorporated plots was not significant (P>0.05). This was also true of the

second season. The result Table 3 indicate that the application of saw dust either as mulch or

incorporated in the soil significantly (p<0.05) reduced the total nitrogen in the soil to levels

below the critical values as earlier reported by Starbuck (1994). In both seasons the control

plots had the highest nitrogen followed by the incorporated plots and nitrogen was least in

mulched plots. The low levels of nitrogen levels in plots where Saw Dust was applied could


be due to the immobilization of nitrogen by micro organisms acting on the carbonaceous saw

dust (Awodun et al 2007; Starbuck 1994; White et al 1934). Saw dust is known to have a

very high C / N ratio of 300 to 500 (Olayinka and Adebayo, 1984). Hence it is recommended

that to enhance release of nutrients from saw dust, the microbial action should be enhanced

by integrating the use of saw dust and urea or other nitrogenous fertilizer to reduce the C/N

ratio of the environment (Olayinka and Adebayo, 1989)

In relation to the above, the study findings on C/N ratio of the soil reveal that saw dust

application significantly statistically (p<0.05) influenced the C/N ratio of the soil in all of the

treatments (appendix 4). Saw dust application as mulch significantly (p<0.05) showed the

C/N ratio (19.22) followed by incorporation (12.68) and lastly the control plots with C/N

ratio as low as 4.92 (appendix 4). The high C/N ratio in the plots where saw dust was applied

is attributed to the high C/N ratio of fresh saw dust which ranges from 300 to 500 (Olayinka

and Adebayo, 1984).

4.1.4 Available Phosphorus

The results from first season analyses (Table 2) indicate that the phosphorus levels of all the

plots were very adequate (Kparmwang et al 2004). The available Phosphorus levels were

highest in the plots where so dust was incorporated into the soil, followed by the control

plots and least in the plots where saw dust was applied on the surface as mulch. Even if there

was a difference in phosphorus levels among the various treatment mentioned above, this

different was not significant in all plots (LSD=63.95) at p> 0.05.

Like wise, the second season results indicate that saw dust application did not have any

significant effect on the phosphorus level as earlier reported in the first season results. How

ever the results show that the application of saw dust to the soil decreased phosphorus levels

as reported by Kirsch (1959) where the incorporation of saw dust reduced the level of

sodium bicarbonate-extractable phosphorus in the soil. The individual treatments data shown

in Table 3 indicate that applied saw dust generally decreased soil phosphorus. An


explanation to this my primarily be because of the retarded microbial activity and an

accompanying decrease in carbon dioxide in the soil as saw dust is decomposing.

4.1.5 Soil Exchangeable bases (K and Ca)

The levels of K and Ca in all plots are generally adequate for satisfactory yields (Kparmwang

et al, 2004). The indicated values show no significant differences in the potassium levels and

the calcium levels in all the plots (p>0.05). On the side of K, is in line with Starbuck (1994)

and Olayinka and Adebayo, (1984) findings that, where saw dust was incorporated into soil,

it resulted into more potassium than other plots but the increase was not significant.

Contrally, the second season results in , indicate that the incorporation of saw dust into the

soil significantly (p>0.05) increased the calcium level in the soil as compared to the mulched

plots, but the difference between the controls and the incorporated plots (Table 3) was not

significant (LSD=1.17). The results also indicate that potassium levels in the second season

were significantly affected by saw dust application (LSD=0.356). Saw dust application on

surface as mulch resulted into significant reduction (p<0.05) in the level of potassium in the

soil making it the lowest recorded among all treatments. The highest potassium level

(1.413me/100g) was obtained by incorporating saw dust into the soil followed by the control

plots (0.923me/100g). Generally, there was an increase in the level of exchangeable bases in

the second season as compared to the first season. The findings partly explains the ability of

saw dust incorporated into the soil to act as a liming material as successfully tried out by Obi

and Ekiperigin, 2001)

4.1.6 Soil aggregation

The effect of saw dust in the aggregate mean weight diameter (MWD) was not significant

(LSD= 0.6). However, it should be noted that plots where saw dust was incorporated had the

highest MWD followed by the mulched plots and least in control plots in the first season

(table 2). In the second season the effect of saw dust application the soil aggregate size

distribution was also not significant (p>0.05) but better soil aggregate size distribution was

recorded in plots where aw dust was applied as the general case in first season. This clearly

depicts the advantages of using organic soil amendment as reviewed by Verma and Bhaghat,


1992; Zake et al, 1994 and Wasswa et al, 2003. These results show that saw dust helped

stabilize soil aggregates, apparently through its decomposition and therefore affecting other

soil parameters relevant for plant growth. The second season results how ever show a general

reduction in soil aggregation as indicated by lower mean weight diameter values than in the

first season.

Table 2: Soil response to application of saw dust in the first growing season

Treatment Soil Characteristics pH O.M (%) MWD Ca

me/100gN% P K

me/100g

NS== Not Significant

Mulch 6.0

4.033

2.253

5.71

0.176

56.2

0.879

Incorporated 6.2 3.97 2.551 6.46 0.178 74.9 0.854

None 5.9 3.24 2.123 7.01 0.223 66.2 0.844

L.S.D(p=0.05) 0.2 0.4 0.6 (NS) 1.6 (NS) 0.09 63.9(NS) 0.2 (NS)

Table 3: Soil response to application of saw dust in the second growing season

Treatment Soil Characteristics

pH O.M (%)

Aggregation (MWD)

Ca (me/100g)

N (%) P (mg/kg)

K (me/100g)

Mulch

5.4

3.62

2.51

5.67

0.12

55.6

0.79

Incorporated

6.3

3.41

2.00

6.93

0.157

54.6

1.413

None

5.8

2.13

1.75

6.10

0.283

75.5

0.923

LSD (p=0.05) 0.2 1.36 0.86(NS) 1.17 0.103 54.67(NS) 0.356 NS == Not Significant

4.2 Maize Crop response to Saw Dust Application

The results on the effects of saw dust on maize growth during the first planting season of

September – December 2007 are not presented because of the adverse weather conditions


(Very heavy rain fall that buried the seedlings before readings were taken and the few which

had survived were later severely affected by the prolonged dry period from October to

December 2007 there by causing lack of statistical significance. So the results presented in

this section apply to the second growing season.

4.2.1 Effect of saw dust application on maize plant height (cm).

Maize plant heights (cm) taken at two different stages that is at 2 weeks after germination

(WAG), and 10 weeks (Anthesis) after germination are presented in Table 4 below. All

treatments influenced plant heights at Anthesis un-like at 2 weeks after germination.

Table 4: effect of saw dust application on maize plant height (cm)

Maize plant heights Treatment

2 WAG 10 WAG

Mulch 9.42 124.5

Incorporated 10.08 176.8

None 10.39 186.8

LSD (p=0.05) 2.9(NS) 19.76

NS== Not Significant

As indicated in the table above, the application of saw dust had no significant influence

(p>0.05) on the maize plant height at 2 weeks after germination. On the other hand, at

Anthesis, saw dust applied as mulch had significant (p<0.05) adverse effect on maize plant

height. As indicated by the means in the table above, maize plants in the Control plots

attained the highest heights followed by the plots where saw dust was incorporated into the

soil. The plant heights in both incorporated and control plots were not significantly different

but highly significant from that attained under the mulched plots (p<0.05). This could be

attributed acidity induced by the saw dust mulch below the critical levels compared to

favourable pH and other favourable parameters in the control and incorporated plots. These

results therefore imply that for better maize plant heights and improved soil conditions like

organic matter, aggregation calcium and potassium, the incorporation of saw dust into the


soil is necessary. This is in line with what Awodun at al (2007) found out in southern Guinea

Savanna zone of Nigeria.

4.2.2 Effect of saw dust application on maize leaf width (cm) and number of leaves

At two weeks after germination, applied saw dust had no significant influence (p>0.05) on

the leaf width and number. How ever the results recorded (figure 1) show that the highest

leaf width was attained in the control plots (1.7cm), followed by the plots where saw dust

was incorporated into the soil (1.567cm) and lowest in mulched plots (1.367cm).

0

2

4

6

8

10

12

Mai

ze le

af w

idth

(cm

)

2 weeks 1.367 1.567 1.7

10 weeks 9.57 11.43 11.3

mulch incorporated none

2 weeks LSD

10 weeks LSD

Figure 1: Response of Maize Leaf Width to Saw Dust Application At Anthesis, saw dust application significantly influenced (p<0.05) the maize leaf width. The

incorporation of saw dust into the soil resulted into significantly wider leaves than in the

mulched plots but not on the control plots (figure 1). This increase in leaf width has a number

of beneficial effects on the yield of maize. It greatly affects the amount of solar radiation

absorbed by the plant to effectively carry out processes like photosynthesis.

Saw dust mulch also significantly (p<0.05) reduced the number of leaves (appendix 1). The

difference was significant through out all treatments (LSD=0.4) with the highest number

recorded in control plots followed by the incorporated plots and lowest in the mulched plots.

This could be attributed to the low levels of nitrogen saw dust treated plots as compared to


the control plots. The leaf number and plant height were also strongly related (R2 = 1) as

presented in figure 2.

4.3 Relationship between maize plant height (cm) and number of leaves, soil pH,

Organic matter and soil nitrogen.

Figures 2, 3, 5 and 5 represent the relationship between maize plant height and number of

leaves, maize plant height and soil pH, maize plant height and Organic matter, and maize

plant height and soil nitrogen respectively.

y = 29.162x - 66.709

R2 = 1

020406080

100120140160180200

2 4 6 8

Number of leaves

Mai

ze H

eigh

t (cm

)

10

Figure 2: Relationship between Maize Plant Height (Cm) and the Number of Leaves

There was a strong relationship (R2=1) between maize plant height and the number of leaves

on the plant in each treatment recorded 10 weeks after germination. This was when maize

had attained a maximum canopy in terms of leaf area index, and above ground biomass. So it

is recommended that most of soil management practices for better maize yields like

application of organic matter, weeding, and fertilizer application, should be optimized up to

this stage, because any management intervention after the Anthesis stage will definitely

benefit the soil but may not increase plant growth characteristics like height and leaf number.


y = 54.91x - 157.61R2 = 1

020406080

100120140160180200

5.2 5.4 5.6 5.8 6 6.2 6.4

Soil pH

Mai

ze H

eigh

t (cm

)

Figure 3: Maize Plant Height (Cm) – Soil pH Relationship

Other regression analyses conducted between maize plant height and soil pH, (figure 3) soil

organic matter (figure 4) and nitrogen (figure 5) also showed a positive relationship. The

results of the regression analysis between maize plant height and soil pH (figure 3) showed a

very strong relationship (R2=1), figure 4 and 5 also followed a similar trend to depict the

relationship between maize plant height and soil organic matter (R2=0.5188) and maize plant

height and nitrogen level (R2=0.6056) respectively. Since plant height directly relates with

the yield of grain cereals, (Olupot 2002), it implies that better build up of these parameters as

influenced by saw dust application is important for attainment of higher maize plant height

and hence better maize grain yield.


y = -29.88x + 253.93R2 = 0.5188

020406080

100120140160180200

0 1 2 3

% Organic Matter

Mai

ze H

eigh

t (cm

)

4

Figure 4: Maize Plant Height (Cm) – Organic Matter Relationship

y = -29.88x + 253.93R2 = 0.5188

020406080

100120140160180200

0 1 2 3 4

% Organic Matter

Mai

ze H

eigh

t (cm

)

Figure 5: Maize Plant Height (Cm) – Soil Nitrogen (%) On the other hand, the regression analysis did not show any relation ship between maize

plant height and soil potassium (R2 = 0.2982) and maize plant height and soil phosphorus

levels (R2 = 0.3482) as presented in appendix 2 and appendix 3 respectively.


CHAPTER FIVE CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

Enhancement of soil productivity through maintaining favourable soil properties using the

locally available materials is essential for sustained agricultural production in Sub Saharan

Africa. This is particularly important to small holder farmers who are resource constrained to

access high external in puts. This study indicated the potential of saw dust as a locally

available soil amendment to improve the level soil organic matter which is central to the

productivity of any agricultural soil in Uganda. Organic matter levels were significantly

higher in saw dust applied plots than in the control plots where saw dust was not applied. The

soil aggregation was favourably affected by saw dust application however the effect was not

significant. Saw dust application did not have any significant effect on the phosphorus level

through out the study.

Saw dust with time significantly increased the supply of exchangeable bases when

incorporated into the soil and this partly explains the high soil pH in this treatment. In all

growing seasons saw dust application either as mulch or incorporated into the soil reduced

the nitrogen levels in the soil. So a combination of nitrogen immobilization effect and

reduced soil pH in the mulched plots severely inhibited maize plant growth characteristics

like Height, leaf width and number of leaves.

Generally, the application of sawdust as mulch had more adverse effects on soil properties

and hence maize plant growth than when saw dust was incorporated into the soil.

5.2 Recommendations

Basing on the adverse effects of saw dust application to the soil and plant growth, the study

recommends that when ever saw dust is to be used by farmers, a sample of saw dust should

be sent to a soil testing laboratory to determine the C/N ratio and nutrient contents prior to its

application as a soil amendment.


The study also recommends that since saw dust application results into nitrogen deficiencies,

it should be used with supplemental nitrogen sources like animal manure and poultry manure

or composting with afore mentioned manures prior to the growing of the crops to over come

this nitrogen inhibition.

More studies are needed to establish better ways on how to improve the performance of saw

dust saw dust under different agro ecological zones of Uganda.


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Appendices

Table 5: effect of saw dust on the number of leaves

Average Number of leaves on the maize plant Treatment

2 WAG 10 WAG

Mulch 3.67 6.7

Incorporated 3.67 8.0

None 4.0 8.9

LSD (p=0.05) 0.76(NS) 0.4

NS == Not Significant

Appendix 2: Maize plant height (cm) – soil Potassium relationship

y = 55.686x + 104.67R2 = 0.2982

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0 0.5 1 1

Soil Potassium (me/100g)

Mai

ze H

eigh

t (cm

)

.5


Table 6: Maize plant height (cm) – soil Phosphorus relationship

y = 1.6748x + 59.031R2 = 0.3482

0204060

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0 20 40 60 80

Phosphorus level (mg/kg)

Ma

eigh

t (cm

)

80

ize

H Appendix 4: effect of saw dust application on C/N ratio of the soil

Treatment

Mulch Incorporated None

C/N ratio (means) 19.22 12.68 4.92

LSD (p<0.05) 6.17


mukiibi edward - Effect of Saw Dust on Soil Physical and Chemical Properties in Ntenjeru Sub County, Mukono District, Uganda

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