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CONSERVATION AGRICULTURE IMPROVINGSOIL QUALITY FOR SUSTAINABLE PRODUCTION
SYSTEMS UNDER SMALLHOLDER FARMINGCONDITIONS IN NORTH WEST INDIA: A REVIEW
R K Naresh1*, S P Singh2, Ashish Dwivedi1, Naval Kishor Sepat3,Vineet Kumar1 and Lalit Kumar Ronaliya1, Vikas Kumar4 and Rachna Singh1
Review Article
India is a country of about one billion people. More than 70% of India's population lives in ruralareas where the main occupation is agriculture. Indian agriculture is characterized by smallfarm holdings. The average farm size is only 1.57 hectares. Around 93% of farmers have landholdings smaller than 4 ha and they cultivate nearly 55% of the arable land. On the other hand,only 1.6 of the farmers have operational land holdings above 10 ha and they utilize 17.4% of thetotal cultivated land. The pace of conservation agriculture and its resultant economic gain inturns depend on the environment influenced by economic, social, ecological and other suchfactors. However, the land is an inelastic factor of production. Therefore, Conservation Agriculture(CA) becomes a distinct though integrated organ of overall agriculture production, because ofits feature of allocation of inelastic factors of production amongst competing crop choices. Theconversion of conventional to zero tillage can result in the loss of total pore space as indicatedby an increase in bulk density. Infiltration is generally higher and runoff reduced in zero tillagewith residue retention compared to conventional tillage and zero tillage with residue removal.Soil water retention in the top 20 cm of the soil profile was higher in CA than in Farmers Plots(FP). The combination of reduced tillage with crop residue retention increases the SOC in thetopsoil. The needed yield increases, production stability, reduced risks and environmentalsustainability can only be achieved through management practices that result in an increasedsoil quality. This paper presents results of a study investigating possible changes in soil physicaland chemical properties under CA, an adapted form of CA that is appropriate for smallholderfarming conditions in North Western India.
Keywords: Conservation agriculture, Sustainability, Smallholder farming system, Agro- ecosystem
*Corresponding Author: R K Naresh [email protected]
ISSN 2250-3137 www.ijlbpr.comVol. 2, No. 4, October 2013
© 2013 IJLBPR. All Rights Reserved
Int. J. LifeSc. Bt & Pharm. Res. 2013
1 Department of Agronomy, Sardar Vallabhbhai Patel University of Agriculture & Technology, meerut-250110 (U.P.).2 Department of Soil Science, Sardar Vallabhbhai Patel University of Agriculture & Technology,meerut-250110 (U.P.)3 Directorate of ER & IPR DRDO Bhawan,Rajaji Marg New Delhi 1100114 Krishi Vigyan Kendra Jhansi,Chandra Shakhar Azad University of Agriculture & Technology, Kanpur (U.P.)
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INTRODUCTIONEvaluating the impact of agricultural practices on
agroecosystems functions is essential to
determine the sustainability of management
systems (Liebig et al., 2001), which cover the
productivity,economic, social, and environmental
components of land use systems (Smyth and
Dumanski,1995). However,decision making for
sustainable management could be improved by
tools that provide integration and synthesis of soil
research results,management priorities,and
environmental concerns (Andrews and Carroll,
2001). Soil quality is considered a key element
used to evaluate sustainable land management
in agro ecosystems (Warkentin, 1995; Wander
and Bollero, 1999; Carter, 2002) through
identification of soil quality indicators (Skukla et
al., 2004). Soil quality, encompasses both a soil’s
productive and environmental capabilities
(Wander et al., 2002), has two parts: an intrinsic
part covering a soil’s inherent capacity for crop
growth and a dynamic part influenced by the soil
management (Carter, 2002). Soil structure
management is a crucial soil physical property
used to infer soil quality (Sánchez-Marañón et al.,
2002). The degradation of soil structure should
be balanced and or exceeded by regeneration in
order to have a sustainable soil management
(Munkholm and Schjonning, 2004).Conservation
Agriculture (CA), defined as minimal soil
disturbance (no-till) and permanent soil cover
(mulch) combined with rotations, was found to
be more sustainable cultivation system for the
future than those conventionally practiced,
because conservation agriculture can recover
soil functioning through improving water
infiltration, reducing erosion, increasing soil
organic matter content, and improving soil
surface aggregates (Hobbs, 2007). The
excessive erosion of topsoil from farmland
caused by intensive tillage and row-crop
production has caused extensive soil degradation
and also contributed to the pollution of both
surface waters and groundwater.
Furthermore, the production of methane from
paddy fields and of carbon dioxide from the
burning of fossil fuels, land clearing and organic
matter decomposition have been linked to global
warming as “greenhouse gases” (Parr and
Hornick, 1992b). Environmental pollution, caused
by excessive soil erosion and the associated
transport of sediment, chemical fertilizers and
pesticides to surface waters and groundwater,
and improper treatment of human and animal
wastes has caused serious environmental and
social problems throughout the world. Often
scientists have attempted to solve these problems
using established chemical and physical
methods. However, they have usually found that
such problems cannot be solved without using
microbial methods and technologies in
coordination with agricultural production
(Reganold et al.,1990; Parr and Hornick, 1992a).
For many years, soil microbiologists have tended
to differentiate soil microorganisms as beneficial
or harmful according to their functions and how
they affect soil quality, plant growth and yield, and
plant health. Beneficial microorganisms are those
that can fix atmospheric nitrogen, decompose
organic wastes and residues, detoxify pesticides,
suppress plant diseases and soil-borne
pathogens, enhance nutrient. The concept of
Effective Microorganisms (EM) (Higa, 1991; Higa
and Wididana, 1991a).EM consists of mixed
cultures of beneficial and naturally-occurring
microorganisms that can be applied as inoculants
to increase the microbial diversity of soils and
plants. EM cultures to the soil/plant ecosystem
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
can improve soil quality, soil health, and the
growth, yield, and quality of crops. The role and
application of beneficial microorganisms,
including EM, as microbial inoculants for shifting
the soil microbiological equilibrium in ways that
can improve soil quality, enhance crop production
and protection, conserve natural resources, and
ultimately create a more sustainable agriculture
and environment.
There are many opinions on what an ideal
agricultural system is. Many would agree that
such an idealized system should produce food
on a long-term sustainable basis. Many would also
insist that it should maintain and improve human
health, be economically and spiritually beneficial
to both producers and consumers, actively
preserve and protect the environment, be self-
contained and regenerative, and produce enough
food for an increasing world population (Higa,
1991). The excessive erosion of topsoil from
farmland caused by intensive tillage and row-crop
production has caused extensive soil degradation
and also contributed to the pollution of both
surface waters and groundwater. Organic wastes
from animal production, agricultural and marine
processing industries, and municipal wastes
(e.g., sewage and garbage), have become major
sources of environmental pollution in both
developed and developing countries.
Furthermore, the chemical-based, conventional
systems of agricultural production have created
many sources of pollution that, either directly or
indirectly, can contribute to degradation of the
environment and destruction of our natural
resource base. This situation would change
significantly if these pollutants could be utilized in
agricultural production as sources of energy.
Therefore, it is necessary that future agricultural
technologies be compatible with the global
ecosystem and with solutions to such problems
in areas different from those of conventional
agricultural technologies. An area that appears
to hold the greatest promise for technological
advances in crop production, crop protection, and
natural resource conservation is that of beneficial
and effective micro-organisms applied as soil,
plant and environmental inoculants (Higa, 1995).
CONSERVATION TILLAGEAND AGRICULTURE?One of the more famous results of poor tillage
choice is the Dust Bowl of the 1930s in the U S
Great Plains. This resulted from excessive tillage
and exposure of soil to wind. The tragic dust
storms of that time and place served as a wakeup
call about how man’s interventions in soil
management and plowing can lead to
unsustainable agricultural systems. In the 1930s
it was estimated that 91 million hectares of land
was degraded by severe soil erosion (Utz et al.,
1938); this area has been dramatically reduced
today. For the next 75 years, farmers have been
adopting conservation tillage practices that reduce
tillage and maintain a residue cover on the soil.
This is called Conservation Tillage (CT) and is
defined as follows:
“Conservation tillage is the collective umbrella
term commonly given to no-tillage, direct-drilling,
minimum-tillage and/or ridge-tillage, to denote
that the specific practice has a conservation goal
of some nature. Usually, the retention of 30%
surface cover by residues characterizes the lower
limit of classification for conservation-tillage, but
other conservation objectives for the practice
include conservation of time, fuel, earthworms,
soil water, soil structure and nutrients. Thus
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
residue levels alone do not adequately describe
all conservation tillage practices” (Baker et al.
2002)
This has led to confusion among the
agricultural scientists and, more importantly, the
farming community. To add to the confusion, the
term conservation agriculture has recently been
introduced by the FAO (Food and Agriculture
Organization website) and others and its goals
defined by FAO as follows:
“Conservation agriculture (CA) aims to
conserve, improve and make more efficient
use of natural resources through integrated
management of available soil, water and
biological resources combined with external
inputs. It contributes to environmental
conservation as well as to enhanced and
sustained agricultural production. It can
also be referred to as resource efficient or
resource effective agriculture.” (FAO)
This encompasses the sustainable
agricultural production need that all humankind
obviously wishes to achieve. But this term is often
not distinguished from conservation tillage. FAO
mentions in its CA website that
“Conservation tillage is a set of practices
that leave crop residues on the surface
which increases water infiltration and
reduces erosion. It is a practice used in
conventional agriculture to reduce the
effects of tillage on soil erosion. However,
it still depends on tillage as the structure
forming element in the soil. Nevertheless,
conservation tillage practices such as zero
tillage practices can be transition steps
towards Conservation Agriculture.”
In other words conservation tillage uses some
of the principles of conservation agriculture, but
has more soil disturbance. FAO has characterized
conservation agriculture as follows:
“Conservation Agriculture maintains a
permanent or semi-permanent organic soil
cover. This can be a growing crop or dead
mulch. Its function is to protect the soil
physically from sun, rain and wind and to
feed soil biota. The soil micro-organisms
and soil fauna take over the tillage function
and soil nutrient balancing. Mechanical
tillage disturbs this process. Therefore,
zero or minimum tillage and direct seeding
are important elements of CA. A varied crop
rotation is also important to avoid disease
and pest problems.” (FAO Website).
Conservation agriculture does not just mean
not tilling the soil and then doing everything else
the same. It is a holistic system with interactions
among households, crops, and livestock since
rotations and residues have many uses within
households; the result is a sustainable agriculture
system that meets the needs of farmers.
SOIL QUALITYWhen evaluating an agricultural management
system for sustainability, the central question is:
Which production system will not exhaust the
resource base, will optimize soil conditions and
will reduce food production vulnerability, while at
the same time maintaining or enhancing
productivity? Soil quality can be seen as a
conceptual translation of the sustainability
concept towards soil. A simpler operational
definition is given by Gregorich et al. (1994) as
.‘The degree of fitness of a soil for a specific use.’.
This implies that soil quality depends on the role
for which the soil is destined (Singer and Ewing,
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
2000). Within the framework of agricultural
production, high soil quality equates to the ability
of the soil to maintain a high productivity without
significant soil or environmental degradation.
Evaluation of soil quality is based on physical,
chemical and biological characteristics of the soil.
With respect to biological soil quality, a high
quality soil can be considered a ‘healthy’ soil. A
healthy soil is defined as a stable system with
high levels of biological diversity and activity,
internal nutrient cycling, and resilience to
disturbance (Rapport, 1995). Management
factors that can modify soil quality include tillage
and residue management systems, as well as
the presence and conformation of crop rotations
(Karlen et al., 1992). Changes in soil quality are
not only associated with management, but also
with the environmental context, such as
temperature and precipitation (Andrews et al.,
2004). A comparative soil quality evaluation is one
in which the performance of the system is
determined in relation to alternatives. The biotic
and abiotic soil system attributes of alternative
systems are compared at some time. A decision
about the relative sustainability of each system
is made based on the difference in magnitude of
the measured parameters (Larson and Pierce,
1994). A comparative assessment is useful for
determining differences in soil attributes among
management practices that have been in place
for some period of time (Wienhold et al., 2004).
In a dynamic assessment approach the
dynamics of the system form a meter for its
sustainability (Larson and Pierce, 2004). A
dynamic assessment is necessary for
determining the direction and magnitude of
change a management practice is having
(Wienhold et al., 2004), especially when
compared to the common, existing farmer
practices and it must be understood that this
assessment normally must involve an adequate
time frame.
Figure 1: The Three Principles of Conservation Agricultureand the Main Practices and Means Needed to Achieve Each Principle
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
SOIL STRUCTURESoil structure or soil architecture is a crucial soilproperty in the functioning of several processesimportant to soils productive capacity,environmental quality, and agriculturalsustainability (Figure 2; Lal, 1991; Kay andMunkholm, 2004; Guber et al., 2005). It plays animportant role in root development, waterretention, infiltration capacity, and soil porosity(Dexter, 1988; Neves et al., 2003; Guber et al.,2005). These effects of soil structure onagricultural production can be felt at differentscales ranging from local (e.g., soil productivity,sustainability), regional (e.g., water quality,landscape) to global one (e.g., global water andenergy balance, greenhouse effect) (Lal, 1991).However, definition of soil structure varied from“the arrangement of the particles in the soil” asdefined by Hillel (1998) or “the spatialheterogeneity of the different component orproperties of soil” (Dexter, 1988), to a morefunctional as “size, shape, arrangement, andcontinuity of solids and voids, continuity of poresand voids, their capacity to retain and transmitfluids and organic and inorganic substances, andability to support vigorous root growth anddevelopment” (Lal, 1991). Likewise, Kay (1990)proposed three dynamic dimensions to
characterize soil structure in the terms of stability,form and resiliency. Structural stability describesthe ability of the soil to retain its arrangement ofsolid (i.e., aggregates) and pore space whenexposed to external force (e.g., tillage, wetting).Whereas structural from refers to total porosity,pore size distribution, and continuity of the poresystem and therefore, describes the arrangementand size of inter-and intra-aggregate pores.Structural resiliency describes the ability of a soilto restore and recover its structural from (i.e.,pore space arrangement) through naturalprocesses after the removal of stress (e.g.,compaction, rainfall impact). This solid-porearrangement and foundation is sensitive to soiltillage operations which usually disrupt surfacelayers of agricultural soils, developing a loosenedunstable structure with a substantial proportion
of inter aggregate porosity (Or et al., 2000).
INFLUENCE OF CONSERVATIONAGRICULTURE ON SOILQUALITYSoil Structure and Aggregation
Tillage Effects
The type and degree of tillage inputs can have a
major influence on soil properties and processes
Figure 2: Schematic Representation of Tillage, Forces, Effect on Soil Structureand Environmental Consequences (Adapted from E l Titi, 2003)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
and thereby modify soil structure (Carter, 2004).
Tillage practice can change the soil aggregate
size distribution which also varied according to
the tillage type (Braunack and Dexter, 1989a).
Ojeniyi and Dexter (1984) reported varied effect
of different tillage practices on the distribution of
both aggregate and pore sizes. Franzluebber and
Arshad (1997) found that macroaggregates
(>0.25 mm) and mean weight diameter were
greater under zero tillage (harrowing following
harvest) than under conventional tillage one fall
tillage with a cultivator followed by two cultivation
in the spring prior to seeding) in coarse-textures
soils. Soil disturbance as a direct result of tillage
is a major cause of organic matter depletion and
reduction in the number and stability of soil
aggregates when native ecosystems are
converted to agriculture (Six et al., 2000).
Management-induced changes in Soil Organic
Carbon (SOC) concentration may significantly
alter aggregate properties (Blanco-Canqui et al.,
2007). Carter et al. (2004) conceptualized the
relationships between soil structure at different
scales, starting from soil profile with peds or
clods, to the formation of aggregates which is
the subject of most of investigations, with the
influenced soil processes as indicated by Figure
3. Consequently, for a soil to have desirable soil
hydraulic and mechanical properties, the different
hierarchical orders should be developed and
stable against the actions of the different stresses
(Dexter, 1988).
Conservation tillage can improve soil structure
and stability thereby facilitating better drainage and
water holding capacity that reduces the extremes
of water logging and drought ( Holland, 2004). In
general, soil organic matter is considered as a
key factor in soil aggregation (e.g., Rasmussen,
1999; Carter, 2002; Six et al., 2004; Carter, 2004)
and so pore space configuration, therefore any
management affect the level and the different
fraction of soil organic matter will highly affect the
soil functions. Abiven et al. (2007) found that,
aggregate stability under slow wetting was
improved after the addition of wheat straw and
well correlated with polysaccharides which prove
the hypothesis that the rapid microbially induced
improvement in aggregate stability that follows
fresh organic residue additions (wheat straw) at
least partly involves labile polysaccharides. Six
et al. (2000), evaluated a conceptual model which
links the turnover of aggregates to soil organic
Figure 3: Soil Structure Over Several Orders Of Magnitude (<m To >Cm)From Soil Profile in the Field to Microscopic Level Along With Some Related
Soil Processes and Conditions (From Carter, 2004)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
matter dynamics in no-tillage and conventional
tillage systems. They argued that the rate of
macroaggregate formation and degradation (i.e.,
aggregate turnover) is reduced under no-tillage
compared to conventional tillage and leads to a
formation of stable microaggregates.
Conventional tillage practices are found to
increase aggregate turnover compared with
conservation tillage (Blanco-Canqui and Lal,
2004). Studying the effects of different tillage
managements on surface soil structure is
important for the development of effective soil
conservation practices in order to avoid risks of
soil deterioration (Zhang et al., 2007).
PHYSICAL PROPERTIESCrop residues play an important role in improving
soil physical characteristics, but the degree of
improvement depends on particle size
distribution. Sandy soils with low SOM contents
lack substantial structure and are prone to severe
erosion. Adding crop residues or manure will
increase microbial activity, which in some studies
has led to the buildup of SOM and formation of
macro- and micro aggregates (Sparling et al.,
1992; Angers et al., 1993). Differences in
aggregate stability also depend on the sources
of the organic materials, such as fungal hyphae
versus microbial polysaccharides (Tisdall, 1991).
On the other end of the particle spectrum, heavy
clay soils are often characterized by poor
structure and aeration, but they can be improved
through the addition of organic amendments.
Therefore, the positive effect of SOM on soil
structure will be more pronounced for a clay soil
than for a silty soil.
In most climates, removal or burning of crop
residues leads to deterioration of soil physical
properties (Kladivko, 1994; Prasad and Power,
1991). In rice, puddling of soil by cultivation in
standing water could adversely affect soil
structure through destruction of aggregates and
peds (Sharma and De Datta, 1985) and leads to
formation of a pan of low permeability immediately
below the cultivated layer, particularly on fine-
textured soils. This hard pan could be detrimental
for the productivity of the upland crop (say wheat)
after rice (Moorman and Van Breeman, 1978; Sur
et al.,1 981). A recent review has, however, shown
that puddling may or may not be detrimental to
the succeeding non-rice crops and soil (Connor
et al., 2003). Recycling of crop residues
influences soil structure, crusting, bulk density,
moisture retention, and water infiltration rate and
may help reduce adverse effects of hard pan
formation in rice-based cropping systems, which
may play an important role in the upland crop
(such as wheat or maize) after rice than the rice
crop.
Aggregation
The role of soil organic matter in aggregate stability
is summarized in Figure 4. Straw incorporation
helps the formation and stability of aggregates
through increase in microbial cells, and excrets
microbial products and decomposition products
released during the death of the microorganisms
(Lynch and Elliott, 1983). The soil organic matter
in turn is protected within aggregates for
decomposition (Dalal and Bridge, 1996). The
amount and chemical composition of organic
residues, temperature, and moisture conditions
are the major factors determining aggregation in
soil (Prasad and Power, 1991). Thus, easily
decomposable plant residues such as green
manure and grain legume residues provide
transient and temporary aggregate stabilizing
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
agents, while cereal crop residues provide
persistent aggregate stabilizing agents (Elliott and
Lynch, 1984). Chaudhary and Ghildhyal (1969)
obtained a close relation (r ¼ 0.76) between
organic C increased by organic materials addition
and aggregate stability of soil under wetland rice.
Likewise, Elliott and Lynch (1984) found that the
effect of straw on aggregation in a silt loam soil
decreased with increasing straw N content in the
range of 0.25 to 1.09%.
Several researchers have reported an
improvement in soil aggregation after
incorporation of crop residues into the soil under
rice-based cropping systems (Bhagat et al.,
2003; Liu and Shen, 1992; Liu et al., 1990; Meelu
et al., 1994; Oh, 1984). In a 10-year study on a
rice–rice cropping system on a vertisol,
application of rice straw incorporated to meet
either 25 or 50% of recommended fertilizer N
requirement increased the water stable
aggregates (Table 1). In a rice–wheat cropping
system on a loamy sand soil, incorporation of
wheat straw over a 5-year period in rice promoted
formation of soil aggregates, particularly 1-2 mm
size, and mean weight diameter (Table 2). A mixed
application of green manure and crop residues
Figure 4: A Generalized Summary of Soil Aggregates Stabilization By Various Sourcesof Organic Matter (Dalal and Bridge, 1996)
Table 1: Effect of Rice Straw Application on Soil Physical Properties in Rice–Rice CroppingSystem over a 10-Year Period on a Clayey Soil
Treatment to Summer Rice Bulk HC Water Stable Porosity Water retention ( kg kg-1 ) MaximumDensity (cm h-1)a Aggregates (%) Water Retention
(Mg m-3 ) (%) 33 K Pa 1.5 M Pa capacity (kg kg-1)
Inorganic fertilizers 1.43 1.18 37.6 46 0.35 0.21 0.49
Rice straw to meet 50 % N 1.26 1.93 51.3 52 0.43 0.28 0.58
Rice straw to meet 25 % N 1.27 1.78 49.6 52 0.41 0.26 0.56
Green leaf manure to meet 50 % N 1.29 1.80 50.1 50 0.42 0.26 0.50
Note: aHC, Hydraulic conductivity, From Bellakki et al. (1998).
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was more effective compared to their separate
applications. Similarly, in a long-term experiment
(1981-1990) on rice–rice rotation in China, Liu and
Shen (1992) noted that application of crop
residues promoted aggregation. The contents of
micro-aggregates (0.25-1.0 mm) were increased
from 10.9% in inorganic fertilizer treatment to
12.1% in milk vetch green manure and to 13.6%
in green manure plus rice straw treatment.
In a 4-year barley-early rice-late rice crop
rotation in China, Rixon et al. (1991) found that
addition of 3 t ha-1 of crop residues in late rice did
not significantly affect distribution and stability of
aggregates and moisture retention characteristics
of a clayed paddy soil. However, after 5 years of
the above study, a continuous improvement in
soil structure, volume weight, porosity,
aggregation, and plasticity was observed (Zhu
and Yao, 1996). The effect of crop residues on
aggregation also depends on the aggregation
potential of the soil. Datta et al. (1989) have shown
that when clay content in soil was low, burying of
Table 2: Effect of Green Manure and Crop Residues on Soil Aggregationand Bulk Density in a Rice–Wheat Cropping System on a Loamy Sand Soil after 5 Years
Treatment Water Stable Aggregates (%) Mean Weight Bulk Density (Mg m-3)
>2 mm 1-2 mm 0.5-1 mm 0.1- 0.5 mm Diameter (mm) 0-10 cm 10-20 cm
Residue removed 9.8 10.0 5.6 11.3 1.42 1.59 1.72
Residue incorporated 11.7 15.0 5.5 11.3 1.56 1.49 1.72
Green manure (GM) 11.1 15.5 6.1 12.0 1.58 1.51 1.71
Crop residue +GM 17.1 11.1 6.9 9.1 1.68 1.48 1.68
Note: From Meelu etal. (1994).
Table 3: Effect of Residue Retained on Water Stability of Aggregates,Clod Breaking Strength and Soil Organic Carbon (%) in a Silty Loam SoilUnder Maize-wheat Cropping System After 3 Years (Naresh et al., 2012)
Crop establishment Water Stable Aggregate Clod breaking Soil OrganicAggregates >0.25 mm (%) Porosity (%) Strength (kPa) Carbon (%)
No- Till Residue removed 66.7 39.6 418.7 0.54
No Till 50% Residue retained 72.9 40.2 367.5 0.58
No –Till 100% Residue retained 79.0 41.3 332.9 0.61
Permanent Beds Residue removed 80.3 40.8 289.7 0.55
Permanent Beds+50%Residue retained 81.9 42.7 235.6 0.59
Permanent Beds+100%Residueretained 82.8 43.2 204.8 0.63
Conventional practices 59.1 36.2 423.8 0.52
C D at 5% 5.3 1.74 95.3 0.53**
Note: **Initial value
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straw had a more favorable effect on the stability
of aggregates, especially of crumbs 3-5 mm in
diameter, than in soil with 27% clay content.
Likewise, Verma and Singh (1974) observed that
wheat straw caused a marked influence on soil
aggregation in four different soils varying in texture.
Maximum aggregation occurred in the sandy
loam, with minimum aggregation in alkali soil.
Application of rice straw to alkali clayey soil
significantly increased water stable aggregates
>0.25 mm. Total organic C also increased, which
resulted in a marked increase of macropores as
well as the aggregate size in the 2.0-0.84 mm
size fractions (El Samanoudy et al., 1993). In a
friable self-mulching clay of the vertisol group, 34
years of either stubble burning or incorporation
had, however, little effect on soil structure (Dexter
et al., 1982). The nature of plant material also
plays an important role in the development of soil
structure. For example, Dhoot et al. (1974)
recorded the highest percentage of water-stable
aggregates in pearl millet-amended soil followed
by rice straw or wheat straw and sesbania green
manure.
Build up of aggregate is a concurrent process
with pore space arrangement and configuration.
Elliott and Coleman (1988) suggested a
simultaneous hierarchical pore formation model
as a mirror image of the aggregate hierarchy, and
they defined four basic hierarchical pore
categories which relate to the aggregate structure
of the soil and provide a basis for predicting how
soil pore networks inf luence ecological
relationships among organisms: (i) macropores;
(ii) pore space between macroaggregates; (iii)
pores between microaggregates but within
macroaggregates; and (iv) pores within
microaggregates, as shown in Figure 5.
Soil Aggregate stability
Aggregate stability, used as a good indicator of
soil structure (Six et al., 2000), is a crucial soil
property affecting soil sustainability and crop
production (Amezketa, 1999). This stability can
be addressed from both the pore and aggregate
viewpoint (Topp et al., 1997). Amezketa (1999)
classified the factors that affect soil aggregate
stability into soil primary characteristics or internal
Figure 5: Inter-intra-micro and Macro-aggregates Hierarchy in a VerticalCross Sectional View of a Highly Structure Soil (Adapted From Elliot and Coleman, 1988)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
factors (e.g., electrolyte, clay mineralogy, and
organic matter) and external factors (e.g., climate
and initial soil condition, soil biology, and
agricultural management). Stability of soil
aggregates in the upper few mm of the topsoil is
important for water, air entry into soil, and also
improves the germination and seedling
establishment by reducing surface crusting and
erosion (Rasmussen, 1999). Tillage practices
can have different effect on topsoil aggregate
stability (Schjonning and Rasmussen, 1989). The
following figure (Figure 6) showed the topsoil (0
to 10 cm) wet aggregate stability measured during
a 13-year period of an 18-year-old field trial with a
continuous growing of spring barley on a silty loam
marsh soil in Denmark. Different soil tillage
systems were adopted including ploughing (A) to
20 cm followed by harrowing (3-5 cm), rotovating(D) (3-5 cm), rotovating (E) (10 cm), and harrowing(F) (3-5 cm). Throughout the measuring period theploughed soil had the lowest amount of water stableaggregates, compared with rotovated soil(Schjonning and Rasmussen, 1989).
However, a general decrease in the aggregatestability was recorded over the investigatedperiod, while shallow tillage was found to diminishsoil structure deterioration through continuedcultivation. Also Pagliai et al. (2004) found similar
results that aggregates were less stable inploughed soils compared with soils underminimum tillage. These results confirm that it ispossible to adopt alternative tillage systems toprevent soil physical degradation and that theapplication of organic materials is essential to
improve the soil structure quality.
Soil Aggregate Properties
Fluctuations of topsoil Wet Aggregate Stability
(WAS) over the course of the study were recorded
in this study. This variation was attributed to the
disruptive effect of rain drops on the topsoil
aggregates, and also the natural reconsolidation
processes interacted with the tillage systems.
Tillage affected WAS under both AD and FM pre-
treatment and over the sampling times (Figure
6), However, results of the study showed that
differences of WAS between CT and RT was not
so distinct with field moist (FM) soil samples,
especially in the wet period (Dec-04 and Apr-05),
while a clear differences was noticed late in the
season (May-04 and Jun-05) when the soil was
slightly dry. Upon air drying, RT had significantly
more stable aggregates than CT during the tillage
year except for the samples right after tillage (Oct-
05) there was no significant difference. However
under field moist conditions, WAS under RT was
Figure 6: Long Term Temporal Change of Soil Aggregate StabilityUnder Four Tillage Treatments (From Schjonning And Rasmussen, 1989)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
significantly higher than under CT except at the
wettest sampling time (Dec-04), while WAS was
higher under CT than RT at Oct-04 sampling time.
At this sampling time, the soil moisture content
of RT soil was 18 % higher than that of CT (13
%). Air-dry samples provided a more sensitive
indicator of the variability of aggregate stability
than field moist soils as also found by Martinez-
Mena et al. (1998). The treatment strongly
affected WAS .Air-drying resulted in significantly
higher WAS, compared with field-moist soil,
except for driest periods. Upon air-drying sample
pre-treatment additional molecular associations
between soil constituents could be formed and
thus conferring greater stability on aggregates
(Haynes et al, 1996). An evidently significant
higher WAS under RT than CT upon air drying
pre-treatment was found (Figure 7). In addition to
WAS, dry aggregate stability (DAS) of 1-2 mm
aggregates was summarized by the
disintegration constant. A significant general
increase in the disintegration constant (k) after
tillage was recorded. Comparison between CT
and RT showed a significantly different k shortly
after tillage (04 and 05) and late in June, while
differences were insignificant in April.
Different aggregate size distribution under
tillage practices and pre-treatments could be
detected from Figure 8. RT resulted in higher
proportions of the large aggregates (> 2 mm) with
AD and FM pre-treatments compared with CT.
These differences were reflected in MWD. Upon
air drying, a shift of large aggregates to smaller
aggregates is evident under both tillage practices
with a large shift under CT. However, slight
changes of the intermediate soil aggregate
proportions could also be noticed, especially
under RT with AD when it is compared to FM
aggregate size distribution. Shortly after tillage
(especially Oct-04) the relative amount of large
stable aggregates (> 2 mm) was higher with CT
than with RT under FM treatment due to the direct
effect of soil inversion and fragmentation after
conventional tilled soil. This was also the case at
the next sampling time (Dec-04) when the soil
was very wet. It seems that, loosening the soil,
conventional tillage forms more large aggregate,
but the persistence of this modification depends
largely on the structural stability and the post-
tillage natural processes.
The results showed that larger aggregates may
Figure 7: Comparison Reduced to Conventional Tillage Effect on (A) WetAggregate Stability (Was) And (B) Mean Weight Diameter (Mwd)
During the Tillage Year 2004-05 With Air Dry and Field Moist Pre-treatment Conditions
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
probably be more sensitive to the natural
processes and therefore more susceptible to
wetting and drying induced structural degradation
than smaller aggregates. RT dramatically
increased the proportion of soil in the >2 mm size
class in AD and FM pre-moisture treatment after
the wettest period (Dec 04) and a less marked
increase in the 1-2 mm size class. This increase
was associated with a reduction in microaggregate
(< 0.25 mm). This development of structural
stability under RT may be related to the
incorporation of organic material which enhances
the aggregation process of the soil as also
indicated by others (Eynard et al., 2004). Results
confirmed that the proportion of aggregates with
diameter >2 mm appeared to be a suitable
indicator of the influence of tillage systems on
aggregation.
Porosity
In a long-term field study in China, rice straw
incorporation increased the porosity and formation
of large micro-aggregates and decreased the bulk
density of paddy soils (Li et al., 1986; Xu and Yao,
1988). Rice straw and rape straw were more
effective in increasing porosity of soils than
sesbania green manure or pig manure (Li et al.,
1986). Bellakki et al. (1998) and Bhagat et al.
(2003) noted a significant increase in the porosity
of fine textured soils after the application of rice
straw and lantana residues. He and Liu (1992)
observed that in rice straw-amended soil, porosity
(>200 mm) increased quickly after drying, which
is favorable for land preparation and sowing of
upland crop in time after rice harvest. Beaton et
al. (1992) reported that addition of rice straw (6 t
ha-1) over a 68-year period compared to inorganic
fertilizers reduced the volume weight and
increased the porosity of paddy soils in Japan.
Soil Hydraulic Conductivity, Infiltrationand Runoff
In spite of the inconsistent results on the effect of
tillage and residue management on soil hydraulic
conductivity, infiltration is generally higher in zero
tillage with residue retention compared to
Figure 8: Aggregate Size (mm) Distribution Proportions (%) Under Conventionaland Reduced Tillage With Air Dry (A and B) and Field Moist (C And D) Pre-treatments
During The Tillage Year 2004-05
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
conventional tillage and zero tillage with residue
removal. This is probably due to the direct and
indirect effect of residue cover on water
infiltration.Soil macroaggregate breakdown has
been identified as the major factor leading to
surface pore clogging by primary particles and
microaggregates and thus to formation of surface
seals or crusts.The presence of crop residues
over the soil surface prevents aggregate
breakdown by direct rain drop impact as well as
by rapid wetting and drying of soils (Le
Bissonnais, 1996). Moreover, aggregates are
more stable under zero tillage with residue
retention compared to conventional tillage and
zero tillage with residue removal (Govaerts et al.,
2009a) Figure 9.
Under these conditions wind erosion and rapid
wetting (i.e., slaking) cause less aggregate
breakdown, preventing surface crust formation
(Le Bissonnais, 1996). In addition, the residues
left on the topsoil with zero tillage and crop
retention act as a succession of barriers, reducing
the runoff velocity and giving the water more time
to infiltrate. The residue intercepts rainfall and
releases it more slowly afterwards. The ‘barrier’
effect is continuous, while the prevention of crust
formation probably increases with time.
Figure 9: Gains in Rainfall Infiltration Rate with CA
Figure 10: Effect of Soil Cover (Straw Mulch) on Infiltration Rate
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Naresh et al. (2011) conducted rainfall
simulator tests on sandy loam soil and concluded
that the time to- pond, final infiltration rate and the
total infiltration were significantly larger with zero
tillage with residue retention than with
conventional tillage Figure 10. They ascribed this
to the abundance of apparently continuous soil
pores from the soil surface to depth under zero
tillage as opposed to a high-density surface crust
in conventional tillage found in an image analysis
of the different soils. Although the infiltration rate
in conventional tillage was considerably higher
than zero tillage without residue retention
(Govaerts et al., 2009a). Similar results were
obtained in bed planting systems in the sandy
loam soils area of western Uttar Pradesh (Naresh
et al., 2011).
Pikul and Aase (1995) found that infiltration
rates were higher when the soil surface was
protected: infiltration over a 3 h period was 52
mm in conventional tillage with a wheat-fallow
rotation and 69 mm in an annually cropped system
with zero tillage. Baumhardt and Lascano (1996)
reported that mean cumulative rainfall infiltration
was the lowest for bare soil and increased
curvilinearly with increasing residue amounts on
a clay loam, but additions above 2.4 Mg ha-1 had
no significant effect because of sufficient drop
impact interception. The corollary of the higher
infiltration with residue cover is a concomitant
reduction in runoff (Rao et al., 1998). In general,
bulk density in the upper layer of no-tillage soils
was increased, resulting in a decrease in the
amount of coarse pores, and lowered saturated
hydraulic conductivity, when compared with the
conventional and reduced tillage soils (Tebrugge
and During, 1999 and Rasmussen, 1999).
Similarly, Srivastava et al. (2000) also found
significantly lower hydraulic conductivity in zero
tillage plots as compared to chiselling and rototilling,
which may be due to more favorable physical
conditions created by chiselling and roto-tilling. After
rice and wheat harvest, the laboratory estimated
Ksat
values in the 0-15 cm soil depth under zero
tillage plots were higher than that of the tilled plots
(Bhattacharyya et al., 2006b and Bhattacharyya
et al., 2008). The decrease of Ksat
by tillage in the
surface soil layer was probably due to destruction
of soil aggregates and reduction of noncapillary
pores (Singh et al., 2002), whereas in zero tillage
plots the pore continuity was probably maintained
due to better aggregate stability and pore geometry
(Bhattacharyya et al., 2006a). Similarly, Increase
in hydraulic conductivity and infiltration in zero
Table 4: Effect of Methods of Planting and Levels of Nitrogen on Bulk Density of Wheat
Planting Method Bulk Density (g cm-3)
0-15 cm 15-30 cm 30-45 cm
Happy seeder 1.40 1.45 1.52
Zero tillage 1.44 1.44 1.55
Rotavator 1.53 1.59 1.56
Conventional tillage 1.46 1.62 1.49
Initial bulk density 1.47 1.46 1.44
Source: Meenakshi, 2010
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
tillage as compared to conventional tillage was
reported by McGarry et al. (2000), apparently
earthworm channels and termite galleries, being
the major contributors.
Similarly, increased earthworm activity in no-
tillage treatments, associated with a system of
continuous macropores, improved water
infiltration rates, was reported by Tebrugge and
During (1999). Crop residues increase soil
hydraulic conductivity and infiltration by modifying
mainly soil structure, proportion of macro pores
and aggregate stability. These increases have
been reported in treatments where crop residues
were retained on the soil surface or incorporated
by conservation tillage (Murphy et al., 1993). Up
to eight fold increases in hydraulic conductivity in
zero tillage stubble retained have been reported
over treatments where stubble was removed by
burning (Valzano et al., 1997). Initial infiltration rate
was lower than that of recorded at harvest of
wheat crop sown with different planting methods.
It could be due to compaction caused in the soil
layers by the previous puddle crop of rice. The
rate of infiltration increased with increase in time
up to 60 min under all the methods of planting of
wheat both at initial and harvest stage. It is more
under conventional tillage because of better
pulverization of soil and lowest under the rotavator
because of compaction in the lower layers of soil
caused by it (Meenakshi, 2010).
Bulk Density, Compaction and PenetrationResistance
In general, incorporation of crop residues into the
paddy soils reduced bulk density, penetration
resistance, and compaction of soils under both
rice–rice and rice–wheat cropping systems
(Bellakki et al., 1998; Meelu et al., 1994; Singh et
al., 1996; Walia et al., 1995). Xie et al. (1987) also
reported that continuous return of rice straw to a
paddy field for 7 years resulted in a soil bulk
density decrease of 0.17 Mg m–3. In another long-
term field experiment over 25 years, incorporation
of crop residues improved the porosity and
decreased penetration resistance of a gleyed soil
(Roppongi et al., 1993). Likewise, combined
application of cereal crop residues and green
manure has proved to be more efficient in
reducing bulk density, penetration resistance, and
crusting of surface soil layers over their separate
applications (Liu and Shen, 1992; Meelu et al.,
1994; Verma and Singh, 1974). Bhushan and
Sharma (2002) reported that with the application
of lantana residues to a silty loam soil
Table 5: Effect of Planting Methods and N Levels on Soil Temperature in Wheat
Planting Method Soil Temperature (0C )
22-3-2010 29-3-2010 7-4-2010 12-4-2010
Happy seeder 30.5 28.0 38.5 41.7
Zero tillage 28.3 28.3 39.0 42.0
Rotavator 28.7 28.7 39.6 42.6
Conventional tillage 28.5 28.5 39.6 43.4
Source: Meenakshi, 2010
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
continuously for 10 years in rice–wheat rotation,
clods <2 cm in diameter increased while those
2-4 cm and 4-6 cm in diameter decreased with
straw additions. The mean weight diameter of
clods varied between 2.15 and 2.34 cm in
lantana-treated soil versus 2.83 cm in the control.
The bulk density and breaking strength of soil
clods were lower in lantana-treated soil by 4–9%
and 29–42% than in control, respectively. About
23-47% less energy was required to prepare seed
bed in lantana treated soil than in control soil. The
long-term addition of residues caused a
fundamental change in soil structural processes.
A significant change in soil consistency and the
related physical properties such as surface
cracking and clod formation occurred after the
addition of residues continuously for 10 years.
Lantana-treated soil would become friable
relatively soon, thereby decreasing the turnaround
time after rice harvest (Tebrugge and During.,
1999). Several studies have reported higher bulk
density under zero tillage at the soil surface
compared with tilled soil (Hill, 1990; Wu et al.,
1992; Bajpai and Tripathi, 2000) and penetration
resistance of the soils (Carman, 1997; Martinez
et al., 2008). Zero tillage direct seeded rice and
zero tillage wheat had significantly higher bulk
density as well as penetration tillage in the 0–5
and 5–10 cm soil profile than with other
conventional tillage systems (puddling in rice and
repeated dry tillage in wheat), whereas these were
higher under conventional-tillage in the 10-15 and
15-20 cm soil layers compared with zero tillage /
no puddling treatments (Jat et al., 2009).
Published studies revealed that puddling induced
high bulk density in subsurface layers (15-30 cm)
in rice based systems (Sharma and De Datta,
1985; Aggarwal et al., 1995; Hobbs and Gupta,
2002). Increased soil bulk density at about 10 to
15 cm depth, just beneath the depth of shallow
tillage was also reported by Rasmussen (1999)
in no tilled soils. The tillage practices in rice (viz
transplanting, direct seeding in puddled soil by
drum seeder, direct seeding in friable soil by seed
Table 6: Total System Productivity Under Tillage Optionsand Straw Levels in Rice-wheat Mungbean Systems (Naresh et al., 2013)
Crop Establishment Grain Yield (t/ha)
Rice Wheat Rice Wheat Mungbean System
ZT-DSR ZT-HS 4.40 5.18 1.34 10.92
WBed-TPR +M WBedZT-DSW +M 5.38 5.51 1.47 12.36
WBed-TPR – M WBedZT-DSW – M 5.19 5.20 1.38 11.77
UPTPRPR + M ZT-DSW PR + M 5.17 4.98 1.36 11.51
UPTPR PR – M ZT-DSW PR - M 5.01 4.80 1.32 11.13
UPTPR + M ZT-DSW + M 4.97 4.75 1.33 11.05
UPTPR – M ZT-DSW – M 4.85 4.67 1.29 10.79
CT-TPR CT-BCW 5.45 4.08 1.21 10.74
C D at 5 % 0.95 0.40 0.32 1.42
Note: Impact of residue management
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
drill and direct seeding by zero –till drill) did differ
markedly in respect of bulk density of upper (0-
15 cm) as well as of lower (15-30 cm) soil layer
except the seed drill method, which showed the
lowest bulk density of the upper layer. Irrespective
of various practices in rice, the bulk density of
both the layers increased markedly with the
rotavator, zero till age and conventional practice
in wheat. The higher bulk density under zero or
reduced tillage might be due to more
compactness of the soil, while the soil became
more porous with the increased intensity of tillage
in conventional practice (Ram et al., 2006;
Dhiman et al., 1998).
At Pantnagar observed tillage caused a
significant difference in bulk density of surface
(tilled) and subsurface (untilled) soil layers
measured at 30 days after transplanting and at
harvesting. A comparatively higher bulk density
in the subsurface (15-20 cm) layer than in the
surface layer may be due to weight of the tillage
machinery. The changes in the bulk density due
to tillage for wheat were significantly lower in the
direct seeding without puddling plots of rice than
in the remaining tillage treatments (reduced,
conventional or rotary puddling). The bulk density
was maximum in the subsurface (1.54 mg/m3)
under zero till condition in the rotary puddled plots
of rice and minimum in the surface soil (1.42 mg/
m3) under conventional tillage conditions in the
direct seeding without puddling plots. In general,
the inf luence of wheat tillage (zero and
conventional tillage) on bulk density was not
significant (Sharma et al., 2004). However, tilling
of soil with any combination of implements
(Chisel, rotavator and disc harrow) reduced the
bulk density; tillage with disc harrow caused higher
reduction in bulk density than the tilling by
rotavator. Tilling with an implement combined with
chisel plough, reduced soil bulk density according
to the influence of soil breaking by the individual
implements (Srivastava et al., 2000). The lower
bulk density was noticed under conventional
tillage than Chinese seeder and Pantnagar zero
till drill (Kumar and Yadav, 2005). Similarly, Kumar
(2000) also found lower value of bulk density
under conventional tillage in comparison to
reduced or zero tillage systems.
Bulk density was not significantly affected by
tillage treatment (Martinez et al., 2008, Dao, 1996
Table 7: Effects of Residue Removal For 13 Consecutive Yearson Soil Properties and Corn Grain and Stover on Yields on an Alfisol
in Western Nigeria (Adapted from Juo et al., 1995; 1996)
Soil Properties With Residue Mulch Residue Removal LSD (.05)
Soil organic carbon 14.5 12.5 4.0
Soil pH 5.1 4.6 0.30
Exchangeable Ca+2 (cmolc/kg) 3.6 1.2 1.4
Exchangeable Mg+2 (cmolc/kg) 0.4 0.25 0.35
CEC (cmolc/kg) 4.5 2.9 1.7
Grain yield (Mg/ha) 2.7 1.5 0.4
Stover yield (Mg/ha) 2.6 1 1.3 0.8
Table 7: Effects of Residue Removal For 13 Consecutive Yearson Soil Properties and Corn Grain and Stover on Yields on an Alfisol
in Western Nigeria (Adapted from Juo et al., 1995; 1996)
Soil Properties With Residue Mulch Residue Removal LSD (.05)
Soil organic carbon 14.5 12.5 4.0
Soil pH 5.1 4.6 0.30
Exchangeable Ca+2 (cmolc/kg) 3.6 1.2 1.4
Exchangeable Mg+2 (cmolc/kg) 0.4 0.25 0.35
CEC (cmolc/kg) 4.5 2.9 1.7
Grain yield (Mg/ha) 2.7 1.5 0.4
Stover yield (Mg/ha) 2.6 1 1.3 0.8
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
and Panday et al., 2008, Naresh et al., 20011).
Contrasting effects of soil management
experiments in bulk density are common and are
mostly related to management factors such as
planting machinery (machine weight, tire width,
inflation pressure), number of machine passes,
as well as the soil water content at which the soil
is tilled (Czyz, 2004; Botta et al., 2005). The initial
values of bulk density at 0-15 cm were lower than
that recorded at harvest under all the methods of
planting except rotavator. The corresponding
values at 15-30 cm depth were higher except zero
tillage and happy seeder. At 30-45 cm, the values
were higher than initial bulk density under all the
methods of planting at harvest. The initial bulk
density decreased in the soil profile of soil from
0-15 to 30-45 but in case of bulk density recorded
at harvest, under happy seeder, rotavator and
conventional tillage was increased up to 15-30
cm and corresponding values at 30-45 cm were
decreased except in case of zero tillage and
happy seeder. The bulk density was same at 0-
15 and 15-30 cm in zero tillage but at 30-45 was
increased at harvest (Meenakshi, 2010, Table 4).
SOIL TEMPERATUREOne of the characteristics of the physical state
of soil is its temperature. This factor is rarely
analyzed, mainly because of its great variability
in time. Radecki (1986) stated that dark soils show
greater warmth of the surface layer directly after
agricultural treatment than when not treated. In
arid and semiarid regions or in summers, crop
residues left on the soil surface as a mulch as
compared to incorporation, removal or burning
are known to be decreased water – supplying
capacity. The primary seat of fertility of many soils
is the topsoil. Direct loss of soil fertility occurs
when surface applied fertilizers or available plant
nutrients attached to soil particles are removed
during runoff and erosion. Indirect loss of soil
fertility occurs in the organic matter that is lost
when top soil erodes. Conversion from
conventional to zero tillage, reduced erosion
(Wright et al., 1999) and avoided surface sealing
because of crop residue cover on the surface
and higher aggregate stability under zero tillage,
which protected soil fertility (Tebrugge and During,
1999; Rasmussen, 1999). Flat residues as a
mulch on the soil surface act as a barrier
Figure 11: Conceptual Model of Nutrient Pathwaysin Crop Residue Amended Soils (Myers et al., 1994)
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Table 8: Effect of Various Tillage And Establishment Techniques On Total N, P And K Uptake InMaize-wheat Rotation Experiment After 03 Years (Naresh et al., 2013)
Crop Establishment Total N uptake (Kg/ha) Total P uptake (kg/ha) Total K uptake (kg/ha)
Maize Wheat Maize Wheat Maize Wheat
T1- PLWB + RNPK 103.85 112.95 25.6 19.49 110.7 112.96
T2 -TLWB + RNPK 99.75 107.56 22.7 16.61 104.3 108.27
T3 - PLNB + RNPK 99.75 109.95 24.8 17.62 106.8 110.35
T4 -TLNB + RNPK 93.05 103.80 20.3 14.85 098.2 096.36
T5 - PLFB + RNPK 94.95 104.65 23.9 15.06 102.6 105.40
T6 - TLFB + RNPK 89.85 100.45 17.5 13.31 81.4 083.56
T7- TLFB + N0P0K0 53.70 58.70 13.7 7.66 57.3 051.18
C D at 5 % 8.95 8.02 1.21 1.15 3.97 4.63
Table 9: Balance Sheet of Total Nitrogen in Maize +Intercrops-wheat Cropping System (Kg/Ha) After 3 Years (Naresh et al., 2013)
Treatments Nitrogen Mean N Soil N at initiation Estimated N Net soillevels removed by + N added after cropping N balance
(Kg/ha) crops –N removed (3 years ) (Kg/ha)
T1 Maize (narrow beds) 80 205 1037 1218 -56
- wheat (check) 120 259 1176 1291 +24
160 298 1255 1337 +56
T2 Maize ( narrow beds )with 80 229 1010 1206 -47
FYM @ 10t/ha-wheat 120 297 1137 1295 +19
160 367 1249 1367 +89
T3 Maize+blackgram paired rows 80 248 1135 1287 +16
in 2:2 row ratio (30/90 cm 120 305 1205 1327 +63
wide beds )-wheat 160 348 1321 1388 +121
T4 Maize+ cowpea paired row 80 253 1174 1304 +43
in 2:2 row ratio (30/90 cm 120 318 1216 1343 +71
wide beds )-wheat 160 353 1345 1399 +139
T5 Maize + pigeonpea alternate 80 247 1024 1232 -41
rows in 1:1 row ratio (30/30 cm 120 323 1145 1301 +47
flat beds ) – wheat 160 364 1299 1384 +119
T6 Maize +blackgram alternate 80 251 1046 1240 -23
rows in 1:1 row ratio (30/30 cm 120 341 1129 1298 +52
flat beds ) – wheat 160 378 1221 1346 +93
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
restricting soil particles emissions from the soil
surface and also increasing the threshold wind
speeds for detaching these particles. It has been
reported that standing residues are more effective
than flat residues in reducing erosion by reducing
the soil surface friction velocity of wind and
intercepting the saltating soil particles (Hagen,
1996). The energy available for heating the soil is
determined by the balance between incoming and
outgoing radiation. Retained residue affects soil
temperature close to the surface because it
affects this energy balance. Solar energy at the
soil surface is partitioned into soil heat flux,
sensible heat reflection, and latent heat for water
evaporation (Bristow, 1988). Surface residue
reflects solar radiation and insulates the soil
surface (Chen and McKyes, 1993, Shinners et
al., 1994). The heat flux in soils depends on the
heat capacity and thermal conductivity of soils,
which vary with soil composition, bulk density, and
Figure 12: Soil Organic Carbon Influenced by Tillage Practices
Figure 13: Grain Yield at Farmer’s Field Under Conventional and No-till (1998-2006)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
water content (Hillel 1998, Jury et al. 1991).
Because soil particles have a lower heat capacity
and greater heat conductivity than water, dry soils
potentially warm and cool faster than wet soils.
Moreover, in wet soils more energy is used for
water evaporation than warming the soil (Radke,
1982). Tillage operations increase the rates of soil
drying and heating because tillage disturbs the
soil surface and increases the air pockets in
which evaporation occurs (Licht and Al-Kaisi,
2005).
Soil temperatures in surface layers can be
significantly lower (often between 2 and 8 °C)
during daytime (in summer) in zero tilled soils
with residue retention compared to conventional
tillage (Johnson and Hoyt, 1999, Oliveira et al.,
2001). In these same studies, during night the
insulation effect of the residues led to higher
temperatures so there was a lower amplitude of
soil temperature variation with zero tillage. Dahiya
et al. (2007) compared the thermal regime of a
loess soil during two weeks after wheat harvest
between a treatment with wheat straw mulching,
one with rotary hoeing and a control with no
mulching and no rotary hoeing. Compared to the
control, mulching reduced average soil
temperatures by 0.74, 0.66, 0.58 °C at 5, 15, and
30 cm depth respectively, during the study period.
The rotary hoeing tillage slightly increased the
Table 10: Effect of Straw Management on the Nutrient Statusof Mahaas Clay and Grain Yield Averaged for Five Cultivars after the 16th Cropa
Straw Treatment Organic C (%) Total N (%) Olsen P (mg kg-1) Exchangable K (mg kg-1) Grain yield (t ha-1)
Removed 1.81b 0.167b 9a 10.5b 3.2b
Burned 1.94b 0.173ab 11a 12.5a 3.4b
Incorporated 2.17a 0.182a 12a 11.6ab 4.1a
Note: aIn a column, figures followed by a common letter are not significantly different. From Ponnamperuma (1984).
Table 11: Per Capita Food Availability in India (Economic Survey, 2008-2009)
Year Population Millions Food Grain Availability (g/person /day)
Cereals Pulses Total Total
1950 363 334 61 395
1960 433 384 66 450
1970 539 463 52 455
1975 - 366 40 406
1980 675 380 31 411
1985 - 416 38 454
1990 833 435 41 476
2000 1015 423 32 455
2005 - 391 32 423
2007 1137 407 36 443
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
average soil temperature by 0.21 °C at 5 cm
depth compared to the control. The tillage effect
did not transmit to deeper depths. Gupta et al.
(1983) also found that the difference between
zero tillage with and without residue cover was
larger than the difference between conventional
tillage (mould board ploughing) and zero tillage
with residue retention. Both mould board
ploughing and zero tillage without residue cover
had a higher soil temperature than zero tillage
with residue cover, but the difference between
mouldboard ploughing and zero tillage with
residue cover was approximately one-third the
difference between zero tillage with and without
residue.
SOIL MOISTURE CONTENTZero tillage achieved a 28% increase in plant
available soil water at sowing as compared to
conventional tillage and an associated increase
Table 12: Fuel wood consumption by Indian household sector (Reddy, 2003)
Year Fuel Wood (mtoe) % of Total Energy Use
1950 54.1 82.7
1960 67.1 84.6
1980 88.1 84.4
2000 114 75.6
Note: Growth rate = 3.7 % yr-1
Table 13: Traditional Biofuels Used in India (Venkataraman et al., 2005)
Source Biofuel Consumption (Tg/Yr) Emissions (Gg/Yr)
1985 1995 1985 1995
Fuel Wood 220 281 110 143
Dried Cattle Manure 93 62 10 8
Crop Residues 86 36 40 21
Total 399 379 160 172
Table 14: Management impact on SOC Poolin a Vertisol After 28 Years (Recalculated from Hati et al., 2007)
Treatment SOC Pool (Mg/ha) Rate of Change (Kg/ha/yr)
Control 11.2c -7.14
100 % N 12.0c 21.4
50 % NPK 13.0bc 57.1
100 % NPK 13.9c 89.3
100 % NPK + Manure 17.8a 228.5
Initial 11.4 –
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
of 1.2 t/ha/year wheat grain (McGarry et al., 2000).
More plant residues were left on or near the soil
surface no til lage which led to lower
evapotranspiration and higher content of soil
water in the upper (0-10 cm) soil layer
(Rasmussen, 1999). The plant available water
content was significantly higher with zero than
conventional tillage in rice-wheat cropping system
(Bhattacharyya et al., 2006b and Bhattacharyya
et al., 2008). Surface residues maintained under
zero til lage system moderate moisture
fluctuations and thus reduce both evaporation and
runoff (Blevins and Frye, 1993). However, different
types and extent of tillage did not have any major
influence on the moisture content at harvest,
although it was high at the time of initial tillage
and reduced with subsequent tillage operations
(Srivastava et al., 2000). It has been well
established that increasing amounts of crop
residues on the soil surface reduce the
evaporation rate (Gill and Jalota, 1996; Prihar et
al., 1996). Residue mulch or partial incoporation
in soil by conservation tillage has also been
shown to increase the infiltration by reducing
surface sealing and decreasing runoff velocity
(Box et al., 1996).
Impact of Residue Management
Since organic matter is a key factor in soil
aggregation, the management of previous crop
residues is a key to soil structural development
and stability. It has been known for many years
that the addition of organic substrates to soil
improves its structure (Ladd et al. 1977). Fresh
residue forms the nucleation centre for the
formation of new aggregates by creating hot spots
of microbial activity where new soil aggregates
are developed (De Gryze et al. 2005,
Guggenberger et al. 1999). Denef et al. (2002)
found that adding wheat (Triticum aestivum L.)
residue in the laboratory to three soils differing in
weathering status and clay mineralogy increased
both unstable and stable macroaggregate
formation in all three soils in the short term (42
days). The greatest response in stable
macroaggregate formation occurred in soils with
mixed mineralogy (a mixture of 2:1 and 1:1 clays
as opposed to soils dominated by 2:1 or 1:1
clays). This could be a result of electrostatic
bondings occurring between 2:1 clays, 1:1 clays
and oxides (i.e., mineral-mineral bindings), in
addition to the organic matter functioning as a
binding agent between 2:1 and 1:1 clays. The
return of crop residue to the soil surface does
not only increase the aggregate formation, but it
also decreases the breakdown of aggregates by
reducing erosion and protecting the aggregates
against raindrop impact. The MWD of aggregates
as measured by dry and wet sieving decreased
with decreasing amounts of residues retained in
a rainfed permanent bed planting system in the
subtropical highlands of Mexico, although partial
residue removal by baling kept aggregation within
acceptable limits (Govaerts et al., 2007c). This
indicates that it is not always necessary to retain
all crop residues in the field to achieve the benefits
of permanent raised beds or zero tillage systems.
Similar results were obtained by Limon-Ortega
et al. (2006) on permanent raised beds in an
irrigated system, where the aggregates showed
the largest dispersion where residue was burned
and the lowest where all residue was kept in the
field. Chan et al. (2002) also found that stubble
burning significantly lowered the water stability of
aggregates in the fractions >2 mm and < 50 m.
CROP RESIDUE MANAGEMENTEFFECTS ON SOIL QUALITYThere are about 850 million food-insecure people
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
Table 15: Effect of Crop Residue Management on Organic Carbon and Total N Content of Soil
Reference and Country
Beri et al., (1995 ), India
Sharme et al., (1987), India
IRRI (1986), Philippines
Liu and Shen (1992), China
Zia et al., (1992), Pakistan
Yadvinder- Singh et al.,(2004 a), India
Dhiman et al., (2000), India
Kumar et al., (2000), India
Prasad et al., (1999), India
Verma and Bhagat (1992),India
Yadvinder- Singh et al.,(2004 a),India
Ponnamperuma (1984),Philippines
Naresh et al., (2011), India
Type of Crop Residue and Soil
Rice straw in wheat and wheat strawin rice; Sandy loam
Rice straw in wheat and wheat strawin rice; Silty clay loam
Rice straw in rice-rice rotation;clayey
Milk vetch green manure or milkvetch + rice straw in rice-ricerotation
Rice straw in rice in rice – wheatrotation;Loam
Wheat straw, green manure andwheat straw + green manure in ricein rice – wheat rotation;loamy soil
Rice straw in wheat and wheat strawin rice in rice-whear rotation;clayloam
Mustard straw in rice in rice-mustard rotation;acidic sandy clayloam
Wheat straw in rice in rice- wheatrotation;sandy clay loam
Rice straw in wheat in rice- wheatrotation;sandy clay loam
Rice straw in wheat in rice- wheatrotation;silty clay loam
Rice straw in wheat in rice- wheatrotation;sandy loam
Rice straw in rice in rice- ricerotation;clayey
Maize straw in wheat in maize-wheat rotation;sandy loam
Durationof Study (Years)
10
6
12
9
3
12
3
2
2
5
7
19 crops
3
Residue Management
Removed
Burned
Incorporated
Removed
Incorporated
Removed
Burned
Incorporated
Removed
Green manure
Green manure + ricestraw
Removed
Incorporated
Straw removed
Straw incorporated
Wheat straw+ greenmanure
Removed
Burned
Incorporated
Removed
Incorporated
Removed
Incorporated
Removed
Incorporated
Removed
Incorporated
Removed
Burned
Incorporated
Removed
Burned
Incorporated
Removed
Burned
Incorporated
Retained
OrganicC (%)
0.38
0.43
0.47
1.15
1.31
1.67
1.74
1.90
1.91
2.06
2.21
0.53
0.63
0.41
0.53
0.59
0.51
0.51
0.86
0.36
0.61
0.53
0.61
0.68
0.84
1.09
1.24
0.38
0.39
0.50
-
-
-
0.43
0.47
0.58
0.53
TotalN (%)
0.051
0.055
0.056
0.144
0.159
0.173
0.179
0.191
0.176
0.190
0.194
-
-
-
-
-
0.062
0.063
0.084
-
-
-
-
-
-
-
-
-
-
-
0.181
0.183
0.202
-
-
-
-
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
in the world (Borlaug, 2007), and an additional
3.7 billion are prone to hidden hunger and
malnutrition due to deficiency of minerals (e.g.,
Zn, Cu, Se, I, B) and vitamins because food is
grown on degraded soils. Most of the food
insecure people live in Sub-Saharan Africa (SSA)
and Asia. The Green Revolution of the 1960s and
1970s that saved hundreds of millions from
starvation in Asia and elsewhere by-passed SSA
because soils of the region are severely degraded
(Lal, 2008c). Resource-poor farmers and small
land holders of SSA and Asia remove crop
residues for use as fodder, fuel, construction
material and other competing uses. Furthermore,
most soils have extremely low levels of SOC
concentration (< 0.5% in contrast to critical level
of 1.1%). In addition, the negative nutrient budget
of –30 to –40 kg/ha/yr of NPK on continental scale
is exacerbated by residue removal and the
attendant increase in soil erosion hazard. Adverse
agronomic and environmental impacts are
confounded by the use of animal dung as
household fuel rather than as soil amendment.
The data in Table 7 from a long-term experiment
conducted on Alfi sols in Western Nigeria, show
that even the use of NT farming on a relatively flat
terrain (< 1% slope gradient) caused severe
decline in soil quality because of the residue
removal. Despite the application of chemical
fertilizers at recommended rates and use of
improved crop varieties, soil quality deteriorated
(e.g., decline in SOC concentration, soil pH,
exchangeable cation, CEC). There was also a
strong increase in bulk density and decrease in
infiltration rate and AWC (Naresh, 2013).
Consequently, maize yields in the first growing
season, after 13 consecutive years of growing 2
crops per year, was 2.7 Mg/ha with residue
retention compared with 1.5 Mg/ha with residue
removal (Table 7; Juo et al., 1995; 1996). It is
apparent therefore, that the agronomic benefits
of improved crop varieties and fertilizer input
cannot be realized unless soil structure and
hydrologic properties are improved with residue
retention and application of other biosolids as
amendments
CROP RESIDUEMANAGEMENT EFFECTS ONNUTRIENT AVAILABILITY INSOILSRice straw is characterized by a high C:N ratio
and abundant K, Si, and C (Ponnamperuma,
1984). Wheat straw has comparable properties
except for low Si and low K concentration. The
successful utilization of crop residues as a
nutrient source relies on manipulating the
biological processes in the soil so as to optimize
nutrient availability with respect to plant demand.
A simplified model of the regulation of nutrient flux
in the agoecosystem is presented in Figure 11.
This conceptual model depicts the flow of carbon
and nutrients among organic residues, organic
and inorganic pools in soil, and the plant.
Pathways of loss are also included.
Decomposition and mineralization of plant
residue are mediated by both soil faunal and
microbial populations. Some of the carbon and
associated nutrients are mineralized immediately
(pathway 1a) or are immobilized in the soil
microbial pool (pathway 2a), later to be
transformed into other soil organic pools via
microbial by-products (3a). Recalcitrant plant
material also may enter the soil organic pools
directly (3b). The carbon and nutrients held in the
various soil organic matter pools are
subsequently decomposed and assimilated by
soil biomass, resulting in additional mineralization
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
(1b). The inorganic nutrients released by
mineralization may be assimilated by soil biota
via immobilization (2). Immobilization occurs
simultaneously with mineralization, and the rate
at which nutrients are available for plant uptake
depends on the net balance between
mineralization (1a plus 1b) and immobilization (2)
.The inorganic nutrients may also be taken up by
plants (pathway 3), lost by leaching or
volatilization (pathway 4), or remain in the soil
(Myers et al., 1994). The size of the inorganic pool
depends on the balance of the various processes
that add to the pool (mineralization) and those
that subtract (immobilization, plant uptake, and
losses). The proportion of N transferred from the
residue to the plant and the rate at which it occurs
are determined by the balance between the rates
of the various processes represented by these
flux pathways. This balance is regulated by a
hierarchy of factors. Environment, which includes
climate and soil, is an overriding control and
determines the rate of the transfer between pools.
The rates also vary depending on the quality of
the decomposing substrate.
By manipulating the quality of crop residues, it
should be possible to manage nutrient release to
coincide with the time course of the nutrient
requirements of the crop (Swift, 1987). When low-
quality crop residues (low N and P, high lignin or
polyphenol contents) are incorporated into the
moist soil, nutrients become available to the
plants. With high-quality residues, nutrients are
initially released rapidly in excess of plant demand
with a risk of nutrients such as N being lost via
leaching or denitrification or a nutrient such as P
becoming chemically unavailable (Anderson and
Swift, 1983).
The soil organic carbon content is an important
factor affecting soil quality, and is an important
source of plant nutrients, especially in
subsistence agriculture. The important effect of
soil organic carbon on productivity and
environmental quality is through its role in
Figure 14: Interactions Between Soil-Associated Fauna and Soil Dynamics
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
supplying nutrients, capacity, and stabilizing soil
structure (Doran et al., 1994). The soil organic
carbon content is a function of soil management,
and change in management can alter soil organic
carbon content. Accumulation of organic carbon
in the upper soil layer was evident under long-
term growth of the population of aerobes, which
are responsible for mineralization of organic
matter, thus intensive tillage leads to lowering of
soil humus content .When comparing SOC in
different management practices, several factors
have to be taken into account. As reported earlier,
bulk density can be affected by tillage practices.
If bulk density increases after conversion from
conventional tillage to zero tillage, and if samples
are taken to the same depth within the surface
soil layer, more mass of soil will be taken from
the zero tillage soil than from the conventionally
tilled soil. This could increase the apparent mass
of SOC in the zero tillage and could widen the
difference between the two systems if there is
significant SOC beneath the maximum depth of
sampling (Vanden Bygaart and Angers, 2006).
Therefore, Ellert and Bettany (1995) suggested
basing calculations of SOC on an equivalent soil
mass rather than on genetic horizons or fixed
sampling depths in order to account for
differences in bulk density. Tillage practice can
also influence the distribution of SOC in the profile
with higher SOC content in surface layers with
zero tillage than with conventional tillage, but a
higher content of SOC in the deeper layers of
tilled plots where residue is incorporated through
tillage (Jantalia et al., 2007, Gál et al., 2007,
Thomas et al., 2007, Dolan et al., 2006, Yang and
Wander, 1999, Angers et al. ,1997). Consequently,
SOC contents under zero tillage compared with
conventional tillage can be overstated if the entire
plough depth is not considered (Vanden Bygaart
and Angers, 2006). Baker et al. (2007) state that
not just the entire plough depth, but the entire soil
profile should be sampled in order to account for
possible differences in root distribution and
rhizodeposition between management practices.
Bessam and Mrabet (2003) reported that crop
residues left on soil surface led to an increase in
Figure 15: Effect Of Conservation Agriculture on Soil Organic Matter and Microbial Biomass
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
Soil Organic Carbon (SOC) from 5.62 to 7.21 t/
ha in 0-25 mm under no-tillage after 4 and 11
years (experimental field, at Sidi El Aïdi, Morocco).
At the same horizon, SOC did not change under
conventional tillage after the same periods. The
results revealed that no-tillage soil had
sequestered 3.5 and 3.4 t/ha of SOC more than
the conventional tillage after 4 and 11 years. The
figure illustrates that over 11 years the horizon
gained 13.6% and 3.3% of its original SOC under
no-till and conventional tillage respectively.
Soil Organic Matter Content
Organic matter consists of dead plant parts and
animal and microbial waste products in various
stages of decomposition. Eventually, these things
break down into humus, which is relatively stable
in the soil. Organic matter has strong impact on
the structure. Accumulation of organic matter and
nutrients near the soil surface under no-tillage and
reduced tillage were favorable consequences of
not inverting the soil and by maintaining a mulch
layer on the surface (Tebrugge and During, 1999).
With annual plough less tillage, plant residues will
be left on the soil surface, resulting in increased
organic matter in the top soil (Rasmussen, 1999).
The study by Gosai et al. (2009) revealed higher
concentration of soil organic matter in the no-till
and shallow-tilled plots compared to other
conventionally tilled plots that confirms to the
findings of Doran (1987), Robbins and Voss
(1991) and Angers et al. (1995). Increase in soil
organic matter under no-tillage may have been a
result of reduced contact of crop residues with
soil. Surface residues tend to decompose more
slowly than soil-incorporated residues, because
of greater fluctuations in surface temperature and
moisture and reduced availability of nutrients to
microbes colonizing the surface residue
(Schomberg et al., 1994).
Gharras et al. (2009) also reported that grain
yields reported from no-tillage pioneer farmers
field showed increased yield obtained in dry as
well wet years. In very dry years with less than
200 mm rainfall, farmers were able to produce
1.1 and 1.5 tons of wheat in two different locations
where no-tillage fields were the only ones
Figure 16 :Effect of Rice Straw Application on Methane Productionin a Sandy Soil (Hou et al., 2000)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
harvested in the entire region. In wet years,
change in farmers perception was observed
towards crop residue left in the field which was
seen as an investment in their soil rather than
wasted biomass. There exist only limited studies
on the long-term effect of crop residue
management on organic matter and N content of
soils under rice-based cropping systems in
tropical and sub-tropical countries (Tables 10). In
these studies, increases in organic matter
content due to crop residue recycling are
relatively small compared to those reported from
temperate regions (Prasad and Power, 1991).
Incorporation of both residues increased organic
C and total N compared to removal or burning of
straw (Dhiman et al., 2000). When only rice or
wheat straw was incorporated, organic C content
did not differ significantly from removal or burning
of straw. Rice straw was more effective in
increasing total N content of soil than wheat straw.
Raju and Reddy (2000) reported that in rice–rice
rotation, incorporation of rice straw to supply 25%
of the recommended N fertilizer dose for rainy
season crop for 6 years significantly increased
organic C content from 0.98% in straw removal
treatment to 1.29%. Sharma (2001) reported that
organic C content increased from 0.56% in straw
removal to 0.66% when both the residues were
incorporated for 2 years in rice–wheat rotation.
Burning and removal of crop residues were at
par for their effect on organic C content.
Soil Carbon Sequestration and MulchFarming
World soils constitute the third largest global C
pool, comprising of two distinct components: (i)
soil organic C (SOC) estimated at 1550 Pg, and
(ii) soil inorganic C (SIC) pool estimated at 950
Pg, both to 1-m depth. Other pools include the
oceanic (38,400 Pg), geologic/fossil fuel (4500
Pg), biotic (620 Pg), and atmospheric (750 Pg)
(Lal, 2004a). Thus, the soil C pool of 2500 Pg is
3.3 times the atmospheric pool and 4.0 times the
biotic pool. However, soils of the managed
ecosystems have lost 50 to 75% of the original
SOC pool. Conversion of natural to managed
ecosystems depletes SOC pool because C input
into the agricultural ecosystems is lower, and
losses due to erosion, mineralization and leaching
are higher than those in the natural ecosystems.
The magnitude of SOC depletion is high in soils
prone to erosion and those managed by low-input
or extractive farming practices. The loss of SOC
pool is also high in soils of coarse texture and
those with a high initial pool. Most agricultural soils
have lost 20 to 40 Mg C/ha due to historic land
use and management.
The maximum soil C sink capacity, amount of
C that can be stored in it, approximately equals
the historic C loss. In other words, most
agricultural soils now contain lower SOC pool
than their capacity because of the historic loss.
The maximum soil C pool is determined by the
climate, parent material, physiography, drainage,
and soil properties including clay content, clay
minerals, and nutrient reserves. Soil drainage and
moisture regime, along with soil aspect and
landscape position, are important controls of soil
C pool.
Land use and soil management techniques
which lead to C sequestration are retention of crop
residues, NT farming and incorporation of cover
crops in a diversified rotation cycle (together also
referred to as CA), INM techniques of using
compost and other biosolids, erosion control,
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
water conservation, contour hedges with
perennials, controlled grazing, etc. An average
long-term rate of SOC sequestration with these
techniques is 200 to 1000 kg/ha/yr for humid
temperate regions and 50 to 250 kg/ha/yr for dry
tropical regions. In addition, the rate of SIC
sequestration as secondary carbonates is about
5 to 25 kg/ha/yr in arid and semi-arid regions. In
contrast, depletion of SOC pool occurs with the
use of excessive plowing, residue removal and
biomass burning, and extractive farming
practices where nutrient balance is often
negative.
Most upland soils in India have a low SOC
concentration, often as low as 0.2% even in the
surface layer. The low SOC concentration in most
soils in India is below the threshold level of 1.1%
for optimal soil processes. The general problem
of low SOC concentration is exacerbated by the
extractive farming practices whereby crop
residues are removed as cattle feed, and animal
dung is used as household cooking fuel. While
fuel wood is commonly used, cattle manure and
crop residues are also extensively used as
household fuel (Tables 11, 12 and 13). Traditional
biofuels have strong impact on local and regional
climate through emission of black carbon.
Therefore application of soil amendments,
including crop residues and animal manure, can
enhance SOC pool and improve crop yields
(Katyal et al., 2001). Venkateswarlu et al. (2007)
reported that application of biomass under rainfed
conditions improved SOC concentration by 24%
than fallowing over a 10-year period. In Punjab,
Ghuman and Sur (2001) and Gajri et al. (2007)
also observed increase in Soc concentration by
application of crop residues as mulch and animal
dung as manure in coarse-textured soils. On a
Vertisol in Central India, Reddy et al. (2007)
reported that application of P fertilizer and manure
improved soil quality. A 30-year experiment
conducted on an Inceptisol in West Bengal
showed that manuring and fertilizer use are
essential to maintaining soil quality. Indeed,
integrated nutrient management or INM (e.g.,
combined application of inorganic fertilizers with
organic manure) is essential to enhancing and
sustaining crop yield (Patra et al., 2000; Manna
et al., 2005; Sharma et al., 2005; Rekhi et al.,
2000; Yadav et al., 2000). The magnitude of
positive impact would increase with continuous
application of mulch over a long period on a
continuous basis.
Extractive farming, with no use of chemical
fertilizers or animal manure and removal of crop
residues for other competing uses, decreases
the SOC pool and reduces soil quality. The data
from a 28-year study conducted on a Vertisol in
India showed that rate of change (kg/ha/yr) in
SOC pool of 0-15 cm depth was –7.1 for control,
21.4 for 100% N, 57.1 for 50% NPK, 89.3 for 100%
NPK and 228.5 for 100% NPK plus manure (Table
14). This rate of C sequestration is about 25% of
the rates observed for similar management under
a temperate climate
Yadvinder-Singh et al. (2004b) reported that
rice residue incorporation increased organic
carbon content of the sandy loam soil more
significantly than straw burning or removal after
7 years (Table 15). Carbon sequestration derived
from changes in soil C content in the soil from
rice residue applied at 7.1 t ha–1 annually for 7
years averaged 14.6%. In another long-term
study, Yadvinder-Singh et al. (2004a) reported that
wheat straw incorporation in rice increased
organic C content from 0.40% in straw removal
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
treatment to 0.53% in straw incorporation
treatment after 12 years of experimentation on a
loamy sand soil. The values after 6 years were
0.38 and 0.49%, respectively, suggesting smaller
increases in organic C between 6 and 12 years
than during 0–6 years. Carbon sequestration
derived from changes in soil C content in the soil
from wheat straw incorporation for 12 years
represented 10% of the added carbon. The rate
of increase in organic C with straw incorporation
is generally smaller in coarse-textured soils than
in fine-textured soils. For example, Verma and
Bhagat (1992) and Dhiman et al. (2000) observed
marked increases in organic C in sandy clay loam
soils with residue incorporation after 4–5 years.
Microbial Biomass
The Soil Microbial Biomass (SMB) reflects the
soil.’s ability to store and cycle nutrients (C, N, P
and S) and organic matter, and has a high turnover
rate relative to the total soil organic matter (Carter
et al. 1999). Due to its dynamic character, SMB
responds to changes in soil management often
before effects are measured in terms of organic
C and N (Powlson and Jenkinson, 1981). The
SMB plays an important role in physical
stabilization of aggregates. The rate of organic C
input from plant biomass is generally considered
the dominant factor controlling the amount of SMB
in soil (Campbell et al., 1997).
With regard to soil fauna, microbial mass
diversity and biological activity are higher in
undisturbed soil or soil system that is managed
using CA techniques compared to those receiving
deep cultivation (Nsabimana et al., 2004;
Spedding et al., 2004). With respect to
microfauna, Cochran et al. (1994) suggest that
management practices that favor bacteria would
also be expected to favor protozoa, since bacteria
are their main food source. Also, the abundance
of mesofauna (in particular, potworm) was
greater where CA was practiced in comparison
to compacted soil (Rohrig et al., 1998).
Summarizing the effects of no-tillage on soil
fauna, Kladivko (2001) concluded that the larger
species are more vulnerable to soil cultivation
than the smaller. A review of 45 studies of tillage
and invertebrate pests (Stinner and House, 1990)
showed that for the investigated species, 28%
increased with decreasing tillage, 29% did not
change with a tillage system, and 43% decreased
with decreasing tillage. Beetles (Coleoptera) and
spiders (Araneae) are important members of the
macrofauna that are usually much reduced by
plow-based tillage operations (Wardle, 1995).
Reduced populations under conventional tillage
are likely due, in part, to physical disturbance and
abrasion from the tillage operation itself, but the
reduction in surface residue cover is probably
more significant.
Franzluebbers et al. (1999) showed that as
the total organic C pool expands or contracts due
to changes in C inputs to the soil, the microbial
pool also expands or contracts. A continuous,
uniform supply of C from crop residues serves
as an energy source for microorganisms. In the
subtropical highlands of Mexico residue retention
resulted in significantly higher amounts of SMB-
C and N in the 0-15 cm layer compared to residue
removal (Govaerts et al., 2007b). Spedding et al.
(2004) found that residue management had more
influence than tillage system on microbial
characteristics, and higher SMB-C and N levels
were found in plots with residue retention than
with residue removal, although the differences
were significant only in the 0-10 cm layer.
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The influence of tillage practice on SMB-C and
N seems to be mainly confined to the surface
layers, with a stronger stratification when tillage
is reduced (Alvear et al., 2005). Alvear et al. (2005)
found higher SMB-C and N in the 0-20 cm layer
under zero tillage than under conventional tillage
(disk-harrowing to 20 cm) in an Ultisol from
attributed this to the higher levels of C substrates
available for microorganism growth, better soil
physical conditions and higher water retention
under zero tillage. Pankhurst et al. (2002) found
that zero tillage with direct seeding into crop
residue increased the build-up of organic C and
SMB in the surface soil. Salinas-Garcia et al.
(2002) reported that SMB-C and N were
significantly affected by tillage, but primarily at the
soil surface (0-5 cm) where they were 25-50%
greater with zero tillage and minimum tillage than
with disk ploughing to 30 cm. At lower depths (5-
10 and 10-15 cm), SMB-C and N were generally
not significantly different. The favorable effects
of zero tillage and residue retention on soil
microbial populations are mainly due to increased
soil aeration, cooler and wetter conditions, lower
temperature and moisture fluctuations, and higher
carbon content in surface soil (Doran, 1980).
Figure 13. Bell et al. (2006) Monoculture of maize
with residue retention resulted in increased SMB
with zero tillage compared to conventional tillage,
but no significant differences in SMB were found
between the same tillage systems with a maize-
wheat rotation and crop residue retention. Each
tillage operation increases organic matter
decomposition with a subsequent decrease in
SOM (Buchanan and King, 1992).
However, wheat in the rotation tends to buffer
against soil C depletion (Govaerts et al. 2007b).
Activity of soil fauna is important in the formation
of organo-mineral complexes and aggregation,
thus enhancing and diversifying soil fauna helps
in improving soil structure. The intensity of soil
tillage strongly influences earthworm populations
and, by their activity, the amount of biopores.
Earthworms support decomposition and
incorporation of straw. Zero tillage proved to be
more efficient than the other tillage systems
(reduced and conventional tillage) in the
conservation of organic carbon and microbial
biomass carbon at the soil surface depth (0-5
cm) as reported by Costantini et al. (1996). The
tillage systems impact on the respiration were
due to the variations caused in the microbial
biomass. No changes were found in carbon use
efficiency by microorganisms as a consequence
of the tillage system employed. Increased number
of beneficial soil fauna with zero till have been
reported relative to traditional tillage (McGarry et
al., 2000). Radford et al. (1995) also showed there
was a four-fold increase in earthworm numbers
with zero tillage as compared to conventional
tillage. Increased earthworm activity in no-till
treatments was also reported by Tebrugge et al.
(1999) and Rasmussen (1999).
EMISSION OF GREENHOUSEGASES
Methane (CH4) and nitrous oxide (N
2O) are
important greenhouse gases, N2O being about
300 and CH4 being 15 times more radiatively
active than CO2 (mass basis, considering
residence time in the atmosphere) (Rodhe, 1990).
Flooded rice soils are a major source of
atmospheric CH4, contributing about 10% of the
total global emissions of CH4 (Mitra et al., 1999;
Neue and Sass, 1996; Rennenberg et al., 1992;
Sass et al., 1990; Wassmann et al., 1998). Global
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
methane emission from flooded rice fields has
been estimated at 20-100 Tg year–1 (Neue, 1993).
In comparison, the total agricultural sources of
N2O are quite small, ranging from 0.03 to 3.0 Tg
N year–1 (IPCC, 1996). Incorporation of organic
materials (crop residues, green manures,
compost) to regenerate depleted soil resources
and promote sustainable food productions in the
tropics should signif icantly increase CH4
emissions. Thus, residue management
strategies may create conflicts between the goals
of sustainable agriculture and mitigation of
greenhouse gases when used in flooded rice-
based systems. Soil properties, water
management, organic amendment, and
temperature have been reported as the major
factors controlling the amount of CH4 emitted from
rice fields (Sass et al., 1991; Schutz et al., 1996).
It has been estimated that CH4 emissions from
rice cultivation in India (45 million ha) should not
exceed 2.5 t year–1. The main reason for low CH4
emissions from rice fields in India is that the soils
have very low organic C or receive very little
organic amendments (Jain et al., 2000). The
burning of crop residues also contributes to the
global CH4 budget. For each ton of crop residue
burned, 2.3 kg CH4 is emitted (Grace et al., 2003).
In rice-wheat cropping system, 0.14 t year–1 will
be emitted, if one-half of the 12 million ha under
rice-wheat cropping system is burned.
METHANEOrganic C from added crop residues, organic
manures, soil organic matter, or rice plant roots
is the major driving force for CH4 production in
rice-based agriculture systems (Wang et al.,
1992; Yagi and Minami, 1990). Numerous studies
from all over the world have demonstrated that
added crop residues, composts, and green
manures enhance CH4 fluxes relative to
unamended controls (Bossio et al., 1999; Chen
et al., 1993; Chidthaisong et al., 1996; Glissmann
and Conard, 1999; Neue et al.,1994; Rath et
al.,1999; Wassmann et al., 1993). The seasonal
emissions from paddy rice with organic additions
ranged from 1.1 to 148 g CH4 m–2 and increased
methane emissions 1.2- to 32-fold over
unamended control soils. Crop residues serve
as a substrate for a complex microbial community,
including methanogenic microorganisms. Most
studies on the microbiological aspect of CH4
production in flooded rice soil have focused on
methanogens (Asakawa and Hayano, 1995;
Asakawa et al., 1998). In addition to
methanogens, the degradation of organic matter
to its most reduced status (CH4), however,
involves at least two other kinds of
nonmethanogens: the zymogenic bacteria and
the acetic acid- and hydrogen-producing bacteria.
Thus, from the point of view of microbiological
ecology, different effects of various organic
fertilizers on CH4 production potential might be
closely related to the amount of easily
decomposable organic matter. In principle, the
degradation pattern in soils with and without
amended straw is similar, with acetate,
propionate, and H2 as the main intermediates of
anaerobic degradation and CH4 being formed from
H2/CO
2 (11-27%) and acetate (84-89%). However,
the early phase of straw degradation differs, as a
large variety of fatty acids accumulate transiently
(Glissmann and Conard, 1999). A study by Weber
et al. (2001) indicated that the methanogens
colonizing rice straw are less diverse than those
inhabiting the soil. Polysaccharolytic bacteria in
rice soils constitute the first step in the degradation
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
process and eventually produce substrates
needed for the production of CH4. Distinct trends
of multiple rate patterns for CH4 emission from
waterlogged soils have been shown in laboratory
and field studies (Hou et al., 2000). The first peak,
between 20 and 40 days at 25oC, probably
originated from the decomposition of easily
decomposable forms of C in the rice straw, such
as microbial products and polysaccharides
(Watanabe et al., 1995). The second change in
rate of CH4 emission observed may have been
associated with the decomposition of structural
components of the rice straw, such as cellulose
and lignin. The effect of rice straw application on
CH4 production potential is shown in Figure 14.
Methane production in the treatment without rice
straw supplement occurred at a much lower rate
during the whole period of incubation, in which
the highest production rate was less than 40 mg
CH4 kg–1 soil day–1. After the application of rice
straw, the CH4 production rate increased
substantially.
Both the quantity and the quality of added
organic materials influence CH4 emission from
soils. Yagi and Minami (1991) showed that while
rice straw increased CH4 emission by a factor of
3.3, addition of rice straw compost increased CH4
emission only slightly compared to the application
of mineral fertilizers. The extent and variability of
observed methane enhancements by organic
additions are governed by several factors, the
most obvious being quantity. Schutz et al. (1989)
established that CH4 emissions from paddy rice
progressively increased with increasing rice straw
additions from 3 to 12 t ha–1. Straw levels over 12
t ha–1 did not increase CH4 fluxes further. Likewise,
Wang et al. (1992) found increasing CH4 flux to
be proportional to rice straw input levels. A field
study (Yagi and Minami, 1990) also showed that
rice straw applied at rates of 6-9 t ha–1 enhanced
CH4 emission rates by 1.8-3.5 times. As reported
by Sass et al. (1991) and Watanabe et al. (1995),
CH4 production was enhanced by the addition of
straw in flooded soil only Watanabe et al. (1995)
proposed a simple straw rate response model to
predict cumulative CH4 emissions from a known
rice straw application to any soil:
[ / 1 0c E xY k a E b E e Y
where Y is the fractional increase in CH4 emission
relative to a chemical fertilizer control, and x is
the level of incorporated organic matter (t ha–1).
Adjustments to the coefficients a, b, and c were
added to account for responses to temperature
(E) and differences of soil type (k). Such
modifications reflect observations that daily and
seasonal CH4 fluxes are temperature dependent
(Parashar et al., 1991; Schutz et al., 1989; Yagi
and Minami, 1991). Incubation studies have
shown that large differences in CH4 production
potential of soils are related to organic C content
(Majumdar et al., 1998). The extent and rapidity
with which added organic materials are
decomposed depend greatly on chemical
composition, including C:N ratio, lignin and
polyphenol content, and other critical compounds.
Yadvinder-Singh and van Cleemput (1998)
reported that maximum methane (9980 mg g–1)
was emitted from soil amended with sugar beet
leaves, and emissions of CH4 from wheat and
rice straw were 4953 and 5030 mg g–1 in 40 days
in a silty clay soil under flooded conditions. The
emissions of CH4 from composted farmyard
manure and poultry manure-amended soils were
very low. From an incubation experiment in a
Chinese flooded rice soil, Hou et al. (2000)
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
reported that organic matter, added as rice straw
and organic manure (pig, chicken, and cattle
manure), increased CH4 production rate
significantly. The results showed that organic
manures had different promoting effects, with pig
manure increasing the CH4 production rate most,
followed by rice straw, chicken, and cattle manure.
The CH4 production potential caused by organic
manures was closely related neither to the total
C added to the system nor to the C:N ratio of the
materials. A significant linear relationship between
CH4 production and the logarithm of the number
of zymogenic bacteria was found, with an r value
of 0.96. This finding suggests that the number of
zymogenic bacteria may be used as an index to
predict CH4 production potential in flooded rice
fields. Bronson et al. (1997a) observed that
organic matter additions as rice straw (5.5 t ha–1,
dry) or green manure (Sesbania rostrata, 12 t ha–
1, wet) stimulated methane flux several-fold. Rice
straw resulted in higher CH4 emissions than GM.
The GM plots showed highest CH4 fluxes in the
first 2 weeks, but thereafter straw–amended
emitted the most CH4. Green manure has more
easily decomposable C than straw, although
more C was added as straw. Sesbania green
manure, being easily degradable material,
required the lower activation energy by
methanogens to use the substrate as C source
than wheat straw (Bhat and Beri, 2002). Rice
straw applied before the winter fallow period
reduced CH4 emission by 11% compared with
that obtained from fields to which the same amount
of rice straw was applied during field preparation.
Surface mulching of straw instead of
incorporation into the soil showed 12% less
emission.
Composts consistently produced lower CH4
emissions than fresh green manures or straws.
Aerobic composting reduces readily
decomposable carbon to CO2 instead of CH
4
(Inoko, 1984) and also modifies the original
organic constituents to forms more resistant to
subsequent degradation (Watanabe et al., 1995).
Consequently, when compost is incorporated into
anaerobic soils, less available carbon is present
for methanogenesis. However, the agricultural
benefit derived from compost is maintained,
especially if composts are applied year after year
(Inoko, 1984). Thus, composting provides a
compatible option for adding organic materials to
flooded soils without substantially enhancing
methane emissions. Following the same
principal, Miura (1995) found that fall rice straw
incorporation or winter mulching combined with
spring incorporation significantly reduced CH4
emissions during the subsequent summer rice
season. Jain et al. (2000) reported that additions
of organic manures and crop residues enhanced
CH4 emissions from rice fields. There were wide
variations in CH4 emissions because of the variety
of organic amendments.
Rice fields amended with biogas slurry emitted
significantly less CH4 than those amended with
other organic amendments. They further reported
that CH4 emission rates were very low (between
16 and 40 kg CH4 ha–1 season–1) when the field
was flooded permanently. Application of organic
manure (FYM plus wheat straw) in combination
with urea (1:1 N basis) enhanced CH4 emission
by 12–20% compared with fields treated with urea
only. The site in New Delhi represents one
example of very low CH4
emissions from rice
fields. Emissions from other sites in northern
India may be higher than those in New Delhi, but
they are still lower than in other rice growing
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
regions in India. Jain et al. (2000) reported that
organic amendment inputs promoted CH4
emissions, but total emission remained less than
25 kg CH4 ha–1. This finding contrasts with results
from other network stations with irrigated rice
where total emissions generally exceeded 100
kg CH4 ha–1 after manure application (Wassmann
et al., 2000a). The low impact of organic manure
in the experiment in New Delhi could be related
to high percolation rates. Constant inflow of
oxygen into the soil and downward discharge of
methanogenic substrate resulted in low CH4
production (Inubushi et al.,1992; Yagi et al., 1994).
Thus, emissions were very low even when
organic matter was applied. In other stations of
the network, organic amendments stimulated
emissions during the first half of the season
(Wassmann et al., 2000b). Ishibashi et al. (2001)
studied the effect of surface application of rice
straw in no-till rice on methane emission in three
soils during rice growing season. It was found
that CH4 emissions from the no-tilled direct-
seeded field on the average were 21, 47, and 91%
of that from the tilled transplanted field in high-
percolating site, low-percolating site, and
extremely low-percolating (4.4 mm day–1) site,
respectively. Straw incorporation leads to
significantly more methane production than
burning or removal. Over the long term, however,
incorporation may provide benefits through the
accumulation of C as soil organic matter.
NITROUS OXIDEThe biologically mediated reduction processes
of nitrification and denitrification are dominant
sources of N2O generation in soils (Paul and
Clark, 1989). Nitrous oxide is also produced to a
much lesser extent by the abiotic process of
chemodenitrif ication (Bremner, 1997).
Denitrification processes can terminate with N2O,
or, more commonly, N2O is further reduced to N
2
gas. Conditions that promote N2O emissions over
N2 are high NO-3 levels and/or increasing O-2
,while increasing organic carbon levels tend to
favor N2 production (Firestone, 1982). Nitrous
oxide emissions from rice fields occur as a result
of nitrification–denitrification during periods of
alternating wetting and drying. Emissions are
usually small in irrigated rice systems with good
water control and small to moderate inputs of
fresh organic material (OM) (Bronson et al.,
1997a, b).Bronson et al. (1997a) reported that
organic amendments, particularly rice straw,
helped in reducing N2O emissions. In the flooded
rice soil, straw addition possibly stimulates O2
consumption in the aerobic soil layer and in the
rhizosphere, resulting in smaller zones in which
nitrification can occur. Enhanced immobilization
of fertilizer N with straw would result in less NH4
available for nitrif ication–denitrif ication.
Additionally, the high CH4 concentration in straw-
amended soil could inhibit nitrification (McCarty
and Bremner, 1991). Methane emissions ranged
from 3 to 557 kg CH4 ha–1 with an average of 182
kg CH4 ha–1. Few measurements have been
published for N2O emissions from flooded rice
soils amended with organic materials. The
existing information indicates that N2O emissions
from flooded soils with organic additions are
similar to or less than soils receiving chemical
fertilizers, indicating that organic amendments do
not appear to influence N2O emissions very much.
Most information on N2O emissions from rice
soils focuses on water management and nitrogen
fertilizers as controlling variables (Cai et al., 1997,
1999). A trade-of relationship between CH4 and
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
N2O, i.e., conditions that favor CH
4 production
suppress N2O and vice versa, is also well
recognized (Mosier et al., 1998a). So, while
organic amendments seemingly have no impact
on N2O emissions from f looded soils,
management practices before or after rice may
produce a significant effect. Aulakh et al. (2001)
showed that denitrification is a significant N loss
process under wetland rice amounting to 33% of
the recommended dose of 120 kg N ha–1 on a
permeable sandy loam soil. Integrated
management of wheat straw (6 t ha–1) and GM
(20 t ha–1 supplying 88 kg N ha–1) and 32 kg N ha–
1 as urea fertilizer N significantly reduced
cumulative gaseous N losses to 51.6 kg N ha–1
as compared to 58.2 kg N ha–1 for 120 kg N ha–1
alone. The gaseous losses under wheat were
0.6-2% of the applied fertilizer N. Interplay between
the availability of NO3 and organic C largely
controlled denitrification and N2O fluxes in flooded
summer-grown rice, whereas temperature and
soil aeration status were the primary regulators
of the nitrification–denitrification processes and
gaseous N losses during winter grown upland
wheat. The irrigated rice–wheat system is a
significant source of N2O, as it emits around 15
kg N2O–N ha–1 year–1.
The quantity of organic additions may also
affect N2O emissions. In one of the few studies
looking at the impact of organic materials on N2O,
Bronson et al. (1997a) suggested that organic
additions to flooded soils stimulated oxygen
depletion to the point of inhibiting nitrification and
thereby N2O emissions. From this, one could
hypothesize that increased oxygen depletion with
more organic material and consequently N2O
emissions would decline even more. Burning of
crop residues also contributes to the global N2O
budget. For each ton of crop residue that is
burned, 40 g N2O is emitted (Grace et al., 2003).
MITIGATION STRATEGIESThe objective of reducing CH
4 emissions must
be combined with improvements associated with
increased yields and straw recycling; adhering
to CH4 emission quotas might increasingly affect
rice production practices. Possible mitigation
options for reducing methane emission from rice
fields include reduced length of flooding,
temporary drainage (Wassmann et al.,2000b),
rice cultivar selection, kind and application mode
of mineral fertilizers, and soil and crop
management strategies to achieve a high
acceptance (Mosier et al.,1998a,b; Neue,1993;
Yagi et al., 1994). CH4 emission was reduced
significantly by early incorporation of rice straw
during the fallow period, adding to the agronomic
benefit of this practice. Bronson et al. (1997b)
recorded seasonal N2O emissions during a fallow
period as high as 172 and 183 mg N m–2, where
rice straw and a green manure had been
incorporated the previous season, respectively.
Such emissions might be considered maximums
because assimilation of nitrogen mineralized from
organic additions by fallow weed species or
upland crops helps to retain N within the system
and minimize N2O emissions (Buresh et al.,
1993). Given the influence of soil type, climate,
and organic additions on CH4 and N
2O emissions,
comprehensive studies are needed to quantify
more thoroughly the trade-of effects between CH4
and N2O during an annual cycle within rice-based
cropping systems. Water management is an
important management factor when trying to
minimize CH4 or N
2O emissions from rice-based
cropping systems. Mid season drainage, which
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
originally was developed in Japan as a means to
supply oxygen to rice roots, is also very effective
in reducing seasonal CH4 emissions from rice
(Jain et al., 2000; Yagi and Minami, 1990). Despite
projected decreases in CH4 emission by such
methods, aerobic soil conditions during fallow and
upland cropping intervals between rice crops
enhance N2O emissions generated by nitrification
of mineralized organic N and subsequent
denitrif ication of NO3 when f looding is
reestablished (Bronson and Mosier, 1993).
Unintentional mid-season drainage is possible in
many rice cropping systems of South and
Southeast Asia where light textured soils or water
distribution and management problems influence
the ability of farmers to keep their soils flooded
(Jain et al., 2000). Site specific adaptations will
be required for an optimum eVect, considering
rice yields, water consumption, and CH4
emissions.
In summary, methane emissions can be
reduced significantly by adopting the following
mitigation practices: water management through
intermittent irrigation or drainage, the use of
composted organic manures instead of fresh
manure, allowing pre-decomposition of crop
residues under aerobic conditions before rice
planting, and the selection of suitable cultivars
that emit less CH4. It appears that composted
organic additions are the best way to meet
sustainable agriculture goals while minimizing
greenhouse gas emissions from paddy rice.
Adding crop residues or green manures in
sufficient quantities to increase soil organic matter
levels or replenish deficient nutrients for flooded
rice exacerbates N2O emissions to unacceptable
levels. Of course, it is important to establish that
CH4
and N2O emissions arising from the
composting process do not exceed emissions
during rice cultivation. Direct dry seeding of rice
as well as other crops following rice into surface
residues will reduce N2O and CH
4 emissions.
Grace et al. (2003) suggested three feasible,cost-
effective agronomic interventions that would have
an immediate effect by reducing greenhouse
gases production in the rice–wheat cropping
systems and that will no doubt be applicable to
other ricebased cropping systems in the tropics:
(1) a reduction in residue burning, (2) a reduction
in flood irrigation frequency for rice, and (3) the
use of minimum or no tillage for upland crops
following rice (e.g., wheat or maize). It was
estimated that Adopting these measures would
result in total savings in CO2 equivalent emissions
of 1680 kg ha–1 year–1.
Soil Quality and Crop Production
Land quality and land degradation affect
agricultural productivity, but quantifying these
relationships has been difficult (Wiebe 2003).
However, it is clear that the necessary increase
in food production will have to come from
increases in productivity of the existing land rather
than agricultural expansion, and that restoration
of degraded soils and improvement in soil quality
will be extremely important to achieve this goal.
However, the rate of increase in crop yields is
projected to decrease, especially in north west
India where natural resources are already under
great stress (Lal, 2006). The effects of soil
degradation or regeneration, and therefore
increased or reduced soil quality, on agricultural
productivity will vary with the type of soil, cropping
system and initial soil conditions, and may not be
linear (Scherr, 1999). The impacts of degradation
on productivity are sensitive to farmer decisions
(Wiebe, 2003), and soil degradation in all its
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
nefarious forms is eroding crop yields and
contributing to malnourishment in many corners
of the globe. The effects of soil quality on
agricultural productivity are greater in low-input
production systems than in highly productive
systems (Scherr, 1999). Govaerts et al. (2006b)
determined the soil quality of plots after more than
10 years of dif ferent tillage and residue
management treatments. There was a direct and
significant relation between the soil quality status
of the soil and the crop yield, and zero tillage with
crop residue retention showed the highest crop
yields as well as the highest soil quality status.
Lal (2004), calculated the relations between
increases in SOC and its concomitant
improvements in water and nutrient holding
capacity, soil structure, and biotic activity and
grain yield and found several positive relations.
Sayre et al. (2005) report on a wheat-maize
rotation in a long-term sustainability trial under
irrigated conditions in north western Mexico that
compared different bed planting systems
(conventional tilled beds and permanent raised
beds). Residue management varied from full to
partial retention, as well as residue burning. Yields
differences between management practices only
became clear after 5 years (10 crop cycles), with
a dramatic and sudden reduction in the yield of
permanent raised beds where all residues had
been routinely burned. In contrast to rainfed low
rainfall areas, in irrigated agricultural systems, the
application of irrigation water appears to ‘hide or
postpone the expression of the degradation of
many soil properties until they reach a level that
no longer can sustain high yields, even with
irrigation. The reduced yields reported after five
years with permanent beds where residues were
burned, were related to a significant decrease in
stable macroaggregation and soil microbial
biomass (Naresh et al., 2010). In high-input
systems, the decreased soil quality status of
management practices is reflected in reduced
efficiency of inputs (fertilizer, water, biocides,
labor) resulting in higher production costs to
maintain the same yield levels, rather than in lower
yields as such (Scherr, 1999).
The effects of soil quality on agricultural
productivity are greater in low-input rain fed
production systems than in highly productive
systems (Scherr, 1999). Govaerts et al. (2006b)
determined the soil quality of plots after more than
10 years of dif ferent tillage and residue
management treatments. There was a direct and
significant relation between the soil quality status
of the soil and the crop yield, and zero tillage with
crop residue retention showed the highest crop
yields as well as the highest soil quality status
(Govaerts et al., 2006b, Govaerts et al., 2005). In
contrast, the soil under zero tillage with crop
residue removal showed the poorest soil quality
(i.e., low contents of organic C and total N, low
aggregate stability, compaction, lack of moisture
and acidity) and produced the lowest yields,
especially with a maize monoculture (Fuentes et
al., 2009, Govaerts et al., 2006b). This is in line
with other studies: for instance Ozpinar and Cay
(2006) found that wheat grain yield was greater
when tillage practices resulted in improved soil
quality as manifested by higher soil organic
carbon content and total nitrogen. Lal (Science,
11 June 2004, pp. 1623-1627) calculated the
relations between increases in SOC and its
concomitant improvements in water and nutrient
holding capacity, soil structure, and biotic activity
and grain yield and found several positive
relations. Also the reverse relation has been
192
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
reported by several authors: reduced physical soil
quality that results in increased erosion potential
caused yield reductions of 30 to 90% in shallow
lands of West Africa (Lal 1987, Mbagwu et al.,
1984). Yield reduction in Africa due to past soil
erosion may range from 2 to 40%, with a mean
loss of 8.2% for the continent (Lal, 1995). The
actual loss may depend on weather conditions
during the growing season, farming systems, soil
management, and soil ameliorative input used.
Globally, losses in food production caused by soil
erosion are most severe in Asia, Sub-Saharan
Africa, and elsewhere in the tropics (Lal, 1998).
In the western Uttar Pradesh fertile lands
improved high-yielding wheat varieties yielded
comparatively higher under conservation
agriculture compared to the farmer practice or
zero tillage with residue removal, all with the same
fertilizer inputs (Naresh et al., 2013). Thus, future
food production targets can only be met when
the potential benefits of improved varieties are
combined with improved soil management
technologies. The latter include, first and foremost,
restoration of degraded and desertified soils,
improvement of soil structure and enhancement
of soil quality and health through increases in
SOM reserves, conservation of water in the root
zone, and control of soil erosion. Once soil quality
and soil health are restored, then, and only then,
are the benefits of improved varieties and
chemical fertilizers realized. The vicious cycle of
declining productivity due to depleted SOC stock
will have to be broken by improving soil quality
through SOC sequestration. This will be an
important and necessary step to free much of
humanity from perpetual poverty, malnutrition,
hunger, and substandard living. Rather than the
seed-fertilizer package, it is crucial to adopt the
strategy of integrated soil fertility management
that is based not only on recycling nutrients
through enhanced productivity and soil organic
carbon levels, but also appreciation of the
importance of soil physical an biological fertility:
a soil may be rich in nutrients but if it has a poor
physical structure and lacks the biological
elements to improve this structure, crop
productivity will be low. Conservation agriculture,
that combines reduced tillage, crop residue
retention, and functional crop rotations, together
with adequate crop and system management,
permit the adequate productivity, stability and
sustainability of agriculture.
CONCLUSIONConservation agriculture improves soil
aggregation compared to conventional tillage
systems and zero tillage without retention of
sufficient crop residues in a wide variety of soils
and agro-ecological conditions. The conversion
of conventional to zero tillage can result in the
loss of total pore space as indicated by an
increase in bulk density. However, the loss of
porosity is generally limited to the plough layer.
There is some evidence that the porosity in the
top 5 cm of the profile may be greater under zero
tillage when residue is retained. The extent of
increase may be a function of enhanced
macrofaunal activity and the build-up of organic
matter at this depth, indicating the importance of
crop residue retention when adopting zero tillage.
Additionally, the adoption of controlled traffic when
converting to zero tillage is important in limiting
the possible loss of pore pace. Where total
porosity decreases in conservation agriculture
compared to conventional practices, this
decrease seems to take place mainly in the
193
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
macropore class with a concomitant increase in
micro and mesopore classes. Despite the
possible decrease in macroporosity in
conservation agriculture compared to
conventional practices, macropore
interconnectivity is reported to be higher with
conservation agriculture because of biopores,
and the maintenance of channels created by
roots. Infiltration is generally higher and runoff
reduced in zero tillage with residue retention
compared to conventional tillage and zero tillage
with residue removal due to the presence of the
crop residue cover that prevents surface crust
formation and reduces the runoff velocity, giving
the water more time to infiltrate. Soil evaporation
is reduced by surface residue cover and
increased by tillage. Soil moisture is conserved
and more water is available for crops with
conservation agriculture. The increased
aggregate stability and reduced runoff in
conservation agriculture result in a reduction of
water erosion. The combination of reduced tillage
with crop residue retention increases the SOC in
the topsoil.
The needed yield increases, production
stability, reduced risks and environmental
sustainability can only be achieved through
management practices that result in an increased
soil quality in combination with improved crop
varieties. The above outlined evidence for the
improved soil quality and production sustainability
with well implemented conservation agriculture
systems is clear, although research remains
inconclusive on some points. At the same time,
the evidence for the degradation caused by tillage
systems is convincing especially for biological
and physical soil quality. Therefore, even though
we do not know how to manage functional
conservation agriculture systems under all
conditions, the underlying principles of
conservation agriculture should provide the
foundation upon which the development of new
practices is based, rather than be considered a
parallel option to mainstream research activities
that focus on improving the current tillage-based
production systems. The maintenance of soil
organic matter levels and the optimization of
nutrient cycling are essential to the sustained
productivity of agricultural systems. Both are
related closely to the bioturbating activities of
macrofauna and the microbially-driven
mobilization and immobilization processes,
which the activities of large invertebrates also
encourage. Maintaining soil organic matter
content requires a balance between addition and
decomposition rates. As changes in agricultural
practices can engender marked changes in both
the pool size and turnover rate of soil organic
matter, it is important to analyze their nature and
impacts. Traditional plough and disc-tillage
cropping systems tend to cause rapid
decomposition of soil organic matter, leave the
soil susceptible to wind and water erosion, and
create plough pans below the cultivation depth.
By contrast, reduced- or zero-tillage systems
leave more biological surface residues, provide
environments for enhanced soil activity, and
maintain more intact and interconnected large
pores and more soil aggregates, which are better
able to withstand raindrop impact. Water can
infiltrate more readily and rapidly into the soil with
reduced tillage and this helps protect the soil from
erosion. In addition, organic matter decomposes
less rapidly under reduced-tillage systems. No-
tillage systems have proved especially useful for
maintaining and increasing soil organic matter.
194
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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013
Conversion from conventional to zero tillage,
reduced erosion and avoided surface sealing
because of crop residue cover on the surface
and higher aggregate stability under zero tillage
conditions. Soil temperature is modified by the
crop residues left on the surface. There are
contrasting views about soil pH, it may increase
or decrease with adoption of zero tillage. Higher
soil organic carbon sequestration was observed
by adopting zero tillage. Increased organic matter
in the top soil has been observed by adopting zero
tillage.
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