int. j. lifesc. bt & pharm. res. 2013 r k naresh et al.,...

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Int. J. LifeSc. Bt & Pharm. Res. 2013 R K Naresh et al., 2013

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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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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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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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

156



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)

157



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)

158



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

159



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).

160



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)

162



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)

163



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

164



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

165



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

166



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

167



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

168



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

169



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

170



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)

171



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

172



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)

173



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

174



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 –

175



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

176



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

-

-

-

-

177



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

178



(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

179



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

180



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)

181



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,

182



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

183



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.

184



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

185



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

186



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)

187



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

188



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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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

190



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

191



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



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



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



Conversion from conventional to zero tillage,

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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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