Agricultural Science Research Journal Vol. 2(1), pp. 30 - 41, January 2012
Available online at http://www.resjournals.com/ARJ
ISSN-L: 2026-6073 ©2012 International Research Journals
Full Length Research Paper
Impact of conservation tillage on soil properties in ricewheat cropping system
Avtar Singh and Jagmohan Kaur
Department of Agronomy, Punjab Agricultural University, Ludhiana-141 004
Corresponding author: [email protected]
Abstract
Rice-wheat cropping system is the predominant and most profitable cropping system and emerge as
the major cropping system in the Indo-gangetic plains leading to the Green Revolution; Punjab,
Haryana,Western Uttar Pradesh (UP) crescent has been the heartland of the Green Revolution (GR). It
occupies an area about 65 mha in these states, out of this rice is grown on 40 mha and wheat on 25mha
and this system contribute more than 70 % of total cereal production in India. In Asia, the rice-wheat
system is grown on an estimated at 23.5 million ha, including China with about 10 million ha, and South
Asia with about 13.5 million ha. The area of rice-wheat system in India, Pakistan, Bangladesh and Nepal
is 10.0, 2.2, 0.8, and 0.5 million ha, respectively. Rice-wheat systems represent 32 per cent of the total
rice area and 42 per cent of the wheat area in these countries. Several problems associated to this
system in the Indo-Gangtic plains, however, the major problems are reduction in organic matter of soil,
depletion of water resources, lowering water quality and goundwater pollution, burning of residue,
reduction in productivity, higher cost of production and environmental pollution. Due to these reasons
the sustainability of rice-wheat system under great threat. Therefore, to achieve sustainable higher
productivity, efforts must be focused on reversing the trend in natural resource degradation by
adopting efficient resource conservation technologies. One of these RCT’s is Conservation tillage,
conservation tillage practices generally result in higher amounts of soil organic matter (OM), reduced
erosion, increased infiltration, increased water stable aggregates and greater microbial biomass carbon
when compared to conventional tillage systems. In this paper discuss the expansion, magnitude of
contribution and problems related to the rice-wheat system and how conservation tillage will help to
achieve the sustainable higher productivity by changing the soil properties.
Keywords: soil properties, conservation, Rice-wheat cropping.
INTRODUCTION
The rice-wheat cropping system is the backbone of
India’s food security. The magnitude of the contribution of
rice-wheat cropping system to the country’s food security
can be gauged from Punjab alone, which has less than
2% of the country’s cultivated land, and provides 60% of
the wheat and 40% of the rice to the Public Distribution
System and national buffer stocks (Swaminathan, 2007).
The support price system for rice and wheat crops,
coupled with timely availability of cheap fertilizers and
irrigation water, made the rice-wheat system the most
profitable option. This enabled rice-wheat to emerge as
the major cropping system in the Indo-Gangetic Plains,
leading to the Green Revolution; Punjab, Haryana,
Western Uttar Pradesh (UP) crescent has been the
heartland of the Green Revolution (GR). These two
crops, grown on an estimated area of about 40 million
hectares (mha) for rice and about 25 mha for wheat,
together contribute more than 70% of total cereal
Singh and Kaur
production in India (Singh, 2000).
In Asia, the rice-wheat system has been practiced for
over 1000 years; it has since expanded and is now
estimated at 23.5 million ha, including China with about
10 mha, and South Asia with about 13.5 mha. The area
of rice-wheat system in India, Pakistan, Bangladesh and
Nepal is 10.0, 2.2, 0.8, and 0.5 mha, respectively. Ricewheat systems represent 32 per cent of the total rice area
and 42 per cent of the wheat area in these countries
(Ladha et al., 2000). During the past 30 years,
agricultural production has been able to keep pace with
population demand for food. This came about through
significant area and yield growth. This growth over the
past 30 years was based on key inputs like variety,
fertilizer and irrigation with most of the investment from
the public sector. Area growth was a result of new lands
being farmed and through increases in cropping intensity,
from a single crop to double or even triple crops per
calendar year. Future growth required to meet population
growth will be close to 2.5% per year and must come
from yield rather than area growth since the latter will
decline as urbanization and industries spread to prime
th
agricultural land. During the last four decades of the 20
century, the global population doubled itself from 3 to 6
billion and it is estimated that by the year 2020, it will
reach the 8 billion mark. Food and nutritional security is
therefore a serious global concern.
The rice–wheat cropping system being the oldest and
most prevalent agricultural practices in India, is also
practised in many other regions of the world and wetland
culture is the predominant soil management system
adopted. Rice occupies 153 m ha land throughout the
world. In India, out of the 43 m ha area under rice
cultivation, puddled rice culture occupies 24 m ha, about
56% of the area (Anonymous, 2005). This involves
ploughing the soil when wet, puddling it and keeping the
area flooded for the duration of the rice crop. Wetland
rice culture thus destroys soil structure and creates a
poor physical condition for the following wheat crop. This
soil condition can reduce wheat yield (Sur et al., 1981;
Boparai et al., 1992) presumably by limiting root growth
and distribution (Oussible et al., 1992). For regeneration
and maintenance of soil structure within this cropping
system, plant residue is very important (Verma and
Bhagat, 1992), but for various reasons, the amount of
residue being returned to the soil is not adequate. Rice
grown with conservation tillage can produce yields similar
to that under conventional puddling with minimized
expenses on field preparations (Sharma and De Datta,
1986).
Besides declining soil fertility, low wheat yields in ricewheat cropping system are also obtained due to a short
turnover period between rice harvest and delayed wheat
sowing due to a number of factors, including delayed rice
transplanting resulting in delayed rice harvest, high soil
moisture content after the rice harvest, delay in removal
of rice straw (a large part of it is being burned in situ,
31
which besides the loss of precious organic C creates
environmental and health problems), etc.
The major sustainability concerns in rice-wheat cropping
system are:
1. Fatigued –natural resources and declining factor
productivity
2. Reduced soil organic matter levels
3. Pesticide –health hazard
4. Sodicity and salinity problems
5. Depletion of ground water levels
6. Lowering of water quality and groundwater
pollution
7. Tillage costs and overall cost rising
8. Increase emission of GHGs (Green house gases)
due to burning of paddy straw
Sustainability is generally related to soil quality, which is
defined as, ‘‘the capacity of a specific kind of soil to
function,within natural or managed boundaries, to sustain
plant and animal productivity, maintain or enhance air
and water quality and support human health and
habitation’’(Karlen et al., 1997). The soil’s ability to
function as a component of an ecosystem may be
degraded, aggraded or sustained as use-dependent
properties change in response to land use and
management. Therefore, to achieve sustainable higher
productivity, efforts must be focused on reversing the
trend in natural resource degradation by adopting
efficient resource conservation technologies. One of
these RCT’s is Conservation tillage.
Conservation tillage practices generally result in higher
amounts of soil organic matter (OM), reduced erosion,
increased infiltration, increased water stable aggregates
and greater microbial biomass carbon when compared to
conventional tillage systems (Reeves, 1997).
All in all, conservation tillage can provide environmental
benefits, including:
� Reduced soil erosion
� Improved moisture content in soil
� Healthier, more nutrient-enriched soil
� More earthworms and beneficial soil microbes
� Reduced consumption of fuel to operate equipment
� The return of beneficial insects, birds and other wildlife
in and around fields
� Less sediment and chemical runoff entering streams
� Reduced potential for flooding
� Less dust and smoke to pollute the air
� Less carbon dioxide released into the atmosphere
Concept of Conservation tillage
Conservation tillage is an important tool for crop residue
32
Agric. Sci. Res. J.
Table 1. Effect of methods of planting and levels of nitrogen on bulk density of wheat .
-3
Bulk density(g cm )
Planting methods
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: Meenakhi (2010)
Table 2. Effect of planting methods and N levels on infiltration rate in wheat
Infiltration rate
-1
(cm min )
5 min
10 min
20 min
30 min
60 min
Happy
seeder
Zero tillage
Rotavator
Conventional
tillage
Before sowing
1.3
3.1
5.9
9.0
13.7
1.7
3.4
5.7
8.0
11.4
1.5
3.0
5.1
7.2
10.4
2.2
4.9
8.4
12.3
15.3
0.6
1.6
3.1
5.2
8.4
Source: Meenakhi (2010)
Table 3. Effect of planting methods and N levels on soil temperature in wheat
Planting methods
Happy seeder
Zero tillage
Rotavator
Conventional
tillage
22-3-2010
30.5
31.4
31.8
31.8
Soil temperature (°C)
29-3-2010
7-4-2010
28.0
38.5
28.3
39.0
28.7
39.6
28.5
39.6
12-4-2010
41.7
42.0
42.6
43.4
Source: Meenakshi (2010)
management, restoration of degraded soil, and for
enhancing C sequestration in soil. Conservation tillage,
any tillage system that maintains at least 30% of the soil
surface covered by residue, was practised in 1995 on
about 35.5% of planted area in USA. It is projected that
by the year 2020, conservation tillage may be adopted on
75% of cropland in USA, 50% in other developed
countries, and 25% in developing countries (Lal,1997).
Definitions: The Conservation Tillage Information Center
(CTIC, 1990 and 1995) defines CT as “any tillage and
planting system that maintains at least 30 % of the soil
surface covered by residue after planting to reduce water
erosion, or where wind erosion is a primary concern,
maintain at least 1000 kg/ha of flat, small grain residue
equivalent on the surface during the critical wind erosion
period”.
There has been a change in the definitions and concepts
involved in the convnetional tillage system through its
evolution since 1930s. CTIC has revised its definitions
since 1989. In fact, convnetional tillage is a generic term
that refers to “ any tillage system that reduces the loss of
soil or water relative conventional tillage” (Mannering and
Fenster, 1983). Under this generic term, there are several
types of convnetional tillage systems that are based on
the principle of crop residue management. The latter
includes a year –round system beginning with the
selection of crops that produce sufficient quantities of
residue including the use of cover crops. Basic concepts
and application of convnetional tillage systems have
Singh and Kaur
33
Table 4. Grain and straw yield as influenced by planting techniques and nitrogen levels
Planting technique
Grain yield
-1
(q ha )
51.8
51.8
44.9
44.8
42.6
41.4
2.3
Conventional tillage (transplanting)
Broadcast sprouted seed after puddling
Broadcast sprouted seed without puddling
Drum sowing after puddling
Drum sowing without puddling
Zero tillage (line sowing)
CD (p=0.05)
Straw yield
-1
(q ha )
93.7
96.2
89.3
84.0
86.4
72.0
7.5
Source: Kumar, (2008)
Table 5. Effect of different treatments on straw, grain and biological yield of wheat
Treatment
Zero tillage in standing stubbles after
removal of loose straw
Conventional tillage with mulching
Conventional tillage without mulching
CD (p=0.05)
-1
Grain yield
-1
(qha )
Straw yield (qha )
Biological yield
-1
(qha )
37.2
56.6
93.8
36.9
38.1
NS
58.1
57.4
NS
95.0
95.5
NS
Source: Singh (2010)
been described by Lal (1989), Blevins and Frye (1993)
and others. Conservation Technology Information Center
(CTIC) (1995) defined a range of convnetional tillage
systems included under CRM (Crop Residue
Management System) as follows:
No-tillage: The soil is left undisturbed from harvest to
planting except for plant nutrient application. “Any tillage
system that causes less than 25 % of row width
disturbance by planting equipment is considered as notillage system”. Weed control is primarily through
herbicides, but cultivation may be used for emergency
weed control.
This has benefited farmers through less cost, more
yield and more income with positive effects on soil health
and environmental quality. One major hurdle to
acceptance was changing the mindsets of all partners
concerned since the phrase “the more you till the more
the yield” was stubbornly adhered to and difficult to
overcome. This technology has been been tested and
now is presently being practiced over 2.0 million hectares
of India (RWC-CIMMYT, 2005).
Ridge-tillage: The soil in ridge-tillage also left
undisturbed from harvest to planting, except that planting
is completed in a seedbed prepared on ridges with
sweeps, disk openers, coulters or row cleaners. Residue
is left on the surface between ridges. Weed control may
be accomplished with herbicides and /or cultivation.
Mulch-tillage: The soil is disturbed prior to planting by
tillage tools such as chisels, field cultivators, disks,
sweeps or blades. Weed control is accomplished with
herbicides and / or cultivation.
Reduce-tillage: Any seedbed preparation system that
leave 15 to 30 % residue cover after planting or 500 to
1000 kg/ha of small grain residue equivalent throughout
the critical wind erosion period is considered a reducetillage system.
Conventional-tillage: Tillage method that leave less
than 15 % residue cover after planting, or less than 500
kg/ha of small grain equivalent throughout the critical
wind erosion period come under the category of
conventional-tillage systems.
Effect of conservation tillage on Soil Properties
One study found that converting from conventional
plowing to conservation tillage resulted in a 56 percent
increase in soil organic carbon over a ten year period (Lal
et al.,1998).While soil carbon content increases might be
slight in the first two to five years, large annual increases
occur in the next five to ten years, and depending on soil,
climate and management conditions, could continue to
build over a 25 to 50 year period.Conservation tillage
greatly influence the physical,chemical and biological
properties of soil ,which in turn affects the crop
production.
34
Agric. Sci. Res. J.
Soil Physical properties
Tillage practices greatly influence the soil physical
properties which inturn affects the soil structure. Rice and
wheat crops have contrasted soil physical requirements
like rice does best in a dispersive soft soil with an
abundant supply of water, while wheat needs a wellaggregated, aerated soil for optimum growth. Soil
physical properties and conservation tillage are
influenced by surface and internal drainage, nature and
amount of clay,climate, drainage, physiography,vehicular
traffic, soil and crop management systems. Because of
the variation in climate and soils, it should be no surprise
that contradicting data appear in the literature, particularly
regarding the relationships of tillage and cropping
systems to bulk density and compaction.
Soil structure and Soil aggregation
Soil structure refers to the size, shape and arrangement
of solids and voids, continuity of pores and voids, their
capacity to retain and transmit fluids, organic and
inorganic substances, and ability to support vigorous root
growth and development. Favorable soil structure and
high aggregate stability are important to improving soil
fertility, increasing agronomic productivity, enhancing
porosity and decreasing erodibility. Soil structure or
spatial heterogeneity dominates all the physical
properties of soil and hence, its functioning. Soil structure
is dynamic and in almost all the soils changes with time
or rainfall after tillage except in the coarsest of soils, it is
because of the structure that water and gases can move
readily through the soil and that aerobic life can occur
within the soil. Improved soil structure enhances nutrient
recycling, water availability and biodiversity while
reducing water and wind erosion, and improving surface
and ground water quality.
Processes and mechanisms involved in soil aggregation
are complex with intricate feedback mechanisms. Soil
aggregation can be improved by management practices
that decrease agro-ecosystem disturbances, improve soil
fertility, increase organic inputs, increase plant cover, and
decrease soil organic carbon decomposition rate.
Water stable aggregates in the upper few mm of the
soil layer may improve the germination and seedling
establishment by reducing crusting and erosion and by
allowing water and air to enter the soil. Better
aggregation (Lal et al., 1994) and improved pore size
distribution (Bhattacharyya et al., 2006a) was observed
by the adoption of zero tillage. The steady-state
infiltration rate and soil aggregation (>0.25 mm) were
higher under permanent beds and double zero tillage and
lower in the convnetional tillage system and also under
convnetional tillage, soil aggregation was static across
seasons, whereas it improved under double no-till and
permanent beds (Jat et al., 2009).Borresen (1997) found
that the aggregates became coarser when the amount of
straw residues on the soil surface was increased.
Bulk density, Compaction and Penetration resistance
Bulk density is a soil physical parameter used extensively
to quantify soil compactness. The bulk density varies with
management as well as with inherent soil qualities.
Because of dependence on inherent soil properties,
measurements of bulk density are of limited value as a
measure of the effect of management of soil
compactness when soils with different inherent
characteristics are compared. Penetration resistance
(MPa) of the soil can be regarded as a factor determining
the quality of its structure. Penetration resistance of soil
depends on its physical and mechanical properties.
Tillage increased bulk density and penetration resistance
of the soils significantly as compared to zero-tillage
(Carman,1997). In rice-wheat cropping system,
Bhattacharyya et al., (2006b) observed that soil bulk
density decreased significantly with conventional tillage at
0-15 and 15-30 cm soil depths and after both rice and
wheat crop. In another study, under rice-wheat system,
zero-tilled plots were more compact after rice harvest and
the levels of compaction reduced after wheat at both (015 and 15-30cm) soil depths. In the 0–15 cm soil depth,
soil bulk density determined after the rice crop was higher
in the zero tillage plots than the convnetional tillage plots
whereas it was not significantly different from
convnetional tillage plots after wheat harvest.The
significantly higher value of soil bulk density after rice
harvest under zero tillage plots in the surface soil layer
may be due to non-disturbance of the soil matrix, which
resulted in less total porosity compared to tilled plots
(Bhattacharyya et al., 2008). In general, bulk density in
the upper layer of no-tillage soils was increased, resulting
in a decrease in the amount of coarse pores, when
compared with the convnetional tillage and reduced
tillage soils and there was no change in resistance with
increasing soil depth under no-tillage contrasted with
lower resistance under ploughing in the upper soil zone
(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;
Singh and Kaur
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 drill and direct
seeding by zero –till drill) did differ markedly in respect of
bulk density of upper (0-15cm) as well as of lower (15 30cm) 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 tillage 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
3
subsurface (1.54 Mg/m ) under zero till condition in the
rotary puddled plots of rice and minimum in the surface
3
soil (1.42 Mg/m ) under conventional tillage conditions in
the direct seeding without puddling plots. In general, the
influence 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 and Panday
et al., 2008). 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.,
35
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 30-45cm, 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).
Soil hydraulic conductivity and infiltration
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 tillage as
compared to convnetional tillage was reported by
McGarry et al., (2000), apparently earthworm channels
and termite galleries, being the major contributers.
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
36
Agric. Sci. Res. J.
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 minutes 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). Thus, contrasting
results are available in the literature regarding soil
hydraulic conductivity and infiltration.
Soil aeration/air permeability
Aeration is important for both the agricultural and
environmental functions of soil. Plant roots and soil fauna
require oxygen, and aerobic microbes are important
decomposers. Air permeability is a measure of how
easily air convection occurs through soil in response to
pressure gradients. Pressure gradients can be generated
naturally by air turbulence above the soil surface, and this
can lead to air flows through the tilled layers of soils
especially when they contain pores larger than about 5
mm (Farrell et al., 1966; Kimball and Lemon, 1971). Air
flow will occur only if there is a continuous network of airfilled pores. Air permeability is the useful indicator of pore
connectivity. Air permeability decreases with increase in
soil bulk density in no tillage just beneath the depth of
tillage (Rasmussen, 1999).
Soil strength and stability
Strength and stability are necessary if soil is to retain its
structure against imposed stresses. These imposed
stresses may be natural such as raindrop impact, or may
be anthropogenic such as those imposed by vehicular
traffic. A complication with soil is that its strength must
not be too great otherwise; plant roots and other
organisms will not be able to penetrate. The term
‘strength’ is used to describe the level of stress (force per
unit area) that a soil can resist without undergoing
irreversible deformation. The term ‘stability’ is used (in
English) to describe the ability to retain a coherent
structure in the presence of free water.
Soil temperature
One 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
beneficial for crop production (Dao, 1993). If used as
mulch, the residue can modify soil temperature (Bhagat
and Acharya, 1988) and soil temperature is lowered by
the plant residues left on the soil surface in no tillage
(Rasmussen, 1999). Surface residues maintained under
zero tillage (ZT) systems moderate temperature (Blevins
and Frye, 1993). A 5-year field study on the rice–wheat
cropping system demonstrated that applying a
combination of rice straw and farmyard manure to wheat
improved soil structure and plant available water content
(Bhagat and Verma, 1991; Verma and Bhagat, 1992).
The soil temperature was recorded during grain filling
stage shown in table 3. In the month of March, lowest soil
temperature was recorded under happy seeder followed
by zero till, rotavator and conventional tillage plots. The
data also showed that soil temperature in the mid March
was high as compared to the end of March. However,
soil temperature from the first week of April till the harvest
0
was increased and crosses over to 40 C. The lower
temperature under the happy seeder and zero tillage
plots was due to the mulching effect of residue
(Meenakshi, 2010). Thus, soil temperature is modified by
the crop residues left on the surface.
Soil moisture content
Zero tillage achieved a 28% increase in plant available
soil water at sowing as compared to conventional tillage
and an associated increase of 1.2 t/ha/year wheat grain
(McGarry et al., 2000). More plant residues were left on
or near the soil surface no tillage which led to lower
evapotranspiration and higher content of soil water in the
upper (0-10cm) soil layer (Rasmussen, 1999). The plant
avilable water content was significantly higher with zero
than convnetional tillage in rice-wheat cropping system
(Bhattacharyya et al., 2006b and Bhattacharyya et al.,
2008). Surface residues maintained under zero tillage
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).
Soil erosion
Soil productivity factors that are usually diminished by soil
erosion include direct loss of soil fertility, loss of soil
organic matter, deterioration of soil structure, and
Singh and Kaur
37
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 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).
no-till conditions and had also been identified by others
(Blevins et al., 1993; Rhoton et al., 1993; Singh et al.,
1994). The organic matter stratification differs between
convnetional and no tillage soil, mainly due to the
remaining plant residue cover on the soil surface which
favours the accumulation of organic matter near the soil
surface (Tebrugge and During, 1999). The conversion
efficiency of residue carbon on soil organic carbon was
lower for plough till (8%) than for no-till (10%) (Duiker et
al., 1999). Higher soil organic carbon sequestration was
observed by adopting zero tillage (Dick et al., 1991 and
Panday et al., 2008).
The soil organic carbon after rice and wheat harvest in
the 0-15 cm soil depth were higher under zero tillage than
under conventional tillage, however, soil organic carbon
content in the 15–30 cm soil layer after 4 years of
cropping remained almost unchanged in both
convnetional and zero tillage (Bhattacharyya et al., 2008).
Soil Chemical properties
Soil organic matter content
Chemistry of soil, defined as the content and availability
of certain substances may also be modified as a result of
various ways and systems of tillage.
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).
Soil pH
One of the important factors determining soil fertility is
pH, which may however, be influenced strongly by
cultivation and crop residue management. Nutrients and
organic matter are accumulated near the soil surface
after no tillage and in the long run soil reaction (pH)
declined (Rasmussen, 1999). In study, Kumar and
Yadav (2005) observed slight decrease in the soil pH
than initial values in conventional tillage, Chinese seeder
and Pantnagar zero till drill. One possible way of
protecting soil from acidification is by returning the crop
residues to the soil (Miyazawa et al., 1993) and pH
increased significantly with crop residue application
(Karlen et al., 1994), thus, there are contrasting views
about soil pH.
Soil organic carbon content
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 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 longterm
Soil Biotic properties
Following the changes in physical properties of soil
(sometimes very short-lived), there also come changes in
its biological life. There are a number of indices
measuring the biological activity of soil; they equally
concern both microflora and microfauna. It is known
beyond any doubt that an increase in soil aeration, also
under the influence of tillage, leads in the first place to a
38
Agric. Sci. Res. J.
growth of the population of aerobes, which are
responsible for mineralisation of organic matter, thus
intensive tillage leads to lowering of soil humus content .
zero tillage (Kumar, 2008). However, the significantly
same grain, straw and biological yield was recorded with
zero tillage in standing stubbles after removal of loose
straw, coventional tillage with and without mulching
(Singh, 2010).
Soil Biota/Microbial biomass/Micro organisms
Activity of soil fauna is important in the formation of
organo-mineral complexes and aggregation, thus
enhancing and diversyfying 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 (0-5cm) 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
convnetional tillage. Increased earthworm activity in no-till
treatments was also reported by Tebrugge et al. (1999)
and Rasmussen (1999).
Effect of conservation tillage on rice and wheat yields
The direct seeded convnetional tillage plots had
statistically similar grain yield as the direct seeded zero
tillage plots, of rice and wheat, after 4 years of cropping
(Bhattacharyya et al., 2008), although about 6% wheat
yield decline under zero tillage was there. But the zero
tillage practice had lower cultivation costs and crops
under zero tillage could be sown earlier than convnetional
tillage (Singh et al., 2002); so zero tillage gets
preference. Researchers from both Pakistan and India
are reporting higher wheat yields following adoption of
zero-tillage in rice–wheat rotations in rice growing belt
(Gupta and Seth, 2007). Transplanting of rice gave the
highest total productivity of the rice-wheat system than
dry seeding method (Dhiman et al., 1998) and also
sowing of wheat by rotavator method (RT) gave the
highest total productivity , followed by zero-till drill
whereas
the productivity was the lowest with the
conventional method (Ram, et al., 2006). Methods of
seeding had significant influence on grain yield of rice.
The grain yield obtained with broadcast sprouted seed
-1
after puddling (51.8 q ha ) was statistically same with
-1
conventional tillage (51.8 q ha ) but significantly higher
than broadcast sprouted seed without puddling, drum
seeding after puddling, drum sowing without puddling and
CONCLUSIONS
The conservation tillage system is an ecological
approach to soil surface management and seedbed
preparation. It minimizes soil erosion risks, conserves soil
water, decreases fluctuations in soil temperature of the
surface layer, improves soil organic carbon content, and
enhances soil structure. Implemented as a science-based
technique,
conversion
from
conventional
to
conservational tillage system may increase soil organic
carbon, improve soil structure, and enhance soil quality
and its environmental regulatory capacity. Also, crop
residue is an important and a renewable resource.
Developing techniques for effective utilization of this vast
resource is a major challenge. Improper use of crop
residues (e.g. removal, burning or plowing under) can
accelerate erosion, deplete soil fertility, and pollute
environment through burning and eutrophication of
surface and contamination of groundwater. Residue
management may save energy, recycle nutrients,
enhance soil fertility, improve soil structure, sequester
carbon, and mitigate the greenhouse effect.
The effect of conservation tillage on soil properties can
be illustrated briefly as below:
1. Improved pore size distribution and better
aggregation this can be obtained by the adoption
of zero tillage. Thus, zero tillage plays an
important role in improving soil structure and soil
aggregation.
2. Surface residues maintained under zero tillage
system moderate moisture fluctuations and thus
reduce both evaporation and runoff and also
increase the infiltration by reducing surface
sealing and decreasing runoff velocity.
3. Contrasting effects of soil management
experiments in bulk density are common. They
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.
4. Contrasting results are available in the literature
regarding soil hydraulic conductivity and
infiltration.
5. Conversion from conventional to zero tillage,
reduced erosion and avoided surface sealing
because of crop residue cover on the surface and
higher aggregate stability under zero tillage
conditions
6. Soil temperature is modified by the crop residues
Singh and Kaur
left on the surface.
7. There are contrasting views about soil pH, it may
increase or decrease with adoption of zero
tillage.
8. Higher soil organic carbon sequestration was
observed by adopting zero tillage.
9. Increased organic matter in the top soil has been
observed by adopting zero tillage.
10. Increased no of beneficial soil fauna with zero till
have been reported relative to traditional tillage.
11. The yield of crop under zero tillage may me
equivalent or somewhat lower than convnetional
tillage, but zero tillage practice had lower
cultivation costs and crops under zero tillage
could be sown earlier than conventional tillage so
zero tillage gets preference.
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