Conservation Tillage for Sustainable Agricultural Productivity
Professor P. O. Aina
Department of Soil Science & Land Resource Management, Faculty of Agriculture, Obafemi
Awolowo University, Ile-Ife, Nigeria.
Abstract
A review of tillage systems applied in crop production shows that conservation tillage in its
many and varied forms holds promise for the sustainability of agricultural productivity and
the environment by reducing production costs, preserving soil quality, reducing herbicide
and weeding labor input costs and greenhouse gas emissions. Constraints to its universal
adoption are discussed, especially with respect to Nigeria’s highly diversified agroecological conditions, terrain, soils and predominant smallholder resource-poor farming
communities. Serious gaps in our knowledge (from the existing limited statistics) of the
ecological suitability of alternative conservation tillage systems and un-networked research
make generalizations from the available information about conservation tillage systems
tenuous at best. Although the adoption in Nigeria is low currently, projections indicate
largely unexplored potential for conservation tillage production system in the country. For
the development and adoption of appropriate conservation tillage production systems, the
future course for a tillage management zoning of the country, regionally coordinated systems
approach research networking, evolution of adaptable conservation-tillage-planting systems
model that is compatible with smallholder farm operations and crop and ecological diversity
is suggested.
1.
Introduction
Farming systems today have more obvious and detectable social, ecological, economic, and
environmental implications than ever before because of the growing concerns about
agricultural sustainability and the environment (Shrestha and Clements, 2003). Agricultural
sustainability implies an increasing trend in per capita productivity to meet the present needs
without jeopardizing the future potential. This demands appropriate methods of land
stewardship for the development of sustainable agricultural systems. An important aspect of
land stewardship is tillage, the agricultural preparation or manipulation of soil employed in
crop production. Soil tillage influences agricultural sustainability through its effects on soil
processes, soil properties, and crop growth. An important effect of soil tillage on
sustainability is through its impact on the environment e.g. soil degradation, water quality,
emission of greenhouse gases from soil-related processes, etc. As a subsystem of a cropproduction system, tillage can be used to achieve many agronomic objectives, including soil
conditioning (modification of soil structure to favor agronomic processes such as soil seed
contact, root proliferation, water infiltration, soil temperature control, etc.), weed/pest
suppression (direct termination or disruption of weed/pest life cycles), residue management
(movement, orientation or sizing of residues to minimize negative effects of crop/cover crop
residues and promote beneficial effects), incorporation/mixing (placement or redistribution of
substances such as fertilizers, manures, seeds, residues, sometimes from a less favorable
location to a more favorable spatial distribution), segregation (consolidation of rocks, root
crops, soil crumb sizes), land forming (changing the shape of the soil surface e.g. ridging,
27
roughening and furrowing). However, tillage may have negative impacts on soil and crop
production, when excessive or inappropriate. Among the disadvantages are land degradation,
compaction of soil below the depth of tillage (i.e., formation of a tillage pan), increased
susceptibility to water and wind erosion, accelerated decomposition of soil organic matter
(negative from a long term perspective), high energy cost of tillage operations, and labor and
temporal obligations. The impact of tillage depends on the combination of tillage operations
and their timing, that is the tillage system, to provide specific functions in given situations.
The ways in which these operations are implemented affect the physical and chemical
properties of the soil, which in turn affect plant growth and crop yield potential. Therefore,
the first step in making sustainable production management decisions is to understand the
practices associated with each tillage system. The tillage systems are described below.
2.
Tillage Systems
2.1
Conventional tillage
Conventional tillage is a tillage system using cultivation as the major means of seedbed
preparation and weed control. Conventional tillage is defined by the Conservation Tillage
Information Center in West Lafayette, Indiana, USA (CTIC, 2004) as any tillage and planting
system that leaves less than 15 percent residue cover after planting, or less than 560
kilograms per hectare of small grain residue equivalent throughout the critical wind erosion
period. It is based on mechanical soil manipulation involving a sequence of soil tillage, such
as moldboard ploughing followed by one or two harrowings, to produce a fine seedbed and
also the removal of most of the plant residue from the previous crop. It embraces primary
cultivation based on ploughing or soil inversion, secondary cultivation using discs, and
tertiary working by cultivators and harrows, drawn by animals, tractors or any mechanically
powered devices. Weeds are controlled by herbicides and cultivation. The mechanical soil
disturbance involved increases the risk of erosion and dust emission (Baker et al, 2005) (Plate
1).
2.2
Intensive tillage
Intensive tillage systems involve often multiple operations with implements such as a mold
board, disk, and/or chisel plow. Then a finisher with a harrow, rolling basket, and cutter can
be used to prepare the seed bed. Intensive tillage systems leave less than 15% crop
residue cover less than 560 kg/ha of small grain residue. These types of tillage systems are
often referred to as conventional tillage systems but as reduced and conservation tillage
systems have been more widely adopted, it is often not appropriate to refer to this type of
system as conventional.
2.3
Conservation tillage
Conservation tillage (CT) is defined by the Conservation Tillage Information Center (CTIC,
2004) as any tillage and planting system that covers 30 percent or more of the soil surface
with crop residue after planting, to reduce soil erosion by water. Throughout much of the US,
the definition of conservation tillage has been maintenance of a minimum of 30% soil cover
with crop residues after planting. Other definitions have arisen for special circumstances such
-1
as 1,120 kg ha of flat, small grain residue equivalents on the soil surface in areas with wind
erosion potential. In Australia, conservation tillage refers to systems that reduce tillage
operations, but not necessarily preserve stubble or residues due to problems with establishing
crops in high stubble loads resulting from slow residue breakdown during dry summers
28
(Lyon et al., 2004). There are many variations of conservation tillage systems covering a
broad spectrum of farming methods primarily aimed at based on reducing soil disturbance,
conserving and managing crop residue to reduce erosion. They include no-till, ridge-till,
mulch-till or strip-till.
2.4
Other tillage systems
Tillage systems that leave less than 30 percent crop residue after planting are not classified as
conservation tillage. However, these systems may meet erosion control goals with or without
other supporting conservation practices, such as strip cropping, contouring, terracing, etc.
2.4.1 Reduced tillage
Reduced tillage systems leave between 15 and 30% residue cover on the soil or 560 to
1100 kg/ha of small grain residue during the critical erosion period. This may involve the use
of a chisel plow, field cultivators, or other implements.
2.4.2 Tillage rotation
Similar to crop rotation, tillage rotation indicates the use of rotation of different tillage
systems. For residue management, rotating tillage systems to coincide with crop rotations is
an option. For example, a no-till system following soybeans and a chisel or disk system
following corn can provide adequate erosion control after soybeans and allows for some
tillage in the less fragile and more abundant corn residue. Rotating tillage systems, however,
slows the development of improved soil structure and may require investment in more
equipment.
2.4.3 Traditional tillage
Farmers in the tropics employ several traditional methods of seedbed preparation. Farmers
make mounds or ridges with manually-operated hoes or with equipment (usually moldboard
plough) drawn by draught animals to dig and turn the soil over, with an effort placed to break
the clods and leave a fine tilth. When animal power is used farmers make several runs with
the mouldboard plough, while they remain unaware of other equipment like harrows and
ridgers. On poorly drained soils, large mounds often 3-4m in conference and about 1m high
are constructed. Various crops are grown on top of the mounds and raised beds. Weeds and
bush regrowth are slashed manually and left on the mounds as mulch or burnt in situ. The
practice of mixed cropping provides a continuous ground cover that protects the soil against
erosion and improves temperature and moisture regime. The depressions or furrows help to
conserve water and minimize risks of drought.
2.5
Comparison of tillage systems
Typical advantages and disadvantages of different tillage systems are shown in Table 1. This
information is useful in determining the suitability of tillage systems or combinations of
systems for various situations. Of the systems compared in the Table, the moldboard plow
system has the greatest fuel and labor requirements for tilling and planting corn and soybeans
(Gallaher and Ferrer, 1987). The most important advantage of conservation tillage is
significantly less soil erosion. The growing concerns about agricultural sustainability and the
environment require reduction of soil erosion. Conservation tillage effectively and
economically reduces soil erosion and the resulting sedimentation, a major water pollutant.
29
Fuel and labor requirements are also reduced with conservation tillage. Compared to the
commonly used disk system, no-till saves about 1-1/2 gal/ac in fuel and 20 minutes of
labor/ac. Labor savings allow a larger area to be farmed without additional equipment or
help. Even if increased acreage is not anticipated, more timely planting may result in greater
yields. In addition, costs for tractors, tillage equipment and maintenance will be less with
fewer tillage operations. Conservation tillage systems therefore represent alternatives at a
time when economics require flexibility in crop production.
3.
Conservation Tillage Systems
Conservation tillage principles and practices have evolved over the past 50 years which focus
upon managing crop residues. Crop residue management is defined by the Conservation
Tillage Information Center (CTIC, 2004) as a year-round system beginning with the selection
of crops that produce sufficient quantities of residue and may include the use of cover crops
after low residue producing crops. Crop residue management includes all field operations that
affect residue amounts, orientation, and distribution throughout the period requiring
protection. Most conservation tillage systems are based on one of the following reduced soil
disturbance planting systems: no-till, ridge-till, mulch-till, or strip-till.
3.1
No-till or Zero-till
The CTIC defines no-till as a system in which the soil is left undisturbed from harvest to
planting except for nutrient injection. Tillage is essentially eliminated with a no-till system.
The only tillage that is used is the soil disturbance in a narrow slot created by coulters or seed
openers (Conservation Tillage Systems and Management, 2000). Planting or drilling is
accomplished in a narrow seedbed or slot created by coulters, row cleaners, disk openers, inrow chisels, or roto-tillers. By disturbing only a narrow slot in the residue-covered soil,
excellent erosion control is achieved (Plate 2). Compared to other tillage systems, no-till also
minimizes fuel and labor requirements. Weed control is accomplished primarily with one or
two properly timed surface applications of pre-emergence or post-emergence herbicides.
Recent advancements in herbicides make weed control with no-till easier than it used to be.
Early preplant applications, longer-lasting residual herbicides, and a wide variety of
postemerge products are helping assure weed control success with no-till.
No-till planting is well suited to many soils but limited application in poorly drained soils.
Residue, when uniformly spread, increases water infiltration and reduces soil moisture
evaporation. No-till has carbon sequestration potential through storage of soil organic
matter in the soil of crop fields. By eliminating tillage, crop residues decompose where they
lie, and growing crops field carbon loss can be slowed and eventually reversed.
Conservation of soil moisture is one of the major advantages of no-till crop production
systems. In a long-term tillage study, higher soil moisture under no-till corn production was
observed as compared with that under conventional tillage throughout the growing season.
Significantly less evaporation occurred under no-till early in the growing season. This
conservation of soil water may carry the no-till crop through short drought periods without
severe moisture stresses developing in the plants. However, the extra water conserved under
no-till can occasionally be detrimental under conditions in which excessive soil water
contributes to denitrification losses. Soil compaction in no-tillage soils was not found to be a
problem. Saturated hydraulic conductivity measurements suggest better water movement in
30
no-tillage compared with conventional tillage. After 10 years of continuous no-till corn
production, no deterioration of soil physical properties was observed. The most obvious
chemical change was the rapid acidification of the soil surface when high nitrogen fertilizer
rates were used. Associated with reduced soil pH were increased levels of exchangeable
aluminum and manganese. Exchangeable calcium was significantly lower for no-till at all soil
depths and all nitrogen fertilizer rates compared with conventional tillage. Potassium was
concentrated in the top 5-centimeter soil layer under no-till and decreased with depth.
Exchangeable magnesium in the 0-to-5-centimeter soil depth declined with increased
nitrogen fertilizer and was lower in no-till than in conventional tillage. Organic matter was
twice as high in the 0-to-5-centimeter soil depth compared with conventional tillage systems.
This modified soil environment affects chemical reactions and the distribution and activity of
microbes. It also has a significant effect on the fate of surface-applied nitrogen fertilizer.
3.2
Ridge-till
Ridge-till is a reduced disturbance planting system in which crops are planted and grown on
ridges formed during the previous growing season and by shallow, in-season cultivation
equipment (Plate 3). In ridge-till, the soil is also left undisturbed from harvest to planting
except for possible fertilizer injection. The ridge beds are established and maintained through
the use of specialized cultivators and planters designed to work in heavy crop residues.
Tillage is generally very shallow, disturbing only the ridge tops. 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. A band application of herbicide behind the planter
provides weed control in the row. Crop cultivation also controls weeds between the rows and
rebuilds the ridges for the following year. Weed control is accomplished with herbicides
and/or cultivation.
Ridge tillage is primarily intended for the production of agronomic row crops like corn,
soybeans, cotton, sorghum, and sunflower. Additionally, when done on contour, the ridges
themselves largely supply the need for larger soil conservation structures like terraces on
many fields. Level or gently sloping fields, especially those with poorly drained soils, are
well suited to ridge systems. A ridge system is an excellent choice for soils that are often too
wet. Ridges in the ridge-till system work quite well to provide drainage on poorly drained
soils. Ridge-till reduces erosion by leaving the soil covered with residue until planting. After
planting, 30%-50% residue may be left, but it is not uniformly distributed. Residue-covered
areas between the rows alternate with residue-free strips in the row area. For erosion control,
the ridges should be 7.5cm-12.5cm higher than the furrows after planting and that ridges be
shaped to shed water to the furrow. For the most effective erosion control, orient ridges
approximately on the contour.
Proper ridge shape and annual maintenance are keys to a successful ridge system. Care is
taken not to damage or destroy the ridges by wheel traffic, particularly during harvest. Ridge
tillage is characterized by the maintenance of permanent or semi-permanent ridge beds across
the entire field. Ridges are maintained year-to-year with a cultivator, making ridge-till well
suited to continuous row crops. Two cultivations are generally required: the first loosens soil
and controls weeds, the second provides additional weed control and rebuilds the ridges. For
ease of planting, the ridges should be rounded or flat topped, and 15cm-20cm tall after
cultivation. In a ridge-plant system, row cleaning devices on the planter move a small amount
of soil, residue and weed seed off the ridge top. Ridge-cleaning attachments include sweeps,
disk furrowers or horizontal disks.
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3.3
Zone or Strip Till
Zone or Strip tillage refers to any system in which a seedbed strip is established through a
cover crop or crop residue, while still leaving a wide, untilled inter-row area (Plate 3). The
Conservation Technology Information Center's definition of no-till includes strip tillage,
provided less than one-third of the total row area is tilled. Strip tillage is similar to no-tillage
except that a narrow 12.5−13.5cm wide seedbed is established for planting, compared to notill in which a mere slot is opened into the soil for planting. The narrow seedbed in zone
tillage is usually created by one or more gangs of fluted coulters mounted on the front of the
planter. The loosening of the soil through zone tillage can also make for a more desirable
seedling environment. Strip tillage operation removes the residue from the row area and
planting with strip-till takes place in the residue free strips.
Zone tillage appears to be one of the key technologies that make killed mulch and living
mulch systems work. In some instances, the tilled zone may need to be fairly wide. It
typically needs to be managed with additional cultivation, hoeing, or traditional mulching
during the cropping season.
While many variations of strip-till have evolved, the most widely practiced strip-till systems
perform the tillage in the fall and usually place nutrients in the tilled zone at the same time. A
subsoiler, fertilizer knife, or multiple coulters perform the tillage allowing fertilizers to be
injected through the knife or behind the coulters. Often, some type of soil mounding disks,
such as anhydrous knife slot closing disks, build up a slight ridge in the tilled zone to aid in
soil drainage. In drilled soybean residue, producers equip their strip tillage implement with
row markers to properly lay out the cleanly tilled strips for planting next spring.
3.4
Mulch-till
Mulch-till is a category that includes all conservation tillage practices other than no-till and
ridge-till. Mulch tillage has already been described as a tillage system in which a significant
portion of crop residue is left on the soil surface to reduce erosion. It is usually accomplished
by substituting chisel plows, sweep cultivators, or disk harrows for the moldboard plow or
disk plow in primary tillage. This change in implements is attractive because residues are not
buried deep in the soil, and good aerobic decomposition is thus encouraged. Weed control is
accomplished with herbicides and/or cultivation.
Two tillage practices that fall into this category are zone-till and strip-till. Both of these
tillage practices involve tilling a strip into which seed and fertilizer are placed. Although
these are popular terms in some areas, they are not official survey categories because they are
considered modifications of no-till, mulch-till or "other tillage types." Less than 25% row
width disturbance is considered no-till. More than 25% row width disturbance would be
considered mulch-till or "other tillage type," depending on the amount of residue left after
planting.
4.
Why Conservation Tillage?
The importance of minimising soil erosion and conserving soil resources first came to
national attention in the US during the ‘Dust Bowl’ period in the early 1930s, when the
combination of intensive tillage, drought, crop failure and wind-driven erosion of millions of
32
acres of farmland occurred in the Great Plains region of the US (Coughenour and Chamala
2000; Chauhan et al. 2006). In the decades following, several reduced soil disturbance or
conservation tillage production systems emerged in the mid-west and the south-east US, to
address soil loss concerns. Similarly, yet somewhat later, recognition of the importance of
controlling soil erosion losses has also been a major driver for the development of
conservation tillage systems in Australia (Coughenour and Chamala 2000). Conservation
tillage, any tillage system that maintains at least 30% of the soil surface covered by residue,
was practised in 1995 on about 40 × 10 6 ha or 35.5% of planted area in USA.
Because of the important role that surface cover or roughness has in mitigating soil erosion
losses, the concept of conservation tillage during this time eventually became linked with the
specific management goal of maintaining at least 30% crop residue on the soil surface after
planting. This has been the primary characteristic used in USDA definitions of conservation
tillage. Reduced soil disturbance, however, is a key element in these definitions.
Research on no-till soils generally shows an increase in N-containing trace emissions upon
conversion from conventional tillage practices. This increase has been attributed to an
increase in soil bulk density under no-till (Six et al., 2004). The researchers suggest that the
positive effects (mitigation) on N containing trace gas emission may take up to 20 years of
continuous no-till management to realize.
4.1 Benefits of conservation tillage
A number of well documented benefits (Beck 1990; Freebairn et al. 1993, Reicosky 1997,
Baker et al. 2005) has been associated with the practices of conservation tillage production
systems which aim to maintain at least 30% of the soil surface covered by residue and reduce
primary, intercrop tillage operations such as ploughing, disking, ripping and chiseling, using
fewer tractor operations. They include the following:
1. Reduces labor, saves time
2. Saves fuel and improves farm profitability
3. Reduces machinery wear
4. Improves soil tilth
5. Increases organic matter and soil biological diversity
6. Traps soil moisture to improve water availability and water use efficiency
7. Reduces soil erosion
8. Improves water quality
9. Improves wildlife habitat
10. Improves water and air quality
11. Sequesters carbon in soil
4.2
Adoption of conservation tillage
The collective advantages of conservation tillage correspond to widespread adoption. Three
important factors have driven the increase in interest in conservation tillage options. These
include the goals of 1) reducing production costs, 2) preserving soil quality, and 3) reducing
herbicide and weeding labor input costs. Recent global estimates of 72-million ha were under
33
conservation tillage during 2001 – 2002 (Derpsch, 2005). This estimate includes about 50%
of the cropland in Brazil and Argentina, 45% in Australia, and 20% in the US. Conservation
tillage was used on about 38%, 109,000,000 acres (440,000 km2), of all US cropland,
293,000,000 acres (1,190,000 km2) planted as of 2004 according to the USDA.
Rapid diffusion of conservation tillage has been called the latest revolution in American
agriculture. Predictions of future trends in use of the technology are also optimistic. In part
due to its success in North America, the technology has also found its way to such places as
Australia, South America and countries of the former Soviet Union. The successful diffusion
of this technology is a result of the efforts of producers, government personnel, agricultural
engineers, members of industry associations, soil scientists and machinery manufacturers. A
number of factors create challenges for the universal adoption of conservation tillage,
especially slow in the tropical environment, such that in some cases, there are still production
disadvantages and lower yields, compared to conventional tillage.
4.3
Constraints to the adoption of conservation tillage practices
Factors for non adoption of conservation tillage include climate, soil, levels of crop residue,
(mixed) cropping systems to name a few. Among the disadvantages are more difficult weed
control, specific machinery and cropping systems requirements, and soil specificity. For
example each crop has specific soil preparation requirements (soil temperature, alleopathic
response, for example) and irrigation needs that create challenges for the universal adoption
of conservation tillage. One of the main obstacles to implementing conservation tillage is
furrow or surface irrigation. Crop residues that build up under conservation tillage can cause
blockage impeding the progress of irrigation. For this reason, maintaining furrows to supply
water is seen as an impediment to the adoption of conservation tillage and cover cropping
practices unless measures are taken to allow efficient irrigation, or unless water delivery
systems are changed to subsurface drip (SDI) or low pressure overhead sprinklers. Moreover,
the increased need for herbicides to control weeds in conventional tillage under furrow
irrigation is potentially an environmental and economic issue for farmers. Reasons of nonadoption of conservation tillage system are summarized as follow:
•
•
•
•
•
•
•
5.
Lack of information on conservation tillage
No farms around practicing conservation tillage could serve as
demonstration/example
Extensionists know very little or nothing about the system
Costs implied by changing the tillage systems
Lack of access to inputs and credits (for purchase of conservation tillage implements)
Risk avoidance (fear of failure or wrong application of new technique in the absence
of guidance phase)
Opportunity costs of crop residues
Nigeria Perspective
Nigeria is located in West Africa, about 10 degrees north of the equator, bounded to the south
by approximately 800 kilometers of the Atlantic Ocean (Figure 1). It occupies an area of
923,800 square kilometers. About 45% of this land area is arable and only about 42% of the
arable land is presently cultivated. Nigeria’s population is estimated at about 150 million,
making Nigeria the most populous country in Africa and the eighth most populous in the
34
world. Approximately one-third of the population live in urban areas while rural areas
account for the remaining two-thirds.
Nigeria is endowed with a wide diversity of climate, vegetation, geography, terrain and soils.
In an almost east-west successive belt, the climate varies northwards from a humid, semi-hot,
equatorial climatic region in the south through wet sub-humid regions and dry sub-humid
regions to the semi-arid and arid regions in the north.
The vegetation varies northwards from mangrove on the coast through the rain forest zone to
desert in the far north. As expected from the extensive land area and geographical location,
Nigeria has a highly diversified agro-ecological condition as indicated in Box 1. This highly
diversified agro-ecological condition makes possible the production of a wide range of
agricultural products and agricultural systems. Agricultural systems which vary among farms
depending on the available resources and constraints, geography and climate of the region,
and the philosophy and culture of the farmer are subsistence agriculture, small-scale farming,
resources-poor farmers, and landless peasants.
The major soils found in the various agroecological zones are highly weathered, acid, coarsetextured, erodible, and are low in organic matter and chemical fertility and aggregates of such
soils are weak, they lose productivity fast and do not retain adequate water and nutrients for
sustainable production (Lal, 1979, Aina, 1979b). These characteristics imply that even with
the best of soil fertility amendments, soil physical conditions must be managed to achieve
sustainable crop production. Agricultural systems are intensively managed and Nigeria’s
warm temperatures and humid environment make an ideal environment for decomposers. For
this reason, Nigeria agriculture soils are relatively carbon poor in comparison to temperate
soils, on average less than 1% soil carbon (Figure 2) compared to 2 to 4 % in temperate soils
(Alabi and Uponi, 2010). Soil carbon, which typically constitutes about half of soil organic
matter, is closely linked to many desirable soil physical, chemical, and biological properties
that are associated with enhanced soil productivity and quality (Reicosky, 1996; Ismail et al.,
1994).
Soil degradation is widespread (Lal, 1988) and constitutes a major economic and ecological
constraint in Nigeria. Soil degradation has been linked with poverty and population
explosion, especially in Africa (Hartemink, 2005). Some forms of soil degradation are more
prominent in one or more zones than others, all forms of soil degradation (Scherr and Yadav,
1996) can be found in Nigeria. Soil erosion remains the major source of land degradation,
water erosion in the humid and subhumid regions (Aina et al, 1977, Oyedele and Aina, 1989
and wind erosion in the dry semi arid and arid regions (Adeoye and Mohamed-Saleem,
1990).
Other forms of soil degradation as enumerated by Lal, (1988) and Scherr and Yadav, (1996)
include:
Humid and Sub Humid Zones
High subsistence agricultural use of the land
Soils of low fertility and low yields
Soil degradation due to fertility depletion, accelerated erosion, structural
35
deterioration & reduction in soil organic matter
Arid and Semi-Arid Zones
Risks of desertification due to degradation and aridization of soil and environment
Perpetual drought stress
Nutrient deficiency and soils of low fertility
Soil compaction
Low carrying capacity of land
Steep lands
Accelerated soil erosion.
mass movement and land slides
Shallow soils of low fertility
Difficulties of mechanizing farm operations
Low carrying capacity and low yields
Wet lands
Perpetual wetness of soil and high water table
Failure of certain crops
In general, Nigeria’s agricultural system is characterized by peasant nature of the production
system with low input technology and low productivity (Eswaran et al., 1997), poor response
to technology adoption strategies, small-holder, subsistence and rain fed, shifting cultivation
and rotational bush or grass fallowing, and rudimentary crop husbandry methods.
Nigeria's soils are rated from low to medium in productivity (Opara-Nadi, 1990; Eswaran, et
al 1997). However, the Food and Agriculture Organization of the United Nations (FAO,
2001) concluded that most of the country's soils would have medium to good productivity if
this resource were managed properly. Because demand for output from agricultural
ecosystems is greater now than ever before, and it is rapidly increasing due to high
demographic pressure, no-input or even low-input agriculture is a non-solution (Sanchez and
Salinas, 1981; Lal, 1990). On account of the low productivity of the major soils, one may
assume it logical to encourage high-input farming. It is aimed at the elimination of soil
constraints by applications of high doses of fertilizers and soil amendments to make the soil
fit for growing high yielding and high demanding crop varieties. But high-input technologies
put small farmers under a high degree of control of commercial delivery systems of
production inputs. Where soil and water constraints are not easily overcome at low cost, the
applicability of high-input technologies diminishes as in the case of the marginal soils of the
36
tropics (Sanchez & Salinas, 1981). In addition, an attempt to eliminate all soil constraint in a
multi stress soil will mean a too strong intervention in the physics, chemistry and biology of
the soil, which may lead to the deterioration of soil productivity. Thus by small farming
standards, high-input technology is environmentally unsound, economically unfeasible, and
socially undesirable. As small farmers do not possess the needed power, ability or
opportunity to take the necessary counter-measures whenever the situation demands
correction, their farming systems will never become self-contained. Adoption of conservation
tillage practices in Nigeria production systems may, in principle, be an appropriate viable
means for improving profitability, reducing energy use and improving soil quality (FAO,
2001; African Conservation Tillage (ACT) Network, 2002; Oni, 2009).
5.1
What is an appropriate tillage system?
There is no one blueprint of a universally applicable sustainable tillage system. Appropriate
tillage practices are those that avoid the degradation of soil properties but maintain crop
yields as well as ecosystem stability. They are soil-and-crop-specific and their adaptation is
governed by both biophysical and socio-economic factors. In addition to increasing crop
yields, tillage methods must also facilitate soil and water conservation, improve root system
development, maintain a favorable level of soil organic matter content, and reverse
degradation in the soil's life-support processes. Conservation tillage provides the best
opportunity for halting degradation and for restoring and improving soil productivity. It has
become an important management tool in sustainable crop production systems throughout the
world. Though conservation tillage crop production practices have been developed over the
past several decades primarily for erosion control in parts of the US, recent concerns
regarding the need to sustain soil quality and profitability, as well as potential global climate
change have reemphasized the importance of conservation tillage and how it might be
implemented on a broader scale to help reduce soil carbon losses and thereby sustain soil
quality and agricultural productivity (Lal, 1998; Horwath, et al., 2002).
The choice of the appropriate tillage system and its profitability is influenced by a range of
factors:
Soil Factor:
Climatic Factors:
Relief (slope)
Rainfall amount and distribution
Erodibility
Water balance
Rooting depth
Length of growing season
Texture and structure
Temperature (ambient and soil)
Organic matter content
Length of rainless period
Mineralogy
Erosivity
Crop factor:
Socioeconomic Factor:
Growing duration
Farm size
37
Rooting characteristics
Land tenure system
Water requirements
Credit availability
Seed
Availability of Power source
Education
Family structure & composition
Role of women
Government policies
Objectives & priorities
Conservation tillage requires a special set of appropriate cultural practices that may be
different from those required for conventional tillage system. That is, there is a need to
develop an appropriate package of cultural practices for a range of soils and agro-ecological
environments for the different conservation tillage systems to be effective. Some of the
cultural practices specifically developed to enhance the effectiveness of conservation tillage
include live mulch farming, use of cover crops and planted fallows, rotational and multiple
cropping, agroforestry and alley cropping, and soil inversion or deep plowing. The ecological
limits for the applicability of these components or sub-systems differ widely. Some crops and
varieties are more suited to conservation tillage than others, so also are the rates, time, mode
and type of fertilizers and other amendments, measures for pest control. It also requires
different seeding equipment and farm machinery to manage the uneven and trashy surface.
Mulching is a key technique in conservation tillage, so cultural practices that ensure the
availability of residue mulch are compatible. Vehicular traffic must be so used to reduce the
risks of soil compaction (Ohu and Folorunso, 1989: Onwualu and Anazodo,1989; Aina,
1994).
From the review of Aina et al, 1991 and Junge et al. (2008) on soil conservation in Nigeria,
substantial work has been carried out to develop technologies that can reverse or prevent land
degradation and sustain productivity. Among the technologies which have been tested are:








Mulching
Cover cropping
Intercropping
Alley cropping
Ridging or Tied ridging
Conservation tillage
Planted fallows
Natural Fallows
Several studies in Nigeria have shown that no-tillage system with crop residue mulch can (i)
maintain productivity of upland soils by reducing erosion (Lal, 1981, 1984; Aina 1988), (ii)
maintain a favourable soil temperature (Hulugalle et al, 1985; Lal, 1986), (iii) improve water
retention capacity (Aina, 1979a; Opara-Nadi, 1990; Opara-Nadi and Lal 1987, 1993), (iv)
improve water use efficiency (Osuji 1984, Osuji et al, 1980; Ojeniyi and Adekayode, 1999.)
and (v) increase nutrient efficiency (Lal, 1979, Hulugalle and Maurya, 1991; Olaoye, 2002).
No-tillage has proven to be an attractive alternative for maize (Zea mays L.) and other row
crops on coarse-textured soils in the humid' and subhumid tropics while in the semi-arid
38
region with fine textured soils, some type of conventional tillage system of mechanical
seedbed preparation (plowing and harrowing) is necessary. The frequency and type of
mechanical operation desired depends on soil characteristics and the crops to be grown. Lal
(1985a) proposed a tentative tillage guide (as shown in Figure 3) for systematic assessment of
the applicability of tillage and no-tillage practices for different soils in the tropics using a
parametric rating system derived from soil and crop climatic properties including erosivity,
erodibility, soil loss tolerance, compaction, soil temperature regime, available water holding
capacity, cation exchange capacity and soil organic matter content as well as quantity of crop
residue on the soil surface at seeding. Separate rating systems are suggested for rice and for
tropical root crops.
6.
Discussion
A crop production system adopted in farms today has more obvious and detectable social,
ecological, economic, and environmental implications than ever before because of the
increasing need to attain agricultural sustainability which is particularly urgent in several
tropical eco-regions and soils of low-carrying capacity in the tropics. This demands that
producers farm in more productive and environmentally sound, ethical, and socially
acceptable manner. In the context of the Symposium theme, the various aspects of the
adoption of tillage practices for sustainable and productive agriculture goes far beyond basic
agronomy. For example, its consideration should include crop yields, weed population
dynamics, soil dynamics, irrigation management, economics, and social and environmental
aspects. In its many and varied forms, conservation tillage production system seems to hold
promise for farming and have the potential to significantly transform major sectors of Nigeria
agriculture in the future, as it cuts operation costs, maintains crop yields, reduces the
likelihood of dust and greenhouse gas emissions, reduces weed pressure and promotes land
stewardship. While conservation tillage can reduce soil erosion, it may increase risks of water
pollution through increased use of pesticides, fertilizer and other agricultural chemicals. In
contrast, conventional till systems may enhance risks of soil erosion, increase rates of
mineralization of soil organic matter and accentuate emission of greenhouse gases from soilrelated processes.
The effectiveness of conservation tillage on soil and water conservation and resource
management is greatly enhanced by adopting a systems approach, which views tillage as an
integral part of a whole system. The efforts of a multi-disciplinary team (comprising soil
scientists, agricultural engineers, agronomists, economists and social scientists) are needed to
develop site-specific tillage methods to achieve both short- and long-term goals of
agricultural sustainability.
Although, national tillage survey and statistics on different forms of conservation tillage in
the different ecosystems of Nigeria are scarce or nonexistent (Aina et al 1992.), estimates of
the use of conservation tillage in Nigeria are quite low currently, projections indicate largely
unexplored potential for conservation tillage in the country (Lal, 1985a, 1985b; Lal, 2001).
Selecting the most appropriate conservation tillage system for a particular soil and cropping
situation will require matching the operations to site-specific knowledge of crop sequence,
topography, soil type, drainage, and weather conditions. Equipment innovations, improved
pest management strategies (for choice of appropriate herbicides, herbicide-tolerant crops),
better understanding of the impact of conservation tillage on water-quality, especially as it is
related to use of agricultural chemicals and widespread farmer and researcher experience will
all contribute to the success of conservation tillage system. These requirements for
appropriate technology call for cooperation in research and in the establishment of data banks
39
operating on a unified information system, the eminence of education, training, and extension
to farmers.
7.
Conclusion and the way forward
In conclusion it is noted that conservation tillage production system seems to hold promise
for farming and have the potential to significantly transform Nigeria agriculture in the future
into a sustainable and productive endeavour. However, efforts towards adoption of
conservation tillage practice in Nigeria need to be put in place. A wide variety of factors have
worked against research and extension efforts for the adoption, and low productive traditional
practice has continued to persist and dominate. For progress to be attained, the definition of
the path to be followed can only be based on the limited local studies and the wide range of
literature items cited. The successful diffusion of this technology will be as a result of the
efforts of producers, government personnel, agricultural engineers, members of industry
associations, soil scientists and machinery manufacturers.
The appropriate approach can therefore be defined and subscribed as one to include the
following components:
i.
Establish tillage management regions for the country, based on climate, adapted crops
and cropping systems.
ii.
A systems approach to multi-disciplinary and multi-sector tillage research network
which captures environmental protection, soil management techniques, agro-forestry
practices and socioeconomic and other concerns of end-users, that is, smallholder
farmers.
iii.
Adaptable model of conservation-tillage-planting systems that is compatible with
smallholder farm operations, a broad range of crop production systems and crop
diversity across tillage management regions
iv.
Farmer-centered, aggressive, on-farm, participatory methodologies in demonstration
and practice as well as publicity for sensitization, with all parties (researchers,
extensionists, farmers, support service providers, government and nongovernment
operators) applying their appropriate and adequate roles.
Identify suitable equipment and promote the same nationally and regionally while
merging resources and eliminating duplication of efforts within and between regions.
Applied field testing with farmers as more research findings are made, especially to
quantify the real gains of the use of various equipment while accommodating the
natural and other development trends and narrowing the gap between research & endusers
Formal networking, collaboration and co-ordination backed by training, support for
equipment supply, including simplification for local manufacture and other support.
v.
vi.
vii.
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44
Table 1. Comparison of selected tillage systems and typical field operations
System
Moldboard
plow
Typical field operations
Fall or spring plow; one or
two spring diskings or field
cultivations; plant; cultivate.
Major advantages
Suited for poorly drained
soils.
Excellent
incorporation. Well-tilled
seedbed.
Chisel plow
Fall chisel; one or two
spring diskings or field
cultivations; plant; cultivate.
Disk
Fall or spring disk; spring
disk and/or field cultivate;
plant; cultivate.
Ridge-till
Chop stalks (on furrow
irrigation); plant on ridges;
cultivate for weed control
and to rebuild ridges.
Strip-till
Fall strip-till; spray; plant on
cleared strips; postemergent
spray as needed.
Less erosion than from
cleanly tilled systems
and less wind erosion
than fall plow or fall disk
because of rough surface.
Well adapted to poorly
drained soils. Good to
excellent incorporation.
Less erosion than from
cleanly tilled systems.
Well adapted for lighter
to medium textured,
well-drained soils. Good
to
excellent
incorporation.
Excellent erosion control
if on contour. Well
adapted to wide range of
soils.
Excellent
for
furrow irrigation. Ridges
warm up and dry out
quickly. Low fuel and
labor costs.
Clears residue from row
area to allow preplant
soil warming and drying.
Injection of nutrients
directly into row area.
Well suited for poorly
drained soils.
No-till
Spray;
plant
into
undisturbed
surface;
postemergent
spray
as
needed.
Maximum
erosion
control. Soil moisture
conservation. Minimum
fuel and labor costs.
45
Major disadvantages
Major soil erosion.
High soil moisture
loss.
Timeliness
considerations. Highest
fuel and labor costs.
Little erosion control.
High soil moisture
loss. Medium to high
labor
and
fuel
requirements.
Little erosion control.
High soil moisture
loss.
No
incorporation.
Narrow row soybeans
and small grains not
well suited. No forage
crops.
Machinery
modifications required.
Cost
of
preplant
operation. Strips may
dry too much, crust, or
erode without residue.
Not suited for drilled
crops.
Potential for
nitrogen
fertilizer
losses.
No
incorporation.
Increased dependence
on herbicides. Some
limitations with poorly
drained
soils,
especially with heavy
residue. Slow soil
warming.
Plate 1: Dust emission during conventional tillage operations
Plate 2: No-till leaves the maximum crop residue for soil protection
Plate 3: Ridge-till system with crops planted on ridges
46
Plate 4: Strip tillage removes crop residue from only the row area
Mauritania
Mali
Senegal
Niger
Chad
Burkina Faso
Guinea
Liberia Ghana
Ivory Coast
1000
0
Nigeria
Cam eroon
1000
2000 Kilometers
Figure 1: Map of Sub-Saharan Region Showing the Location of Nigeria
47
Figure 2: Organic carbon distribution in Nigeria soils (Alabi and Uponi, 2010)
Figure 3: Tillage systems and conservation objectives for the tropics
(Lal, 1985a)
48