A short introduction to tillage.
Plants require an environment in which nutrients, water and oxygen are available for their development, growth and reproduction. Virtually all arable production is on natural soils in the open. A soil can be regarded as a system, in which solids with certain textures (the soil minerals, i.e. clay, silt, sand, gravel and rocks), water (with dissolved solutes), air and organic matter are arranged in a specific form, known as structure. Plants develop best when they are able to extract the necessary elements through their roots. Unless the temperature of the soil is a restrictive factor (too cold or too hot), the only important factor in the initial phase is the availability of water, enabling the seeds to germinate. If the above conditions obtain, there is no reason for any manipulation of the soil. In their natural environment, plant species were able to survive in a balanced ecological system (competition) without any human interference. The introduction of a specific plant or crop does, however, inevitably disturb the balance; planting or sowing becomes necessary and the soil has to be opened up and even in the most primitive stage, farmers have to walk or drive on the field. Weeds can generally be considered as those plants that grow on a place and at the time where the farmer doesn’t want is; since they compete for light, water and nutrients, they have to be controlled. This requires often operations during which the farmer has to enter the field. The same applies to the harvesting operations, where often heavy machinery is used and large amounts of produce have to be transported.
General Tillage Objectives
Although tillage has been practiced for millennia all over the world, the reasons for applying it merit some discussion. Soil tillage is one of the operations performed in arable crop production whose objectives form part of the production process, but where the direct results may differ from these objectives. The aim of arable cropping may be to produce the maximum yield of certain crops, a special quality of a crop or the highest possible financial return. The financial benefit obtained from arable production is obviously the final outcome of a complicated process depending upon many variables, such as the type of crop, soil type, climatic conditions, type of farming, standard of mechanization, prices of crops, implements and inputs, interest rates and tax, and soil tillage is one of these variables.
Two aspects need to be emphasized in this connection:
1. A change in the proportion of tillage costs usually leads to a considerably smaller change in the proportion of total production costs. 2. Tillage may influence other production costs.
Both aspects may be very important. For example, a 20% reduction in tillage costs saves only 2% of the total production costs when tillage accounts for 10% of the total input. The actual proportion of tillage costs in the total costs depends upon the input of each production factor, such as water (irrigation), fertilizers, chemicals, etc. A mere 2% saving is insufficient to persuade farmers to adopt a new soil tillage system, especially if no higher yields can be expected or an increased risk is possible. As regards the second aspect, tillage operations are in fact often intended to facilitate other field work by changing the structure of the soil. For instance, it is usually easier to sow in a seedbed than on untilled soil, or the construction of a ridge with a very small number of clods may considerably reduce the work required for harvesting tuber crops.
So, when analyzing the ways in which tillage may influence crop growth, we should distinguish between its effect upon the soil structure and weed population and the effect of the soil structure and weed population upon crop growth.
As far as the soil structure is concerned, it should in theory be possible to predict the tillage effect of any specific implement if the soil and performance parameters are adequately described. This would permit a description of the soil structure in terms of its bulk density, structural homogeneity and strength . The farmer generally knows from his experience what the effect of a certain soil structure (as a result of tillage) will be on the growth and development of the crop. The relationship between tillage prior to crop growth and the yield at a much later date is generally so complex that a clear connection between tillage and yield can be expected only when a specific restrictive growth factor is affected by tillage. The influence of tillage upon other field operations is generally not restricted to one growth period and the long term effects of tillage must be given consideration. For example, if a tillage operation for optimizing the sowing conditions increases soil erosion by creating a soil structure susceptible to erosion, this damage is an indirect result of the tillage operation. Since the effect may continue for many years, that operation is likely to have a detrimental effect upon economic yield.
So, when analyzing the ways in which tillage may influence crop growth (the agronomic aspects), we should, distinguish between its effect upon the soil structure and weed population and the effect of the soil structure and weed population upon crop growth. As far as the soil structure is concerned, many attempts have been made to predict the tillage effect of any specific implement. If the soil and performance parameters are adequately described, a description/quantification of the soil structure in terms of its bulk density, structural homogeneity and strength may be possible. On the other hand, when describing the relationship between soil structure and crop growth, other aspects of the soil structure, such as air, water, temperature and mechanical resistance, are relevant. The relationship between these two groups of structural features should be established if the connection between tillage and crop growth is to be understood. The farmer generally knows from his experience what the effect of a certain soil structure (as a result of tillage) will be on the growth and development of the crop.
The Objectives Of Groups Of Tillage Operations
Different tillage operations have different purposes. Generally speaking, there are four groups of tillage operations which, in a complete system, typically in a temperate climate, are performed in the following sequence: a. Stubble or post harvest cultivation. This consists of shallow operations carried out shortly after the harvest to clear the field of weeds and crop residue and to restore the soil structure. This group also includes tillage during fallow periods (for water conservation, weed control and improvement of the soil structure and fertility). b. Main (primary) tillage. This is normally the deepest operation which is performed during the period between two crops to control weeds, restore the soil structure in the arable layer where most of the roots will develop and to prepare the land for seedbed preparation. c. Seedbed preparation. These shallow operations are intended to prepare a seedbed or make the soil suitable for (trans)planting. They include weed control and structural improvement for germination and early growth. d. Crop management tillage operations. These are very shallow operations controlling weeds, breaking up surface crusts to improve water infiltration and crop emergence and for forming ridges which encourage early growth and facilitate the harvesting of root crops. A complete sequence of tillage operations may not be necessary or not possible because the interval between the two crops is too short or the circumstances unfavorable; in such cases the system is simplified while still achieving maximum efficiency. Although soil tillage generally has the same aims irrespective of the climatic conditions, the priority of the various objectives differs. High and stable crop yields can be achieved only if the soil tillage system employed is suitable for the region and adapted to the cropping and production system. Soil tillage can be defined as a sequence of mechanical manipulations of the topsoil in which all the operations are dovetailed and adapted to the overall production technology. Three principal objectives can be mentioned:
Elimination and permanent control of the original vegetation (often considered as weeds); Creation of conditions favoring the germination, emergence and growth of the cultivated plants; Conservation and improvement of the soil as the growth medium for cultivated crops.
The status of the various types of tillage applied in Europe can be seen in this website:
It is based on statistical data collected in the EU countries on the farming systems used.
Taken from Soil Tillage in Africaː needs and challenges FAO SOILS BULLETIN 69 http://www.fao.org/docrep/t1696e/T1696e00.htm#TopOfPage
O.A. Opara-Nadi, College of Agriculture and Veterinary Medicine, Imo State University, Okigwe, Nigeria http://www.fao.org/docrep/t1696e/t1696e09.htm
Tillage includes all operations of seedbed preparation that optimize soil and environmental conditions for seed germination, seedling establishment and crop growth (Lal 1983). Tillage is defined as the soil-related actions necessary for crop production (Boone 1988). According to Antapa and Angen (1990), tillage is any operation or practice taken to prepare the soil surface for the purpose of crop production. The definition by Ahn and Hintze (1990) states that tillage is any physical loosening of the soil as carried out in a range of cultivation operations, either by hand or mechanized. The overall goal of tillage is to increase crop production while conserving resources (soil and water) and protecting the environment (IBSRAM 1990). The benefits of tillage are:
1. seedbed preparation,
2. weed control,
3. evaporation suppression,
4. water infiltration enhancement, and erosion control. These benefits together result in increased and sustained crop yields. The definitions of tillage, as given above, embrace the concepts and features of both conservation and conventional tillage systems.
Conventional Tillage Systems
These involve the mechanical soil manipulation of an entire field, by ploughing followed by one or more harrowings. The degree of soil disturbance depends on the type of implement used, the number of passes, soil and intended crop type.
In the humid and sub-humid regions of West Africa, and in some parts of South America, traditional tillage is practised mostly by manual labour, using native tools which are generally few and simple, the most important being the cutlass and hoe which come in many designs depending on function (Morgan and Pugh 1969). To facilitate seedbed preparation and planting, forest undergrowth or grass is cleared with a cutlass and trees and shrubs left, but pruned. The cut biomass and residues are disposed of by burning in situ. This type of clearing is non-exhaustive, leaving both appreciable cover on the soil, and the root system which gives the topsoil structural stability for one or two years (Aina et al. 1991)
Conservation Tillage Systems
Conservation tillage as defined by the Conservation Tillage Information Center (CTIC) excludes conventional tillage operations that invert the soil and bury crop residues. The CTIC identified five types of conservation tillage systems:
1. no-tillage (slot planting),
2. mulch tillage,
3. strip or zonal tillage,
4. ridge till (including no-till on ridges) and
5. reduced or minimum tillage.
The no-till system is a specialized type of conservation tillage consisting of a one-pass planting and fertilizer operation in which the soil and the surface residues are minimally disturbed (Parr et al. 1990). The surface residues of such a system are of critical importance for soil and water conservation. Weed control is generally achieved with herbicides or in some cases with crop rotation. According to Lal (1983), no-tillage systems eliminate all preplanting mechanical seedbed preparation except for the opening of a narrow (2-3 cm wide) strip or small hole in the ground for seed placement to ensure adequate seed/soil contact. The entire soil surface is covered by crop residue mulch or killed sod. A review of tillage studies in Nigeria (Opara-Nadi 1990) shows that no-tillage with residue mulch is appropriate for Luvisols in the humid tropics. No-tillage is used in mechanized wheat farming in northern Tanzania and for some perennial crops, for example coffee plantations (Antapa and Angen 1990). Several studies (Smika and Unger 1986; Unger et al. 1988; Parr et al. 1990) have reported the success of no-tillage systems in many parts of the USA. Though the use of no-till is increasing, adoption has been slow. Parr et al. (1990) report that in the USA, no-till is practised on less than 10% of the farmland that is in some form of conservation tillage.
No-till fallow is a type of no-tillage system which is used in the dryland areas in the USA. No-till fallow has been most successful in summer rainfall areas (Parr et al. 1990). A major goal of fallowing is to recharge the soil profile with water so that the risk of failure for the next crop is greatly reduced (Unger et al. 1988). According to Parr et al. (1990), the potential benefits of no-till fallow, compared with other tillage systems, are more effective control of soil erosion, increased water storage, lower energy costs per unit of production and higher grain yields. A major disadvantage of no-till fallow (sometimes referred to as chemical fallow) is its heavy use of herbicides for weed control.
Mulch tillage techniques are based on the principle of causing least soil disturbance and leaving the maximum of crop residue on the soil surface and at the same time obtaining a quick germination, and adequate stand and a satisfactory yield (Lal 1975, 1986b). Lal further reported that a chisel plough can be used in the previously shredded crop residue to break open any hard crust or hard pan in the soil; care should be taken not to incorporate any crop residues into the soil. The use of live mulch and crop residue in situ involves special mulch tillage techniques or practices. In situ mulch, formed from the residue of a dead or chemically killed cover crop left in place (Wilson 1978a, b), is generally becoming an integral component of mulch tillage techniques.
Stubble mulch tillage or stubble mulch farming (sub-tillage) is a crop production system involving surface residues that was first used by a farmer in Georgia, USA, in the early 1930s for controlling water erosion (Unger et al. 1988). It was developed primarily for controlling wind erosion, but its value for reducing runoff and controlling water erosion was also soon apparent (Smika and Unger 1986). This practice is carried out by small- and large-scale farmers in Tanzania for perennial crops like coffee and banana, as well as annual crops such as wheat and barley (Antapa and Angen 1990).
Strip or zonal tillage
The concept of strip or zonal tillage is described by Lal (1973, 1983). The seedbed is divided into a seedling zone and a soil management zone. the seedling zone (5 to 10 cm wide) is mechanically tilled to optimize the soil and micro-climate environment for germination and seedling establishment. The interrow zone is left undisturbed and protected by mulch. Strip tillage can also be achieved by chiselling in the row zone to assist water infiltration and root proliferation.
In this system, the soil is left undisturbed prior to planting but about one-third of the soil surface is tilled at planting with sweeps or row cleaners; planting of row crops is done on preformed cultivated ridges, while weeds are controlled by herbicides. Ridge till has been gaining popularity as a conservation practice for maize and soybean production in the USA (Parr et al. 1990).
Reduced or minimum tillage
This system covers other tillage and cultivation systems not covered above but meets the 30% residue requirement (Laryea et al. 1991). In Africa, the term minimum tillage is not always employed with the same meaning as in temperate countries, and may also be used differently in the different contexts of shifting cultivation (still the dominant system in most of Africa) and mechanised agriculture (Ahn and Hintze 1990).
Ahn, P.M. and Hintze, B. 1990. No tillage, minimum tillage, and their influence on soil properties. In: Organic-matter Management and Tillage in Humid and Sub-humid Africa. pp. 341-349. IBSRAM Proceedings No.10. Bangkok: IBSRAM.Aina et al. 1991
Antapa, P.L. and Angen, T.V. 1990. Tillage practices and residue management in Tanzania. In: Organic-matter Management and Tillage in Humid and Sub-humid Africa. p. 49-57. IBSRAM Proceedings No.10. Bangkok: IBSRAM.
Lal, R. 1973. Effects of seedbed preparation and time of planting on maize (Zea mays) in Western Nigeria. Experimental Agriculture 9:303-313.
Lal, R. 1975. Role of mulching techniques in tropical soil and water management. IITA Technical Bulletin No. 1, Ibadan, Nigeria.Lal 1983.
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Unger, P.W., Langdale, G.W. and Papendick, R.I. 1988. Role of crop residues - improving water conservation and use. In: Cropping Strategies for Efficient Use of Water and Nitrogen. W.L. Hargrove (ed.) pp. 69-100. American Society of Agronomy Special Publication No.51.
Wilson, G.F. 1978a. A new method of mulching vegetables with the in situ residue of a tropical cover crop legume. Proceedings of 10th International Horticultural Congress, Sydney, Australia.
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