In conventional tillage combined primary and secondary tillage operations are performed in preparing seed bed by using animal or tractor, which cause hard pan in sub soils resulting in poor infiltration of rain water, thus it is more susceptible to run off and soil erosion. Farmers usually prepare fine seed bed by repeated ploughing, when the animal of the farm is having less work.
Research has shown that frequent tillage is rarely beneficial and often detrimental. Repeated use of heavy machinery destroys structures, causes soil pans and leads to soil erosion. Moreover energy is often wasted during tillage processes. All these reasons led to the development of modern concepts namely the practices like minimum tillage, zero tillage, stubble mulch farming and conservation tillage, etc.
Minimum Tillage
Minimum tillage is aimed at reducing tillage to the minimum necessary for ensuring a good seedbed, rapid germination, a satisfactory stand and favourable growing conditions. Tillage can be reduced in two ways by omitting operations, which do not give much benefit when compared to the cost, and by combining agricultural operations like seeding and fertilizer application.
(a) Advantages (especially in coarse and medium textured soils)
• Improved soil conditions due to decomposition of plant residues in situ.
• Higher infiltration caused by the vegetation present on the soil and channels formed by the decomposition of dead roots.
• Less resistance to root growth due to improved structure.
• Less soil compaction by the reduced movement of heavy tillage vehicles.
• Less soil erosion compared to conventional tillage.
(b) Disadvantages
• Seed germination is lower with minimum tillage.
• More nitrogen has to be added as the rate of decomposition of organic matter is slow. This point holds good only in temperate regions. Contrary to this in tropics, minimum tillage recommended to conserve organic matter in the soil.
• Nodulation is affected in some leguminous crops like peas and broad beans.
• Sowing operations are difficult with ordinary equipment.
• Continuous use of herbicides causes pollution problems and dominance of perennial problematic weeds (weed shift).
• Minimum tillage can be achieved by the following methods:
(a) Row zone tillage – Primary tillage is done with mould board plough in the entire area of the field, secondary tillage operations like discing and harrowing are reduced and done only in row zone.
(b) Plough-plant tillage – After the primary tillage a special planter is used for sowing. In one run over the field, the row zone is pulverized and seeds are sown by the planter.
(c) Wheel track planting – Primary ploughing is done as usual. Tractor is used for sowing, the wheels of the tractor pulverize the row zone in which planting is done.
Zero Tillage/No Tillage/Chemical Tillage
Zero tillage is an extreme form of minimum tillage. Primary tillage is completely avoided and secondary tillage is restricted to seedbed preparation in the row zone only. It is also known as no-tillage and is resorted to places where soils are subjected to wind and water erosion, timing of tillage operation is too difficult and requirements of energy and labour for tillage are also too high. Weeds are controlled using herbicides. Hence, it is also referred as chemical tillage. There are two types of zero tillage.
(a) Till Planting is one method of practicing zero tillage. A wide sweep and trash bars clear a strip over the previous crop row and planter–opens a narrow strip into which seeds are planted and covered. In zero tillage, herbicide functions are extended. Before sowing, the vegetation present has to be destroyed for which broad spectrum non-selective herbicides with relatively short residual effect (Paraquat, Glyphosate etc.) are used and subsequently selective and persistent herbicides are needed (Atrazine, Alachlor etc.).
(b) Sod planting or sod culture: Sod refers to top few centimeters of soil permeated by and held together with grass roots or grass-legume roots. Planting of seeds in sods without any tillage operation is known as sod culture or sod seeding. Usually legumes or small grains are mechanically placed directly into a sod.
Advantages
• Zero tilled soils are homogenous in structure with more number of earthworms. These soil physical properties are apparent after two years of zero tillage.
• The organic matter content increases due to less mineralization.
• Surface runoff is reduced due to the presence of mulch.
Disadvantages
• In temperate countries highest dose of nitrogen has to be applied for mineralization of organic matter in zero tillage.
• Large population of perennial weeds appears in zero tilled plots.
• Higher number of volunteer plants and build up of pests are the other problems.
Stubble Mulch Tillage or Stubble Mulch Farming
In this tillage, soil is protected at all times either by growing a crop or by leaving the crop residues on the surface during fallow periods. Sweeps or blades are generally used to cut the soil up to 12 to 15 cm depth in the first operation after harvest and the depth of cut is reduced during subsequent operations. When unusually large amount of residues are present, a disc type implement is used for the first operation to incorporate some of the residues into the soil.
Two methods are adopted for sowing crops in stubble mulch farming.
• Similar to zero tillage, a wide sweep and trash-bars are used to clear a strip and a narrow planter-shoe opens a narrow furrow into which seeds are placed.
• A narrow chisel of 5–10 cm width is worked through the soil at a depth of 15–30 cm leaving all plant residues on the surface. The chisel shatters tillage pans and surface crusts. Planting is done through residues with special planters.
Disadvantages
• The residues left on the surface interfere with seedbed preparation and sowing operations.
• The traditional tillage and sowing implements or equipments are not suitable under these conditions.
Conservation Tillage
Though it is similar to that of stubble mulch tillage, it is done to conserve soil and water by reducing their losses. Modern tillage methods are practiced in western countries especially in USA. In India, it is not suitable due to several reasons. In USA, straw and stubbles are left over in the field but in India, it is a valuable fodder for the cattle and fuel for the home. Use of heavy machinery in India is limited and therefore, problem of soil compaction is rare.
The type of minimum tillage that can be practiced in India is to reduce the number of ploughings to the minimum necessary i.e., unnecessary repeated ploughings/harrowing can be avoided.
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