Role of Tillage in Soil Moisture Conservation

Tillage may be described as the practice of modifying the state of the soil in order to provide conditions favourable to crop growth.

The objectives of tillage in dry lands are to:

• develop desired soil structure for a seedbed, which allows rapid infiltration and good retention of rainfall.

• minimize soil erosion by following practices as contour tillage, tillage across the slope etc.

• control weeds and remove unwanted crop plants.

• manage crop residues, through mixing of trash is desirable for achieving good tilth and decomposition of residues. However, the retention of trash on top layers is also useful in reducing erosion. On the other hand, complete coverage of residues sometimes necessitates control of insects or to prevent interference with precision planting operations.

• obtain specific soil configurations for in situ moisture conservation, drainage, planting etc.

• incorporate and mix manures, fertilizers, pesticides or soil amendments into the soil.

• accomplish segregation by moving soil from one layer to another, removal of rocks or root harvesting.

Hence, attention must be paid to the depth of tillage, time of tillage, direction of tillage and intensity of tillage.

(a) Depth of tillage – The depth of tillage depends on soil type, crop and time of tillage. Deep tillage of 25–30 cm is beneficial for deep heavy clay soils to improve permeability and to close cracks formed while drying. In soils with hard pans, deep tillage once in 2–3 years with chisel plough up to 35–45 cm depth at 60–120 cm interval will increase effective depth for rooting and moisture storage. Deep tillage is preferable for cotton, red gram and other deep-rooted crops. It is not recommended for shallow, gravelly, light textured soils.

Medium deep tillage of 15–20 cm depth is generally sufficient for most soils and crops. It is recommended for medium deep soils, shallow rooted crops, soils with pan free horizon and for stubble incorporation. Shallow tillage up to 10 cm is followed in light textured soils, and shallow soils and in soils highly susceptible to erosion. In soils prone for surface crusting, shallow surface stirring or shallow harrowing is useful.

(b) Time of tillage – Early completion of tillage is often helpful to enable sowing immediately after rainfall and before the soil dries up. Summer tillage or off-season tillage done with pre-season rainfall causes more conservation of moisture and also enables early and timely sowing. It is particularly useful for pre-monsoon sowing.

(c) Direction of tillage – For moisture conservation, ploughing across slope or along contour is very effective. Plough furrows check the velocity of runoff, promote more infiltration when water stagnates in the depressions caused by plough furrows and improves soil moisture storage.

(d) Intensity of tillage – It refers to the number of times tillage is done. Frequent ploughing in shallow light textured soils will pulverize the soils into fine dust and increase the susceptibility to erosion. In heavy soils, leaving the land in a rough and cloddy stage prior to sowing is useful for more depression storage. The concept of minimal tillage is also practiced in dry lands. Here tillage is confined to seeding zone only and the inter-space is not tilled. It not only saves time, energy and cost but also helps moisture conservation. The practice of “set line cultivation” adopted in some dry regions is an example of minimum tillage. Here the seed row space is fixed and season after season, tillage is done only in this seeding strip. The intervening strip is not tilled.

(e) Modern concept of tillage – In dry lands, rainfall is received simultaneously over a large area. In order to ensure timely sowing before soil dries up, the interval between land preparations and sowing must be narrowed down. This calls for completion of tillage over a large area in quick time. Dependence on bullock power and traditional wooden plough may not help in this regard. Use of more efficient tillage implements and mechanization of tillage operations are warranted. Tillage in dry lands also encompasses land shaping for in situ soil moisture conservation. Implements that can carryout tillage and land shaping in one single operation will help in saving time and cost. If land preparation, land shaping and sowing can be done in one single operation it can save considerable time. This is termed as once over tillage, plough planting or conservation tillage. Suitable tractor drawn machinery like a broad bed former cum seeder, basin lister cum seeder, which can complete the land shaping and sowing simultaneously, can be used:

1. minimum/optimum/reduced tillage.

2. conservation/mulch tillage.

3. zero tillage.

(i) Minimum/optimum/reduced tillage:

The objectives of these systems include

(a) reducing energy input and labour requirement for crop production,

(b) conserving soil moisture and reducing erosion,

(d) keeping field compaction to minimum.

(ii) Conservation/mulch tillage: The objectives are to achieve soil and water conservation and energy conservation through reduced tillage operations. Both systems usually leave crop residue on the surface and each operation is planned to maintain continuous soil coverage by residue or growing plants.

The conservation tillage practices may advance some of the goals of alternative farming such as increasing organic matter in soil and reducing soil erosion, but some conservation tillage practices may increase the need for pesticides. Conservation tillage changes soil properties in ways that affect plant growth, and reduce water runoff from fields. The mulched soil is cooler and soil surface under the residue is moist, as a result many conservation tillage systems have been successful.

(iii) Zero tillage or no-till system: Here, the crop residue is usually shredded and planting is done without pre tillage. No till planting has problem of adequate weed control.