Land preparation
Soil tillage or land preparation is one of the routine activities in most agricultural systems. Often, land preparation starts with burning fallow vegetation or previous crop residues in order to clear the land or to scare away wild animals or snakes.
Burning is usually followed by soil tillage. Depending on the possibilities of the farmer, tillage can range from very extensive to very intensive. But why do farmers plough?
In the first place to prepare an adequate seedbed which permits a good germination of the seeds. They think that a soil well tilled, loose, levelled and with a lot of fine particles favours the contact between the seeds and the soil, which in turn lead to sowing at an adequate depth. In second place, farmers plough in order to control weeds. Other reasons for tillage may include enhancement of soil water storage and retention and warming-up of the soil.
Box 1. Functions of soil tillage
- Prepare seedbed
- Manage crop residues
- Incorporate fertilizers and agro-chemicals
- Control weeds
- De-compact dense layers
- Increase water infiltration
- Shape the soil surface (levelling, ridging)
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Unfortunately, the method used to achieve any of the above mentioned objectives of tillage might produce a conflict with the other objectives. Each additional tillage operation for weed control also buries more residues and exposes moist soil to the surface, causing additional water loss. As the number of tillage operations is increased, the aggregation of soil is decreased leaving the soil more vulnerable for soil erosion (Godwin, 1990).
In this way, tillage operations will eventually have negative effects on the soil productivity and the economic return of the crops. They are responsible for the destruction of the soil and crop residues. Tillage also affects the availability of water and nutrients in the soil. Among the costs of tillage one should also count:
- Increased erosion and loss of fertility.
- Increased evaporation and moisture loss.
- Decreased capability of the soil to hold water.
Eroded soil can move on to other places, like ditches, lakes and reservoirs, water harvesting tanks or to the neighbour's field, taking with it organic matter, nitrogen, phosphorus and pesticides. Preventive measures, like the construction of terraces, are expensive. It is far more effective and cheaper to refrain from tillage and conserve the residues on the soil surface.
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