8 - Green Manure

Summary

Green manure, cover crops and catch crops are terms used to indicate the same purpose of maintaining soil fertility and productivity, rather than a focus on commercial harvest.

A green manure crop is usually grown to generate additional biomass to maintain soil organic matter as well as to increase nitrogen availability. A cover crop is grown to prevent soil erosion during the non-crop season, by keeping the ground covered with a living vegetation with living roots holding on to the soil. This again is a means of managing soil organic matter as the top soil has the maximum humus and is often washed by rains, drifted by wind, and burnt by sun. A catch crop is grown to retrieve nutrients still present in the soil following the harvest of the main crop. This will have the double advantage of not allowing the nitrogen to be wasted, as the biomass is either recycled or fed to cattle, and the grains adding to the income. A classical instance of a catch crop in rain-fed agriculture in southern India is the horse gram, which can grow on residual moisture and produce a better crop, especially if there is a shower in the middle of the season. The biomass serves as feed to cattle and the pulse becomes food for people. The land is covered at least for three months and since horse gram is a leguminous plant, some amount of nitrogen is fixed in the soil.