Role of green manures in soil fertility

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Nitrogen is an essential nutrient needed by plants but which is easily lost when the soil is poorly managed. In sustainable agriculture, green manure or cover crops play a major role in improving soil fertility and farm productivity.

This type of manure refers to crops or plants that are grown between the main crops to provide soil cover and to improve the quality of the soil. This is especially important among small scale farmers who find it expensive to buy mineral fertilizers.

Using legumes like lablab and mucuna, it is possible to ensure adequate supply of good quantities of nitrogen into the soil. This is through fixation of nitrogen in the roots of these legumes. When ploughed back into the soil, the legumes ensure nitrogen and other nutrients are recycled (returned) into the soil. The nutrients are released slowly to the soil as the dead plants rot. Since legumes grow fast, they accumulate a lot of biomass within a short time. They can increase plant nutrients in the soil, especially nitrogen through biological nitrogen fixing and therefore improve crop yields.

These crops minimize soil erosion by reducing the impact of rain on the soil. They suffocate and kill weeds even the destructive ones like Striga, thus reducing labour costs for weed control. They are also an important source of human food and livestock fodder.

Studies conducted in Kenya by the Legume Research Network show that green manures when used with farmyard manure save farmers the cost of buying chemical fertilizers. The table below can help farmers choose the best green manure crop they can use to increase nitrogen and other nutrients to their soils for increased farm productivity and income.

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