Manures are organic substances obtained from the decomposition of vegetables and animal wastes through the action of microbes. The contain a mixture of various nutrients recycled by biomass wastes. Farmers in our country have traditionally used cow-dung as manure for replenishing soil nutrients.
Manures serve the following functions:
1. They improve the physical condition of the soil. They restore soil texture for better retention of water and aeration.
2. They keep up the humus status of the soil.
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3. They maintain optimum conditions for the activities of soil micro-organisms.
4. They make good a small part of the plant nutrients removed by crops.
5. Green manures add substantial amounts of organic matter as well as nitrogen to the soil.
Thus, manures supply almost all the elements of fertility which crops require for proper growth.
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Limitations of Manures
1. Manures are relatively bulky materials. Being voluminous, it is not convenient to store and transport them.
2. They can supply nutrients only to a limited extent and cannot replenish the massive depletion of nutrients caused by high yielding verities of staple crops.
Hence, manures are always used in combination with chemical fertilizers which contains nutrients in concentrated form.