Manures And Fertilisers
Manures and fertilisers enhance fertility of soil. If crops are grown on a piece of land one after the other, minerals of the soil get depleted and soil becomes infertile. The crop yield becomes low. Repeated growing of crops removes the three most important elements (nitrogen, phosphorus and potassium) from the soil. Manures and fertilisers are added to the soil to make up for the loss of these elements.
Manures are natural fertilisers which are being used since ancient days. Manure consists of organic substances obtained from the decomposition of animal wastes, dead plants and animals by the action of microbes. Manures add small quantities of nutrients and large quantities of organic matter to the soil, thus making soil soft for the better growth of plant.
Manures are of the following three types:
Farmyard manure (FYM) is the decomposed mixture of cattle excreta (dung), litter (bedding material for animals) and leftover organic matter (roughage or fodder). FYM is rich in potassium, phosphorus and nitrogen. It contains about 0.5% potassium oxide, 0.15% phosphorus pentoxide and 0.5% nitrogen.
Compost is prepared from straw, sewage waste, vegetables and animal refuse, weeds etc. It is a biological process in which aerobic and anaerobic microorganisms decompose sewage wastes into compost. Decomposition occurs from 3 to 6 months. Compost prepared from garbage and town soil contains 1.4% nitrogen, 1% phosphorus and 1.4% potassium.
Green manuring is the practice of ploughing green legume-bearing plants into the soil for improving its fertility. Crotalaria juncea (sun hemp) and Cyamopsis tetragonoloba (guar) are commonly grown for this purpose. These crops are grown and ploughed into the field before flowering. This makes the field suitable for the cultivation of wheat, rice, maize etc., which require a lot of nutrients.
Fertilisers are inorganic chemicals synthesised in industries. They contain essential plant nutrients such as nitrogen, phosphorus and potassium. They are prepared in a concentrated form. Hence, it is easy to transport them.
Types of Fertilisers
Nitrogenous fertilisers are rich in nitrogen elements. These are urea, sodium nitrate, ammonium sulphate, ammonium nitrate and calcium ammonium nitrate.
Phosphatic fertilisers are rich in phosphorus. These are phosphate and superphosphate. Phosphatic fertilisers are good for better fruit production.
Potassic fertilisers are rich in potassium, a macronutrient of the plant. These are potassium chloride, potassium sulphate and potassium nitrate.
Complex fertilisers contain two or three elements such as nitrogen, phosphorus and potassium. These are urea ammonium phosphate, nitro phosphate and diammonium phosphate.
Biofertilisers are biologically active products of bacteria, algae and fungi. They enrich the soil nutrients, especially nitrogen. Biofertilisers are used for specific crops such as legumes (pulses), oil seeds and rice. Some of the biofertilisers used in India are Rhizobium in leguminous plants, Anabaena in Azolla and free-living bacteria in soils such as Azatobacter and Bacillus polymyxa.