1.Bulky organic manures:
The bulky organic manures are organic in nature and required in huge amounts. All these bulky organic manures are bulky in nature and supply
i) plant nutrients in small quantities, and
ii) organic matter in large quantities. Eg. FYM, Composts, Green manures, Sewage sludge. Of the various bulky organic manures FYM, Compost and Green manures are widely used .
The effect of bulky organic manures on soils is three fold . I. Since these manures contain plant nutrients, they have direct effect on plant growth like any other commercial fertilizer. Bulky organic manures contain nutrients in small quantities, therefore large quantities of these are needed. Besides the major nutrients,they also contain traces of micro-nutrients. II. Bulky organic manures increase organic matter content and hence improve the physical properties of soil. This effect is very important in case of most of our arable land. Such manures increase the humus content of soil and consequently water holding capacity of sandy soils also increased and the drainage of clayey soils is improved. III. Bulky organic manures provide food for soil microorganisms.This increases the activity of microbes which in turn help to convert unavailable plant nutrients into available form. Organic manures have been the traditional means of improving soil fertility. The organic matter that is applied thorough organic manures has very complex effect on soil and on plant growth. The main effects are Effect of organic matter on soil properties: I. Improvement of soil physical properties 1) Improvement of soil structure 2) Improvement of water holding capacity 3) Improvement of soil aeration 4) Reduction of soil loss through erosion II. Improvement of chemical properties 1) Supply of essential plant nutrients in balanced ratio 2) Slow release of nutrients 3) High residual value III. Improvement of biological activity 1) Stimulation of soil fauna and flora B. Concentrated organic manures: Like bulky organic manures, these organic manures contain plant nutrients and considerable amount of organic matter. They have direct effect on plant growth. Nitrogen content is higher in concentrated organic manures and varied from 2.5 percent in mahua cake to 7.9 per cent in decorticated safflower cake. In addition to nitrogen all the oil cakes contain P2O5 (0.8 to 2.9 %) and K2O (1.2 to 2.2%) since they contain nitrogen in relatively large quantities ,they are usually classified as organic nitrogenous manures . By virtue of this high nitrogen content they enrich the nitrogen status of soil.
