COMPOST

COMPOST

 Large quantity of fresh crop residues, on application directly to soil, causes extremely severe nitrogen immobilization and development of excessive reduced condition in the soil. To overcome such problems organic residues are piled up, moistened, turned occasionally to aerate and allowed adequate time to decompose partially and bring down the carbon nitrogen ratio to about 30. This process is called composting. Compost, is utilized for improving or maintaining soil fertility. The collected organic refuse may be of rural and urban origin and may include straw, leaves, paddy husk, ground nut husk, sugarcane trash, bagasse, cattle dung, urine, crop residues, city garbage, night soil, sewage, kitchen and vegetable wastes, hedge clippings, water hyacinth and all other residues counting organic matter. During composting under thermophilic and mesophilic conditions in windrows, heaps or pits adequate moisture and aeration are essential. The final product is brown to black colored humified material which on addition to soil replenishes plant nutrients, maintains soil organic matter content and helps in improving the physical, chemical and biological conditions of the soil.  

REQUIREMENTS OF COMPOSTING 

 In general, composting is carried out in open pit or above ground, by filing alternate layers of organic wastes and other materials including top soil, cattle dung, half decompose farm yard manure, rock phosphate and other amendments. If the organic wastes are largely high-carbohydrate materials, some fertilizer nitrogen is needed. The addition of poultry waste and farm yard manure while layering the compost pit, tends to speed up decomposition and helps to improve the texture of the product. The optimum C:N ratio of the composting materials is below  40. Good aeration in the compost pile is essential. It is good to mix succulent organic materials with the materials that decompose slowly. This prevents packing into soggy anaerobic mixtures. Since composting is a biological process, sufficient moisture for the proper development of microorganisms is essential. The materials should not be too dry or soggy. The requirement of moisture for microorganisms is almost similar to that of higher plants. The optimum moisture content of the composting materials has been found to be 60 percent of the total water holding capacity of the substrate. 

MICROBIOLOGY OF COMPOSTING

 At the initial stage, the easily degradable organic matters like carbohydrates, fats, proteins get degraded by the action of mesophilic fungi.  Due to its action, some amount of heat energy is formed hence, the temperature of the composting substrates is 40 0 C or less, mesophilic fungi and acid producing bacteria appear. The proportion of the three groups of organisms -- bacteria, fungi and actinomycetes is related to dominance of organic constituents., Water soluble simple sugars encourage rapid bacterial proliferation while starch benefits the actinomycetes in particular substrates rich in proteins or amino acids stimulate the spore forming bacilli. Details of microbial genera capable of utilising cellulose, hemicelluloses, starch, lignin etc. may be seen in Table-5. At the end of mesophilic action, the thermophilic fungi/bacteria will start its action and degrade some part of organic matters.  Hence the temperature of 650 C to 700C attained during aerobic decomposition in compost pit leads to the destruction of most of the pathogens, parasites and weed seeds present in the original material. In addition to the effect of higher temperature, some pathogens and parasites are also killed due to their failure to withstand the competition with other microorganisms. The Actinomycetes and spore forming bacteria start its action to decompose cellulose and Hemicellulose present in the waste. During anaerobic decomposition, as prevailed in biogas plant and Bangalore method of composting, temperature does not rise to the extent lethal to parasites in a relatively short time. When sewage sludge or night soil is composted, anaerobic decomposition should be proceeded by aerobic composting at least for a week. The natural death of pathogens and parasites occurs under anaerobic environment and the microbial antagonism eventually eliminates them in relatively longer period of six months. After decomposition of maximum amount of organic matters, the temperature of the medium will slowly decrease.  During the temperature from 600c to 400c again, the thermophilic fungi start to decompose remaining part of organic matter.  After this, the temperature again decreases further.  The white colour fungi commonly appears on the waste that shows presence of mesophilic fungi.  During this fourth phase, the temperature comes down to amount 30-400c.  In this stage, again mesophilic fungi start its action and degrade some amount oflignin.  After this, i.e. in final stage of this composting process, the temperature remains constant.