ABSTRACT
Composting is the controlled rotting of organic matter. The purpose of composting is to convert organic material that is unsuitable for incorporating into the soil of cropland into a material that is suitable for mixing with the soil. The main drawback of raw, uncomposted organic matter for land application is its wide carbon to nitrogen (C:N) ratio. Incorporation of organic matter with a wide C:N mass ratio above 35:1 is likely to stimulate immobilization of available nitrogen and other plant nutrients in the soil. Immobilization is the consumption of available soil nutrients by microorganism that are rotting organic matter in the soil. Immobilization occurs when the organic matter being decomposed does not contain enough nutrients to feed the microorganisms that are doing the rotting, so the organisms obtain the nutrients from the soil. Immobilized nutrients are unavailable to plants until they are released from the cells of the dead microorganisms that consumed them. Among materials that have wide C:N ratios and that should be composted are sawdust, woodchips, bark, straw, paper, dead leaves and needles of trees, dead garden residues, cotton cloths, and manures with a lot of bedding. During composting, carbon as carbon dioxide is lost more rapidly than nitrogen is lost from the organic materials with the result that the C:N ratio of the final product is much narrower than that of the original organic materials. Generally, composting of organic matter with C:N below 35:1 is not needed with regards to immobilization of nitrogen, and the materials can be applied directly to the land. If the C:N ratio is close to 35:1 to 50:1, some nitrogen fertilizer can be supplied to avoid immobilization of nitrogen from the soil. If the C:N ratio is very wide (>100:1), composting is recommended before incorporation into the land.
