Decay and Nutrient Cycling
Soil organisms are the chief agents of decay of organic matter. Decomposition and mineralisation of organic matter results in release of inorganic nutrients which can be absorbed by roots to sustain plant growth. In soil, the decomposers, that include a vast variety of bacteria, actinomycetes and fungi act on the organic matter. These organisms bring about the hydrolysis and oxidation of organic compounds through their enzymes. Complex organic compounds are broken down into simpler compounds until at last, carbon, hydrogen and oxygen are finally released as carbon dioxide and water. Other nutrients contained in the organic matter are released in inorganic form. You might recall that the conversion of nutrients present in the organic matter into inorganic form is termed as mineralisation. The whole process is as follows. Organisms like the fungi, ants, beetles, mites, slugs and snails, sometimes invade fragments of litter even before they fall on the ground. In subsequent transformations, each type of organic substance (carbohydrates, proteins and fats) as well as each stage in the breakdown of these substances, has its own specific set of saprophytes which act upon the organic material so that decay progresses by stages. For example, proteins are broken down successively into amino acids, ammonium salts, nitrites and nitrates, each step being the result of action of a different organism or group of organisms. Therefore, the process of decomposition consists of several overlapping cycles. As a result of decomposition of organic matter humus is formed. which is quite resistant to further alteration. You have already studied it earlier.