Factors Influencing rate of Organic Matter Decomposition
In addition to the composition of organic matter, nature and abundance of microorganisms in soil, the extent of C, N, P and K., moisture content of the soil and its temperature, PH, aeration, C: N ratio of plant residues and presence/absence of inhibitory substances (e.g. tannins) etc. are some of the major factors which influence the rate of organic matter decomposition.
As soon as plant and animal residues are added to the soil, there is a rapid increase in the activity of microorganisms. These are not true soil organisms, but they continue their activity by taking part in the decomposition of organic matter and thereby release of plant nutrients in the soil. Bacteria are the most abundant organisms playing important role in the decomposition of organic matter. Majority of bacteria involved in decomposition of organic matter are heterotrophs and autotrophs are least in proportion which are not directly involved in organic matter decomposition. Actinomycetes and fungi are also found to play important role in the decomposition of organic matter. Soil algae may contribute a small amount of organic matter through their biomass but they do not have any active role in organic matter decomposition. The various microorganisms involved in the decomposition of organic matter are listed in the following table.
Achromobacter, Bacillus, Cellulomonas, Cellvibrio, Clostridium, Cytophaga, Vibrio Pseudomonas, Sporocytophaga etc.
Aspergillus, Chaetomium, Fusarium, Pencillium Rhizoctonia, Rhizopus, Trichoderma, Verticilltttm.
Micromonospora, Nocardia Streptomyces, Thermonospora
Bacillus, Achromobacter, Cytophaga Pseudomonas, Erwinia, Vibrio, Lactobacillus
Aspergillus, Fusarium, Chaetomium, Penicillium, Trichoderma, Humicola
Flavobacterium, Pseudomonas, Micrococcus, Arthorbacter, Xanthomonas
Humicola, Fusarium Fames, Pencillium, Aspergillus, Ganoderma
Achromobacter, Bacillus, Clostridium
Fusarium, Fomes, Aspergillus, Rhizopus
Micromonospora, Nocardia, Streptomyces,
Bacillus, Clostridium, Pseudomonas
Bacillus, Achromobacter, Cytophaga, Pseudomonas
Mucor, Fusarium, Aspergillus, Trichoderma
Streptomyces, Nocardia, Micromanospora
Proteins & Nucleic acids
Bacillus, Pseudomonas, Clostriddum, Serratia, Micrococcus
a) Aeration: Good aeration is necessary for the proper activity of the microorganisms involved in the decomposition of organic matter. Under anaerobic conditions fungi and actinomycetes are almost suppressed and only a few bacteria (Clostridium) take part in anaerobic decomposition. The rate of decomposition is markedly retarded. It was found that under aerobic conditions 65 percent of the total organic matter decomposes during six months, while under anaerobic conditions only 47 percent organic matter can be decomposed during the same period. Anaerobic decomposition of organic matter results into the production of large quantity of organic acids and evolution of gases like methane (CH 4) hydrogen (H2) and carbon dioxide (CO2).
b) Temperature: The rate of decomposition is more rapid in the temperature range of 30° to 40°’ At temperatures below or above this range, the rate of decomposition is markedly retarded. Appreciable organic mater decomposition occurs at 25° C and further fluctuation in the soil temperature has little effect on decomposition.
c) Moisture: Adequate soil moisture i.e. about 60 to 80 percent of the water-holding capacity of the soil is must for the proper decomposition of organic matter. Too much moisture leads to insufficient aeration which results in the reduced activity of microorganisms and there by checks the rate of decomposition.
d) Soil PH/soil reaction: Soil PH affects directly the kind, density and the activity of fungi, bacteria & actinomycetes involved in the process of decomposition and thereby rate of decomposition of organic matter. The rate of decomposition is more in neutral soils than that of acidic soils. Therefore, treatment of acid soils with lime can accelerate the rate of organic matter decomposition.
e) C: N ratio: C: N ration of organic matter has great influence on the rate of decomposition. Organic matter from diverse plant-tissues varies widely in their C: N ratio (app. 8-10 %). The optimum C: N ratio in the range of 20-25 is ideal for maximum decomposition, since a favorable soil environment is created to bring about equilibrium between mineralization and immobilization processes. Thus, a low nitrogen content or wide C’.N ratio results into the slow decomposition. Protein rich, young and succulent plant tissues are decomposed more rapidly than die protein-poor, mature and hard plant tissues. Therefore, C:N ratio of organic matter as well as soil should be narrow/less for better and rapid decomposition. Thus, high aeration, mesophilic temperature range, optimum moisture, neutral/alkaline soil reaction and narrow C: N ratio of soil and organic matter are required for rapid and better decomposition of organic matter.