Transformation of organic matter in composting


The organic matter in compost undergoes complex transformation under the action of microorganism, which can be summarized into two processes:
One is the mineralization process of organic matter, that is, the complex organic matter is decomposed into simple substances, and finally carbon dioxide, water and mineral nutrients are generated;
The other is the humification process of organic matter, that is, organic matter is decomposed and then synthesized to form a more complex special organic matter humus. The two processes are carried out at the same time, but in the opposite direction. Under different conditions, the intensity of each process is obviously different.

1、 Mineralization of organic matter

(1) decomposition of nitrogen-free organics. Polysaccharide compounds (starch, cellulose, hemicellulose) are first hydrolyzed to monosaccharide under the action of hydrolase secreted by microorganisms. Glucose decomposes rapidly under the condition of good ventilation, and intermediate products such as alcohol, acetic acid, oxalic acid are not easy to accumulate, eventually forming CO2 and H2O, and releasing a large amount of heat energy at the same time. In case of poor ventilation, monosaccharide will decompose slowly, generate less heat and accumulate some intermediate products organic acid under the action of anaerobic microorganism. In addition, CH4, H2 and other reducing substances can also be produced under the condition of extremely anaerobic microorganism.

(2) decomposition of nitrogen-containing organic matter. The nitrogen-containing organic compounds in compost include protein, amino acid, alkaloid, humus, etc. Except humus, most of them are easy to decompose. For example, under the action of protease secreted by microorganisms, proteins are degraded step by step to produce various amino acids, which are then ammoniated and nitrated to form ammonium salt and nitrate respectively, which can be absorbed and utilized by plants.

(3) transformation of phosphorus containing organic matter. The phosphorus containing organic compounds in compost, under the action of many kinds of saprophytic microorganisms, form phosphoric acid, which can be absorbed and utilized by plants.

(4) conversion of sulfur-containing organic compounds. In the process of fertilizer production, sulfur-containing organic matter is produced by microorganism. Hydrogen sulfide is easy to accumulate in the gas environment, and it will be toxic to plants and microorganisms. However, under the condition of good aeration, hydrogen sulfide is oxidized to sulfuric acid under the action of sulfur bacteria, and forms sulfate with the base in composting, which not only eliminates the toxicity of hydrogen sulfide, but also becomes the sulfur nutrient that plants can absorb. In the case of poor ventilation, anti sulfurization occurs, which makes sulfuric acid change into H2S loss and produces toxicity to plants. In the process of compost fermentation, the aeration of compost can be improved by turning over regularly, so the anti sulfuration can be eliminated.

(5) transformation of lipids and aromatic organics. Tannins and resins are complex in structure and slow in decomposition, and their final products are also CO2 and water; lignin is a particularly stable organic compound in compost containing plant raw materials (such as bark, sawdust, etc.), which has complex structure, aromatic core, and exists in plant tissues in the form of polymerization, so it is very difficult to decompose. Under the condition of good ventilation, it decomposes slowly mainly through the action of fungi and actinomycetes. Its aromatic nucleus can be changed into quinone compound, which is one of the raw materials for the re synthesis of humus. Of course, these substances will continue to be decomposed under certain conditions.
In conclusion, the mineralization of compost organic matter can provide quick nutrients for crops and microorganisms, provide energy for microbial activities, and prepare basic raw materials for the humification of compost organic matter. When composting is dominated by aerobic microbial activities, the organic matter rapidly mineralizes and generates more carbon dioxide, water and other nutrients, decomposes rapidly and thoroughly, and emits a lot of heat energy; when composting is dominated by anaerobic microbial activities, the decomposition speed of organic matter is slow, and often not thorough, with less heat energy released, and the decomposition products are easy to accumulate organic acids and CH4, h in addition to plant nutrients When 2S, PH3, H2 and other reducing substances reach a certain degree, they are harmful or even harmful to crop growth. Therefore, the windrow turner during composting fermentation is also used to change the type of microbial activity to eliminate harmful substances.

2、 Humification process of organic matter
There are many opinions about the formation process of humus, which can be generally divided into two stages: the first stage, the decomposition of organic residues to form the original materials of humus molecules, such as polyphenols, nitrogen-containing organics (amino acids, peptides, etc.); the second stage, the polyphenol oxidase secreted by microorganisms oxidizes polyphenols to quinones, and then quinones condense with amino acids or peptides to form Quinones Humus monomer. Because there are many kinds of phenols, quinones and amino acids, and the way of condensation is different, the humus monomers formed are also diverse. Under different conditions, these monomers further condensed to form molecules of different sizes.
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