The role of biomineralization of nitrogen in organic matter in the decomposition of crop residues

Nitrogen as an essential nutrient element for organisms has many different oxidation numbers. Nitrogen cycling is sum of the changes and transformations of these oxidation numbers of nitrogen. One of the important nitrogen cycling process is mineralization that has important role in soil fertility. Mineralization has two stages that accomplishes by Nitrosomonas and Nitrobacter respectively. The environmental conditions and type of nitrogen containing material affect the activity of these microorganisms and consequently affect the rate and amount of mineralization. Generally, inappropriate ventilation and anaerobic conditions, drought, salinity and soil compaction decrease the amount of mineralization. Plowing the soil and plant residual management has positive effects on mineralization. The decomposition of Organic residues degradation is related to the ratio of soil C/N. Nitrogen-rich compounds, like legumes, vegetables and weeds, and animal fertilizers that have low C/N, decompose at a higher rate, and, by decomposition, more nitrogen is released. Lignine-rich and rough residues such as palm, sugarcane bagasse, cereals and wood remnants with high C/N have a slower decomposition. The number C/N=24 is considered as an indicator in organic matter decomposition and nitrogen mineralization. If residues such as wheat straw with C/N=80 are added to the soil, the microorganisms use soil nitrogen storage to adjust their C/N and thus to supply their nitrogen, causing a shortage of nitrogen.  Conversely, if residues such as young hay with C/N=13 are added to the soil, the excess nitrogen will reach to plant. Therefore, plant residues management and crop rotation is very important. In practice, in order to prevent of nitrogen deficiency in plant, organic residues with low nitrogen contents should add nitrogen to the as soil as chemical fertilizer. In some areas, residues of previous crops are burned which reduces the storage of organic matter and soil fertility, air pollution and increase greenhouse gases. This is while these residues can have many useful uses. Due to low contents of organic matter in most of country’s soils and dry climates, it is necessary to apply of managing practices in order to maintain and increase soil organic matter.