The Significance of Microbial Transformation of Nitrogen Compounds in the Light of Integrated Crop Management

Nitrogen (N) is widely distributed in the lithosphere, hydrosphere, atmosphere and biosphere. It is a basic component of every plant cell as well as microorganisms, as a component of proteins, nucleic acids and chlorophyll. It enters soil with organic and mineral fertilizers, plant and animal residues and biological nitrogen fixation. There are various forms of nitrogen in soil, and this element is usually transformed by microorganisms. The transformation of nitrogen compounds (ammonification, nitrification and immobilization) is significantly influenced by climatic conditions and the physicochemical properties of soil. Microbial mineralization of nitrogen organic matter results in the enrichment of soil with this element, which is necessary to generate a yield. The amount of nitrogen entering soil through the mineralization of crop residues ranges from 15 to 45 kg N/ha in cereal residues and from 80 to 144 kg N/ha in winter rape residues. Biological nitrogen fixation can increase the nitrogen content in soil by 30–50 kg/ha/year. In recent decades, the mismanagement of mineral fertilizers has drastically changed the natural balance of the nitrogen cycle. Every year huge amounts of nitrogen compounds enter the aquatic ecosystems and cause their eutrophication. That is why it is important to have adequate knowledge of sustainable fertilization so as to practice integrated crop management.