Conversions and Pathways of Organic Carbon and Organic Nitrogen in Soils

In mineral cultivated soils in the aspect of agricultural utilization, the content of soil organic matter is one of the most important parameters which influences the physical, chemical, and biological properties. The turnover of organic matter in soil and especially its basic elements carbon and nitrogen are the main investigated elements in the aspect of their dynamics. Full understanding of their turnover is possible by the application of sequential fractionation methods in which mobile and active fractions of those elements are separated. In this chapter we present a few groups of organic carbon compounds present in soil with the possible ways of their turnover (immobilization–mineralization process) as well as some chemical methods which are used for the separation of selected biologically active compounds (humic and fulvic acids, polysaccharides, organic acids, phenols) or further degradation methods like chemolysis, susceptibility for oxidation, and fractional separation with the application of different chemical reagents (KMnO4, H2SO4, K2Cr2O7). The nitrogen element in soils is mainly organic compound in form (95 %) but is available for plants (\( {{\mathrm{NH}}_4}^{+} \), \( {{\mathrm{NO}}_3}^{-} \)) for only 5 % of the total content. Dynamics and direction of the turnover processes of organic nitrogen compounds in soils on the big scales depend upon the quality and quantity of those compounds. This chapter contains discussion about the turnover of protein, amino acids, and amino sugars, nitrification and denitrification processes, as well as isolation of different groups of organic nitrogen compounds by chemolysis. Also a new method of sequential fractionation of organic matter from mineral soils is proposed in which through fractional separation the amount of carbon and nitrogen can be determined. For the agricultural utilization especially of fertilizers, the possibility of calculating the amount of nitrogen mineralization during vegetation period from so-called easily mineralized forms of organic nitrogen compounds is proposed, which helps to calculate the dose of nitrogen applied as a fertilizer. This step in the equilibrium of nitrogen in soils prevents pollution of the environment.