Organic Forms of Soil Nitrogen

This chapter presents an account of present knowledge of the forms of organic nitrogen (N) in soils as a basis for understanding how N behaves in the soil-plant system. The main identificable organic N compounds in soil hydrolysates are the amino acids and amino sugars. Environmental conditions in aquatic sediments are particularly suitable for the preservation of microbially produced substances. In general, higher percentages of the N in Histosols and lake sediments occur in the form of amino acids, a result that can be explained by less extensive microbial turnover of organic N in aquatic sediments. Humic and fulvic acids contain the same forms of N that are obtained when soils are subjected to acid hydrolysis. A variety of complex factors may affect the distribution of amino acids in soils, including synthesis and destruction by the indigenous biota, adsorption by clay minerals, and reactions with Quinones and reducing sugars.