The origin and nature of organic nitrogen in soil as assessed by acidic and alkaline hydrolysis

The origin and nature of much of the organic nitrogen in soil is unknown or speculative. Alkaline hydrolysis was used to fractionate soils into alkali‐soluble and insoluble fractions. Alkali‐insoluble residues from a wide variety of soils contained largely fixed ammonium or chitin or both. Acid hydrolysis of alkali‐insoluble residues from soils, microbes, insects and well‐rotted plant litter confirmed the presence of hexosamine‐N. The hexosamine‐N derived from estimates of soil biomass accounted for less than 10% of the chemically determined hexosamine‐N values. It is suggested that most of the hexosamines are held in complexes formed between chitin complexed with other materials, e.g. pigments, that occur predominantly in the cell walls of microbes and insects. These complexes show resistance to enzymes during the life of soil organisms that persists after their death.