Organic Nitrogen in Soils

This chapter reviews and summarizes knowledge concerning the nature of the organic nitrogen in soils. Two methods are available for determination of total nitrogen in soils and other complex materials containing several forms of nitrogen: the Kjeldahl method, which is essentially a wet-oxidation procedure; and the Dumas method, which is fundamentally a dry-oxidation technique. The amount of organic nitrogen in soil tends to be related to the amounts of organic phosphorus and sulfur as well as to the amount of organic carbon. Most of the information available concerning the amounts and forms of amino acid-N in soils has emerged from studies involving hydrolysis of soils or soil organic matter preparations with strong mineral acid. One of the major contributions of soil organic matter to soil fertility is that it supplies a considerable quantity of nitrogen for crop growth and acts as a natural storehouse for this important plant nutrient.