Chapter 10 - Organic Forms of N in Soil

Abstract

This chapter discusses the chemical nature of N in soil humus with emphasis on incorporation, stabilization, and availability of immobilized fertilizer N in soil. The studies on soil N availability and on indices of N availability have been discussed, with reviews of humic substances (HS) as related to soil fertility. 15N studies demonstrate that from 20 to 40% of the fertilizer N added to agricultural crops of the temperate-zone soils is incorporated into organic forms during the first growing season. In comparison to the native humus N, more of the newly immobilized N occurs as amino acids and amino sugars, and less occurs in unidentified forms. The newly immobilized N is more susceptible to mineralization or extraction. Stabilization processes, including polymerization reactions between amino compounds and polyphenols, lead to the incorporation of N into humic structures and a gradual reduction in N availability. The chapter concludes with the studies that are involved in a broad range of conventional and solid-state techniques and have been applied to the characterization of organic N complexes.