Environmental influences on nitrogen transformation of different quality tree litter under submerged and aerobic conditions

Trees in farming systems can improve fertility of soils through mineralization of N in their litter. This study was to determine the quality parameters (i.e., chemical composition) of organic residues that are associated with N mineralization in soils under submerged and aerobic conditions, and to demonstrate that aeration conditions should be taken into account in categorization of organic residues as N sources in farming systems. Incubation experiments were conducted in Aeric Paleaquult soil under submerged and Oxic Paleustult soil under aerobic conditions. Treatments included litter and some fresh materials from trees as well as rice straw available in farming systems of Northeast Thailand. S. grandiflora and L. leucocephala (32 g kg⁻¹ N) had the highest net N mineralization in both conditions. Some lower-quality (< 20 g kg⁻¹ N) residues did exhibit low net N mineralization during the 16-week period under submerged conditions, but displayed almost no net N mineralization in aerobic conditions. Under submerged conditions, their net N mineralization was higher and more rapid. The nitrogen content of the residues was the most important factor controlling N mineralization under both conditions. Polyphenols exerted the highest negative influence on N mineralization in aerobic conditions, but exhibited no negative effect in submerged conditions. In categorizing organic residues for their effective use in soil fertility management, soil aeration conditions, as well as other environmental factors, should be taken into consideration in addition to residue quality.