Effect of Soil Texture on Nitrogen Mineralized from Cotton Residues and Compost

The N mineralized from microbial decomposition of crop residues is an important source of N for crop production. Our objective was to develop a better understanding of how soil properties affect the N mineralized from decomposing crop residues to help better account for spatial differences in N availability when applying N fertilizer. Four soils varying in texture and organic matter concentration were selected from a Georgia Coastal Plain field. In the laboratory, the soils were mixed with cotton (Gossypium hirsutum L.) leaves (C to N ratio = 15.5), cotton stems (C to N ratio = 28.8), or compost (C to N ratio = 28.8) and incubated at field capacity and 23°C for 179 d. Rates of application were 2056 mg plant material kg−1 soil and 15 000 mg compost kg−1 soil. The time spans of initial N immobilization and the amounts of N immobilized and mineralized differed considerably between soils. The soils with greater clay concentrations had longer time periods of initial N immobilization and mineralized less N from the added materials. The net N mineralized from the decomposing cotton residues was low after 179 d in all four soils (−2.6 to 11.0% of total), but greater amounts of N were mineralized from decomposition of compost (5.1 to 23.1% of total).