Influence of Soil Moisture Content on Time Courses of Nitrogen Mineralization and Immobilization Caused by Applications of Different Plant Residue to Soils with Different Textures

Abstract

                A laboratory aerobic incubation experiment was conducted at room temperature to determine the influence of soil moisture contents on time courses of N mineralization and immobilization caused by application of different plant residues. The experiment was carried out in a completely randomized design with a 4 x 3 x 3 x 6 treatments and three replications. The experimental treatments were factorial combinations of four factors: (1) four plant residue types (control, leucaena, sesbania, stubble of faba bean and stubble of maize; (2) three soil textures (loamy sand, loam and clay soil); (3) three moisture levels [50, 75 and 100 % field capacity (FC)]; and (4) six incubation periods (0, 15, 30, 60, 90 and 120 days). The treated samples were analyzed for mineral N (NH₄⁺ + NO^-₃) to determine mineralization and immobilization of N.

                Incorporation of sesbania residue in soils resulted in N mineralization with the rates decreasing with increase in time of incubation. Throughout 120 days of incubation (DI), N mineralization increased with the increase in soil moisture content up to 100 % FC in case of the loamy sand soil but up to 75 % FC in case of the clay soil. In case of the loam soil, N mineralization was not affected by soil moisture content during 30 DI but increased with increase in soil moisture content up to 100 % FC after 30 DI. Incorporation of leucaena residue in soils resulted in either no or slight change in mineral N in the soil during 30 DI regardless of kind of soil. The mineralization and immobilization if occurred either ended after 90 DI or continued to more than 120 DI depending on kind of soil. Incorporation of faba bean stubble or maize stubble in soils mostly resulted in immobilization of N in the soils during the early stages of incubation time and thereafter it either continued up to 120 DI or stopped depending on kind of soil. Both in case of immobilization and mineralization, they mostly increased with soil moisture content up to 100 % FC. For sesbania residue, most suitable soil moisture levels for maximizing N mineralization were 100 % FC in the loamy sand and loam soils and 75 % FC in the clay soil whereas those for leucaena residue were 75 % FC in the loamy sand and clay soils and 100 % FC in the loam soil. In case of incorporation with faba bean or maize stubble, N immobilization could be limited by limiting soil moisture content regardless of soil texture. However, after some specific times of incubation, increases in soil moisture content enhanced N mineralization in the loamy sand and loam soils.