Influence of Rates of Application of Different Plant Residues on Time Courses of N Mineralization and Immobilization in Soils with Different Textures

Abstract

                An aerobic incubation experiment was conducted at room temperature (19 to 23 °C) to determine the influence of rates of application of different plant residues on time courses of N mineralization and immobilization in soils with different textures. The experiment was carried out in a completely randomized design with three replications. The experimental treatments were factorial combinations of four factors: (1) three rates of plant residue applications (0, 1.25, 2.50 and 5.00 mg of plant residue g-1 soil); (2) three soil textures (loamy sand, loam and clay soils); (3) four plant residue types (leucaena, sesbania, faba bean stubble and maize stubble); and (4) six incubation periods (0, 15, 30, 60, 90 and 120 days). The treated samples were analyzed for extractable mineral N (NH₄⁺ + NO^-₃) to determine mineralization and immobilization of N.

                 From the results, the following conclusions and recommendations were drawn. (1) Application of sesbania residue into soils resulted in N mineralization with the rate that increased with fineness of soil texture but decreased with increasing time of incubation. In the cases of the loam and clay soils, N mineralization increased with increasing rate of residue up to 5.00 mg g^-1 soil throughout the incubation period but, in the case of the loamy sand soil, N mineralization increased up to the highest rate after 30 days of incubation (DI). (2) Application of leucaena residue into soils resulted in N immobilization that increased with fineness of soil texture during 0-15 DI. N mineralization, increased with fineness of soil texture and rates of application up to 5.00 mg g^-1 soil after 15-30 DI onwards, but decreased with time of incubation. (3) Application of faba bean stubble or maize stubble resulted in N immobilization at the rate that increased with fineness of soil texture. In the loamy sand soil N immobilization was mostly observed throughout 120 DI. In the loam and clay soils, N immobilization that increased with fineness of soil texture occurred during 0-15 DI. After 15-30 DI, N mineralization, at the rate that was independent of the rate of residue application in the case of the loam soil but decrease with increase in the application rate in the case of the clay soil, took place.