CROP RESIDUE DECOMPOSITION AND NUTRIENT MINERALIZATION IN SOIL WITH DIFFERENT TEXTURES

The sustainability of conservation farming systems is closely linked to return of nutrients to the soil through decomposition of crop residues. The aim of this study was to evaluate decomposition of crop residues and nutrient mineralization in soils with different textures over a 175-day incubation period. The experimental design consisted of a 6 x 4 x 5 factorial arrangement - six treatments, composed of four crop residues (corn, brachiaria, common bean, and Stylosanthes) and two controls, both without residues, and only one with the addition of inorganic nutrient sources; four different textures formed from the same soil; and evaluation after five incubation times (0, 25, 75, 125, and 175 days). A completely randomized design was used, with four replicates. Release of CO2-C, decomposition rate, and mineralization kinetics of N, P, K, Ca, Mg, S, Zn, and Cu were evaluated in the crop residues. Soil texture did not influence the amount of CO2-C released, the remaining dry matter, or nutrient mineralization of crop residues. Stylosanthes and brachiaria residues had greater release of CO2-C and reduction in dry matter than the other residues. The mineralization of N, P, and S was inversely proportional to the C/N, C/P, and C/S ratios. The decomposition of crop residues was regulated by the N and water-soluble extractive contents, and mineralization of macronutrients was governed by their respective initial contents in the residues.