Decomposition and Nutrient Release from Grass Residue in Tropical Conditions

The use of grasses as ground cover in tropical climate guarantees soil protection against erosion processes, however, its capacity for nutrients mineralization is poorly understood. In this sense, the aim of the study was to evaluate the decomposition of vegetable residues from grasses and the mineralization of macronutrients in tropical conditions. The study was conducted in a randomized block design with four replications, in a 4 x 9 factorial scheme with four cultural residues: sorghum, millet, black oats, and fallow; and nine evaluation times: 0, 14, 28, 42, 56, 70, 84, 98, and 112 days after setting up the study (DAA), in the field. Vegetable residues were disposed on the soil surface for remaining dry matter (RDM), half-life (t(1/2)) and mineralization rates. Lower decomposition rates were observed in sorghum and millet residues, with RDMs of 40% and 31% when compared to oats and fallow (17% RDM). Thus, the waste mineralization rates decreased in the following order: fallow = oats > millet > sorghum. The mineralization of macronutrients was considered high and decreased in the following order: K > P > N > C > Mg > S > Ca, corresponding to 96, 88, 88, 80, 76, and 74%. The fallow, millet, oat, and sorghum residues released 84, 17, 225, and 17 kg t(-1) of N, P, K, and S, with different mineralization rates. The largest fraction of these nutrients was mineralized in the first 30 DAA, what indicates its potential use in agriculture.