The objective of this work was to evaluate the release of P and K from residues of single oat, vetch and forage radish and from mixtures of oat and vetch, under notillage system. The residues were placed in 0.5 mm mesh nylon bags (20x20 cm), which were placed on soil surface and taken out at 15, 29, 43, 59, 71, 82, 112 and 182 days after. At each sampling date the material was dried at 65ºC and the amount of dry matter remaining and its concentration of P and potassium were determined. It was adjusted the asymptotic model [(Pr and Kr = Ae-kt + (100 - A)] to observed values for the remaining P and K (Pr and Kr) which was used to estimate the rate (k) of P and K release and the proportion of these nutrients of the labile (A) and recalcitrant (100 - A) pools of crop residues. The rate of K release was 4.5 times greater than was for phosphorus. The amount of remaining P in the initial phase of the decomposition was inversely proportional to the concentration of water soluble P in the residues. In the residues of the oat + vetch mixture the P and K release were slower than the observed for single species. These results indicate a greater potential of synchrony between commercial crops P and K demand and P and K release from residues of oat + vetch mixture as compared to single vetch.
Avena strigosa; Vicia sativa; Raphanus sativus; crop residues
