In no-tillage systems there is a tendency of better P use, particularly in areas under longstanding cultivation, but this observation still awaits confirmation. This study had the objective to quantify the inorganic and organic P fractions and evaluate the responses to different P levels in common bean (Phaseolus vulgaris L.) and brachiaria (Brachiaria decumbens) grown in succession, on a Oxisol with distinct previous land use. The experiment was conducted in a greenhouse with samples from the 0-20 cm layer of a clay Oxisol. The experiment was arranged in a completely randomized design, in a 2 x 4 factorial scheme with four replications, comparing two land uses (soil under longstanding agricultural use with liming and phosphate fertilization and adjacent soil under native cerrado vegetation) and four P rates (0, 120, 240, and 480 mg dm-3 as triple superphosphate based on total P2O5 content). The bean plants were cut after grain harvest and succeeded by brachiaria plants cut twice at flowering. Phosphorus fractions were determined in soil samples of each experimental unit, before and after incubation treatments and after bean and brachiaria cultivation. Phosphorus fertilization increased soil inorganic P forms, which were higher in soils with a history of cultivation and fertilization. Phosphorus fertilization increased soil organic P forms, which were higher in the native soil without cultivation and fertilization records, at the highest P fertilization rates and after bean and brachiaria cultivation. Bean and brachiaria responses to soil phosphate fertilization were lower in previously cultivated and fertilized soils.
no-tillage system; phosphorus dynamics and availability
