Distribution of inorganic phosphorus fraction in soil management systems

The intensity of the reactions of the phosphate fertilizer in the soil shou ld vary in function of the different management systems. The study had the objective of evaluating the modifications in the inorganic fractions of P a s affected by soil tillage and crop sequence. In May 1997, three soil layer s of four long-term field experiments, involving no-tillage and conventiona l tillage with different crop sequences, were sampled. The total P and six fractions of inorganic P were evaluated. The medium content of total P was much higher than the native P. Total P increased in the upper soil layer un der notillage. Available (resin and NaHCO3 0.5 mol L-1) and nonlabile inorg anic P (HCl 1.0 mol L-1) were higher in the surface layer under no-tillage than in conventional tillage. The highest concentrations of inorganic P wer e moderately labile (NaOH 0.1 mol L-1). The crop sequences did not influenc e the fractions of inorganic P.