The ion exchange resin method used in some laboratories in Brazil requires soil grinding for the determination of available P. As a consequence of grinding, the extraction of internal labile P in aggregates is expected, increasing the concentration of available-P. On the other hand, finer grinding increases the exposure of soil particle surface, which creates additional sites for further P adsorption. The aim of this study was to evaluate extraction efficiency available-P by Mehlich-1, and anion exchange resin in beads and anion exchange resin in membrane form, in soil samples submitted to different grinding levels. Two experiments were carried out with three P extraction methods. In the first experiment samples collected from 14 non-cultivated soils were used, ground at two levels. The second experiment was performed with three soils, selected among the 14 previously used soils, which were fertilized and cultivated with corn. Results showed that grinding of soil samples did not increase P extraction by Mehlich-1 and membrane resin in non-cultivated as well as in maize-cultivated soils. In the case of the bead resin extraction method, grinding led to an increased P extraction, mainly in fertilized, cultivated soils. The available P measured by the extraction methods and plant response were highly correlated, although the correlation was slightly lower for ground samples.
soil analysis; particle size; phosphorus extraction; buffer capacity
