Solution equilibrium phosphorus in clay and silt fractions of Oxisols after particle size analysis pre-treatments

The presence of highly stable microaggregates can hamper soil dispersion in some Oxisols. These very clayey groupings maybe not completely disaggregated by chemical and mechanical dispersion. Due to their size, the silt proportion of the soil is overestimated. A laboratory experiment was conducted to verify the use of the solution equilibrium P (SEP) to evaluate the response to particle size analysis pre-treatments in Oxisols. The treatments were at-ranged in a 7 x 2(2) factorial design, in randomized blocks with four replications. The factors were samples of seven Oxisols dispersed with 0.1 mol L-1 NaOH, with and without pre-treatment to remove organic matter (-OM) and poorly crystallized iron oxides (-Ox). SEP was determined in samples of the dispersed clay and silt fractions and in the silt fraction, after a second dispersion with 0.1 mol L-1 NaOH. It was observed that SEP is sensitive enough to identify differences between the treatments applied. This indicates the usefulness of SEP as an auxiliary determination in soil dispersion studies.