The phosphorus is retained in the soil solid phase with several degrees of energy, which depends on the characteristics and amount of the soil colloids. The no tillage system (NT) may promote phosphorus accumulation in different forms from those observed in the conventional tillage (CT) and thus, may modify the dessorption capacity of the soil. The objective of this work was to estimate the phosphorus dessorption capacity of different soils submitted to NT and CT. Samples from three soils with variable clay contents (Rhodic Hapludox - 680g kg-1 clay, Rhodic Hapludox - 530g kg-1 clay and Rhodic Paleudult - 220g kg-1 clay) cultivated under NT and CT were submitted to successive extractions with anion exchange resin (AER) and adjusted first order kinetics equations to estimate the maximum phosphorus dessorption of the soil. The dessorption by the first extraction and maximum dessorption were higher in the superficial layer of the soil under NT, comparatively to CT. Only one extraction with AER represented, on average, 38, 46 and 49% of the maximum dessorption on soils with high, medium and low clay content, respectively, while that estimated by Mehlich 1 extractor represented, for the same soils, 32, 46 and 89% of the maximum dessorption.
soil phosphorus; soil extractants; no-tillage system; lability
