The evaluation of P availability in soils with different mineralogy using a same methodology can produce inappropriate estimates. The aim of this work was to evaluate P availability using different chemical extractors in soil with high Ca concentration, in comparison with hemathitic soil, and to study the relations between the critical levels and the P adsorption as a function of the soil incubation time. An experiment using subsurface samples of a Orthic Ebanic Vertisol (VEo) (Mollisol), clay textured with predominance of 2:1 clay mineral rich in Ca and a Distroferric Red Nitosol (NVdf) (Nitosol), high clay content, predominantly hematitic, colleted at the semi-arid and humid regions of Pernambuco State, Brazil, respectively. The P doses were defined as a function of the levels 0, 0.2, 0.4, 0.8 and 1.0 of the Maximum Capacity of P Adsorption (MCPA) of each soil and incubated for 90, 60, 30, 15 and 0.5 days. The experiment was carried out in a greenhouse in a factorial scheme (2 soils, 5 P doses and 5 different periods of incubation), in a randomized blocks design, with three replicates each. The available P was determined by the extractors Mehlich-1, Mehlich-3 and Bray-1 and corn was used as indicative plant. The capacity of prediction of available P by Mehlich-1 was not suitable for the soil with predominance of 2:1 clay mineral rich in Ca. For this special case, the highest operationallity of Bray-1 accredits this extractor as the most recommended. The critical levels in the soil decreased with the increase in incubation time, independently of the soil.
P labile; P extractors; maximum capacity of P adsorption
