SUMMARYDespite the large number of studies addressing the quantification of phosphorus (P) availability by different extraction methods, many questions remain unanswered. The aim of this paper was to compare the effectiveness of the extractors Mehlich-1, Anionic Resin (AR) and Mixed Resin (MR), to determine the availability of P under different experimental conditions. The laboratory study was arranged in randomized blocks in a [(3 x 3 x 2) + 3] x 4 factorial design, with four replications, testing the response of three soils with different texture: a very clayey Red Latosol (LV), a sandy clay loam Red Yellow Latosol (LVA), and a sandy loam Yellow Latosol (LA), to three sources (triple superphosphate, reactive phosphate rock from Gafsa-Tunisia; and natural phosphate from Araxá-Minas Gerais) at two P rates (75 and 150 mg dm -3 ), plus three control treatments (each soil without P application) after four contact periods (15, 30, 60, and 120 days) of the P sources with soil. The soil acidity of LV and LVA was adjusted by raising base saturation to 60 % with the application of CaCO 3 and MgCO 3 at a 4:1 molar ratio (LA required no correction). These samples were maintained at field moisture capacity for 30 days. After the contact periods, the samples were collected to quantify the available P concentrations by the three extractants. In general, all three indicated that the available P-content in soils was reduced after longer contact periods with the P sources. Of the three sources, this reduction was most pronounced for triple superphosphate, intermediate for reactive phosphate, while Araxá phosphate was (1) REUSMO: FÓSFORO EXTRAÍDO COM RESINAS TROCADORAS DE ÍONS E MEHLICH-1 DE LATOSSOLOS SUBMETIDOS A FONTES E DOSES DE FÓSFORO E TEMPOS DE CONTATO

the Mehlich-1 (M-1) extractant and Monocalcium phosphate in acetic acid (Mcpa) have mechanisms for extraction of available p and s in acidity and in ligand exchange, whether of the sulfate of the extractant by the phosphate of the soil, or of the phosphate of the extractant by the sulfate of the soil. in clayey soils, with greater p adsorption capacity, or lower remaining p (rem-p) value, which corresponds to soils with greater phosphate buffer capacity (pbc), more buffered for acidity, the initially low ph of the extractants increases over their time of contact with the soil in the direction of the ph of the soil; and the sulfate of the M-1 or the phosphate of the Mcpa is adsorbed by adsorption sites occupied by these anions or not. this situation makes the extractant lose its extraction capacity, a phenomenon known as loss of extraction capacity or consumption of the extractant, the object of this study. twenty soil samples were chosen so as to cover the range of rem-p (0 to 60 mg L -1 ). rem-p was used as a measure of the pbc. the p and s contents available from the soil samples through M-1 and Mcpa, and the contents of other nutrients and of organic matter were determined. for determination of loss of extraction capacity, after the rest period, the ph and the p and s contents were measured in both the extracts-soils. Although significant, the loss of extraction capacity of the acidity of the M-1 and Mcpa extractants with reduction in the rem-p value