Efeito da concentração de fósforo da solução de equilíbrio utilizada para análise do fósforo remanescente em solos da região nordeste do brasil

Abstract

The remaining phosphorus measures the amount of P remaining in the equilibrium solution in response to a P concentration added to the soil. In Brazil, determination of the remaining P is done using a solution of 0.01 mol L-1 CaCl2 containing 60 mg L-1 of P in a soil / solution ratio of 1:10. However, this concentration may be high and unsuitable for the soils of the Northeast region of Brazil, since they have low phosphorus sorption capacity when compared to the soils of the other regions of Brazil. The objective of this work was to evaluate the effect of different initial concentrations of P of the equilibrium solution used for P-rem analysis in 52 soils of the Northeast region of Brazil. Initial concentrations of 20, 30, 40, 50 and 60 mg L-1 of P of the equilibrium solution were tested for the determination of Prem in 52 representative soil samples from the Northeast region of Brazil. The determination of the remaining P followed the methodology proposed by Alvarez et al. (2000). Soils with higher clay contents showed low values of P remaining, probably because these soils presented higher CMAP in relation to the others. In the studied soils, the increase in the initial concentration of P in the equilibrium solution increased the mean P-values found and consequently decreased the coefficient of variation (CV) of these values. The CV values for the studied soils decreased by almost 1% for each increase of 1 mg L-1 of P in the equilibrium solution. In the studied soils, the increase of the initial concentration of P in the equilibrium solution increased the mean of the P-values found and, consequently, the coefficient of variation of these values decreased. Therefore, the initial concentration of P in the equilibrium solution of 60 mg L-1 of P is recommended for the determination of the remaining P in soils of the Northeast region of Brazil