Phosphorus retention in soils of Zona Da Mata, Pernambuco, Brazil

Abstract

A laboratory study was conducted to determine the P adsorption maxima in soil as calculated by the Langmuir isotherm. The samples analyzed were from the topsoil (A Horizon) of 16 soil units from reconnaissance survey of the soils of the Zona da Mata of Pernambuco, conducted by the Divisão de Pedologia e Fertilidade do Solo (DPFS) and Instituto de Pesquisas e Experimentação Agropecuárias do Nordeste (IPEANE). Equilibrium concentration of P was established between 0 and 20 ppm. The statistical analysis revealed good correlations between the adsorption maxima (ŷ, µg of P adsorbed per g of soil) and moisture equivalents (x), as shown by the following coeficients and regression equations: r= 0.65*** and ŷ = 6.439 + 11.069x for 17 samples without correction for the effect of exchangeable Al; r = 0.74*** e ŷ = -101.978 + 12.673x for 17 samples with correction for the effect of exchangeable Al. By comparative study between the above correlation coefficients, it was concluded that for the soils studied P in the soil was retained both by adsorption of soil particles and a P exchangeable Al interaction. Surface adsorption of P was the dominant factor in the retention of P in these soils. Only when exchangeable aluminum was approximately 1 me per 100 g, did the P exchangeable Al interaction become important. It was assumed in this work, that all of the exchangeable aluminum in the soil reacted completely with the (PO)₄ ions. It was observed that in clay textured soils the P adsorption maxima, as expected, were larger than in sandy textured soils.