Factors affecting phosphorus sorption in loess soils of the semiarid Argentina

Abstract

Previous results showed that phosphorus sorption strongly correlated with contents of active Al and Fe oxides and organic matter (OM) in soils of the-Semiarid Argentinean Pampas. Objective of this study was to determine the relative influence of these soil compounds on P sorption. It was hypothesized that contents of OM and Al and Fe oxides should decrease P sorption in the studied soils. With this purpose, sorption isotherms were carried out on non treated soils and on soils samples pre-treated with H2O2 (OM destruction), acid oxalate (AcOx, destruction of amorphous oxides) and boiled acid oxalate (BAcOx, destruction of crystalline oxides). Results showed that OM destruction did not affect none of the constants deduced from Freundlich isotherm (a, l/b and BCO.3). This was probably due to the variable effect of OM on these constants in each soil. On the other hand, constant a decreased 20 to 88% after elimination of crystalline oxides, and 17 to 48% after elimination of amorphous oxides, BCO.3 decreased 33 to 87% after elimination of crystalline oxides, and 21 to 44% after elimination of amorphous oxides, and 1/b remained unchanged. Such results indicate that P sorption (a), as well as the ability of the soil to liberate P to the soil solution (BCO.3), were highly influenced by the amount of amorphous and crystalline Al and Fe oxides and that the retention energy of P (1/b) remained unchanged.