Lime and rates and sources of phosphorus as influencing soybean yield and chemical properties of Pelotas soil (Alfisol)

Abstract

The effect of five phosphates as sources of phosphorus for soybean (Bragg cultivar) was evaluated in two rates (100 and 200 kg/ha of total P₂O₅), on limed and unlimed soil conditions. The experiment was carried out under field conditions, during the soybean growing season of 1973/74, 1974/75, 1975/76 and 1976/77, at UEPAE Pelotas station. The pH and the exchangeable Ca + Mg content from the soil were increased with Gafsa phosphate, but mainly with lime, Thomas slag and Yoorin thermophosphate application. The exchangeable Al content was eliminated by lime application and decreased annually by application of Gafsa phosphate, Thomas slag and Yoorin thermophosphate, when the lime was not applied. Thomas slag and Yoorin thermophosphate were the best phosphates for grain yield and do without lime: however, under limed soil conditions all phosphates had some efficiency, except for the Gafsa phosphate in the first growing season.