Response of sweet sorghum to a partially acidulated rock phosphate: I. Greenhouse studies using a red yellow latosol

Abstract

The usefulness of a rock phosphat from Araxá, MG, Brasil, partially acidulated with sulfuric acid (FAPS) was studied, rock phosphate (FA), gafsa phosphate (FG), and simple superphosphate (SPS) being used for comparison. There successive crops were employed in order to assess the residual value, both in presence an in the absence of liming. The analyses of data obtained allowed for the following conclusions to be drawn: the efficiency of FAPS in relation to that of SPS decreased from the first to the third crop, reaching 70% as general ave rage; in the presence of liming, however, the efficiency did not decrease so much, 80-90% being obtained; FG gave results equivalent to those obtained with SPS; liming decreased the relative efficiency of the rock phosphates, especially that of FA which fell from circa 50% to 40%; available P content in the soil was increased as consequence of varions treatments including FAPS plus lime; FAPS acted as a source of P, Ca, and S; its performance in closer to that of SPS than to that of the original FA.