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

Abstract

The response of sweet sorghum to a partially acidulated (with sulfuric acid) rock phosphate (FAPS) was studied using the original ground phosphate (FA), Gafsa rock phosphate (FG) and simple superphosphate (SPS) for comparison. The soil, a Dark Red Latosol (LE, Haplorthox) was collected in Botucatu, SP. Three successive crops were conducted without new applications of P sources, both in the presence and in the absence of initial liming. The analyses of the data obtained allowed for the following conclusions to be drawn: in the three successive crops combined, dry matter production in the presence of FAPS and no lime applied was 71% of that obtained when powder SPS was used; the efficiency of FA was 17%, where as that of PG was 150%; In the presence of liming,, however, the following values were obtained: granulated SPS - 89%; FAPS - 98%; FA = 30%; FG = 83%. Liming increased the uptake of P from powder SPS, FA and FAPS. FAPS acted also as source of Ca and S. After the third crop, in the absence of liming, SPS left In the soil the highest concentration of available P (Olsen), being followed by FG, FAPS and FA. Liming, however, decreased the amount of residual available P due to SPS, FA, and FG. In the whole the behaviour of FAPS was more similar to that of SPS than to the effect of PA.