Interim Evaluation of Phosphogypsum as an Ameliorant for Soil Acidity in Sugarcane

Results are reported of a 3x3x3 factorial trial in which phosphogypsum (PG), dolomitic limestone (DL) and single superphosphate (SS)were applied to sugarcane. The trial was situated on a Kranskop form soil with a moderately toxic aluminium (AI) content. Based on the combined yield responses from the plant and first ratoon crops, treatments with SS were superior to those with PG, and little response was obtained from DL. The high P in-furrow treatment (90 kg P/ha) gave a highly significant response of 3 t/ha sucrose compared with 2,1 t/ha from the best PG treatment (5 t/ ha). Leaf P and Ca also increased with both PG and SS application. Chemical changes in the soil following PG application resulted in considerable leaching of Mg below the 400 mm soil depth. Improved chemical changes included increased pH and Ca levels in the subsoil together with a reduction in exchangeable AI. The SS/PG interaction, evidence from third leaf P analyses, and lack of any marked response to liming coupled with good root development to depth indicated that yield response to PG was due mainly to its P content. Enhanced Ca content and diminished acid saturation in the subsoil may be beneficial.