Phosphate Sources and Filter Cake Amendment Affecting Sugarcane Yield and Soil Phosphorus Fractions

The use of mineral phosphate fertilizers associated with organic residues can improve fertilizer use efficiency and consequently decrease their usage costs. Soil application of filter cake (FC) can provide nutrients and enhance physical quality. This study aimed to evaluate the effects of different phosphate fertilizers [rock phosphate (RP) and triple superphosphate (TSP)] applied at different rates (90 and 180 kg ha-1 P2O5) associated with filter cake (10 Mg ha-1 dry matter) on the soil phosphorus (P) fractions after two consecutive seasons of sugarcane in two distinct soils, sandy and clayey. Yield was significantly improved with FC addition in the first year in both soils, while inorganic P sources did not influence crop yield at either location and in both years. Organic and residual P forms were only slightly altered in the sandy soil. The most significant changes occurred in the labile and moderately labile P fractions in both soils. Filter cake was an effective source of nutrients for plant development, increasing the levels of soil available P and keeping it at agronomically adequate levels for up to two years, however it was not able to facilitate the P release from mineral fertilizers, irrespective of the source or rate.