Manufacture and agronomic evaluation of potential phosphate fertilizers

Abstract

Phosphorus (P) is the most limiting nutrient for crop yields in tropical soils. More than 90 % of the phosphorus sources used in Brazil and around the world are fully soluble, however, mainly in tropical soils, the use of fully soluble sources may not be the most appropriate, since the P supplied through fertilizer, at the same time increasing the concentration of P in soil solution favoring the absorption by the roots, may be also "fixed", transformed into non labile forms. Theoretically, the ideal phosphate fertilizer should supply the initial demand of the plant and also provide slow releasing of P during the crop cycle, enabling synchronization between the plant demand and the dissolution of the P source. The manufacture of a fertilizer by mixing in the same granule the phosphate rock (PR) + fully acidulated phosphate (AP) + elemental sulfur (S0) could increase the solubility of the little soluble P fraction (PR), obtaining a fertilizer with "synchronized" release, which satisfies the need of P in the beginning of the plant growth and provide a gradual supply of P along the crop cycle, resulting in agronomic efficiency better than the completely acidulated source of P. This project aimed evaluate the agronomic effectiveness of phosphate fertilizers produced from the mixture in the same granule PR + AP + S0, compared to a fully acidulated phosphate. The following are the objectives: (i) quantify and evaluate the effect of S0 and AP in increasing the availability of P from PR, using the isotopic dilution method with 32P, (ii) evaluate the ratio between the soluble fraction (AP) little soluble fraction (PR) and S0 in the mixture, (iii) evaluate the AP (TSP and MAP) in the mixture, (iv) evaluate the application form (broadcasted and located in-furrow) and the residual effect of P sources and; (v) evaluate the diffusion of P and the reaction products of manufactured phosphate fertilizers (mixed).