Agrosica: A Novel Product for Promoting Increased P Use Efficiency in Tropical Soils.

Phosphate fertilizers are critical for crop production in tropical soils, which have high P-fixing capacity and Al saturation, as well as low pH and Ca contents. The need of high P rates for high yields has raised concerns about the sustainability of cropping systems in Brazil, which is a key country for global food security. We have produced and tested a by-product of phosphoric acid production (fluorite with silicon oxide, hereafter called AgroSiCa) as an amendment for decreasing P adsorption and Al toxicity, while providing Si and Ca to crops in tropical soils. The experiment was conducted in greenhouse conditions in a completely randomized design consisting of 3 soils (2 Typic Dystrustox and 1 Typic Dystrustept), 3 doses of AgroSiCa (0, 2.0, 4.0 t/ha), 2 soil layers, and a control of each soil, with 3 replicates. Soil and soil solution samples were collected following the reaction with AgroSiCa for analyses of P and Al fractions. AgroSiCa application decreased labile aluminum in the solution of all soils, with a greater effect in top soil layers (0-10 cm). There also was an increase on more labile fractions of P following the application of AgroSiCa, which shows that the product can increase the efficiency of phosphorus fertilization and contribute to a more rational use of P sources in tropical agroecosystems. Additional experiments are underway to assess the benefits of AgroSiCa when used prior, together, or after the application of P fertilizers.