Enhancing Wheat and Soybean Yields in a Subtropical Oxisol Through Effective P Fertilization Strategies

Abstract

Phosphorus (P) deficiency limits agricultural production in tropical and subtropical soils, where soil mineralogy is dominated by kaolinite, iron, and aluminum oxides. The aim of this work was to compare two application methods of P, to the soil surface and to the sowing line, to determine the most effective strategy to increase wheat and soybean yields on an oxidic subtropical soil in Brazil under field conditions. Additionally, four inorganic P fertilizers (monoammonium phosphate (MAP); single superphosphate (SS); triple superphosphate (TP); and natural rock phosphate (NP)) in a wheat crop and four different P rates (zero, 0; low, 45; medium, 90; and high, 180 kg ha−1 of P2O5) of TP in a soybean crop were tested after being applied to the soil surface and to the sowing line. A significant increase in yield (54%) was only found when TP was applied to the sowing line in comparison with the soil surface in wheat plants, probably due to its high solubility. However, the application method did not produce a significant effect in soybean yields, probably because this crop has a different P requirement and root distribution pattern than wheat. In the case of P fertilizers applied to the soil surface, higher wheat yields were observed with NP and MAP in comparison with TP. Finally, a linear increase was observed in soybean yields while increasing the P rate, finding significant differences between the plants fertilized with the highest P rate and the non-P-fertilized plants (24% yield increase in the first case). Our results highlight the need for specific P fertilization strategies for the different crops grown on subtropical regions where soil mineralogy curbs P availability.