Tropical soybean yield response to reduced or zero phosphorus fertilization depends on soils

Abstract

Abstract Oxisol soils with high P sorption capacity are widespread in Brazil, which is the world's second largest producer of soybean [Glycine max (L.) Merr.]. To counter low P availability within highly weathered soils, Brazilian soybean producers commonly fertilize with approximately twice as much P as is harvested in soybean. This has led to the accumulation of P in the soil, especially during the 2000s and 2010s, but the degree to which producers can capitalize on this residual soil P stock to offset fertilizer inputs remains unclear. We tested the effect of residual soil P in a field trial in Mato Grosso, Brazil on a field that has been fertilized for a decade. We grew soybean under three P treatments: 0, 50, and 100% of the farm's standard P fertilization rate for soybean (38 kg P ha−1 yr−1). This experiment was conducted for one growing season on two sites within the same farm field that had different soil texture, Al2O3 + Fe2O3 (R2O3), soil test P, and degree of P saturation. Soybean yield on the soil with greater clay content and R2O3 showed yield declines under reduced P input but yields on sandier soils that had higher soil test P were unaffected by reduced P inputs. These results highlight opportunities to enhance P fertilizer use efficiency in intensive tropical agriculture on highly weathered soils by using site‐specific soil fertility management to harness residual soil P.