Low Soil Phosphorus Rates Sustain High Potato Yields in High P-Testing Tropical Oxisols while Foliar Application Enhances Uptake but Not Yield

Potato yield is highly dependent on phosphorus (P) availability. Although high rates of P fertilizers are commonly applied to potatoes even in high P test soils, the efficiency of these practices is questionable. Foliar P fertilization, particularly during the tuber bulking stage, has emerged as a potential complementary strategy. This study aimed to evaluate whether adjusting the conventional P application rate at planting and applying in-season foliar P could optimize potato production. A field experiment was conducted on tropical Oxisols with high P-resin concentrations (74–123 mg P dm −3 ) in three site-years in southeastern Brazil. Treatments included five soil P rates at planting (0, 22, 44, 88, and 177 kg P ha −1 ) combined or not with three foliar P applications (1.3 kg P ha −1 each) during tuber bulking. Even without soil- or foliar-applied P, potatoes grown in these soils exhibited adequate P nutrition and high tuber yields (43.1–54.8 Mg ha −1 ); however, minimum soil P rates still enhanced tuber initiation and yield. Foliar P application increased leaf P concentration, uptake, and recovery efficiency across all planting P rates but did not improve tuber yield or quality. Increasing planting P rates produced modest yield gains (6.5%), with estimated optima at 33 or 53 kg P ha −1 depending on the regression model. Potatoes can still respond to P fertilization even in soils testing high in P, but substantially lower P rates than those traditionally used in commercial production are sufficient to achieve high yields. Foliar P application did not improve tuber yield or quality.