Reducing Phosphorus Fertilizer Input in High Phosphorus Soils for Sustainable Agriculture in the Mekong Delta, Vietnam

High rates of phosphorus (P) currently being applied to soils for the production of vegetables in the Mekong Delta, Vietnam, has led to concern regarding negative effects on the economy and the environment. This research presents a comprehensive study on the determination of P supplying capacity in this region of Vietnam to examine the possibility of reducing P fertilizer input. In total, 120 soil samples were collected to evaluate total P and Bray 1 available P in the soils. Phosphorus maximum sorption, degree of P saturation, P release, and the effect of P fertilizer on corn ( Zea mays L.) yield in greenhouses and fields were also determined. Total P concentrations in 57% of the soil samples evaluated yielded high P concentrations (>560 mg P/kg), while 74% of the samples had high Bray 1 available P concentrations (>20 mg P/kg soil). Maximum P sorption ranged from 149 to 555 mg P/kg soil, respectively, and had negative correlation with available P ( r = −0.63*). The percentages of P saturation ranged from 0.63% to 5.5% and correlated with available P ( r = 0.98**). Maximum P release ranged from 1.2 to 62 mg P/kg soil, respectively, and correlated with available P ( r = 0.96**). Corn grown in soils with available P concentrations >15 mg P/kg did not respond to P fertilizer in greenhouse or field experiments. We conclude that many farmers in this region can reduce P fertilizer input, thus increasing their profits and reducing negative environmental impacts associated with excess soil P for sustainable agriculture.