Phosphorus uptake of rice plants is affected by phosphorus forms and physicochemical properties of tropical weathered soils

Phosphorus (P) deficiency is a major constraint for rice production in the tropics. Field-specific P management is key for resource-limited farmers to increase yields with minimal inputs. We used soil P fractionation analysis to identify the relevant factors controlling P uptake and the responses to P fertilization of rice in flooded and highly weathered soils. Phytometric pot-based experiments and a modified Hedley fractionation analysis were repeated for soils from extensive regions and from geographically adjacent fields in Madagascar. Large field-to-field variations in indigenous P supply from soils (total P uptake of rice when P is omitted) and fertilizer-P recovery efficiencies (increased P uptake when P is applied) were observed not only for soils with various geological backgrounds but also for soils from adjacent fields. Regression models indicated that the indigenous P supply in soils was largely controlled by readily available inorganic and organic P pools (r2 = 0.72), whereas fertilizer-P recovery efficiencies were controlled by the abundance of oxalate-extractable aluminum and iron in soils (r2 = 0.81). Spatial heterogeneity even within adjacent fields leads to benefits from field-specific fertilizer management based on indigenous P supply from soils and fertilizer-P recovery efficiencies evaluated by different soil properties.