Soil phosphorus retention can predict responses of phosphorus uptake and yield of rice plants to P fertilizer application in flooded weathered soils in the central highlands of Madagascar

Efficient phosphorus (P) fertilizer management is highly required for resource-limited farmers to achieve higher yields in typical P-deficient farmlands in sub-Saharan Africa. Although soil P retention has been conventionally used to estimate the possible responses to P fertilizer applied to soils, its applicability has not been clearly confirmed at the field level. In this study, the applicability of P retention to predict the response of rice plants to P application was investigated using pot experiments with soils collected from various locations (N = 62) and on-farm experiments at two nutrient-poor sites (N = 38) in the central highlands of Madagascar. Further, we explored a simple prediction method of P retention for multiple location assessment in local farmers' fields using an alternative property of soils collected from rice fields in the same region (N = 213). P retention was negatively correlated with the increase in rice Puptake (Delta P-uptake, r = 0.550) in the pot experiment and with the increase in yield (Delta Yield, r = 0.697) in the on-farm field experiment as a response to P application. Path analysis revealed that oxalate-extractable aluminum (Alox) content was the most important factor of P retention across all the soils, indicating that rice plants grown on soils with higher Alox and P retention are less sensitive to P application. Given its high correlation with P retention (r = 0.642) and its simplicity in measurement, we proposed the use of moisture content of air-dried soils (omega(air)) as a parameter to predict soil P retention. It was further confirmed that omega(air) had a significant negative correlation with Delta P-uptake based on the pot experiment across a wide range of soil statuses (r = -0.518). However, omega(air) could not clearly explain Delta Yield within a small range of soil properties in the field experiment. Overall, soil P retention can predict the responses of rice plants to P application in the typical P-deficient and low-yielding lowlands in the central highlands of Madagascar, and this simple evaluation technique using air-dried soil moisture content will be helpful for the assessment of multiple rice fields on a broad scale.