Effect of increasing rate of P fertilization on available P content in soil and plant uptake: implications for P management

The application of phosphorus (P) is necessary for sustainable crop production. Its application rate is often based on soil analysis. However, the P availability is not always properly evaluated for optimal P management. The effect of long-term P fertilization on soil P availability, yield, and plant uptake of P was investigated using data from a long-term field experiment. We hypothesized that: 1) an increasing rate of P fertilization increases soil P content, yield, and P uptake, and 2) annual change of P uptake and P content increases from negative to positive values at an increasing rate of P addition. Different strategies of P management were evaluated using experimental results. Increasing inputs of P in mineral or organic form increases soil P content. However, the effect on yield is limited and unused P accumulates in soil. High yield ensuring strategy of P fertilization is therefore not useful as a way of P management. Results suggest that keeping soil P content in the range of 50-80 mg P kg-1 and organic fertilization (and probably also legume cropping) are useful ways of using P from fertilizers or soil reserves. Results also suggest that Mehlich III soil test brings useful information for P management.