Reaching the target soil phosphorus concentration zone for optimum crop yields and limited P losses to water

The aim of this review study was to merge the knowledge and legislation about phosphorus (P) in Europe. Our final goal was to generate recommended measures to reduce phosphorus losses from agriculture to surface waters. Phosphorus (P) concentrations in European surface waters generally exceed ecological thresholds. The Nitrates Directive and the Water Framework Directive ask the Member States to address this problem. The resulting monitoring networks and P concentration standards differ widely among Member States. Because agriculture is considered to have a large impact on the surface water P concentrations, the diffuse P losses from soils with high P contents are targeted. Attempts have been made to reduce the soil P concentration under the threshold above which P losses increase exponentially (dashed line in Figure 1). However, agro-economical interests should also be taken into account. Farmers are reluctant to reduce P fertilisation because they fear that reduced soil P concentrations will result in reduced crop yields and quality (solid line in Figure 1). A target zone of soil P concentrations with optimum crop yields and limited P losses can be defined (grey zone in Figure 1). In order to reach or stay in this target zone, fertilisation recommendations should be adapted to include the risk for P losses. Soil P application standards are ideally differentiated to soil P concentrations. In this way, soils with large P concentrations should receive less P in order to reduce the P losses (movement from the right-hand side of Figure 1 towards the target zone) and soils with small P concentrations can receive more P to ensure satisfactory crop yields (movement from the left-hand side of Figure 1 towards the target zone).