Opportunities for optimizing phosphorus inputs in EU agricultural soils

Abstract

Excessive phosphorus (P) fertilization has resulted in elevated soil P concentrations in some regions in the EU. Legacy soil P imposes a risk for soil functioning and may lead to P losses into the aquatic environment. Recent proposed EU policies aim to optimize P inputs and mitigate excessive soil P concentrations. We present a framework to estimate how much and where P inputs in EU agricultural (cropland and grassland) soils can be optimized. The framework, with assumptions on optimal soil P concentrations and modelled soil P balances, allows calculating how much of the EU agricultural area experiences a build-up or maintenance of soil P concentrations despite having high soil P concentrations. Next, we calculated how much P inputs can be reduced to reach maintenance situation (inputs equal outputs) or to reach optimal soil P concentrations. Assuming optimal soil P concentrations (Olsen) being 20 – 40 mg kg⁻¹, we calculated that current P inputs across the EU can be reduced by 21 % without adverse impacts on crop production, in line with EU policy objectives. The most appropriate strategy strongly depended on the farming system properties and varied across the European regions. The results are discussed in view of current or desired policies limiting P application rates. The framework, with suggested future improvements on uncertainties in data and models, can guide policy makers and land managers to set targets on P application rates, thereby reconciling agronomic and environmental objectives.