Predicting phosphorus losses with the PLEASE model on a local scale in Denmark and the Netherlands

To reduce P losses from agricultural soils to surface water, mitigation options have to be implemented at a local scale. For a cost-effective implementation of these measures, an instrument to identify critical areas for P leaching is indispensable. In many countries, P-index methods are used to identify areas at risk for P losses to surface water. In flat areas, where losses by leaching are dominant, these methods have their limitations because leaching is often not described in detail. PLEASE is a simple mechanistic model designed to simulate P losses by leaching at the field scale using a limited amount of local field data. In this study, PLEASE was applied to 17 lowland sites in Denmark and 14 lowland sites in the Netherlands. Results showed that the simple model simulated measured fluxes and concentrations in water from pipe drains, suction cups, and groundwater quite well. The modeling efficiency ranged from 0.92 for modeling total-P fluxes to 0.36 for modeling concentrations in groundwater. Poor results were obtained for heavy clay soils and eutrophic peat soils, where fluxes and concentrations were strongly underestimated by the model. The poor performance for the heavy clay soil can be explained by the transport of P through macropores to the drain pipes and the underestimation of overland flow on this heavy-textured soil. In the eutrophic peat soils, fluxes were underestimated due to the release of P from deep soil layers.