The trade-off between the reduction of phosphorus losses and the maintenance of soil quality in legislation

Phosphorus (P) is a major factor contributing to the eutrophication of fresh water bodies. To limit P losses from agricultural soils and to improve the ecological status of surface waters, the P fertilization rate can be limited by legislation. However, limitations by P application standards may result in a decrease of the soil organic matter (SOM) content as fertilizer types that contribute substantially to the maintenance of SOM often have a high P content. As the SOM content is critical for good soil quality, a reduction in the SOM content might decrease crop yields, especially in regions where intensive horticulture is practiced. Horticultural crops contribute less to the SOM content than arable crops and grassland. In 2019, the national and regional regulations regarding P fertilization were obtained from 20 European regions. Thirteen regions have introduced a P legislation. In 9 of the 13 regions with a P legislation, the P losses are balanced against the maintenance of SOM content by slow P soil mining, legally reducing P availability and/or lowering P application rates in soils with high SOM content. Considering the slow effect of lower P application rates on soil P mining and the possible negative effect on the SOM content, other mitigation measures might be required. For drained fields, iron coated sand filters are a promising sustainable technique to drastically reduce diffuse P losses. Taking into account the transport way (erosion or leaching) of P losses and hydrological conditions, and connectivity between the field and surface water, targeted measures might be more cost-effective to reduce P losses than reduced P fertilization rates.