Towards effective legislation to mitigate the impact of soil P on waterbodies in NW European agriculture

Phosphorus (P) is considered the main limiting nutrient for algal growth in freshwater systems (Correll, 1998). Many waterbodies in North West Europe exceed the environmental P thresholds required for good ecological status (EEA, 2015). Agriculture is considered one of the major sources of P enrichment but the diffuse agricultural P losses can be difficult to tackle. In contrast to nitrogen (N), there is no European P directive, or other specific overarching P regulation for agriculture in the EU. Several EU Member States seek to address agricultural P losses by national or regional legislation, but this P legislation differs widely between countries and regions (Amery & Schoumans, 2014). Even in NW Europe, where widespread high soil P contents provide strong justification for P regulation, legislation varies from no direct regulation to strict maximum P application rates. Current regulations focus largely on mitigating current P losses, limiting field P application rates of chemical fertiliser and/or manure to reduce direct P losses and further soil P build-up. However, legacy soil P, hydrology, transfer pathways and connectivity are equally or more important factors affecting P loss, but these are seldom considered in P legislation. Information regarding the development of P legislation and current regulations were gathered for six NW European countries and regions: Flanders (Belgium), The Netherlands, Northern Ireland (UK), England & Wales (UK), Denmark and the Republic of Ireland. The legislative P controls adopted in the six case-studies are considered in relation to the relative importance apportioned to current P pressures, legacy soil P levels and hydrological factors influencing diffuse P transfers. For example, in some countries maximum P application rates have been regulated according to the amount of legacy P already present in the soil. Approaches are discussed for integrating legacy soil P, hydrology, transfer pathways and connectivity into legislation in order to effectively reduce soil P losses.