A quick scan to reduce P emissions from agricultural soils to surface water

Leaching of phosphorus (P) from agricultural soils is an important factor determining the surface water quality in the Netherlands. The ongoing reduction in P application rates will prevent a further enrichment of the soil with P and improve surface water quality in the forthcoming decade. However, these measures are not sufficient to reach surface water quality standards of the European WFD in 2015 in all sensitive areas. Geographically differentiated information on the effect of different mitigation options on the P emission is essential for a cost effective implementation of the water framework directive. A quick scan of the effect of five promising mitigation measures in 2027 (manure policy, controlled drainage, mining, improvement of the soil structure, converting agriculture to nature) has been carried out for the Netherlands. Basis of this quick scan is a detailed map of the present P emissions to surface waters, based on the observed P contents in the soil and the simple emission model PLEASE (van der Salm et al., 2014). PLEASE is a static model which as such cannot be used as a tool to predict future P emissions. To predict reductions in P emissions this model has been combined with simple rules based on more detailed models (national emissions model STONE) or expert knowledge. Strong differences were found in the effect of a selected measure. The median reduction of the five measures is close to zero, whereas the 95 percentile ranges from 0.2 kg/ha for the present manure policy to more than 4 kg/ha for mining. Selecting the right measure at the right place is thus of utmost importance to decrease the emissions in a efficient way. The effects of the measures show distinct regional differences. Improving the drainage system, by converting conventional drainage to controlled drainage, is the most promising measure in the western and northern part of the Netherlands. In the sandy parts of the country, mining (no P- application) and the transformation of agriculture to nature have the largest impact on P losses. The effects of the current manure policy are minimal. The average reduction in P emission in the Netherlands in 2027, as a response to the most efficient measure, is 25%. Phosphate losses to surface waters mainly occur in a narrow zone across watercourses. In large parts of the Netherlands this zone is less than 5 m. wide. Measures might thus be partly restricted to these zones.