Determining Phosphorus and Sediment Release Rates from Five Irish Tillage Soils

The aim of this study was to compare the nutrient and sediment releases from five Irish tillage soils, inclined at 10- and 15-degree slopes, under a simulated rainfall intensity of 30 mm h–1 in a controlled laboratory study. Using the relationship between soil test phosphorus (STP) in the five soils and the dissolved reactive phosphorus (DRP) released in surface runoff, a runoff dissolved phosphorus risk indicator (RDPRI) was developed to identify the STP level for Irish tillage soils above which there may be a potential threat to surface water quality. The results of this study indicated that tillage soils may produce surface runoff P concentrations in excess of 30 μg L–1 (the value above which eutrophication of rivers is likely to occur and the maximum allowable concentration of DRP in rivers under the EU Water Framework Directive, WFD) if their Morgan’s phosphorus (Pm), Mehlich 3 phosphorus (M3-P), and water extractable phosphorus (WEP) concentrations exceed 9.5 mg L–1, 67.2 mg kg–1, and 4.4 mg kg–1, respectively. This work reinforces the statutory agronomic based requirements of the European Communities (Good Agricultural Practice for Protection of Waters) Regulations 2009 (S.I. no. 101 of 2009). A statistical analysis showed that WEP gave the best prediction for runoff DRP.