The aim of this study was to compare the nutrient and sediment releases from 5 Irish tillage soils, inclined at 10 and 15-degree slopes, under a simulated rainfall intensity of 30 mm hr-1 in a controlled laboratory study. Using the relationship between soil test phosphorus (STP) in the 5 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 phosphorus (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 Morgans P (Pm), Mehlich 3 P (M3-P), and water extractable P (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.