b'13Right Time, Right PlaceSlurry Application Strategies forReducing Phosphorus loss in Overland FlowDoody DG1, Vadas P2, Anderson A1, Adams R1, Fenton O3, Tuohy P4 and Hawkins J MB51Agri-food & Bioscience Institute Northern Ireland2USDA Agricultural Research Service, Madison, Wisconsin USA3Teagasc, Johnstown Castle Ireland4Teagasc, Moorepark Ireland5Rothamsted Research, North Wyke, EnglandSlurry application to grasslands remains a high-risk practice in climates with high rainfallfrequency and low soil moisture deficit for much of the year. SurPhos is a daily time-stepmodel that simulates surface application of slurry, soil phosphorus cycling and dissolved reactive phosphorus (DRP) loss in overland flow (kg/ha/day) for a range of mitigation strate-gies, over multiple years, to sites with different antecedent conditions. The model was evaluated under Irish conditions using data from a two-year study of P loss in overland post application (R2 = 0.74). Subsequently, the model was applied to 4 sites in Ireland & the UK that provided 84 plot-years of data for low (n=27), medium (n=28), and high (n=29) overland flow potential sites to evaluate the impact of application timing, rate, and P content of slurry and soil conditions on DRP loss in overland flow. For example, simulated average DRP loss during the closed period (15th Oct -31st Jan) was 0.4, 1.0 and 1.92 kg P ha-1 on low, medium and high runoff sites respectively,compared to average losses of 0.14, 0.2 and 0.45 kg P ha-1 during the rest of the year.On an annual basis, full implementation of the Nitrate Action Programme regulations resulted in 41%, 55% and 63% reduction in DRP export from fields with low, medium and high overland flow potential. Overall, results demonstrate what reductions in P export can be achieved if slurryapplications are consistently targeted at the right place and time.57'