Evaluating Scenarios to Reduce Phosphorus Transport in Surface Waters from Slurry Applications in Temperate Grasslands

This study evaluates a range of scenarios to reduce soluble reactive phosphorus (SRP) losses using the surface runoff phosphorus transport model (Surphos) to simulate the application of liquid manure (slurry) to grassland catchments. Surphos was applied using data from two contrasting sites in the Republic of Ireland and Northern Ireland. It explored scenarios that investigated changes to the timing of slurry applications, based both on policy (i.e. a "closed" period where regulations prohibit any slurry spreading) and on climate-based restrictions, where soil moisture and antecedent rainfall were important factors. The observed data showed a considerable spatial variability in runoff at both sites, which resulted in a corresponding variable range of SRP losses predicted by the model. However, at both sites the model results showed that maintaining a closed period led to a greater reduction in SRP losses than opening this period up to slurry applications under climate-based restrictions.