Grassland reseeding - improving grassland productivity and reducing soil surface phosphorus accumulations

Long-term phosphorus (P) accumulation in agricultural soils presents a particular challenge for water quality improvement. P is commonly elevated in soils managed for intensive livestock production due to repeated over-application of slurry and fertilisers. High legacy nutrient accumulations can result in poor water quality via transport pathways such as surface runoff, subsurface drainage, and soil erosion. To achieve the EU Water Framework Directive aims, improved management strategies are required for diffuse and point P sources. Reseeding is known to improve grassland productivity and enhance overall soil health. However, soil disturbance associated with reseeding could have positive and negative impacts on several other soil functions (including improved microbial activity, but also increasing the potential for sediment and nutrient losses). This study investigated the role of reseeding in reducing nutrient surpluses in surface soils and identified potential trade-offs between production, environment, and soil health. At a study site in the Blackwater catchment in Northern Ireland, we collected high-resolution gridded soil samples for P analyses and combined this with GIS-based interpolation. We found that large decreases in sub-field scale nutrient content occurred following reseeding. This indicates that this strategy is effective in reducing soil surface P accumulations. However, it is unclear whether this P becomes available for grass uptake during re-growth or whether it increases the pool of mobile P which can be lost in surface runoff, subsurface drainage, and soil erosion. This paper discusses the results in the context of other conventional approaches used to reduce soil surface P accumulations and their associated shortcomings for practical implementation.