Minimizing nutrient losses to freshwater from pasture-based dairy systems

Pasture-based dairy systems have expanded in regions with suitable climates, often driven by consumer demand for perceived environmental, animal welfare, and nutritional advantages. Expansion and intensification of such systems have increased nitrogen (N) and phosphorus (P) losses to water, contributing to eutrophication and groundwater contamination. To support sustainable milk production and reduce environmental impact, it is necessary to understand the transport pathways of nutrient losses and the actions that will mitigate the same. Nutrient losses arise from interactions between sources, mainly animal excreta, imported feed and fertilizer, soil, and pasture, and transport pathways such as runoff (surface or near surface in tile drainage) and leaching. Whereas urine patches dominate N loss in pasture-based systems, through nitrate (NO₃-N) leaching, dung and soil are key P sources, especially via surface runoff under wet or compacted soil conditions. Actions to mitigate losses must be tailored to N or P and range from farm system management practices, such as improved nutrient management, manure handling, and strategic grazing or housing/off-paddock infrastructure, to edge-of-field mitigations like appropriate placements of wetlands, riparian buffers, denitrification beds, and detainment bunds. Targeting actions to critical source areas can greatly enhance their cost-effectiveness. Successful implementation of actions depends on aligning environmental benefits with farm profitability, supported by policy instruments that blend voluntary and regulatory approaches.