Reducing phosphorus losses from agricultural land to surface water

Enrichment of surface waters with phosphorus (P) leads to algal growth and eutrophication. About 27% of agricultural land exceeds optimal soil P levels, posing a risk of P loss to surface waters. Agricultural P loss driven by soil, fertilisers, crop residues, and livestock. Much P loss comes from critical source areas (CSAs) with changing topography. Targeting mitigation actions to CSAs enhances their cost-effectiveness. Phosphorus (P) enrichment of water impairs its quality by stimulating algal growth and eutrophication, affecting an estimated 1.7 billion people. Remediation costs are substantial, estimated at $1 billion annually in Europe and $2.4 billion in the USA. Agricultural intensification over the past 50 years has increased P use brought into the system from mined fertiliser sources. This has enriched soil P concentrations and loss to surface waters via pathways such as surface runoff and subsurface flow, which are influenced by precipitation, slope, and farming practices. Effective mitigation of losses involves managing P sources, mobilisation, and transport/delivery mechanisms. The cost-effectiveness of mitigation actions can be improved if they are targeted to critical source areas (CSAs), which are small zones that disproportionately contribute to P loss. While targeting CSAs works well in areas with variable topography, flatter landscapes require managing legacy sources, such as enriched soil P to prevent P losses.