Phosphorus leaching under cut grassland

Phosphorus (P) transfer from agricultural land to surface waters cancontribute to eutrophication, excess algal growth and associated water quality problems. Grasslands have a high potential for P transfer,as they receive P inputs as mineral fertilizer and concentrates cycled through livestock manures. The transfer of P can occur through surface and subsurface pathways, although the capacity of most soils to fix inorganic P has meant that subsurface P transfer by leaching mechanisms has often been perceived as negligible. We investigated this using large-scale monolith lysimeters (135 cm deep, 80 cm diameter) tomonitor leachate P under four grassland soil types. Leachate was collected during the 1997-98 drainage year and analysed for a range of Pfractions. Mean concentrations of total P routinely exceeded 100 mu g l-1 from all soil types and, therefore, exceeded P concentrations above which eutrophication and algal growth can occur. The majority of the leachate P was in algal-available Mo-reactive (inorganic) forms, although a large proportion occurred in unreactive (organic) forms. We suggest that subsurface transfer by leaching can represent a significant mechanism for agricultural P transfer from some soils and must be given greater consideration as a potential source of diffuse P pollution to surface waters. [ABSTRACT FROM AUTHOR]