Phosphorus leaching under cut grassland

Phosphorus (P) transfer from agricultural land to surface waters can contri bute to eutrophication, excess algal growth and associated water quality pr oblems. Grasslands have a high potential for P transfer, as they receive P inputs as mineral fertiliser and concentrates cycled through livestock manu res. The transfer of P can occur through surface and subsurface pathways, a lthough the capacity of most soils to fix inorganic P has meant that subsur face P transfer by leaching mechanisms has often been perceived as negligib le. We investigated this using large-scale monolith lysimeters (135 cm deep , 80 cm diameter) to monitor leachate P under four grassland soil types. Le achate was collected during the 1997-98 drainage year and analysed for a ra nge of P fractions. Mean concentrations of total P routinely exceeded 100 m u g l(-1) from all soil types and therefore, exceeded P concentrations abov e which eutrophication and algal growth can occur. The majority of the leac hate P was in algal-available Mo-reactive (inorganic) forms, although a lar ge proportion occurred in unreactive (organic) forms. We suggest that subsu rface transfer by leaching can represent a significant mechanism for agricu ltural P transfer from some soils and must be given greater consideration a s a potential source of diffuse P pollution to surface waters. (C) 1999 Pub lished by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.