Transfer of phosphorus from small agricultural basins with variable soil types and land use

Three small rural basins in England with different soil types and farming systems were monitored from November 1994 to July 1998 to determine the amounts, forms, timing and pathways of diffuse phosphorus (P) transfer in land runoff. Annual loads of total phosphorus (TP) measured in two lowland basins and one upland basin ranged up to 4.2 and 1.4 kg ha-1, respectively and were heavily dependent on basin flow. In all three basins, most P was transported in particulate (PP) form during high flow rates in winter when stream biological activity is low. However, comparison of two monitoring programmes in one basin also indicated elevated loads of soluble P under lower intensity storms. Monitoring of individual field tile drains in the two lowland basins indicated that much of the P transfer was agriculturally derived. The amount of flow needed to generate P transfer was greater, and the concentration of P in the runoff under equivalent flows was lower, under upland grass than under arable or mixed arable/grass cropping.