PHOSPHORUS LOSSES FROM ARABLE LAND IN ENGLAND

Concentrations and annual loadings of molybdate reactive P (MRP) and t otal (including particulate) P (TP) are reported from field drainage, catchment and erosion experiments in England. Annual losses through fi eld drains and in catchment runoff were 0.035-0.74 kg MRP/ha and 0.35- 2.64 kg TP/ha, but those in surface runoff from experimental plots mea suring erosion were generally much greater (often > 3 kg MRP/ha and up to 32 kg TP/ha in a wet year). Amounts of TP in drainflow and catchme nt runoff depended upon factors influencing soil dispersibility, such as particle size distribution and calcium carbonate content. The resul ts to date suggest that P losses in surface runoff and erosion from ar able fields to water are best limited by: (a) maximizing crop cover, u sing minimal cultivation practices and where possible planting crop ro ws across rather than up and down the slope, (b) avoiding cultivation practices that result in dispersion of soil particles, and (c) avoidin g application of P fertilizer to wet soils when rainfall is likely soo n after application. Consideration should be given to maintaining fiel d drains below peak efficiency to reduce subsurface P losses.