A review of New Zealand research measuring phosphorus in runoff from pasture

New Zealand pastoral farm land is intensively grazed and receives predomina ntly single superphosphate fertilizer. Resource managers and policymakers a re concerned about the effects of such land use on P enrichment of waterway s and lakes. This paper reviews New Zealand research on the effects of agri cultural land use on P losses in water runoff and highlights priorities for management and future research. Diffuse agricultural sources contribute ab out 91% of total P entering fresh waters annually, with 0.11 to 1..67 kg P ha(-1) yr(-1) being removed, mostly in particulate forms. Despite a number of studies showing good site-specific correlation, no widely applicable soi l test method for estimating runoff dissolved P concentration has been foun d. The effects of (i) fertilizer application in increasing surface runoff P concentrations (ii) riparian areas in both source and control roles, and ( iii) subsurface drainage, in reducing losses of P in surface runoff from pa sture land, are reported, A catchment scale simulation model, Basin New Zea land (BNZ), for intensively grazed pastures, has been produced based on CRE AMS (chemicals, runoff, and erosion from agricultural management systems). This model adequately predicts P loss at the field scale but is less reliab le at the catchment scale, which indicates differences in predominant P and sediment sources at the two scales. Corrective management has alleviated e utrophication problems in some lakes and waterways; however better informat ion is yet required to understand, model, and manage the more insidious los ses of P to waterways from New Zealand farm land.