A Review of New Zealand Research Measuring Phosphorus in Runoff from Pasture
2000
Gillingham, Allan G. | Thorrold, Bruce S.
New Zealand pastoral farm land is intensively grazed and receives predominantly single superphosphate fertilizer. Resource managers and policymakers are concerned about the effects of such land use on P enrichment of waterways and lakes. This paper reviews New Zealand research on the effects of agricultural land use on P losses in water runoff and highlights priorities for management and future research. Diffuse agricultural sources contribute about 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 soil test method for estimating runoff dissolved P concentration has been found. 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 pasture land, are reported. A catchment scale simulation model, Basin New Zealand (BNZ), for intensively grazed pastures, has been produced based on CREAMS (chemicals, runoff, and erosion from agricultural management systems). This model adequately predicts P loss at the field scale but is less reliable at the catchment scale, which indicates differences in predominant P and sediment sources at the two scales. Corrective management has alleviated eutrophication problems in some lakes and waterways; however better information is yet required to understand, model, and manage the more insidious losses of P to waterways from New Zealand farm land.
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