Management of Phosphorus Losses From Artificially Drained Grazed Pastures.

The productive capacity of many grazed pasture systems is maintained or improved by the use of artificial drainage. Although traditionally thought of as an issue associated with surface runoff, artificial drainage provides an effective conduit for the loss of phosphorus (P) from land to surface waters. Coupled to drainage, sources of P loss in grazed pastures are more complicated than cropping systems due to the greater number of possible sources and hydrologic regimes and soil types. It is also true that the magnitude of P losses tend to greater with increasing intensity. New Zealand has a wide diversity of soil type, climate regimes and also one of the most productive (and intensive) dairy production systems in the world. This review outlines the range of P losses associated with drainage of dairy pasture in New Zealand, outlines the factors that exacerbate the P losses and regional to national efforts to manage these factors to minimise P losses.