Critical nitrogen application rates affecting nitrate leaching in NZ dairy pastures

Abstract

Over the past decade, there has been a rapid increase in dairy farming in New Zealand, with the dairy cattle population increasing from about 3 million in 1982 to 4.4 million in 1998. Much of this expansion has been occurring in the South Island, e.g. in Canterbury and Southland. A number of the newly established dairy farms are on free-draining coarse-textured or stony soils. Nitrate leaching from intensive agricultural systems, e.g. dairy farms, is considered a major contributor to increased nitrate concentrations in ground and surface waters (Cameron et al, 1997). The objective of this research programme was to determine nitrate leaching losses on dairy pasture systems as affected by the application of dairy shed effluent (DSE), nitrogen (N) fertilisers and cow urine on free draining soils using large, undisturbed soil lysimeters. The data obtained were used to develop a simple, semi empirical computer model to estimate nitrate leaching losses and critical N application rates in order not to exceed the drinking water standard of nitrate (11.3 mg N L⁻¹) in the drainage water.