A review of nitrogen losses due to leaching and surface runoff under intensive pasture management in Australia
Burkitt, LL, A review of nitrogen losses due to leaching and surface runoff under intensive pasture management in Australia, Soil Research, 52, (7) pp. 621-636. ISSN 1838-675X (2014) [Refereed Article]
This paper reviews the literature on nitrate leaching and nitrogen (N) runoff under intensive dairy pasture systems in Australia and draws comparisons with research undertaken under similar climates and farming systems internationally, with the aim to inform future research in this area. An Australian nitrate-leaching study suggests that annual nitrate-leaching loads are lower (3.714.5 kg N ha1 year1 for nil N and 622 kg N ha1 year1 for 200 kg N ha1 applied) than the range previously measured and modelled on New Zealand dairy farms (~18110 kg N ha1 year1). It is likely that nitrate-leaching rates are higher in New Zealand because of the prevalence of free-draining soils and higher average stocking rates. However, this review highlights that there are insufficient Australian nitrate-leaching data, particularly following urine application, to undertake a rigorous comparison. Median N surpluses on Australian dairy farms are higher (198 kg N ha1) than values for an average New Zealand farm (135 kg N ha1). Given the facts that many soils used for intensive pasture production in Australia are lightly textured or free-draining clay loams receiving average rainfall of >800 mm year1, that herd sizes have risen in the last 10 years and that water quality is a concern in some dairy catchments, nitrate leaching could be an issue for the Australian dairy industry. Australian data on surface runoff of N are more available, despite its overall contribution to N losses being low (generally <5 kg N ha1 year1), except under border-check flood irrigation or hump-and-hollow surface drainage (323 kg N ha1 year1). More research is needed to quantify surface N runoff and leaching following effluent application and to examine dissolved organic forms of N loss, particularly in view of the continued intensification of the Australian dairy industry.