Current and future direction of nitrogen fertiliser use in Australian grazing systems
Rawnsley, RP and Smith, AP and Christie, KM and Harrison, MT and Eckard, RJ, Current and future direction of nitrogen fertiliser use in Australian grazing systems, Crop and Pasture Science, 70, (12) pp. 1034-1043. ISSN 1836-0947 (2019) [Refereed Article]
The nitrogen (N) nutrition of dairy pasture systems in southern Australia has changed from almost total dependence on legumes in the early 1990s through to almost complete reliance on N fertiliser today. Although some tactical N fertiliser is applied to sheep and beef pastures to boost late winter growth, most N fertiliser usage on pastures remains with the dairy industry. Intensification of the farming system, through increased stocking rates and a greater reliance on N fertiliser, has increased N loading, leading to higher potential N losses through volatilisation, leaching and denitrification. With increasing focus on the environmental impact of livestock production, reducing N loading on dairy farms will become increasingly important to the longer-term sustainability of the dairy industry, possibly with the expectation that Australia will join most of the developed countries in regulating N loading in catchments. This paper examines N usage in modern pasture-based dairy systems, the N cycle and loss pathways, and summarises a series of recent modelling studies and component research, investigating options for improving N use efficiency (NUE) and reducing whole-farm N balance. These studies demonstrate that the application of revised practices has the potential to improve NUE, with increasing sophistication of precision technologies playing an important role. This paper discusses the challenge of sustainably intensifying grazing systems with regard to N loading and what approaches exist now or have the potential to decouple the link between production, fertiliser use and environmental impact.