Useful performance indicators for improving nitrogen management within grazing-based dairy farms

Cameron J P Gourley1, Kerry J Stott2 , Sharon R Aarons1, Innocent Rugoho1

1 Agriculture Research, Ellinbank Centre, Department of Economic Development, Jobs, Transport and Resources, Ellinbank, Victoria 3821, AUSTRALIA

2 Agriculture Research, Parkville Centre, Department of Economic Development, Jobs, Transport and Resources, 32 Lincoln Square North, Carlton, Victoria 3053 AUSTRALIA

Abstract

Nitrogen (N) inputs are critical for productive and profitable grazing-based dairy systems, but inefficient use can contribute to excess N in the broader environment. Whole-farm N balance (WFNB) provides the commonly used recovery metrics: N use efficiency (NUE), milk production N surplus and N surplus/ha; all recognised as environmental performance indicators. We determined annual WFNB for the Australian dairy industry over a 22 year period, and for a diverse range of 16 commercial dairy farms for the 2013/2014 production year. The industry as a whole demonstrated a long-term declining trend in all N recovery metrics, associated with ongoing intensification. Individual farms in a single production year had a wide variation in NUE, productivity N surplus and N surplus/ha, and a poorly defined relationship between NUE and N surplus/ha. At an industry level, the determination of average farm NUE, milk production N surplus and N surplus/ha provides a useful environmental performance indicator but total industry N surplus needs to be adjusted for changes in contributing land area. For individual farms in any production year, we suggest that in addition to quantifying annual N surplus, employing standardised indices that specifically target key N fluxes and utilisation efficiencies at the component level. These will establish more appropriate industry benchmarks for improving N recovery and inform and improve on-farm N management decisions.