|GOURLEY, C - Department Of Primary Industries|
|AARONS, S - Department Of Primary Industries|
Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2011
Publication Date: 6/15/2011
Citation: Gourley, C.J., Aarons, S.R., Powell, J.M. 2011. Nitrogen use efficiency in grazed and confinement dairy production systems. Agriculture, Ecosystems and Environment. DOI:10.1016/j.agee.2011.05.011.
Interpretive Summary: Pasture- and confinement-based dairy farms differ considerably in feed, animal and manure management. Different approaches are therefore needed to understand and improve nutrient management. Nitrogen use efficiency was determined on pasture-based dairy farms in Victoria, Australia and confinement-based farms in Wisconsin, USA to highlight the different challenges and opportunities for improving nutrient management. Enhanced profitability and environmental performance can be obtained through improved feed management on pasture-based systems, and through improved manure management on confinement-based dairy farms. This information can be used to assist in the development of performance goals and to monitor and evaluate the impacts of feed and manure management practices on nitrogen use, productivity and environmental outcomes.
Technical Abstract: Grazing and confinement-based dairy operations in industrialised nations continue to intensify. In general, farm numbers are declining, while milk production per cow and reliance on imported feed and fertiliser are increasing. While greater nitrogen (N) input is a key contributor to increasing productivity in these systems, there is a decreasing reliance on N recycling, increasing nitrogen surpluses, and greater environmental losses. In confinement-based dairy operations, farmers generally manage mixed animal and cropping operations, and have more control of the nitrogen intake of cows, which in turn influences the quantity and N concentration of manure N, and the capture, storage and land application of excreted manure N. In grazing-based dairy operations, farmers manage grazed pastures, and although they also purchase feed, they generally have less control of dairy cow diets, with feed quality and N content varying throughout the year. Additionally the direct deposition of manure N by grazing animals can result in a heterogeneous nutrient distribution, with high N loads in some areas which may pose a greater risk of nutrient loss. The aim of this paper is to describe the various factors and processes that impact on N use efficiency (NUE) in commercial grazing and confinement dairy production systems in Victoria, Australia and Wisconsin, USA and present NUE information relating the conversion of feed N into milk, and the proportion of manure nitrogen collected and recycled. Feed NUE values were similar for the 17 Victorian and 12 Wisconsin dairy farms involved in the study. The Victorian herds ranged from 0.15 to 0.35, with a median value of 0.22, while the Wisconsin dairy herds ranged from 0.17 to 0.34, with a median of 0.26. However, there were highly significant (P<0.001) regional and seasonal differences between the relationship between feed NUE and feed N intake, with Wisconsin systems more efficiently converting dietary N into milk. On the Victorian dairy farms, the greatest proportion of excreted manure N was deposited on grazed pastures. Correspondingly, the largely confinement dairy systems in Wisconsin collected a much greater proportion of excreted N than the Victorian grazing systems. However, both systems used only a small proportion of the land base to apply collected manure. Additionally, substantial amounts of excreted manure N was deposited in unproductive and non-collected areas of dairy farms in both regions. We propose that the assessment of NUE for within-farm components of dairy production systems could be used on both grazing and confinement-based dairy farms to assist in the development of performance goals and to monitor and evaluate the impacts of feed and manure management practices on N use, productivity and environmental outcomes.