Submitted to: Environmental Science and Policy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2010
Publication Date: 4/27/2010
Citation: Powell, J.M., Gourley, C.P., Rotz, C.A., Weaver, D.A. 2010. Nitrogen Use Efficiency: A Performance Indicator for Dairy Farms. Environmental Science and Policy. 13:217-228. Interpretive Summary: Escalating fertilizer and feed costs, declining product prices, and increasing regulations to reduce nutrient loss have created new pressures to improve nutrient use in agricultural production. Of particular importance is nitrogen use efficiency (the percentage of applied nitrogen incorporated into a product) because of high nitrogen use in agriculture (due to its great potential to increase production) and also because of its potential to pollute the environment. The purpose of this study is to provide an overview of factors and processes that impact nitrogen use efficiency (NUE) in dairy production; to evaluate gaps between NUE obtained on commercial farms (actual-NUE) and under experimental conditions (potential-NUE); to identify practices that may bridge these gaps; and to evaluate the possibility of using NUE as a performance indicator for dairy farm performance. We found that nitrogen use efficiency (NUE) for feed (percent feed N converted to milk) ranges from 16-36%, for manure/fertilizer (percent manure/fertilizer N converted to crops/pasture) ranges from 16 to 77%, and whole-farm NUE (percent of all N imported onto a farm that is exported off the farm) ranges from 8 to 64%. Factors that impact NUE in dairy production are (1) biological potentials to convert applied nitrogen into products, (2) the nitrogen farmers apply to avoid risk, and (3) the nitrogen farmers apply in excess to achieve potential and avoid risk, which is wastage. These three factors need to be considered when devising recommendations to enhance NUE. This information will be useful to dairy producers, nutrient management consultants and policy makers who are looking for the most effective ways to reduce the environmental impact of dairy production while also improving the economic sustainability for dairy producers.
Technical Abstract: Escalating fertilizer and feed costs, declining product prices, and increasing regulations to reduce nutrient loss have created new pressures to improve nutrient use in agricultural production. Of particular importance is N use efficiency (the percentage of applied N incorporated into a product), because of high N use, and the great potential of N to increase production and pollute the environment. The purpose of this study is to provide an overview of factors and processes that impact N use efficiency (NUE) in dairy production, evaluate gaps between NUE obtained on commercial farms (actual-NUE) and under experimental conditions (potential-NUE), identify practices that may bridge these gaps, and evaluate the possibility of using NUE as a performance indicator for dairy farm performance. In general, feed-NUE (feed N transformed into milk) is higher on confinement- (21 to 36%) than on grazing- (16 to 25%) based farms; manure/fertilizer-NUE (manure N and fertilizer N incorporated into crops and pasture) varies greatly (16 to 77%) and is very site-specific; and whole-farm NUE (8 to 64%) declines as stocking rates increase, which increases reliance on imported feed and limits possibilities for effective manure N recycling. Actual-NUEs are lower and much more variable than potential-NUE which indicates significant improvements in NUE are attainable on many commercial dairy farms. Optimal stocking rate and manure N crediting can enhance NUE, farm profits and environmental outcomes of dairy farms. Concepts of NUE could be used to engage dairy producers in collaborative assessments of gaps between their actual N use and the biological potential of N use, to develop performance goals for N use in various production components, and to monitor and evaluate the impacts of alternative feed, manure and fertilizer management practices on N use, profitability, and environmental outcomes.