|DE KLEIN, CECILE - Agresearch
|MONAGHAN, ROSS - Agresearch
|ALFARO, MARTA - Inia Remehue - Osorno
|GOURLEY, CAMERON - Agriculture Research And Development, Department Of Economic Development, Jobs, Transport And Resou
|OENEMA, OENE - Wageningen University
Submitted to: Soil Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2017
Publication Date: 8/7/2017
Citation: De Klein, C., Monaghan, R.M., Alfaro, M., Gourley, C., Oenema, O., Powell, J.M. 2017. Nitrogen performance indicators for dairy production systems. Soil Research. 55:579-488.
Interpretive Summary: Nitrogen inputs, such as feeds, fertilizers and biologically fixed nitrogen, are critical for maintaining agricultural production and ensuring food security. However, inefficient and excessive nitrogen use can lead to nitrogen loss and environmental degradation. There are many different metrics used to measure nitrogen use on a farm. This paper reviews two indicators used to study dairy production systems: 1) nitrogen use efficiency (percent of nitrogen used to make product, such as milk), and 2) nitrogen surplus (nitrogen inputs that are in excess of what the animal needs). Results indicated that realistic goals for nitrogen use efficiency and nitrogen surplus depend on the soil and climate conditions in which a dairy system operates and on the economic and environmental goals the system aims to achieve. Global and national measures of nitrogen use efficiency are of limited value if the ultimate goal for setting targets is to reduce the environmental impacts of nitrogen use. Whole-farm level targets based on nitrogen surplus would instead be more useful indicators for this purpose. This information will help producers, consultants, and policy makers assess and improve nitrogen use efficiency on farms and reduce the nitrogen being lost to the environment.
Technical Abstract: Nitrogen (N) is invaluable for maintaining agricultural production and ensuring food security, but inefficient use of N can lead to environmental losses. Nitrogen performance indicators are useful tools to evaluate N use outcomes of an agricultural system and/or the risk of environmental N losses. This paper reviewed N use efficiency (NUE; the ratio between N outputs in products over N inputs) and N surplus (the difference between N inputs and N outputs) indicators for dairy production systems. Using case study examples, we also assessed realistic goals for these indicators and discussed key issues associated with their use. Published values of crop NUE and crop N surplus generally ranged between 55-90% and 25-230 kg N/ha/year, respectively, while commonly reported animal NUE and animal N surplus values ranged between 15-35% and 110-450 kg N/ha/year. Whole-farm NUE and whole-farm N surplus values ranged between 10-65% and 40-700 kg N/ha/year. In a New Zealand catchment study, whole farm NUE was affected more strongly by differences between catchments (e.g., soil and climatic conditions) than by differences in management. In contrast, N surplus values differed both between-catchment and within-catchment and were good indicators of N losses to water. Nevertheless, realistic goals for both NUE and N surplus depend on the agro-climatic context in which a dairy system operates and on the economic and environmental goals the system aims to achieve. Crop and animal NUE values can be valuable indicators for optimizing fertilizer and feed use, and minimizing N losses. However, global or even national whole-farm NUE values appear to be of limited value if the ultimate goal for setting targets is to reduce the environmental impact of N use; whole-farm level targets based on N surplus would instead be a more useful indicator for this purpose. Regardless of the metric used, all metrics are calculated based on estimates of N inputs and N outputs. Therefore, it is important to agree on which items should be included in the input and output terms, and that all inputs and outputs are measured or adequately estimated to ensure that comparisons between different systems are equitable. Systems that export manure N or import large amounts of purchased feeds may need to adjust calculated N inputs to account for this. Finally, any NUE and N surplus targets should also be set in the context of other agro-environmental considerations such as losses of phosphorus and fecal organisms to water, carbon footprints, and energy and water use efficiencies.