Nitrogen use efficiency indicators for the Australian cotton, grains, sugar, dairy and horticulture industries

There are multiple ways that nitrogen (N) use efficiency (NUE) can be assessed, and NUE indicators are documented in the scientific literature for measuring crop N uptake efficiency, crop N utilization efficiency, and several other agronomic efficiency indicators. At present, however, there is no consensus as to how NUE should be calculated and reported across the different agricultural industries in Australia, which makes it difficult to communicate NUE data to stakeholders in a consistent manner. This variation in NUE terminology and definitions also makes it difficult to perform long-term industry-specific assessments of NUE, inform N management practices, and therefore guide future research and development. The work reported in this article was undertaken to address the lack of harmonization of NUE terminology and definitions that is evident in Australia. Metrics used to measure NUE both in Australia and internationally are critically reviewed and collated, and used to define, describe and interpret guidelines for a suite of NUE indicators. This suite of key NUE indicators can be applied to assess cross-sector productivity, profitability and environmental aspects of N fertilizer use, and for effective communication of NUE research findings and implications. The following NUE indicators are proposed: (1) Fertilizer N utilization efficiency (NUtE), (2) Fertilizer N uptake efficiency (NUPE), (3) Agronomic efficiency of applied fertilizer N (AE), (4) Partial factor productivity of applied N (PFPN), and (5) Marginal return on applied fertilizer N (MRF). The calculation, interpretation and cross-industry usefulness of these NUE indicators are presented and discussed. Worked examples are provided based on data derived from the Australian Government's More Profit from Nitrogen (MPfN) Program, which enabled industry-specific NUE values to be determined. These values were used to compare and contrast NUE between industries and identify opportunities where NUE could be potentially improved by management strategies. Further, an NUE indicator framework was adapted for the Australian irrigated cotton and sugarcane cropping systems based on a generic framework developed by the EU Nitrogen Expert Panel. This concept could be applied to other industries as data from the MPfN Program become available.