Nitrogen Use Efficiency (NUE) – An Indicator for the Utilisation of Nitrogen in Agricultural and Food Systems

Keywords: agricultural systems, Europe nitrogen, nitrogen balance, nitrogen surplus, yield.

There is a need for communications about resource use efficiency and for measures to increase the use efficiency of nutrients in relation to food production. This holds especially for nitrogen. Nitrogen (N) is essential for life and a main nutrient element. It is needed in relatively large quantities for the production of amino acids (protein), nucleic acids and chlorophyll in plants. However excess N is a threat to the environment and potentially to our health.

The ambition of the EU Nitrogen Expert Panel is to promote efficient nitrogen use in food production. In this paper we propose an easy-to-use indicator framework for ‘nitrogen use efficiency’ (NUE) that is applicable to all agricultural systems and food systems. It is based on the mass balance principle, i.e. using N input and N output data for its calculation: NUE = N output / N input. NUE values have to be interpreted in relation to productivity (N output) and N surplus (i.e. the difference between total N input and harvested N output).

For estimating NUE and communicating the results, data and information are required about (i) the total N inputs into a system and the N output in harvested products, (ii) the nature of the system (e.g. farm, crop system, livestock housing system, food system) and its boundaries, (iii) the time span of the analyses, and (iv) possible changes in the stock of N in the system. The NUE indicator concept is presented via a two-dimensional input – output diagram. This allows the presentation of NUE, N output and N surplus in a coherent manner, together with possible reference or target values.

We show that the NUE concept is applicable to N fertilisation trials, farms and crop production systems at the national level. Changes in NUE over time due to the effects of technical progress, market changes and policy measures can be presented easily in the two-dimensional input – output diagram. The concept allows us to examine differences in NUE between farms, between specific systems, between countries, and between years. NUE can also serve as an indicator for ‘sustainable intensification’ of food production. For proper comparisons, a clear and approved protocol is needed for uniform data and information collection, processing and reporting. Also, the proposed reference values need further underpinning.

Nitrogen use efficiency impacts upon many of the recently approved Sustainable Development Goals (SDGs) for the post-2015 era, for which concrete targets, pathways and indicators need to be developed at country scale and below. The proposed NUE indicator is suitable for setting realistic targets and the monitoring of progress towards these, particularly in relation to SDG 2 (Food and nutrition security), SDG 12 (Sustainable consumption and production), SDG 14 (Marine ecosystems) and SDG 15 (Terrestrial ecosystems).

Prof. Dr Oene Oenema, Alterra, Wageningen UR, The Netherlands, on behalf of the EU Nitrogen Expert Panel.

33 pages, 13 figures, 1 table, 44 references