Rationale and definition:
Nitrogen plays a central role for the productivity, sustainability and environmental impact of crop and animal production systems. Nitrogen is essential for feeding the world’s population and to enable intensive farming, which in turn limits the conversion of land to agriculture.
Most of the anthropogenic nitrogen produced enters global cycles as fertilizer in crop production. Hence, optimizing nitrogen management so that high yields can be achieved with high nitrogen fertilizer efficiency is a core component of food security as well as environmental sustainability. At the same time, some food systems (e.g. smallholder food production in sub-Saharan Africa) consume more nitrogen than is replenished – they “mine” nitrogen from soils. An effective nitrogen indicator therefore needs to track the levels as well as efficiency of nitrogen use.
Nitrogen use efficiency is based on the mass balance principle and defined as nitrogen output in harvested products divided by the nitrogen inputs to the farm or the food system. It must be corrected for changes in the stock of nitrogen inside the system.
The indicator can be presented graphically by mapping nitrogen input against nitrogen output. For each food system and agro-ecological area, optimal ranges of nitrogen use efficiency can be defined, which in turn makes it possible to determine whether a given system uses nitrogen optimally or has too low/high nitrogen use efficiency. Additionally, the presentation of the indicator can identify minimum nitrogen use levels that denote minimum food production thresholds. Food systems, such as many smallholder farmers in Africa, that use too little nitrogen would therefore be encouraged to increase nitrogen use. Finally, the graphs can specify the acceptable nitrogen balance surplus for each food system.
Such a graph is illustrated schematically below (Figure 7). All values are purely indicative and for illustration purposes only.
Figure 7: Example for acceptable boundaries of nitrogen output/input ratios, nitrogen use efficiency, minimum productivity levels, and maximum nitrogen surplus balance at a national scale. The example only serves to illustrate the interpretation of the proposed indicator.94
Targets for crop nitrogen use efficiency are context-specific, primarily depending on climate, yield, current nitrogen use, soil quality, irrigation, and other crop management practices. This indicator needs to be interpreted in relation to other indicators, such as the crop yield gap indicator and the water productivity indicator. A possible target range for this indicator would require careful consideration.
Tracking nitrogen will require major improvements of the necessary data collection systems in two ways: (i) annual nutrient use and crop removal statistics at sub-national level and by crops (fertilizers and other nutrient sources) and (ii) regular field monitoring of nitrogen use efficiency and other nutrient-related indicators (e.g. soil fertility, management practices for better nutrient stewardship).
Currently this indicator is not used widely. It has recently been recommended by a task force of the UNEP Global Partnership on Nutrient Management (GPNM), the EU Nitrogen Experts Panel, and other expert groups.
Food production systems are extremely diverse and context specific. Therefore it is important that nitrogen indicators can be tracked at different geographic scales (local, national, global) as well as by farming systems (e.g. maize, wheat, cassava). Nitrogen use efficiency can be estimated at different scales. Countries can track it for each major farming system, agroecological zone, and/or watershed.
Comments and limitations:
This indicator tracks only nitrogen use and is complemented by a national indicator for phosphorus. We believe that nitrogen and phosphorus are the two most important nutrients to track, but we underscore that sustainable food systems will require sound management of many other nutrients, including potassium and soil organic matter.
Preliminary assessment of current data availability by Friends of the Chair:
Primary data source:
Potential lead agency or agencies:
Data for this indicator could be collected by FAO working with the International Fertilizer Industry Association (IFA) and national agencies.1
Dobermann, A. and Nelson, R. et al (2013). Solutions for Sustainable Agriculture and Food Systems. Technical report of the SDSN Thematic Group on Sustainable Agriculture and Food Systems: Paris, France, and New York, USA.