Impact of Reactive Nitrogen and Nitrogen Footprint

Nitrogen is essential for all lives since reactive nitrogen (all nitrogen except for nitrogen gas) constitutes protein and nucleic acid. Synthesized ammonia, chiefly used for nitrogen fertilizers, greatly supports human food production for the growing population. The growing use of synthetic fertilizers and fossil fuels has increased reactive nitrogen emissions to the environment, leading to adverse effects on human and ecosystem health. This global issue of maximizing the benefits of reactive nitrogen while minimizing nitrogen pollution is one of the key issues for the twenty-first century. To communicate this nitrogen issue to stakeholders in different industries including farmers and consumers, the nitrogen footprint (NF) has been developed as an indicator to quantify direct and indirect reactive nitrogen emissions throughout the lifecycle of goods and services of our consumption. We introduce methodologies of the NF models in relation to other environmental footprints and demonstrate three applications of nitrogen footprint models. The feed-sensitive NF model has been developed as a bottom-up approach and applied to fish and seafood analysis with two sets of parameters called virtual nitrogen factors (VNFs) for the world and Japan. Using the Japanese VNFs, effects of dietary changes to the food NF of Japan and possible reduction scenarios for our food choice were assessed. The global NF model has been constructed as a top-down approach and applied to assess 188 countries in 2010 using multi-region input–output analysis to trace international supply chains. These NF models contribute to the development of sustainable food systems and integrated nutrient management addressing trade-offs between different nitrogen pollutants and other environmental issues.