-Fundamental information towards sustainable nitrogen use-
The research group consisting of National Agriculture and Food Research Organization (NARO) et al. have elucidated the nitrogen (N) flows and N balance in Japan from the FY 2000 to 2015 for all human activities and the environmental media, where reactive N (N compounds other than stable dinitrogen) lost to the environment was also evaluated. The N budgets revealed that the amount of N waste per capita, 41-48 kg per year, was approximately double of the world average for the same period and the amount of reactive N lost to the environment was reduced into approximately one-third of the total N waste. This research provides beneficial information to the sustainable N use, e.g., technological development and policy planning to address the N pollution while receiving the benefits of N as fertilizers and industrial materials.
Reactive N provides us great benefits as fertilizers and industrial materials. Since the development of the Harber-Bosch process in the early 20th century, the amount of artificially created reactive N from stable dinitrogen in the atmosphere has increased, now it is in the same order of the natural N fixation. On the contrary, human activities such as production and consumption of food and non-food products and energy consumption with fossil fuel burning create a huge amount of reactive N, most of which is lost to the environment and causes N pollution. It is assessed that the alteration of the global N cycle due to human activity has already exceeded the planetary boundaries of the Earth system. Japan is a country largely depending on import for various resources such as food, feed, and fuel. Therefore, the country may collect reactive N from the rest of the world and eventually release it to the environment. However, lacking in the information of the national scale N budgets in Japan so far has prevented grasping the whole picture of N use and N pollution in the country.
Meanwhile, the research group led by NARO has calculated the N flows between each of human activities (energy, industry, agriculture, forestry, fisheries, human consumption, waste, wastewater, and international trade) and environmental media (atmosphere, forests, terrestrial water, coastal zones) from the FY 2000 to 2015 and evaluated the N balance in Japan. The amount of N waste from human activity was estimated to be 5.26 to 6.09 million tons per year, of which 1.86 to 2.29 million tons was lost to the environment as reactive N. The annual per capita N waste was estimated to be 41-48 kg, approximately double of the global average (22-23 kg) estimated using Sutton et al. (2021) for the same period. Although the amount of N waste is subject to the economy, it remained mostly stable for 16 years, while the amount of reactive N lost to the environment has decreased over the years. Reactive N lost to the environment was suppressed to approximately one-third of the total N waste. For example, the reactive N lost to the environment was 1.96 million tons to the N waste of 5.76 million tons in FY2010, where 64% of reactive N was emitted to the atmosphere and 36% was to water bodies.
The N budgets reveals the amounts of N waste and reactive N lost to the environment for respective human activities that provides awareness of the N issue, that is, the benefits of the human N use accompanied by the threats of N pollution. The N budgets provide fundamental information to identify the N flows in-between human activities and environmental media which should be addressed with priority, and to evaluate the effects of current and new technologies and policies to increase N use efficiency and to reduce N pollution.
This research result was published in the international scientific journal Environmental Pollution (available online 9 June 2021).
Hayashi K, Shibata H, Oita A, Nishina K, Ito A, Katagiri K, Shindo J, Winiwarter W (2021) Nitrogen budgets in Japan from 2000 to 2015: Decreasing trend of nitrogen loss to the environment and the challenge to further reduce nitrogen waste. Environmental Pollution https://doi.org/10.1016/j.envpol.2021.117559