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647. Agricultural Nitrogen Pollution - From Planetary to Regional Boundaries

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In 2009, Nature published an opinion article introducing the concept of planetary boundaries, which proposed nine boundaries, including climate change, biodiversity loss, and the nitrogen cycle, as guidelines to help humans ensure the stability of the Earth system.

Six years later, an article published in Science indicates that three of the planetary boundaries have already been exceeded, and among them, the use of nitrogen fertilizers has been recognized as having gone far beyond the limits.

On the other hand, regional differences in the action with ecosystems regarding nitrogen fertilizer pollution from agricultural and other sources have not been considered, while rates of chemical fertilizer use vary widely from region to region of the world. While parts of Northwest Europe, India and China emit very large amounts of greenhouse gases from nitrogen fertilizers, many parts of sub-Saharan Africa and South America have room to intensify their use of nitrogen fertilizers without significant environmental pollution. A study has now been published in Nature that assesses for the first time the marginal use of nitrogen fertilizers at the regional level. 

The study compared regional constraints on natural and water quality, such as loss of biodiversity, deterioration of drinking water quality, and algal bloom development, against nitrogen oversupply and loss at the regional level. (The paper does not examine the effects of nitrous oxide emissions on climate change or the health hazards of ammonia-induced air pollution, but it does examine what meeting the planetary boundary for environmental pollution limits means for global nitrous oxide emissions.)

The paper not only corrects for the global bias in nitrogen inputs, but also says that even if optimal redistribution of nitrogen fertilizer were made, the global nitrogen global limit would be exceeded under current nitrogen use efficiency. In order to feed the world's population without exceeding the regional and global nitrogen limit, it is necessary to greatly improve nitrogen use efficiency in agriculture. In addition, we need to recognize the diversity of the world's agriculture and, at the same time, work together to reduce nitrogen emissions from non-agricultural sources, such as sewage water.

The study highlighted differences in the problems posed by nitrogen in different regions. Excesses in Europe and China, for example, contrast with the situation in Southeast and South America and Sub-Saharan Africa, where underuse requires a bit more additional nitrogen fertilizer for food production. In the latter, the use of too little fertilizer can lead to depletion of soil nutrients and, in extreme cases, to soil degradation to the point where it is no longer suitable for food production. There is no one-size-fits-all solution for planetary boundaries, and it would be useful to consider innovations at the local level that address similar issues.

 

References
Schulte-Uebbing L.F., Beusen A.H.W., Bouwman A.F. et al. From planetary to regional boundaries for agricultural nitrogen pollution. Nature 610, 507–512 (2022). https://doi.org/10.1038/s41586-022-05158-2
Steffen W. et al. Planetary boundaries: Guiding human development on a changing planet, Science (2015). https://www.science.org/doi/10.1126/science.1259855
Rockström J. et al. A safe operating space for humanity, Nature (2009). https://www.nature.com/articles/461472a

 

Contributor: IIYAMA Miyuki (Information Program)

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