Material flow and ecological network analysis of China’s coupled nitrogen and phosphorus flows shows trade-offs and synergies between food and energy systems.
Nitrogen and phosphorus are essential nutrients for agricultural production. Their continuous supply is therefore vital for food production. In the industrial high-yielding agriculture, synthetic fertilizers are the most important sources of the essential nutrients for plant growth. However, their supply can be threatened by shocks and disturbances in resource flows due to, for example, extreme weather events, pandemics or global geopolitical or economic conflicts. Network resilience of the nitrogen and phosphorus flows is a system attribute measuring the ability of the networks to withstand disturbances and supply continuous access to nutrients. It assesses the level of specialization and diversity of resource pathways and is therefore a useful tool to analyse the threats to food production.
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In addition to boosting global food production, the increased application of synthetic nitrogen and phosphorus fertilizers has led to the transgression of the safe boundaries for global nutrient use1,2,3. Their overuse in many areas has led to major environmental problems, such as freshwater eutrophication, biodiversity loss and climate change1. Conversely, their underuse has led to soil nutrient depletion and reduced food production in other areas2,4. Balancing their use is therefore necessary, yet not an easy task. Nitrogen and phosphorus flows are highly interlinked and critical also to other systems, such as energy production. Owing to the complex nature of nitrogen and phosphorus flows, so far, no quantified and comprehensive view exists of the coupled flows and how they would evolve under different scenarios in the future.
Writing in Nature Food, Luo et al.5 respond to these challenges by applying material flow and ecological network analysis and assessing the networkresilience of China’s coupled nitrogen and phosphorus cycling network. China is a particularly interesting and globally important case because it is struggling with opposite pressures; on one hand to increase food production and the application of synthetic fertilizers to meet the needs of the increasingly urbanized and affluent population6, and on the other hand to reduce the environmental consequences of the nutrient overuse7. The application of nitrogen and phosphorus synthetic fertilizers is three and five times the global average, respectively5. Luo et al. found that the network resilience in China’s coupled nitrogen and phosphorus flows has decreased during the past 40 years, and it will continue to decrease in the future scenarios, suggesting that China’s nitrogen and phosphorus supply is increasingly vulnerable to shocks in supply.
Both nitrogen and phosphorus flows and their supply and demand will be heavily impacted by the transition towards cleaner energy production. China’ clean energy scenarios towards 2060 will substantially increase the use of nitrogen as green ammonia for shipping fuels, leading to increased nitrogen emissions to the environment. Phosphorus, on the other hand, will be demanded as a result of the rise in the use of lithium batteries. This will, in turn, intensify the competition from the limited nutrient resources between food and feed sectors and consequently have negative impacts on network resilience of coupled nitrogen and phosphorus systems.
However, the interlinkages in nitrogen and phosphorus flows can also reveal potential for synergistic solutions. Luo et al. discuss how reducing synthetic fertilizer use by improving fertilizer use efficiency and increasing the use of organic fertilizers could increase both nitrogen and phosphorus network resilience. Additionally, increasing aquaculture feed efficiency, reducing food loss and waste, and promoting more plant-based diets would increase network resilience and reduce the food sstems pressures on the environment.
Luo et al. also suggest that China could increase food trade, both imports and exports, and become a bigger trading hub for food commodities. This would increase the network resilience of both nitrogen and phosphorus flows by having more diverse supply channels; however, the implications to the increased imports or exports on the availability of limited global resources such as land and energy should be carefully assessed. Generally, more research is warranted to analyse the impacts of China’s actions to other countries and to global sustainability.
Overall, the findings of Luo et al. highlight the importance to have a systems perspective, as nitrogen and phosphorus flows will affect each other and have implications to both food and energy systems and beyond. A comprehensive systems view is therefore essential when planning for sustainability interventions; it is a condition to understand the linkages and trade-offs and find synergistic solutions fr more sustainable food and energy systems.
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