Gu and colleagues identified a group of 11 key measures, including enhanced-efficiency fertilizers, 4R nutrient stewardship (right fertilizer type, right amount, right placement and right time), irrigation and legume rotation, which could effectively reduce total N losses by 30–70%, while increasing yield and N use efficiency by 10–30% and 10–80%, respectively. Using data from 2015, the authors estimated that the net economic benefit to the whole of society resulting from abatement of reactive N losses from croplands, considering benefits to crop yield, human health, ecosystems and climate change, is approximately 25 times that of the implementation cost.
To inform future policymaking, Gu and colleagues explored cropland N inputs and flows up to 2050 under different N mitigation scenarios. Implementing 4R nutrient stewardship would incur a net cost of US$18 billion, while the total net cost for the introduction of new cultivars, optimal irrigation and tillage was estimated at US$25 ± 8 billion. However, the total implementation costs of enhanced-efficiency fertilizers, organic amendments including manure and straw, crop legume rotation and application of buffer zones would be −US$5 billion, with an approximately US$120 billion benefit resulting from increased crop harvest and an approximately US$180 billion benefit for human health, ecosystems and climate. Potential policy approaches include internalization of pollution costs to provide access to financial capital through a N credit system that gathers the financial budget to implement these strategies — benefiting the whole of society through reactive N abatement and increased food supply.
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