Research on A Framework for Sustainable Nitrogen Management Based on Whole-chain Quantification in Food Systems
[Objective]The environmental emission of nitrogen(N)permeates through the entire food chain and ecological system.Nitrogen-efficient technologies in crop or livestock production alone have proven ineffective in controlling N pollution,necessitating the innovation of systematic research and management methods.[Method]Based on the concept of cascade flow and the whole-chain N research framework(CAFE),N fluxes in four nested systems of cropping system,animal-crop system,food system,and regional ecosystem in various countries or regions were quantified,N surplus and N use efficiency in each subsystem were analyzed.The driving factors of N surplus increment between adjacent subsystems were analyzed,and the promising strategies were proposed.[Result]Applying CAFE to 13 representative countries reveals that the N surplus in most countries increased and the nitrogen use efficiency(NUE)decreased with the increase of the level of managed system.The N surplus in the animal-crop system,food system,and regional ecosystem increased by 138%(median),230%,and 287%,respectively,based on the cropping system.The N surplus eventually increased from 3-153 kg·hm-2 in the cropping system to 63-464 kg·hm-2 in the regional ecosystem.At the same time,NUE decreased from 55%(median)in the cropping system to 34%in the animal-crop system and 18%in the food system.N loss increases gradually from crop production to primary agricultural products,food production,and consumption.Although the trend of N surplus increase is consistent across all countries,the magnitude of the increase varies considerably among countries,determining the different priorities for improving N management in each country.For China,as the high nitrogen surplus mainly comes from the cropping system,efforts need to be made to reduce the N surplus in cropland by promoting best management practices and adjusting the structure of N inputs.For most western countries,the system outside the cropland contributes more to the total N surplus,and attention should be given to the N recycling of related systems.For example,the Netherlands needs to focus on matching crop-livestock structure,increasing feed self-sufficiency rate,and reducing livestock density to decrease N surplus in the animal-crop system.Japan needs to further reduce food waste or increase circulation,while African countries need to reduce crop storage waste and improve overall productivity.[Conclusion]The analysis of the global CAFE system shows that the main factors affecting the surplus increment across systems include the structure of N input in cropland,livestock density,feed self-sufficiency rate,and the relationship between food trade and domestic supply and demand.However,these factors have not yet received attention in global N management.CAFE provides a consistent quantitative method for global N whole-chain management,which is helpful for cross-regional comparison,experience sharing,and policy formulation.
Nitrogen flowWhole-chain nitrogen quantificationNitrogen surplusNitrogen use efficiencySystem coupling
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