Changing food nitrogen flow in a food-exporting city

Abstract

IntroductionNitrogen (N) plays a significant role in food systems, but only a fraction of N is effectively utilized and the rest is lost to the environment and negatively affects the ecosystem. So far, there has been relatively little research on N flow associated with the food production and consumption of production-oriented cities in developing countries.MethodsIn this study, we present a comprehensive analysis of N flow in the food production and consumption system of Changchun in China between 1991 and 2014, and define three types of nitrogen use efficiency (NUE) and compare them.Results(1) Total new N input into the food system in Changchun increased by 63.75% (240.8 to 394.3 Gg N yr−1) during the study period, mainly attributable to the high volume of food exports(total output from 47.63 to 72.51 Gg N yr−1). (2) Changchun typically exhibited lower apparent NUE and virtual NUE of the food system, while its actual NUE was typically higher, compared to food-importing cities. (3) The consumption of crop food witnessed a decrease from 24.2 Gg N in 1991 to 18.7 Gg N in 2014, whereas the consumption of animal food showed an upward trend from 2.5 Gg N to 7.7 Gg N. Both urban and rural residents consumed less grain food but more fruits and meat. (4) The total N loss has increased from 131.3 Gg N in 1991 to 266.6 Gg N in 2014. The crop production caused 58.1% of the total N loss in 2014, and the atmospheric loss accounted for 40.2% of the total.ConclusionThe study has revealed the distinctive features, fluctuations, and underlying drivers of N flow in the food-exporting city, setting it apart from food-importing city. These findings provide a valuable point of reference for the implementation of customized and diversified nitrogen management strategies in these specific urban areas.