Driving forces of nitrogen input into city-level food systems: Comparing a food-source with a food-sink prefecture-level city in China

Nitrogen input is an important index for indicating nutrient resource use and pollution potential of city-level food systems, which have received increasing attention in studies of global nutrient cycles and their management. However, limited understanding has been developed, of driving forces and their quantitative impacts on nitrogen input into city-level food systems. This study adopts the Logarithmic Mean Divisia Index (LMDI) method and develops a decomposition model for two distinct city-level food systems in China. Four driving factors population, level of consumption, supply-demand ratio, and nitrogen cost of food production are determined, and their respective impacts for the two city-level food systems are evaluated and compared. For the food-source city (Changchun), the supply-demand ratio is the most important contributor to the growth of nitrogen inputs, and population exerts a weak positive effect; whereas for the food-sink city (Xiamen), population is a strong positive factor, but its pulling-up effect is offset by the supply-demand ratio, ultimately contributing to the decline of nitrogen inputs. The nitrogen cost is largely affected by the structure of agricultural production. The level of consumption presented an increasing positive effect before 2003, but that effect gradually diminishes afterward, for both cases. In accordance with the driving factors, management strategies for nitrogen input are suggested from a three-pronged production-trade-consumption perspective. The decomposition model also applies to other city contexts and contributes to providing tailored insights into sustainable nutrient use in city-level food systems.