The nitrogen and carbon footprints of vegetable production in the subtropical high elevation mountain region

Mountain vegetable production has become a critical source of low heat-resistance vegetables in summer in subtropical regions, but evaluations based on life-cycle assessment (LCA) that are relevant to the environment and economics have not been reported. We conducted a survey to compare the cabbage yield and resource inputs for small-holder farms at a high (HEL, 900–1500 m) and low (LEL, 200–600 m) elevations in a subtropical region in Southwest China. We used LCA to quantify the nitrogen (N) and carbon (C) footprints, and used the yield and environmental impacts gap method to determine the potential to mitigate the environmental impacts of farming at HELs and LELs. The results show that the respective average reactive N (Nr) and greenhouse gas (GHG) emissions for the HEL and LEL were 137.0 kg N ha−1 and 6785 kg CO2-eq ha−1, and 126.7 kg N ha−1 and 6153 kg CO2-eq ha−1, respectively. The N and C footprints for the HEL were 17.3% and 16.2% lower, respectively, than those for the LEL due to the higher yield at the HEL. The average cabbage yield was 26.5% greater at the HEL (53.2 t ha−1) than at the LEL (42.0 t ha−1). The average total N application rate at the HEL was 455 kg N ha−1, which was 6.0% greater than that at the LEL. There was great potential for yield increases and the mitigation of N and C footprints by farmers at both the HEL and LEL. Compared to the average of all surveyed farmers for HEL and LEL, those farmers whose yields and N fertilizer production efficiency were both higher than the average of all surveyed farmers (HH groups) reduced their N and C footprints by 44.7–49.4% and 44.4–51.2%, respectively, with 34.4–52.3% higher yield and 9.2–19.8% lower N application rate. This study indicates that high yield, low environmental cost, and high economic benefit can be achieved by advancing agronomic management based on the best farmers’ practices for vegetable production in a subtropical high-elevation mountain region.