Balancing Yield and Environmental Sustainability in Chinese Watermelon Production: A Life Cycle and Nitrogen Management Study

China produces 61.0% of the world’s watermelons, yet a life cycle assessment (LCA) of its production system is lacking. Here, we combined farmer surveys and field experiments to assess resource depletion and environmental impacts across North China (NC), Northwest China (NW), and Southwest China (SW), and to quantify the mitigation potential through optimized nitrogen (N) management. NC achieved the highest yield but also the highest resource use and emissions per hectare. In contrast, SW performed best per ton of fruit produced due to lower input intensity. Nitrogen fertilizer dominated greenhouse gas emissions and eutrophication potential, with over 85% of its impact arising during the field application stage. Grouping farms by yield and N partial factor productivity revealed a mitigation potential of 46.5–55.4%, enabling both high yield and high efficiency. Field experiments confirmed that reducing N input by 14.3–40.0%, as recommended regionally, stabilizes yield while significantly lowering environmental burdens. Our findings validate that region-specific N optimization is a key strategy for achieving sustainable watermelon production in China.