Excessive synthetic fertilizers elevate greenhouse gas emissions of smallholder-scale staple grain production in China

Smallholder farmers produce one-third of the world's food and over 80% of China's; therefore, they must be at the forefront of developing a sustainable food system. Greenhouse gas (GHG) emissions from these farms cannot be ignored. In this study, we created an agricultural environmental impact evaluation framework for China based on a localized database through an extensive survey. The survey was based on face-to-face interviews by 120 investigators with 1015 smallholders in 100 villages within Chinese major agricultural regions. The GHG emissions of each smallholder farmer's staple grain production was assessed on a case-by-case basis. Structural equation models were used to analyze the influence paths of production behavior. The results showed that GHG emissions from smallholder grain production exceeded average global levels. Despite some regional differences, synthetic fertilizers were the main source of GHG emissions from all farm inputs. Increased farm size can reduce nitrogen fertilizer use. The GHG emissions can be reduced by 203.59-279.90 Tg CO2eq, and profits would increase by 62.05-92.42 billion CNY in China, when all smallholders are managed in the same way as the top 25% or 10% of outstanding producers without applying higher nitrogen fertilizer application than the national recommendation. It is urgent and necessary for smallholders to change production practices to reduce their reliance on fertilizers to achieve climate goals.