Optimizing carbon and nitrogen cycles towards net-zero greenhouse gas emissions in agrifood systems: a case study in Quzhou, China

Agrifood systems emit substantial amounts of greenhouse gases (GHG) into the atmosphere, but simultaneously sequester carbon (C) originating from atmospheric CO₂ in soils. Their net effects on the GHG balance are rarely documented. This study aimed to quantify C cycles and GHG emissions in agrifood systems at both village and county levels and explore the potential to transition towards net-zero emissions. We integrated a modified material and nutrient flow model (NUFER) and a soil C cycle model (RothC) to calculate C cycles in the case area of Quzhou, China. Results showed that net photosynthesis predominantly contributed to C input to the agrifood system, while soil respiration and microbial respiration during manure storage accounted for most of the C output at all village types. Net CO₂ emissions from the agrifood system in Quzhou were positive because the amount of C sequestration in soils (819 kg C ha^-1 yr^-1) could not offset CO₂ emissions (847 kg C ha^-1 yr^-1) from fossil fuels used in the agrifood system, despite village-level variations. Scenario analysis demonstrated that the system could achieve net-zero CO₂ emissions by adopting good management practices and recycling organic wastes. In addition to these measures, achieving net-zero GHG emissions may necessitate replacing fossil fuels with clean energy. Policies and incentives to promote net-zero emissions and circular agriculture can be mutually reinforcing. This is the first study quantifying C cycles in an entire agrifood system as well as its net CO₂ and GHG emissions, facilitating the transition towards net-zero emissions and climate neutrality.