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.