Life cycle assessment of liquid digestate application strategies for rice agri-food chain in "Zero-waste City"

Maximizing the productivity of arable land, providing high-quality food, and reducing negative environmental impacts are paramount importance to the agricultural sector. This study used the life cycle assessment (LCA) method to assess the environmental impacts of liquid digestate application and quantitative fertilizer application on the agri-food chain in a rice production system in Guangze County, Fujian Province, China (one of "Zero-waste City" pilots). Results showed that the 100-year global warming potential (GWP100) was reduced by 60%, 49%, and 35% by replacing chemical fertilizer application with 25%, 50%, and 100% of digestate application, respectively. In general, the 25% digestate replacement scenario was the most favorable alternative in terms of GWP100, acidification potential (AP), eutrophication potential (EP), marine aquatic ecotoxicity potential (MAETP), and abiotic depletion, fossil (ADP-fossil) with a 1.52-fold, 67%, 55%, 43%, and 1.63-fold decrease compared to the current status. The application amount of nitrogen fertilizer was reduced by 75%, and applying the remaining 25% nitrogen in liquid digestion mode had a good positive effect on guaranteeing the high yield and quality of rice. The results can provide a basis for promoting the application of liquid digestate in rice-planting system and the recycling development mechanism of rice agri-food chain system in "Zero-waste City".