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BACKGROUND Rice–duck coculture is an ecological agricultural mode; however, the nutritional and environmental benefits of transforming from conventional rice monoculture to rice–duck coculture are unknown. Based on survey data and the life‐cycle assessment approach, this study conducted a carbon footprint evaluation of conventional rice monoculture (CR), organic rice monoculture (OR), and organic rice–duck coculture (ORD) using different functional units. RESULTS The carbon footprint per hectare of ORD (7842 ± 284 kg CO2eq ha−1) was slightly lower than that of CR (7905 ± 412 kg CO2eq ha−1), while higher than that of OR (7786 ± 235 kg CO2eq ha−1). Although the rice yield of ORD was slightly lower than that of CR, its nutrient density unit (NDU) did not decrease significantly due to the additional duck yield. Thus, the carbon footprint per NDU of ORD was significantly lower than that of OR by 24.3% (P < 0.05) and was 5.8% higher than that of CR, but this was not statistically significant. Due to the higher economic profits of ORD, its unit of carbon footprint per economic profit was significantly reduced (by 47.1–75.7%) compared with the other two farming modes, while the net ecosystem economic budget was significantly increased by 98.5–341.9% (P < 0.05). CONCLUSION Transforming from a rice monoculture to a coculture system will contribute to a win–win situation for human health and environmental sustainability. This study highlighted the abundant nutritional output function of the rice–duck coculture and analyzed the urgency and necessity of transitioning from traditional agriculture to ecological agriculture from the production and consumption perspectives. © 2022 Society of Chemical Industry.

Previous studies have mainly focused on cadmium (Cd) contamination in conventional rice monocultures, and no research on rice-crayfish coculture has been reported. In this study, a Cd-contaminated (0–30 mg kg−1) rice-crayfish co-culture system was established by adding exogenous Cd. The results showed that the Cd concentration in each tissue of rice and each organ of crayfish increased with increasing soil Cd concentration. Specifically, the Cd concentration in each rice tissue was as follows: root > stem > leaf ≈ panicle > grain > brown rice, and the jointing and heading stages were critical periods for the rapid enrichment of Cd in the aboveground tissues of rice. The Cd concentration in each organ of crayfish was as follows: hepatopancreas > gut > gill ≈ exoskeleton > abdominal muscle. Cd was gradually enriched in the abdominal muscle after 30 days of coculture between crayfish and rice. Pearson’s correlation analysis showed that the soil’s total Cd concentration, available Cd concentration, and water Cd concentration were positively correlated with Cd content in various tissues of rice and various organs of crayfish, whereas EC and TDS in water were markedly related to rice stems, leaves, stalks, and small crayfish. According to the maximum limit of Cd in grain (0.2 mg kg−1) and crustacean aquatic products (0.5 mg kg−1) in China, the safe threshold of soil Cd for rice and crayfish under the rice-crayfish coculture system is 3.67 and 14.62 mg kg−1, respectively. Therefore, when the soil Cd concentration in the rice-crayfish coculture system exceeds 3.67 mg kg−1, the safety risk to humans through the consumption of food from this coculture system will increase. This study provides a theoretical basis for safe food production in a rice-crayfish coculture system using the established Cd pollution model.