Water balance simulation and water-saving potential analysis of integrated rice-crayfish farming based on an innovative nested tank model

Integrated rice-crayfish farming is an agricultural cultivation model that has become popular and developed rapidly in China in recent years. It integrates rice planting and crayfish farming into one system, boasting favorable environmental benefits and economic returns. In current context of global water scarcity, ensuring the sustainable development of rice-crayfish co-cultivation systems necessitates in-depth research on water consumption characteristics and water-saving potential of this agricultural model. In this study, an innovative nested tank model was developed to simulate the water balance of rice-crayfish fields. Three rice-crayfish field observations confirmed the high performance and good fit of the model, with a Nash efficiency coefficient (NSE), correlation coefficient (R²), relative error (ε), and root mean square error (RMSE) ranging from 0.81–0.97, 0.91–0.98, 2–4 %, and 15.8–39.2 mm, respectively. The ε between the simulated and observed total irrigation amounts ranged from 0.49–10.70 %. The developed model was applied to assess the water-saving potential and benefit-enhancing performance of 60 combinatorial schemes. These schemes were designed by varying three factors: five crayfish ditch area ratios (5 %, 10 %, 20 %, 30 %, and 40 %), four crayfish ditch excavation depths (0.8 m, 1 m, 1.5 m, and 2 m), and three irrigation schemes (FI1: shallow-shallow, FI2: shallow-deep, FI3: deep-deep), under three typical annual rainfall frequencies (15 %, 50 %, and 85 %). Through systematic evaluation of the simulation results, the optimal scheme was identified as 5 %-1.5-FI1. The irrigation quota of the optimal scheme was reduced by 54.4 % compared to the least favorable scheme (40 %-2-FI3), with a cost-benefit ratio of 1.6 times higher. The drainage volumes and the irrigation water productivities of the optimal and least favorable schemes showed no significant differences. Overall, the optimal scheme can reduce irrigation water consumption and improve economic benefits, providing a reference for irrigation management and field layout optimization of rice-crayfish co-culture fields.