Water quality assessment and economic benefit evaluation of integrated rice-red crayfish cultivation system under different stocking densities

Objective To compare the water environment quality and economic benefits of rice-red crayfish integrated cultivation model under different stocking densities and traditional rice monocropping model, and explore the scientific model of rice-red crayfish cultivation in Dongting Lake area.

Method Using the method of plot experiment, three treatments were set up: Low density rice-red crayfish treatment with stocking density of 300 kg·hm⁻², high density rice-red crayfish treatment with stocking density of 375 kg·hm⁻² and rice monocropping treatment. Water samples were collected and physicochemical properties were analyzed at different growth stages of rice. Comprehensive water quality index (WQI) was used to evaluate the water quality of three models, and the economic benefits of different models were compared.

Result Total dissolved solids, pH, NH₄⁺-N, chemical oxygen demand, and dissolved oxygen were the primary five factors affecting water quality changes. Compared to low density rice-red cayfish, the high density rice-red cayfish model showed increases in total nitrogen content by 10.5%, total phosphorus content by 3.6%, and chemical oxygen demand by 26.2%. At the rice maturation stage, the WQI for the low density rice-red cayfish model reached 0.72, significantly higher than high density rice-red cayfish, indicating that lower stocking densities reduce ecological risks of discharging water during rice maturation. The cost and benefit calculations showed that the integrated rice-crayfish model’s economic benefits were 7-10 times higher than the rice monocropping model, and low density rice-red cayfish’s economic benefits were 1.47 times higher than high density rice-red cayfish model.

Conclusion The suitable breeding density of rice and red crayfish can effectively reduce the pollution of agricultural non-point sources, significantly increase the economic and envrionment benefits of rice fields, and has a good popularization potential. These findings provide data support for formulating measures to prevent agricultural non-point source pollution in the Dongting Lake region.