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 their physico-chemical properties were analyzed at different growth stages of rice. Comprehensive water quality index evaluation method was used to evaluate the water quality of three models, and the economic benefits of different models were compared.

Result Total dissolved solid content, pH, NH₄⁺-N content, chemical oxygen demand, and dissolved oxygen content were the primary five factors affecting water quality changes. In ripening stage, compared to the ditch water of low density rice-red cayfish theatment, the ditch water of high density rice-red cayfish treatment showed increases in total N content by 10.5% (P<0.05), total P content by 3.6%, and chemical oxygen demand by 26.2% (P<0.05). At the rice ripening stage, the water quality index of the low density rice-red cayfish treatment reached 0.72, significantly higher than that of high density rice-red cayfish treatment. The cost and benefit calculations showed that the integrated rice-crayfish model’s economic benefits were 6−9 times higher than that of rice monocropping model, and low density rice-red cayfish’s economic benefits were 1.47 times of high density rice-red cayfish treatment.

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