| Modern agriculture faces the challenges of high production cost,low resource use efficiency and environmental pollution.Whether using biodiversity with species facilitation could help modern agriculture to increase production and reduce negative environmental impact has been concerned.Integrated rice with fish(fish here refers a wide range of aquatic animals like carps,crabs,crayfish,etc)is one of the approaches to increase utilization of biodiversity in agriculture.Integrated rice-fish system in China has a long history,and has developed rapidly in the last decades.Diverse rice-fish systems such as rice-carp,rice-crab,rice-crayfish and rice-soft-shelled turtle have been widely practiced.The rice-crayfish(Procambarus clarkii)is the most important integrated rice-fish system that play important role in improving local rural economy.In this study,I studied the ecological and economic effects of rice-crayfish by literature and statistical data analysis,and the field and farmer surveys.The main results are as follows:(1)Eeffects of rice-crayfish system development on grain crop planting areas.The statistical data analysis showed that the sown area and yield of rice,and sown area wheat remained stable during 2010-2019 when rice-crayfish system developed rapidly in Qianjiang City,Jianli County and Honghu City of Hubei Province,where rice-crayfish were widely practiced by local farmers.(2)Output effects of rice-crayfish system.Farm survey and meta-analysis showed that rice yield in rice-crayfish system did not significantly reduce compared to rice monoculture.The profit income in rice-crayfish system was 3.27 times as many as in rice monoculture although the cost-benefit ratio in rice-crayfish system was 5.5 % higher than that in rice monoculture.(3)Effects of rice-crayfish system on soil N use efficiency and soil fertility.Field survey showed that fertilizer nitrogen(N)input,and apparent N uptake efficiency in rice-crayfish system decreased by 21.6 % and by 30.6 % respectively compared to rice monoculture.Field survey and meta-analysis showed that the soil organic matter(SOM),soil total N and soil available N in rice-crayfish system were significantly higher than that in rice monoculture.However,SOM,soil total N,soil available N,soil total phosphorus(P)and soil available P in rice-crayfish system tended to decrease after the rice-crayfish were practiced for years..(4)The resources utilization of rice-crayfish system.Emergy analysis showed that emergy self-suifficiency ratio decreased by 18 % and emergy investment ratio increased by 1.08 in rice-crayfish system compared to rice monuculture.The emergy value per unit matter and per unit energy were 2.24 and2.47 times respectively in rice-crayfish as much as in rice monoculture.The results indicated that rice-crayfish system had less dependence on natural resources,while had dependence on social and economic input,and the resources use efficiency rice-crayfish system is lower than rice monoculture.The results described suggested that rice-crayfish system could help to improve rural economy,reduce N fertilizer input while not reduce soil fertility in general.From the view of emergy,however,resources use efficiency tended to decrease in rice-crayfish system compared to rice monoculture. |
