Ecological Analysis Of Representative Rice-based Ecosystems In China

Both rice production and aquaculture are facing the problem of food-demand increasing, limited resources, and environment pollution. The integrated rice-fish systems has been demonstrated as a sustainable approach to solve the problems above. The past research mostly focused on the biological control efficiency to the pest and weeds in rice-based ecosystem. However, the systematic studies on common mechanisms of various rice-fish co-culture models are rarely reported. Meta-analysis and field experiments were conducted to evaluate the ecological benefits of rice-fish farming. We selected the representative rice-based co-culture models of rice-fish, rice-crab and rice-soft-shelled turtle (Trionyx sinensis) co:culture in China to examine the greenhouses emission, land productivity and nutrient utilization. The results are obtained as follows:(1) Analysis of rice-fish culture in ChinaTotal area of rice-fish farming in China now is about1332.9k ha, accounted for4.48%of the total rice planting area. Water supply is one of the most important factor to limit the distribution of the rice-fish culture and61.5%of them practiced in the single and double cropping of rice area in Yangtze River Delta.(2) Effect of fish presence and N management on methane emission in rice-fish ecosystemField experiment showed that mean methane flux of rice-fish co-culture (RF) decreased by26%compared to rice monoculture (RM). This indicated that the fish presence decreased methane emission. What’s more, mean CH4flux decreased when increasing the fertilizer N ratio (decreasing feed N ratio) in rice-fish field under the condition of applied120kg N ha-1. Meta-analysis obtained similar results of that methane flux declined when the fertilizer N amount increasing in paddy soils. These results implied that some optimal field managements could be adaption into consideration to minimize methane emission in rice production.(3) Productivity of three representative rice-fish culture modes in ChinaExperiment of nitrogen management showed that rice yield had no significant difference when decreasing the fertilizer application (increasing feed application), while fish yield significantly increase. Experiment of rice-crab co-culture showed that rice and crab yields was significantly higher in Rice-Crab than that in rice monoculture (RM) and crab monoculture (CM) respectively. Experiment of rice-soft-shelled-turtle co-culture showed that the rice-turtle system (RT) without fertilizer and pesticide not only exported rice production, but also gained higher turtle yield than turtle monoculture (TM). These results suggest that rice-fish co-culture can increase the land productivity with lower dependence on chemical input.(4) Nitrogen utilization in the three leading rice-fish culture modes in ChinaIn rice-fish ecosystem, the nitrogen utilization ratio is90%, which is significantly higher than fish monoculture (FM) of13.7%. The Rice-Crab had a34%higher of total N use than CM, and higher fertilizer N use than RM. Nitrogen utilization ratio in RT significantly higher than the treatment of TM. These results indicate that rice-culture can increase the nutrients utilization rate, which can decrease the potential of environment pollution.