| This study takes the Rice-Crab culture and Aquaculture integrated System as the object,combines rice-crab culture and aquaculture of fish,and utilizes the purification ability of rice to absorb and utilize nutrients that cannot be used in the process of aquaculture.The water that has been absorbed and purified by the paddy fields flows back to the Intensive fish pond system.By studying the changes of physical and chemical indicators of water quality,the growth of various aquatic products,the dynamic distribution of microbial communities,and the change rules of various nutrient elements in this complex ecosystem,we can reveal the dynamic characteristics of nitrogen,phosphorus and other nutrients in the system and comprehensive water quality regulation technology.Exploring the efficiency of material recycling,conversion and utilization,energy flow efficiency and economical ecological benefits in the rice-crab culture and aquaculture integrated system,and finally achieve the purpose of optimizing the system,improving the system’s water saving,emission reduction and efficiency.The main findings and conclusions are as follows:1.Comprehensive control technology of water quality in rice-crab culture and aquaculture integrated system.Coupling the rice-crab culture system with the Intensive fish pond system,the strong absorption effect of rice on the water body can maintain the stability of pond water quality,and can improve the size and plumpness of river crabs,rice yield and fish survival rate,etc.The high PO43--P and circulating water input to the pond system can maintain the algae growth and renewal in the pond water,increase the DO of the water,and reduce the toxic and harmful substances in the water such as NO2--N,NH3-N and suspended flocs（Consists by aging algae,residual bait feces and fish secretions）.Rice-crab culture system has a good effect on the purification of NO2–-N,NH4+-N and suspended solids in the tail water of the pond,and the removal rate of NO2–-N can reach 30.26%～71.84%,The removal rate of suspended solids can reach32.84%～46.44%,and the removal rate of NH4+-N can reach up to 110.68%;the experimental point is located in the saline-alkali area,and the characteristics of the paddy field system such as large area and shallow water will cause the precipitation of salt ions in the soil,and then the salinity of the water in the rice-crab culture system surface and in the ditch increased,and the intensive fish pond system can significantly reduce the total alkalinity of the water.Therefore,the development of the rice-crab culture and aquaculture integrated system in the saline-alkali land area is helpful to improve the soil salinity and alkalinity of.2.Effects of pond water in rice-crab culture and aquaculture integrated system on rice growth.Research on rice growth dynamics shows that under the rice-crab culture and aquaculture integrated system,the irrigation of fish pond water is helpful for rice tillering and can significantly increase the number of rice tillers.Therefore,the irrigation amount and frequency of fish pond water can be appropriately increased during the tillering stage of rice.Compared with the control group irrigated with water from the Yellow River,the outer diameter of the stem base and the outer diameter of the ear base were thicker,and the stem length and plant height were smaller in the experimental group irrigated with pond water.Irrigation of rice with pond water can help rice resist lodging.The experimental group has low 1000-grain weight and high moisture content.It can be speculated that irrigating fish ponds will delay the growth period of the rice,resulting in a late maturity of the rice.In order to maximize the yield,we should appropriately delay the harvesting time of the rice.The dry weight of paddy per hole and the average yield per mu of the experimental group were higher than those of the treatment group,indicating that the irrigation of fish ponds could significantly increase the yield of rice.The grey correlation analysis method of rice showed that whether or not irrigated fish pond water had little effect on the composition factors of rice rhizomes and yield,and the analysis of rhizomes and culm composition factors:the most relevant indicators of the experimental group and the control group were the stem length and plant height.and ear length,yield component factor analysis:the largest correlation index between the experimental group and the control group is the number of grains per ear and the rate of ear formation.According to the distance from the water inlet,each paddy field in the experimental group was divided into water inlet area,middle area and water outlet area.Grey correlation analysis was carried out on them.Diameter and outer diameter of ear base,the most relevant indicators of rice in the middle area are the outer diameter of ear base and culm length,and the most relevant indicators of rice in the water outlet area are root length and ear length;,the middle area is the effective ear number,and the effluent area is the aboveground biomass dry weight.3.The change rule of microbial community structure in rice-crab culture and aquaculture integrated system.Microorganisms in water and soil environments:At the phylum level,Actinomycetes,Proteobacteria,and Pasteurella predominated in water samples collected at the inlet of the entire system,and Actinomycetes and Proteobacteria predominated in all water samples,Chloroflexbacteria,Actinomycetes,Proteobacteria and Firmicutes predominated in the soil of the rice-crab co-cropping system.The bacterial communities between the sample groups were compared,and the similarity analysis of OTU levels showed that there were significant differences between crab species（R=0.054,P=0.002）and between male and female crabs（R=0.026,P=0.04）.,but there was no significant difference between aquaculture ponds and paddy fields（P=0.39）.The two modes of rice-crab culture and pond culture had no significant effect on the gut bacterial community structure of river crabs.Crab gut microbes:At the phylum level,Firmicutes accounted for about 78%of all sequences analyzed in the gut,and Proteobacteria,Bacteroidetes,Actinobacteria,Cyanobacteria,and Pasteurella accounted for 78%of the sequences,respectively.1%or more.The results of Spearman correlation analysis showed that the dominant phylum Firmicutes was negatively correlated with body width and body weight of river crabs,while OTU2976 was negatively correlated with body length,width and body weight of crabs and wet weight of crab shells.The similarity of OTU and OTU2976 was 97.2%,indicating that the high abundance of OTU2976 in the intestinal microbes of crabs may come from the environment.This may be one of the reasons for the small size of river crabs in Ningxia.This study shows that the microorganisms in the environment have a greater impact on the gut of the crab,adding probiotics to the water to improve the microbial structure of the water community may improve the intestinal flora of the crab,thereby promoting the growth of the crab.4.Analysis of economic benefits of rice-crab culture and aquaculture integrated system..In 2020,the total fish output from aquaculture is 302,622kg,and the average output is 15,650kg/hm2,which is significantly higher than that of single pond and circulating tank culture.The average profit of fish ponds is also higher,about 76,200yuan/hm2;The total output of river crab is 8733kg.The average output value of rice-crab co-cultivation fields can reach 37,290 yuan/hm2,and the profit is 24,934yuan/hm2;while the average output value of individual rice fields is only 29,565yuan/hm2,and the profit is 16,821 yuan/hm2.Under this composite mode,the rice-crab co-cropping mode is more profitable by 8,113 yuan/hm2than the single-plant rice field.In 2021,due to the construction of the factory area and local policies,the construction will continue until June,and the breeding density of the fish pond system is low.123230kg,the total output of rice is 312723kg,and the total output of river crab is7174kg.During the construction process,a large number of crabs died,so the stocking density of river crabs in 21 years was high,but the total output decreased significantly.Due to the significantly higher fish price in 2021,the average profit of fish ponds is about 128,000 yuan/hm2higher than that in 2020,but the average output value of rice and crab fields is 33,455 yuan/hm2,which is lower than that in 2020.5.Emergy analysis of rice-crab culture and aquaculture integrated system.The rice-crab culture and aquaculture integrated system has a higher purchase emergy value（70%～80%）,and the cost of fertilization,labor and daily management is significantly higher than other production modes.The environmental load rate of this integrated ecosystem（0.24～0.4）and sustainable development index（1.64～3.23）are better than the rice-fish culture alone（environmental load factor 2.44,sustainable development index is 0.92）,and because the rice-fish culture alone has a better purchase of emergy Both input and output are relatively small,so it is far lower than the emergy investment rate（2.09）of this integrated ecosystem（62.66～96.44）.The rice-crab culture and aquaculture integrated system has the advantages of strong production vigor,great development potential,high energy utilization rate,and low environmental load rate.6.A Study on Nitrogen and Phosphorus Nutrition Budget of rice-crab culture and aquaculture integrated system.In 2020 and 2021,the total nitrogen input of the integrated ecosystem was 53413.5kg,and the total phosphorus input was 12448.29kg;the total nitrogen output was 20687.45kg,and the total phosphorus output was2936.07kg.In the system nitrogen and phosphorus input,daily feeding is the main source,accounting for 59.45%and 56.69%of the total;nitrogen fertilizer is the secondary source of nitrogen input,accounting for 20.33%of the total input;compound fertilizer is the second source of phosphorus input The main source,accounting for19.07%of the total input.The utilization rate of nitrogen in the integrated system is33.36%,and the utilization rate of phosphorus is 17.65%;the utilization rate of nitrogen in the aquaculture system in the integrated system is 22%,and the utilization rate of phosphorus is 21.29%;the utilization rate of nitrogen in the rice-crab culture system is22%.The utilization rate of phosphorus is 54.19%,and the utilization rate of phosphorus is 11.95%.The nitrogen use efficiency of the rice-crab culture in this rice-crab culture and aquaculture integrated system（45%-73.59%）was significantly higher than that of the single rice-fish culture（27.42%-40.05%）.The utilization rate of phosphorusof the aquaculture system in this rice-crab culture and aquaculture integrated system（21%-21.3%）was significantly higher than the utilization rate of phosphorus（9.78%-13.81%）under the single pond culture system. |
