| Integrated rice–crayfish(CR)model is a highly efficient artificial ecosystem in which the rice(Oryza sativa)is cultivated in gleyed paddy fields along with crayfish(Procambarus clarkii),which fully uses the shallow water environment and the winter idle period of rice paddies,and organically combines the agriculture and aquaculture to attain the rice and crayfish double harvest.Currently,the CR model is mainly distributed in Hubei,Jiangsu,Jiangxi,Hunan,Anhui Provinces and other middle and lower reaches of the Yangtze River,and the area is the largest in Hubei Province.Compared with the traditional rice monoculture(MR)model,the CR model not only can greatly improve the utilization rate of farmland resources,and increase paddy ecological system stability and the ability to resist external shocks,but also can promote the material on the circulation,prevent the overflow of energy flow,improve the structure and function of paddy ecosystem.In the CR model,Burrowing activity of P.clarkii can improve soil permeability,allow the nutrients and dissolved oxygen in water to reach the base layer,perturb the soil redox interface,change soil microbial community structure and composition,and increase the conversion of soil organic carbon and nutrient release rate.In addition,the circular trench around the paddy fields as refugia of P.clarkii can decrease the water level of top layer in gleyed paddy fields,intensify the soil and air circulation,and reduce the soil reduction status,thereby affecting soil fertility change.In this study,we studied the change characteristics of soil physical,chemical and biological traits,rice yield and its composition,and rice nutrient uptake under the CR model by using 10–year long–term experiment in gleyed paddy field in low lake area of Jianghan Plain.The effects of carbon(C),nitrogen(N)and phosphorus(P)on the nutrient evolution of paddy soils were evaluated by analysis of the input,output and equilibrium of C,N and P in the integrated rice–crayfish ecosystem.The main results were as follows.(1)Compared with the MR model,the CR model had significantly decreased the soil compactness in 15–30 cm soil layer,especially at a depth of 25 cm(nearly 30%),decreased soil bulk density,and increased the soil total porosity and capillary porosity.It also had significantly increased the > 2 mm coarse aggregates contents in the 0–20 cm and 30–40 cm layers,but decreased the 2–0.25 mm small aggregates and < 0.053 mm powder–viscous aggregates in the 0–10 cm layer compared to the MR model,promoting micro–aggregates into larger aggregates.The CR model increased soil water–stable aggregates(> 0.25 mm)content,aggregate mean weight diameter(MWD)and geometric mean diameter(GMD)in the 0-40 cm layer,but decreased aggregate fractal dimension(D)in the 0-20 cm layer,increasing the stability of soil water–stable aggregate.In terms of soil physical properties,the CR model can reduce soil compactness,increase soil permeability,and improve the soil aggregate structure.(2)Compared with the MR model,the CR model significantly increased the contents of soil organic matter,total potassium(K)and available N in the 0-40 cm layer,total N in the 0-30 cm layer,total P and available P in the 0-10 cm layer,available K in the 20-40 cm layer,and NO3––N in 10–30 cm layer.The total amount of reducing matter of the CR model was lower in the 0-10 cm soil layer than that of the MR model,but it was higher in the 20-30 cm soil layer.In terms of soil chemical properties,the CR model can improve the soil total and available nutrient,reduce the total reducing substances in the surface soil(0-10 cm),but increase the risk of soil gleying below 10 cm depth.(3)Compared with the MR model,the CR model significantly increased the contents of total organic carbon,particle organic carbon,and dissolved organic carbon in the 0-40 cm layer,easily oxidized organic carbon in the 10-40 cm layer,microbial biomass carbon in the 20-40 cm layer,and soil carbon pool management index in the 10-30 cm layer.The CR model significantly increased the organic carbon content of <0.053 mm micro–aggregates in 0–30 cm layer,and each size fraction aggregate in 20–30 cm layer compared to the MR model.In terms of soil carbon pool,The CR model can increase the contents of total organic carbon and its activity fractions,improve the soil carbon pool management index.(4)Soil invertase,urease and acid phosphatase activities showed a decreasing trend in CR model compared with the MR model in 0–40 cm layer,and the urease activity of the 10–20 cm layer was significantly lower in CR model than in the MR model.Biolog ECO analysis revealed that compared with the MR model,the CR model significantly increased the soil microbial utilization rate of carbon sources,soil microbial community abundance,degree of dominance,and diversity indices in the 20–30 cm soil layer,but significantly decreased the number of dominant soil microbe species and carbon source utilization rate in the 0–10 cm soil layer.PLFAs method analysis indicated that there were considerably more aerobic bacteria,arbuscular mycorrhizal fungi,and gram–negative bacteria in the 20–30 cm layer in the CR model than in the MR model.Principal components analysis revealed that microbial community composition in the CR model differed from that in the MR model in the 20–30 cm layer.Higher proportions of gram–negative bacteria,aerobic bacteria and fungi in the 20–30cm soil layer were observed for the CR model than the MR model.Pearson’s correlation analysis showed that soil organic fractions,enzyme activity,total P,and bulk density were the key determinants of soil microbial community composition,and p H and soil enzyme activity had a closer relationship with soil microbial community diversity.In terms of soil biological traits,the CR model decreases the soil enzyme activities,changes the soil microbial community structure and functional diversity in the subsurface soil(20–40 cm).(5)Compared with the MR model,the CR model increased the grains per panicle and rice grain yield,and the rice grain yield of the CR model in 2015 and 2016 were increased by 6.41% and 3.66%.The nutrient accumulation of N,P and K,and its agronomic nutrient use efficiency showed an increasing trend in CR model compared with the MR model in rice grain,rice straw and rice overground part,and the nutrient accumulation of rice overground part was in the order of K > P > N.Economic benefit analysis revealed that the gross output and profit were higher in CR model than in the MR model by 46611.0 ￥/hm2 and 23811.0 ￥/hm2,increased by 188.0% and 218.0% respectively.In terms of rice grain yield and economic denifit,the CR model can increase rice yield and farmers’ income,having obvious economic and social benefits.(6)The CR model and MR model both acted as a net C sink,and the C storage potential was higher in the CR model than in the MR model by 6.38%.In soil subsystem,the N was surplus,and P was deficient,while soil N and P in MR model were deficient.The ratio of output to input ratio of C,N and P in P.clarkii subsystem ranged from 0.51 to 0.65,and the highest value was noted at the ratio of output to input of N.The ratio of output to input was lower in CR model than in MR model,which suggested the surplus of N and P in CR model were higher than in the MR model,improving soil N and P accumulation. |
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