Dynamic Effects Of Straw Returning On Water Quality And Soil Environment In Continuous Cropping Mode Of Rice And Crayfish

The comprehensive rice and crayfish breeding model is an ecological agriculture model combining rice field with breeding.Under the premise of planting rice as the center to ensure that the yield of rice is not reduced,dig trenches around the rice field and scientifically culture Procambarus clarkii increased farmers'economic benefits,and in recent years has become the main mode of breeding Procambarus clarkii.At present,researches on this model at home and abroad have mainly focused on the culture technology and nutritional quality of Procrustus clarkii,but there are few reports on straw recycling in the rice and crayfish ecosystem.For this reason,this study investigated the effects of straw and nitrogen fertilization during the continuous cropping of rice and crayfish to adjust the different return C/N on the cultivation water body,soil nutrients and enzyme activities.The method of returning to the field has a great impact on the physical and biological characteristics of the soil.Therefore,different straw returns were set to further explore the effects on the aquaculture water body,soil nutrients and enzyme activities.At the same time,the Illumina Miseq Qualcomm with 16S r RNA gene was used.Quantitative sequence technology to explore the changes of soil microbial community diversity and species composition in different treatments.1.Effects of straw returning and nitrogen fertilizer on dynamic changes of aquaculture water,soil nutrients and enzyme activities during continuous cropping pattern of rice-crayfishIn order to explore the reasonable way of returning straw to the field during continuous cropping of rice and crayfish,this study takes the adjustment of C/N return to the field as the starting point of straw and nitrogen fertilizer application,and passed field trials in 2017-2018.?CK?,single application of straw C/N is 35:1?S?,return to straw to the field and nitrogen fertilizer adjustment C/N is 25:1?SN1?,return to straw to the field and nitrogen fertilizer adjustment C/N is 15:1?SN2?and single nitrogen fertilizer treatment?N1?.The results showed that:1)The total phosphorus content in the water body of the CK group was the lowest,and the total phosphorus content in the S group was the highest;the total nitrogen?TN?content in each period was the lowest in the CK group,followed by the SN2 treatment.The ammonia nitrogen?NH₄⁺-N?contents in each treated water body was lower than the safety tolerance limit of Protocladium crassicolor.2)After the straw was returned to the field,the soil organic matter contents was increased,of which the SN2 treatment group was the most significant,an increase of 56.1%compared with the straw before the return to the field;the SN2 treatment group increased the soil nitrate nitrogen content by 240%;the return of the straw to the field reduced the soil bulk density.The SN2 processing group has the lowest bulk density.3)Low nitrogen fertilizer or returning straw to the field combined with high nitrogen fertilizer can significantly increase soil polyphenol oxidase activity,and the SN2 treatment group has the highest enzyme activity,and the enzyme activity tends to decrease with the increase of C/N.Among the three kinds of straw returning to the field,the soil urease activity of the SN2 treatment group was lower than that of other treatments only in the first month after returning to the field.The N1 treatment group showed higher enzyme activity in the early stage and began to decrease in the later stage.2.Effects of different straw return amount on the dynamic changes of aquaculture water body,soil nutrients and enzyme activities during continuous cropping pattern of rice-crayfishAccording to the test results in Chapter 2,under the premise of adjusting the carbon to nitrogen ratio of 15:1 by returning straw to the field and applying nitrogen fertilizer,the effects of different amounts of returning straw to the farming water body,soil nutrients,and enzyme activities were affected.The trial was conducted during the continuous rice and crayfish cropping in 2019,and a field trial was adopted.A total of4 treatments were set up:the straw was not returned to the field without nitrogen fertilizer?CK?,the amount of straw returned to the field was 1500 kg�hm^-2?S1N1?,the amount of straw returned to the field was 3500 kg�hm^-2?S2N2?,the amount of straw returned to the field was 4500 kg�hm^-2?S3N3?.The results showed that the dissolved oxygen was 6.68?14.59 mg�L^-1 when oxygenation was not used.During the return of straw to the field,the concentration of ammonia nitrogen and nitrite nitrogen in the water body increased with the increase of the amount of returning straw,but it was lower than the safety tolerance value of crayfish.In the early stage of returning the soil,the inorganic nitrogen forms mainly existed in the form of ammonium nitrogen,and in the later stage,they mainly existed in the form of nitrate nitrogen.The different straw return measures had no significant effect on organic matter.Returning straw to soil reduced soil urease activity,and increased soil alkaline phosphatase,invertase,and cellulase activities.Among them,the increase in enzyme activity was the largest under the treatment of 4500 kg�hm^-2.3.Effects of different straw return amount on soil microbiological effects during continuous cropping pattern of rice-crayfishIllumina Miseq high-throughput sequencing based on 16S r RNA gene was used to study the effects of different straw returns and nitrogen fertilizer soil bacterial community during rice and crayfish continuous cropping based on the results of Chapter 2.The effects of different returning amount on soil bacterial diversity and community structure were explored.A total of 4 treatments were set up:the straw was not returned to the field without nitrogen fertilizer?CK?,the amount of straw returned to the field was 1500 kg�hm^-2?S1N1?,the amount of straw returned to the field was3500 kg�hm^-2?S2N2?,the amount of straw returned to the field was 4500 kg�hm^-2?S3N3?.The results showed that the three different straw returning treatments significantly increased soil MBC and MBN content,and decreased the MBC/MBN ratio.The return of straw to the field enhanced soil microbial diversity.The bacterial Alpha diversity index under S2N2 treatment was higher than that of other treatments.Different field treatments include Proteobacteria,Chloroflexi,Acidobacteria,Bacteroidetes,Nitrospirae,and Gemmatimonadetes.Mainly.Multi-level species difference analysis?LEf Se?showed that different treatments had a greater effect on the changes of soil flora structure at the genus level,and S3N3 treatment was similar to the CK microbial community structure.Redundant analysis?RDA?showed that the environmental factors that had a greater effect on the soil flora were soil total nitrogen,total phosphorus,microbial biomass carbon,available phosphorus,and urease.