Effects Of Straw Returning And Feeding On Soil Nitrification And Microorganism In Rice-crayfish Ecosystem

The rice-crayfish coculture(RC)is a pretty eco-agricultural mode formed by the symbiosis of rice cultivation and the feeding of crayfish,which takes an advantage of an efficient use of resources and has specific ecological benefits.Otherwise,this mode is generally followed by rice straw returning to the field and feeding crayfish.In order to determine the effect of the rice–crayfish coculture after rice straw returning and feeding on soil nitrification and microorganism,six groups of treatment RC with straw returned and feeding(S+F),RC with straw returned and no feeding(S+NF),RC with straw removal and feeding(NS+F),RC with straw removal and no feeding(NS+NF),RM with straw returned(RM+S),RM with straw removal(RM+NS),were set to study the soil physicochemical property,the intensity of soil nitration,soil microorganism and the soil nitrification mechanism in this mode.The main results are as follows:1.Effects on soil physicochemical properties: the soil fertility could be significantly improved by increasing the contents of ammonium nitrogen and microbial nitrogen after straw returning and feeding treatment.The contents of ammonium nitrogen and microbial nitrogen in soil reached the peak at the stage of tillering and jointing,and then gradually decreased.Furthermore,soil nitrate nitrogen and microbial biomass carbon content were decreased,and Eh was decreased to enhance the reducibility of soil after straw returning and feeding treatment.The reducibility of soil was enhanced in a short time due to the straw returning and feeding treatment.The co-cropping mode of rice with crayfish and straw mulching could maintain the soil temperature during the winter soaking period.2.Effects on soil nitrification: compared with the RM model,the soil nitrification in the RC group was increased by 12.72 % in rice season,but decreased by 31.15 % in winter soaking season,and the annual nitrification intensity decreased by 1.75 % on average.Straw returning reduced the nitrification intensity by 7.94 % in rice season,10.02 % in winter soaking season and 8.97 % in average.Feeding treatment increased the soil nitrification intensity by 10.58 % in rice season,13.89 % in winter soaking season and 11.14 % in the whole year.3.Effects on soil ammonia oxidation microorganisms: the various periods of soil microbial AOA and AOB ammonia oxidation function,nir K,nir S,nos Z gene abundance,were also observably improved in the treatment with straw returning and feeding,and all appear peak in rice tillering jointing stage,winter bubble phase nitrifying microorganism AOA and AOB abundance was reduced,denitrification function gene nir K,nir S,nos Z abundance appeared rising trend,which said the nitrification was restrained,and denitrification was active.4.The effects of different treatments on the diversity of soil microbial structure showed that: rice-crayfish ecosystem straw returning and feeding treatment could significantly improve the soil microbial abundance and structural diversity.The content of total phospholipid fatty acid in soil increased by 14.99%-51.72%,the abundance of bacteria increased by 20.43%-177.59%,the abundance of fungi increased by 5.61%-22.22%,the abundance of anaerobic bacteria increased by 14.98%-48.84%,the abundance of aerobic bacteria increased by 4.87%-32.55%,the abundance of actinomycetes increased by 10.10%-43.41%,and the abundance index of microorganism increased by 4.79%-15.42% after straw returning to field and feeding.5.Study on soil nitrification mechanism in RC mode of treatment with straw returning and feeding: soil nitrification,AOA and AOB abundance,soil microbial nitrogen and soil ammonium nitrogen contents all decreased gradually after the peak at the jointing stage of rice tillering,and their seasonal variation showed strict consistency.In the tillering and jointing stage,the content of ammonium nitrogen in soil was increased,and the soil oxidation and permeability were good,which had a positive promoting effect on the metabolism of microbial community,so that the soil microbial abundance was improved and the nitrification intensity was promoted.Straw returning and feeding treatment would also affect the soil nutrient status,change the soil environment,which might has a long-term impact on microorganisms and various biochemical processes,thus affecting the occurrence of nitrification.