Effects Of Returning Ways On Soil Fertility And Microbial Diversity In Paddy Fields In Northeast China

Straw is one of the most important biomass resources in China.There are many ways to use straw.Straw returning is of great value to soil fertility restoration.Soils in Northeast China are gradually degraded due to long-term farming and excessive use of fertilizers.Straw returning can provide soil nutrients and alleviate the problem of soil degradation.However,the annual average temperature in Northeast China is low,and the straw yield is large,and the decomposition time of straw is slow after straw returning to field.To solve the problem that straw is difficult to decompose due to perennial low temperature in Northeast China,improve paddy fertility and promote microbial activities,and explore effective straw returning methods.The experiment was carried out in Tailai County,Heilongjiang Province in April,2021.Two straw returning methods were used: direct straw returning with microbial agent(MD),compost straw returning with microbial agent(MC),At the same time,the direct return of straw without microbial agent(D)and compost return of straw without microbial agent(C)were set up to explore the effects of microbial agent and returning method on soil organic matter and other nutrients and enzyme activities.Illumina Mi Seq high-throughput sequencing technology was used to explore the effects of MD and MC on microbial community structure in cultivated land.Soil samples were collected in April,June,August and October to study the effects of different returning methods on soil fertility and enzyme activities.To provide theoretical basis for preventing soil degradation and promoting straw resource utilization in Northeast China.The results are as follows:Firstly,through the experimental results of measuring various indexes of soil fertility and enzyme activity,the average contents of soil organic matter(SOM),humus(HS),humic acid carbon(HA-C),fulic acid carbon(FA-C)and enzyme activities of straw returning combined with microbial agent were higher than those of straw returning without microbial agent,indicating that the soil fertility of straw returning with microbial agent was higher than that of straw returning without microbial agent.Secondly,during the whole straw returning period,the average contents of SOM,HS and FA-c in MD treatment increased by 2.28 g/kg,7.82 g/kg and 5.26 g/kg,respectively,compared with MC treatment,while the ha-C content in MD treatment decreased by 5.50% compared with MC treatment.Compared with MC,available P and ammonium n in MD increased by 7.57 mg/kg and 2.27 mg/kg,respectively,and reached the peak value in June.The total phosphorus content accumulates with the increase of straw returning time.The activities of urease,sucrase,cellulase and alkaline phosphatase in soil showed that MD was 1.50%,2.80%,3.20% and 9.70% higher than MC,respectively.Through high-throughput sequencing of soil microorganisms in MD and MC.The results showed that both MD and MC increased the richness of soil bacteria Chao1,but decreased the Shannon index and Simpson index.However,the abundance and diversity of fungi decreased significantly in August,and the unclassified fungi increased significantly at this time.The Actinomycetes and Basidiomycetes increased significantly in MD treatment compared with MC treatment.Among MD bacteria,Flavobacterium,Nocardioides,Cryobacterium,Polaromonas and Rhodoferax were more dominant than MC.In MC,Lysobacter,Bacteroidetes＿vadin HA17,SBR1031,Methylobacter,Pseudomonas,Skermanella and Anaerolinea were found is superior to MD;Alternaria,Schizothecium,Serendipita,Mrakia,Pseudogymnoascus,Pseudeurotium and Microascus were more dominant in MD than in MC.In MC,Fusarium,Coprinopsis,Acremonium,Tausonia,Humicola and Mrakiella were more dominant than MD.In MD,Agromyces produce organic acids and Nocardiaceae produce antibiotics to improve soil organic matter and antibacterial activity.Trichoderma,Carnitaceae and other saprophytes can produce cellulase to improve the decomposition efficiency of straw.The relative abundance of bacterial and fungal communities was positively correlated with total phosphorus(TP),humic acid carbon(HA-C),humus(HS)and fulic acid carbon(FA-C)contents.In conclusion,MD has a better improvement effect on soil fertility than MC among the two returning methods.Both methods can increase soil bacterial richness and affect soil microbial community structure.