Effects Of Fertile Soil Layer Construction On Enzyme Activity And Microbial Community In Northeast China Meadow Soil

The meadow soil is a clay loam with a high clay content.Perennial large-scale mechanical operations lead to the emergence of a hard plow layer in the soil,which significantly reduces the permeability and water infiltration capacity of this layer,limits the exchange of water,air and heat in the soil,hinds the growth and development of crop roots,and limits the high and stable yield of crops.Straw returning is one of the effective ways to solve these problems.This study intends to investigate the effects of different straw returning methods on enzyme activities and microbial diversity of northeast meadow soil,in order to explore the effectiveness of straw returning methods on the reconstruction of soil microbial flora in topsoil,and explore reasonable straw returning methods to improve the structure of meadow soil and fertilize the meadow soil.In order to provide a theoretical basis for ensuring our country’s food security and realize the strategic goal of "storing grain in the ground".The positioning test was conducted in Shifang Village,Fujin City,Heilongjiang Province,the core black soil area of Northeast China,from 2018 to 2021.The test soil was meadow soil,and five treatments were set up: Traditional tillage(T15),straw shallow mixing(T15+S),simple deep tillage(T35),corn straw deep mixing(T35+S),corn straw deep mixing with organic fertilizer(T35+S+M),The effects of different straw returning methods on soybean yield,soil physicochemical properties,soil enzyme activity and activity metrology,soil microbial diversity and community structure were investigated.(1)After three consecutive years of treatment,T35+S and T35+S+M significantly increased soybean yield by 23.2% and 38.1%.In the 0 — 15 cm soil layer,T15+S treatment effectively improves organic matter(SOM),total nitrogen(TN),alkaline nitrogen(AN),effective potassium(AK)content 8.9%,2.3%,6.9% and 11.4%(P<0.05),T35 treatment effectively improves total nitrogen(TN),effective phosphorus(AP)content 11.8%,18.9%(P<0.05),T35+S treatment effectively improves the content of organic matter(SOM),total nitrogen(AN),effective phosphorus(AP),effective potassium(AK)7.2%,23.7%,54.5%,15.2%(P<0.05),T35+S+M treatment effectively improves the content of organic matter(SOM),total nitrogen(TN),effective phosphorus(AP),alkaline nitrogen(AN),effective potassium(AK)by 10.9%,22.5%,61.8%,6.8% and 26.5%(P<0.05),T15+S,T35,T35+S,T35+S+M treatmenst effectively reduces Soil volume(SBD)15.6%,7.0%,17.2% and 18.8%(P<0.05),T35,T35+S and T35+S+M treatments all effectively increased p H units by 0.13,0.08 and 0.19.In the 15 — 35 cm soil layer,there is no significant change in T15+S treatments compared with all physical and chemical properties of T15,T35 treatments effectively improves organic matter(SOM),total nitrogen(TN),effective phosphorus(AP),alkaline nitrogen(AN)content 4.0%,15.5%,105%,6.4%(P<0.05),T35+S treatments effectively improves the content of organic matter(SOM),total nitrogen(TN),effective phosphorus(AP),alkaline nitrogenisation(AN),effective potassium(AK)49.8%,62.0%,453.8%,3.1% and 42.8%(P<0.05),T35+S+M treatments effectively improves the content of organic matter(SOM),total nitrogen(TN),effective phosphorus(AP),alkaline nitrogen(AN),effective potassium(AK)25.7%,20.9%,321.5%,16.2% and 30.7%(P<0.05),T35,T35+S,T35+S+M treatment effectively reduce soil volume by 10.7%,16.4%,25.7%(P<0.05),and T35+S+M treatments effectively increased by 0.49 p H units(P < 0.05).(2)T35 treatmenst can reduce soil carbon and nitrogen related enzyme activities,but T35+S and T35+S+M treatment can alleviate their effects on enzyme activities.T15+S treatment increased soil nitrogen related enzyme activities,and T15+S,T35 and T35+S+M treatments significantly increased soil phosphorus related enzyme activities.(3)The limitation of soil microbial resources was studied by enzyme stoichiometry.Based on the analysis of soil carbon,nitrogen and phosphorus related enzymes,enzyme C/N,enzyme C/P and enzyme N/P,enzyme stoichiometric scatter diagram,vector length and vector Angle,In the study area,soil microorganisms in the meadow soil were limited by carbon and phosphorus,but not by nitrogen,and there were differences in the resource constraints of soil under different treatments.Deep-turning treatment increased the phosphorus restriction by microorganisms in 0—15 cm and 15—35 cm soil layers respectively,but compared with T15 treatment,T15+S treatment had no significant effect on phosphorus restriction.(4)In the 0—15 cm soil layer,soil bacterial Chao1 index of T15+S,T35 and T35+S+M increased by 0.6%,1.4% and 8.1%,respectively,compared with T15 treatment.In the 15—35 cm soil layer,Compared with T15+S,T135+S and T35+S+M,the Chao1 index of soil bacteria increased by 2.7%,4.2% and 4.3% respectively.In 0—15 cm soil layer,the highest chao1 index,Shannon index and Simpson index were found in T35 treatment,which increased by 11.1%,5.45%and 2.1% compared with T15 treatment,respectively.The dominant bacteria in the bacterial microbial community were Proteobacteria,actinomycetes and firmicutes,while the dominant bacteria in the fungal microbial community were ascomycetes,basidiomycetes and chytridomycetes.Different straw returning methods could significantly increase the relative abundance of the microbial dominant bacteria and change the composition of the microbial community,and the effect of deep-turning treatment was particularly significant.(5)PCo A analysis showed that different soil depths and straw returning methods had great effects on bacterial communities,and T35+S and T35+S+M treatments had the most significant effects.(6)RDA analysis showed that soil p H,BG enzyme activity,AN and SOM were the most important environmental factors affecting soil bacterial community.p H,AN,AP and SOM were the most important environmental factors affecting soil fungal community.In conclusion,straw shallow-mixed returning tended to reduce soybean yield and increased the nutrient content of 0—15 cm in the surface layer,but had no significant effect on the nutrient content of 15—35 cm in the bottom layer.Straw deep-mixed returning to field(T35+S)and straw and organic fertilizer deep-mixed returning to field(T35+S+M)significantly increased soybean yield,increased nutrient content in 0—15 cm and 15—35 cm soil layers simultaneously,increased soil AP enzyme activity,alleviated soil carbon restriction,improved soil bacterial community composition,and improved soil fertility.To improve crop yield,it is suggested that the meadow soil in northeast China can be fertilized by corn straw returning(T35+S)and deep-mixed corn straw returning combined with organic fertilizer(T35+S+M).