| Conservation tillage is one of the important internationally recognized agricultural technologies.It is of great practical significance to accelerate the research of conservation tillage technology for environmental protection and agricultural development.A large number of studies have proved that straw is a good agricultural ecosystem at home and abroad,but the relationship between different tillage methods and straw returning to the field on soil fertility and rice wheat yield is still lack of long-term positioning research.This study was conducted in the long-term positioning experimental field of Yangzhou University School of agriculture in 2017-2018.Six treatments were set under the condition of rice wheat double cropping:continuous no tillage straw mulching returning(NTS)and rotation tillage 1(RT1),RT2,CTS,MTS and CT.Nanjing 9108 was used for rice and Yangmai 22 was used for wheat to study the effects of different tillage methods and straw returning on soil physical and chemical properties,microbial community structure and rice wheat yield,reveal the characteristics of soil fertility,analyze the distribution and diversity of soil microbial community structure,provide ideas for explaining the driving mechanism of soil microorganisms,and provide ideas for conservation tillage and straw returning in this region Field related technology provides theoretical reference.The results of this study are as follows:1.Compared with other treatments,the content of organic matter in farmland soil was significantly increased by the treatment of returning straw to the field(CTS).CTS and NTS could increase the content of alkali hydrolyzed nitrogen in soil surface.Different tillage methods and straw returning had little effect on the content of soil available P,but could increase the content of soil available K.On the one hand,continuous no tillage results in the increase of soil bulk density,on the other hand,it results in the increase of organic matter content in the surface soil.Straw returning can improve the content of soil organic matter,total nitrogen,alkali hydrolyzed nitrogen and available potassium,and supply soil nutrients effectively.2.The effect of the combination of different tillage methods and straw returning on soil enzyme activity is different.The activities of urease,acid phosphatase and sucrase in the soil after wheat and rice were increased to a certain extent,and the activities of catalase in the soil were decreased.The activities of acid phosphatase,sucrase and urease in the soil surface after wheat and rice were all increased under the condition of continuous straw mulching.In different tillage methods,no tillage and rotation tillage provide conditions for the release of catalase in the soil.In a word,urease,sucrase and acid phosphatase were more easily released in the field of straw returning.Compared with the field of straw returning,the activity of catalase was increased3.Compared with conventional tillage,no tillage is not conducive to the growth and reproduction of bacteria in the lower soil layer,resulting in the decrease of bacteria in the lower soil layer,while straw returning provides suitable living conditions for bacteria in the surface soil layer,and promotes the increase of bacteria in the surface soil layer.In the depth of 0-20cm,Proteobacteria and acidobacteria are the most abundant.No till straw increased the relative abundance of Proteus and decreased the relative abundance of acidobacteria.At the same time,straw returning increased the relative abundance of Proteus and acidobacteria.The highest relative abundance is betaproteobacteria in 0-20cm soil,which tends to increase with the increase of soil depth.The lowest relative abundance is alpha Proteobacteria,which decreases with the increase of soil depth.On the whole,the β-Proteus of CT and NTS were higher than other treatments.Under the condition of straw returning to the field,the change of diversity index of bacterial community structure in the lower layer of soil was increased and the variation of microbial diversity decreased with the increase of soil depth was slowed down by different degrees of less tillage and ploughing,which confirmed the difference of environmental factors and community characteristics in the lower layer of soil caused by the combination of different tillage methods and straw returning to the field,and affected the community level of bacteria.4.Compared with no tillage,less tillage and ploughing increased the number of fungi on the surface of soil,and the OTU decreased with the increase of soil depth.Ascomycota was the most abundant one,followed by Basidiomycota.Both ploughing and straw returning can improve the relative abundance of Ascomycetes.accelerate the decomposition of organic matter,facilitate the accumulation and increase of soil nutrient content,and promote the growth and development of plants.The yield of Basidiomycota was increased by the application of less straw and continuous no straw mulching,and the relative yield of fungi community was increased by the application of less straw.From the perspective of fungal diversity index,under the condition of straw returning to the field,less tillage can improve the number of fungi and species richness to a certain extent.The combination of no tillage and straw returning to the field is conducive to the increase of the number of fungi and the increase of species richness.In addition,no tillage and straw returning to the field are more conducive to the diversity change of soil surface fungal community.In a word,straw returning changed the structure of fungus colony,increased the quantity of fungus community,increased the richness and diversity of fungus colony,and improved the soil micro environment.5.In different tillage methods,although the number of wheat ears is lower under no tillage,the number of grains and 1000 grain weight are higher,so the theoretical yield and actual yield are higher.In rotation tillage,the yield of no tillage was higher than that of conventional tillage;the combination of different tillage measures and straw returning had little effect on the number of grains per ear of rice,among which the number of grains per ear was higher under the condition of less tillage,tillage and straw returning,and the yield of rice under no tillage straw covering was significantly lower than that of conventional tillage.The yield of wheat and rice increased with less straw,while that of rice decreased with no straw. |
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