Effects Of Corn Straw Returning On Soil Carbon And Nitrogen Components And Microbes In Songnen Plain

Songnen Plain is the main spring corn（Zea mays L）producing area in our country,with a large of corn straw surplus.The corn straw returning directly is an effective way to fertilize soil and increase the comprehensive utilization rate of straw.Soil organic carbon affects soil nutrient supply,and long-term agricultural planting results in the decrease of soil organic carbon content and soil fertility.Nitrogen is an important nutrient element for crop growth,and also a major limiting factor for farmland productivity and crop growth.Soil nitrogen supply capacity directly determines crop yield.Soil microbes play an important role in straw decomposition and soil carbon and nitrogen cycling.Corn straw is rich in a large number of nutrients such as carbon,nitrogen,phosphorus and potassium.Direct returning can increase the source and supply of soil carbon and nitrogen,change the composition and function of soil microbes,affect soil carbon sequestration and nitrogen supply,and then affect soil fertility and crop yield.This experiment was conducted in the campus test base of Northeast Agricultural University from 2021 to 2022.Using the frame-mounted continuous located experiment started in 2016,corn straw return amounts were set at 0 g/frame,65 g/frame（9.2 t/hm²）,130 g/frame（18.4 t/hm²）,195 g/frame（27.6 t/hm²）and 260 g/frame（36.8 t/hm²）.One group planted corn for years,the other group was fallow（no crops）.The changes of soil carbon,nitrogen and microorganisms were measured.The test results show that:（1）The contents of TOC,DOC,LOC and LFOC increased significantly when corn straw was returned for 6 years,and the increasing effect was more obvious with the increased of straw returning amount.Compared with corn planting,fallow is more conducive to the increase of TOC,DOC and LOC content,but not conducive to the increase of LFOC.The content of TOC,DOC,LOC and LFOC showed a significant linear regression relationship with straw returning amount.The slope of the regression equation of TOC,DOC and LOC in the corn planting was higher than that of fallow,while the slope of the regression equation of LFOC was lower than that of fallow.（2）The contents of total nitrogen,available nitrogen,acid hydrolysis nitrogen and acid inhydrolysis nitrogen in soil increased significantly when corn straw returned for 6 years,and the increasing effect was more obvious with the increased of straw returning amount.Compared with corn planting,fallow is more conducive to the increase of TN,NH₄⁺-N,TAHN,ASN,AAN and AIN contents,but not conducive to the increase of AN,NO₃^--N,AMN and HUN.The content of TN,AN,NH₄⁺-N,NO₃^--N,TAHN,AMN,ASN,AAN,HUN,AIN showed a significant linear regression relationship with straw returning amount.The slope of regression equation of AN,NO₃^--N,TAHN,AMN,ASN and AAN in the corn planting was higher than that of fallow,while the slope of the regression equation of TN,NH₄⁺-N,HUN and AIN was lower than that of fallow.（3）The soil microbes in the experiment were mainly bacteria,and the average relative abundance reached 90.49%.Proteobacteria,Actinobacteria and Acidobacteria were the dominant phyla in the soil.Carbohydrate metabolism,amino acid metabolism,energy metabolism and nucleotide metabolism are the main functions of microbes.Glycoside hydrolase and glycosyltransferase are the main processes of microbial carbon conversion.Denitrification and nitrate reduction are the main processes of microbial nitrogen conversion.After corn straw returned for 6 years,the relative abundances of Proteobacteria,glycoside hydrolase and dissimilated nitrate reduction were significantly increased,while the relative abundances of Acidobacteria,carbohydrate metabolism,amino acid metabolism,energy metabolism,nucleotide metabolism and glycosyltransferase were significantly decreased.The relative abundances of Actinobacteria and denitrification were significantly decreased under the condition of planting corn,but significantly increased in fallow conditions.（4）Compared with fallow,corn planting increased the relative abundance of Proteobacteria,Acidobacteria,glycoside hydrolase,denitrification and nitrate reduction,decreased the relative abundance of Actinomycetes,increased the relative abundance of carbohydrate metabolism,amino acid metabolism,energy metabolism and nucleotide metabolism in the no straw returning soil,and decreased the relative abundance of that in the straw returning soil.Compared with fallow,corn planting decreased the relative abundance of glycosyltransferase in the no straw returning soil and increased the relative abundance in the straw returning soil.（5）TOC,DOC,LOC and LFOC were significantly positively correlated.There was no significant correlation between ASN and NO₃^--N,AMN and HUN,while there was significant positive correlation between other soil nitrogen components.TOC was positively correlated with TN,TAHN,ASN,and AIN,DOC was positively correlated with TN,ASN,AIN,LOC was positively correlated with TN,ASN,AIN,and POC was positively correlated with AMN.Soil C and N components affected soil microbial community structure and function.Proteobacteria and glycoside hydrolase were positively correlated with soil C and N components（except ASN）,while Acidobacteria and glycosyltransferase were negatively correlated with soil C and N components.