Effects Of Chinese Milk Vetch Combined With Chemical Fertilizer On Bacterial Community,Soluble Organic Carbon And Soluble Organic Nitrogen In Different Paddy Soils

Chinese milk vetch is the most common green manure in southern China.Application of Chinese milk vetch to the field plays an important role in sustainable rice production and soil fertility.The transformation of carbon and nitrogen are series of complex microbial processes.However,the effects of Chinese milk vetch combined with chemical fertilizers on soluble organic matter and bacterial communities in paddy soils with different fertility level are still unclear.In this study,the dynamic changes of soil bacterial community,the dynamic changes and potential leaching loss of soluble organic matter during rice growth stage in three different paddy soils,including red clayey soil,yellow podzolic paddy soil and grey paddy soil,under two treatments of chemical fertilizer and Chinese milk vetch combined with chemical fertilizer were studied by the technologies of Real Time Quantitative PCR,High-throughput Sequencing,TOC and Continuous Flow Injection Analyzer.The aims of this study are to reveal the effects of Chinese milk vetch combining with chemical fertilizer on bacterial community,soluble organic carbon and soluble organic nitrogen,to evaluate the risk of dissolved organic matter leaching loss and provide basis for the prevention of soil soluble organic carbon and soluble organic nitrogen in subtropical different paddy soils.The results showed as follows:?1?There were significant differences in soil physical,chemical and biochemical properties between the three types of paddy soils,which showed obvious hierarchical differentiation.?2?The dominant bacterial communities in three types of paddy soils used were Proteobacteria,Chloroflexi,Actinobacteria,Acidobacteria,Nitrospirae,Firmicutes,Gemmatimonadetes and Planctomycetes,the relative abundance of each phylum was more than 1%,16S rRNA gene abundances ranged from 2.78×10⁹-5.40×10⁹ g^-1 copy number,showing a trend of“increasing-decreasing-increasing”in rice growth stages.The bacterial diversity index showed a dynamic change in rice growth stages with the highest in ripening stage.The PERMANOVA result indicated that the soil type accounted for 27.6%variation of bacterial community structure,the rice growth stages accounted for 13.0%variation of bacterial community structure,while the fertilizer treatment explained only 2.5%variation of bacterial community structure.Different fertilization treatments had no significant effect on the soil bacterial community.The result of RDA showed that the ratio of soil soluble organic carbon and soluble organic nitrogen,soil total carbon,total nitrogen and pH were important environmental factors impact to bacterial community.?3?The contents of soluble organic carbon in three different types of paddy soils ranged from 29.16 to171.04 mg kg^-1.The dynamics of soluble organic carbon contents in the topsoil showed the variation trend of“increasing-decreasing-increasing”in rice growth stages.Yellow podzolic paddy changed greatly during the rice growth stages.The contents of soluble organic nitrogen ranged from 2.00 to 25.71 mg kg^-1,which showed a dynamic change of“increasing-decreasing-fluctuating”during rice growth stages.Soil type and sampling time were the main impact factors leading to the difference of soil soluble matter,and different treatments have no significant effect on the dynamics of soil soluble organic carbon and soluble organic nitrogen contents.The results of grey correlation analysis indicated that soil organic matter,soluble organic nitrogen,bacterial Shannon index,bacterial ACE index and clay content were the main factors affecting soil soluble organic carbon;total soil soluble nitrogen,bacterial abundance,soil soluble organic carbon and bacterial ACE index were main impact factors of soil soluble organic nitrogen.?4?Different soil fertility level,treatments and sampling time have significant effects on the concentrations of dissolved organic carbon and dissolved organic nitrogen in both surface water and 40-60 cm soil layer of paddy fields.Soil fertility level significantly affected the potential leaching loss of dissolved organic matter,with the least potential leaching loss of dissolved organic carbon in the red clayey soil(0.3 t C ha^-1 crop^-1),and the least potential leaching loss of dissolved organic nitrogen in the grey paddy soil(10.68 kg N ha^-1 crop^-1).The application of Chinese milk vetch could reduce the potential leaching loss of soluble organic nitrogen,which reduced about 2.49-8.02 kg N ha^-1 crop^-1,but could not reduce the potential leaching loss of soluble organic carbon.Both dissolved organic carbon and dissolved organic nitrogen in the surface water were increased significantly after fertilization.It was very important to manage the field water within 7 days after fertilization,especially in red clayey soil and yellow podzolic paddy soil,for preventing the loss of dissolved organic carbon and dissolved organic nitrogen.