Microbial Mechanisms Of Soil Carbon And Nitrogen Accumulation Under Long-term Rice-green Fertilizer Multiple Cropping

Green manure is an important source of organic manure.Planting green manure to press green and return to field has positive effect on soil improvement,it can improve soil physical structure and physicochemical properties,enhance the biological activity of soil,increase soil organic matter and nutrient element content.Therefore,green fertilizer multiple cropping is important measures to enriching the soil,improve soil environment,increase food output and agricultural productivity.In the past,the accumulation of carbon and nitrogen in green fertilizer multiple cropping soil was discussed.However,there is still a lack of research on its deep accumulation mechanism.Based on this,in this paper,40 years of rice-green fertilizer multiple cropping soil was used as the object of long-term positioning experiment,soil samples of past years and fresh samples of current season were tested by long-term experiment.Traced by ¹⁸O and ¹⁵N isotopes,microbial marker identification and other technologies,from the perspectives microbial on carbon utilization efficiency,nitrogen utilization efficiency,biomass carbon turnover and microbial residue contribution.Systematic illustrates the microbial mechanism of soil organic carbon and nitrogen accumulation differences under long-term rice-green fertilizer multiple cropping.The main results are as follows:（1）The contents of soil organic carbon（SOC）and total nitrogen（TN）accumulated with the increase of planting years.Compared with fallow treatment in winter,rice-green fertilizer combined cropping did not significantly change soil organic carbon content,while the increase of soil total nitrogen was lower.（2）In the season of green manure,compared with rice-winter fallow treatment,The growth rate and respiration rate of soil microorganisms were increased by rice-green manure multiple cropping,CUE of soil microorganisms increased by25.1%-28.3%.In the early season and late rice season,compared with rice-winter fallow treatment,rice-ryegrass and winter rape multiple cropping increased the microbial respiration rate,rice-milk vetch multiple cropping decreased the microbial respiration rate.The growth rate of microorganisms was decreased by the rice-green manure multiple cropping in the early season,CUE of soil microorganisms decreased by 1.3%-21.4%.The growth rate of microorganisms was increased by the rice-green manure multiple cropping in the late rice season,CUE of soil microorganisms increased by 14.5%-17.8%.（3）Compared with rice-winter fallow treatment,the microbial synthesis rate of organic nitrogen was increased in each treatment of rice-green manure multiple cropping in different planting seasons.Rice-milk vetch treatment increased the total nitrogen mineralization rate in different seasons.The rice-ryegrass multiple cropping increased the total nitrogen mineralization rate in both early and late rice seasons.However,rice-rape treatment only increased the total nitrogen mineralization rate in the early rice season.The microbial NUE increased by 21.7%-38.3%in the green fertilizer season,in early rice and late rice season,there were different degrees of decrease.（4）The microbial turnover time of soil microbial biomass carbon was 50-242days.In the season of green manure,the rice-green fertilizer compound cropping treatment was shorter than the rice-winter fallow treatment.The results showed that the turnover rate of microbial biomass was higher after green manure was turned over and returned to the field,the activity of microorganisms was improved and the turnover of soil organic carbon was promoted.（5）The carbon and nitrogen of soil microbial residues increased with the increase of planting years.Compared with rice-winter fallow treatment,the carbon and nitrogen contents of microbial residues increased by 11.8%,10.4%and 15.4%in rice-green manure multiple cropping,the ratio of microbial residual C and N to soil organic N and total N increased by 21.1%-24.1%and 24.5%-27.2%respectively.In conclusion,long-term rice-green fertilizer multiple cropping promoted the accumulation of soil organic carbon and total nitrogen.Rice-green fertilizer multiple cropping promoted the participation degree of microorganisms in soil organic carbon and total nitrogen accumulation,accelerated the turnover time of microbial biomass,improved microbial respiration rate and total nitrogen mineralization rate.There was no significant difference in organic carbon content between rice and winter fallow treatment,the nitrogen supply capacity was improved and the total nitrogen content was lower than that of rice-winter fallow treatment.