Effects Of Planting Patterns And Nitrogen Fertilizer Allocation On Rhizosphere And Non-Rhizosphere Nitrogen And Microorganisms In Paddy Field

The application rate of nitrogen fertilizer is generally higher in China.Long-term overuse of nitrogen fertilizer will not only reduce the utilization efficiency of nitrogen fertilizer by crops,but also threaten environmental safety.Paddy-upland cropping rotation,a crop production method in paddy fields,can improve soil quality in paddy fields and affect the process of soil nitrogen migration and transformation.In recent years,the maize-rice rotation system has been given more attention.However,there is limited information on nitrogen and microbial community in rhizosphere and non-rhizosphere soils of paddy field in maize-rice rotation.Therefore,this experiment conducted maize-rice rotation and double rice cropping in 2017 and mainly focus on its influence within rhizosphere and non-rhizosphere soil properties.Besides,the impact of residual nitrogen fertilizer in the first season on soil nitrogen content and crops growth in the latter season.In order to explore a reasonable fertilization ratio,different nitrogen fertilizer allocations were arranged as follows,the no-fertilization control(F0),and the first season and the second season fertilization were 150-300 kg N/ha(F1),225-225 kg N/ha(F2)and 300-150 kg N/ha(F3).The nitrogen content,microbial biomass,enzyme activity and bacterial community composition in rhizosphere and non-rhizosphere soil were determined to investigate the effect of planting patterns and nitrogen fertilization allocations on these indexes,so as to provide a scientific basis for optimizing the management system of paddy-upland crop rotation and maintaining environmental health.The main results were as follows:(1)Application of nitrogen fertilizer can increase soil nitrogen content,but the effect of nitrogen fertilizer allocation was not significant on soil nitrogen content.The aerobic condition under upland crop in the paddy-upland crop rotation system was beneficial to the transformation of soil nitrogen from ammonium nitrogen to nitrate nitrogen,which changes the nitrogen form in the soil.Compared with double rice cropping,the content of ammonium nitrogen in rhizosphere and non-rhizosphere soil under maize-rice rotation decreased by 18.45%and 12.00%,respectively.Meanwhile,nitrate nitrogen content in rhizosphere and non-rhizosphere soil increased by 45.71%and 112.05%,respectively.The effect of maize-rice rotation on soil ammonium nitrogen content was present in the first season while the effect of maize-rice rotation on soil nitrate nitrogen content could last for two seasons.In addition,soil total nitrogen content under maize-rice rotation was lower than double rice cropping at maturity stage of the second season.The content of ammonium nitrogen in rhizosphere soil of maize was higher than that in non-rhizosphere,and the content of nitrate nitrogen was lower than that in non-rhizosphere.The content of ammonium nitrogen in rhizosphere soil of rice was lower than that in non-rhizosphere,and the content of nitrate nitrogen was higher than that in non-rhizosphere.Those phenomenons indicated that there were differences in rhizosphere environment under different crops in paddy field.(2)Soil microbial biomass and enzyme activity are important indicators involved in soil nitrogen cycling,and maize-rice rotation had a significant impact on it and can last for two seasons.Compared with double rice cropping,the soil microbial biomass carbon and microbial biomass nitrogen ratio(MBC/MBN)and nitrate reductase activity decreased in the maize-rice rotation system,and the urease activity increased,indicating that the nitrogen bioavailability was improved and the denitrification was weakened,which improves the nitrogen utilization rate to some extent and potentially reduces the amount of gaseous nitrogen loss.Microbial biomass and enzyme activities were quite different between rhizosphere and non-rhizosphere soils.On the whole,the nitrate reductase activity in rhizosphere was higher than that in non-rhizosphere.The MBC/MBN and urease activity in the rhizosphere were lower than those in the non-rhizosphere,but the difference between the rhizosphere and non-rhizosphere was affected by the crop growth period.(3)The main bacteria in the soil are Proteobacteria,Chloroflexi,Acidobacteria,Nitrospirae and Actinobacteria.Planting patterns,nitrogen fertilizer allocation,and sampling locations could affect the abundance of bacterial communities in the soil,which in turn affected the carbon and nitrogen cycle in the soil.Soil nitrate nitrogen content,pH,C/N,urease activity and other indicators have an impact on soil bacterial communities.(4)The yield of rice in maize-rice rotation system was 25.10%higher than the second rice yield of double rice cropping.Application of nitrogen fertilizer increased crop yield.Under the conditions of this experiment,the maximum yield of maize-rice rotation was obtained at 225-225 kg N/ha(the sum yield of two season crops),while the double rice cropping yield reached the maximum yield at 300-150 kg N/ha.Since the pot experiment conditions have an impact on the results,the further research should be confirmed in the field trial in the future.