Effects Of Mixed Organic And Inorganic Fertilizer And Arbuscular Mycorrhizal Fungi On Maize Nitrogen Absorption And N₂O Emission

To determine the most suitable mixed organic and inorganic N fertilizer and the role of arbuscular mycorrhizal fungi in the growth of summer maize.The effects of mixed organic and inorganic N fertilizer and mycorrhizal fungi on summer maize grain yield and soil nitrous oxide emissions were investigated using a two-factor design in a pot experiment.During the summer maize growing periods from June to September 2019 and 2020,set no fertilizer control（CK）,inorganic N fertilizer 180 kg N ha-1（NPK）,organic fertilizer replacing 25% inorganic fertilizers（organic fertilizer 45 kg pure N + chemical fertilizers kg N ha-1,25M）,organic fertilizer replacing 50% inorganic fertilizer（organic fertilizer 90 kg pure N +chemical N 90 kg N ha-1,50M）,eight replicates of each treatment;AMF treatments:four replicates of mixed organic and inorganic N fertilizer treatments with the presence of AMF（A+）,four replicates of mixed organic and inorganic N fertilizer treatments without AMF（A-）.Maize yield,biomass,root characteristics,aboveground and root nitrogen accumulation,soil NH₄⁺,NO₃^-,organic carbon content,soil p H,electrical conductivity and AMF colonization were determined.A static box method was used to collect nitrous oxide gas and a meteorological chromatograph was used to determine the concentration of nitrous oxide.The effects of mixed organic and inorganic N fertilizer and arbuscular mycorrhizal fungi on maize yield and nitrous oxide emission were analysed,to provide a theoretical basis for nitrogen fertilizer management,maize yield increase and stabilization,reduction of chemical fertilizer use,improvement of nitrogen fertilizer utilization and sustainable agricultural development.The main research results were as follows:1.Both mixed organic and inorganic N fertilizer and arbuscular mycorrhizal fungi significantly increased maize yield.Compared to CK treatment,NPK,25 M and50M treatments increased yield by 103.32%,77.15% and 73.10%,and increased66.81%,50.68% and 40.70% for harvest index,respectively.The maximum grain yield was 40.18 g plant-1 under NPK condition.Higher grain yield and harvest index were obtained when organic fertilizer was replacing for 25% of chemical fertilizer,while yield was reduced by 2.29% when the rate of application exceeded 25%（50M）.2.Soil N₂O emission varied dynamically during the periods of maize growth in2019 and 2020,with a steady overall trend and varied from 77.59 to 557.61 μg m-2 h-1in the rate of nitrous oxide emission.Compared to CK treatment,three fertilizer treatments significantly increased N₂O flux rate and cumulative N₂O emission.Compared to NPK treatment,the 25 M and 50 M treatments reduced the N₂O flux rate by 21.46% and 7.74%,and the cumulative N₂O emission by 15.73% and 7.48%,respectively.3.The results of correlation analysis showed that maize grain yield was positively correlated with AMF colonization,and the abundance of nir K and nir S were positively correlated with N₂O flux rate and cumulative N₂O emission.AMF colonization was negatively correlated with the abundance of nir K and nir S,N₂O flux rate,and cumulative N₂O emission.Maize root length,root surface area,root volume,root diameter and soil organic carbon content were positively correlated with maize grain yield,biomass and plant nitrogen accumulation,and soil conductivity was negatively correlated with maize grain yield,biomass and plant nitrogen accumulation.4.The results of principal component analysis showed that the abundance of nir K and nir S,soil NH₄⁺,NO₃^-and organic carbon content were positively correlated with soil N₂O flux rate and cumulative N₂O emission,while AMF colonization was negatively correlated with soil N₂O flux rate and cumulative N₂O emission.5.The results of the structural equations showed that both N addition and arbuscular mycorrhizal fungi had significant positive effects on root volume,maize grain nitrogen accumulation and maize plant nitrogen accumulation,and that N addition and mycorrhizal fungi could increase maize root volume,increase maize biomass and harvest index,and ultimately increase maize grain yield by increasing grain and plant nitrogen accumulation.Harvest index,the abundance of nir K and nir S had a positive effect on the N₂O flux rate,while grain nitrogen accumulation had a negative effect on the N₂O flux rate.Nitrogen addition had a significant positive effect on the abundance of soil nir K and nir S,while arbuscular mycorrhizal fungi had a significant negative effect on the abundance of nir K and nir S in soil.This indicates that N addition can promote soil N₂O emission by increasing maize root volume and the abundance of nir K and nir S in soil;and that the arbuscular mycorrhizal fungi can reduce soil N₂O emission by increasing grain nitrogen accumulation and decreasing root volume and the abundance of nir K and nir S in soil.Combining maize yield and ecological benefits,the use of suitable organic fertilizer to partially replace chemical nitrogen fertilizer under equal nitrogen condition and inoculation with mycorrhizal fungi can improve maize grain yield,increase maize biomass and nitrogen accumulation,while reducing the rate and cumulative of N₂O emission.In conclusion,we conclude that replacing 25% of chemical fertilizer with organic fertilizer（25M）is the best proportion to achieve stable yield,reduce N fertilizer input and N₂O emission,and that mycorrhizal fungi can increase yield and reduce N₂O emission by improving plant root characteristics and reducing the abundance of key functional genes for denitrification in the soil.