Effects Of Different Fertigation Modes On Ratoon Sugarcane Yieid And Nitrous Oxide Emission From Soil

Reducing nitrous oxide（N₂O）emission from farmland can effectively alleviate the greenhouse effect.In order to pursue high yield of crops,high amount of irrigation and fertilization will lead to the increase of N₂O emission.To obtain the water and fertilizer management mode of high yield and N₂O emission reduction of ratoon cane and explore the factors affecting N₂O emission in sugarcane field,the effects of different fertigation modes on sugarcane yield,N₂O flux,inorganic nitrogen content,enzyme activity and microbial community composition and abundance in soils were investigated using field experiments,and then the relationships between soil N₂O flux and each soil index were analyzed.A fertigation mode with high yield of ratoon cane and lower N₂O emission from soil was revealed.The results show that:（1）Reasonable fertigation mode was benefical for higher sugarcane yield.In different drip irrigation levels and N fertilizer fertigation proportions experiment,the yields of W₁（soil moisture 70%-80%θ_f（field capacity））and W₂（soil moisture 80%-90%θ_f）were 102.4 t·hm^-2 and 97.8 t·hm^-2respectively under F₅₅（50%basal fertilizer,50%fertigation topdressing）.In different drip irrigation and fertigation levels experiment,the yields of W₇₅（irrigation amount 45 mm）and W₁₀₀（irrigation amount 60 mm）were 113.6t·hm^-2and 126.4 t·hm^-2respectively under F₁₂(N 300 kg·hm^-2,P₂O₅ 180kg·hm^-2,K₂O 240 kg·hm^-2).（2）Reasonable fertigation mode can effectively reduce N₂O flux.In different drip irrigation levels and N fertilizer fertigation proportions experiment,the N₂O fluxes of F₅₅ and F₃₇（30%basal fertilizer,70%fertigation topdressing）were lower under W₁,while in different drip irrigation and fertigation levels experiment,,the N₂O fluxes of W₇₅ and W₁₀₀ were lower under F₀₉(N 225 kg·hm^-2,P₂O₅ 135 kg·hm^-2,K₂O 180 kg·hm^-2).（3）Fertigation mode had significant effects on the content of inorganic nitrogen and the activities of soil enzymes related to nitrogen transformation.The inorganic nitrogen content and nitrite reductase activity in W₂F₅₅ and W₁₀₀F₁₂ treatments were at a high level at all growth stages.（4）Irrigation and fertilization significantly affected the composition and abundance of soil microbial community.Denitrifying bacteria（mainly Actinobacteria and Proteobacteria）play an important role in sugarcane soil nitrogen transformation and N₂O emission under fertigation condition.（5）N₂O flux from sugarcane soil was negatively correlated with ammonium nitrogen content,urease and nitrate reductase activities and the abundance of Mesorhizobium in soil（r=-0.572～-0.326,n=24）,and positively correlated with Singulisphaera＿acidipila and Nitrosospira（r=0.549～0.574,n=24）.Thus N 300 kg·hm^-2,P₂O₅ 180 kg·hm^-2,K₂O 240 kg·hm^-2,ratio of basal fertilization to topdressing of 5:5 for nitrgen fertilizer and soil water content at70%-80%field capacity were the optimal water and fertilizer management mode to increase sugarcane yield and reduce N₂O emission,and soil ammonium nitrogen content,urease and nitrate reductase activities and part genus of denitrifying bacteria abundance affected N₂O emission.