Effect Of Nitrogen Fertilizer Managements On Nitrogen Balance Of Greenhouse Vegetable Cultivation

The application rate of fertilizer for greenhouse vegetable cultivation in China far exceeds the demand of vegetables,resulting in high greenhouse gas emissions and loss from nitrogen leaching,increasing the risk of greenhouse effect and soil non-point source pollution.It is very important to explore nitrogen loss and nitrogen balance characteristics of greenhouse vegetable fields for rational fertilization.This study is based on field in situ experiments from 2019 to 2021.The dry and wet deposition,ammonia（NH₃）volatilization,nitrous oxide（N₂O）and nitrogen oxides（NO_X）emissions,nitrogen leaching loss,nitrogen uptake by plant,etc were monitored.The nitrogen inputs,nitrogen uptake,reactive nitrogen losses were applied to evaluate the environmental effects of greenhouse vegetable cultivation and identify optimized nitrogen managements that not only ensure the yield and quality of vegetables,but also reduce environmental pollution.The following treatments were designed in the experiments:no nitrogen fertilizer control（CK）,nitrogen-reduced urea fertilizer（50%CF）,inorganic fertilizer（100%CF）,nitrogen-reduced organic fertilizer（50%OF）and organic fertilizer（100%）for cucumber in 2019;no nitrogen fertilizer control（CK）,50%organic fertilizer and 50%controlled-release fertilizer（50%OF+50%SF）,25%organic fertilizer and 75%inorganic fertilizer（25%OF+75%CF,conventional fertilization）,50%organic fertilizer and 50%inorganic fertilizer（50%OF+50%CF）,organic fertilizer（100%OF）for tomato,cabbage and lettuce in 2020-2021.The main research results are as follows:（1）Application rate of nitrogen fertilizer accounted for about 95%of nitrogen inputs,nitrogen in irrigation water and seedling accounted for 0.5%-4.0%,nitrogen in dry and wet deposition accounted for 0.3%-2.3%.The annual dry deposition and wet deposition of nitrogen in greenhouse were 5.5-15.0kg N·hm^-2 and 1.7-2.5 kg N·hm^-2,respectively.（2）The N₂O emissions during cucumber growing season with treatments of CK,50%CF,100%CF,50%OF,100%OF were 1.8,12.6,38.6,5.4 and 51.7 kg N₂O-N·hm^-2,respectively.The cumulative N₂O emissions with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF during tomato,cabbage and lettuce growing seasons were 3.9,16.6,26.0,21.8 and 31.9 kg N₂O-N·hm^-2,respectively.Reduced nitrogen fertilizer application,controlled-release fertilizer application could effectively reduce N₂O emissions.50%nitrogen reduction application could reduce N₂O emission by67.3%-89.6%.Controlled-release fertilizer application could reduce N₂O emission by 24.2%.（3）The NH₃ volatilizations during cucumber growing season with treatments of CK,50%CF,100%CF,50%OF,100%OF were 0.3,4.7,15.2,0.6 and 6.1 kg NH₃-N·hm^-2,respectively.The cumulative NH₃ volatilizations with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF during tomato,cabbage and lettuce growing season were 3.6,8.0,18.0,11.8和9.1 kg NH₃-N·hm^-2,respectively.Reduced nitrogen fertilizer,controlled-release fertilizer application,and increasing the proportion of organic fertilizers could effectively reduce NH₃ volatilizations.50%nitrogen reduction fertilization application could reduce NH₃ volatilization by 69.2%-90.6%.Controlled-release fertilizer application could reduce NH₃ volatilizations by 32.6%.Compared with conventional fertilization（25%OF+75%CF）,50%OF+50%CF and 100%OF could reduce NH₃volatilization by 34.4%and 49.3%.（4）The NO_X emissions during cucumber growing season with treatments of CK,50%CF,100%CF,50%OF,100%OF were 0.6,9.3,35.0,0.9 and 6.5 kg NO_X-N·hm^-2,respectively.The cumulative NO_Xemissions with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF during tomato,cabbage and lettuce growing season were 0.6,4.5,28.2,12.6 and 6.4 kg NO_X-N·hm^-2,respectively.Reduced nitrogen fertilizer application,controlled-release fertilizer application,and increasing the proportion of organic fertilizers could effectively reduce NO_X emissions.50%nitrogen reduction application could reduce NO_X emissions by 73.4%-86.6%.Controlled-release fertilizer application could reduce NO_X emissions by 64.2%.Compared with conventional fertilization（25%OF+75%CF）,50%OF+50%CF and 100%OF could reduce NO_X emissions by 55.3%and 77.3%.（5）The N loss from leaching during cucumber growing season with treatments of CK,50%CF,100%CF,50%OF,100%OF were 65.7,204.0,235.5,138.7 and 188.2 kg N·hm^-2,respectively.The cumulative N loss from leaching with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF during tomato,cabbage and lettuce growing season were 35.4,77.9,109.5,94.3 and 83.1 kg N·hm^-2,respectively.Reduced nitrogen fertilizer application,controlled-release fertilizer application,and increasing the proportion of organic fertilizers could effectively reduce nitrogen leaching.50%nitrogen reduction application could reduce nitrogen leaching by 13.4%-26.3%.Controlled-release fertilizer application could reduce nitrogen leaching by 17.3%.Compared with conventional fertilization（25%OF+75%CF）,50%OF+50%CF and 100%OF could reduce nitrogen leaching by 13.9%and 24.1%.（6）The nitrogen uptake by plants during cucumber growing season with nitrogen treatments of CK,50%CF,100%CF,50%OF,100%OF were 188.1,238.2,263.4,227.2 and 242.5 kg N·hm^-2,respectively.The cumulative nitrogen uptake with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF)during tomato,cabbage and lettuce growing season were 391.2,522.6,552.4,569.9 and 572.7 kg N·hm^-2,respectively.Reduced nitrogen fertilizer application and controlled-release fertilizer application could reduce nitrogen uptake;increasing the proportion of organic fertilizers could increase nitrogen uptake,but there were no significance.（7）The yields of cucumber with treatments of CK,50%CF,100%CF,50%OF,100%OF were 40.7,48.4,49.5,46.2 and 46.5 t·hm^-2.The total yields with treatments of CK,50%OF+50%SF,25%OF+75%CF,50%OF+50%CF,100%OF of tomato,cabbage and lettuce were 207.7,235.9,248.2,254.5 and 244.7 t·hm^-2.The average Vc content of edible parts of the three vegetables were 6.6,7.2,7.6,7.7 and 8.8 mg·100g^-1,and the average nitrate content were 330.9,392.1,484.4,447.6,409.3 mg·kg^-1.Reduced nitrogen fertilizer application,controlled-release fertilizer application and increasing the proportion of organic fertilizers have no significant effects on yields and quality.In summary,reducing nitrogen fertilizer application,applying controlled-release fertilizer,increasing the proportion of organic fertilizers could reduce reactive nitrogen loss.The treatment of50%OF+50%CF could reduce reactive nitrogen loss significantly,increase nitrogen utilization and maintain vegetable yield.Therefore,it could be recommended as fertilization practice to achieve green and low-carbon vegetable production.