Effect Of Nitrification Inhibitor On The Response Curve Of Nitrogen Fertilizer In Vegetable Ecosystem

The proportion of vegetable production in the whole agricultural production is getting larger and larger with the increase of people's living standard and demand.The characteristics of high intensification,high multiple crop index and large amount of fertilization of planting vegetables caused a large number of N₂O emissions from vegetable soil so that vegetable ecosystem has become an important N₂O source in the farmland.Few researches have been done on N₂O emissions from vegetable fields and the effect of nitrification inhibitor on response curves of nitrogen fertilizer is relatively rare.N₂O fluxex of treatments of CP N fertilizer which contains nitrification inhibitor and conventional urea from typical vegetable ecosystem in southeast China where Lettuce,Tung choy,Baby bok choy and Coriander herb were planted were monitored continuously by using static chamber-gas chromatography from April 2013 to April 2014.Effects of CP N fertilizer on vegetable yields,nitrogen use efficiency,N₂O emissions,net ecological benefit of vegetable production and response curves of nitrogen fertilizer under different N application rates were studied.The main results were listed as follows:1.Vegetable yields increased with increasing N input at N application rate of 0-1280 kg N ha-1 yr-1,but they decreased when N application rate exceeded 1280 kg N ha-1 yr-1.Vegetable yields increased by 54.1-102.3,36.0-58.6,152.7-195.6 and 200.1-360.8%when N fertilizers were applied during the growth period of Lettuce,Tung choy,Baby bok choy and Coriander herb.With application of CP N fertilizer,vegetable yields increased by 6.2-19.2,5.0-11.4,6.1-14.4 and 6.2-20.0%,at the same time nitrogen uptake of plant increased by 1.8-21.8,7.9-21.6,6.1-30.6 and 15.6-22.5%compared to conventional urea during growth period of Lettuce,Tung choy,Baby bok choy and Coriander herb.Nitrogen use efficiency improved 0.3-7.3,2.0-12.8,1.1-11.6 and 3.4-7.7%with the use of nitrification inhibitor compared to conventional urea during four vegetable seasons.The N fertilization raised total vegetable yield 69.3-107.8 t ha-1 yr-1 and increasing rate of yield was 79-123.0%compared to CK treatment.The application of CP N fertilizer increasd total yield,total N uptake and total nitrogen use efficiency 5.7-15.2%,8.6-20.5%and 1.7-8.5%,respectively,at the rates of 640-1920 kg N ha-1 yr-1 compared to CK treatment.The quadratic model best described the response of vegetable yields to N application rates no matter with or without nitrification inhibitor and nitrogen use efficiency significantly and negatively correlated with the amount of nitrogen and it decreased with increased nitrogen levels no matter with or without nitrification inhibitor,the application of nitrification inhibitor made response curves upward.2.Vegetable field is an important source of N₂O emissions.The N fertilization increased N₂O emissions.Seasonal variation of N₂O fluxes of all treatments were basically the same,but they were different in various vegetable seasons.N₂O fluxes varied in the range of 5.5-6200.1 ?g N m-1 h-1.The N₂O fluxes of CP N fertilizer were lower than those of conventional urea.The application of CP N fertilizer cut down total N₂O emissins 3.7-10.3 kg N ha-1 yr-1 and decreasing rate was12.4-22.5%,it also significantly decreased N₂O emission factors from 0.84-1.22%to 0.25-0.56%?p<0.05?and reduced yield-scaled N₂O emissions 23.7-27.3%?p<0.05?,at the same time,it decreased global warming potential of N₂O 1.8-4.8 t CO₂ eq ha-1?12.4-22.0%?at the rates of 640-1920 kg N ha-1 yr-1 compared to conventional urea.Total N₂O emissions inceased with increasing N input rates as exponential function and yield-scaled N₂O emissions inceased with increasing N input rates as cubics function no matter with or without nitrification inhibitor and the response curve of N₂O emissions to N application rates of with application of CP N fertilizer changed more slowly than that of conventional urea.The addition of NI made response curves downward.3.The N input increased content of NH₄⁺-N and NO3--N in soils and it could increased NH₄⁺-N content significantly?p<0.05?compared to CK treatment.Under the same N level,the NH₄⁺-N content of the treatment of CP N fertilizer was higher than that of conventional urea.The content of NH₄⁺-N increased by 23.4-36.7%significantly?p<0.05?and the content of NO3--N decreased by 30.2-50.7%with application of CP N fertilizer so that the apparent nitrification rate reduced 12.8-22.6%and nitrification was inhibited effectively.4.The carbon cost increased remarkably?p<0.05?because of N₂O emissions from vegetable field and the production and transportation of N fertilizer and carbon cost increased with increasing N input.The application of CP N fertilizer could reduce carbon cost 181.7-501L1 CNY per hectare at the rate of 640-1920 kg N ha-1 yr-1 compared to conventional urea.The N fertilization improved economic benefit and net ecological benefit 10.5-16.5 and 9.2-14.4 ten thousand CNY per hectare?p<0.05?,respectively.Net ecological benefit increased 1.5-3.5 ten thousand CNY?7.2-18.4%?when nitrification inhibitor was applied at the rate of 640-1920 kg N ha-1 yr-1 and the net ecological benefit improved significantly at N levels of 640 and 960 kg N ha-1 yr-1?p<0.05?.In the hole year,the output/input raised 0.3-1.1 with addition of nitrification inhibitor.The relationship between net ecological benefit and N rate was quadratic function that was downward opening and the addition of nitrification inhibitor made response curve upward.The optimum N application rate was 960 kg ha-1 yr-1 for conventional urea and 640 kg ha-1 yr-1 for CP N fertilizer through the method of life cycle assessment.Therefore,appling nitrification inhibitor to vegetable field will be an effective means to mitigate N₂O emission at the same time increase yield and economic benefit.