不同氮水平下黄瓜-番茄日光温室栽培土壤N_2O排放特征

Characteristics of greenhouse soil N_2O emissions in cucumber-tomato rotation system under different nitrogen conditions

为探讨日光温室黄瓜—番茄种植体系内N2O排放动态变化及其对不同氮水平的响应规律,采用密闭静态箱法,研究了常规氮量（黄瓜季1 200 kg/hm2,番茄季900 kg/hm2）、比常规氮量减25%（黄瓜季900 kg/hm2,番茄季675 kg/hm2）、减50%（黄瓜季600 kg/hm2,番茄季450 kg/hm2）以及不施氮对日光温室土壤N2O排放的影响。结果表明,温度是影响日光温室土壤N2O排放强度的重要因素,4-10月（平均气温为27.4℃）的N2O排放通量最高达818.4μg/（m^2·h;而2-3月（平均气温15.1℃）以及11-12月（平均气温14.7℃）期间的N2O排放通量最高仅为464.5μg/（m^2·h,比4-10月的N2O排放峰值降低了43.2%。N2O排放峰值在氮肥追施后5 d内出现,N2O排放量集中在氮肥施用后7 d内,可占整个监测期（271 d）排放量的64.7%~67.8%。施氮因增加了土壤硝态氮含量而引起N2O排放爆发式增长,0~10 cm土壤硝态氮含量与N2O排放量呈指数函数关系（P〈0.01）。日光温室黄瓜—番茄种植体系内的N2O排放量为0.99~9.92 kg/hm2,其中75.6%~90.0%由施氮造成。与常规氮用量相比,氮减量25%和50%处理的N2O排放量分别降低了40.4%和59.3%,总产量却增加4.9%和7.4%。综上所述,合理减少氮用量不仅可显著降低日光温室土壤N2O排放,而且不会引起产量的降低。该研究为日光温室蔬菜生产构建科学合理的施氮技术及估算中国设施农田温室气体排放量提供参考。

Nitrous oxide（N2O） is one of the most important greenhouse gases contributing to global warming and depletion of the stratospheric ozone layer. Arable land with nitrogen fertilizer application is one of the major sources of N2 O emission, and the nitrogen fertilizer rate in greenhouse vegetable field is higher than that in farmland in China. However, few studies have measured N2 O emissions from solar greenhouse vegetable fields, especially in cucumber-tomato rotation system. In order to identify the annual dynamic of greenhouse soil N2 O emissions and investigate the impacts of nitrogen application rate on N2 O emissions, the closed static chambers method was used in cucumber-tomato rotation system in greenhouse in the Northern Plain of China. The study included four nitrogen treatments, traditional nitrogen rate（cucumber, 1200 kg/hm2; tomato, 900 kg/hm2）, reduced by 25%（cucumber, 900 kg/hm2; tomato, 675 kg/hm2） and 50%（cucumber, 600 kg/hm2; tomato, 450 kg/hm2）, and a control（no N application）. Results showed that temperature was an important factor affecting the N2 O emission intensity in greenhouse. The highest of N2 O fluxes was 818.4 μg/（m^2·h occurred from April to Oct., when the average of air temperature and soil temperature were 27.4℃ and 26.1℃, respectively. While N2 O fluxes was 464.5 μg/（m^2·h occurred from Feb. to March（average air temperature=15.1℃, average soil temperature =15.0℃） and Nov. to Dec.（average air temperature =14.7℃ and average soil temperature=13.7℃）, this was significantly lower than that from April to Oct. Compared to the N2 O flux from April to Oct., there was a 43.2% reduction in N2 O fluxes from Feb. to March and Nov. to Dec. The peak of N2 O emissions occurred in the first five days after topdressing of urea. The N2 O emission occurred most in the first seven days after urea topdressing, which accounted for 64.7%-67.8% of total emissions during the 271 d study period. Soil moisture was not a limiting factor on N2 O fluxes in greenhouse cucumber and tomato fields, because the soil water content was suitable（water filled pore space of 40.0% to 66.6%） and fertilization was usually followed by irrigation in the experiment. N2 O emission increased drastically with an increasing in soil nitrate content after nitrogen application, and there was an exponential relationship between N2 O emission fluxes and 0-10 cm soil nitrate content（P0.01）. Compared to traditional nitrogen rate,N2 O flux peaks reduced by 40.4% and 59.3% when the nitrogen rate was decreased by 25% and 50%, respectively. The cumulative N2 O emissions were 0.99-9.92 kg/hm2 in the cucumber-tomato rotation system, of which 50.5%-56.9% was from cucumber growing season. Taking N2 O emissions from the N0 treatment as the background emissions, the annual N2 O emission factors of nitrogen input were 0.29%-0.43% during the cucumber and tomato growth period, increasing gradually with the nitrogen application rates. About 75.6% to 90.0% of the N2 O emissions were caused by nitrogen application in greenhouse vegetable fields. Less N2 O emissions were produced when less nitrogen fertilizer was used. Compared to the traditional nitrogen rate treatment, cumulative N2 O emissions of minus 25% and 50% nitrogen compared to traditional treatment were reduced by 40.4% and 59.3%. At the same time, the decreased nitrogen rate increased the total yield by 4.8% and 7.4%. In summary, for present solar greenhouse vegetable production in the North China Plain, appropriate reduction of nitrogen application rate can significantly reduce the N2 O emissions without any negative effect on yield. The research provides a reference for nitrogen management for greenhouse vegetable production and fills the information gap for N2 O emission from greenhouse under current management practice in China.