Characteristics of greenhouse soil N2O emissions in cucumber-tomato rotation system under different nitrogen conditions

Abstract: 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 N2O emission, and the nitrogen fertilizer rate in greenhouse vegetable field is higher than that in farmland in China. However, few studies have measured N2O emissions from solar greenhouse vegetable fields, especially in cucumber-tomato rotation system. In order to identify the annual dynamic of greenhouse soil N2O emissions and investigate the impacts of nitrogen application rate on N2O 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 N2O emission intensity in greenhouse. The highest of N2O fluxes was 818.4 μg/ (m2·h) occurred from April to Oct., when the average of air temperature and soil temperature were 27.4℃ and 26.1℃, respectively. While N2O fluxes was 464.5 μg/(m2·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 N2O flux from April to Oct., there was a 43.2% reduction in N2O fluxes from Feb. to March and Nov. to Dec. The peak of N2O emissions occurred in the first five days after topdressing of urea. The N2O 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 N2O 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. N2O emission increased drastically with an increasing in soil nitrate content after nitrogen application, and there was an exponential relationship between N2O emission fluxes and 0-10 cm soil nitrate content (P<0.01). Compared to traditional nitrogen rate,N2O flux peaks reduced by 40.4% and 59.3% when the nitrogen rate was decreased by 25% and 50%, respectively. The cumulative N2O 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 N2O emissions from the N0 treatment as the background emissions, the annual N2O 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 N2O emissions were caused by nitrogen application in greenhouse vegetable fields. Less N2O emissions were produced when less nitrogen fertilizer was used. Compared to the traditional nitrogen rate treatment, cumulative N2O 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 N2O 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 N2O emission from greenhouse under current management practice in China.