N₂O Emissions From A Vegetable Field With Fertigation Management Under Greenhouse Conditions In Beijing Suburbs

The rotation of fruit vegetables and leafy vegetables is a more typical cropping pattern in China as a big country for production and consumption of vegetable. As higher fertilizer, frequent irrigation and multiple cropping indexes in Greenhouse vegetables fields, lower water and fertilizer use efficiency and more N2 O emissions are caused. Fertigation, an alternative cropping management practice by combining fertilization and irrigation, is being applied in China and abroad to reduce emissions while increase fertilizer use efficiency. But the study of application effect of fertigation on greenhouse vegetable fields is rare in China. So it is necessary to clearly study on N2 O emission from greenhouse vegetable field with fertigation. In this study, a field experiment was conducted at a vegetable field with cucumber and celery planted under greenhouse conditions in the suburbs of Beijing from Mar. 2013 to Dec.2014. At the same time, laboratory culture experiment has been adopted to achieve the emission mechanism. The main conclusions from our study are represented as follows:(1) The field observations indicated that short but sharp N2 O emission peaks occurred after fertilization and irrigation. The farther away from basal fertilization after which N2 O emission peaks lasted for 10-15 days, the lower and shorter N2 O emission peaks lasted ahout 2-3 days. N2 O emission factors of farmers’ practice(FP) treatment in 2013 and 2014, and the farmers’ practice with drip irrigation treatment(FPD) treatment in 2013 during the cucumber growing season were 1.62%, 1.42% and 1.46%. However N2 O emission factors of other treatmens ranged from 0.15% to 0.83%, which were lower than the IPCC default values by 1%.(2) Compared to the farmers’ practice(FP) treatment, the farmers’ practice with drip irrigation treatment(FPD) and optimal fertilization with drip irrigation treatment(OPTD) treatments not only improved water and fertilizer use efficiency, but also reduced N2 O emission. In 2013 and 2014 two rotation cycles, the accumulative N2 O emission of FP treatment was 31.00±2.15kg·N·hm-2 and 26.36±2.43 kg·N·hm-2. FPD and OPTD treatments reduced the cumulative N2 O emissions with 4.16%-30.77% and 42.71%-50.26%, respectively. Meanwhile, water and fertilizer use efficiency increased by 26.33%-76.91% and 33.29%-43.15%.(3) The seasonal variation of N2 O emission was mainly controlled by soil temperature, soil moisture, and Inorganic nitrogen in this study. Throughout the observation period, soil inorganic nitrogen content was consistent with the N2 O emission, and drip irrigation promoted the accumulation of soil nitrogen. During the cucumber growing season, the N2 O fluxes were significantly correlated with the soil water filled pore space(WFPS) for all the treatments(P<0.05). During the celery growing season, the N2 O fluxes were significantly correlated with soil temperature for all the treatments(P<0.05).(4) Incubation experiment could reveal the differences of N2 O emissions for treatments. N2 O emission of was not significantly associated with inorganic nitrogen but was significantly associated with DOC. Under the levels of nitrogen, the N2 O emission of low humidity(WFPS < 60%) was low and short. However, under High humidity(60% < WFPS < 80%), the process of denitrification occurred. And N2 O emission flux was high and long.