Assessment of direct carbon dioxide emission factor from urea fertilizer in temperate upland soil during warm and cold cropping season

2017 
Abstract Urea [(NH 2 ) 2 CO] is synthesized by combining ammonia (NH 3 ) and carbon dioxide (CO 2 ). The consumption of atmospheric CO 2 for urea production was considered carbon (C) removal by the Industrial Processes and Product Use sector. Based on this evaluation, the Intergovernmental Panel on Climate Change proposed a default value (0.2 kg C per kg urea) for the CO 2 emission factor from urea, which is equivalent to the mass percent of C in urea. However, all the C in urea might not be discharged to the atmosphere during the cropping season because some bicarbonates can be released from agricultural fields. To estimate the direct CO 2 emission factor, different levels of urea were applied to cultivate red pepper and garlic during the warm and cold seasons, respectively, and CO 2 emission rates were monitored during the cropping seasons. The seasonal CO 2 fluxes increased significantly with increasing urea application levels, reaching maximum values of 268–273 and 233-250 kg N ha −1 for red pepper and garlic, respectively, and clearly decreased thereafter. Calculated by linear regressions between urea application levels and seasonal 13 CO 2 fluxes originating from 13 C-urea, the direct CO 2 emission rates from urea were projected to be 0.062–0.063 and 0.050–0.052 kg C per kg urea for red pepper and garlic cultivation, respectively. Thus, we suggest revising the current IPCC default value (0.2 kg C per kg urea) for the CO 2 emission factor from urea to be approximately 0.06 and 0.05 kg C per kg urea for warm and cold cropping seasons, respectively, in temperate upland soils.
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