Source partitioning and emission factor of nitrous oxide during warm and cold cropping seasons from an upland soil in South Korea.

Nitrous oxide (NO) is a major greenhouse gas (GHG) with high global warming potential. A majority of the NO flux comes from agricultural sources, mainly due to nitrogen (N) fertilization. The soil NO flux, induced by N fertilization, mainly originated from two different sources, i.e., fertilizer and soil organic nitrogen (SON). It is essential to know the individual contribution of these two different sources in total NO flux for planning necessary mitigation strategies. It is also indispensable to know the seasonal difference of emission factors (EF) for having more accurate NO inventory. Therefore, an experiment was conducted in a South Korean upland soil during summer and winter seasons using N labeled urea as an artificial N source and source specific NO emissions were distinguished under different environmental conditions. To characterize the NO emissions from urea, 0, 50, 100 and 200% of the Korean N recommendation rate was selected for specified crops. The Korean N recommendation rate for red pepper (Capsicum annuum) and garlic (Allium sativum) was 190 and 250 kg N ha, respectively. Direct emissions from urea were estimated from the difference of NO flux emitted from N-urea treated soil and the natural abundance of NO. From total NO fluxes, urea originated NO flux was 0.87% and 0.13% of the applied N in warm and cold seasons, respectively and the rest comes from SON. Nitrous oxide EF in the warm season was 2.69% of applied N and in the cold season that was 0.25%. Nitrous oxide fluxes showed a significant exponential relationship with soil temperature. The results show the necessity of considering the different NO EF for warm and cold cropping seasons to reduce uncertainty in NO inventory. The findings of this research may help better understand NO source partitioning and the emission budget from warm and cold cropping seasons.