The effect of mineral fertilizer (F) and mineral combined with organic fertilizer (MF) on N 2O flux in grassland and cornfield was investigated for one year in Southern Hokkaido, Japan. Annual N 2O flux was higher in grassland than in cornfield, and it was higher in MF plot (14.9 kg N/ha/period) than in F plot (11.1 kg N/ha/period) in grassland. However, in cornfield, the annual N 2O flux was equal between both plots (5.6 kg N/ha/period). These results clarified that high nitrogen application was not always responsible for the high soil N 2O flux. N 2O flux was significantly correlated with air, soil temperature and water-filled pore space. More than 80% of the annual N 2O flux occurred before freezing and less than 4% during melting period. Denitrification was the main process of N 2O flux during study, it was evidenced by the distribution of N 2O and NO ratio which is from 1 to 1000. The denitrification activity (DEA) potentially increased in grassland soil in the beginning and the end of winter season when NO 3-N was abundant; on the other hand the abundance of carbon potentially increased DEA in cornfield soil.
