Nitrous oxide fluxes from soil under different crops and fertilizer management

Abstract

The effect of mineral fertilizer (F) and mineral combined with organic fertilizer (MF) on N2O flux in grassland and cornfield was investigated for one year in Southern Hokkaido, Japan. Annual N2O 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 N2O 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 N2O flux. N2O flux was significantly correlated with air, soil temperature and water-filled pore space. More than 80% of the annual N2O flux occurred before freezing and less than 4% during melting period. Denitrification was the main process of N2O flux during study, it was evidenced by the distribution of N2O 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 NO3-N was abun­dant; on the other hand the abundance of carbon potentially increased DEA in cornfield soil.