Abstract: In order to clarify factors affecting soil N₂O fluxes in artificial alfalfa grasslands in the semiarid region of China, the N₂O fluxes from soil and soil-vegetation system of artificial alfalfa in different planting years (1, 3, 4, 5, and 8 years old) were measured by using Static box-Gas Chromatography. The results showed that the N₂O fluxes from the soil and soil-vegetation system of artificial alfalfa were affected by planting years, and the N₂O fluxes of artificial alfalfa were in order of 4 years >5 years >3 years >8 years >1 year. The N₂O fluxes from the soil and the soil-vegetation system exhibited a seasonal variation of higher in spring and summer and lower in autumn, with highest values in midMay and midAugust, and being a source of N₂O. The N₂O fluxes from the soil-vegetation system were higher than that from the soil in different planting years. N₂O fluxes from the soil had significant positive correlations with the soil organic carbon, total nitrogen, C∶N ratio, ammonium nitrogen, nitrate nitrogen, soil temperature of soil layer (0-5 cm), and had a significant quadratic negative correlation with soil water content (0-10 cm). N₂O fluxes from the soil-vegetation system had a significant positive relationship with aboveground biomass. Soil total nitrogen, nitrate nitrogen, 0-10 cm soil water content and aboveground biomass were considered as the critical factors controlling N₂O fluxes of artificial alfalfa.

Key words: temperature, CO₂, diurnal variation of photosynthesis, photosynthetic pigment, rice