Abstract: Nitrous oxide (NO₂) is a major atmospheric greenhouse gas. The soil physical properties and fertility will directly affect the production and release of NO₂. Alfalfa has the advantages to improve soil physical properties and fertility,and the soil physical and chemical properties variation degree is associated with fixed the number of alfalfa planting years. A static chamber-HPLC method was used to detect NO₂ emission fluxes in the fallow field,3,4,and 10 years-aged lucerne (Medicago sativa) field at the Loess Plateau. In addition,the DeNitrification-DeCoposition (DNDC) model was also applied to estimate the NO₂ emission variations in our study,which fit pretty well with the measured NO₂ emission fluxes. Compared to the fallow field,observed values of the N₂O emission increased with the ages of lucerne field. Interestingly,the detected negative NO₂ emission values in our analysis were disparate with the model calculations. The time of released NO₂ from differently aged lucerne field fluctuated and accumulated highly between 170-240 days during the growing season,the most release was estimated at 210 day in the DNDC model. Although the DNDC model could estimate the NO₂ emission fluxes in lucerne field at the Loess Plateau,further parameter modifications are required to include the negative flux emissions in the analysis.

Key words: nitrous oxide, emission flux, lucerne field, growth years, DNDC model, Loess Plateau