Abstract: This paper compares the effects of different lucerne planting patterns on the dynamic flux of soil greenhouse gases (CO₂, CH₄ and N₂O) in dry farmlands of the Loess Plateau.Effects of soil temperature, soil water content, and soil enzyme activities on greenhouse gas emissions were studied, using static chamber gas chromatographic techniques to measure CH₄ and N₂O and a LI-8100 measurement system to determine CO₂ flux. The research included 6 treatments: lucerne-lucerne (L-L), lucerne-fallow (L-F), lucerne-wheat (L-W), lucerne-corn (L-C), lucerne-potato (L-P) and lucerne-millet (L-M). The results showed that farmland soil served not only as source of atmospheric CO₂ and N₂O,but also as sink of atmospheric CH₄, with seasonal gas fluxes higher in summer and autumn than in spring and winter. L-L had the highest cumulative emission of CO₂ and L-W had decreased 42% compared with it, while L-C had the highest cumulative emission of N₂O and L-P had the lowest. The CH₄ absorption of L-M was higher by 62.71% and 31.87%, respectively, than L-F and L-L.The calculated global warming potential was L-L>L-M>L-C>L-P>L-F>L-W. Correlation analysis showed there were significant relationships between greenhouse gas fluxes and activities of soil enzymes urease, and catalase, and with soil temperature (P<0.01).Gas fluxes were also correlated with soil water content in some soil layers; stepwise regression analysis found that soil temperature and catalase activities were the dominant factors affecting CO₂ and CH₄ flux. Soil temperature influenced greenhouse gas emission significantly. N₂O flux displayed no significant correlation with biological factors, but was positively correlated with soil temperature and soil water content. In general, planting of other crop species after lucerne cropping reduced intensity of soil greenhouse gas emission, and the overall greenhouse gas emission of the farmland, and the treatment L-W was the most effective.

Key words: lucerne-crop, greenhouse gases, emission flux, urease, catalase