黄土高原雨养农业区不同种植模式土壤温室气体排放特征

研究陇中黄土高原旱作农田,设置了苜蓿-苜蓿(L-L)、苜蓿-休闲(L-F)、苜蓿-小麦(L-W)、苜蓿-玉米(L-C)、苜蓿-马铃薯(L-P)和苜蓿-谷子(L-M)6个处理,采用静态箱-气相色谱法和碳通量测量系统LI-8100对苜蓿后茬轮作不同作物土壤温室气体排放动态及其影响因素进行了测定与分析。研究结果表明,农田土壤表现为CO₂源、N₂O源和CH₄吸收汇,且呈现夏秋高,春冬低的季节性变化特征。L-L处理的CO₂累积排放量最高,L-W处理较之降低了42.43%;L-C处理的N₂O累积排放量最高,L-P处理最低;CH₄吸收量以L-M处理最高,较L-F和L-L分别增加了62.71%和31.87%,综合增温潜势表现为L-L>L-M>L-C>L-P>L-F>L-W。相关分析结果表明,CO₂、CH₄、N₂O排放量与脲酶、过氧化氢酶活性及土壤温度呈极显著相关(P<0.01),与土壤水分在不同土层有显著相关性;逐步回归分析发现,土壤温度、过氧化氢酶是CO₂和CH₄排放的主导因素,土壤温度极显著影响气体排放,N₂O排放主要受到环境因子的影响。综合来看,与长期苜蓿连作相比,黄土高原地区苜蓿种植一定年限之后轮作粮食作物能减少土壤温室气体排放量,减弱农田温室气体的增温效应,其中以小麦效果最佳。

Characterization of greenhouse gases emissions from rainfed soils in different cropping systems on the Loess Plateau

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.