| This paper take the dry farmlands of Loess Plateau as research object,comparing the effects of different lucerne-crop rotation paterns and alfalfa grassland under different growth years on dynamic variations of soil greenhouse gases emissions and effects of soil temperature ? soil water content ? soil enzyme activities on greenhouse gases,static chamber-gas chromatographic techniques and carbon flux measure system LI-8100(LI-COR,USA)were used to continuously measure and analyze the greenhouse gases fluxes,the 6 treatments included 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 different cultivating ages of lucerne respectively are 5 years,12 years and 14 years.Through the study of CO2?CH4 and N2 O emission dynamic variations and mechanism for lucerne-crop rotation systems and alfalfa grassland soil under different years of growth on Loess Plateau rainfed agricultural area,to reveal the relationship between soil greenhouse gas emission fluxes and the environmental and biological factors,in order to provide scientific basis and effective theory reference for lucerne land rational utilization on western Loess Plateau and productivity sustainable development on rainfed agricultural area.The research main conclusions are as follows:(1)The farmland soil served not only as source of atmospheric CO2?N2O,but also as sink of atmospheric CH4,and have the seasonal variation characteristics of summer and autumn are higher than spring and winter.L-L has the highest cumulative emission of CO2,L-W has decreased by 42.43%,CO2 accumulative emission under different treatments were L-L>L-M>L-P>L-C>L-W>L-F;Compared with L-F and L-L,the CH4 accumulative absorption of L-M increased by 62.37% and 31.68%,which is the highest,CH4 accumulative absorption under different treatments were L-M>L-W>L-P>L-C>L-L>L-F;L-C has the highest cumulative emission of N2 O and L-P is the lowest,N2 O cumulative emission under different treatments were L-C>L-M>L-F>L-L>L-W>L-P.(2)From the view of diurnal dynamics,the curves of day change of soil CO2 flux have a single-peak value,and it is high in the day and low in the night,the maximal emission flux appeared at 12:00-14:00,and the minimum emission appeared at 2:00.The soil CH4 was mainly manifested as absorption,the curve of diurnal variation of CH4 showed two single peak,the emission flux was highest at 14:00 and 20:00,and L-P?L-C?L-M were the emission sources;Within one day,N2 O flux reached the emission peak at about 16:00,reaching the lowest emission peak at 4:00 am,and the L-L was the absorption.(3)The CO2 cumulative emissions of alfalfa under different planting years were5a>14a>12a;With the growth of alfalfa,the cumulative absorption of CH4 was decreased,and5 a alfalfa has the highest absorption,14 a alfalfa was the lowest.The N2 O emission was the single peak,reaching the peak emission in July,and the cumulative emission were14a>12a>5a.(4)Stepstep regression analysis showed that in the rotation systems,the soil temperature and catalase were the dominant factors affecting CO2 and CH4 emissions,and N2 O was mainly affected by environmental factors;In the alfalfa field with different growth,CO2 flux is mainly restricted by soil temperature and water content,CH4 flux affected by environmental and biological factors,which of the soil temperature and urease influenced dominatly,while soil temperature has the most significan influence on N2 O flux.(5)In the rotation systems,the calculated global warming potential under different treatments were L-L>L-M>L-C>L-P>L-F>L-W,it showed continuous cropping alfalfa has obvious greenhouse effect,lucerne-crop rotation after planting a certain yeas of alfalfa can reduced soil greenhouse gases emission,which of the L-W is the best;In alfalfa grassland under different growth years,the calculated global warming potential were 5a>14a>12a,therefore,alfalfa planting a number of years should be ploughed in time to reduce the greenhouse effect and alleviate the climate warming. |
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