Research On Carbon Sequestration Effect Of Alfalfa Grassland In Different Management Modes

Alfalfa artificial grassland in loess hilly and gully regions of southern ningxia wasstudied in a space series of replaced time courses. With the management mode of mowing inthe earlier years and abandonment in the later years, the variation of vegetation and soilcarbon storage and rate in different restoration years were studied.1、 During2a-30a,the alfalfa was still the dominant of the artificial grassland.Theimportance value of alfalfa decreased from97.33to22.20with the increase of restorationyears.The Margalef, Alatalo and Shannon-Wiener index increased by1.22,1.55and0.40respectively and the simpson index decreased by0.70.2、 With the change of management mode, the organic content, total nitrogencontent and phosphorus content declined first and then rose.The changing trend of soilvolume weight showed in opposite direction.It changed in2a in the trends of all of them.Bothsoil organic content and total nitrogen content reached maximum in the0-10cm layer.3、 Both of the above and under ground biomass of alfalfa rose first and thendiclined and the root biomass increased.with the change of management mode.The biomasscarbon storage in10a showed significantly higher than that in2a and30a.The root carbonstorage of mowing field in10a was above the grassland without artificial thinning at70.3%.4、 Soil organic carbon（SOC） of the0-100cm layer increase with the addition ofrestoration years and it ranged from6.08kg m^-2to12.58kg m^-2. SOC in surface soil （layer0-20cm） fell slightly in early stage （0-2a） and then rose rapidly. In30a, the increase amplitudeturned to be123%and it reached the maxmum.SOC in this layer.Biomass was an importantfactor of soil organic storage and there was a significant correlation between them.5、 The total organic sequestration of artificial grassland increased by0.1kg m^-2inearly stage.The growing rate of it in mowing field reached the maximum66.7%in10a.Thetotal organic storage of grassland without artificial thinning reached only58.3%of mowingfield. The organic sequestration rate of grassland during2a-10a increased from0.05kg m^-2a^-1in early age to0.52kg m^-2a^-1.The average organic sequestration rate decreased but was stillhigher than early stage.There were significantly negative linear correlation between soilvolume weight and total organic sequestration of artificial grassland and R2=0.943.Inaddition,there was significant correlation between the biomass of other species and totalorganic storage.The emerge of other species,succession of community and variation ofcommunity structure had a great influence on total organic sequestration of artificialgrassland.