The Dynamic Characteristics Of Soil Carbon、nitrogen、phosphorus Under Typical Artificial Vegetations In Loess Gully Region

This study took Robinia、Caragana microphylla、abandonment stand in loess Gullyregion as objects, discussed the dynamics of soil fertility and organic carbon under differentartificial vegetations by using soil samples taken and experimental analysis in Ansai country.The main research items were total nitrogen, total phosphorus, available nitrogen, availablephosphorus, organic carbon and labile organic carbon content. The main conclusions showedas follows:(1) Total nitrogen、total phosphorus、available phosphorus、available nitrogen contentunder typical artificial vegetations was decreased with soil depth increased, which was moreobvious for Robinia. The total nitrogen、total phosphorus、 available phosphorus、available nitrogen content presented a trend of Robinia>Caragana microphylla>abandonment;Consequently, typical artificial vegetations showed the potential of promoting soil nitrogen、phosphorus pools. And Robinia respectively improved contents and the quality of soilfertility.(2) After13years of returning farmland, the contents of total organic carbon and threelabile organic carbon of artificial vegetations were improved mainly in0～40cm soil layercompared with the farmland. In0～100cm soil layer, the contents of soil organic carbon andthree labile organic carbon decreased with the increase of soil depth, and showed the order ofRobinia> Caragana microphylla>abandonment>farmland in soil profile. Within the samedepth, three labile organic carbon contents and their efficiency ratios followed the order oflowly labile organic carbon(0.67～2.02g·kg-1;0.47%～33.00%)>mid-labile organiccarbon(0.12～1.38g·kg-1;6.44%～22.52%)>highly labile organic carbon(0.12～1.38g·kg-1;6.44%～22.52%). the CMI of highly labile organic carbon of forest lands was increasedmainly in0～100cm soil layer compared with the farmland, and the increasing rate presenteda trend of Robinia(213.9%)>Caragana microphylla(152.4%)>abandonment(82.6%). And theCMI of lowly and mid-labile organic carbon were evidently higher in0～100cm soil layer inRobinia、Caragana microphylla than that in farmland. Consequently, artificial vegetationsshowed the potential of promoting soil labile carbon pools. And Robinia respectivelyimproved contents and the quality of labile organic carbon in soil. (3)In general, the contents of total organic carbon and labile organic carbon in0～100cmsoil layer under different artificial vegetations increased significantly withthe increasing of growing years. soil total organic carbon and labile organic carbon in0～40cm soil layer were began to increase after10years of farmlands being converted to forestlands,years, while in40～100cm soil layer it began to increase after20years of farmlandsbeing converted to forestlands. Among the carbon indices, LOC/TOC and did not change withthe increasing carbon pool content during long-term conversion under different artificialvegetations, just reflecting the active content of soil carbon pool. In contrast, CMI showedidentical trends with total organic carbon and labile organic carbon, and showed higherincreases in0～40cm soil layer and lower increases in40～100cm soil layer. between CMIand content of soil carbon pool a positive linear correlation was confirmed. in addition, after40years of farmland being planted to forestlands, CMI among different forestlands showedan order: Robinia> Caragana microphylla>abandonment,which was the same sequences ofsoil total organic carbon and labile organic carbon in the different artificial vegetations soil.Thus, CMI could be a better indicator for the changes in soil organic carbon pool underdifferent artificial vegetations.(4)Total nitrogen was positively related to soil available nitrogen, and total nitrogen wasrelated to soil total phosphorus, and total phosphorus was positively related to soil availablenitrogen. The statistical analysis indicated that the labile organic carbons were related withsoil fertility at significant or very significant level, showing that labile organic carbon contentcould be used to reveal the influence of artificial vegetations on soil organic carbon andcarbon management index in Ansai area.