| Vegetation restoration is the most effective measures which increase soil organic carboncontent and improve soil structure on the Loess Plateau in China, which are also able to makefull use of the function of the soil-plant compound system to improve the local environment,promote the regional ecological restoration. This article chooses Yan River basin in loesshilly-gully region as study area, in view of the soil aggregate among different vegetation types,including forest vegetation type, grassland vegetation type and forest-steppe vegetation type.Le Bissonnais method and Yoder method is used to analyze the soil classification in this study,and XANES method is also used to qualitative analysis the soil organic carbon functionalgroup. This study revealed the influencing factors of soil organic carbon caused by differenceof vegetation in the course of soil aggregate formation. Through comparing the LB methodthree treatmeats （slow wetting, prewet stirring, fast wetting） and Yoder method, this studycalculates aggregate stability index: aggregate weight percentage which is greater than0.25mm diameter, relative slaking index, average weight diameter, geometric mean diameter,value of erodibility factor （K）, and evaluate the soil aggreg ate stability under differenterosion environment, explore soil aggregate stability under different vegetation types. Thisresearch not only provides new evidence that how to improve soil aggregate structure andraise soil erosion resistance ability during vegetation restoration process, but also provides ascientific basis for vegetation rehabilitation and reconstruction on the loess plateau;evaluation of ecological benefits and soil quality evaluation.（1）The aggregate particle size distribution under three vegetation types like irregular "U"word by dry sieving method, the particle at the size>5mm and <0.25mm aggregate contentare higher than others,0.25-1mm and2-5mm,1-2mm is lower in turn. Forest vegetation andforest-steppe vegetation>0.25mm soil aggregate content of0-10cm soil layer are lower thansoil aggregate content of10-20cm soil layer; But the grassland vegetation of0-10cm soillayer>0.25mm soil aggregate content is slightly larger than10-20cm soil layer.（2） Aggregate content at the size of <0.25mm is highest; the other fraction in the order of particle at the size of>5mm,2-5mm,0.5-1mm, the percentage content of0.25-0.5mm isthe lowest level. The soil aggregate content at the size of>0.25mm in0-10cm layer is higherthan that in10-20cm soil layer; the soil aggregate content at the size of>0.25mm in0-10cmlayer of forest-steppe vegetation was slightly less than that in10-20cm soil layer.（3） The comparison of the three LB treatments showed:1) the WS treatment was themost destructive to the stability of soil aggregates and the soil water-stable aggregate particlesize was mainly concentrated in the <0.2mm size group; this illustrated that heavy rain andrirrigation were the main factors destroying soil aggregates in the Loess hilly region;2) theSW treatment was the least destructive to soil aggregate stability and soil water-stableaggregate particle size was mainly concentrated in the>2mm size group; this shows that lightrain or drip irrigation did not have strong damaging effects on soil aggregates;3) thedestructiveness of FW on soil aggregate structure was intermediate between that of the WSand SW treatments, indicating that the soil water-stable aggregate particle size was evenlydistributed. The experiment shows that the main destructive mechanism of soil aggregatestructure in this region was dissipation and mechanical slaking. Aside from considering theimpact of natural factors, one should use irrigation methods that cause minimal damage to soilaggregates as part of a larger effort to reduce soil erosion.（4） The results also showed that the MWD and GMD of soil water-stable aggregates insoils from the forest vegetation type was highest in0-10cm layer and10-20cm layer, and thatof soils from the steppe vegetation type was lowest, and SW> FW> WS; but the value of theerodibility factor （K） of soils from the forest vegetation type is lower than the value of K fromsoils of the forest-steppe vegetation type, and that of the forest-steppe vegetation type liessomewhere in between. Among three kinds of treatment in the LB method, soil erosionresistance ability after SW treatment is the strongest in the0-10cm and10-20cm layer, theerosion resistance ability after WS treatment was the weakest, FW treatment results betweenthe two.（5） In the same slope, both R0.25and RSI indexes of forest vegetation type in0-10cmlayer and10-20cm layer is higher than that of forest-steppe vegetation type, and steppevegetation type is lowest in the same slope and layer. Under the same conditions, MWD valueand GMD value of forest vegetation type are also higher than that of forest-steppe vegetationtype, and that of steppe vegetation type are lowest; but K value law among three vegetationtypes to the contrary. And under the same vegetation type, K values of shade hillside slopesand shade gully slope are generally smaller than that of sunny hillside slopes and sunny gullyslope; slope of the same vegetation types had a greater influence on the soil erosion resistance.（6）Alkoxycarbonyl and aromatic carbon absorption peak performance in0-10cm soil inforest vegetation is higher than that in forest-steppe vegetation, and that in grasslandvegetation is lower than that in forest-steppe vegetation, organic carbon content of functionalgroups present this law. Similarly, in the10-20cm soil, soil organic carbon functional groupsshowed the same law. Same vegetation type in the0-10cm soil the alkoxy carbon and thearomatic carbon absorption peak is greater than10-20cm of soil, soil organic carbon contentof functional groups can be seen, soil organic carbon accumulation is mainly concentrated inthe0-10cm soil layer. At the same time, the soil aromatic carbon absorption peaks ofsignificantly lower than the alkoxy carbon absorption peak shows the aromatic carbon contentbelow alkoxycarbonyl content. |
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