Study On Soil Nutrition Variation Characteristics Under Different Artificial Vegetation In The Loess Plateau

Selected different types of restored vegetations which are located in Ansai countyexecuted by the Grain-to-Green programme, we analyzed soil chemical property，soil carbonfractions and stoichiometry under different types of restoration vegetations in Zhifanggouwatershed,Ansai county,which is belonging to hilly-gully region of Loess Plateaou.Theresults revealed the relationship between the variation of soil properties and vegetationsrestoration, which can be utilized to provide provide the basis of how to assess the restorationvegetation model in the region of converting farmland into forest in the Loess Plateau.Themain conclusions are as follows:(1) in the aspect of accumulation of soil nutrient, the trends of variation of soil nutrientwere basically the same,however content under different types of vegetations weredistinct.Content of soil total nitrogen,total phosphorus,available phosphorus,availablepotassium were significantly different which was resulted from different types ofvegetations.Soil nutrient was declined with soil depth,but the situation was trending towardsstability in deep soil layers.The restoration vegetations with long years is better than that forshort years among different types of restoration vegetation.The effect of arbor inaccumulating soil fertilizer is better than Shrub, the same effect of shrub is better than theverbiage.Locust indicated better improvement of the soil nutrient in several different types ofvegetation recovery model.Caragana appears the constant trend in terms of improvement ofsoil nutrient.However, content of soil nutrient differs from different types of vegetations.(2) soil organic carbon of soil sand particles is declined with soil depth under differentartificial vegetations. This tendency was the same as the soil organic in soil profilesvertically.Soil sand particles organic carbon of locust in different growth years is highestamong different types of vegetations.Soil sand particular organic carbon of sloping land isminimum, due to the soil structure is destroyed by tillage and mineralization decomposition ofsoil sand particulate organic carbon is accelerated. Soil clay dispersion organic carbon content in soil shallow layer was greater than in the soil depth layer, and was consistent with thedistribution of sand organic carbon and total organic.Clay dispersion organic carbon contentof Locust caragana、waste grassland was relatively higher than other vegetation in0～40cmsoil shallow layer.Different types of artificial restoration vegetation increased total organiccarbon and active organic carbon content significantly in0～200cm soil layers,the order ofincrease amplitude was Caragana40> Locust40> Locust30> Locust20> Mixed forest>Caragana20> waste grassland> orchard,which demonstrated that the artificial vegetation hadeffect of increasing soil carbon poll.In terms of content of soil organic carbon on the entiresoil profiles, artifical vegetation made the soil organic carbon increased mainly in0～40cmshallow layers, the effect of Locust40a was the better, orchard and waste grassland was thelowest.However,total organic carbon and active organica carbon were raised significantlyamony30a～40a in40～200cm soil layers,which revealed that the effection of soil carbonpoll in soil deep layers in hilly region of loess Plateau required years of growth. In the samesoil layer, the differences content between organic carbon and active organic carbon result inthe different active organic carbon and organic carbon ratio.The ratio was declined with soildepth under different types of artificial vegetations.In0～10cm soil layers, active organiccarbon ratio order was Locust40> Caragana40> Mixed forest> Locust30> Locust20>Caragana20> Waste grassland> Orchard> Slope farmland.(3) The carbon storage was declined with soil depth for different artificial vegetation.Carbon storage in shallow soil layer (0~10cm）was significantly higher than deep soil layer. In0~10cm soil layer, Locust40（12.87Mg/hm2）> Locust30（7.86Mg/hm2）> Locust20（7.96Mg/hm2）> Mixed fores（t10.55Mg/hm2）> Caragana40（7.48Mg/hm2）> Caragana30（5.12Mg/hm2）> Waste grassland（3.95Mg/hm2）> Orchard（3.71Mg/hm2）> Slope farmland（3.34Mg/hm2），in deep soil layer（100~200cm）,carbon storage accounted for largerproportion of total reserves, Locust40（35%），Locust30（44%），Locust Locust20（40%），Mixed forest（29%），Caragana40（44%），Caragana30（42%），Waste grassland（45%），Orchard（43%），Slope farmland（48%）.Overall, Locust and Caragana in different soil layerscould increase carbon storage with growth years.For soil nitrogen storage, the distribution of nitrogen storage in soil layers was basicallysimilar to carbon storage. Distribution of nitrogen storage was declined with soil depth indifferent artificial vegetation. The theory of nitrogen storage in shallow soil layers was notclear. Similarly, in deep soil layer（100~200cm）, nitrogen storage accounted for largerproportion of total reserves, Locust40（39%），Locust30（43%），Locust20（26%），Caragana40（43%），Caragana30（45%），Mixed forest（44%），Orchard（40%），Slope farmland（42%），Waste grassland（49%）。 (4)The study of stoichiometry shown that the C:N ratio, C∶ P,ratio, N∶ P ratio wasdeclined with the soil depth, C∶N ratio was between0.66-16.58, C∶P,ratio wasbetween0.4-18.2, N∶P ratio was between0.02-3.8. Soil C∶N ratio was relatively loweramong different types of vegetations, which indicated the relatively faster organic carbonmineralizition. The lower N∶P ratio of Loucst implied that the nitrogen was the mainlimiting factor of Locust growth.