Effects Of Different Land Use Types On Deep Soil Water Content And Carbon Distributionin The Loess Plateau Of Northern Shaanxi Province,China

The Loess Plateau of the arid and semi-arid area located in the northwest of China,wherein soil water content is the main limiting factor for plant growth owing to arid climate,scarce rainfull and buried deed groundwater.Since the implementation of the project of returning farmland to forest and grass,the land use type has tremendous changes,Which has great influence on soil moisture and soil carbon distribution in the Loess Plateau,and soil carbon storage is great significance for global climate change and carbon cycle in the Chinese Loess Plateau region.There is a lot of research on the distribution and storage of soil moisture and t soil organic carbon in the different land use types.However,most studies on soil moisture and soil carbon are mainly in 0-5 m and 0-3 m soil profiles,while less studies are made on soil inorganic carbon and deep soil moisture and soil carbon distribution and storage.In this paper,we select the representative land use mode of the economical plantation in Mizhi,reforestation area in Shenmu and wind break and sand fixation forest distract of Yuyangin Yulin of Yulin in northern Shaanxi.To study soil moisture and soil carbon distribution and Soil water consumption depth in 0~20 m profiles under different land use types.To explore different land use type on soil moisture and soil carbon distribution and eco-environment in deep soil profile in loess hilly region of northern Shaanxi province.The main findings are as follows:(1)The results show that in the soil profile of 0-20 m,land use patterns had a significant impact on soil moisture distribution.There were significant differences of soil water storage for the economical plantation,pruning Ziziphus jujuba plantation > Z.jujuba plantation with 587.9 mm difference There was no significance of soil water storage between Caragana korshinskii plantation and degraded artificial vegetation or between pine forests and natural grass field,degraded artificial grassland > C.korshinskii plantation with 98.8 mm differences at Shenmu,,and natural grassland> Pinus sylvestris plantation with 7.5 mm difference at Yuyang district,.The pruning Z.jujuba tree reduced soil water consumption and was beneficial to sustainable use of soil water content due to the decreased crown width and thus reduced transpiration.There were no obvious differences of soil water content between C.korshinskii plantation and degraded artificial grassland due to the historical alfalfa planting which characterized by high water consumption due to its deep root distribution and large biomass.In contrast,Pinus sylvestris plantation and natural grassland had similar and low averaged soil water content with 3.4% and 3.6%,respectively,mainly due to the sandy soil texture and weak soil water holding capacity.In addition,with increasing soil depth,soil water content increased in this area,indicating that it was very limited for plant water uptake into deep soil.Except for the underlying control of soil texture to soil water content in the soil profile,different vegetation played a key role in the dynamics of soil water content due to the difference of root zones.It was very important to choose the right type of vegetation in different regions of the Loess Plateau regarding the sustainable use of deep soil moisture.(2)The results showed that: there are no significant differences in the distribution of pH and EC on soil profile and the distribution ranges are 8.14-9.78 for pH and 46.3-763 ?S/cm for EC,respectively;the order of SOC is: pruning jujube tree(2.00 g/kg)> jujube tree(1.54 g/kg)>Caragana(0.97 g/kg)>degraded artificial grassland(0.81 g/kg)>Pine forests(0.70 g/kg)>natural grass field(0.45 g/kg),indicating the significantly different for SOC between land use types(P <0.05).And the order of SIC is: pruning Ziziphus jujuba tree(11.66 g / kg)>= Ziziphus jujuba tree(11.59 g/kg)> Caragana korshinskii(9.62 g/kg)>degraded artificial grassland(8.07 g/kg)> Pinus sylvestris forests(4.32 g/kg)>natural grass field(0.47 g/kg).Although there are no significant differences of SIC under the economical plantation of Mizhi and the reforestation area of Shenmu between soil profile,it is significant difference of SIC between the economical plantation and the windbreak and sand-fixation forest plot(P <0.05);There are significant differences in soil carbon density among the three areas.The SIC density for pruning Ziziphus jujuba tree,Ziziphus jujuba tree,Caragana korshinskii,degraded artificial grassland,Pinus sylvestris forest and natural grass field is 6.19,7.71,10.70,10.78,5.91 and 1.03 times of its corresponding SOC density,respectively.In summary,there are obvious differences in soil carbon between different land use patterns,and also the content of SIC in soil profile is much larger than that in SOC.(3)There are some differences in the content of chloride in the soil profile under different land use patterns.This is mainly due to the interference of human factors,and the difference in the chloride profile in the active layer of soil water consumption is due to the consumption of vegetation chloride accumulation caused by the difference.There were some differences in soil water use active layer under different land use conditions,and the thickness of active layer of soil water consumption was obviously different.The land use of soil water active layer was the highest.The active depth was 13.0 m.