Soil Water Environment Under Plantation And Suitable Setting Of Vegetation Around Taiyuan

Studies concerning soil water environment under plantation have their scientificsignificances to realize causes of soil desiccation and dried soil layers' spatial distribution in aeration zone. Simultaneously, they have their practical significances to realize soil desiccation's affection on groundwater and to prevent new ecological degeneration, to construct ecological environment and develop agriculture and forestry effectively. It is reasonable and dependable to put soil moisture of layers in the middle and deep position as criterions to grow plantation and discover a proper plant density because of the phenomenon that modern loess plateau's soil moisture is controlled by the changed modern climate and the principle that vegetation's setting must correspond with current soil moisture situation. Therefore, our study is practically valuable for ecological construction around Taiyuan, to ensure its environmental or economic benefits and to prevent new ecological degeneration.Based on the theory that soil moisture manifests the relation between global change and regional response, this thesis studies soil water's characteristics under plantation around Taiyuan and takes a further discussion of dried layer's occurrence.The study's field works include drilling soil samples from 0-6ms underground. Based on these samples, we take a method which combines field works and theoretical analysis, as well as qualitative means and quantitative means.After our theoretical analyses and calculation with corresponding models to the samples, we reach some recognitions as the following:1. Seasonal dried soil layers in our research area usually form in fall or spring and winter. Because of a low precipitation and a rough landform around Taiyuan, seasonal dried soil layers may occur in all the four seasons, but may occur in summer with a lower probability.2. It is a common phenomenon that soil under plantation around Taiyuan has a dried soil layer. In the southeast of Shanxi like in Changzhi, located in the semi-humid zone, there exist weak dried soil layers. In the south of Shanxi like Linyi and Ruicheng, located in severe-semi-arid zone, there exist severe dried soil layers. The middle Shanxi and north of Shanxi like Taiyuan, Xinzhou, Yuci, Taigu in loess hilly region or plain, located in the severe-semi-arid zone, there exists severe dried soil layer or weak dried soil layer. The northeast of Shanxi like Shouyang, located in weak-semi-arid zone, there mostly exist weak dried soil layers. The Yanbei region like Datong, located in the severe-semi-arid zone, there exist severe dried soil layer. The west of Shanxi like Lishi, located in weak-semi-arid zone, there exist the severe dried soil layers.3. Made sure the depth of lasting dried soil layer under arbor forests. Most arbor forests or farmlands around Taiyuan have dried soil layers exceeding the depth of 6m, while terrace in slope field have dried layers exceeding the depth of 7m. Dried soil layer's upper bound has a depth of 100cm in medium arid zone (mean precipitation: 395mm) and a depth of 150cm in normal arid zone (mean precipitation: 440mm-490mm).4. Find the deep dried soil layer in farmlands in Taiyuan and surrounding areas. There are weak or medium dried soil layers in corn fields and wheat fields etc. all around Taiyuan. The main cause that makes vegetation prone to suffer drought is seasonal dried soil layer. Weak dried soil layer in corn fields in middle of Shanxi reaches below 6ms. Weak dried soil layer in south Shanxi also reaches 6ms because of lasting drought. 4m depth of corn fields in west Shanxi is close to the weak dried soil layer. Weak dried soil layer in corn fields in north Shanxi also reaches 6ms. The seasonal dried soil layers and depth soil layers have seriously influenced the water cycle of farmland soil. Low precipitation is a main cause of dried soil layers. But attentions should be also paid to the rise of farm productivity and the increase of plant density.5. Using GIS software and indexes of soil moisture and other factors, soil moisture environment of Taiyuan and its surrounding areas will be divided into three different parts: area with abundant soil moisture, area with general soil moisture, area with low soil moisture. Based on extent of soil desiccation, Taiyuan and its surrounding areas will be divided into three different parts: area with slightly dried soil layers, area with medium dried soil layers, area with severely dried soil layers.6. Based on an index portraying dried soil layer of the loss of moisture, we raised a model:Soil moisture lack extent R = (Field capacity W- Soil moisture W_h) / Field capacity W.7. The model of vegetation construction in Taiyuan and surrounding area. Plantation should be restored in a place which is sufficient for water. We should follow the rules of deduction, and mainly resort to natural reconstruction. For instance, we can plant poplar, walnut or trees with similar water rate in a density less than 1111 plant/hm~2 in Changzhi. We can plant poplar in a density of 500-600 plant/hm~2 in valleys or shady slope in Jingle, almond in a density of 600-700 plant/hm~2 in plains of Lanxian. We can plant Chinese pine in a density of 500-600 plant/hm~2 in loess liang and loess mao. We can plant poplar or walnut or Chinese pine in a density less than 900 plant/hm~2 in weak-semi-arid zone. We can plant apple tree or pear tree in a density of 700-800 plant/hm~2, or phoenix tree in a density of 500-600 plant/hm~2, or bark pine or cypress in a density of 600-700 plant/hm~2, or Chinese jujube in a density less than 1000 plant/hm~2, or poplar in a density less than 1000 plant/hm~2 in plains of Taiyuan. We can plant poplar in a density less than 600 plant/hm~2 in valleys or shady slope in Yangqu.