| As the typical ecological transition zone and environmental fragile area of semi-humid and semi-arid region, Northwestern Shanxi Loess Hilly Area was drought, in which natural rainfall was the only source of soil moisture and one of the major limiting factors of vegetation construction. Therefore, it was of great significance to carry out a study on soil moisture for vegetation restoration in this area. This paper took Zhang Jiaping forest land of Wuzhai County in the Loess Hilly Region of northwestern Shanxi Province as the test area, and was mainly about the soil moisture’s dynamic monitoring of the three different-aged Caragana forests and the uncultivated land by using the method of field tests as well as laboratory analysis within the growing season (April to October) in 2013. Quantitative study was applied in the analysis of the soil hydro-physical properties of 0-100cm soil profiles in different-aged Caragana forests, the regularity of seasonal dynamic changes and annual changes of soil moisture of 0-600cm soil profiles within the growing season, and the vertical variation of soil profile moisture and soil moisture availability. Meanwhile, this paper, combining the precipitation and soil moisture variation of the vertical profile, analyzed the desiccated intensity of different-aged Caragana forests, and the desiccated layer thickness of the soil and water restoration status. By analyzing, the main findings were as follows:1. The soil hydro-physical properties in different-aged Caragana forests showed some regularity. Compared with the uncultivated land, the soil bulk density, porosity (capillary porosity, non-capillary porosity total porosity) and the aeration of 0-100cm soil profiles had been greatly improved, and the capacity of the soil ventilation and permeability was significantly improved for the work of mineralization and decomposition of litter and roots action in research area. The difference of forests’soil bulk density, capillary porosity, non-capillary porosity and moisture capacity between Caragana forests was significant with different ages (p<0.05), but no significant difference in change with soil depth. However, the changing difference of total soil porosity, soil saturated water and capillary water with different ages was not significant, which was changing with soil depth.2. The soil moisture of different-aged Caragana forests had a significant temporal variation and vertical distribution. The dynamic change of soil moisture content and seasonal variations of rainfall was consistent within the growing season in different-aged Caragana forests and the uncultivated land. The overall performance of the soil moisture in different sample plots was that 10a Caragana> 20a Caragana> the uncultivated land> 35a Caragana. But the annual changes were quite different. The soil moisture differences between months were significant except for the 35a Caragana. The dynamic change of soil moisture content within the growing season was broadly divided into following situations:soil moisture was greatly reduced in the early growing season (April-May); soil moisture was significantly increased in the interim growing season, and in mid-August reached the maximum; September was a downward trend; soil moisture increased rapidly in the end of the growing season (October), reaching the maximum or the second largest value of the growing season.In 0-300cm soil depth, the soil moisture decreased as the increasing soil depth, while in 300-600cm soil depth, the soil moisture increased with soil depth. Both of them had taken the 200-300cm soil depth as the critical lows. Due to the different forest ages, the uses of soil moisture changed with the soil depth and presented different vertical distribution. All sample plots didn’t exist highly efficient water layer, and there was no difficult effect-invalid water layer except for the 35a Caragana, which had a 3.4% difficult effect-invalid water layer near 300cm depth. With the increasing age, the effective average relative humidity of soil moisture in Caragana forests was decreasing. The thickness of easy efficiency aquifer decreased, but the thickness of mid-efficiency aquifer increased.3. The overall change of water storage in different-aged Caragana forests was that 20a Caragana>10a Caragana>35a Caragana>the uncultivated land. Except for some soil water storages of soil profile had a small deficit, the rest showed a surplus. The average soil desiccation index SDI values were between 55%-92% in 0-600cm soil profiles. Soil desiccation level reached mild to moderate desiccation intensity. The average thickness of desiccated soil layer was 447cm. The density of dry soil and the depth of drying were gradually increasing with the growth of forest age and the depth of drying increases with the forest age. The soil moisture of desiccated soil layer in continuous wet years and years of continuous flat water could be restored of itself to a state of stable soil humidity by rainfall replenishing, but in the case of consecutive years, it needed at least 4a, and even more 20a. Considering all precipitation years, the year needed for water restoration of desiccated soil layers in all sorts of ground increased with the forest ages, and the difficulty of soil moisture restoring gradually showed an increasing trend. |
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