Study on soil moisture variation characteristics of different economic forest lands in karst gorge area：A case study of Huajiang demonstration area in Guizhou Province

The study area is located in the Guanling-Zhenfeng Huajiang demonstration area in the southwestern Guizhou Province. The total area of the study area is 51.62 km2, with the karst area of 45.39 km2, and the altitude is 500-1，200 m. It is a typical karst plateau gorge area in Guizhou with exposed and broken surface and undulating terrain. Hylocereus undulatus Britt, Zanthoxylum bungeanum and Lonicera japonica Thunb are typical economic plants in this area. In this study, this three economic forest lands were selected as the sampling plots to conduct a long-term monitoring on soil moisture and rainfall and to reveal the dynamic characteristics of the soil moisture and the influence of different economic plants on the dynamics of soil moistures along soil profile. This research is also to provide scientific basis for vegetation restoration and sustainable development of the ecological environment in karst rocky desertification area. Three observation points are equidistantly arranged in each plot with three probes installed in an observation point. A soil moisture sensor (EM 50, Meter Corporation, USA) was used to continuously monitor the volumetric soil water content. At each observation point, the probes were installed at the depth of 10 cm, 25 cm and 40 cm to the soil surface, respectively, which monitored the soil water content 24 hours a day and the monitoring was conducted in five month time from May to September, 2018. During the monitoring process, the soil moisture content was recorded at a 10-minute interval. In the meantime, the rainfall data is monitored by a small meteorological observatory (ATMOS, Meter Corporation, USA). Based on the monitoring data, the coefficient of variation of soil water storage and soil water content were calculated.SPSS 20.0 was used for statistical analysis of the data, and Origin 8.5 was used for mapping. The result showed that the variation of soil water storage in the three economic forest lands was consistent with rainfall in both quantity and time. The soil water content reached a maximum value in August and its fluctuation slightly lagged behind the precipitation. During the observation period, the soil water contents in the 40 cm deep soil layer showed a difference in the three types of land, which were Hylocereus undulatus Britt field (478.97 mm)> Lonicera japonica Thunb field (372.64 mm)> Zanthoxylum bungeanum field (322.15 mm) , respectively, with the water contents of 35.97%, 27.36%, and 23.55%. In a conclusion, the Hylocereus undulatus Britt field has the best water holding effect, followed by Lonicera japonica Thunb field, and Zanthoxylum bungeanum field, which plays an important role in improving the water and soil conservation function of the area. Therefore, in the process of rocky desertification control in Huajiang karst plateau gorge of Guizhou Province, Hylocereus undulatus Britt will be helpful to be planted in an appropriate amount to achieve the effect of ecological restoration and promote the development of local industries.