Monitoring of soil water content in Haloxylon ammodendron plantation using electrical resistivity tomography

Soil water plays an important role in the plant growth in the arid and semiarid areas, and it is a factor influencing the distribution and quantity of vegetation in arid and semiarid areas. Through long-term and continuous monitoring and assessing soil moisture rapidly and accurately, it can provide guidance for vegetation construction and ecological restoration in the arid and semiarid areas. Haloxylon ammodendron is an endemic tree, and also a main species for sand fixation in Ulan Buh desert. The main aim of the study was to test the usefulness of such geoelectrical method for the assessment of spatial and temporal variability of soil water content in Haloxylon ammodendron plantation. For that purpose, five sample lines were set up in Haloxylon ammodendron plantation, three geoelectrical measurement campaigns were performed in 19 August, 2 September, and 12 October 2016. For each campaign, 5 two-dimensional (2-D) geoelectrical tomographies were carried out in the wenner array using a fixed electrode spacing of 0.5 m. After each campaigns the ERT were followed by soil samplings carried out with auger directly below the respective geoelectrical profiles. Direct measurements of soil electrical conductivity and soil water content were conducted on the soil samples in situ and in the laboratory. The results showed that soil water content was significantly related to soil electrical resistivity data, by the power model y=81.09x-0.65(R2=0.72, P<0.01, n=187). A reliable linear relationship between the calculated and measured soil water content data was found (R2=0.80, P<0.01, ME=-0.54%, RMSE=2.38%, n=190). Five sampling lines of the soil electrical resistivity at three times gradually decreased with the increase of soil depth, while soil water content was the opposite. After the heavy rain event, the spatial distribution pattern of soil water in 2-D profile changed apparently due to rainfall interception by trees, root water uptake and preferential infiltration associated with stem flow. Soil water content was in an increasing tendency after two days of the rain event. As the time continuing, soil water content of soil surface between 0-50 cm showed a significant decrease due to the evaporation and root water uptake. Soil water content of at the depth of 100 cm below the ground had a tendency to increase because of infiltration, indicating that continuous heavy rainfall can effectively supply soil water in the soil surface below one meter. The analysis and monitoring result of the temporal and spatial variation of the soil water content showed that ERT can monitor soil water content quickly and accurately in the field over a long time scale, and moreover, it was not intrusive. It also can provide large-scale and high resolution image of soil water content and water infiltration process. From the analysis and monitoring result of the temporal and spatial variation of the soil water content, we conclude that ERT can be an effective method for monitoring and assessing soil water content and reserves, and thus it allowed us to understand the hydrological processes in sand dune environments. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.