A field test to investigate spatiotemporal distribution of soil moisture under different cropland covers in the semiarid Loess Plateau of China

In order to simultaneously describe the spatial and temporal variations of soil moisture and the influence of land cover conditions in the semiarid Loess Plateau in Northwestern China, a field test was performed. In this study, four cover conditions were considered, including bare soil without any cover, non-vegetated soil with plastic mulch (PM), potato field with PM and maize field with PM. The actively heated fiber optics (AHFO) method was used to capture spatial soil moisture distribution, and the frequency domain reflectometry (FDR) sensor with a temporal spatial resolution of 3 min was used to record temporal moisture variation. The experimental results indicate that if the soil moisture remains constant and the cumulative precipitation slowly increases, the in-situ apparent effective soil hydraulic conductivity can be inferred from the precipitation rate. The in-situ measured apparent effective soil hydraulic conductivity has been found to be 7.09 × 10 –7 m/s in this study. The estimated evapotranspiration rate was 5.68 mm/d as inferred from linear reduction rate of soil moisture after a rainfall, which agreed well with the reported average value in semiarid regions. The PM can effectively prevent water loss due to field evapotranspiration and result in aggravation of spatially uneven distribution of subsurface soil moisture under the same cover condition and depth. The growth of plant roots facilitates water holding capacity and evapotranspiration rate of soil and reduces its temporal stability.