Two-dimensional monitoring of soil water content in fields with plastic mulching using electrical resistivity tomography

Plastic mulching (PM) has become an important agricultural practice to improve crop yields worldwide, while there is still a lack of methods to quantify the complex spatial variations of soil water content (SWC) in the PM field. In this study, a methodology for using Electrical Resistivity Tomography (ERT) to get SWC information in the PM field was presented. Its performance in monitoring SWC was validated, and the spatial variation of SWC was analyzed using the ERT results. A simplified Waxman and Smits model was selected to calibrate the pedo-physical relationship, and it showed good performance (coefficient of determination > 0.92). With the calibrated model, the SWC obtained using ERT showed good agreement with soil moisture sensors in different soil layers (RMSE < 0.027 cm3 cm−3). The ERT results showed that rainfall and drying events have different effects on SWC at different growing stages. At the early stage, rainfall and drying events mainly influenced SWC on the bare strip, while at the later stage, rainfall and drying events had more obvious effects on the zone near the planting hole. On a seasonal scale, a higher SWC was not only found in the middle part of the mulched strip, but also in the bare strip, while a lower SWC was found in positions near the planting hole. At the same time, a high-resolution ERT measurement revealed that the SWC was also largely influenced by the soil heterogeneity. As such, SWC in the mulched strip was not necessarily higher than in the bare strip as we had supposed, but showed a high degree of irregularity in two dimensions. Considering the irregularity of SWC in two dimensions, our study calls for replacing point-scale measurement with two-dimensional monitoring methods when acquiring SWC information in a field with PM.