Performance of an Electromagnetic Sensor for Field Monitoring of Volumetric Water Content in Water-Absorbing Polymer Amended Soil

Water-absorbing polymer (WAP) is gaining a lot of attention because of its potential applications in agriculture, green infrastructure, and ecological restoration of arid lands. Because of its higher water absorbency (more than 100 times its weight), the application of WAP can increase water retention characteristic (WRC) of soil. Accurate measurement of volumetric water content (VWC) of the polymer amended soil is essential to measure the WRC of soil and appraise those observations. The utilization of electromagnetic (EM) sensor (such as ECH2O 5TM) for the determination of VWC is common practice in different geo-environmental projects. The accuracy of this sensor for the measurement of VWC in WAP amended soil needs to be ascertained before deploying it in the field. The objective of this present study is to evaluate the performance of the EM sensor for the measurement of VWC in WAP amended soil. For this purpose, an experimental methodology has been proposed under controlled laboratory conditions using a cohesionless soil with four different concentrations (0, 0.1%, 0.2%, and 0.4% on w/w basis) of WAP. The accuracy of the EM sensor is found to be very good in the case of bare soil. However, with the increasing concentration of WAP, the error in the VWC measurement also increases. Two different approaches, including polynomial calibration and linear calibration, were proposed to calibrate the EM sensor for accurate measurement of VWC in WAP amended soils. The results indicate the significance of material-specific calibration of the EM sensor for improving the measurement accuracy.