Laboratory Calibration of Capacitance-Based Soil Moisture Sensor to Monitor Subsurface Soil Moisture Movement in Laterite Soil

Abstract

Subsurface soil moisture movement in the unsaturated zone plays a critical role in the replenishment of groundwater table. This comprehension can be vital for the terrain with lateritic soil followed by the charnockite bedrock system. The conventional techniques to determine the subsurface soil moisture and its movement is cumbersome owing to high cost, large scale time consumption, field drudgery and greater possibility of manual errors. Among many other modern technologies for the measurement of volumetric water content, capacitance-based moisture sensors are capable and less expensive, thus, making them highly suitable for the research scholars worldwide. The study involves the use of TEROS 12 moisture sensors. The capacitance-based sensor TEROS 12, equipped with advanced soil moisture technique curtails the constraints in the conventional technique of soil moisture assessment and can provide precise measurements if suitably calibrated for the site specific soils. The study involves a soil specific calibration of TEROS 12 moisture sensor which was performed for the laterite soil to incorporate the sensor with the automated soil moisture monitoring system. The reliability of the sensor TEROS 12 was assessed by comparing its moisture measurements with that of the gravimetric method. The calibration was performed for three TEROS 12 moisture sensors in order to monitor the interflow at three varying soil depths in the vadose zone. The R2 values obtained from the calibration of sensors at depths of 0-0.4 m, and 0.8-1.2 m were 0.996, 0.994 and 0.992 respectively. Further, during validation it was found that the new measurements coordinated with the gravimetric measurements to a greater extent and increased the preciseness as compared to that of uncalibrated values of moisture contents, thereby establishing TEROS 12 capacitance-based sensor as a reliable and cost effective moisture sensor.