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Field Calibration of a Time Domain Reflectometry Sensor with an Extension Pipe for Soil Water Content Measurement

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2022 ASABE Annual International Meeting  2201013.(doi:10.13031/aim.202201013)
Authors:   Rehnuma Mobin Maisha, Dean D. Steele
Keywords:   Irrigation, Sensor calibration, Soil moisture sensor, Soil water content, TDR, Water management


Application of proper irrigation scheduling and utilization of efficient agricultural technologies such as variable rate irrigation can improve irrigation efficiency. The Time Domain Reflectometry (TDR) soil moisture sensor measures the soil moisture content remotely with the help of dataloggers and telemetry systems. This study was conducted to calibrate the Acclima TDR-310H soil moisture sensor and develop a site-specific calibration equation. The target depths were 15 and 45 cm at three field sites with five stations each for a total of fifteen stations. These field sites in southeastern North Dakota, US, had sand, loamy sand, clay loam, sandy clay loam, and sandy loam soils. Soil samples were first tested by the TDR sensor and then soil cores were collected in the same TDR sensor volume. Gravimetric water content (θg), bulk density, and volumetric water content (θv) were determined in the lab. The TDR sensor results were compiled by pairing the sampled soil property measurements (θv-Sample) with the collected sensor data (θv-TDR). The sensor underestimated θv and a calibration equation of θv-Sample= 0.9498 θv-TDR + 3.5683 with R2 = 0.8984 was produced. A t test was performed on the calibration equation to identify the accuracy. The results showed that the 95% confidence interval for slope was 0.82 < b < 1.08 and for intercept was 0.72 < a < 6.42. This paper will present additional information on the calibration process, statistical analyses and use of the Acclima TDR-310H sensor as a standard of comparison with other sensors.

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