Abstract:Using undisturbed soil samples with different soil textures, the mass volume moisture content is measured and the volume moisture content of capacitive frequency domain reflectometry (FDR) soil moisture sensor is compared, and the calibration equation of the sensor is obtained. The whole process of comparative measurement from water content saturation to almost no free water was repeated for several times for each sample, and the dynamic measurement repeatability on different soil moisture was obtained. At the same time, in each comparative measurement of soil samples, rotate the soil moisture sensor to obtain the repeatability of static measurement in different directions on the same soil moisture value. Based on the measured data, the repeatability difference between the dynamic error and the static error is analyzed. The experimental research shows that the undisturbed soil calibration of FDR soil moisture sensor has good full-scale repeatability under the condition of little difference in ambient temperature. The maximum undisturbed soil sample dynamic error of volume moisture content is 3. 57% ( cm 3·cm -3 ), the minimum is 2. 29% ( cm 3·cm -3 ), and the average is 2. 81% (cm 3·cm -3 ); The maximum error of directional static volume moisture content is 0. 22% (cm 3·cm -3 ), the minimum is 0. 01% (cm 3· cm -3 ), and the average is 0. 02% (cm 3·cm -3 ). The undisturbed soil has good dynamic repeatability and can be used as the standard material for post station calibration. The error of directional static volume moisture content is small and can be ignored in the measurement.