CALIBRATION OF TIME DOMAIN REFLECTOMETRY (TDR) SOIL MOISTURE POINT PROBE FOR TWO SOILS

Abstract

Maintaining adequate soil moisture in the root zone is crucial in achieving good plant growth. Accurate measurement of soil moisture is essential to keep the right level of soil moisture. Many studies have reported the successful application of Time Domain Reflectometry (TDR) for soil moisture measurement. This study was initiated to obtain calibration curves for soil water content determinations by TDR for two soil types. Measurements were taken in the laboratory for a silt loam and a sandy loam soils, using TDR Soil Moisture Measurement Instrument, Moisture PointTM Model MP-917, and Moisture Point Probe type-K. TDR probe calibration was performed for two soil types contained in wooden boxes (100 cm x 100 cm x 80 cm). The calibration was accomplished by comparing the volumetric moisture content (qTDR) and time delay (tTDR) response of TDR probe to that of the gravimetric volumetric moisture content (qgrav). The TDR measurements were taken, in triplicates, at four depths (0-15 cm, 15-30 cm, 30-45 cm, and 45-60 cm) for 38 days after wetting the soil. Soil samples for the gravimetric moisture content measurements were collected from the same locations from where TDR readings were taken. The study has demonstrated that the TDR technique is a reliable alternative method for measuring soil moisture content. The moisture content measurements obtained with TDR were comparable to that of the gravimetric method and showed a good relationship to gravimetric determinations (r 2 =0.85 for silt loam and 0.89 for sandy loam).