Water content measurement in forest soils and decayed wood using time domain reflectometry

Abstract

The use of time domain reflectometry to measure moisture content in forest soils and woody debris was evaluated. Calibrations were developed on undisturbed soil cores from four forest stands and on point samples from decayed logs. An algorithm for interpreting irregularly shaped traces generated by the reflectometer was also developed. Two different calibration equations were needed to estimate volumetric moisture content at the four sites, but commonly implicated soil characteristics (organic matter content, bulk density, and soil texture) could not fully account for the differences between calibrations. The calibrations differed from previously published calibrations for mineral and organic soils. Estimation of moisture content in decayed wood was possible with a single significant regression. The standard errors of estimate for volumetric water content were less than 0.02 m3 m−3 for the soil calibrations and just over 0.06 m3 m−3 for the decayed wood calibration. We found we could reliably interpret most traces from field samples using an automated algorithm, but had to use a modified algorithm for one of the sites. This study suggests a need to calibrate time domain reflectometry measurements for individual forest sites and advises caution when using systems that have preprogrammed calibration and trace analysis routines.