Field measurements of topsoil moisture profiles by vertical TDR probes

A recently developed inverse method for the estimation of water content profiles from single time domain reflectometry (TDR) waveforms in laboratory has been adapted and applied to field measurements of topsoil moisture profiles in a pyroclastic sandy loam. Three metallic probes of the lengths of 30 cm, 45 cm and 60 cm were vertically installed in an experimental field for the measurement of vertical water content profiles. One 15 cm long probe was inserted vertically into soil surface and five 10.5 cm long probes were buried horizontally at various depths for the measurement of local values of mean water content by means of the classical TDR approach. The experimental campaign Lasted 28 days, during which daily rainfall heights and daily maximum and minimum temperatures were measured at the experimental field. TDR waveforms acquisition was carried out twice a day. The agreement between Local volumetric water content measurements and vertical profiles was in general satisfactory, although some of the vertical profiles failed in detecting a layer with systematically smaller water content values indicated by the horizontal probe buried at the depth of 30 cm below soil surface. Such small water content values could be probably ascribed to the presence of a large amount of pumice stones in the soil around that depth, affecting the water content measured by TDR probes and thus increasing estimated moisture spatial variability. (c) 2007 Elsevier B.V. All rights reserved.