| heal.abstract |
Evaluation of the ML2 theta probe was performed in a variety of porous media such as mineral soils, peat and composts, combinations of composts, peat and perlite in various volume percentages. This was performed in laboratory columns under temperature-controlled conditions. A number of previous calibration curves referring to the same principle of soil moisture determination, via the determination of the soil dielectric constant, were comparatively examined together with the calibration curve proposed by the manufacturer. A specific calibration in accord with the manufacturer's linear √ε - Θ curve (where ε denotes the soil dielectric constant and Θ the volumetric water content) was followed. It was shown that for the mineral soils the manufacturer's calibration curve in all cases, except sands, kaolin and perlite, appeared to exhibit an overestimation. The most reliable results were obtained by the present soil-specific calibration curve. For the organic porous media again, the specific calibration curve was the most reliable. The manufacturer's calibration curve was shown to deviate from the prescribed limits of Θ in many cases. More specifically, it was shown that both overestimations and underestimations could be obtained for the composts, whereas a clear underestimation was observed in the mixtures. Other calibration equations examined appear to give better or worse results compared with those of the manufacturer, always depending on the nature of the porous materials. Soil-specific calibration is necessary and improves the results in most cases. Copyright © 2008 John Wiley & Sons, Ltd. |
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