A combined penetrometer is an appropriate tool to measure the soil cone resistance and the water-content profile. As arelatively new technique, acombined capacitance-penetrometer for the simultaneous measurement of cone index and soil water content was developed at the Department of Agricultural Engineering of Bonn University in 2002. The objective of this study was the evaluation of the effectiveness and applicability of the innovated penetrometer with a focus on three aspects: (1) A capacitance sensor with two electrode configurations was calibrated for silt loam, sandy loam, and sand. The calibration results show that both electrode configurations have sufficient water-content sensitivity, but soil-specific calibrations seem necessary.(2) Under laboratory conditions, the dynamic resolution and response of the capacitance-penetrometer were validated, and its radius of influence was determined.(3) The field measurement results demonstrate that this measurement technique can be used to improve the interpretation quality of soil cone index data.

A polarized He-Ne laser light was used in a laboratory environment to measure soil moisture content. Depolarization of the light beam was used as an indicator of dielectric constant, which, in turn, indicated soil moisture content. Fourier analysis was used to analyze the signals. The DC component and the second harmonic of the Fourier spectrum were used to calculate the degree of depolarization. This method greatly reduced the effects of noise from various sources on the measurement of degree of depolarization. Three soil types (silt-loam, loam, and loam-sand) were tested. For all three soil types, degree of depolarization decreased with an increase of moisture content. The change was most significant for loam, followed by silt loam and loam sand.