In-field calibration of a dielectric soil moisture meter designed for use in an access tube

Abstract

The in-®eld calibration of a dielectric probe to measure soil water content is described. The probe uses an access tube analogous to that of the neutron probe. The dielectric constant was measured at soil depths of 10, 20, 30, 40, 60 and 100 cm. Cores of soil were then taken from the face of pits dug 30 cm from the access tube and their soil water contents determined by oven drying. The dielectric constant values measured by the probe were calibrated against water contents from these cores. We found that sensor depth needed to be included to achieve a good calibration model that explained 72% of the variance. It is argued that depth needs to be included because of artefacts introduced during the installation of the access tube.

The effect of soil strength on the yield of wheat

“…Although the data in Fig. 4 suggested more water was extracted from the loam than the sand, this deduction may be unsafe because of shrinkage of the loam away from the access tube, leading to underestimation of the soil water content (Whalley et al 2004). Nevertheless, the The dashed line in panel is the curve fitted to dry matter yield and mean penetrometer resistance (as described above) for data from Whalley et al (2006) where soil strength was manipulated by irrigation.…”

“…Soil moisture sensors were installed in one block on each site. Two access tubes for dielectric meters of soil moisture (Profile Probe, Delta-T Devices, 128 Low Road, Burwell, Cambridge, UK) that measure soil water content at depths of 0.1, 0.2, 0.3, 0.4, 0.6 and 1.0 m were installed in each plot on the instrumented block (see Whalley et al 2004). On the sand these sensors were logged, but water content was measured manually on the loam at approximately weekly intervals by inserting the profile probes into the access tubes.…”

Does Soil Strength Play a Role in Wheat Yield Losses Caused by Soil Drying?

“…Dielectric meters of soil moisture (Profile Probe, Delta-T Devices) were installed in all the plots of block 2 to measure soil water content at depths of 0.10, 0.20, 0.30, 0.40, 0.60, and 1.00 m (Whalley et al, 2004). In 2004, water potential was also monitored at these depths in the non-irrigated plots with novel porous-matrix sensors of matric potential.…”

Prediction of the penetrometer resistance of soils with models with few parameters

“…The matric potentials were monitored at a depth of 20 cm with a combination of water-filled tensiometers and porous matrix sensors (Whalley et al, in press). The soil water content was also monitored at a depth of 20 cm with a dielectric soil moisture meter (Whalley et al, 2004).…”