A Novel Probe Design to Optimize Soil Profiling Measurements.

Quantifying the vertical profile of important soil properties is a vital part of many research and operational needs. Historically, this was done by digging a pit and installing sensors at specified depths horizontally into the undisturbed wall of the pit, then re-filling the pit taking care to reconstruct the soil profile that existed prior to this significant disturbance. This is a costly and labor-intensive process. More recently, several companies have produced probes that incorporate several sensors for which installation only requires auguring a small hole close to the size of the probe. Some of the key challenges associated with this general design are insuring good soil contact and the potential for preferential vertical flow of water along the sides of the probe. Two methods have been used to obtain good soil contact: slurry and a tapered design. The former is simply making a slurry out of water and the soil removed with the auger and does a good job of ensuring there are no air gaps. However, this soil mixture may not be representative of the full soil profile and therefore may bias the measurements. The tapered design does a nice job of getting good soil contact, but requires a custom auger for installation. No physical design that we’re aware of explicitly addresses the issue of preferential flow. We designed and tested a new design for profiling soil water, electrical conductivity and temperature that addresses both issues of soil contact and preferential flow in a novel way. Results of these tests including installation and intercomparison with existing sensing options will be presented.