Laboratory Calibration, In‐Field Validation and Use of a Soil Penetrometer Measuring Cone Resistance and Water Content

Concurrent and coincident measure of penetrometer cone resistance (PR) and water content (WC) were optimized by hourly in‐field validation of data from time domain transmissiometry (TDT) for WC and piezoelectric force sensor for PR. A piezoelectric force sensor coupled to a cone is followed by a helical wrapped TDT sensor on a single penetrometer shaft. Detailed laboratory calibrations, coupled with in‐field validations, were important to assure the quality of data, which facilitated detailed analyses of PR and WC patterns. The piezoelectric sensor relied on a calibrated spring for the in‐field validation. The calibration of the TDT sensor had three stages: a series of fluids of known dielectric constant; soil columns at known, variable water contents; and field soils at a range of ambient conditions. The penetrometer was used to study soil strength and WC behavior in time and space along 300‐m plots. The treatments were conventional and no‐till, each at two levels of traffic. The crop was corn ( Zea mays L.), continuous and in rotation with soybean [ Glycine max (L.) Merr.] and wheat ( Triticum aestivum L.). The PR vs. WC relationships for two depths (0.21 and 0.27 m), below the level of cultivation, were similar to those at the 0.10‐m depth for the nontrafficked no‐till plots. These relationships for the 0.21‐ and 0.27‐m depths were not influenced by tillage, traffic, and corn cropping system treatments. The variable depth of plowing in tilled plots was found to influence the data consistency for the 0.21‐m depth, indicating the penetrometer's high sensitivity to the soil conditions.