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

Abstract

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.