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SPECIAL SECTION - ADVANCES IN MEASUREMENT AND MONITORING METHODS

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

^a Eastern Cereal & Oilseed Research Centre, Agriculture & Agri-Food Canada, 960 Carling Ave., Ottawa, ON, K1A 0C6, Canada
^b Environmental Sensors Inc. (ESI), Suite 100, 4243 Glanford Ave., Victoria, BC V8Z 4B9, Canada
^* Corresponding author (toppc{at}agr.gc.ca).

Received 14 April 2003.

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.

Abbreviations: PR, penetrometer cone resistance • SEE, standard error of estimate • TDR, time domain reflectometry • TDT, time domain transmissiometry • WC, water content