Submitted to: ASAE Annual International Meeting
Publication Type: Other
Publication Acceptance Date: 7/13/2000
Publication Date: N/A
Interpretive Summary: Precision agriculture is a crop management strategy which seeks to address within-field variability. An important aspect of within-field variability is soil physical condition. Soil electrical conductivity (EC) is gaining acceptance as an indicator of soil physical properties such as salinity, moisture content, clay content, and topsoil depth. Another automated device to collect soil physical condition data is the cone penetrometer, which measures the force required to penetrate the soil. A new, commercially available penetrometer incorporates an EC sensor in the tip, allowing simultaneous measurement of both parameters. In this research we compared the EC penetrometer to standard penetrometers. We found that penetration resistance measured with the EC penetrometer was significantly different than that measured with a standard penetrometer, but that it was possible to convert between the two. We also found that the simultaneous EC Cand force data collected with the EC penetrometer allowed a more complete soil characterization than either alone. This work is important because it presents the first independent evaluation of the performance of an EC penetrometer. The research will benefit other researchers by documenting the differences between data collected with the EC penetrometer and other, standard penetrometers that are currently in use. It will also benefit extension specialists and crop advisors by allowing them to understand some of the benefits and limitations of these new devices that they may want to use in their programs.
Technical Abstract: An automated cone penetrometer that measured soil electrical conductivity (EC) with depth in addition to cone index (CI) was evaluated. The EC- sensing penetrometer operated at a faster insertion speed and exhibited a non-standard cone geometry. Cone geometry had a significant effect when comparing the EC-sensing penetrometer to standard large and small cones. There was also a significant effect of cone size between the two standard cones. It was possible to develop CI-dependent transformation equations to convert data collected with one tip to correspond with data from another tip, but a large amount of scatter was present in the relationship. No significant effect of insertion speed was detected between the standard insertion speed of 30 mm/s and the EC-sensing penetrometer speed of 40 mm/s. Data collected along a transect on a claypan-soil field showed interrelationships between EC, CI, and soil moisture. However, value was seen in quantifying all three parameters simultaneously to more completely characterize soil variability. In this no-till field, CI values were generally above the 2 MPa level thought to impede root growth. The highest CI values were seen in the row middle under the tractor tire, while the lowest values were seen in the crop row. Penetrometer EC data exhibited trends similar to mobile EC data collected along the same transect and should be useful for calibrating and/or understanding the response of mobile, profile-weighted EC measurements.