A penetrometer's measurement of soil strength is very sensitive to soil compaction. However, using strength data for definitive interpretations of soil compaction requires correlations to other standard compaction tests or additional knowledge of soil moisture and soil characteristics. The hand-held electronic cone penetrometer can help pinpoint compaction problems that might require more extensive soil testing. It's also useful for looking at variability or changes in soil strength caused by equipment, vehicles, and foot traffic. Researchers are evaluating ways to use hand-held electronic cone penetrometers to help predict the likelihood of serious compaction in susceptible areas.

Reliable data requires penetrometer operators to insert the probe into the ground at a consistent speed. Certain soil or sampling conditions can greatly alter penetrometer readings and make them much less useful. An operator's field notes are helpful when data require editing because of unusual conditions, such as very rocky soils, large roots, hardpans or plowpans, voids such as gopher holes or large root channels, buried organic materials, and very dry conditions. The repetition tests conducted during this evaluation verify the need to probe several locations in a given area to better understand variations in soil conditions and operator inconsistency.

Vegetation growing near the soil surface can interfere with the hand-held electronic cone penetrometers, causing false depth readings. The Spectrum Field Scout SC–900 reported errors, rejecting the file, when weeds, sticks, or grasses were near the testing area. MTDC fabricated a ground target (a piece of U-shaped metal), similar to the one provided by Eijkelkamp and Agridry, to help reduce the error messages on the Spectrum Field Scout SC–900.

The graphic readouts on the Eijkelkamp Penetrologger and the Rimik CP40 are useful in the field. Both penetrometers give an indication of the insertion speed so the operator can speed up or slow down as necessary. If the penetrometer is not inserted at the proper speed, the operator has the option to reject or keep a specific file. The Rimik CP40 can be programmed to a specific insertion speed, sounding an alarm or rejecting data (based on the operator's preference) if the speed is not correct.

The Spectrum Field Scout SC–900 stops taking readings and requires the operator to start over if the proper speed is not maintained. This feature is frustrating because many times operators can tell that they hit a void or rock and could note this in a logbook. In tough conditions, it can be very frustrating to get one complete full depth reading with the Spectrum Field Scout SC–900.

The probe on the Eijkelkamp Penetrologger was longer and thinner than the probes on the other two units. This variation allows for deeper depth recordings, but the probe tends to bow in hard soils. Eijkelkamp offers a thicker rod, but it requires using a larger diameter cone that is more difficult to insert into compacted soils. In sandy or less compacted soils, the larger cone provides a broader range of testing capabilities.

Eijkelkamp recommends that the operator program a field plan with plot names, the number of measurements per plot, and the penetrometer parameters before taking readings. This programming is best done in the office using a computer, but can also be done in the field using the Eijkelkamp Penetrometer's touch screen. The Rimik CP40 and the Spectrum Field Scout SC–900 simply assign a file number as each probe insertion is completed.

Downloading information from the penetrometers to a computer is reasonably easy for all three penetrometers. Importing the information into spreadsheets is more difficult. The data from the Spectrum Field Scout SC–900 can be downloaded as well-formatted text files that need very little manipulation. Data from the Eijkelkamp Penetrologger and the Rimik CP40 require more manipulation when they are imported into a spreadsheet. We had to download each file individually from the Rimik CP40 because information could not be separated easily when more than one file was downloaded at a time.

The Rimik CP40 and Spectrum Field Scout SC–900 are designed to record location data from an external GPS receiver (not provided) at each probe location. The Eijkelkamp Penetrologger has no provisions for GPS. Because only two units had GPS capabilities, the GPS option was not tested by MTDC.