Measuring soil compaction using a penetrometer (soil compaction tester)
Pennsylvania State University,Department of Crop and Soil Sciences, Agronomy Facts 63, 2002

Soil compaction can easily reduce crop yields by 10 percent, and can lead to water and soil quality degradation due to increased runoff and soil structure destruction.

Penetrometer: A diagnostic tool to measure the extent and depth of subsurface compaction is a penetrometer, or soil compaction tester.