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Competency Area 4: Soil health and compaction

PO 35. Understand the appropriate use of a soil penetrometer and how to detect compaction layers.

The penetrometer can be a useful tool in soils that don't have many rocks. It needs to be used when the soil is at field capacity (thoroughly moistened to depth of penetration resistance measurement). The penetrometer needs to be pushed into the soil at a rate of about 1 inch/second.

Most penetrometers have indentations on the rod every 3 inches. Use this to determine at what depth the penetration resistance increases above 300 psi. Push the penetrometer in further, and record at what depth the penetration resistance decreases below 300 psi. If there is a mild plow pan, penetration resistance might not quite increase to 300 psi, but even above 200 psi root penetration is affected.

Penetrometer image source: