New Device Measures Soil Compaction

A new device developed by an Agricultural Research Service scientist may be the best yet for measuring soil compaction, which causes problems by preventing moisture from seeping down to plant roots. Compacted soil also increases water runoff and wind erosion.

Agricultural engineer Randy L. Raper of the ARS National Soil Dynamics Laboratory in Auburn, Ala., has led the development of technology – in cooperation with Auburn University – that uses one sensor to measure soil strength at all depths in the top 18 inches of soil. Raper's invention is known as OMIS (for On-the-fly Mechanical Impedance Sensor).

OMIS isn’t the first device developed to measure soil compaction. Scientists have developed and tested several others, but those only measured soil at a few depths. Often this isn't sufficient, particularly in the Southeast, where compaction varies and may be caused by a thin hardpan. Hardpan is a dense layer of soil that restricts root growth and the movement of moisture, air and beneficial organisms through the soil.

Raper's invention consists of a sensor attached to the front of a shank. As a tractor pulls the shank, it is moved up and down like a needle on a sewing machine. As the tractor moves forward, the sensor is cycled up and down to measure the soil strength.