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 throughout each field 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. So farmers need to check compaction at various soil depths, not just the few that other devices measure.

Raper's invention consists of a sensor attached to the front of a shank. As the shank is pulled by a tractor through the field, 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.

Farmers can use Global Positioning System technology to create soil compaction maps and adjust their tillage depths. OMIS could also be customized to measure other properties, such as electrical conductivity and the amount of moisture in the soil.

Raper is continuing to improve the technology for field use and hopes the new invention will be on the market in a few years. A patent application has been filed, and ARS is looking for a licensee to commercialize the device.

ARS is the U.S. Department of Agriculture's chief scientific research agency.