Researchers at the ARS Cropping Systems and Water Quality Research Unit in Columbia, Mo., led by agricultural engineer Kenneth A. Sudduth, have designed and are evaluating the sensor.

Compaction is a key factor in soil productivity. Soil has many properties that determine its value for crop production. For roots to thrive, the soil must provide the right amount of water, as well as have good texture and the correct amount of nutrients. The level of soil compaction is equally important. If the soil is too compacted, there will not be enough pores to allow the roots to respire properly. If the soil is too loose, nutrients will leach through the root zone too rapidly and will not be useful to the plant.

Soil compaction is primarily caused by farm equipment traffic. It can vary widely over fields and thus can contribute to different yields in different areas.

Researchers and consultants have traditionally used a cone penetrometer to measure compaction in the field. The instrument is pushed into the ground to measure compaction at a single location. Using a penetrometer to map compaction variations within a field requires a lot of effort. To get an accurate map, the penetrometer data must be collected at many locations. Scientists and farmers would benefit from the new instrument, which is easier to use and gets better results.

Maps of compaction measurements will show the farmer where compaction may be a problem within a field. This new information should also help to interpret the yield maps that many farmers already use. Understanding yield variations and the causes for them is an important step toward making better use of precision agriculture.

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