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New Tool Swiftly Tests Soil's Strength

By Tara Weaver
October 6, 1998

A new and improved tool that gauges a field's soil strength will give farmers and researchers a quick way to tell if plant roots will have a hard time pushing down into the soil.

Agricultural engineer Randy L. Raper developed the tool, called a multiple-probe soil cone penetrometer. It tests soils for compaction or for layering that restricts root growth. The information helps farmers decide what type and depth of tillage is best for their fields.

In Auburn, Ala., Raper works at the National Soil Dynamics Laboratory, part of the Agricultural Research Service. ARS is the chief scientific research agency in the U.S. Department of Agriculture.

Dense, high-strength soil tends to restrict root growth. The condition can be caused by heavy agricultural equipment. On the other hand, loose, low-strength soil allows roots to penetrate downward and reach moisture during summer dry spells.

Raper's multiple-probe device measures soil strength across an entire row—a great time-saver compared to manual one-probe devices that require five insertions to obtain the same data. The improved device, mounted on a tractor, generates information on an entire row in approximately one minute. Older probes take 10 minutes and have to be manually pushed into the ground.

The improved device is also more sensitive than previous models, sensing depth to the millimeter and penetration force to within 0.1 pound per square inch. Raper and colleagues have used the device to measure soil compaction in several soils throughout the southeast.

Scientific contact: Randy L. Raper, ARS National Soil Dynamics Laboratory, Auburn, Ala., (334) 844-4654, fax (334) 844-8597,

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