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Study: Up to 40% Yield Hit from Compaction

Farmers are always tempted to work wet fields in spring, but here are a few good reasons why they should keep the tractor in the shed until soils dry properly. Ohio State University (OSU) researchers have found that, depending on soil type, compaction can ding yields up to 40% and last as long as eight years.

Those are just a few recent observations from an ongoing, 20-year compaction study at OSU - one of the few long-term compaction studies in the nation. The 40% yield cut occurred after just one year of harvest traffic on clay soils.

"We know that equipment causes compaction, but we wanted to know how long that compaction lasts and how severe it really is," says Rattan Lal, OSU soil scientist with the Ohio Agricultural Research and Development Center.

OSU researchers at Hoytville, Ohio, used this 600-bushel grain cart with 20-tons of weight on a single axle to simulate damage from soil compaction. (PHOTO: Randall Reeder, OSU Extension agricultural engineer)

Compaction destroys the soil structure and causes erosion by keeping water out. It prevents plant roots from penetrating deep into the soil, and traps carbon dioxide while preventing oxygen from reaching plant roots. The result suffocates the plant either killing the plant or impacting yield performance

"It's better to take steps to prevent compaction rather than struggle to try to eliminate it," says OSU Soil Scientist Rattan Lal.

Lal and his colleagues made a one-time pass with a single axle 20-ton grain cart and a single axle 10-ton grain cart across fields with two types of soils: clay and silt loam. They then measured how long it took for the fields to recover from the effects of compaction. While compaction from clay soils persisted for years, silt loam soils escaped serious compaction problems.

"Unlike silt loam soils, clay soils drain poorly and don't respond to the freezing and thawing process during winter, so compaction tends to persist more and its impact on crop growth and yield is much more severe," Lal says.

You can reduce the threat of compaction by managing your soils and cropping practices:

• Use minimal tillage techniques, such as chisel plowing or sub soiling.

• Rely on soil critters, such as earthworms, to break up the soil through natural processes. Compaction can decrease earthworm populations by 70% in clay soils and 50% in silt loam soils.

• Grow a cover crop, such as alfalfa, which has a taproot system and can extend deep into the soil.

• Leave crop residue in the field. The residue acts as a buffer to dissipate any wheeled traffic.

• Use dual-axle instead of single-axle equipment and wider tires to distribute weight.

• Practice controlled traffic -- a method whereby all farm equipment is the same width so that traffic is confined to specific paths year after year, and the remainder of the soil is untouched.