Farmers at a late summer field day got a “mole’s eye view” of soil compaction.

Experts from the University of Minnesota Extension and North Dakota State University Extension built unusual layered soil pits to show the effects of wheel traffic and heavy machinery on soil structure.

Three-foot-deep soil pits were excavated in a harvested wheat field on the Don and Dan Bradow farm, French, MN. Then the black soil was put back into the pits in 4-in. layers, with each layer separated by a 2-in. band of light-colored, washed sand. Picture a seven-layer chocolate cake with caramel frosting between each layer.

Loaded grain carts and tractors with a variety of tire and track configurations were driven over the pits one or more times. Then the pits were opened up again, revealing the layers of soil and sand. The compaction effects of heavy field equipment, multiple machinery passes and incorrect tire inflation were visible in the undulating layers below ground.

Because the layered soil pits are an artificially created environment, the effects of machinery traffic were not exactly the same as they’d be in a field, notes Jodi DeJong-Hughes, a University of Minnesota Extension tillage expert. But the pits are a great way to visualize the unseen damage that can be done to your soil during field operations, she says.

“Heavy field equipment can compact the soil down to 4 ft. and affect crop yields for years to come,” DeJong-Hughes says. A multi-state study from 1988 to 2002, for example, shows that deep compaction depressed corn and soybean yields about 5% for 12 years, compared to an uncompacted control – even though no further compaction occurred during those 12 years, says Randall Reeder, a retired Ohio State University Extension ag engineer.

“However, small changes in your management and equipment maintenance can have significant positive effects in your fields,” DeJong-Hughes says. Controlling axle loads, properly inflating tires and avoiding tillage when soil is wet are examples.