Compacted soil compresses yields. That's a no-brainer. But a recent Iowa State University study shows that compacted fields can yield a whopping 10-20% less by reducing soil moisture and air available to roots.
The four-year continuous corn study was conducted on alluvial soil in Southeast Iowa. It found that soil farmed with equipment exerting a 6 psi. surface pressure yielded 9 bu./acre more corn than corn grown using more conventional equipment with 16 psi. tire pressure. Much of the reduction may result from plants seeded into that spring's traffic tracks, the study says. In an earlier study on the same soil, corn yield was depressed 27 and 18 bu./acre, respectively, for plants growing in higher-pressure wheel-type tracks and lower pressure track-type tracks, as compared to plants growing in adjacent untracked soils.
The most notable changes in soil from compaction are in soil bulk density, soil strength, porosity and hydraulic properties such as infiltration rate and hydraulic conductivity, says Mark Hanna, Iowa State University Extension agricultural engineer.
So it makes sense to maintain the right kind of tires at the proper inflation, says Randall Reeder, an Ohio State University Extension agricultural engineer. “It keeps money in your pockets,” he says. “And, farmers should invest in radial, rather than bias tires,” he says. “Even though radial tires are more expensive, they outperform bias tires because of their design.”
As equipment grows in size, there should be a paradigm shift toward radials with larger footprints, says Kevin Lutz, technical manager for Michelin North American agricultural tires. For larger equipment, engineers recommend radials with a 20% larger footprint than standard profile tires, and a broad, flat tread. The oversized footprint helps to decrease ground surface pressure, increase traction, reduce wheel slip and improve fuel economy. The good news is that these tires usually fit on existing rims.
The most cost-effective option for moving primary tillage tractors up to large-volume tires is to replace worn tires with radials.
Reeder adds that most farm tires are over-inflated and cause excess slippage. “Check tire pressures once a week during busy seasons,” he says, and be sure to keep tires at the correct pressure to improve traction and wear.
Check out Michelin's Web site at www.michelinag.com  to help calculate correct tire pressures for your situation, and to reduce soil compaction, solve power hop issues and to mount your tires properly.
For more information on the study, see www.extension.iastate.edu/Publications/PM1901B.pdf .
How To Reduce Compaction
Use controlled traffic lanes because most compaction occurs in the first pass or two of a vehicle.
Stay out of wet fields.
Use larger diameter wheel rims and large tires to lower surface pressure by lengthening and spreading out the wheel print.
Soil Compaction Quiz
What is the cost of soil compaction?
How can you determine that you have soil compaction?
How does soil compaction affect soil moisture?
Soil compaction may cost you several bushels per acre, and more horsepower and fuel are needed for tillage. Tillage to help remedy compaction costs $7-10/acre to loosen shallow compaction; $15-20/acre to reach deeper layers.
Dig up plant roots, use push rods, or use a shovel. The first symptom of possible compaction is often stunted crop height. Carefully digging up plants to determine root depth and comparing them to nearby roots on uncompacted soil can rule out other agronomic problems. Other possible symptoms include sideways root growth, nutrient deficiencies, herbicide injury, or slow plant emergence. These can be symptoms of other problems as well.
Soil compaction reduces infiltration, reducing water recharge to lower depths.