Deep Soil Compaction - Is It Your Yield Thief?

Oct 12, 2015

By Douglas B. Gucker, Univesity of Illinois

Have you noticed that your field is not draining as fast as it did a decade ago? Do your yields vary greatly between a "dry" year and a "normal" one? Have you checked your soil for deep soil compaction or subsoil compaction? Compaction that is deeper than 8 inches.

The use of heavier equipment, multiple field operations, operating in less than ideal conditions due to time constrictions, and the consolidation of crops used in a rotation, all provide elements for "more extensive and deeper compaction" according to research out of the University of Nebraska.

Over the past 4 years, I have had the opportunity to view several soil pits in local fields. The disturbing fact is that most of these pits have a compacted layer below 12 inches deep in the soil.

Deep or subsoil compaction is caused by total axle load of the equipment. For example, a 12-row combine fully loaded as an axle weight of about 26 tons. Research shows that loads of these magnitudes will the soil to compact down to a depth of 24 inches. A loaded 1200-bushel grain cart will have an axle load of 35 to 40 tons, which will cause the soil to compact to a depth of 36 inches or more.

How do you get rid of compaction? The "freeze-thaw" cycle is helpful for compaction down to about 4 inches. A ripper implement used in dry subsoil can relieve compaction below 10 inches deep. The ripper needs to be operated 1-2 inches deeper than the compacted layer in dry soil to shatter the layer. If the ripper is operated in moist subsoil, it will actually add compaction down to that depth.

Make sure your implement is operating at the depth you think it is. Research out of the University of Minnesota has shown that a disc-ripper implement actually operates about 2 inches shallower than it is set. This appears to be due to the fact that the disc gangs throw soil causing the implement to ride higher.

Another way to attack deep soil compaction is through the continued use of cover crops. Research is showing that cover crops used repeated on the same field, year after year, create root channels through the compacted soil zones that subsequent crops can follow.

Confining field traffic to travel zones keeps the deep compaction restricted to travel lanes and not the whole field. University of Nebraska research has shown that in the course of a year, if random field traffic patterns are used for tillage, planting and harvest operations then almost 90 percent of the field has been subjected to soil compaction.

The key to higher crop yields may be as simple as checking your soil for compacted layers. Digging a hole 18 inches deep (and big enough a 5-gallon bucket can fit in it) will give you the opportunity to explore whether your field has subsoil compaction.

The photo shows a site where I found a compacted layer that extended 4-12 inches deep. There were literally no corn roots below about 5 inches.

Source: illinois.edu

Video: Why Your Food Future Could be Trapped in a Seed Morgue

In a world of PowerPoint overload, Rex Bernardo stands out. No bullet points. No charts. No jargon. Just stories and photographs. At this year’s National Association for Plant Breeding conference on the Big Island of Hawaii, he stood before a room of peers — all experts in the science of seeds — and did something radical: he showed them images. He told them stories. And he asked them to remember not what they saw, but how they felt.

Bernardo, recipient of the 2025 Lifetime Achievement Award, has spent his career searching for the genetic treasures tucked inside what plant breeders call exotic germplasm — ancient, often wild genetic lines that hold secrets to resilience, taste, and traits we've forgotten to value.

But Bernardo didn’t always think this way.

“I worked in private industry for nearly a decade,” he recalls. “I remember one breeder saying, ‘We’re making new hybrids, but they’re basically the same genetics.’ That stuck with me. Where is the new diversity going to come from?”

For Bernardo, part of the answer lies in the world’s gene banks — vast vaults of seed samples collected from every corner of the globe. Yet, he says, many of these vaults have quietly become “seed morgues.” “Something goes in, but it never comes out,” he explains. “We need to start treating these collections like living investments, not museums of dead potential.”

That potential — and the barriers to unlocking it — are deeply personal for Bernardo. He’s wrestled with international policies that prevent access to valuable lines (like North Korean corn) and with the slow, painstaking science of transferring useful traits from wild relatives into elite lines that farmers can actually grow. Sometimes it works. Sometimes it doesn’t. But he’s convinced that success starts not in the lab, but in the way we communicate.

“The fact sheet model isn’t cutting it anymore,” he says. “We hand out a paper about a new variety and think that’s enough. But stories? Plants you can see and touch? That’s what stays with people.”

Bernardo practices what he preaches. At the University of Minnesota, he helped launch a student-led breeding program that’s working to adapt leafy African vegetables for the Twin Cities’ African diaspora. The goal? Culturally relevant crops that mature in Minnesota’s shorter growing season — and can be regrown year after year.

“That’s real impact,” he says. “Helping people grow food that’s meaningful to them, not just what's commercially viable.”

He’s also brewed plant breeding into something more relatable — literally. Coffee and beer have become unexpected tools in his mission to make science accessible. His undergraduate course on coffee, for instance, connects the dots between genetics, geography, and culture. “Everyone drinks coffee,” he says. “It’s a conversation starter. It’s a gateway into plant science.”