A backhoe, shovel and tile probe can reveal your corn crop’s hidden yield barriers
Evaluating a corn crop is kind of like finding a mate: What you see at first glance is interesting, but it doesn’t tell you much. If you don’t learn more, you might make a serious mistake. Whether it is corn or people, what matters most is what lies beneath the surface.
That’s why the most important tools that Farm Journal Field Agronomist Ken Ferrie and Associate Field Agronomist Missy Bauer use in the corn field are backhoes, shovels, soil probes, hatchets and knives. "You’ve got to look belowground," Ferrie says.
What you’re looking for. "If you don’t know what’s going on with your corn crop’s roots, you are likely to blame problems incorrectly on products such as seed, fertilizer or herbicides," Bauer says. She and Ferrie dished the real dirt about evaluating roots, soil condition and the effects of tillage at last summer’s Farm Journal Corn College.
"When we look beneath the surface, we’re trying to identify soil density changes," Bauer explains. "You can think of density as the amount of air space between soil particles—the less air space, the more dense the soil is.
"It’s like a 5-gal. bucket full of golf balls compared to a 5-gal. bucket full of peas. There’s far more air space among golf balls than among peas," she says. "With corn, we are concerned with what happens to roots when they encounter abrupt changes in soil density. Roots grow horizontally along dense layers, rather than downward at a 30° to 40° angle.
"If roots grow along a horizontal layer, they may not penetrate to depths where they can reach water and nutrients," Bauer adds. "Things always look a lot better on top if there is uniform soil density down below."
Dense layers also keep water from infiltrating. "In the spring, density layers can hold water up, causing the soil to stay saturated for a longer period of time or to pond on the surface," she says.
"If it stays wet too long, you may sacrifice yield by planting late or in less than ideal conditions. Saturated soils also can lead to seedling diseases and denitrification."
Roots can tell you how your crop is faring—but it takes the tools we mentioned to give them a voice.
In this soil pit, the blue marker on the left identifies a shallow tillage layer put in by a soil finisher. The density change can also be seen to the right of the middle corn plant, where loose soil created by the soil finisher has been swept away. The blue marker on the right marks a tillage layer, or density change, where a moldboard plow went through. No residue has been buried beneath this layer, but a buried cornstalk is visible above and to the right of the marker.
Start with a soil pit. "If you have never dug a soil pit, I strongly recommend you do it," Bauer says.
"A soil pit adds to your understanding because you can see everything that’s going on," Ferrie says. "Of course, you can’t dig a pit in every field. But digging one or two pits will give you knowledge that will help you interpret what you discover with your spade and tile probe."
In the pit, Bauer performs a three-step inspection: feeling the condition of the soil with the aid of a knife; evaluating root growth; and looking for moisture layers.
"Work the soil with a knife, from the top down," Bauer says. "You will soon learn to feel changes in soil density, where it’s looser or tighter. Where there is a change in density, measure the depth from the surface. See if the change in density, or the new layer, is turning the plants’ roots."
- Late Spring 2012