Compaction and dense soil may be standing between you and top corn yields by creating a barrier to root penetration and water movement. Compaction and soil density are not the same thing, says Missy Bauer, agronomist for The Andersons, based in Maumee, Ohio. She shared her observations with attendees at Farm Journal's first Corn College, held this past summer near Heyworth, Ill.
"Compaction is platy structure that develops when individual soil particles (sand, silt or clay) are compressed together, or flattened out, by wheel tracks or tillage," Bauer says. "Dense layers are created when the air is pushed out from between soil particles. They can occur when soil is loosened by tillage, while exerting downward pressure with a field cultivator or other horizontal tillage tool."
Squeezing out air means the soil has fewer macropores, which foster water movement. So you have to saturate the soil zone to create head pressure to push water down into the profile.
You can have dense layers and soil compaction. "If you do horizontal tillage, you create a density layer," Bauer says. "If you do the tillage when it's wet, you will also have compaction."
A study at the Corn College site, using barrels hammered about 4" into the soil, revealed how much impact changes in soil density, created by tillage tools, can have on water infiltration and movement. Where a disk ripper or chisel plow was followed by a harrow—and there were no soil density changes—3" of water infiltrated into the soil in less than two hours.
A "W" pattern—loose soil where the shanks ran with columns of undisturbed soil in between—creates uneven emer-gence and impacts root development.
Where a soil finisher followed a disk and created a density layer, water infiltrated the top 3" of the soil but then stopped infiltrating for a while. It took two to three hours for the water to move through the dense layer.
The worst case involved a moldboard plow followed by a field cultivator. "In this case, we had a field cultivator layer and also a plow sole," Bauer says. "A little water soaked in, but then it sat and sat. We had saturated conditions for a long time. It took more than 22 hours for water to soak in.
"If a field stays wet longer in the spring because dense layers prevent water from moving downward, it may lead to seed rot, seedling blight and replanting. In August, dense layers have the opposite effect, preventing water from moving upward through the soil."
Some simple spadework in the field will reveal underground yield barriers. Start by digging several plants and studying root balls. Crown roots can tell you if you have a density problem and, if so, how bad it is.
"Brace roots are important for standability," Bauer explains. "But for yield, your high-dollar roots are the first three sets of crown roots."
To find the crown roots, first remove the plant's brace roots. Then, locate the mesocotyl—the white tubular connection between the crown and the seed. ("The crown develops ¾" below the soil surface," Bauer notes. "So if you want to know your planting depth, measure the length of the mesocotyl and add ¾" to it.")
- February 2009