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.")
The mesocotyl attaches to the center of the crown. Moving outward from the mesocotyl, the first set of roots you see growing around the crown is the first set of crown roots—they will be the smallest crown roots in diameter. A bit farther outward will be the second set—a little thicker in diameter—and then the third set, a little thicker yet.
Crown roots are key. "The first two sets of crown roots are the big nutrient-uptake roots," Bauer says. "They help get a lot of nutrients into the plant early on. The third set of crown roots becomes a key factor in July and August, keeping the plant alive late in the year, when it is trying to pull moisture from below."
Usually there will be four roots in each of the first two sets. If any of them are turning outward, rather than growing downward at a 35° to 40° angle, that suggests they have run into an area of denser soil and are having trouble penetrating it. "Roots can't handle the sudden change in density," Bauer says.
"If only the first set of crown roots are turning, that's not a perfect situation, but the crop probably will be OK in July and August," Bauer notes. "But if all three sets are turning, you have a problem."
A huge volume of roots that are growing downward underneath the plant is good. "If you hold the root ball upside down, roots should be pointing upward, not straight out," Bauer says.
You also can find density changes with a tile probe. "Push the probe into the soil, and note where the density changes and you have to push harder," Bauer says. "Then push some more and see if there's another change in density."
If you use conventional tillage, you may have a density change at the depth of your plow and another, closer to the surface, where you ran a field cultivator or similar secondary tillage tool.
|Working with Residue
What happens on the soil surface affects what happens underneath—that's why growing crops requires a systems approach.
"Leaving crop residue on the surface has many benefits," says Missy Bauer, field agronomist for The Andersons, based in Maumee, Ohio. "The residue protects the soil surface from the effect of raindrops, which leads to erosion. Lack of residue may lead to crusting and sealing, when soil particles are broken apart into finer pieces.
"With sandy soil, residue protects the crop from the effects of blowing sand particles, which can actually cut off corn plants. It also helps prevent water from evaporating from the soil," Bauer says.
The percentage of the soil surface that is covered by residue can range from 90% for no-till to 78% for strip-till, to 10% for moldboard plowing (as measured at the Corn College plots). "Think about how much residue you need to maintain on the surface of your own fields to reduce erosion," Bauer says.
Surface residue also has a downside, but you can minimize it. "If you have a lot of surface residue, it will reduce soil temperature," Bauer says. "In May, in the Farm Journal Corn College plots, soil covered by residue was 4½°F cooler than bare soil. I've seen studies where, early in the season, the difference was 7°F to 10°F.
"You don't want to delay planting, waiting for the soil to warm up and dry out, because planting date is correlated to yield," Bauer continues.
"But you can overcome the effect of residue by doing strip-tillage or putting row cleaners on your planter. In a corn/soybean rotation, row cleaners are very important; in continuous corn, I wouldn't think of planting without them," she adds.
"Floating row cleaners with a depth band wheel provide the most consistent control. This will lead to more consistent planting depth and uniform emergence, which is required to maintain ear count."
Another disadvantage of residue is that it can be pinched in the seed trench, where it wicks water, actually pulling it away from the seed.
"For seed to start germinating, it must take up at least a third of its weight in water," Bauer says. "So if one seed has residue near it and another one doesn't, they may germinate at different times. If the second seed germinates more than 48 hours later, you will have a smaller plant, without a good, harvestable ear. If you lose ear count, you lose yield."
Keep disease resistance in mind when you select hybrids because residue on the surface increases disease pressure, Bauer adds.
Remember, too, that residue management starts at harvest by installing equipment on your combine to spread residue uniformly across the width of your header. "Think of residue like fertilizer because it ties in with your nutrient-cycling program," Bauer says. "If your applicator spreads fertilizer unevenly across your field, you wouldn't be happy with him."
"You also can utilize a tile probe when doing primary tillage in the fall," Bauer notes. "For example, if you're using an in-line ripper, probe in between the shanks and see how uniformly you're fracturing the soil. If a spot in the middle is hard, you need to change the depth or move the shanks closer together."
Another tool for locating density changes is a soil penetrometer. The gauge on a penetrometer shows how much pressure (in pounds per square inch, or psi) it takes to push through layers of soil. "Don't worry about the numbers on the gauge because they will be different in dry soil or wet soil," Bauer says. "Just watch for the change in psi. Personally, I feel you can do just as good a job with a tile probe."
The best way to see what's going on below the surface of your fields is to dig a soil pit. "If you've never dug a soil pit on your farm, I highly encourage it," Bauer says. A backhoe makes the best soil pit, but if you don't have one, a shovel works. "With a shovel, make sure you stretch your pit across two rows of corn," Bauer says. "With either tool, you can see a lot."
The soil density session led by Ohio agronomist Missy Bauer received high marks from the 2008 Corn College class. In 2009, attendees will have hands-on opportunities to learn how to maximize corn yields and minimize inputs.
Dig your pit deep enough to see where the B soil horizon begins. "In most soils, you find the B horizon by looking for color change," Bauer says. "Measure the depth of the A horizon. That tells you how deep to run tillage tools. For example, run an in-line ripper 2" into the B horizon—you want to get underneath the A horizon, lift the whole profile up and set it back down, creating vertical fractures."
Next, look at root growth patterns and examine the crown roots. See whether roots are being turned by soil density layers created by tillage.
Finally, see if roots are turning sideways instead of penetrating the B horizon. "If you find a major change in density between the A and B horizons, use an in-line ripper or disk ripper, not a chisel plow," Bauer advises.
If you find residue in August that was incorporated last fall but has not yet decomposed, it indicates a lack of oxygen in the soil because of a dense layer. In that case, consider doing vertical tillage.
If you're in the process of transitioning from horizontal to vertical tillage, make sure you're not loosening soil in a "W" pattern, with loose soil where the shanks ran but with columns of undisturbed soil in between, running all the way to the surface. "A ‘W' bottom is often created by shallow primary tillage," Bauer explains.
"The loose soil requires a conventional tillage setup on your planter; while the columns are like planting into no-till," Bauer says. "The result will be uneven emergence and uneven tasselling, which will reduce ear count."
The quest for uniform emergence and growth underlies everything you do. "You must protect ear count," Bauer says. "A thousand ears per acre equals 5 bu. to 7 bu. of corn."
Even with compaction and soil density problems, corn may still look good and yield well if you get plenty of rain, Bauer notes. But rather than gambling on favorable weather, it's better to weatherproof your soil by finding and removing yield-limiting layers.
After listening to Bauer and to presentations by Farm Journal Field Agronomist Ken Ferrie, some members of the Corn College audience plan to take Bauer's advice.
"We're going to dig soil pits," said Clyde Mostoller Sr., Mountain Lake Park, Md. "I had it confirmed today why roots grow out to the side
[instead of downward]."
"We have never dug any soil pits, but we're going to do that now, and take a look at our corn roots," said Tom Van Hise, who farms with his brother, Brian, near Rochelle, Ill. "We may have some hard soil down there. We are getting good yields now, but I think maybe we can do better."
|This summer, Farm Journal welcomes back graduates of the 2008 event—to move to the next level—and invites other producers to experience our Corn College. Led by Field Agronomist Ken Ferrie, the 2009 event will focus on capturing every bushel possible from every acre for maximum profitability. Early bird registration (prior to June 1) is $350; regular registration is $425; and registration for multiple attendees from one farm is $300. E-mail questions to CornCollege@farmjournal.com. To register, call (800) 909-3681.
You can e-mail Darrell Smith at firstname.lastname@example.org.