Listen to Your Roots

July 25, 2009 01:39 PM

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Your high-yielding 2010 corn crop starts now—right now—with an in-field checkup.

Corn roots can tell you how to set the stage for a bin buster next season by removing the dense, impenetrable layers of soil that restrict water movement and root growth.

By scouting fields, digging soil pits and finding soil density problems now, you can plan how to fix them using vertical tillage next fall, explains Farm Journal Field Agronomist Ken Ferrie.

"If you don't correct soil density problems, they'll hang around, limiting yield, until you do,” Ferrie adds. "Often, we'll find a tillage layer in a field and the operator will say, ‘It can't be from tillage; I didn't do any this spring.' After we talk some more, he'll remember he worked it wet the year before.”

About now, you're probably thinking: Sure, scouting for density issues sounds like a good idea, but, wait a minute, how am I supposed to examine 2,000 acres of corn? The answer, Ferrie says, is to do some homework before you head for the field and prioritize the areas you need to scout.

The first thing to consider is that not all soil density changes are man-made. Some occur naturally.

toTo learn more about soil pits, search the February 2009 issue to read Examples of natural density issues include sand lenses and hardpan layers that are too deep to reach with tillage equipment and soil types, such as Bryce and Swygert silty clay loams, which are common in Illinois. They are rich and black on top, just like highly productive Drummer and Sable silty clay loams. But unlike the deep uniform Drummer and Sable soils, the texture of Bryce and Swygert changes about 11" below the surface. There, the soil is underlain with a near-impenetrable layer of blue clay, which makes it almost impossible to drain or irrigate.

"You can't do much about natural density and texture problems, but you must know where they are so you can respect them and farm them accordingly,” Ferrie says. "You can learn about your soil types by studying soil survey descriptions.”

Tillage records. The second tool you need for efficient scouting—and one of the most important—is tillage records. "If you didn't record tillage information this past spring, sit down with your employees and reconstruct it now before the information fades from your memories,” Ferrie advises.

"Of the compaction issues I work with, more than 70% result from the first tillage pass in the spring,” Ferrie says. "Of course, you always try not to work fields in less than ideal conditions, but sometimes you have to in order to dry them out. Make these fields and the ones you rutted up with the combine the previous fall top priority for summer scouting.”

After tillage history, consider soil type and drainage when you prioritize which fields and which areas to scout first. Well-drained fields are likely to have the fewest soil density problems.

Your own observations from the spring and early summer will help you prioritize your scouting. "If a field is no longer draining the way it used to, or not draining as well as a neighboring field, there may be a dense layer above the tile line,” Ferrie says.

"Another sign is a low area that collects surface water faster than it used to or holds water longer than it used to, causing the corn to struggle if the season is wet. If the season is dry, these areas may be the first ones where the corn leaves roll. If there's a dense layer, the roots won't be able to reach water lower in the soil profile, and water won't be able to percolate upward to reach the roots.”

Finally, review yield maps and Normalized Difference Vegetation Index (NDVI) photos, and take them with you to the field. "If an area keeps getting ‘whupped on' year after year, you need to do a ground inspection,” Ferrie adds.

Of course, you'll want to check for insects and disease as you scout your fields. These problems will make density issues even worse.

Digging soil pits with a backhoe is ideal, but it's not practical in most cases. In the real world, you can find problem layers using a soil penetrometer or tile probe and a long-blade "sharpshooter” spade.
"As you probe or dig, watch for inconsistencies, where it requires more or less pressure to push the probe through the soil profile,” Ferrie explains. "If you're digging in silt loam soil that has run out of water, the
entire profile may be difficult to penetrate, but that may also just indicate the structure of that soil type.”

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Density changes.
"Even though that soil is dense, it still may be uniform, and uniformity is what roots care about. When they run into a layer of soil that suddenly is more dense, they stop penetrating downward and grow along the top of the layer,” Ferrie says.

Root diameter expands to its genetic maximum as long as the soil will allow it, he explains. So, with a given hybrid, the root diameter will be larger in a loose soil than in a tight soil.

"The root system adjusts to the bulk density of the soil, but it can't make sudden changes,” Ferrie says. "If the root is growing in a looser soil and encounters a denser layer, the point will turn and the plant will have to grow new roots to adjust to the density of the new layer of soil. If the root is growing from a dense soil into a looser one, it will have a lot fewer problems.”

In Ferrie's experience, 70% of compacted layers are located near the surface of the soil. "Pay attention to what happens in the top 3" or 4",” he says. "Often, a beginner won't notice that his probe pushed easily through the top several inches of soil and then was harder to push. Because the probe is 3' or 4' long, there's a tendency to look only for deep problems.”

It's the same when using a shovel. "Often, the shovel pushes easily into the soil and then stops at 4",” Ferrie says. "Without even thinking about it, the operator uses his foot to push it deeper, never realizing he has found a problem at the 4" depth.”

The ability to detect soil density layers comes with practice. You can speed up your learning curve by digging a pit, finding layers and pushing your probe through them to see what it feels like. "Once you're ‘calibrated,' you can detect layers anywhere in the field,” Ferrie says. "Then you can cover a lot of acres quickly.”

When your probing reveals a dense layer, it's time to dig a pit. In tall corn, you need good lighting to study the soil and roots, so cut away a few plants to let sunlight hit the face of the pit.

Use your spade to dig a pit across a row without wheel tracks. "Push in the shovel and start to lift,” Ferrie says. "If only one plant moves, you probably don't have surface compaction. But if several plants move, you probably are underneath a compacted layer.”

After digging up a plant, leave the soil attached and study the roots to see if they are turning and growing along a compacted layer of soil.

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Find the key roots. "The first three crown roots are the most important,” Ferrie says. The first two sets of roots bring most of the nutrients into the plant until it is waist-high, but they aren't strong enough to push through much dense-soil resistance.

"The third set of crown roots keeps water available to the plant during July and August, as well as transporting lots of nutrients. If they turn and grow sideways along a dense soil layer, rather than penetrating downward, they can cost you yield,” Ferrie says.

"Use a hatchet to trim away the later-emerging crown and brace roots so you can examine the first three sets of crown roots. All three sets should grow downward from the crown at about a 30° angle.” As you examine the roots, evaluate the plant's general health.

Now, finish digging the pit across the row. Where the wall of the pit is smeared by the shovel, pick away the smeared soil with a knife. A sheath knife with a fixed blade works best because it can't fold back on your fingers. A folding lock-blade also works, but you'll have to clean out the hinge.

"Examine the soil and look for sudden changes in moisture, color, texture and structure, which may indicate changes in density,” Ferrie says.

Select a plant at the edge of the pit, start at the base and, using your knife to pick away the soil, follow a root downward. "See if it penetrates the layers or if it turns and grows along one of them,” Ferrie says. "Leave the root undisturbed, and let it talk to you.”

When you find compacted layers, write down the information or enter it in a handheld computer. "If you don't record the data, you'll forget it by fall,” Ferrie warns. "I've seen farmers forget to take out layers because they failed to record where they were. All their scouting and digging was wasted.”

After scouting, think about what you can do to fix the problems you found. Prioritize fields into Groups A, B and C, in order of importance. "Prioritizing fields is very important because you may not have time to do vertical tillage in every field,” Ferrie cautions.

Prioritize fertilizer and, especially, lime applications to help ensure you get tillage accomplished on fields that need it. "If it takes a week for your dealer to get to you, consider ordering lime ahead of time and having him dump it in the field, so it's ready to apply as soon as they harvest,” Ferrie suggests. "You might also add some part-time help to start doing tillage while you are still harvesting.”

Knowing where your density problems are and how to fix them means you won't waste a minute next fall working for higher yields in 2010.


Let Tillage Records Guide Your Planting
Tillage records are essential to help you prioritize summer scouting for soil density problems. But they are just as important at planting time.

"Anytime you plan to no-till, you have to consider what tillage equipment you used and what the conditions were like the last time you worked the field,” says Farm Journal Field Agronomist Ken Ferrie.

"Last spring, some farmers were thinking about no-tilling continuous corn because they had not been able to till the previous fall.

"If they worked the field wet in the spring of 2008 and did not remove the compaction layer the previous fall, they would have been no-tilling on top of that compaction layer in 2009,” Ferrie explains.

If you know that you have serious density issues in a field because of tillage, Ferrie recommends you consider planting an early maturing soybean variety or wheat in that field. "Then you'll have time to fix the problem with vertical tillage after you harvest the crop,” he says.

If you are farming large acreages, you and your employees simply can't remember what tillage conditions were like in every field months or even a year later. "That makes tillage records extremely important,” Ferrie says. "But we find that very few farmers keep them.”


You can e-mail Darrell Smith at

To learn more about what a soil pit can teach you, visit Select the February 2009 issue to read "Dig for Higher Yields.”


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