Yields take root when plants are given a chance to build the biggest and best transportation system to ferry nutrients and water quickly and efficiently. Roots are roads to top yields. 

The best genetics, a perfect fertility program and an optimum herbicide regimen can't overcome the fundamental need for robust roots. That's why it is crucial to manage soil density to construct the best roots possible. 

Yield robbers. Soil density problems undermine yields for millions of fields each year by changing the way roots, water and oxygen move through the soil. And because the yield-robbing conditions are underground, they often go unnoticed. 

To illustrate the importance of uniform soil density and help map a route to better yields, FARM JOURNAL launched an ambitious, multiyear project in 1996. Hosted by McLaughlin-Dooley Farms near Leroy, Ill., the effort takes in 500 acres in a corn-soybean rotation. The acres include a variety of soil types, ranging from light silt loams to heavy clay loams. 

The range of soil types is significant as soil properties have a baseline impact on density. Types of tillage, timing of tillage, flotation for equipment and Mother Nature are also key factors. Weather, of course, often determines how important the other factors become. A steady supply of moisture can mask the impact of tillage layers or compaction. Likewise, a short supply can amplify the effect of tillage layers and other stresses. 

Soil density refers to the amount of pore space between soil particles. The finer the particle (such as clay), the tighter the space between the particles. Yet space does exist. 

Roots work effectively in almost any soil type or condition. What they can't handle is a sudden change in soil density. As roots begin to grow, they size themselves to the porosity of the soil around them. Root diameter has a direct correlation to soil conditions and genetics, not yield potential or plant health. 

Corn roots in a sandy soil are bigger in diameter than corn roots from the same hybrid in a clay loam. Chances are that the corn in the clay loam will outyield the corn on sandy soil - even though the root diameter is smaller. 

Healthy roots are white, round and grow downward at a 35° angle, starting from the crown on a corn plant or the taproots on a soybean plant. Roots that look tan to gray in color or are flat, and roots that hit a roadblock and run laterally, often indicate density problems. That's one reason soil density can be confused with compaction. 

Compaction is the most widely recognized source of soil density changes. It's not the only one, though. Tillage, naturally occurring horizon changes and dry-weather-induced collapsed clay soils are a few of the other causes of sudden density changes that do not involve compaction. 

The most dramatic shifts in soil density occur in clay or clay loam soils. This occurs because clay particles are made of lattices with water between the lattices. When water is drawn out during periods of hot, dry weather, the soil collapses. 

Rules of the road. Each of the fields in the project was divided down the middle. McLaughlin-Dooley employees farm one side using a tillage system typical on many Midwestern farms. They make one pass with a field cultivator in the spring and plant into soybean stubble. They fall chisel cornstalks, make a pass or two in the spring, and plant. 

FARM JOURNAL field agronomist Ken Ferrie takes charge of the other side, using a systems approach that pays careful attention to how each decision and operation affects the soil. McLaughlin-Dooley performs the work, but at Ferrie's direction. 

At the beginning of the project, each field was chosen carefully, making sure both sides have equal yield potential and that yield-limiting factors such as fertility were removed. Each field was soil tested by soil type, checked for soybean cyst nematode levels and mapped with a Global Positioning System (GPS). 

Pits were dug on both sides of the fields - to determine soil density conditions by the soil profile and tracking the routes taken by roots in the previous crop year. To eliminate existing problems and make sure soil density was uniform at the beginning of the project, each field was deep ripped. 

The soybean stubble was ripped twice, from two directions. The cornstalks were ripped once and combination chiseled from the opposite direction. (It took more than one pass to eliminate density problems). 

All the fields had compaction - ranging from 9" to 13" deep - as a primary soil density problem. Deel ripping below the density change was used to eliminate it. 

Two near-identical sets of equipment are used to plant and harvest the crops, with a chief difference - flotation. When possible, equipment used on the uniform-density side field employs rubber tracks while the while machinery on the McLaughlin-Dooley side rides on tires. 

Caterpillar supplied two tracked tractors, a Challenger 45 and a Challenger 85E, as well as a grain cart on rubber belts. Both Claas of America and Caterpillar have supplied tracked combines to the project. 

Post herbicide and fertility programs are the same for both sides of the field. Also, both sides are scouted for corn borer and diseases, and then treated equally. 

Ferrie evaluates the plots throughout the growing season and coti the yields by soil type. 

Yield signs. Even though the site of the McLaughlin-Dooley farm has been blessed with good growing conditions since the project began, the plots document a yield advantage to maintaining uniform soil density. Final data will be assembled after the 2000 season, but some trends are emerging in certain soil types. 

"While some lighter soil types have not shown a response, I've been surprised to see some clear yield differences," says Ferrie. 

"We haven't had the kind of weather extremes that really test the importance of uniform soil density." 

As expected, the payoff seems strongest in heavier soils. The higher the clay content, the bigger the impact. "A couple of corn fields have shown a consistent 5-bu. to 7-bu. advantage to keeping uniform density," says Ferrie. "We've also seen a 3-bu. difference in soybeans for 1999." 

Those yield boosts came in the heavy clay loam fields where soils were saturated in the spring. 

Fields like that are what motivated McLaughlin-Dooley Farms to get involved in the project. "It seemed like we needed to be doing something to pull better yields off some of our fields," says Mike McLaughlin, who farms with partners Steve McLaughlin (his brother), Cole Dooley and employee Derek Strunk. 

What we found. In addition to yields, other differences are showing up. One is pH. Even though the pH was even on both sides of all the plot fields at the beginning of the project, a couple of fields are now out of sync. For example, soil tests of one field last fall show that the McLaughlin-Dooley side needs lime on two-thirds of the area. None is needed on the uniform-density side. 

"That was one of the biggest surprises in 1999," says Ferrie. "There hasn't been a yield difference large enough to trigger it. The better percolation on the uniform-density side helps the soil buffer itself." 

A second sign pointing to soil density differences are the maps produced by the Profiler 3000 from Veris Technologies, Inc. The mobile hydraulic penetrometer takes continuous readings to a depth of 36 " in about 40 seconds. It records the numbers in 1" increments along with GPS position, and later maps the resistance in pounds per square inch (psi).

The machine also is equipped with an electro-conductivity (EC) tip to take EC readings at the same time. 

"The Profiler has the ability to rapidly characterize the soil density and textural changes in the top 3"," says Eric Lund, Veris Technologies. "It can help you identify areas of superior performance as well as problem areas. It also can help troubleshoot places where there are yield variations." 

Lund used a prototype machine at the test plots and produced maps that clearly show what you can feel with a hand-held penetrometer in the field. 

"The psi difference shows how the density changes in the soil profile," says Ferrie. "The maps visualize and verify what we're seeing in the fields [on the McLaughlin-Dooley side]. [The soil profile] also shows a sudden density change 4" below the surface where the field cultivator ran." 

The field cultivator created a horizontal layer by fluffing the upper 4" of the soil, which drastically changed the soil density. This allows water to penetrate the soil faster than it can drain through the rest of the soil. 

"It allowed for large root diameters, but created such a sudden density change that the roots couldn't adjust quickly enough," says Ferrie. 

The Veris yield results are supported by the roots dug in the field. Each season, Ferrie digs up several plants growing on both sides of the field. The roots - by their size and the direction they travel - illustrate the differences in uniform density. 

Throughout the project, Ferrie has concentrated on increasing tillage in bean stubble (using an in-line ripper) and decreasing tillage in cornstalks. 

"We want to be in position where our spring tillage doesn't create a sudden density change," he says. "We either no-till drill beans or drill them into stalks ripped the previous fall. We gauge what to do by weather and soil density conditions." 

One management tool that has made a significant difference for Ferrie's uniform-density side is the introduction of a new-style tillage tool in the spring. The McFarlane chopper harrow replaces the field cultivator on Ferrie's side. (McLaughlin-Dooley continue with their regular program using a field cultivator). 

The machine levels from the surface, without putting in a horizontal tillage layer that can create a yield-reducing density change. The chopper harrow, which uses ranks of reels, levels and dries the field ahead of the planter. Meant to operate at 8 mph to 10 mph, the harrow uses spiral reels to chop residue and loosen the soil without significantly disturbing it. 

A five-bar flexible spike tooth harrow follows the reels, stirring, leveling and firming the soil. Finally, a spreader board feathers residue while leveling the field a bit more. 

Using the McFarlane tool leaves a seedbed rich with residue, more like no-till conditions than where a field cultivator has run. That prompted us to add Yetter Residue Manager Coulter Combinations to the front of the planter. The coulter supplies a touch of tillage and the tines sweep residue aside. 

"The planters had residue removers to begin with, but the coulter improved stands after we reduced the amount of spring tillage we're doing," says Ferrie. "It wouldn't take much of a seed-to-soil contact problem to sabotage yields and overtake the advantage of uniform soil density." 

The project culminates with the 2000 harvest. Look for our wrap-up article on the project in spring 2001. 

Meanwhile, for more information, refer to these earlier FARM JOURNAL articles: "Manage Down Under for Yields Up Top," December 1996; "Down to the Root," Mid-January 1997; "In the Root Zone," April 1998; and "Better Roots, Better Yields," March 1999. 

Editor's Note: For additional information on maintaining uniform soil density, watch "Rooting for Higher Yields, " a FARM JOURNAL video workshop featuring field agronomist Ken Ferrie. You can order the $39 video by calling tollfree (877)526-8464. 

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