Are your tillage practices justified by real crop responses?

“Individual farmer decisions about tillage system choice are often more motivated by traditions, prior experiences and what the neighbors are doing than by reliable research,” says Tony Vyn, Purdue University Extension agronomist and cropping systems specialist.

Vyn and other Midwest soil experts dispel some common tillage misconceptions.

Myth 1: The yield gap between conventional tillage and no-till always gets smaller over time

No-till crop performance compared to conventional tillage doesn’t always improve, Vyn says. In Purdue University’s long-term tillage research plots on silty clay loam soils, the yield penalty for no-till corn-after-corn hasn’t budged in nearly 40 years. The same is true in Iowa, says Antonio Mallarino, Iowa State University Extension agronomist. “In a normal year, we see 8 to 15 bu./acre less for no-till corn, no matter what we do.”

Nor can no-till overcome the yield reduction that comes with later planting, Vyn says. “There’s a belief that in a good no-till system, even if you have to wait to plant, yields will still be as good as those of a conventional farmer who planted earlier.

"That’s usually not true,” he says.

However, over the years, no-till performance does improve over conventional tillage “on soils with low organic matter or poor water infiltration because of susceptibility to crusting,” Vyn says.

Under no-till, “these soils get better with time. Residue cover and organic matter gains near the surface promote biological activity, better water infiltration and nutrient availability.”

Tillage costs can offset yield gains. Fall chisel plowing, for example, averages about $16/acre, according to the 2014 Iowa Farm Custom Rate Survey, and spring field cultivation runs another $14/acre.  

Myth 2: Full-width tillage is necessary for successful continuous corn production

Field trials throughout the Midwest show that strip-till provides the same yields as conventional tillage in both corn-soybean and continuous-corn rotations, says Dave Franzen, North Dakota State University soil scientist. Strip-till leaves about two-thirds of the soil surface undisturbed.

In North Dakota, for example, average corn yields over 11 site years were 154 bu./acre for strip-till and 148 bu./acre for conventional tillage. In Indiana, continuous-corn yields from 2001 to 2008 were 195 bu./acre for both fall chisel plow and strip-till.

“Strip-till is good for any soil type and texture, from high clay to sandy,” Franzen says. “It has the conservation benefits of no-till with the drydown and warming benefits of tillage. It makes ‘no-till’ in corn economically feasible in areas where it was not feasible before.”

But Vyn warns against expecting any tillage or residue management program to overcome the continuous-corn yield penalty.

“We have been working on this for 40 years and we have never seen the same yields in continuous-corn as in corn-after-soybeans,” he says.

Decades of field trials throughout the Corn Belt show average yield losses associated with corn-after-corn of 10% to 20%, says Joe Lauer, University of Wisconsin Extension corn agronomist. Losses can even be much greater in poor weather years. 

Myth 3: Fall chisel plowing avoids nutrient stratification

Stratification of immobile nutrients in the soil occurs with no-till and reduced tillage. The majority of phosphorus (P) and potassium (K) is concentrated in the top 3 or 4 in. of soil, regardless of the tillage method, according to research from Iowa State University and Purdue University.

“The common perception is that if I chisel plow after broadcasting phosphorus and potassium, I’ll mix nutrients to the depth of tillage,” Vyn says.

“But that doesn’t happen. Chisel plowing results in almost as much nutrient stratification as no-till.”

You should still soil sample down to 6 in., says Jodi DeJong-Hughes, a University of Minnesota Extension tillage specialist. “You do get some mixing of nutrients with chisel plow or disk ripping.”

Data from around the Corn Belt shows that phosphorus and potassium stratification is rarely a problem for crop growth, Mallarino says. Toward the west into the Great Plains, where there’s less rainfall, nutrient stratification may become an issue, however.

In Iowa, he says, crops respond about the same to broadcast, planter-banded or deep-banded phosphorus, regardless of tillage system.

The exception is with ridge-tilled corn, in which there is an advantage to inject or deep-band potassium into the ridge. In strip-till and no-till, there is also a small yield increase for deep-banding potassium, but that advantage is often offset by the extra cost to deep-band, he says.

From an environmental standpoint, no-till greatly reduces phosphorus loss to surface waters, Mallarino adds. “Injecting or subsurface-banding of phosphorus may not increase yield, but it reduces dissolved phosphorus loss compared to broadcast application.”

Myth 4: Shallow vertical tillage is the perfect compromise between no-till and conventional tillage

Shallow vertical tillage tools are made up of rows of vertical coulters designed to cut up residue at fast operating speeds and penetrate the top 2 or 3 inches of soil. Can this hot new form of tillage answer the shortcomings of both no-till and conventional tillage?

Slicing up corn residue helps to warm and dry the soil, widening the spring planting window, DeJong-Hughes says. The vertical coulters don’t lift or turn the soil, which lowers the risk of smearing in wet field conditions. But if your goal is to alleviate compaction in the upper soil layer, “shallow vertical tillage doesn’t really loosen soil much relative to no-till,” Vyn says. “If you want to loosen soil, strip-till is better.”

Although vertical tillage tools leave residue on the surface like no-till, the chopped stalks are not very well anchored, DeJong-Hughes says, so they can blow in the wind or wash away, reducing the conservation benefits.

And unlike more aggressive tillage methods, shallow vertical tillage is not intended to incorporate fertilizer or destroy weeds, such as marestale. “Shallow vertical tillage annoys it, but doesn’t control it,” says Bryan Young, Purdue University Extension weed scientist.

Likewise, using shallow vertical tillage tools to incorporate fertilizer “may not be enough” to prevent significant nutrient losses, says Marla Riekman, a soil management specialist with Manitoba Agriculture, Food and Rural Development.

In demonstration trials in Manitoba, one pass of a vertical tillage tool with wavy coulters left about 25% of broadcast urea on the surface. After a second pass, about 15% of the granules were still unincorporated, leaving nitrogen vulnerable to volatilization.

Implement companies are coming up with more aggressive “vertical” tillage tools that move soil sideways. Some have coulters with adjustable angles or shanks that can be raised and lowered on-the-go for variable tillage depths. This raises the risks of creating compaction zones and damaging soil structure in the top layer, DeJong-Hughes says.

On the other hand, “In Minnesota, we do a lot of disk-ripping at 12 inches,” she adds. By comparison, “lightening up tillage depth to 3 in. looks good.”

Myth 5: What’s right for my neighbor is right for me

“There’s no universal tillage solution,” says Francisco Arriaga, a University of Wisconsin Extension soil science specialist. The best choice “depends on your soil type, terrain, farming operation and personal preferences.”

Tim Kampmeier and his sons farm clay loam soils near Chokio, Minn. So that their heavy black soil dries out and warms up in the spring, “we need to dig it a little,” he says. However, wind erosion is a risk in western Minnesota’s flat, open landscape, so residue cover is important, he adds.

Normally, the Kampmeiers run a Sunflower disk ripper after harvest, but they would like to reduce tillage intensity and speed up fall field work. “We’re thinking maybe we don’t have to go as deep,” Kampmeier says.

This fall, they plan to try a Salford 5100 vertical tillage tool, which runs 2 to 5 in. deep and cuts up residue. In addition to effectiveness, equipment cost, durability and warranty will be key factors in their decision, along with “ease of operation and maintenance,” Kampmeier says.

BONUS TIP: Think Different

Tillage is not the only way to correct soil compaction.

In the Midwest, where many soils have high clay content, annual wetting and drying cycles create deep cracks that can repair compaction damage, says Dave Franzen, North Dakota State University soil scientist. These soils can “heal themselves” without tillage, he says. 

Biological “tillage” can also ease compaction, says Hal Weiser, soil specialist with the North Dakota Natural Resources Conservation Service in Jamestown. Cover crops such as cowpea, oilseed radish and lupine have “a deep taproot that can alleviate compaction.” Aggressively rooted annual rye is another great compaction buster, Weiser says. “Alfalfa, if you have a market, is also excellent.”

If you are considering deep tillage, “have an assessment first to see if you really do have compaction,” Weiser adds.