Fall Tillage Factors

Category: Fall Tillage |
New university studies on how different tillage methods impact soil warming and health help answer producer questions. By Marilyn Cummins

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As a soil physicist at North Dakota State University, Aaron Daigh gets a lot of questions from growers about tillage methods and residue management as they make their tillage plans for fall. “A lot of folks are concerned about ‘Is the ground going to dry out and warm up fast enough?’ with certain tillage methods. We get that question all the time,” Daigh says. “It is hard to get them warmed up because there is so much clay and so much water that’s held in that clay” in many fields. The other big question he gets is about how much residue to leave, remove from or incorporate in a field for optimum warming at planting and for long-term soil health.

Daigh, along with Jodi DeJong-Hughes, regional Extension educator in crops and soils for the University of Minnesota, set up tillage studies starting in 2014 to try to answer questions about what’s best for both soil and yields in their states. Daigh also calls on his experience working in Iowa and working with long-term studies across the Midwest.

The four-year studies are designed to monitor soil warming, moisture content and thermal properties under chisel plow, vertical tillage, strip till with shank, strip till with coulters and no-tillage in a corn/soybean rotation on various soils with a range in texture. Both Daigh and DeJong-Hughes have worked with continuous corn and no-till fields as well.

What Warms Up Best?

“The one thing that we’ve seen in our study, and if you look out at other studies that have been done across the world, they have one similarity,” Daigh says. “When it’s dry, it doesn’t matter what tillage you do. The soil is going to warm up and dry down the same.” But in a wet spring, the differences appear, and the research is revealing options that can warm and dry the soil without having to “turn it black.”

How soil warms and dries with different tilling operations. Average soil temperatures and volumetric moisture levels taken from thaw to crop canopy closure to a depth of 4 inches below four tillage systems near Wahpeton, North Dakota, and Fergus Falls, Minnesota, in 2015. Source: Aaron Daigh, North Dakota State University / Photo Illustrations: Jamie Cole

How soil warms and dries with different tilling operations. Average soil temperatures and volumetric moisture levels taken from thaw to crop canopy closure to a depth of 4 inches below four tillage systems near Wahpeton, North Dakota, and Fergus Falls, Minnesota, in 2015. Source: Aaron Daigh, North Dakota State University / Photo Illustrations: Jamie Cole

With strip tilling, using either a shank or a coulter, “You can do 22-inch or 30-inch rows with this 8-inch berm that’s nice and clear of residue, and in between you essentially have no-till” where the residue is concentrated, DeJong-Hughes says. “Our data shows that soil in the berm warms up as well as chisel-plowed ground, if not better,” as well as conserving soil moisture to help in dry springs. DeJong-Hughes also cites the advantage of being able to apply nutrients like phosphorus and potassium with a strip-tilling pass in the fall. She says leaving some cornstalks standing can help wick water down into the soil, and less tillage reduces crusting issues and water ponding. “Even building structure in clay soils will help it drain a lot faster, too,” she says. “If you seal up the soil, water doesn’t get in and then your tile doesn’t work.”

What About Residue Management?

About that other common question—residue management, Daigh says so much of the conversation is about leaving a certain percentage of the field covered with residue, such as the 30% soil surface coverage considered the minimum for conservation tillage. “Those numbers go well with being able to cut down on wind and water erosion, but that percentage of residue cover isn’t necessarily the best question when it comes to warming up,” he says. “It’s not the cover of the residue that matters most. Your ground can warm up very differently on two fields with the same amount of residue coverage; it’s just which one has a thicker residue layer.”

Daigh says that’s why they included shallow vertical tillage (1 to 2 inches deep, maximum) in the study, and they found the vertically tilled soil will warm up to a level closer to the chisel-plowed soil than to the no-till.

“It’s mainly just we’re slicing up and sizing the residue on top, and thinning it down, really,” he says. “It’s still a lot of residue coverage, but it does a really good job of warming up.” He likes it as an option for producers who have gone to zero-till in corn-on-corn rotations, building up good soil structure but possibly so much residue that yields start to decline.

Every four or five years, no-till growers of continuous corn can use shallow vertical till to “thin down that corn residue without breaking up any of that aggregation and soil health that you’ve built up over that last half-decade,” Daigh says.

Best Practices

In summary, considerations for tillage system decisions include the crop rotation on the field, amount of residue present, soil type and compaction levels, climate, weed pressure, use of cover crops, nutrient management needs, and the tillage equipment and labor available. Producers may decide to till in the fall to take the pressure off spring soil preparation, control weeds, address compaction and/or apply nutrients that need to be incorporated, DeJong-Hughes says.

“With tillage, we talk about reducing depth, reducing passes and making choices on a field-to-field basis, even still using the equipment they have,” she adds. “Even the chisel plow can become a reduced-till system, though. You can get it to leave a lot more residue than it leaves right now by changing out wide, twisted shanks for straight points that do some tillage, but still leave a lot of residue. It’s an affordable way to start to reduce tillage.

“There are a variety of tillage options available that can improve soil health,” DeJong-Hughes says. “I recommend that producers look at each field individually to find the best tillage practices to suit their soils and operations.”

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