There are still arguments pro and con on the value of deep or vertical tillage. Matt Rezac is on the pro side and credits vertical tillage for his stronger soybean and corn yields.
“With vertical tillage, we don't have any compaction and are able to take in moisture throughout the year,” says the Weston, NE grower.
Rezac is one of many growers who have had it with hardpan. The clay loam soil of the eastern Nebraska region, like other clay-based fields in many production areas, can present severe compaction problems. Bigger tractors and combines, not to mention grain carts, spray rigs or other equipment or trucks that cross fields help create compaction.
For some fields, the hardpan might as well be concrete. Moisture cannot break through. Neither can roots in search of nutrients deep in the soil.
Rezac farms in 30-in. rows in a no-till program. “For about seven years we rotated 30-in. corn with soybeans planted in 15-in. rows,” he says. “But when we heard about the benefits of vertical tillage, we switched the beans to 30 in. and we're seeing good results with it. We have better root development and yields are better.”
He uses a Blu-Jet ripper plow with straight shanks that penetrate about as deep as he wants. The ripper is run in late fall. “We always go deep enough to make sure compaction is broken up,” he says.
The nine-row plow requires a lot of horsepower to pull it, even when Rezac cuts back to a 5-shank set up.
“We use an 8400 John Deere front-wheel assist pushed to about 240 hp to pull it,” he says. “The process enables us to plant right over the till slots.”
Bean yields are in the high-50 to 60-bu. range. Corn yields are up to 150 bu. He credits much of his yield success to vertical tillage.
“The ability to break down compacted areas has really helped,” says Rezac. “I think we're seeing a better root mass with it.”
Paul Jasa, Extension engineer, University of Nebraska, says “slot ripping,” such as that used by Rezac, allows roots and water to penetrate into the soil, especially if the rows of the next crop follow the slots.
“Parabolic-shanked subsoilers heave the soil surface too much to allow slot planting of the next crop,” he points out. “Secondary tillage may be used in the spring to level the field before seeding. But subsoiled fields can redevelop a compacted layer if the loosened soil is worked when wet or if wheel traffic isn't controlled. Soil heaving and the need for secondary tillage to smooth the field can be reduced by using a coulter in front of a straight-legged subsoiler shank.”
Jodi DeJong-Hughes, Extension educator, University of Minnesota in Marshall, says vertical and deep tillage are synonymous. The need for and/or the depth of tillage vary from one region or state to another.
“In the Midwest, our soils are geologically young and well structured, so if you do the vertical tillage, make sure you don't drive on it afterward,” she says. “You may re-pack the soil down to the depth of the shank, especially in a moist soil.”
She says “studies are all over the board” on the value of vertical tillage in the Midwest. Results will vary, depending on the contour of a field, and of course, soil type and rainfall amounts and whether there is a compacted layer in the soil.
For a field having several valleys and hills, production on deep-tilled land can be up or down. “It has potential to help more on low-lying areas,” DeJong-Hughes says. “It's not as effective in the middle of the field and decreases yield on hilltops, where there isn't as much top soil and the tillage may dry out the soil.”
She points out two myths about compaction in more northern states; one that freeze-thaw cycles will alleviate much compaction and another that deep tillage or subsoiling will handle what the environment cannot.
“The belief that freeze-thaw cycles will loosen compacted soils may have developed years ago when compaction would have been relatively shallow because machinery weighed less, and grass and legumes were grown in the rotation,” she says. “Although soils in Minnesota are subject to annual freeze-thaw cycles and freeze to depths of 3 ft. or more, only the top 2-5 in. will experience more than one freeze-thaw cycle per year.”
Compaction caused by heavy axle loads on wet soils can extend to depths of 2 ft. or more. “Since this is well below the depth of normal tillage, the compaction is more likely to persist compared to shallow compaction that can be largely removed by tillage,” says DeJong-Hughes, stressing that compaction past 18 in. is not easily remedied.
Jasa says up to 85% of soil compaction damage happens during the first pass of the tires. “Grain carts should be following the same tracks as the combine,” he says. “A lot of producers think they should spread out compaction, but they are less likely to have compaction issues if they keep traffic controlled.
“It's important not to leave a track in the first place. To reduce compaction, avoid being out in the field when the soil is too wet and avoid tillage,” Jasa says. “If ruts are formed during harvest, tillage can break up compaction, but the soil must be dry to fracture compaction. However, tilling destroys soil structure and allows more tracks.”
Jasa says each shank in a subsoiler will require at least 20-30 PTO hp for deep tillage. DeJong-Hughes says up to 50 hp may be needed on more northern soils.
“Subsoiling depth should be 50% deeper than the compacted layer with shank spacing equal to the tillage depth for greatest shattering,” says Jasa. “However, tillage at this depth has a high power requirement which quadruples as tillage depth is doubled.
“An alternative is to operate the subsoiler 1-2 in. below the compaction layer with shank spacing equal to the row spacing. The compacted zone will be most shattered, in a V-shaped pattern, when the soil is dry to the tillage depth,” he adds.
Deep tillage is often best performed in late summer or fall, but can be done whenever the soil is dry enough. “To ensure that the compacted zone has been shattered properly, dig a hole and look for the V-shaped wedge of loosened soil,” says Jasa.
Some deep tillage tools may work better in some areas than others. In southern production areas, bent-leg paratills have shown strong results. They not only break the hardpan, they also lift the soil to enhance the root zone region. DeJong-Hughes says older, less structured soil in southern states have likely responded better to the paratill plows.
However, such tools haven't proven themselves better than straight-shanked subsoilers in some northern states, she says, meaning “you cannot promote one type of subsoiler for everyone.”
Consistently higher yields through deep tillage are hard to find in parts of the Midwest. “When they occur, they are variable and relatively small,” says DeJong-Hughes. “It's difficult to accurately predict the effects from subsoiling because of differences in soils, degree of subsoil compaction, soil moisture, future traffic, weather conditions and differences in the crop grown and in tillage methods.”
For sloped fields, a better tile drainage system might help produce better yield increases than deep tillage, she says.