Ken Ferrie, Farm Journal Field Agronomist, recently fielded several questions from farmers during a virtual agronomic forum to help reset how they think about tillage, soil structure and long-term crop performance.
Following is the first question, which came in from a farmer in northeast South Dakota. The grower explains that some of his acres were disk-ripped last fall while others were chisel plowed. This spring, he plans to use either a high-speed disk or a VT super coulter to finish and ready the seedbed in those fields. He asks Ferrie which tool would be the best one to use.
Start By Assessing Fall Tillage Results
If the goal is to go with vertical tillage this spring, Ferrie advises the farmer to first confirm that his fall tillage achieved full-width shatter in the top 4" to 6" of soil.
He advises the farmer on how to go about the process of evaluation:
1. Raise the front cutters on the fall tool so residue can still flow but so the blades aren’t doing most of the tillage.
2. Then, dig behind the implement and look for shattering across the full width of the machine, 4 to 6 inches deep.
3. Once full-width shatter is verified, lower the cutters only enough to hit the residue level you want on top, not to drive the tillage.
He offers a practical rule of thumb: tillage depth ≈ half the shank spacing.
- On a chisel plow at 14” to 16" spacing, that means running 7” to 8" deep, which is very achievable, Ferrie says.
- On a disk ripper at 30" spacing, that would require 15" deep tillage—and is where most farms hit the wall on horsepower or traction, he notes.
Ferrie points out that many disk rippers were built for horizontal systems, where columns of untilled soil are left from the surface down. In a horizontal program, a spring horizontal pass shears off those columns and smooths everything for planting.
Why Tool Choice Depends On Soil Structure
This is where the tool decision becomes critical. Ferrie explains:
- The VT super coulter “levels from the top” but does not knock out those vertical columns of untilled soil left by horizontal fall tools.
- If the columns remain, they create a rough ride and uneven crop development: Corn over shattered, well-structured soil grows faster. Corn rooted in intact, dense columns lags behind.
Ferrie offers the farmer a simple in-field test for evaluation purposes: drive a pickup crossways over the fields where fall tillage was done.
“If the pickup bounces hard, and you feel it in the dash and your seat, you do not have full-width shatter—columns are still intact. In that case, use the high-speed disk to shear those columns horizontally,” Ferrie advises.
If the ride feels “soft, squishy, and smooth,” with no bouncing, you’re likely looking at good full-width shatter. Under those conditions, Ferrie advises going with the VT super coulter, because the underlying soil structure is already fairly consistent.
Check out Ferrie’s latest Boots In The Field podcast to learn his answer to these two additional questions:
- Does vertical tillage on wet soil create a drastic density layer?
- If I don’t put ‘gang angle’ on my vertical harrow, I can’t get the weeds out. How can I manage weeds?”
Get Ferrie’s insightful and detailed answers to those questions here:
