September 4, 2020
As a result of the derecho windstorm on Aug. 10, millions of acres of corn in Iowa face challenging conditions with tangled stalks and the crop flattened in many fields. In some cases, farmers may not be able to harvest all the corn, as harvesting machinery can’t pick up all the stalks to feed them into the combine. The unharvestable areas of fields will require some type of fall management to ensure the future crop planted in that field next spring can achieve even emergence and normal early plant growth.
Combine headers contribute to crop residue management by sizing and distributing corn biomass. Even in no-till situations, where you plan to plant no-till next spring, a mechanical process will be needed this fall or next spring to reduce the size of the stalks and other crop residue laying on the field. Stalk chopping or some type of tillage will be needed in unharvestable fields to achieve the field conditions you’d normally expect after the combine pass.
To better understand the options available, Iowa State University ag engineer Ryan Bergman and ISU Extension agronomists Mark Licht, Meaghan Anderson and Angie Rieck-Hinz coordinated a field demonstration in a heavy downed cornfield in Story County. Their purpose was to evaluate the effectiveness of various options to process unharvestable stalks. These options ranged from vertical tillage tools to tandem disks to disk rippers. The ISU specialists documented each approach and gauged performance based on several factors including:
size reduction of corn crop residue
incorporation of residue into the soil
suitability for future planting applications including cover crops and spring-planted crops
The ISU team concluded that, ultimately, the right selection for each producer will be driven by the outcomes the farmer is trying to achieve and how these outcomes meet the needs of their crop production system.
Vertical tillage, low aggressiveness
Two low-aggressive types of vertical tillage tools were operated in the downed corn demonstration. Both were configured with gang angles of less than 5 degrees and used wavy coulter blades. Vertical tillage tools are designed with tight blade spacing that increases residue processing. The vertical tillage tool was operated at 10 mph.
Overall, the low-aggressive vertical tillage tool did an excellent job to knock down and process the corn residue. Of all the tillage tools, the low-aggressive vertical tillage looked most like what would be expected after a normal combine pass.
For soil disturbance and crop residue incorporation, the residue size was reduced but the low-gang vertical tillage created very little soil disturbance. For farmers who no-till, processing a downed cornfield with a low aggressive vertical tillage will maintain strong root engagement and will be most similar to how field conditions and residue would look after a typical harvest.
For future applications, to plant cover crops in this amount of crop residue a drill will be preferred over a broadcast seeder due to the thick mat of processed residue on the soil surface.
For no-till farming, row cleaners on the planter will be effective to move the residue next spring to enable a successful planting season.
Vertical tillage, high aggressiveness
An adjustable vertical tillage tool was configured for a 10-degree gang angle to increase the aggressiveness of the tool. At steeper gang angles, more aggressive incorporation of crop residue and soil is expected. Standard wavy coulter blades were used. The vertical tillage tool was operated at 10 mph.
The more aggressive gang angle did increase the amount of residue chopping. Corn residue in the high-aggressive vertical tillage situation was generally smaller in size and more consistently chopped than the low-aggressive vertical tillage setting.
Regarding soil disturbance and crop residue incorporation, the aggressive vertical tillage setting did engage the soil and created moderate mixing action of residue and soil. Overall, the amount of ground cover was still well above 50%, but the thickness of this crop residue on the soil surface was reduced due to the improved mixing action.
For future applications for using this tillage tool, consider using it to get the field ready for seeding cover crops. The increased soil mixing resulted in an excellent seedbed for broadcast seeding of cover crop seed and for drilled applications. The final field conditions could be successfully no-tilled next spring with appropriate row cleaners on a planter.
A tandem disk with notched front blades and smooth rear blades was also evaluated. This particular tandem disk is not used often, and the disks were not very sharp. Also, the weight of the disk was less than a newer series implement with less than 150 pounds per blade of downforce. This would represent a typical older disk that is likely available on many farms. The notched front blades normally would help with residue chopping. The disk was operated at 6 mph.
While the tandem disk did an effective job at laying the stalks down and crimping the crop residue, it was ineffective at cutting or chopping most of the residue. Many long stalk pieces, exceeding 24 inches, were still present after the tillage pass.
Three aspects are working against this particular tillage tool. First, the blades were dull. Second, the disk was not heavy enough to effectively cut the stalks. And third, the slower speed of the tool reduced the cutting action. Alternative tandem disks that are heavier and sharper would likely improve the outcome. Wavy blades would also increase the effectiveness of crop residue chopping.
Regarding soil disturbance and crop residue incorporation, minimal soil disturbance or residue incorporation occurred as the disk generally ran over the top of the crop mat. On occasion, the front notched disks would catch and engage soil to promote limited additional ground contact with the crop residue. After a second pass with the tandem disk, moderate incorporation of crop residue was achieved. For cover crops, a drill will be preferred over a broadcast seeder due to the thick mat of processed residue on the soil surface.
For no-till planting in the spring, it would be a challenge in this field condition due to the lengths of the remaining crop residue pieces. In particular, the long residue pieces will likely create challenges with row cleaners and cause some down time during the spring planting process.
A European-style high-speed disk with 20-inch-diameter notched blades in the front and rear was also demonstrated. High-speed disks provide improved cutting action due to their increased weight and speed. The high-speed disk in this trial provided 300 pounds per blade of downforce and was operated at 10 mph.
The high-speed disk did an effective job at reducing the size of crop residue pieces left on the field. Comparing all tools evaluated, the high-speed disk was ranked just behind the aggressive vertical tillage in terms of reducing the size of cornstalk pieces.
For soil disturbance and residue incorporation, the extra weight of the high-speed disk created good soil disturbance and effectively incorporated residue into the soil profile. Compared to the vertical tillage tool, the high-speed disk was more aggressive at mixing crop residue into the soil, and it buried residue into the 1- to 3-inch layer of topsoil, as opposed to vertical tillage that incorporated shallower in the soil.
For future applications, the high-speed disk would work well for fields where you want to seed cover crops. The increased soil mixing resulted in an excellent seedbed for broadcast seeding of cover crop seed or drilled applications. The final field conditions after using a high-speed disk this fall could be successfully no-tilled next spring with appropriate row cleaners mounted on a planter.
Modified disk ripper
Using a modified disk ripper was also evaluated in this trial, after removing the ripper shanks from the tool. With the ripper shanks attached, the tool would quickly plug up with cornstalks in these challenging conditions.
For this trial, the remaining disks were spaced 18 inches apart and individually mounted which increased the flow of crop residue and prevented plugging. Adjustments were made to the rear-closing disks to moderately level the field, although the final conditions were significantly more uneven compared to the other tools evaluated. The modified disk ripper was operated at 6 mph.
The front disks reduced the size of the crop residue, but the wider spacing of the disks compared to other tools in this demonstration resulted in less consistency in the residue size and left generally longer residue pieces than other tools.
Regarding soil disturbance and crop residue incorporation, the modified disk ripper achieved the highest level of soil incorporation and mixing of the corn residue. The ground cover in many areas of the field was less than 50% after using the modified disk ripper. Regarding future applications for using this tool, it would work well for getting the ground reader for seeding cover crops. Broadcast seeding or drilling will be suitable to establish a fall ground cover.
However, due to the aggressive nature of this tool, a subsequent pass in the spring will be required to level the soil surface prior to planting.
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