New tools make it easier to remove shallow and deep water impediments
Soil compaction and density changes instigate undue stress on plants by interrupting water movement and
ultimately reducing yield. Once you locate impediments to water movement at or beneath the soil surface, it’s time to devise a plan to fix them.
“The toolbox of options ranges from deep aggressive tillage to cover crops,” says Farm Journal Field Agronomist Ken Ferrie. “Many of today’s tools were not available 10 years ago.”
Your choice of barrier-removing tools is influenced by the location of the impediment (at the surface, 3" to 5" deep or 6" to 10" deep), your cropping system, your soil type and your geographic location.
“Many impediments require multiple years of treatment before they are completely removed,” Ferrie notes. “It’s also important that whatever you do to remove impediments doesn’t prevent planting into a warm, moist, mellow seedbed the following spring. If you wind up with a poor stand of corn, fixing the density problem won’t help much.”
Drawing upon actual field conditions, Ferrie details the following six scenarios and offers solutions:
Scenario 1: Poor surface structure or the natural texture of your soil causes poor water infiltration. In this case, Ferrie advises planting covercrops to improve aggregate stability and adopt a reduced tillage system (no-till, strip-till or light vertical tillage) to build and maintain a healthier surface structure.
Scenario 2: A dense layer 6" to 10" deep inhibits water movement in a corn/soybean rotation. There’s little risk of soil erosion, and the farmer has no experience with no-till. With deep impediments, Ferrie advises running an in-line ripper in the fall on soybean stubble deep enough to completely shatter the soil all the way across the implement, while maximizing surface residue cover. Even if soil erosion is not a threat, residue on the surface prevents crusting and guards against wind erosion.
“Your ripper must be in-line, not staggered,” Ferrie continues. “The shank spacing determines the depth at which you can get uniform fracturing of the soil. As a rule of thumb, the depth of shattering will be half the distance of the shank spacing. So if shanks are on 30" centers, the machine will till 14" to 15" deep.”
Soil must be lifted uniformly from shank to shank, so it flows through the implement like a wave. You can set the tool by visual inspection. If it runs too shallow, it will be very aggressive around the shank, but there will be no effect between the shanks, Ferrie describes. Adjust the depth until shattering is uniform all the way across.
“After shattering soil, leave the surface as level as possible so the soil will dry uniformly in the spring and apply a burndown herbicide application for weed control,” Ferrie adds.
The standard for level soil is less than 3" peaks and valleys after the soil overwinters. “This is not too difficult to achieve in silt loam to loamy soils,” Ferrie says. “But in heavier clay loam soils, you might need additional coulters in front of the ripper. If shanks are on 30" centers, put the coulters on 15" centers, and run them hub-deep. On the rear of your tool, use an aggressive rolling leveling device. It should act as a depth stop, tucking soil back in after it is fractured.”
If you anticipate more than 3" peaks and valleys after overwintering, run a vertical harrow in the fall to level the surface while maintaining residue cover. Avoid tools such as soil finishers or disks that bury residue and leave the soil surface exposed.
Maintaining a healthy soil structure, free of water impediments, will require management changes. “Vertical tillage tools don’t remove weeds like soil finishers, field cultivators or disks,” Ferrie points out. “To avoid weed problems, you must adopt a weed control program similar to no-till.”
If you have been planting into a conventional tilled seedbed, equip your planter to manage residue. “Row cleaners are very important,” Ferrie says. “Depending on your soil type, you might need a combination of row cleaners and coulters.”
You also might need to adjust your nitrogen fertilizer program. “In the spring, apply nitrogen and herbicides, make one vertical harrow pass and plant,” Ferrie says. “If you surface-apply your nitrogen, it’s essential to either lightly incorporate it with the vertical harrow or apply a urease inhibitor to protect it from volatilizing.”
Completely removing impediments in this scenario will probably take six years, ripping the soil every two years, ahead of corn. In the second year, the field will be planted to soybeans, preferably no-till, Ferrie advises. “If you’re uncomfortable with no-till, work the corn residue once with a vertical harrow to size the residue and warm the soil a little before planting,” he adds.
In the third year, when the field goes back to corn, it’s time to rip again. “Experience has shown you are doing good to get rid of one-third of a dense layer with each ripping (although the first one makes the biggest difference),” Ferrie says. “A crisscross pattern is best. So if you ripped at an angle to the right of the rows the first year, rip at an angle to the left the next time.”
After the third ripping, the deep dense layer should be gone. “By this time, you will be comfortable with your new nitrogen and herbicide programs,” Ferrie says. “It’s a great time to transition into a full no-till program. Make your last in-line ripper pass with the rows to leave the field smoother for your transition into no-till.”
If you’re uncomfortable with no-till, your growing season is too short or your soil needs drainage, strip-till ahead of corn. “You can use a knifed strip-till bar in the fall or a zone-warming coulter bar in the spring,” Ferrie says.
“Or you can continue to in-line rip ahead of corn and no-till your soybeans into cornstalks. By deep ripping only one out of every two years, the soil won’t get as soft and spongy. You will still fight pinch rows and wheel track compaction as you did in tilled soil, but it won’t be as bad,” he says.
Scenario 3: Similar to scenario 2, this corn/soybean rotation has a dense soil layer 6" to 10" deep that limits water movement. In this case, the sloping land is subject to erosion.
“Because we are dealing with a deep layer and erosion is a concern, correct it with deep-rooted cover crops, such as cereal rye, annual ryegrass or radishes, rather than tillage,” Ferrie says. “To reach a water-impeding layer that deep, the cover crop must grow to a substantial size. Your ability to use cover crops will be influenced by where you live and the maturity range of your corn crop.
After you have removed density layers created by horizontal tillage implements, switch to vertical tillage tools to avoid putting them back in. If possible, convert to a no-till or strip-till regimen.
“But trying to fix a serious deep impediment with cover crops might take too long and be too expensive compared to tillage. If we use tillage, the preferred option is a deep disk-ripper that can reach below the 10" layer.
“These tools require enough horsepower to pull them at the depth of the layer. Doing shallow tillage above the impediment will increase the risk of erosion, which might be worse than leaving the impediment alone. Because you are doing deep, aggressive tillage, do it in cornstalks ahead of soybeans to reduce the erosion hazard.”
Try to leave the field level and avoid burying all the residue. “This is a function of the levelling mechanism on the rear of the tool and the depth and angle of the cutting disks in front,” Ferrie says. “You may need to make a vertical harrow pass after disk-ripping to level the surface. As you set up your harrow, be conscious of how much residue you want to maintain on the surface.
“In the spring, if the field is level enough, apply a burndown herbicide and then plant soybeans. If it is not level, apply burndown and make one vertical harrow pass before planting.”
The following year, no-till the corn. “If you’re not comfortable with no-till, make one light pass with a vertical harrow to size the residue,” Ferrie says. Equip your planter and manage your nitrogen as you would for no-till.
Because disk rippers are aggressive, you probably can remove dense layers in two passes, making this a four-year plan with tillage every other year. “Change the angle of tillage each year,” Ferrie says. “After four years, if you are comfortable with no-till and your soils are suited for it, transition to full no-till or use strip-till for corn and no-till for soybeans. You might have to contour the strips on erosive areas.
“If you’re not comfortable with complete no-till, use a shallower chisel plow on cornstalks every other year and no-till the corn. This will reduce the amount of surface residue.”
If some areas are too steep for tillage, you might have to solely depend on cover crops, while ripping less erosive parts of the field.
Scenario 4: Continuous corn creates a high-residue environment, and a deep dense soil layer restricts water movement. The first year, run a disk ripper deep enough to get under the dense layer, Ferrie says. To keep the soil from getting too soft, use a shallow chisel plow in year two. In year three, run the disk ripper again at a different angle.
“After removing the dense layer, switch to a shallow chisel plow or a hybrid chisel (narrower shank spacing and plenty of clearance for residue),” Ferrie advises. “If the surface is not level after chiseling, make one vertical harrow pass in the fall followed by a second vertical harrow pass in the spring. It probably will require two passes to level this kind of ground for corn planting. If you prefer, you can make both passes in the spring.
Shallow layers of dense soil, 4" to 5" deep, are more common than deeper layers. They typically are created by horizontal tillage tools such as soil finishers and disks, Ferrie says.
Scenario 5: A corn/soybean rotation with a shallow dense layer. “Use a shallow chisel plow or hybrid chisel on cornstalks,” Ferrie advises. “For a layer 6" deep, you’ll need a tool that goes 7" to 8" deep to get below it.”
Cover crops, such as radishes and cereal rye or annual ryegrass, have more impact on shallow layers than on deep ones. “But because shallow layers cost more in yield than deep layers, you might want to be more aggressive and use tillage,” Ferrie says.
“If it looks like you are going to wind up with more than 3" peaks and valleys after overwintering, level the surface with a vertical harrow in the fall, so you can apply herbicides in the spring,” Ferrie says. “If necessary, make one more vertical harrow pass in the spring and then plant soybeans. Follow that with no-till corn. If you’re not comfortable with no-till, make one pass in the spring with a vertical harrow to size residue and warm the soil, or go to strip-till.”
If the layer is only 4" deep, you can probably remove it with one tillage pass,” Ferrie says. “If it is 6" or 7" deep, you might need two passes over four years.”
Scenario 6: Continuous corn with a shallow dense layer. “Use a chisel plow or a hybrid chisel, and level the surface in the fall,” Ferrie advises. “In continuous corn, you probably will need two levelling passes—one in the fall and one in the spring.”
Because you’re incorporating lots of residue into the planting zone, your planter must be equipped to deal with it, and you must be conscious of the carbon penalty (an influx of residue stimulates microbial populations, which temporarily tie up nitrogen, making it unavailable to young corn plants). “You will need to change your nitrogen regimen,” Ferrie says. “Repeat this program until the impediment is removed.”
Don’t substitute a disk-ripper for a chisel plow or hybrid chisel.“Due to the shank configuration of disk rippers, if you run them shallow, you won’t get complete shattering of the soil,” Ferrie explains. “That will cause seedbed problems when you plant behind a vertical-till harrow. If you run a disk-ripper deep, it will burn up soil carbon and make the soil soft.”
As you proceed through this two-,four- or six-year journey of impediment removal, push penetrometers and dig soil pits to check progress. Make sure roots are growing downward rather than sideways across dense layers.
“Signs of improved water movement will include increased tile flow, less standing water, fewer seedling blights and fewer drought issues,” Ferrie says. “Your eyes will tell you when you have fully transitioned from a dense layer to a healthy vertical growing environment.”
Prevent Water Barriers From Returning
Once you remove a water-impeding dense soil layer,your challenge is to keep it from reappearing. “If you’re in a corn/soybean rotation farming well-drained, healthy soil, the ideal way to do that is with no-till,” says Farm Journal Field Agronomist Ken Ferrie. “If old-crop residue builds up or you want to dry soil faster, you can run a vertical harrow as needed.”
But what if you farm in a cool climate with a short growing season or your soil is poorly drained? “In years past, if 70% of a field was ready to plant while 30% was still too wet, you would run a finishing tool before planting corn,” Ferrie says. “But that no longer is an option because it will put in a dense soil layer.
“In this situation, strip-till might be the answer,” he adds. “It warms and dries soil for planting like horizontal tillage, with the soil conservation and health-building benefits of no-till.”
You can strip-till in the fall or spring. With fall strip-till, you run knives to build a mound to plant into the following spring. “In some areas, you can apply anhydrous ammonia as you strip-till in the fall,” Ferrie says. “But the most important task with strip-till is to build a seedbed. In some areas, the best time to strip-till is not the best time to apply ammonia; in that case, apply a different form of nitrogen next spring or sidedress your ammonia.”
Never force a strip-till bar through wet soil. “If you slab the soil instead of building a mound, it will turn out worse than not strip-tilling at all,” Ferrie says.
“Sometimes spring weather might require you to ‘freshen’ strips using a strip-till bar equipped with coulters,” Ferrie says. “Or you can run a vertical harrow to speed drying and use auto-guidance to steer your planter on the strips.”
With fall strip-till, you might need to contour across sloping land to prevent soil erosion. “With spring strip-till, when you want to warm the soil for planting, run coulters rather than knives,” Ferrie says. “In the spring, you might want to band fertilizer as you strip-till to reduce weight on your planter.”
Always follow strip-till corn with no-till soybeans, Ferrie concludes.
Impediment Removal Tools
Barriers to water movement can occur at the surface, 3" to 5" deep or 6" to 10" deep:
- For infiltration problems resulting from poor surface soil structure or the soil’s natural texture, plant cover crops to build aggregate stability and reduce tillage.
- To fix bulk density issues 3" to 5" beneath the soil surface, chisel shallowly, plant deep-rooted cover crops and strip-till, or combine two or three of those practices.
- If your water-impeding layer is 6" to 10" deep, turn to deeper tools, such as in-line rippers, disk rippers and hybrid chisels; base your choice on conditions in each field.
As a limited yet vital input, water demands a high level of diligence. The Water Management series details how farmers can manage earth’s most valuable resource to boost yields and profit.