|Prioritize fields to ensure tillage is completed on your most compacted areas.
Pinch-row compaction has existed since we first went to the field with a tractor. But today's heavy tractors and center-fill planters make it a growing concern, especially in wet springs like that of 2009, says Farm Journal Field Agronomist Ken Ferrie. It's just one more reason to adopt a tillage game plan this fall.
Pinch-row compaction results when soil next to a row is crushed by a heavy tractor wheel, restricting a root's growing space. "Two rows—one on each side of the wheel—can get hammered pretty hard,” Ferrie says. "The heavier the tractor and the wetter the ground, the more compaction you get.”
"We had never seen symptoms of pinch-row compaction caused by the planter before this year, but it was very noticeable in 2009,” says Aaron Gingerich of Lovington, Ill. "It looks like the streaks of stunted corn that sometimes show up in the wheel tracks you made where you field cultivated prior to planting,” he says. "But those streaks run across the field at an angle, while pinch-row compaction follows the row.
"The shortest row of corn was between the tractor's dual wheels, but the rows on each side were shorter, also,” Gingerich continues. "Six rows were affected with a 24-row planter.”
Gingerich dug up corn plants to examine the effect. "The roots were wider than the seed trench, but they were pinched on each side,” he says.
Yield hit. Hand-checking prior to harvest suggested yield loss in Gingerich's affected rows at 12 bu. to 15 bu. per acre, and much more where the compaction was aggravated by other problems, such as standing water.
Typically, corn rows affected by pinch-row compaction yield 7 bu. to 10 bu. per acre less than other rows in the field, Ferrie says. "If the compaction is severe, they can yield much less,” he adds.
Center-fill planters aggravate pinch-row compaction. "The weight of a full seed hopper, and starter fertilizer tanks if you have them, goes to the planter's carrying wheels—not to the depth wheels, as it does on planters with individual seed boxes,” Ferrie says. "That puts added weight on the tongue, which puts more weight on the tractor.”
The effect is severe enough to show up in normalized difference vegetation index (NDVI) images and to feel with a spade when you probe fields. "Pinch-row compaction is worse in tilled fields than in strip-till or no-till,” Ferrie says. "In conventional tillage, the ground is softer and the pinch-row compaction goes deeper.
"It's a problem in no-till and strip-till, too. You have to plant into those tracks next year. Pinch-row compaction can go deep enough that freezing and thawing may not help.
"There isn't much you can do to prevent pinch-row compaction. You can lighten the intensity by removing extra weight on the tractor and carrying less gallonage in the fertilizer tanks and less seed in the hopper—but most farmers don't want to do that,” Ferrie says. "If your planter has a center-fill hopper and individual row boxes, you could use only the boxes when running on wet soil. But mostly, pinch-row compaction is the price we pay for the convenience of center-fill planters. It just makes managing compaction that much more important.”
Three kinds of compaction. Some fields could be feeling the effect of three sources of compaction. "The effect is cumulative,” Ferrie says. "If soil had compaction from running combines and grain carts in wet conditions, that compaction is still there. If soil was worked wet last spring, more compaction was created.”
Regardless of what caused your compaction, you must get all the way underneath the compacted layer and lift it up. You need to do that without subjecting your soil to wind or water erosion or violating your highly erodible land conservation plan.
"The more aggressive your vertical-tillage tool, the more soil you fracture, the faster you will fix the problem,” Ferrie says. "But the more aggressive your tillage, the less residue you will leave on the surface. It's a trade-off.
"If you're working in soybean residue, you need to be especially sensitive. Use an in-line ripper or a chisel plow with straight points, rather than twisted shanks, to maintain as much surface residue as possible.”
In corn residue, you have more leeway. "With shallow compaction, a coulter chisel may be all you need,” Ferrie says. "If compaction is deep—if you tracked or rutted up the soil enough to require filling in the ruts last spring—you may need a disk ripper.”
Level the surface. Leave the field as level as possible for spring. That may require a leveling device behind the tillage tool—such as rolling baskets, leveling boards or tines—or a pass with a vertical-till secondary tillage tool.
|The effect of pinch-row compaction shows up as red streaks, indicating less plant vigor, in this NDVI image. The compaction was greatest in the wet areas.
"Our goal is not to leave soil level enough to plant but to have less than 3" peaks and valleys,” Ferrie explains. "That allows the field to dry more uniformly, whether you use horizontal or vertical tillage in the spring. If you have 6" peaks and valleys, the peak tends to be too dry and the valley too wet; if you run a tool deep enough to level the surface, you get into wet soil.
"Holding peaks and valleys to 3" or less permits a winter application of lime—and fertilizer, if runoff is not a concern—on frozen soil. In the spring, your custom applicator can apply a preplant herbicide before the field greens up because he won't have to wait for you to make a leveling pass, and you can incorporate the herbicide without streaking.”
Your compaction game plan should set priorities. If harvest runs late, you may not be able to vertically till every field, so you need to head for the trouble spots first. If you mapped compacted areas last summer and prioritized your fields for vertical tillage, you're ready to roll. If not, think about where you created ruts or observed large yield swings resulting from compaction as you harvested.
"Because time will be limited, consider organizing a tillage team from among your employees or hiring extra part-time help, so you can till right behind the combine,” Ferrie says.
Include fertilizer and lime application in your plan. "Order fertilizer and lime ahead of time so it will be ready to apply after harvest,” Ferrie advises.
Next spring, you want to level the field and create a uniform seedbed without putting in a compaction layer. "I recommend vertical tillage for leveling, especially if you are going back to no-till or strip-till after fixing a compaction problem, ” Ferrie says.
Compaction Versus Dense Layers
Although their effect on roots is the same, soil compaction and soil density are different. "Compaction is platy structure that develops when individual soil particles are compressed together, or flattened out, by wheel tracks or tillage,” says Farm Journal Associate Field Agronomist Missy Bauer. "Dense soil layers are created when air is pushed out from between soil particles. Dense layers can occur when soil is loosened by tillage while you assert downward pressure with a horizontal tillage tool.”
You can have soil compaction and dense soil layers, Bauer adds: "Horizontal tillage creates a density layer. Tillage when it's wet causes compaction.”
Compaction and dense soil layers also keep water from percolating into soil. A Farm Journal Corn College demonstration compared three soil treatments. In the first treatment, a disk ripper or chisel plow was followed by a harrow, so no density changes were created. There, 3" of water infiltrated in less than two hours.
In the second treatment, a soil finisher followed a disk, creating a denser layer of soil. There, water soaked into the top 3" of soil, but when it reached the denser layer it stopped infiltrating for a while. It took two to three hours for the water to move through the denser layer.
Worst of all was a moldboard plow followed by a soil finisher, which created a change in soil density (from the field cultivator) with a plow sole underneath (created by the moldboard plow). The soil was saturated for
22 hours before the water penetrated both barriers.
You can e-mail Darrell Smith at email@example.com.