If you paid attention in science class, you know Newton’s third law states that for every action, there is an equal and opposite reaction. That law, says Levi Powell, also applies to the row unit on your planter.
“Everything that is ground-engaging and putting force on the soil means the soil is putting equal and opposite force back on the row unit,” says Powell, a technical project specialist at Iowa State University. “You have to counteract those forces, which is what planter downforce systems are designed to do.”
An integral part of the planter ecosystem, downforce is a topic Powell and his colleagues field the most questions about when they’re out on the Extension trail meeting with farmers.
Downforce margin or gauge wheel load is critical to ensuring seed depth is consistent throughout the field. This helps establish uniform germination and emergence, which can ultimately affect yield.
Settings for downforce are highly variable and need to be monitored often as soils and moisture conditions change going across the field and from field to field.
To understand how to set downforce margin, Powell says it is important growers have a general understanding of the forces acting on the planter.
First is the downward force exerted by the row unit’s inherent weight. This will vary based on the model of the row unit but will typically range between 150 and 200 pounds.
While Powell says this weight alone is typically enough in normal conditions to allow the opening discs to penetrate the soil to the necessary depth for planting, it’s going to take a lot more weight in a dry year.
“Despite the color of your planter, what’s going on underneath it is still the same. When you set your downforce margin, you are setting the amount of load you want to be carried on the gauge wheels at any given time as you travel through the field. Depending on your brand of planter, the gauge wheel load metric is referred to differently and may be called margin, downforce, or gauge wheel load,” he explains. “If you’re struggling with downforce, you’re probably going to notice it on your end wings. If you don’t have enough weight out there, those row units are going to feel it first.”
Powell outlines the three jobs downforce is tasked with and why it’s important for growers to pay attention to each.
Task No. 1: Maintain ground contact.
A certain amount of weight or downforce is required to push the seed opener into the soil before the gauge wheel encounters the surface. “You need to keep that row unit in the ground,” Powell says.
In the cab, downforce margin or gauge wheel load can be adjusted to maintain the ground contact percentage at an average of 97% to 100%. If ground contact falls below this range, it’s an indication the planter is struggling to maintain consistent planting depth. If the ground contact percentage maintains 100% and doesn’t fluctuate, that could mean there is too much downforce.
Task No. 2: Set the soil structure.
This is the part Powell says farmers tend to gloss over, but he emphasizes that it’s just as important as ensuring the row unit maintains ground contact.
“If the row unit is hitting the ground, farmers feel they don’t need to look any further because they think they’re doing a good job,” he says. “They also need to care about what’s being carried on the gauge wheel, because the amount of gauge wheel load is what sets the desired soil structure.”
Acting as little steam rollers, gauge wheels press out air pockets and densify the soil, setting the soil structure around the furrow.
“This is the first soil roots will see as they start to come out,” Powell explains. “We need those roots to go into a nice home. If we’ve got large air pockets and the roots are coming into that zone, they’ll still grow, but they’re going to struggle more than neighboring plants and cause uneven emergence.”
How much force does it take to get that soil structure set? Powell says you need this to be adequate for the conditions, but not in excess.
“In a dry year, it can be particularly difficult to set the soil structure well. If there’s moisture, it’s easier to set that soil structure because it doesn’t take as much force,” he says. “This is what you must determine when you’re in the field planting. No matter what color planter you’re running, that number and the math on how it acts are the same.”
While each downforce system comes with preset numbers, he says those should be considered a starting point. Growers should determine the number that works best for their soil conditions, Powell says. “You are not locked into those preset numbers: 90% of the time, growers don’t have enough gauge wheel load because they’re concerned about sidewall compaction, so they will go too far in the other direction to ensure that doesn’t happen. You need to flirt with that line.”
To check seed depth, Powell says most farmers get out of the cab and go about 30 or 40 feet behind the planter and start digging the seed to see what it looks like. He suggests you stop at the row unit first.
“With the planter in the ground, look in the area between the gauge wheel and closing system where the furrow is still open; see what your furrow looks like,” he says. “If there’s a bunch of loose dirt crumbling around it, you probably need more gauge wheel load. You want that furrow to hold its shape. There should be no air pockets in the sidewalls. You need to densify, but not compact, that soil next to the furrow and really set the structure well, so the closing wheel can come through and do a good job of tamping down the soil around the seed.”
Task No. 3: Establish furrow structure.
As you cut that V in the ground to place the seed, it needs to hold together long enough for the closing system to come through and do its job. Ideally, you want the furrow to close from the bottom up, putting firm moist soil around the seed.
If the furrow is falling apart before you close it, loose dry soil can fall in from the top, reducing the seed-to-soil contact potential. “In 2021, farmers couldn’t hold a furrow together to save their lives because there was no moisture in the top couple inches of the soil,” Powell says. “In those conditions, you’ve got to do the best you can, and it’s going to take some downforce to get you there.”
Depending on your brand of planter, the gauge wheel load metric is referred to differently. It may be called downforce, margin, or gauge wheel load.