When farmers ask Matt Duesterhaus whether they can reduce soybean planting populations and still produce high yields, his brief answer is it depends on the specific cards in their hand.
“Some of those cards are dealt by Mother Nature, and others the farmers get to draw,” says Duesterhaus, a field agronomist with Crop-Tech Consulting, Inc., based in Illinois. “Growers holding all the right cards with regard to their soil, weather conditions, seed quality and weed pressure have advantages that allow them to lower populations more readily than those that don’t.”
He offers seven additional considerations for determining soybean populations for 2023.
1. Evaluate weed pressure by field. Duesterhaus says weed pressure is his No. 1 consideration for whether soybean planting populations can be reduced, given the struggle many growers have today with herbicide resistance. “If you’re growing organic soybeans or in a constant battle with weeds, lower soybean populations are out of the equation. High populations and quick canopy coverage are a crucial and effective part of your weed management in those scenarios,” he says.
2. Look at soil types and fertility. Highly productive areas are where you can usually trim populations. “Higher fertility and adequate soil moisture will promote more growth and height in the soybeans plants, as well as more branches to make up for fewer plants,” he says. “We see this in fields with a manure history as well.” In those fields or parts of fields that are producing shorter soybeans (or fields with tough clays or sand) that’s when farmers need higher populations to reach canopy quickly.
“This is our basis for encouraging farmers to adopt variable rate soybean populations. It’s opposite to how we approach variable rate corn population” he adds.
3. Know your seed quality and genetics. Evaluate emergence scores and send seed samples to a seed lab for a cold test. “It provides an indicator of how your seed will handle cool, wet conditions at planting and germination, and not many seed tags give you the cold score,” says Ken Ferrie, Farm Journal Field Agronomist. “As we are planting soybeans earlier and earlier, the cold score has become more valuable.”
4. Seed treatments are advised. Any time you consider lowering planting population, Duesterhaus says he advises using a seed treatment. “We want to maximize the percent of plant emergence, so we have to protect that seed from insects, disease and other potential stresses,” he says.
5. Equipment use matters. “When lowering populations, treat soybean planting more like you treat corn planting,” he advises. “Consider how to achieve uniform seed placement by looking at factors such as seedbed quality, planting into moisture at a uniform depth, closing the trench and using row cleaners.”
6. Row Spacing. Duesterhaus says 30″ row spacing concentrates more plants in a smaller area, which does two things. First, it can help with the “hill drop or push effect” during emergence. Secondly, when there is a missing plant, the next plant to fill in the gap is closer in 30″ rows than if it were in narrow rows. Farm Journal Test Plot research shows the biggest downside to 30″ beans goes back to point No. 1 – getting good weed control and canopy can be more challenging.
7. Harvest considerations. You want to capture every bushel of yield possible, and field quality impacts harvest success. “Consider whether you will be able to run the combine head shaving the ground to get those lower pods that come with lower populations,” Duesterhaus says. “One of the benefits of planting a higher population is a higher pod set, which can make harvest easier, especially if you have rocks.”
One question a lot of growers have is what to do with soybean populations when planting beans in March or early April.
“If you want to plant early for your area, stick to your standard planting population,” he advises. “We know there’s a higher risk of emergence issues, frost and freeze damage, but the soybeans will also have more early growth and branching, and the result is neutral.”