How low can you go with soybean seeding rates and still harvest high yields?
Perhaps a better question Brian Scott set out to answer five years ago was, how low could he go with populations and still produce the most profitable soybean crop possible on his northwest Indiana farm?
In 2024, the answer was 100,000 seeds per acre – a rate that penciled out to an investment of $53 per acre in seed. Yield results at harvest averaged 76 bu. per acre.
“We had really good results and set a lot of yield records in our fields last year,” says Scott, who farms 2,500 acres of corn, soybeans, popcorn and wheat with his dad near Monticello, Ind. The field shown below was split between two populations of the same variety in 2024: 100K on the left and 40K on the right.
“Driving by, you’d never know there was a difference,” he says.
Scott says the family’s ongoing objective for evaluating seeding rates each year is to find that fine line between cutting seed costs and growing the most profitable soybean crop.
Lower Rates Are A National Trend
The move to lower seeding rates has been a national trend for more than two decades, according to USDA-ERS.
Average seeding rates for U.S. soybeans declined nearly 22% between 1997 and 2018, according to the agency’s May 2024 oil crops outlook.
Key contributors to the downward trend include improved genetics, seed treatments and a widespread shift toward planting in conventional rows instead of drilling or broadcasting soybeans, USDA reports.
Highly productive areas are where you can usually trim soybean populations, according to Matt Duesterhaus, Crop-Tech Consulting field agronomist in Illinois.
“Higher fertility and adequate soil moisture will promote more growth and height in the soybean 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 in fields with tough clays or sand) that’s when farmers need higher populations to reach canopy quickly, Duesterhaus adds.
Base Decisions On Multiple Years Of Experience
Plant height is a positive only to a point. The family started reducing seeding rates 10 years ago as they found plants were getting too tall and lodging. At the time they were planting a rate of 165,000 seeds per acre.
“The beans were getting chest high in August, especially if we got some rain. And we were like, oh, that’s not good, so we dropped to 140,000 an acre which took care of the lodging issues,” Scott recalls.
Since then, they have evaluated planting populations as low as 40,000 seeds per acre.
“We planted a block last year at 40,000 that averaged 69 bushels at harvest,” Scott says. “They were massive plants; the stalks were as big around as my thumb at the soil’s surface.”
Those results (shown in the photo above at populations ranging from 40K at the far left to 160K at the far right) were just the opposite of his experience the year before, in 2023.
“We got some heavy rains, and at that 40,000 rate the beans struggled to break through the crust. It was a really thin stand, and we had maybe 25,000 plants at harvest,” Scott recalls.
Today, he says 100,000 seeds per acre is the average planting rate for soybeans across the family’s farm.
“We grow mostly seed beans, and I kind of had to convince the company that it would work,” Scott says. “I joke about it a little bit with our seed salesman that they’ll be able to sell us more seed when we buy another 80 acres with the money we save.”
To maximize yield results in most environments, Purdue Extension adds that “growers should have no less than 100,000 uniformly standing plants per acre in 7.5" and 15" rows and no less than 80,000 uniformly standing plants per acre in 30" rows.”
Your Farm, Your Results
Scott is a proponent of on-farm field tests and routinely shares what he learns with other farmers and general consumers via his blog “The Farmer’s Life” on YouTube and Facebook. Check out this link to learn more about his work in 2024 to evaluate planting populations.
When testing lower soybean populations, he would encourage other growers to consider these three factors:
1. Variety Selection
While yield is always the primary factor when selecting a variety, he’s found bushy varieties are usually the best choice for wide rows.
“You have to seek out bean varieties that branch well and can compensate for lower plant populations,” Scott says, noting he plants bushy varieties at 1.5” deep in 30” rows. His family plants 30” rows because they own one planter, using it for both corn and soybeans.
2. Seed Treatments
Scott routinely use seed treatments with fungicide and insecticide to protect seed, which is especially important when going with lower populations and planting early or in challenging conditions.
3. Weed Control
Scott maintains a robust weed-control program using pre-emergence and postemergence herbicides featuring residual control. Given the operation’s 30” rows, he says preventing weeds from emerging is particularly important as the crop is often slower to canopy than if they planted in narrow rows.
“We do a burndown treatment with a residual right before planting,” Scott says. “We’ve had really good luck coming back in our first post pass with putting down another residual in the last few years – that seems to be helping quite a bit. Then, we usually come back a second time with a post application during the summer.”
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-resistant waterhemp, pigweed and ragweed species.
“If you’re growing organic soybeans or in a constant battle with weeds, lower soybean populations are out of the equation,” Duesterhaus says. “High populations and quick canopy coverage are a crucial and effective part of your weed management in those scenarios.”
‘Go Slow, But Give It A Try’
Scott encourages other farmers to try cutting seeding rates on a small scale and evaluate how the various rates perform.
He typically puts in a 120’ strip of each seeding population, which gives him three passes at harvest with the combine to evaluate.
“Just put a block out in the field somewhere and either keep track of it on your monitor or throw some survey flags out, and pick it out at harvest,” he advises. “Try it on a small scale, and then go from there the next year.”
Your next read: With Soybean Planting Populations, How Low Can You Go?
