Could reducing your soybean seeding rate increase profit per acre by $40 per acre? In the right situation, yes, according to results from 2023’s Farm Journal Test Plots. Of course, the wrong choice will reduce profit. That’s why it’s important to find the best population, row width and plant characteristics for each soil type and planting date.
Choosing the right variety, row width and population has changed a bit since the Farm Journal Test Plots were launched in 1992, says Ken Ferrie, Farm Journal field agronomist. In the early ’90s, farmers planted higher populations to offset lower seed quality and inconsistent spacing and depth control and to aid in weed control. Bushy varieties were recommended for wide rows and straight-line varieties, with less branching, for narrow rows.
In the past 30 years, we’ve learned a lot from the Farm Journal research:
1. On average, narrow rows yield more.
They canopy quicker, which reduces water loss through evaporation and provides better late-season weed control, especially of waterhemp and Palmer amaranth.
2. Population is more about weed control.
“At the same population, narrow rows have outyielded wide rows most years from 1992 to 2023,” Ferrie explains. “The sooner we close the rows, the more sunlight we harvest, leading to higher yield.”
3. Technology has a big impact.
“Modern planters offer better singulation and depth control,” Ferrie says. “Genetically modified (GMO) soybeans opened up many herbicide options. New seed treatments let beans stay in the ground for two or three weeks before emergence, opening early planting windows, and early planting increases yield. Interestingly, early planting reduces the yield advantage of narrow rows because it gives wide-row beans more time to close the rows.”
4. Plant type matters.
While yield is always the primary factor when selecting a variety, bushy varieties are usually the best choice for wide rows, and straight-line varieties are usually best for narrow rows.
After three decades, the Farm Journal Test Plots are still churning out data to help farmers refine production practices.
“We’re continuing to look at population, asking how low we can go,” Ferrie says, “and studying the best uses of bushy and straight-line varieties and the impact of planting date.”
Read on for details on the latest findings from the Farm Journal soybean studies:
Push Population on Lighter Soil
In a 2022 population study, planted in April in 15" rows, 90,000 plants per acre yielded 97 bu. per acre; 120,000 plants yielded 94.5 bu.; and 150,000 yielded 95.1 bu. Reducing population from 120,000 saved $17 per acre on seed. Increasing yield by 1.9 bu. per acre increased income by $23.18 per acre (at $12.20 per bushel). Together, the seed savings and increased yield boosted total profit per acre by $40.18.
But how low can populations go? In 2023, Ferrie tried pushing population lower than ever. They planted 60,000, 90,000 and 120,000 seeds per acre (obtaining final stands of 44,000, 67,000 and 88,000 plants per acre). The northeast Iowa field contained soils with productivity ratings from 34 to 95 (using Iowa State University’s CSR2 productivity index).
This graph to the right shows the results. The highest yield came from the lowest population on the most productive soil. On less productive soils, higher populations yielded more.
Early Planting Pays . . . Usually
This 2023 central Illinois test plot, like earlier studies, suggests planting soybeans early boosts yield — unless weather throws you a curve. Ferrie and his staff compared beans of three maturities, 4.6, 3.7 and 2.6, on April 12 and May 17. The 2.6 maturity group soybeans bucked the usual pattern, yielding more with late planting.
“That probably was because of the weather,” Ferrie says. “It was dry through June, and the late-planted, 2.6-maturity soybeans — a very early soybean for this locality — probably were able to take advantage of rain that fell late in the season. But when they were planted early, the 2.6 maturity beans were too mature for the late rain to help. So when planting early, plant your full-season soybeans (based on your maturity zone) first and finish with your shorter-season soybeans.”
Population and Plant Type Affect Yield
A 2023 study compared bushy and straight-line varieties at three populations. As with the early planting study, weather — the sixth driest June on record in central Illinois — influenced the results of this plot.
“With the dry June, soybean growth stopped for three weeks, and the rows could not close,” Ferrie says. “That reduced late-season weed control —you could pick out the wide and narrow rows and the high and low populations by the amount of late-season weed escapes. And sunlight that hit the ground was not driving photosynthesis. Consequently, at the lowest population of 50,000, the bushy variety yielded significantly more.
“To maximize yield we must close the rows,” Ferrie emphasizes. “Once rows are closed, population and plant type carry less weight.”
Choose the Right Plant Type
The study below compared the two plant types on two planting dates and two row widths at a population of 140,000.
Thank You to Our Test Plot Partners
AgriGold, Case IH, Great Plains Manufacturing, Matt Shoup, Precision Planting, Unverferth Manufacturing Company, Yetter Farm Equipment
