Soybean yield isn’t just about hitting a target population; it’s about uniform emergence, even spacing and consistent plant development.
Pioneer agronomist Paul Hermans is challenging farmers to consider all three when developing a seed selection plan for their soybean crop.
WHY IT MATTERS: Efficient soybean planting strategies can maximize yield and help mitigate the risk of white mould in some regions.
Seeding rate decisions are based on achieving both agronomic and economic optimum output. Hermans says crop success is influenced by several factors, including yield environment variability such as soil type, management zones and water-holding capacity.
Adjusting the planting date can also affect performance, with earlier planting increasing node and pod development. Hermans recommends planting as early as conditions allow to maximize yield potential.
During his research trials, Hermans said he and his team wanted to determine the if adjusting the planting date would have an impact on yields. The team did a soybean planting between May 1 and 7, then repeated the same trials 14 days later.
“On average we got three to five bushels more yield,” he said.
Hermans and his team also conducted a study in 2024 in eastern Ontario following a severe white mould outbreak in 2023. The trial evaluated the effect of seeding rate on soybean yield in Eastern Canada. He noted that in 2024, white mould pressure remained low.
In eastern Ontario, white mould, also known as sclerotinia stem rot, is playing a larger role in determining seeding rate decisions.
“White mould is a big disease factor, so we look at reducing populations to help combat it,” he said.
He encourages growers to contact their local representatives to help determine the right rate for their specific fields.
Defining soybean seeding rates
Traditionally, high-productivity fields require a lower seeding rate.
Research conducted by Hermans and his team revealed that results from local variety plots showed yields were generally about five bushels per acre higher than average.
The research found that adequate moisture during and immediately after planting allowed for excellent stand establishment, averaging 90 per cent of the seeding rate. Adequate rainfall throughout the growing season, especially in August, supported those higher yields.
It also demonstrated that growers should adjust seeding rates based on yield environment, crop rotation, residue cover, tillage practices and planting date.
If results fall short, Hermans says growers should consider replanting at the V2 (second trifoliate) stage in late May or early June. He believes replant risk can be reduced with good soil fertility. Research has shown a correlation between yield and potassium levels.
Potassium regulates stomatal opening and closing, controlling how the plant uses water. Soybeans require about 50 per cent moisture content to germinate, compared with 30 per cent for corn. Planting depth can also influence moisture availability.
He noted that planters typically provide more consistent depth than drills, but yield data shows only about a half-bushel advantage with a planter.
Yield level affects attrition
Higher-yield environments can lead to greater plant attrition. Hermans believes yield environment is the most critical factor in setting soybean populations.
During his research trials, Hermans discovered that as yield potential increases, soybean populations can be reduced due to larger plants and more nodes per plant, which lead to more pods per acre.
His team found that yield at the 80,000 seeds-per-acre rate was significantly lower than at 160,000, but neither differed significantly from the 120,000 rate.
The research also showed that the average number of pods per plant at the lowest seeding rate was more than double that at the highest rate — making it clear that pod number was the yield component playing the greatest role in compensating for lower plant populations.
Hermans urges farmers to watch for uneven emergence, noting a three-day planting delay can translate into a one-day later harvest.
“So if you plant three weeks beyond mid-May, expect a one-week-later harvest,” he said, adding that soil crusting and heavy residue can prevent even emergence.
He noted that today’s soybean varieties are more robust and branch more than those grown 15 to 20 years ago. Ideally, growers should target two million nodes per acre to achieve high yields.
“I always tell growers that two-thirds of your yield comes from the number of seeds you’re taking off per acre, and one-third comes from seed size,” he said.
Hermans said balancing plant population and growth depends on the yield environment. Limitations become more pronounced with later planting, reducing growth potential.
“It’s best to have beans flowering by July 1 to capture as much sunlight as possible during the reproductive phase, which drives seed size,” he said.
Applying a variable-rate seeding strategy
Variable-rate technology can maximize profit per acre while reducing seed costs. It is also an efficient way to manage soybean populations across different yield and moisture-holding environments within a field.
With spring planting approaching, Hermans encourages farmers to take a measured approach to soybean planting. He recommends using variable-rate technology to adjust seeding rates across a field based on soil conditions and yield potential, improving performance and efficiency.
“Don’t push when conditions are not ideal. Don’t mud the crop in,” he said. “Watch planting depth and manage residue with row cleaners.”
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