With less costly soybean seed and the wide range of which soybean plant populations produce similar yields, soybean seeding rates have not historically been as closely calculated as those for corn. But soybean seed costs have risen to the point at which farmers don't want to plant more seeds than they need for top yields, according to University of Illinois crop sciences professor Emerson Nafziger.
"Although we often don't see this, it's possible in some cases that high soybean plant populations might increase lodging or stress, and actually result in lower yields, especially in wider rows, where plants are closer together," he added.
With yields usually maximized at 80,000 to 100,000 plants per acre, Nafziger suggests aiming to establish 100,000 to 120,000 plants, which allows for lower- than-expected emergence.
Seed quality isn't much of an issue
Nafziger said that decreased pod set due to stress in 2012 means that seed this year tends to be larger than normal. This can sometimes mean more stress cracks or mechanical damage, but germination percentages are generally reported to be good and it appears that seed quality isn't much of an issue.
"Even with good seed germination, we often find soybean seeds establishing plants at lower percentages than we see with corn," Nafziger said. "This is in part due to lower standard (warm) germination percentages and partly to the fact that soybean seeds, which need to stay healthy long enough to drag the large cotyledons up and out of the soil, often struggle to emerge, especially if conditions are wetter or cooler than normal, or if soils form a crust after planting.