Soybeans are built to “improvise, adapt and overcome,” says Purdue Extension soybean specialist Shaun Casteel. But whether they can actually do that in your fields early in the season depends heavily on a few management decisions you control.
Here are three takeaways from Casteel’s recent presentation at the 2026 Illinois Soybean Field Advisor Forum that focus on his planting and replanting recommendations.
1. Before You Plant, Check The Forecast For The Following 24 Hours
Many farmers aim for the “50°F soil temp” rule when heading to fields to plant and, while that’s on track, Casteel thinks that’s only half right.
“Soybeans can germinate at [temperatures] as low as 36 to 43 degrees,” he said. “But it’s not necessarily soil temperature [we’re concerned about], even though that’s what we’re measuring, it’s the water temperature.”
A soybean seed must absorb (imbibe) approximately 50% of its own dry weight in moisture for germination to start. But if it absorbs cold water, the seed can be injured, resulting in damaged cell membranes, reduced germination, and dead or weak seedlings.
Casteel’s recommendation: if a cold front with rain is headed your way and likely to occur in the next 12 to 24 hours, hold off on planting, even if the soil temperature looks OK or you feel the calendar is pushing you to plant.
He adds that the time to soybean germination and emergence is related to heat unit accumulation (GDDs), noting there “is >50% emergence after 140 to 160 air GDDs.”
2. Aim for 1.5" Planting Depth and Good Seed-to-Soil Contact
Planting depth is important for soybeans’ ability to emerge well, and it also plays a big role in setting up root hair growth, nodulation and the plants’ access to nutrients.
“If you don’t have good root hair development, guess what? You don’t have good nodulation, you don’t have a good nitrogen supply. Kiss those high yields goodbye,” Casteel says.
As a rule of thumb for planting, he recommends farmers place soybean seed at 1.5” deep with a variance of between 1.25” to 1.75” depending on soil moisture and residue.
He advises against chasing moisture too deep, like you might if planting corn, as soybeans don’t handle deeper planting well. What happens if you plant too deep? Casteel says there are commonly three results:
1) The hypocotyl has to pull cotyledons farther to reach the surface. 2) That extra distance costs time and energy, so emergence is slower and less uniform. 3) In cool or crust-prone soils, deep-planted beans are more likely to stall or die before they break through the soil surface.
3. Don’t Be In A Hurry To Replant Soybeans. Evaluate Your Stand Thoroughly First.
Casteel urges farmers to be more cautious about replanting soybeans. His own line in the sand is around 70,000 plants per acre. At or above that level, with healthy, evenly distributed plants, his data shows soybeans usually deliver about 95% of full yield potential, making a replant hard to justify. He also notes that stands in the 66,000 to 100,000 range often end up with very similar yield results.
The reason is soybeans will compensate. In delayed-emergence and overseeding studies, Casteel says he found that when part of the stand emerged late, the original plants simply “branched more and produced a larger share of the yield.”
In one scenario he evaluated, the original plants contributed 60% of the yield and the late-emerging plants 40%, yet the total yield matched a uniform stand. In a V2-type “replant” timing, roughly 95% of yield still came from the original soybean plants and only 5% from the later ones.
Because of that, Casteel says most soybean replants at V2 are “just making us feel good rather than making us more money.” Once plants are established and starting to branch, overseeding or tearing them up rarely changes the final bushels much, but it does add cost and risk.
Where he says a “full reset” is likely needed is when stands are around 50,000 to 60,000 plants per acre and it’s still roughly the first week of May—before the original plants have much node development or branching. Outside of that scenario, his research and experience say the better decision is usually to leave the stand alone and let soybeans compensate.
If you can manage that, Casteel contends soybeans will usually do what they’re designed to do: “They can improvise, adapt and overcome. It’s our job not to get in the way,” he says.
Hear Casteel’s complete presentation at the Field Advisor Forum on YouTube here. Be sure to check out what he says about managing corn residue after the 2026 harvest, so it doesn’t negatively impact your soybean crop the following year.
