When fields are ready to plant, soybean growers often head to their best ground first. Connor Sible is asking you to consider doing the opposite.
“If you want to maximize soybean yields across your entire farm — not just in one field — start by planting your lowest soil-testing fields first and save the highest soil-testing fields for last,” he advises.
That shift in focus is counter to what many farmers currently do, and it is at the heart of the planting strategy he recommends. The University of Illinois row-crop field researcher and assistant professor contends that it’s when and where you pull the planter into each field that can raise your overall farm average.
In practice, that means when an early planting window opens in April or the first of May and several soybean fields are dry enough for a green light, the first acres you plant should be the ones with lower soil test values — not the “good” fields on the soil test map.
“This gives the late-planted soybean the advantage it needs to put on more bushels relative to early planting,” Sible says. “Between the soil testing data and the planting date response data we have, it makes a lot of sense.”
Why Early And Late Soybeans Behave Differently
Sible says there is a decade-plus of field trials from the University of Illinois comparing planting dates, soil tests, and yield responses, verifying that this change in planting strategy makes sense. The full study, led by Marcos Loman and advised by Fred Below, summarizes their findings and is available here.
Part of Sible’s explanation is that early-planted soybeans in April tend to yield more overall, but these beans grow slowly at first in cool, often wet soils with lower solar radiation. Their nutrient uptake is long and gradual.
“Early soybean, while yielding higher, has slower growth and probably doesn’t need fertilizer” he says.
Because those plants grow and require nutrients slowly, the soil can usually keep up with nutrient demand, even in lower-testing fields. That’s why he says early planting is the best “boost” you can give to weaker ground.
Later-planted soybeans, going in during late May or even into June, are going into a different environment: warmer soils, longer days and more solar radiation.
“Late-planted soybean, while lower yielding and a lower total nutrient requirement, grow so fast that if we want to optimize the return on fertilizer investment, it’s probably going to pay back better on late-planted beans,” Sible says.
Fast-growing late-May soybeans in Illinois pull nutrients at a higher rate, and Sible’s data shows they respond more strongly to higher soil test levels and applied fertilizer. That’s why he wants the best-testing fields held back for the later planting window.
“Late-planted beans grow so fast, the soil (fertility) probably cannot keep up,” he explains. “The late-planted soybean benefits more from that high soil test environment.”
How Farmers Can Implement The ‘New’ Planting Strategy
Sible is quick to acknowledge that in the real world, farmers will start the planting process in whatever field is fit at the time.
“Obviously you’re going to plant the driest field first,” he says, noting that central and northern Illinois have had recent rainfall.
But once more than one field is ready, he contends farmers can start making more intentional choices.
His recommended process for soybean planting looks like this:
- Sort fields by crop and soil test.
Start out by grouping soybean fields by soil test levels — lower-testing and higher-testing, especially for phosphorus and potassium, but considering overall fertility. - Identify likely early-plant candidates.
Look at drainage, residue and soil type to consider which soybean fields typically dry out first. Within that group, mark the lower-testing fields. - Use early planting on “weaker” fields.
When an early planting window opens and several soybean fields are fit, move the planter to the lower soil-testing soybean fields first — those that usually don’t win the “yield contest” on your farm. - Reserve high-testing fields for later.
If weather or logistics push some soybean acres into late May or early June, prioritize the higher soil-testing fields for those later planting dates, where their strong fertility levels can support rapid growth. - Align fertilizer decisions with timing.
On early-planted soybeans, especially in lower soil-testing fields, be conservative with extra fertilizer unless there is a clear nutrient deficiency. On late-planted soybeans in high-testing fields, consider that any fertilizer investment is more likely to deliver ROI.
“If we line up planting date, soil test and fertilizer strategy, we can do a better job of maximizing soybean yield across the farm,” Sible says.
From Field-by-Field To A Higher Farm Average
Sible frames his planting strategy for soybeans as a mindset change. Instead of asking, “How do I make my best field even better?” he wants farmers to ask, “How do I pull my whole average up?”
“The principle is pretty simple,” he says. “Early planting is a powerful yield tool — use it where the soil is weakest. High soil fertility is a powerful growth tool; use it where beans are going in late and growing fast.”
Farmers won’t always see the highest absolute yield on those late-planted, high-testing fields, he acknowledges. Weather and your calendar date still matter. But he believes the relative performance and return on fertilizer can improve when planting order and soil tests work together.
For growers struggling to manage tight margins, it’s a strategy that costs nothing to try except a reshuffled planting list.
“Hopefully you can take these concepts back and take them to your acres,” Sible says. “It’s about getting the most from the whole farm, not just one field.”
Sible laid out his planting recommendations for soybeans during the 2026 Crop Management Conference at the University of Illinois.
