Manage Soybeans Throughout the Growing Season

Shine More Light on Soybeans

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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(Photo by Jim Patrico, Photo Illustration by Barry Falkner)

Soybeans may have the reputation of being a fickle crop, but agronomist Dustin Bowling maintains they are merely misunderstood.

"Too often, we try to lump soybeans into the category of the corn plant. We know what has let us push the needle on corn yield, and we try that on soybeans," says Bowling, Missouri-based agronomist for AgriGold.

"We end up scratching our head because we have a hard time getting the soybean to react to those management tactics and chalk it up to the soybean being too stubborn. We tell ourselves it is going to do what it wants, no matter what we do," he says.

Instead, he urges farmers to treat the soybean like a factory by adjusting management practices to meet the biological needs of the plant throughout the growing season. "Think of it as providing everything that factory needs to keep the lights on and running efficiently all season long," Bowling says.

With favorable market prices and pricey nitrogen pressuring corn and cotton acres, soybeans are in the spotlight this year, notes Kris Ehler, a farmer and agronomist for Ehler Brothers, a family-owned seed business based in Thomasboro, Illinois.

"Let's be honest, soybeans have been paying the bills on many central-Illinois acres over the past few years. It's time to quit treating them like a rotational crop," he says. Relying on seed companies to bring yield isn't enough, Ehler adds. "A half-bushel or three-tenths of a bushel-yield increase per year is not going to cut the mustard if we want to remain sustainable."

Jeremy Ross, University of Arkansas System Division of Agriculture soybean specialist, has already seen practices and attitudes shift dramatically in the Mid-South. "Farmers in this state used to tell you they were a cotton or rice farmer," he says. "But, we had 16 farmers exceed the 100-bushel-per-acre mark in our state soybean contest this year [2021], and it was a first for 10 of those farmers."

Taking clues from the state's "Grow for the Green" yield contest from 2009-2021, Ross says winners have moved planting dates up by nearly a month on average. Seeding rate has dropped to 134,000 seeds per acre compared to 160,000 to 170,000 seeds per acre on average in that same time frame. More racehorse soybean varieties compared to workhorses have also increased yield potential but often also demand more management if they aren't as hardy, he explains.

Soybean-growing systems continue to vary by region. Some southern growing areas still rely heavily on determinate varieties, which have longer maturities and cease new vegetative growth soon after flowering.

But, Ross sees growers in his state moving to more indeterminate varieties, which continue to flower and are of shorter maturities.

"The real difference, though, is farmers pushing soybean yields are walking these fields hard and being timely with what needs to be done," Ross adds. "They are using sensors to indicate root growth and whether a late dose of irrigation will be economical to push seed fill. I wouldn't say we've got all the answers, but we're figuring some things out."


Bowling likes to separate the soybean-growing season in four quarters: stand establishment, vegetative growth, flowering and pod fill.

"We are looking at the key things we can do to put the plant in the position to win or take advantage of what Mother Nature provides during those periods," he says.

It all starts with understanding how the crop harnesses light energy to fix carbon dioxide through photosynthesis. Plants breathe in carbon dioxide through stomata in their leaves. Corn, for example, is classified as a C4 plant. It can close stomata to conserve water but continues to respire under hot, dry conditions.

Soybeans, on the other hand, are a C3 plant. Soybeans close the microscopic pores in the leaf when subjected to enough heat or other stress.

"At their bare bones, corn and soybean are just wired differently," Bowling explains. He points to the volume of the biomass produced by each as another example. Consider how much soybean end use is produced at 120,000 seeds per acre compared to what 30,000 corn seeds will yield, he suggests.

"A corn plant operates at a sprinter's level because of its C4 metabolism. It's going to react very quickly to nutrients you give it and keep pushing toward the goal at a faster rate -- accumulating a lot more carbon and a lot more natural resource fixation along the way," he says. If you ever wondered why common waterhemp can so quickly outdistance a soybean crop, consider that it is also a C4 plant, Bowling notes.

Soybean plants are more like a cross-country runner. "They've got the long game in mind and chug along at a steady pace. We know that available water at pod fill is still a big deal for yield, but we want to get the plant to that point in the best shape possible so it can finish," he says.


That's why Ehler is an advocate for earlier planting to push the plant to begin flowering before summer solstice (June 21) to take advantage of the most sunlight possible. He figures he gives up 4â??10 to 5â??10 of a bushel per day after April 25. The 2020 season has been the only year in the past 13 seasons that required some replant because of cold conditions, but he also depends on seed treatments and inoculants to help protect the seed.

On average, indeterminate soybean plants add one main stem node every 3.7 days after the first trifoliolate appears until seed development begins. An earlier start to the growing season results in more stem nodes for flower, pod and seed production. The quicker the canopy closes, the more competitive the crop is with weeds, too, particularly those like waterhemp and Palmer amaranth that emerge throughout the season.

Understanding how much the soybean crop removes from the soil is also key, as is understanding the 17 macronutrients, secondary nutrients and micronutrients required to make that soybean plant resilient. Starter fertilizers aren't just for corn anymore, particularly when planting early, Bowling says.

The second quarter is the most forgiving in terms of management. "Here, we are typically focusing on herbicide program completion and avoiding damage below the cotyledons. Nutrient needs by the plant slow and are minimal during this period," he says.

R1 marks the beginning of flowering as the plant starts its reproductive process. "During this period, maximizing photosynthesis, water and sunlight directly correlate with yield gains," Bowling points out.

The plant gets hungry again as it still needs to achieve two-thirds of its height, he explains. For example, at full bloom, which lasts for 16 days, the plant sucks down 7.81 pounds of nitrogen per acre per day, 1.75 pounds of phosphorus and 5.75 pounds of potassium. Those needs continue to build as the plant moves into early pod and soft seed.

"Less than 10% of the total nitrogen is used in the first 51 days -- or in other words, 91% of it is used in the second half of the soybean's growth cycle," Bowling says. "Like nitrogen, a relatively small percentage of phosphorus and potassium are utilized in the first two quarters of soybean plant growth, with the remainder taken up later in the growing season."

R3, or pod formation, is what Bowling calls fourth quarter. The source-to-sink relationship begins to change with all resources going toward the seed. Foliar feeding opportunities, fungicide applications and irrigation are all tactics being deployed to extend grain fill.

"We're using tissue testing and all kinds of tools to unlock the mysteries of this crop," Bowling says. "We're learning more every year, but taking our clues from the soybean itself is key."


Soybean Extension specialists from 15 states have collaborated to detail soybean-management tactics by growth stage. The publication is part of the Science for Success series sponsored by the United Soybean Board and discusses risks and management options from emergence through seed fill. It also explores common misconceptions associated with these growth stages.

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Cameron And Greg McClure
St. Francisville, Illinois

Greg McClure and his son, Cameron, farm near St. Francisville, Illinois. They have been participating in AgriGold's Yield Masters program to explore opportunities and barriers to increasing soybean efficiency. Here's a snapshot of their soybean-management journey.

Q: What's been your crop rotation, and is that changing?

A: Until 2017, we continually planted 60% of our acres to corn with some fields having corn for 10 or more consecutive years. From 2017 through 2020, we tried to operate on a 50-50 ratio while rotating every acre between corn and beans annually. As demand has increased back toward soybean meal in many livestock diets and future demand for soybean oil to be used in biofuels, we decided in 2021 to pursue several acres of high-management bean-on-bean production. Interestingly, we harvested the highest single bean yield ever seen on our farm on those very acres by focusing on those aspects we were afraid would hinder yields. We are carefully monitoring the practice with an eye on long-term trade-offs.

Q: What are a few things that you've worked on regarding soybean management? What has been your biggest surprise?

A: 1. Early planting. We see nearly a half-bushel-per-day yield drag for every day we delay planting past the ground being ready. We start the process in the fall with ground and equipment preparation to increase our odds of planting as early as possible. Extremely early planting into cold ground temperatures may reduce plant populations, but we still see added yield. There is a time element and hormone balance that we believe affects the plant structure in a way that promotes increased reproduction.

2. Plant protection. We apply fungicides and insecticide to every acre of soybeans. In our high-humidity, low-sunlight region, we see yield increases by preserving the leaf integrity for photosynthesis and sugar production.

3. Plant structure. We firmly believe the larger the stem diameter, the greater the genetic potential of the plant. We focus on the first 30 to 60 days of the plant's life to increase cytokinin production by building the correct root structure, using the right nutrients that create vegetative growth, while minimizing internode lengths and applying the nutrients that are necessary to increase reproductive energy to be stored in the plant. Our goal is to build a robust plant structure through balanced nutrition that can store enough reproductive energy to support a heavy seed load.

Our biggest surprise has been using a variety with a propensity for lateral proliferation. We continue to be amazed by the fact that we see very little yield difference in all planting populations between 30,000 and 110,000.

Q: Do you see ways to manage moisture in late August/early September to increase seed fill?

A: Managing moisture during grain fill starts up front with building the correct plant structure. We must ensure we have adequate root growth; manage the vegetative growth characteristics focusing on larger stem diameter and shorter internodes; protect plant health; and make sure our plants have the right mineral balance to use water efficiently during photosynthesis and respiration. Building a healthy soil with the right nutrient ratios and properly timed and correct placements of additional applications of nutrients, as well as stress mitigation products, allow us to use water more efficiently within the plant, thus decreasing the amount of water needed to reach our yield goals. Focusing on increasing calcium and manganese uptake early as well as raising potassium levels within the plant during reproduction phases are a couple of management keys to managing water efficiency and reducing water consumption.

Q: Is management all about yield?

A: Management is about maximizing ROI (return on investment) per acre. While we do several acres of trials annually, we realize we will fail more often than we succeed while attempting to prove new concepts or products. We will not slow down on trials, since this is where innovation and advancement occur. We know we have to manage our financial risk with unproven practices on a large number of acres. Those that are proven to have a positive ROI are moved to more acres across the operation.

Q: What is the biggest thing you've learned about managing soybeans?

A: The biggest thing I've learned the past five years about managing soybeans is exactly that: Manage them. Prior to 2017, we did very little to manage our soybeans. Today, we believe as an industry, we still know more about capturing genetic potential of corn than soybeans. That thought fueled us to go all in on soybean research and trials believing that we would find increasing our bean yields might happen quickly. While several management practices are the same between corn and soybeans, with examples being seed spacing, even emergence, pest and disease protection all driving yield, we are also discovering there are plenty of management practices which need to be different. The more we study plant hormones, C3 versus C4 plants and monocot versus dicot plants, we begin to understand some of the mistakes of our past which has robbed yield from us and what we should do differently to capture as much genetic potential as possible.


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