Fred Below became a household name among U.S. farmers in the mid-2000s with his presentation, The Seven Wonders of the Corn Yield World. Known for his wit and self-deprecating humor, the University of Illinois crop physiologist says the success he had with the presentation was akin to having a top 10 hit song.
“I was off to the races with this. I mean, I milked that puppy for all it was worth,” Below told a packed room of farmers and agronomists during a Soybean Field Advisor Forum in Champaign, Ill.
The Illinois Soybean Association (ISA) took note of Below’s success with addressing corn yields and approached him to see if he could work similar wonders with soybeans. It turned out he could, and in 2012 Below unveiled the Six Secrets of Soybean Success to help farmers understand those management factors that could affect soybean yield. However, at that point, Below says he didn’t have enough experience with soybean research to rank or give a bushel-per-acre value to each of the six secrets – insights he believed would help farmers grow even more beans.
A few years later, armed with more research data and experience, Below has finally achieved that goal, resulting in what he calls the new aspect of his original six secrets.
He says these six factors can work together synergistically to deliver 80-bushel yields: weather (30 bu.), genetics/variety (30 bu.), row spacing (7 bu.), foliar protection (6 bu.), fertility (5 bu.) and seed treatment (2 bu.).
1. Weather Is The No. 1 Factor (30 bu.)
Mother Nature always has the final say in crop yields, and how the weather plays out in a given season is beyond farmers’ control. Even so, Below says the single most important thing soybean growers can do is plant their crop early. He offers two reasons why that’s vital.
First, you get more leaf area coverage on the ground earlier in the season. Vegetative growth helps soybeans capture available sunlight and to close the rows. Row closure minimizes water loss to evaporation and aids in weed control.
The second major advantage of an early planting date is you end up with more nodes. Below says you need enough plants and nodes per acre to support the number of pods necessary to hit your yield goal.
Of the three components of soybean yield – pods per acre, beans per pod, and bean weight – pod number per acre is usually most important.
“One more pod on every soybean plant can be worth 2 bushels,” he says. “The reason is those pods have seeds – usually three – and seed number is almost always the main determinant of soybean yield.”
The weight of the soybean seed is important, too. Below says the average weight of a soybean seed is 150 milligrams, and that increasing the weight of each seed in the pod just 2 milligrams will contribute a bushel.
2. Soybean Varieties Are Not Created Equal (30 bu.)
The second-most important factor for high-yield soybeans is selecting varieties that are going to yield well. Sounds like a no-brainer, but Below says farmers often underestimate the importance of this decision.
“Oh, man, you have no idea how important this is. I’ve talked to growers who just agonize for days over what corn hybrids to plant, and then they turn around and buy any old bag of soybeans. Big mistake,” he says.
University of Illinois research indicates the fullest relative maturity for a given region consistently delivers the highest yields.
Various studies Below and his team have done the past few years bear out that fact. A 2021 study in central Illinois study involved 26 soybean varieties with a relative maturity range of 2.5 to 4.4, planted in 30-inch rows using standard management practices. The top-yielding variety produced 100.6 bu. per acre, and the lowest yielding variety delivered 73 bu. per acre – a difference of 27.6 bu. per acre. In that study, the fullest relative maturity varieties delivered most of the highest yields, notes Connor Sible, research assistant professor at the University of Illinois, and one of Below’s colleagues.
Furthermore, in a three-year study Below and Sible conducted on soybean varieties and yield, they found that one increase in maturity group was worth 6 bushels per acre.
3. Narrow Rows Are Usually Better, But Not Always (7 bu.)
Below says selecting the correct row spacing can contribute up to 7 bu. per acre.
In the university’s studies, narrow rows (20 inches) typically out-yielded wider rows (30 inches).
“We can’t plant 15-inch rows with our four-row equipment, but we can plant 20-inch rows, so we compare 20-inch rows to 30-inch rows,” Below explains.
The advantage of a narrow row is it closes the canopy quicker and intercepts more light.
“Sometimes there’s a disadvantage. There can be less air movement that goes down the row, and that can lead to certain diseases like white mold, but the idea is to intercept more light,” he says.
Below says his team also looked row spacing in their variety testing trials. He says Illinois data shows row spacing doesn’t matter if you plant early.
“When planting early, 30 inches are as good as 20,” Below says. “But if you plant late, you need the 20. It’s the exact same thing with population, too. If you plant early, you don’t need as many plants. If you plant later, you need more plants to intercept light faster.”
4. Foliar Protection Pays Off (6 bu.)
Below says fungicides and insecticides act synergistically to protect photosynthetic activity of soybean leaves.
“Foliar protection is worth 3 to 6 bushels regardless of planting date,” he says.
5. High-Yielding Soybeans Need Adequate Fertility (5 bu.)
Below says soybeans require more nutrients than most farmers realize, especially if they are shooting for 80-bushel yields.
During his presentation, Below shared a chart showing the fertility levels soybeans need to reach 80 bushels: 327 pounds of nitrogen, 57 pounds of P2O5, 227 pounds of K2O, 23 pounds of sulfur, 6.4 ounces of zinc and 6.1 ounces of boron per acre.
One piece of data that surprised Below is that early planted soybeans respond less to fertilizer applications than later planted beans.
Researchers suspect this is because an earlier planted crop has more time during the growing season to collect the nutrients it needs from the soil. Plants can also move some nutrients from their leaves to help produce heavier seeds, and earlier planting leads to bigger plants with more nutrient reserves to redirect toward yield.
“If I have to grow 80 bushels early or late planted, the amount of nutrients that I need are the same. But if I’m planting early, I’ll have a longer season to take that up. It’s like the tortoise and the hare — slow and steady,” says study co-author Connor Sible.
Sible notes in a university article that yield of an unfertilized soybean crop planted late is more closely associated with soil test values than with the early planting of soybeans.
University of Illinois news writer Megan Allen addresses the subject in more detail in her article Timing matters: Early planting benefits soybean in unfertilized, low-fertility fields.
6. Treated Seeds Emerge And Grow Better (2 bu.)
Below says naked soybean seeds don’t emerge and grow as well as treated ones.
A good seed treatment can significantly contribute to soybeans at each development stage, he says. For farmers who plant soybeans early, they are even more important in providing protection to seeds and seedlings from disease and pests.
Some Prerequisites Are Crucial To Yield
While Below encourages growers to focus on the six secrets to yield, he says there are some crucial prerequisites that must be met in order for farmers to grow 80-bushel soybeans consistently.
“I can’t tell you how important good drainage is and that soybeans don’t like compacted soil,” he says. “Weeds don’t add to yield either, by the way. You really have to get weeds early and keep them under control.”
Two other table stakes he says for achieving high soybean yields are good soil pH and having an adequate baseline level of phosphorus (P) and potassium (K).
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