6 Secrets to Higher Soybean Yields

March 7, 2013 11:32 PM
6 Secrets to Higher Soybean Yields

Why is it that farmers competing in state and national soybean yield contests routinely grow 60 or even 85 bu. per acre yields when the national average is closer to 44?

That’s the question that motivated some ground-breaking research by Fred Below, a crop physiologist at the University of Illinois. The wise-cracking, caffeinated professor presented his top-line results to a standing-room-only audience of farmers at last week’s 2013 Commodity Classic.

There’s a lot more at stake in the answer to this question than a simple scientific inquiry. To feed an extra 2 billion mouths over the next 40 years, "we need to double the production of all grains," says Below. But at current rates of productivity gains, it will take 100 years to reach 85 bu. per acre.

"Fortunately, there’s a lot of low-hanging fruit," says Below. In fact, nearly every tactic Below tried – whether it was adding more nitrogen or planting in denser rows – improved yields. The best course of action, he says, is "intelligent intensification," academic-speak for putting more of the right stuff in the ground at the right time.

Before diving into his secrets, Below listed some "pre-requisites." He assumes that farmers are draining their fields properly, that they engage in early weed control – "no matter how satisfying it may be to let them grow then go out in the field and kill them with glyphosate" – and are maintaining proper pH levels for soils.

Here’s a rundown on the six "secrets" Below revealed, one at a time.

1. Weather

Because he figures everyone could guess weather was among the secrets, he lists it first. But it may belong at the top, since according to his studies it has a greater influence on yields than anything else. That’s unfortunate because it can’t be controlled.

Fluctuating weather conditions in Below’s home state of Illinois have resulted deviations from trend-line yields of 0.7 bu. per acre over the past 20 years.

Good weather, of course, influences early planting, which can create opportunities for early vegetative growth and node formation. "I think we need to plant earlier, but it’s the weather that determines the planting date," Below says.

Even if you plant early, the professor says, you need to plant the right seed and protect it. The impact of heat and drought can be mitigated by management practices that promote strong root development, such as fertility, enhanced seed emergence, and disease control. Ethylene blocking compounds that alleviate corn stress may work on soybeans as well, he adds.

But there’s nothing like a good rain in August. That’s what saved Below’s test crops last year. "When any of my agronomic schemes don’t work," he says, "I just blame the weather, and I’m usually right."

2. Fertility

Soil fertility, Below says, may be the most overlooked component of soybean management. "I don’t think we’re adequately fertilizing soybeans, or we’re losing a lot from corn," Below says. The popular approach of adding nitrogen during the growing season may backfire as well. "If you put in too much, in late June or early July, you can shut down the nodules. Then you wind up with worse performance."

Soybeans obtain between 25 and 75% of plant nitrogen from the soil, with the balance supplied from symbiotic fixation. "When we get to 85 bu. per acre, we’re mining 100 pounds out of the soil," he says.

Some growers, Below said, incorrectly believe that because they applied adequate fertilizer to their corn crop the preceding year that phosphorous (P) and potassium (K) fertility are less critical for soybean production.

A typical fertilizer program for soybeans, for instance, might involve fertilizing the previous year’s corn crop with an equivalent of two years of fertilizer. A 230-bu. corn yield, however, removes nearly 100 pounds of P2O5 from every acre. This doesn’t leave much for the soybean crop in the second year.

Many people think potassium is the key nutrient for soybeans, Below says. While it is important, corn stover could provide half the potassium that soybeans need. Phosphorus, he says, "is the biggest problem, and it’s probably due to the way we fertilize corn." Phosphorus is quickly immobilized in soil and may not be available in sufficient quantity.

Below grew an additional 4.3 bu. per acre through better fertilization. Besides the weather, fertility is the most important variable he tested.

3. Genetics/variety

Below believes that farmers don’t spend enough time researching soybean varieties. He found big differences in yield, even among varieties of the same maturity. Yields varied by as much as 20 bu. per acre when grown at the same location.

Some variation was due to differences in susceptibility to diseases like white mold. But he also noted big differences between seeds with varying insect resistance. All told, Below attributes an additional 3.2 bu. per acre upside to selecting the right seed.

4. Enhance seed emergence and vigor

Through the use of fungicidal, insecticidal and plant growth regulator seed treatments, early season growth and vigor will be protected from yield robbing stresses such as disease and insects. The professor says healthier leaves result in bigger seeds, which can dramatically improve yields. "It has a huge impact," he said.

Below argues that insect and disease control is especially critical with soybeans because so many pests can limit yield or reduce grain quality.

5. Seed treatment

Soybean seeds have their highest yield potential, of course, when first planted. After that, the basic idea is to relieve as much stress on the plants as possible. Seed treatments that promote seed germination, seedling establishment, and early vigor, help in this respect.

Some fungicides and insecticides may also promote "physiological vigor," he says. "At my research site, when I had seed with a complete treatment, I saw an enormous improvement in yield." All told, the researcher attributes an increase of 2.6 bu. per acre to seed treatment.

6. Use narrow rows

Below’s research turned up a distinct advantage to planting soybeans in narrow rows of 20 inches, rather than 30 inches. This allows more space between plants within a row and increased branching. That in turn creates more opportunities for precision fertilizer placement in a corn-soybean rotation. Twenty-inch rows also improve light interception, though reduced air circulation may create more pressure for disease.

Though 15-inch soybean rows have gained in popularity in recent years, Below believes that there’s an advantage to planting both corn and soybeans in 20-inch rows. Farmers could use the same equipment for precision fertilizer placement. And by alternating crops, soybeans could take advantage of the residual fertility from the previous band.

Unfortunately, farmers who employed all these secrets wouldn’t get a yield increase equal to the combined value of doing them individually. The whole, in other words, isn’t equal to a sum of the parts. But you do get some added benefit by combining approaches.

For instance, in Below’s research, applying fungicide at the R3 growth stage improved yields by 2.1%. Applying insecticide at R3 resulted in a 3.7% yield increase. But doing both only improved yields by 3.8%.

Soybean Yield Secrets

In terms of yield percentage improvements

Fertility (extra N,P,S and Zn) 4.3%
Variety (fuller maturity for region) 3.2%
Foliar protection (fungicide and insecticide) 3.6%
Seed treatment (fungicide, insecticide, and nematicide) 2.6%
Row width (20-inch versus 30-inch) 2.1%


Read more information about Below and his research.



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