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Myth-Busting Soybean Style

From soil temperature at planting to nutrient management, Wisconsin’s Shawn Conley blows up 4 soybean myths.

Shawn Conley, soybean specialist, says farmers have adhered to a longstanding set of soybean production principles that appear logical. But some of these principles are – well, myths. Here’s more from Conley, who spoke at the University of Missouri’s Crop Management Conference in December.

Myth: You don’t need seed treatment

Pay attention to the percent germination score on the 2019 seed tags. “We hear through the grapevine that seed quality is going to be down nationwide,” Conley says. 

Also, certain varieties may not be available when you want them. Be wary of discounted seed varieties, as some will be offered without a replant policy. “If you see a cheap unit of seed, there’s probably a reason,” he advises.

Farmers may want to cut costs in 2019, but cutting back on seeding rate or seed treatments is unwise. “The data suggests that adding a seed treatment generally enhances or improves overall germination rate,” Conley says. Be sure to ask your dealer if the seed-applied treatment protects against phomopsis seed decay. Many off-patent treatments will not be effective against phomopsis.

Myth: Soil temperature must be 50°F. before planting

The default planting date for soybeans tends to be when farmers get done with corn, and since the baseline soil temperature for corn planting is 50°F., soybeans should therefore follow suit. Trouble is, that’s not correct. Soybeans can handle cold just fine. Sure, short-term freezing temperatures will chill them, and a hard freeze will kill them. But emerged beans can handle 28°F. for four hours. “In early-season environments, the soybean plant is more resilient than we give it credit for,” Conley says. The upshot: You can plant soybeans much earlier than you think, perhaps even ahead of corn.

Myth: Soybeans always fix N for the next crop

It is true that as a legume, soybeans are able to produce a lot of nitrogen through fixation. But it’s also true that soybeans use a lot of nitrogen. An 80-bushel-per-acre crop requires 300 pounds of nitrogen per acre, most of which is delivered to the grain elevator as protein.

Most soils, with adequate biological fixation, can meet that demand. Yet, there may not be as much fixed nitrogen carrying over to the next crop as was previously thought.

That’s due in part to improvements made by soybean breeders to maximize yield even in tough environments. For instance, there are more days of the yield-influencing reproduction stage in today’s soybean varieties than those that were available a generation ago.

“Breeders have also reduced the yield penalty for thin stands by half,” Conley says. Under high seeding rates, there are more pods on the main stem. In low seeding rates, branches hold more pods. “That has cut our yield penalty for thin stands in half,” he explains.

The upshot is, the soybean plant physiology has adapted to become more efficient at pulling nitrogen out of the soil and putting it into the seed. The plant uses almost 90% of the nitrogen available in the soil, leaving very little for the next crop. “In Wisconsin, we don’t give soybeans an N credit because it’s so efficient,” Conley says.

You would think – incorrectly – that adding foliar nitrogen would therefore boost yields. It’s OK to add starter fertilizer, but limit it to 30 pounds in a 2×2 configuration. More than 30 pounds of added nitrogen complicates biological fixation. “Soybeans are lazy,” he explains. “They would rather get N for free than work for it.”

Conley adds that his shop frequently receives phone calls about whether inoculants are working. He urges growers to dig a plant that’s in the V1-V3 growth stage. “At the radicle, you’ll see a mass of 10 to 15 nodules. That tells us inoculants are working,” he says. If that mass is not present, inoculants didn’t work.

Myth: Soybean plants won’t begin flowering until summer

It’s been said that soybeans won’t begin flowering until June 21. Why then? It’s the summer solstice – the longest day of the year. That may have been true years ago. But as farmers push planting dates earlier in the calendar year, soybean plant development is much further along on June 21. “It is at the unifoliate stage at the front end of summer solstice compared with the back end. That’s what induces flowering earlier,” Conley says.

Why is this important? According to the label, XtendiMax herbicide cannot be applied to Xtend soybeans after soybeans begin blooming. Conley warns that you may think you have a longer window in which to apply XtendiMax herbicide than you actually do.  

The specialist adds that white mold tends to be a problem when soybeans flower earlier, requiring growers to scout and manage accordingly.

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