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Switching to soybeans? Don't rush it

It's early May, and there's snow on the ground in parts of corn and soybean country. That's had a lot of farmers wavering about the planting decisions they made well before Mother Nature threw a major wrench in spring conditions.

So, is it time to start switching from corn to soybeans? The calendar may be telling you it is, but it's important to take into account both crops' ability to stave off damage from cold, wet conditions that may last well into May, says one agronomist.

"How early is 'early' when it comes to soybean planting? Based on planting date responses we have seen in recent years, we consider the period from mid-April through the first week of May as providing the best chance at high yields," says University of Illinois Extension crops specialist and agronomist Emerson Nafziger. "In general, the planting date response of soybean parallels that of corn on a percentage (not bushel) basis, but lags the response in corn by a week to 10 days."

So, you've got an extra week. But that's just by the book. Throw in this spring's conditions and it may tell you to do something altogether different.

"It is clear that early planting only increases the yield potential in soybeans -- it will do little to prevent yield loss if weather conditions, especially in August, result in crop stress. And in a season like 2012, with very dry conditions through July and then adequate rain in August and September, planting early can actually decrease yield in some cases. This happens because extended stress through flowering can cause the soybean plant to lose its ability to respond favorably to improved conditions by setting and filling more pods," Nafziger says. "Conversely, a wet start to the season followed by dry weather will often mean more benefit from early planting, if that means producing and starting to fill more pods before stress begins."

So, early planting's not the best for soybeans. What about when you compare that crop to its rotational partner? Corn is generally better equipped to stave off damage from early-season inclement conditions like the ones facing a lot of farmers in a lot of areas.

"Even with good seed germination, we often find soybean seeds establishing plants at lower percentages than we see with corn," Nafziger says. "Part of this is due to lower standard (warm) germination percentages, and part to the fact that soybean seeds, which need to stay healthy long enough to drag the large cotyledons up and out of the soil, often struggle to emerge, especially if conditions are wetter or cooler than normal, or if soils form a crust after planting."

If you do eventually decide to plant soybeans instead of corn on some acres that have been delayed because of the weather, there are a few things to keep in mind, especially this year following the 2012 drought.

"While we tend to be a little more relaxed about getting just the right seeding rate for soybeans than we do for corn, soybean seed costs have risen to the point where we don’t want to overseed as much as we have in the past. Though we rarely see this, it’s also possible in some cases that high soybean plant populations might increase lodging or stress, and actually lower yields, especially in wider rows, where plants are closer together. With yields usually maximized at 80,000 to 100,000 plants per acre, aiming to establish 100,000 to 120,000 plants is a reasonable target, and one that allows for lower than expected emergence," Nafziger says. "Decreased pod set due to stress in 2012 means that seed this year tends to be larger than normal. This can sometimes mean more stress cracks or mechanical damage, but germination percentages are generally reported to be good, and it appears that seed quality isn’t much of an issue."

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