Soybean School: How much nitrogen and when?

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Grain farmers are known for their generosity when supplying nitrogen to the corn crop, but many growers get stingy when providing nitrogen to the soybean crop.

That’s a situation University of Illinois plant physiology professor Fred Below sees too often when it comes to managing the oilseed crop. In his presentation last month at the Ontario Agricultural Conference, Below notes that it takes four to five times the amount of nitrogen to produce one bushel of soybeans compared to a bushel of corn. “It’s a huge nitrogen-requiring crop,” he says.

Below concedes that soybeans have the ability to fix their own nitrogen through nodulation, but he adds that root nodules can only supply about half of the crops needs. The rest of the nutrient is sourced from previous crop residue breakdown and application.

Based on his research, Below says the optimum time to apply nitrogen to soybeans is prior to planting. On this episode of the RealAgriculture Soybean School, he notes that most research suggests that nitrogen should be applied at R3, before the nodules lose activity and their ability to supply the plant. “But a lot of the time when you plant soybeans, they come out of the ground and look yellow for a while — that’s because the nodules aren’t active yet.”

By applying nitrogen pre-plant, growers will give plants a boost to produce greener leaves, grow faster and also enhance nodulation, says Below. He adds that a pre-plant strategy will become even more important as growers continue to plant soybeans earlier in the spring. (Story continues after the video)

In the video, Below also shares research on the most effective nitrogen sources for soybeans. He’s a fan of controlled-release sources that can be applied at planting such as poly-coated urea. Based on his research, he believes sources that provide readily available plant nitrogen such as UAN and ammonium nitrate tend to be the best choices.

When it comes to application, Below recommends broadcast over precision in-row placement. “Broadcast was clearly the best in our trials because you don’t get a heavy dose that can inhibit the development of the nodules.”

Click here for more Soybean School videos.

Other Episodes

Soybean School (view all)Season 11 (2022) Episode 21

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