Soybean School: How much nitrogen and when?

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."

#farming #nitrogen #fertilizer #agronomy

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