From the Farm: Nitrogen Misconception

The Morning Show

Farmers have been rotating crops for many years, planting corn after soybeans, with the thought the corn could take advantage of all the nitrogen soybeans put into the soil. If that is your perception, buckle your seatbelt as you watch Stu’s report from the farm.

Stu Ellis

If you, your Dad and your Granddad expected soybeans to bolster corn yields, that popular theory is blown away by University of Illinois crop physiologist Fred Below…

Fred Below

Its not that soybean nodules are a bad thing, stu, they do provide some of the nitrogen that the crop needs. The problem is, that with the yields we are growing, the nodules only provide about half the nitrogen that soybean needs. That means the rest of it has to come out of the soil. So in today’s modern yields, there isn’t any such thing as a soybean nitrogen credit, what it really is, is a corn residue penalty. That’s why when you rotate corn with soybean you can get by with a little less nitrogen fertilizer because you have a year for that residue to degrade and that means that residue does not immobilize as much of the nitrogen. So its really a corn residue penalty, not a soybean nitrogen credit, like we used to think.

Stu Ellis

A lot of farmers are going to say really, how did this change?

Fred Below

Well, I think its changed slowly, Stu as we’ve increased soybean yields. So if you think about the nodules, they are expensive to the plant. And so the plant is going to use the cheapest source of nitrogen first, which by the way is going to be the soil. Like I said the soybean only gets about half its nitrogen from the nodules, the rest of it has to come from the breakdown of residue, or the release of nitrogen from the soil. So again I want to dispel the idea that soybean adds nitrogen into the soil. And I don’t want growers to think if I grow soybean a couple years in a row, I’m going to build up my soil nitrogen. Nothing could be further from the truth.

Stu Ellis

And that’s your morning jolt from Dr. Fred Below. I’m Stu Ellis with WCIA3 your local news leader.

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