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Understanding Yellowing Soybeans


“What’s wrong with my soybeans? They just aren’t very deep green, and they’re growing slowly.” A question we’ve heard all too often this growing season.

In the past, the problem has often been Iron Deficiency Chlorosis (IDC) and HPPD inhibitor chemical carryover. But this year, another factor may be at play.

Not all nitrogen is created equal.

Nitrogen is responsible for protein production, which in turn is responsible for much of the overall crop growth - especially with a crop like soybeans, which are 40% protein. But, it needs to be in the right form.

This season, we’ve seen alarmingly high nitrate levels from residual N left behind from last year’s corn crop. The University of Minnesota even saw many fields with 155 lbs of nitrogen credit in the soil.

What’s the problem?

When nitrate is present, the N2-fixing bacteria won’t colonize, and the plant will abort nodules. This also causes the soybeans to resort to utilizing the N that is available from the soil—the nitrate—AKA the most inefficient form of N for protein production.

To complete the protein synthesis process, nitrate first has to be converted to nitrite, then ammonia, then amino acids before the final conversion to protein. As the nitrate goes through this process, it is stored in plant tissue, and when over-accumulated, induces stress that makes the soybean appear a light green/yellow color.

With excess nitrate in the soil, it’s common to have excess nitrate in the plant—causing the discoloration many growers are seeing in their fields.

There’s still time!

While some growers may fear that their crop is too far gone once it reaches this state, there are options for reversing the problem.

Cobalt is one of the best defenses against yellowing soybeans. Products like BW-Fixate use cobalt to drive N2 fixation, increasing protein production and, ultimately, raising yields.

If your soybeans just aren’t looking right, talk to your local BW agronomist and we’ll get your fields in shape.

Want to learn more about what's happening in soybean fields? Check out this update from Mason Claude, BW Agronomy Research Lead.