Extra nitrogen doesn't always translate to extra yield in soybeans. Consider the practice carefully. (DTN photo by Pamela Smith)

We have heard a lot about applying nitrogen (N) on soybeans over the past few years. It comes with mixed reviews because supplemental N application only provides a yield benefit about half the time. Commodity prices over the past few years have also dimmed the prospect of return on investment.

Still, we don't want to abandon the concept as a potential practice just yet. It still has a place when applied in the right situation at the right time with the right product.

The challenge is figuring out exactly when it pays and a recommended supplemental rate. Soil texture (potential N supply), soil pH and electroconductivity (affects N fixation) and the growing season (available moisture) all factor into the opportunity to get a yield response.

Ignacio Ciampitti, agronomist and soybean specialist at Kansas State University, has been studying N use in soybeans. He identified that measuring uriede concentrations in the plant can measure N fixation. Uriedes are the primary end product of the fixation process.

According to Ciampitti's research, supplemental N isn't reducing N fixation as we have long assumed. Therefore, applying fertilizer won't shut down fixation.

Nitrogen fixation is primarily affected by environment and particularly soil. "In some soils, plants are only capable of producing 30% of their N needs, while in other soils as much as 80%," Ciampitti said. "In these contrasting environments, plants either rely more on N fixation or on soil sources. We are just beginning to understand in which soil environments N fixation responds and need to calculate a soil's N supplying power to compensate."