Blanket applications of foliar fertilizer in soybeans offer no economic or yield benefit when no nutrient deficiency is visible. That's the firm conclusion from Science for Success, a landmark research project funded by U.S. state soybean boards.

In 2019-2020, 46 trials across 16 states tested six macro- and micronutrient combinations at the R3 growth stage. The takeaway: without deficiency symptoms, foliar feeding did not enhance yield.

"That conclusion still holds," says Laura Lindsey of Ohio State. Shawn Conley, University of Wisconsin, agrees: "Only when a deficiency is identified, applications like manganese or iron are clearly beneficial."

A 2014-15 manganese trial in Ohio saw a 2.1 bu/acre increase only in one environment, which had interveinal chlorosis and high pH (7.7).

What if a deficiency appears mid-season? That's a different story. A new Science for Success project focuses on in-season potassium management, with promising results from Arkansas.

Does more fertilizer mean more yield? Not always. As University of Minnesota agronomist Seth Naeve explains, other factors like water, heat, or pests can limit yield, rendering added nutrients ineffective.

An Alternative View from the Field

Steve Gauck, Indiana farmer and agronomy manager at Beck's, once agreed with those findings-until Practical Farm Research (PFR) data showed certain nutrients at key times boosted yield.

Now, foliar feeding is part of his operation, but it's not one-size-fits-all. "We don't do a big R3 shot. We apply nutrients when the plant needs them most," he says.

His case shows: targeted, knowledge-based applications may work-but routine blanket foliar fertilizer does not.