Micronutrient applications remain a sound strategy where deficiencies may exist. University plant pathologists and soil fertility specialists both urge farmers to monitor fields with a prior history of nutrient deficiencies and perform soil or tissue tests for confirmation.

"Soil conditions like compaction will limit manganese availability, high phosphorus (P) levels limit zinc availability, and high (soil) organic matter often limits copper," says Brandt’s Smith. "We find zinc use in corn can help with phosphate deficiency, root development and early growth. Manganese applied to soybeans is useful for photosynthesis, pest resistance and energy production."

Micronutrients are essential for plants to complete life cycles, says Fabian Fernandez, University of Illinois soil fertility specialist, "just as important as N, P and K. But whether or not micronutrients need to be added to individual fields or even parts of fields is open for discussion. Deficiencies are not common and often are related to soil type."

While Fernandez says Zn may help with germination, he does not see much response in yield from general Zn applications. Upper Midwest farmers with low organic matter or sandy soils or very high P levels from common inorganic fertilizer applications may see the most response, he says.

"Just as with other nutrients, when a micronutrient is deficient you will be able to tell by looking at the crop. Those are fields I would treat with the nutrient that is a problem," he says. "I also would apply micronutrients if I am interested in seeing the potential for a response, on a trial basis only, having strips with and without the micronutrient applied."

Dan Kaiser, University of Minnesota Extension soil scientist, concurs. He recommends soil sampling and a Zn soil test where there may be indication of potential problems in cornfields.

Iron deficiencies are common in soybeans grown west of the Mississippi River, Kaiser and Fernandez say. Manganese deficiencies are more common east of the river; high-pH soils are the trigger, experts say.

"I find it hard to recommend manganese applications in soybeans. We see no clear or consistent responses to micronutrient use," he says. "We have research looking at the uptake of nutrients and how the various elements are related. But for now, we do not see many deficiencies, so farmers do not need much in the way of micronutrients. I suggest interested farmers look at on-farm micronutrient test strips and see if it returns for your operation.