Opportunity for significant yield increases with targeted applications

ST. LOUIS — The availability of micronutrients can vary significantly across a field.

“We need to take advantage of that and target application to parts of the field while thinking about return to investment,” said Dorivar Ruiz-Diaz, professor and soil fertility specialist at Kansas State University.

“We’ve done a lot more work with pH and we know pH is highly variable in the field which is why we recommend variable application,” Ruiz-Diaz said during a presentation at the InfoAg Conference, hosted by The Fertilizer Institute.

“I think there’s opportunity to see significant yield increases that will be economical for farmers if we target to take advantage of the responsive areas,” he said.

For example, Ruiz-Diaz said, the critical value for zinc is 1 part per million.

“Some fields are fairly uniform and other fields are highly variable,” he said. “Some areas are way above the critical value and won’t benefit from zinc fertilizer applications.”

Manganese levels in fields tend to be opposite, Ruiz-Diaz said.

“Areas with the lowest manganese concentration have the highest zinc levels,” Ruiz-Diaz said.

“One nutrient that is particularly challenging is iron,” he said. “Here the pH is much higher and the iron is the lowest so the pH is driving the availability of the iron.”

In some cases, Ruiz-Diaz said, the removal of phosphorus can relate closely to zinc.

“However, that relationship is not the same for other micronutrients,” he said. “Micronutrients behave differently so we need to manage them differently.”

In a research trial, one pound of zinc per acre was applied in furrow, close to the roots of the corn.

“This field saw a yield increase of more than 10 bushels per acre,” Ruiz-Diaz said. “So, there is a potential to see a significant yield response.”

Iron chlorosis can be a challenge for some farmers.

“Soybeans are very sensitive to iron chlorosis,” Ruiz-Diaz said. “The soybeans will germinate and shortly after that stop growing and in many cases die.”

Iron chlorosis can also have a yield impact on corn and sorghum.

“We have been using chelated fertilizer sources for many years however in the case of iron chlorosis we haven’t seen the level of yield response to some of the chelated iron sources,” Ruiz-Diaz said.

“One of the challenges with chelates is that some types may not be stable at higher pH levels,” he said.

“We’ve used EDDHA, a chelating agent, and had good results in soybeans and sorghum for iron chlorosis,” he said. “We were able to fix the issue in many cases, but it may not be economical unless we can take advantage of strategic application and target the areas that can benefit.”

In a research trial, three pounds of EDDHA was applied in furrow on a sorghum field.

“We still had some iron chlorosis show up, so it was not a complete fix,” Ruiz-Diaz said. “The yields increased 27 bushels over the control sorghum, and with the cost of application at $30, the application did make money.”

Micronutrient fertilizer sources are not necessarily the same in terms of plant availability and cost, Ruiz-Diaz said.

“There are big opportunities for high return to investment if we target areas for applications of micronutrients,” he said. “However, blanket applications have not been effective, and they are difficult to be economical because of the high prices of fertilizers.”