Are your crops getting the micronutrients they need when they need them? A recent Purdue University study suggests that it may be past time to pay more attention to micronutrient availability – if you plan to manage the high-yield details.

"Increased yield levels are resulting in higher nutrient removal rate in the grain. In particular, where there is no regular history of manure application, we need to pay more attention to the soil's capacity to meet nutrient removal needs," says Tony Vyn, co-author of the study and professor of agronomy, Purdue University.

Just as high-yielding hybrids take up more nitrogen, they also take up more micronutrients such as zinc, iron, manganese and copper. Vyn suggests that micronutrients could be a yield-limiting factor under high-potential environments. Although many soils have supported crops without any signs of nutrient deficiencies in over a century, bigger plants and more grain harvested mean more micronutrients exported, eventually leading to depletion and deficiency. Sometimes contaminants in lime or macro-nutrient fertilizers applications, or even mineral weathering, can help restore some soil micronutrient concentrations. Knowing the soil test levels for essential micronutrients is a place to start the diagnosis.

Soil-root interface

Even micronutrient sufficient soils may not be enough. Co-author Ignacio Ciampitti, assistant professor of agronomy, Kansas State University, points out that nutrient availability is more complex than simple soil nutrient concentrations. "Nutrient availability is also related to the plant's ability to take up each nutrient at the soil-root interface," he says. "Root system health and soil structure are key factors in micronutrient availability. As root surface area expands, it is quite possible that lower soil micronutrient concentrations are needed to adequately support uptake requirements. More investigations are needed in order to confirm this pattern."

Achieving an ideal soil-root interface depends on having soil conditions that make soil-bound micronutrients soluble to plants. "Multiple factors come into play, including how good the entire production management system is, as well as the soil itself, soil pH, soil moisture, structure, compaction, the hybrid and timing," says Vyn. He emphasizes the need for more research to better understand these factors, in particular timing and placement of application, on fields where micronutrient deficiencies have been observed.

"We are trying to drive home how much micronutrient uptake takes place during grain fill," says Vyn. "We found that 50% of iron and 30% of manganese enters the plant after flowering. Up to 55% of zinc found in the corn plant at maturity enters the plant after silking. However, optimum timing of micronutrient uptake, in terms of high-yield component formation, was not tested in that study of different hybrids, N rates and plant populations."

Foliar micronutrients

For Charles Schulze, who farms near Waynesfield, Ohio, timing is key. For the past 15 years, he has relied on in-furrow liquid starter to ensure micronutrient availability to boost the plant and root system. About 10 years ago, he added a foliar micronutrient application in late June to corn and soybeans and a late-July application to soybeans. Combined with a basic fertility program and sidedressing nitrogen, he claims a 10-12 bu./a. increased yield in corn and a 7-10-bu./a. yield increase in soybeans from the comprehensive program.

"I believe spoon-feeding my crops has to be better than all at once," says Schulze. "Once I saw the plant health and yield benefits from the starter and then the foliar, I ramped up the program accordingly."

Schulze broadcasts phosphorus and potassium in front of the corn planter, lays down a 06-24-06 liquid starter with manganese, boron and zinc and other additives in-furrow along with about 20% of his nitrogen as 10-34-0 dry in a 2x2 alongside the row. That is followed by anhydrous sidedressed for the bulk of his N and the foliar applications.

The starter package from his retailer, Trupointe Co-op's Progressive Crop Technology (PCT) division in Kettlersville, Ohio, includes a growth promotant to insure fast and uniform germination. It relies on orthophosphorous for rapid uptake and includes bacteria and fungi to jumpstart the interaction of micronutrients with plant root hairs. EDTA as a chelate ensures the micronutrients are released farther into the season.

Not for every producer

While Trupointe agronomist Matt Harbur is enthusiastic about the benefits of the program they offer, he cautions it is not for every producer. He agrees with Vyn that anything less than a well-managed system is not going to accrue full benefits.

"Yield depends on overall management skills," says Harbur. "If you aren't taking care of basics, why invest in micros? If the basics are in place, why not be proactive to ensure environmental conditions don't dial back yields?"

 "The idea is to improve nutrient availability, enhance the plant immune system and stimulate root growth and root hairs, which in soybeans are critical to improving nodulation, " says Harbur. "We also include phosphite and monopotassium phosphate. They work like a vaccine to stimulate the plant to produce disease-fighting proteins. Once produced, they are stored and available for a robust defense against disease or other pests. We also use low salt formulations to reduce burning with the foliar applications."

Schulze sees a benefit from each step in the program, especially the final soybean foliar application. "I feel the second trip over the soybeans keeps late-setting pods from aborting and gives me more seeds per pod," he says.

Schulze knows the liquid starter has an impact, thanks to an 'accidental' side-by-side event last year. "I forgot to activate the liquid starter valve at the beginning of one pass," he recalls. "When I came into sidedress, the corn was three inches shorter than surrounding corn that received the starter."

A 3-in. difference means significantly more leaf area available for photosynthesis with implications clear to harvest and Schulze's bottom line. "The PCT program paid off before we had high corn and soybean prices and I'm confident it will pay off now," says Schulze.