Headlines questioning the efficacy of foliar fertilizers in soybeans come as no surprise to chemical engineer Jae Fielding. Molecular science shows plant leaves and key components of many, but not all, foliar fertilizer products are literal polar opposites — chemically guaranteed to repel each other, he says, no matter the crop.
“It’s like trying to shove two magnets together. If the components of a foliar applied fertilizer product are going to make it into the leaf instead of rolling off, they must at the very least be nonpolar and nonionic,” he says.
Unfortunately, many foliar fertilizer products contain critical components—sometimes more than one—that are either polar or ionic. Salts, such as ammonium nitrate and potassium chloride, are common polarized problem components. They need to be neutralized to make it into the plant.
Fielding, a retired 26-year Dow Chemical employee in Polymer Chemistry and current Kugler sales representative who also assists in product research and production, says there are four attributes an effective Nitrogen foliar fertilizer product should possess.
- Fertilizer molecules and polymers must have a nonpolar molecular structure.
- Fertilizer molecules and polymers must have non-ionic molecular structures.
- The product must contain soluble carbon.
- Nitrogen in an available form.
Shifting to neutral. It’s not enough that the key components and polymers lack magnetic charge, the foliar fertilizer product in its entirety needs to be neutral. Soluble carbon serves to neutralize ionic or polar aspects of carriers, including water.
“Soluble carbon has surfactant properties. It helps neutralize the foliar fertilizer product along with any tank-mixed products. Water polarity is also reduced, increasing the ability of all applied products to stick to plant leaves,” Fielding says.
Stoking the fire. Neutrality ensures components are chemically able to cross into the plant. Nitrogen is what fuels results. The macro nutrient is critical to plant growth and is a component of chlorophyll. That’s why leaves turn yellow when they’re nitrogen deficient.
“Nitrogen applications facilitate creation of more chlorophyll which results in greener, bigger leaves that in turn photosynthesize more light,” says Fielding. The results of photosynthesis are measured in yield.
It can’t be just any nitrogen for a foliar application, though. Applying 28 percent nitrogen (UAN) or 32 percent nitrogen (UAN) as a foliar will burn crop leaves—reducing productive chlorophyll, he says.
In the right form, nitrogen is readily absorbed by plant leaves without damage. Well-fed plants increase their rate of photosynthesis, drawing more water and nutrients from the soil. Foliar feeding fosters top-down and bottom-up nutrition simultaneously, Fielding says.
Foliar feeding can be a highly effective component of a strategic, efficient, and responsible fertility program. Splitting fertilizer applications throughout the season mitigates financial risk to growers and minimizes environmental nitrogen loss.
Slow-release foliar products, like Kugler’s KQ-XRN, create the possibility of further extending nitrogen delivery. In the case of KQ-XRN, three separate polymer components keep applied fertility on the leaf releasing nitrogen for up to six weeks.
Beyond soybeans. The effectiveness of foliar fertilizer applications in soybeans specifically was recently called into doubt by a study published in 2021. Qualified State Soybean Boards funded field trials of six commercially available foliar nutrient treatments in 16 states. Data showed little to no benefit to the applications.
While jarring, this information requires a more critical look, Fielding says. “The products tested do not represent all foliar fertilizer products. It’s apples to oranges or worse. Polymers, surfactant characteristics, fertilizer components, polarity, and more can all have significant impacts on performance,” he says.
Performance of these and other foliar fertilizer products on soybeans is also unrelated to their performance on other crops. Foliar feeding can produce dramatic outcomes in a variety of crops and across a range of conditions.
“For best foliar fertilizer application results, farmers should select products specifically engineered for foliar feeding that meet the basic criteria of being nonpolar and nonionic. As with any other product or practice, doing their own on-farm, side-by-side trials before committing the whole farm is a sound strategy,” Fielding says.