Meeting Soybean Fertility Needs

By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff.

One goal of the Ohio Soybean Council is to make Ohio’s soybean farmers more profitable. With the task of increasing soybean yields and increasing the return on investment (ROI), a number of production practices are often considered. One of those practices, promoted by Ag retailers, is the application of foliar fertilizer. In a multistate trial conducted in 2019 and 2020 by Emma Matcham, a PHD student at the University of Wisconsin, prophylactic foliar fertilizer was applied. “A prophylactic application means that in the trial we were applying fertilizer before there was noticeable nutrient deficiency expressed in the crop,” said Matcham. “For this research, 46 trials were conducted in 16 states across the eastern half of the U.S. Some of the products included macronutrients such as Nitrogen (N), Potassium (K), and Sulfur (S), some micronutrients, and some products included a combination.

All products were sprayed at the R3 growth stage to coincide with a fungicide and insecticide application. There were a wide variety of growing environments and average yield ranges.”

Each plot had 7 treatments, with 6 different products along with one untreated control. “Most of the products had application rates with under 1 pound per acre of the nutrient components. Soil test were taken from each plot to ensure there was not a nutrient deficiency in the soil to begin with. Plant tissue samples were taken before and after the application to see how the leaves changed before and after the applications,” said Matcham, “The final results showed that there was not much difference in the yield between the treatments. In the average across all the states, we found that there was a similar variation in yield across the treatments. The statistics are still being run to determine if there was a statistically significant difference between the treatments and the untreated control.”

“We expected there to be a significant difference in yield between site years,” said Matcham. “Looking at the interaction between treatments and sight years, there was not a significant difference in yield between treatments, or the combination of treatments and sight years.”

“This is really important,” said Matcham. “What is says is that in our study we are not seeing a benefit to prophylactic nutrient application. This is because in the overall average across all of the site years, we are not seeing an increase in yield associated to any of the treatments on their own. We also are not seeing a difference in how the treatments are responding. There is not a significant difference in yield between foliar nutrient products.”

While only 6 products were tested in this multi-state study, Matcham is confident that the results would be similar for the products not tested. “Looking back at research trials over the past 30 years, similar results were found in previous trials conducted in Iowa and Michigan in the 1990’s and 2010’s,” said Matcham.

As new products come out, Matcham suggested three important things to think about. “Farmers should ask themselves three key questions when considering a foliar fertilizer product,” said Matcham. “Are you seeing trial results that took place over multiple years and multiple sites? Can you get information from someone not selling the product? Can you try the product on some test strips on your own farm before trying it on a larger scale?”

“On sandy soils, sometimes Manganese (Mn) is limiting, but using Mn foliar fertilizer prophylactically is not always effective,” said Matcham.

If a farmer is evaluating foliar fertilization applications and trying to decide whether or not to do it, and if so when to pull the trigger; return on investment (ROI) must be considered,” said Dr. Steven Culman, Soil Fertility Specialist for The Ohio State University. “Even if there is a yield increase, it may not increase ROI or profitability.” Dr. Culman conducted similar trials in Ohio, and did not find any positive response in yield.