A recent study conducted by agronomists from 16 U.S. states shows that the use of foliar-applied nutrient products on soybean crops does not consistently increase yield. The study, which was conducted over the 2019 and 2020 growing seasons, tested six foliar nutrient treatments on soybean grain yield and composition at 46 different sites.

Results showed that soybean grain yield and composition differed among sites but not among foliar fertilizer treatments. The study concludes that the prophylactic use of foliar fertilizers is likely to decrease the profitability of soybean production. As such, foliar fertilizer products tested in this study and similar products should not be recommended to U.S. soybean farmers in the absence of visual symptoms of nutrient deficiency.

This finding is important for the soybean farming industry as many farmers have been interested in using foliar-applied nutrient products to increase soybean yield since the 1970s, despite limited evidence that these products offer consistent yield increases when used prophylactically. The recent renewed interest in foliar fertilizer products for soybean production has likely been driven by elevated soybean prices.

“As a group of soybean agronomists, we have developed a network for testing products and technologies that spans the entire country,” said Seth Naeve, University of Minnesota Extension soybean agronomist and a co-author on the study. “This allows us to ask very highly applied questions and examine where specific products are most likely to lead to increased yields and profits. We simulate how farmers might choose and deploy these products and determine their likelihood of success.”

The study's results are consistent with past research on foliar fertilizer and soybean yield, which has shown inconsistent impacts. While some studies have shown small increases in yield with early-season prophylactic foliar fertilizer application, the magnitude of yield improvement is relatively small and generally does not pay for the cost of application. Moreover, it is difficult to identify field conditions where agronomists should recommend foliar fertilizer application in soybean because past studies have shown that soybean yield response is rare.

“While the results of this trial may not be very exciting, negative results can be as important for farmers as positive ones,” Naeve added.

The study was led by Dr. Emma Matcham as part of her doctoral research at the University of Wisconsin, in collaboration with agronomists from 15 other states. Dr. Matcham is now an Assistant Professor at the University of Florida. The research team hopes that the results of this study will help soybean farmers make informed decisions regarding the use of foliar-applied nutrient products on their crops.

Read the full study in Agronomy Journal.