By Mike Staton
There continues to be interest in applying foliar fertilizers to soybeans. This is true even though foliar fertilization has produced mixed results in hundreds of university trials conducted across the U.S. This article summarizes the results from on-farm soybean foliar fertilizer trials conducted in Michigan over the past five years. The research was conducted by the Soybean Management and Research Technology (SMaRT) project, a partnership between Michigan State University Extension (MSUE) and the Michigan Soybean Promotion Committee.
The effects of five foliar fertilizers (3-16-16, 3-18-18, 26-0-0, various boron carriers and manganese sulfate monohydrate) on soybean yields has been evaluated in on-farm replicated trials in Michigan. The 3-16-16 was evaluated at 27 locations and the 3-18-18 was evaluated at 24 locations in 2009 and 2010. Both products were applied at R1 and again at R3. All of the 3-16-16 applications also contained trace amounts of micronutrients and the second application of 3-16-16 contained sugar to improve nutrient uptake. The 3-16-16 and the 3-18-18 foliar fertilizer treatments were less profitable than the untreated control treatment when all locations were combined and analyzed.
The 26-0-0 foliar fertilizer was evaluated at 18 locations in 2011 and 2012. One gallon of 26-0-0 per acre was applied between R2 and R4. Again, when all 18 locations were combined and analyzed, the foliar fertilizer treatment was less profitable than the untreated control treatment.
Various boron fertilizers were compared to an untreated control at six locations. The trials were conducted on potentially responsive sites and the boron was applied at 0.25 pounds of actual boron per acre at R1. The foliar boron treatments did not increase soybean yields compared to the untreated control.
Two trials evaluating the effects of manganese foliar fertilizer applications on soybean yields were conducted in 2013. The first trial compared manganese sulfate monohydrate fertilizer to a popular EDTA chelate manganese fertilizer at two highly responsive sites (muck soils). The manganese sulfate monohydrate increased soybean yields by 1.9 bushels per acre and income by $23 per acre over the EDTA chelate. The second onfarm research trial evaluated the effect of applying a manganese foliar fertilizer to soybeans without visible manganese deficiency symptoms. This trial was conducted at two potentially responsive sites (lakebed soils with pH levels of 7.4).
The trial results confirmed that manganese foliar fertilizer applications made in the absence of visible deficiency symptoms will not increase soybean yields. In fact, research conducted by the Ohio State University in 2008 and 2009 showed that foliar applications of manganese fertilizer in the absence of foliar deficiency symptoms actually reduced soybean yields.
Due to the low probability of realizing an economic return, applying foliar fertilizers to soybeans is not recommended by MSUE. The exception to this is foliar applications of manganese fertilizer when manganese deficiency symptoms are visible. Please see the MSU Extension news article on identifying and correcting manganese deficiency in soybeans for more information.