MSU Extension Soybeans

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 United States. This article summarizes the results from 117 on-farm soybean foliar fertilizer trials conducted in Michigan over the past 10 years. The research was conducted by the Soybean Management and Research Technology (SMaRT) project, a partnership between Michigan State University Extension and the Michigan Soybean Promotion Committee. 

Ten foliar fertilizers (3-16-16, 3-18-18, 2-14-14-2, 26-0-0, three boron products, manganese sulfate monohydrate, 0-0-25-17 and 0-0-19-13) were compared to an unfertilized control in on-farm, replicated trials in Michigan between 2009 and 2018. In 2016 and 2017, field-specific prescription foliar fertilizer mixtures were compared to an unfertilized control. Cooperating producers were encouraged to equip and operate their sprayers to maximize canopy penetration and leaf coverage. We also eliminated sprayer tracks from being a factor by ensuring that tracks were either present or absent from the harvested area in all treatments in each trial. Each of the projects will be briefly summarized in this article.

A 3-16-16 foliar fertilizer was evaluated at 27 locations in 2009 and 2010. The fertilizer contained trace amounts of chelated micronutrients and was applied with 1 qt/ac of sugar at R1 and again at R3. The first application was at 1gal/ac and the second was at 0.5 gal/ac. A controlled-release nitrogen fertilizer was included in the second application. The 3-16-16 increased yields and income at two of the 27 sites (7% of the time) and decreased yields at one site. When all sites were combined, the 3-16-16 was less profitable that the unfertilized control.

A 3-18-18 foliar fertilizer was evaluated at 24 locations in 2009 and 2010. The fertilizer was applied alone at 1 gal/ac at R1 and at 2 gal/ac at R3. The 3-18-18 foliar fertilizer treatments increased soybean yields and income at two of the 24 sites (8% of the time) but were less profitable than the unfertilized control treatment when all locations were combined.

A 2-14-14-2 foliar fertilizer was evaluated at two sites in 2011. The product was applied at 2.25 gal/ac with sugar at the V3 to V4 growth stages. The yields produced by the foliar fertilizer and the unfertilized control were not significantly different at either location.  

The 26-0-0 foliar fertilizer was evaluated at 18 locations in 2011 and 2012. The fertilizer also contained trace amounts of micronutrients. A single application of 26-0-0 at 1 gal/ac was applied between R2 and R4. The 26-0-0 increased soybean yields and income at three of the 18 locations (17% of the time). When all 18 sites were combined, the 26-0-0 also produced 0.6 bu/ac more than the untreated control. However, this was not enough to cover product and application costs. 

Three boron fertilizers were compared to an untreated control at nine locations from 2011 to 2013. The trials were conducted on potentially responsive sites (coarse-textured soils with low organic matter levels) and the boron was applied at 0.25 lb. 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 dollars per acre over the EDTA chelate. The second on-farm 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.

A single application of potassium thiosulfate (0-0-25-17) was compared to an unfertilized control at four locations in 2014. The 0-0-25-17 was applied at 1 gal/ac at the R1 growth stage. The 0-0-25-17 did not increase yields at any of the locations. The lack of response to the potassium provided by the fertilizer is easily explained by the fact that the soil test potassium levels were high to very high in all the trials.

Field-specific prescription foliar fertilizer mixtures were compared to an unfertilized control at nine locations in 2016 and 11 locations in 2017. The foliar fertilizer mixtures were based on composite soil samples collected from the trial areas. Foliar fertilizers were applied at V4 when the row spacing was 15 inches or less and at R1 when the rows were wider than 15 inches. The prescription foliar fertilizer mixture increased soybean yields at three of the 20 sites (15% of the time). However, the yield increases were large enough to be profitable at only one site.

A single foliar application of a 0-0-19-13 fertilizer and a proprietary adjuvant was compared to an unfertilized control at nine locations in 2018. The fertilizer was applied at 1 qt/ac and the adjuvant was applied at 6.4 oz/ac. Both products were applied at R1. The foliar application did not increase soybean yields in any of the trials even though potassium soil test levels were low at two sites and sulfur soil test levels were low at five sites.

The foliar fertilizer application was less profitable than the unfertilized control in 109 of the 117 trials conducted in Michigan since 2009. Due to the low probability (7%) of realizing an economic return, applying foliar fertilizers to soybeans is not recommended by Michigan State University Extension unless visible manganese deficiency symptoms are present. Please see the MSU Extension news article on identifying and correcting manganese deficiency in soybeans for more information. Foliar fertilizer applications are more likely to produce an economic return when nutrient levels in the soil are low or root uptake is reduced due to restricted root growth.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.