Soybean Response to Broadcast Application of Boron, Chloride, Manganese and Zinc.

Micronutrients at low concentrations are considered essential for plant growth. There has been increased pressure for farmers to apply micronutrients to soybean (Glycine max Var Merr.) due to a perception that deficiencies have increased.  The objective of this study was to evaluate soybean yield and quality response to broadcast micronutrients. A study was conducted in Minnesota from 2013 to 2014. Treatments consisted of B (0 or 2.2 kg ha^-1), Cl (0 or 22.4 kg ha^-1), Mn (0 or 11.2 kg ha^-1), and Zn (0 or 11.2 kg ha^-1) applied using a factorial design replicated four times. Soybean grain yield did not respond to Cl and Mn application. Yield reduction occurred following B application at two site-years. The only positive impact of micronutrient occurred at one location where Zn resulted in slight yield increase. Application of B and Zn significantly increased the respective tissue concentrations in grain and trifoliate tissues. Application of Cl increased the concentration of Cl in soybean trifoliate at R2 but Cl concentration in the harvested grain was not affected by fertilizer application.  Trifoliate and grain Mn concentration was not affected by Mn fertilizer application. The data indicate that B, Cl, and Zn were available to the plant from the applied fertilizer but were seldom to never required to increase soybean grain yield while there was no evidence that Mn was taken up by the plant indicating that the soil likely supplied all the Mn required to produce maximum grain yield.