Evaluation of Manganese and Glyphosate Formulations and Timing on Soybean Yield.

Soybean “flashing,” or yellowing of leaves, is sometimes associated with glyphosate application in glyphosate-resistant soybeans, a suspected symptom of manganese deficiency.  Though the tissue analyses usually show adequate manganese content, the chlorosis indicative of manganese deficiency reflects the possibility that antagonism between glyphosate and manganese may exist and negatively affect manganese metabolism and soybean yield.  It is suggested in the literature also that manganese application to plants without deficiencies may be detrimental to plant performance.  This experiment utilized two formulations of glyphosate differing in adjuvants and salt formulation (potassium and isopropylamine) and three manganese formulations (mannitol, glucoheptonate, and EDTA) on glyphosate-resistant soybeans in a randomized complete block design on two sites in Ohio (Northwest and Western research stations) in 2007.  Treatments included tank-mixing each glyphosate product with a manganese product, and sequential foliar manganese applications 7 to 10 days after glyphosate treatments.  Soybean yield data was collected by combine harvesting and analyzed.  At the Northwest site, there was a yield increase associated with any foliar manganese application versus no manganese applied.  There were differences between the glyphosate formulations and the glyphosate and manganese source comparisons.  At the Western site, foliar manganese application depressed soybean yield compared to the untreated plots, regardless of manganese or glyphosate formulation.