Foliar Manganese Recommendations for Michigan Soybeans On Chronically Mn Deficient Soils.

Soybeans are produced on significant calcareous lakebed and organic muck landbases in Michigan.  The high pH of these soils, and for muck soils, high organic matter concentrations, decreases Mn availability, making management of this nutrient a particular challenge.  The relatively localized acreage on which these conditions can be found has resulted in the development of few specific recommendations for Mn in these production scenarios.  Foliar applications of Mn are effective at supplying plant Mn demands, but 1-2 applications are frequently necessary on calcareous soils and 3-4 on muck soils.  In order to minimize individual spray applications, producers often tank-mix glyphosate herbicide with Mn fertilizers.  However, interactions have been documented between glyphosate and Mn in spray solutions and in the soybean plant.  These effects are known to vary with Mn form and timing.  Manganese fertilizer recommendations are needed that take into account Mn fertilizer efficiency as part of broader management systems.  Management scenarios examined include attempting to minimize all Mn nutrition stress, avoiding Mn applications three days prior or seven days following glyphosate application, and tank-mixing Mn and glyphosate herbicide.  Results from this work will not only inform producers of how best to manage Mn nutrition, but provide information on how best to manage inherent Mn deficiencies as part of their broader management systems.