This study investigated the effects of micronutrient fertilization on corn and soybean grain yields through two field experiments conducted from 2012 to 2014 in Iowa on Marcus silty clay loam. The trials evaluated both soil applications (boron, manganese, and zinc) and foliar applications (boron, copper, manganese, zinc, and a multi-nutrient mixture). Baseline soil tests indicated that initial levels of copper, manganese, and zinc were generally adequate or high relative to regional sufficiency thresholds, while soil boron levels fell into intermediate ranges. Although fertilizer treatments frequently increased the concentration of micronutrients within the harvested grain, neither soil-applied nor foliar-applied micronutrients produced statistically significant grain yield increases for corn or soybean in any trial or year. The authors concluded that standard regional soil-test interpretations successfully predicted the lack of yield response for copper, manganese, and zinc. However, for boron, interpretations used in certain states incorrectly suggested a potential response even though none was observed. Overall, the findings indicate that micronutrient fertilization provides no economic grain yield benefit for corn and soybean when initial soil test levels are sufficient.