This Ohio State Extension bulletin (AGF-519) synthesizes 194 micronutrient fertilizer trials in Ohio corn, soybean, and alfalfa (1976-2017) to guide practical management. Per Tri-State Fertilizer Recommendations, Ohio soils generally supply adequate micronutrients, but deficiencies of B, Cu, Mn, and Zn can occur under specific conditions: Cu on acidic peat/muck (pH<5.3) or black sand for corn/wheat/oats; Mn on peat/muck (pH>5.8) or lakebed soils (pH>6.2) for soybean/corn; Zn on peat, muck, or mineral soil (pH>6.5) for corn and soybean. Recommended tissue sufficiency ranges (ppm) for corn (ear leaf at silking) are Mn 20-150, Fe 21-250, B 4-25, Cu 6-20, Zn 20-70; for soybean (upper trifoliate before flowering) Mn 21-100, Fe 51-350, B 21-55, Cu 10-30, Zn 21-50, Mo 1.0-5.0.

Across 33 corn trials, micronutrient fertilization raised yield by under 1%; across 144 soybean trials it raised yield about 1%, with Mn the only micronutrient showing consistent (though infrequent) response — significant in 6 of 109 soybean Mn trials and 3 of 23 Mn-blend trials. B had no effect in 8 of 9 corn trials. Three recent studies (2013-2016) found soybean responsive to foliar Mn in only 1 of 32 paired trials (sandy, dry soil), and no yield response from B/Cu/Fe/Mn/Zn blends applied broadcast or foliar to corn or soybean at three sites, with tissue levels within sufficiency ranges.

Recommendation: because soil tests poorly predict micronutrient availability and yield responses are rare, growers should combine visual deficiency scouting, soil testing, plant tissue analysis, yield-map monitoring, and awareness of high-risk soil/crop combinations (Table 1) before fertilizing. Always leave an unfertilized check strip and use yield monitors or weigh wagons to verify an economic response before adopting micronutrient fertilization broadly.