This Iowa State Integrated Crop Management blog (2024) addresses whether growers need micronutrients in their soil fertility program for corn and soybean. Micronutrients (B, Cl, Co, Cu, Fe, Mn, Mo, Ni, Zn) are needed in very small amounts (usually 1-3 lb/acre). Iowa soils generally supply adequate micronutrients except on sandy soils, highly weathered soils, acid organic soils, and calcareous soils. A key exception is iron deficiency chlorosis (IDC) in soybean on calcareous soils in north-central and western Iowa; in-furrow fluid iron chelate can raise yield on these soils but not to levels seen on noncalcareous ground.

Decades of Iowa State University micronutrient research (1960s-2015) across many soil types and pH ranges, testing stand-alone, foliar, and soil-applied micronutrient products, found no consistent yield response for most micronutrients. Occasional yield responses occurred with zinc in corn, and with molybdenum in soybean only on extremely acidic soils (pH ≤5.4) -- a condition better corrected by liming. Because of this inconsistency, most micronutrients (unlike P and K) have not been successfully calibrated to soil/tissue tests; zinc is the exception, with enough Iowa/north-central regional data to correlate soil test levels with corn and sorghum response.

Recommendations: before considering micronutrients, first correct soil pH, maintain optimal P and K, and apply sulfur; then apply zinc according to soil test results for corn/sorghum. Only explore other micronutrients if budget allows, and first ask whether soil pH is optimal, soils are sandy, or deficiency symptoms are visible. For on-farm trials, include an untreated check, test multiple rates, and use both soil and tissue testing to identify which micronutrient (if any) is actually limiting, since most products showed no response beyond zinc.