This South Dakota State University Extension chapter (iGrow Corn Best Management Practices, revised 2023) provides fertilizer recommendation guidance for corn, including a specific section on zinc (Zn) and iron (Fe). Micronutrient deficiencies generally result from environmental conditions and can be temporary; soil testing is recommended when deficiency is suspected. In most cases, secondary nutrients (Ca, Mg, S) and micronutrients (B, Zn, Fe, Cu, Mo, Mn) have limited impact on South Dakota corn yields.

Zinc deficiency can occur on coarse-textured soils, eroded soils, organic soils, or soils with high phosphorus levels; cool, wet soil conditions can worsen Zn availability, causing feathering/striping symptoms on the youngest leaves. Zinc recommendations (Table 23.8, based on zinc sulfate) by DTPA soil test level: 0-0.25 ppm (very low) and 0.26-0.50 ppm (low) = 10 lb Zn/acre; 0.51-0.75 ppm (medium) = 5 lb/acre; 0.76-1.00 ppm (high) = 2.5 lb/acre; >1.00 ppm (very high) = 0 lb/acre. As of 2015 these rates were under revision, with initial analysis suggesting 2.5 lb Zn/acre for the high range.

Iron deficiency may occur on leveled or eroded soils where calcareous subsoil is exposed, producing yellowing with interveinal striping on younger leaves. Fe recommendations by soil test ppm: 0-2.5 (low) and 2.6-4.5 = 0.15 lb Fe/acre; >4.5 ppm = 0 lb/acre. Correcting Fe deficiency is difficult; applying manure or biosolids is suggested as an effective approach to minimize yield loss from Fe chlorosis.