This Penn State Extension article explains routine mid-season tissue testing to detect micronutrient sufficiency in corn and soybean before deficiencies become visible ("hidden hunger"). Soil tests are considered unreliable for micronutrients such as iron, zinc, manganese, boron, and copper, making tissue testing especially useful for these elements. Sampling: for corn, collect the ear leaf at silking; for soybean, clip the uppermost fully-developed trifoliates prior to or at early flowering (sampling after pod set is not recommended). Take at least 10, preferably 20-30, plants per field/sub-field, avoid diseased, pest-damaged, drought-stressed, or flooded tissue, and ship samples in breathable paper bags to prevent mold. Reported sufficiency ranges (ppm) for corn ear leaf: manganese 20-150, iron 20-250, boron 4-25, copper 6-20, zinc 20-70. For soybean uppermost leaves: manganese 21-150, iron 50-350, boron 20-50, copper 10-30, zinc 20-50. Values above range are not yield-limiting but may signal other fertility issues (e.g., high iron/manganese can indicate low soil pH). Values below range indicate the nutrient may be yield-limiting. For corn, rescue applications at silking are often impractical due to sprayer clearance; soybean, being shorter and more plastic in growth, can more feasibly receive foliar rescue micronutrient applications since only small doses are needed. Even without a rescue treatment, a low result flags problems to address via soil testing before the next season, since tissue levels reflect uptake, not necessarily true soil deficiency.