Micronutrient deficiencies are expressed through specific plant distress indicators. For example, yellow streaking occurs between leaf veins due to insufficient iron. Twisted leaves of corn with white streaks indicate a lack of zinc. I've even diagnosed boron deficiency in beets from observing the blackening of heart roots, a call that soil tests cannot diagnose alone.
Iron Deficiency
- Visual sign: Interveinal chlorosis in young leaves
- High-risk crops: Soybeans, azaleas, blueberries
- Fix: Apply 2 lb/acre iron chelate + lower soil pH below 6.5
Zinc Deficiency
- Visual sign: Stunted growth with twisted leaf ribs
- High-risk crops: Corn, pecans, citrus
- Fix: Band 5 lb/acre zinc sulfate at planting
Soil tests are known to miss 40% of active deficiencies, while testing plant tissue, particularly during flowering, tends to provide results that the soil can't. A recent client had a field of stunted wheat that tested "fine" for soil manganese, but tissue analysis was < 10 ppm. Foliar application resolved rapid necrosis in about 10 days. Always test both soil and tissue and do it quickly!
- pH imbalances mask the availability of nutrients, for instance, molybdenum is hidden in acidic soils but is unleashed when lime is applied to raise pH. I wrote a TEP report for an alfalfa grower who limed an over-limited field of alfalfa, losing 30% yield from molybdenum toxicity. Always balance pH first, then apply micronutrients second. Then observe any changes quarterly.
Prevent repeated problems by utilizing micronutrient-amended compost. Before planting, continue to incorporate compost with 50 lb/acre of boron into broccoli beds. In citrus crops, amend fertilizer blends with zinc-coated urea. Utilize GPS soil sampling to map deficiency areas, which will reduce costs by treating only specific areas.
Read the full article: 7 Essential Micronutrients for Plants: Complete Guide
