How do I identify micronutrient deficiencies in plants?
Written by
Tina Carter
Reviewed by
Prof. Martin Thorne, Ph.D.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
