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Iron deficiency is not as common in Illinois as other parts of the Corn Belt, particularly in states like the Dakotas, Nebraska, Western Minnesota and Northwestern Iowa due to the presence of either poorly drained or tight clay soils with high pH, and calcareous soils.

Symptoms of iron deficiency are chlorotic leaves, hence the name “Iron Deficiency Chlorosis,” or IDC for short. The primary symptom of iron deficiency is interveinal chlorosis. Symptoms don’t appear on the cotyledon or unifoliate leaves, but do appear on the trifoliate leaves beginning as early as the first trifoliate stage. Iron chlorosis, like most micronutrient deficiencies, appears in spots and usually in a random pattern, depending on chemical and physical soil differences in the field.

Many growers experience these IDC symptoms early in the season. However, these spots appearing in random patterns may also be symptomatic of SCN (soybean cyst nematode) and/or lack of nitrogen fixation in saturated soils. If the spot has a high pH and is calcareous, it is probably IDC. Young plants can die, remained stunted throughout the season, or eventually grow out of it as the roots explore more soil volume to extract iron from. And spots in fields prone to IDC don’t always show symptoms from year to year. So, identification and management can be a challenge.

IDC is caused by the unavailability of iron, not a deficiency of the nutrient. In a recent NCSRP report on IDC, Phillip McClean, professor at North Dakota State University, explains the process soybean plants go through. 

“First, to separate the iron from the soil particles, the plant must release acid into the soil. The soil then releases iron in an Fe (III) state and the plant must convert it to an Fe (II) state to use it. The third step involves the iron crossing the root tissue and entering the plant itself. Once inside the plant, the iron is transported into the xylem or water-conducting tissues of the plant. For the fifth and final step, the iron must bind to an acid molecule to be brought to the leaves.” – Phillip McClean

If anything goes wrong with McClean’s five-step absorption process the iron can’t make it into the leaf and leaves become chlorotic, reducing the plant’s ability to photosynthesize and stunting plant growth.

So, what can be done about it? Seed companies have released varieties with good IDC scores meaning they can tolerate IDC better than others and not become chlorotic. But McClean points out that no variety, even with a good IDC, is totally immune.

Other management practices include:

1. Plant soybeans in fields with low carbonates and soluble salts.
2. Choose an IDC-tolerant soybean variety. 
3. Plant soybeans in wider rows. 
4. Apply chelated iron fertilizer (e.g., high-quality FeEDDHA) in-furrow at planting. 

Agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com