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Managing Iron Deficiency Chlorosis in Soybean

What is IDC?

Managing Iron Deficiency Chlorosis

Iron Deficiency Chlorosis (IDC) in soybean is a problem for soybean production in South Central, Southwest, West Central, and Northwest Minnesota. The symptoms are interveinal chlorosis of the leaves with the leaf veins remaining dark green. The enzymes involved in chlorophyll formation need iron, so when active iron (Fe) is low in leaves, chlorosis occurs. The soil usually has a large amount of iron but it is not in the soluble form needed by the plant. The most soluble form in oxidize soils is Fe(OH)3, where Fe is in the Fe(III) form. This iron becomes less soluble at higher soil pH and especially when the soil has large amounts of calcium carbonate.

Managing Iron Deficiency Chlorosis

Plants prefer to take up the reduced form of iron (Fe II). Plants have adapted mechanisms to help extract iron from the soil. Type I plants, such as soybean, azaleas, and blueberries, excrete acids and chemical reductants from their roots. The acids make the Fe(OH)3 more soluble and the reductants change insoluble Fe(III) to more soluble Fe(II). Type II plants such as corn and grasses excrete iron chelators that bind Fe(III) and the plants are able to absorb the iron through the root. Plants do vary in their ability to get Fe out of the soil. Azaleas and blueberries only survive in acid soils where Fe(OH)3 is more soluble. Because of this, Azaleas and blueberries are chlorotic in soils with a pH greater than 5.5 while soybeans can adequately grow when pH is less than 7.5.

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Where do we find IDC in Minnesota fields?

Soybean IDC generally occurs in shallow depressions. IDC is generally worse on the rims of the potholes where higher concentrations of calcium carbonate have been deposited, caused by historic soil conditions when the soils were wet prairies (before tile drainage and farming), Figure 2. The intensity and extent of IDC depends on the soybean variety and factors that affect soil nitrate and bicarbonate contents.

Typical soil association
Figure 2: Typical soil association from the western Minnesota prairie pothole area. IDC typically is found in low-lying area (Okoboji and Harps soils), where salts and carbonates accumulate over time.

How to manage IDC

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Daniel E. Kaiser, Extension nutrient management specialist and Paul R. Bloom, emeritus professor

Reviewed in 2018

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