Iron Chlorosis – Soybean varieties differ in their tolerance to IDC (Iron Deficiency Chlorosis). Choosing the most tolerant variety is the most practical option a grower has if iron chlorosis has been a problem in the past or if the level of salt and carbonates are high. Planting higher populations and planting in rows rather than solid seeding beans may help in overcoming iron chlorosis. Seed treatments with iron or foliar applications of iron compounds may or may not help overcome iron chlorosis (research is ongoing). Spot treatments of foliar iron compounds, if applied between the first and third trifoliate stages has some potential benefits, but consistency of crop response has been variable.
The level of soluble salts and carbonate in the soil are two major contributing factors related to iron chlorosis in soybean. Soil testing iron chlorosis hot spots in fields will help identify soluble salt or carbonate as part of the problem. If neither of these is a problem, SCN levels should be tested. Soil pH is a poor indicator and does not correlate very well with iron chlorosis. Soil pH is a poor predictor of iron chlorosis because some high pH soils have high levels of salts and carbonates and other high pH soils have low salts and carbonates. Soluble salts in soils are usually a drainage or high water table issue. Soluble salts will move with the water through the soil profile. If the water table comes close enough to the soil surface, evaporation draws water to the surface where it evaporates and leaves the salts behind on the soil surface. Did you notice the white areas on the soil surface in fields this spring prior to the field being cultivated, especially in the low spots of a field or on the side hills of fields? More than likely, that is the soluble salts that are at the soil surface and indicates the problem in the soil profile. Carbonates are a permanent soil feature and will not change unless the soil is removed or replaced (unlikely to happen). AGVISE offers a routine test for carbonate level in the soil. Gypsum will not reduce the soluble salt content or the carbonate level in the soil and is not recommended for situations of iron chlorosis on soybeans. Foliar applications of micronutrients on soybeans have not shown consistent yield increases with the products currently available. There is considerable ongoing research directed towards managing iron chlorosis in soybeans. As the research becomes available we will try to keep you updated.