Soybean acreage is increasing and IDC (iron deficiency chlorosis) is an issue that can cause severe yield loss. University research in the 1990’s showed that soils with high levels of carbonates (CCE – calcium carbonate equivalent) and salts (electrical conductivity) are much more likely to develop severe iron chlorosis (IDC). With this research in mind, AGVISE Laboratories developed a routine laboratory test method to determine soil carbonates to help growers make management decisions. AGVISE did an educational project on IDC in 2001 where we sampled 104 soybean fields which had IDC areas. We tested the carbonates, salts and soil pH of the IDC areas and adjacent areas with green healthy soybeans. From the data we collected, we developed a table which helps predict the risk and severity of IDC based on the carbonate and salt level of the soil (see table below). The data we collected showed that soil pH did not help predict which fields would have severe IDC. As an example, the pictures below show two areas in the same field with a pH of 7.8-7.9. The area with IDC symptoms has high carbonates and salts and the adjacent area with green healthy soybeans has lower carbonates and salt levels. The pH in these areas is almost the same at 7.8 and 7.9, so pH does not help determine the risk of IDC.
Soil testing each field for the level of carbonates and salts will help you make decisions on planting soybeans. When choosing which fields to plant soybeans on, always choose the fields with the lowest carbonate and salt levels. If you decide you are going to plant soybeans on a field with moderate carbonates and salts, be sure to plant a soybean variety that has a high tolerance to IDC (most varieties are now rated for tolerance to IDC). IDC risk and severity is worse in wet cool springs. Research has also shown that high residual soil nitrate can also increase the risk of IDC. University research has shown that placing EDDHA Ortho Ortho iron fertilizer with the seed at planting can also reduce the severity of IDC and increase yield.