URBANA, Ill. —  A University of Illinois soil fertility specialist says he has been getting some questions about iron deficiency chlorosis (IDC) in soybean. John Jones, assistant professor of agronomy and soil fertility extension specialist for the U of I, has confirmed that some producers’ fields he has inspected have an “appreciable amount” of carbonate in the soil surface. Jones wants Farm World readers to know their options for treating IDC, including what he calls the best choice: variety selection. 

“We’ve seen some soybean symptomology that looks like IDC. It’s in soils that have a lot of calcium and magnesium carbonates in the surface of the soils in certain parts of the field where there usually is a depression or an area where historically water has led to carbonates being soluble and then re-precipitating down in the low areas of fields,” said Jones. 

“You see this kind of chlorosis, or yellowing, of leaves, but you see green leaf veins. We’re seeing calcium carbonates that are sitting on the soil surface in many of these areas. We test that by using hydrochloric acid and looking for effervescence of those carbonates in the field. We run those samples in the lab as well.” 

As expected, the researchers are finding that soils that have an IPH of 10 percent to 12 percent carbonates experience more frequent occurrences of IDC.  While it is not necessary for soils to have high levels of carbonates to contain IDC, it can be a harbinger of conditions that could potentially result in the yellowing of soybean plant leaves. 

Iron products have an ability to green up tissue after IDC has been identified, but Jones noticed that such treatments rarely translate to yield response. Iron deficiency is best managed at the beginning of the cropping year by choosing varieties that have good IDC scores, according to the soil fertility specialist.

“Most seed companies are screening their soybean varieties for IDC, and evaluating their products in areas where IDC is more prevalent. Usually that means places like the Red River Valley basin in Minnesota and North Dakota or in central Iowa, but we have similar soils in pockets from east-central up to northern Illinois. It’s those poorly drained soils where we get carbonates precipitating and forming in low areas, where the essential forms of iron that soybeans need are not available,” Jones said. 

IDC can also be exacerbated by high soil nitrate concentrations, which can often form in soil depression areas. At least one study has also suggested narrower row spacing can lend to similar soil symptomology, according to Jones. 

“One of the telltale signs is that you will see green wheel tracks in a lot of these areas. Tracks of tillage tractors or planter tractors, maybe your sprayer, soybeans will look healthier within the wheel tracks (with IDC in soils),” he said. “That’s generally attributed to a reduction in oxygen in those areas, or water or nitrates in some cases.”

Jones has received upwards of ten phone calls from producers within the past two weeks seeking assistance with identifying and responding to suspected IDC pressure in soybean fields, he said on July 10. In addition, he’s seen examples of potassium deficiency in some fields. 

“We may just be in a year where things are a little bit worse with the relatively dry (2024) fall and then some high saturation events. In most parts of Illinois we don’t consider an IDC rating as something that is going to influence what (soybean) variety you are going to plant. But in some of these fields it is certainly showing up that variety selection made a big difference, at least at this point in the season,” Jones said.