Why Are My Soybeans Turning Yellow? Understanding Iron Deficiency Chlorosis (IDC) in Minnesota

Iron deficiency chlorosis (IDC) is a common challenge for soybean growers across central, northwestern and southwestern Minnesota. In the 2026 growing season, yellow soybean fields have once again become a familiar sight across many parts of the state. IDC occurs when soybean plants cannot obtain or use enough iron to support normal growth. Because iron is essential for chlorophyll production, deficient plants develop the characteristic yellowing between the leaf veins, while the veins remain green. Since iron is not mobile within the plant, symptoms first appear on the youngest leaves, making IDC easy to recognize but often difficult to manage.

Why is soybean susceptible to IDC?

Most of the Minnesota soils contain abundant iron, but in poorly drained, alkaline soils, especially those with high concentrations of calcium carbonate (lime), most of the iron exists as ferric iron (Fe³⁺), an insoluble form that soybean roots cannot readily absorb. As a Type I plant, soybean has evolved mechanisms to overcome this limitation by releasing acids that increase iron solubility and enzymes that convert Fe³⁺ into ferrous iron (Fe²⁺), the form that can be taken up by the roots. However, these mechanisms become less effective as soil pH and calcium carbonate increase because less iron dissolves into the soil solution, and the acids released by the roots are rapidly neutralized. Consequently, soybeans can develop iron deficiency chlorosis even when the soil contains abundant total iron.

Conditions that increase IDC severity

University of Minnesota Extension shows that IDC becomes more severe when soil and environmental conditions further reduce the plant’s ability to acquire or utilize iron. High calcium carbonate directly neutralizes the acids released by soybean roots, while wet, poorly drained soils increase carbon dioxide and bicarbonate concentrations around the roots, making iron even less available. Cold, waterlogged soils intensify these effects, and the decomposition of fresh crop residues or manure can further increase bicarbonate production. This is easy to spot in lower areas of our fields. High soil nitrate can also increase IDC severity. During nitrate uptake, soybean roots release bicarbonate, increasing pH around the roots and reducing iron availability. In addition, nitrate metabolism in the leaves raises leaf pH, thereby slowing the conversion of ferric iron (Fe³⁺) to the physiologically active ferrous form (Fe²⁺). Together, these factors restrict iron uptake and utilization, thereby increasing the severity of chlorosis despite abundant soil iron.

IDC sometimes could be confused with severe symptoms caused by Soybean Cyst Nematode

Iron deficiency chlorosis (IDC) can be confused with soybean cyst nematode (SCN) because both can cause yellowing and stunting. However, IDC is characterized by interveinal chlorosis in young leaves and is driven by soil conditions that limit iron availability, whereas SCN is a root-feeding nematode, as evidenced by white or yellow cysts on soybean roots. This is an example that scouting for disease and nutrient deficiency ID is key to determining the cause of IDC and mitigation measures.

 

 

 

 

 

 

 

 

 

 

 

A Minnesota field experience

In July 2025, we scouted two soybean fields with clear IDC symptoms, one in McLeod County (heavy clay soil) and one in Norman County (sandy loam soil). In each field, we collected soil, plant tissue, and SCN samples from an IDC area and a nearby healthy area. We avoided the lowest saturated spots, and both fields were planted with IDC-tolerant varieties.

The soil results showed different causes of IDC at each location. In McLeod County, the IDC area had a pH of 7.9, nitrate at 15.6 ppm, available iron at 6.4 ppm, and 11.4% calcium carbonate equivalent, much higher than the healthy area (2.5%). These results suggest that high pH, high calcium carbonate, and elevated nitrate were the main drivers of IDC. In Norman County, pH, available iron, and calcium carbonate were similar between the IDC and healthy areas, with calcium carbonate below 4.5% in both. However, nitrate reached 19.2 ppm in the IDC area compared with only 3.3 ppm in the healthy area, suggesting nitrate may have contributed to chlorosis.

The plant tissue results were also interesting. In both counties, IDC plants contained higher iron and manganese concentrations than healthy plants. This agrees with previous research showing that IDC plants can accumulate iron in the leaves but cannot use it efficiently. This is one reason why plant tissue analysis alone is not a reliable tool to diagnose IDC.

The SCN results added another piece to the puzzle. In McLeod County, SCN populations averaged only 1,270 eggs per 100 cc of soil, below the economic threshold. In Norman County, however, the IDC area averaged 13,650 eggs per 100 cc, compared with 2,017 eggs per 100 cc in the healthy area. While this does not prove SCN caused IDC, it suggests that high SCN populations may increase plant stress and worsen chlorosis.

The main lesson is that IDC rarely has a single cause. In McLeod County, the main factors were high calcium carbonate, high pH, and elevated nitrate. In Norman County, elevated nitrate and high SCN populations were strongly associated with IDC, while pH and calcium carbonate were not. Comparing IDC and healthy areas within the same field can help identify the factors contributing to chlorosis and improve management decisions

General management practices

There is no single solution for IDC because its severity depends on both soil and environmental conditions. Dr. Daniel Kaiser of the University of Minnesota considers the most effective management practice to be selecting an IDC-tolerant soybean variety adapted to your field. Ask your seed dealer for IDC ratings and choose varieties with proven performance in high-risk fields. Other practices that can help reduce IDC include applying an ortho-ortho iron chelate in-furrow at planting, increasing seeding rate, and using a companion crop. Research from the University of Minnesota and NDSU shows that, from both a yield and economic standpoint, the greatest benefit comes from variety selection, followed by seed-placed ortho-ortho iron chelate, increased seeding rate, and companion crops. The best approach is to match these practices to each field based on its IDC risk, soil conditions, and your farming operation.

Ongoing IDC research

Research on IDC continues across Minnesota and North Dakota. This season, Dr. Seth Naeve (University of Minnesota) and Dr. Ana Carcedo (North Dakota State University) are leading a multistate, on-farm project, “Exploring environmental, variety, and management effects on IDC for delineating guidelines,” supported by the Minnesota Soybean Research & Promotion Council and the North Dakota Soybean Research & Promotion Council. The project is evaluating the interaction between soybean variety tolerance, ortho-ortho iron chelate application, seeding rate, and companion crops to develop practical management recommendations for IDC. One of the key questions is whether it is more profitable to plant a defensive IDC-tolerant variety with fewer inputs or a high-yielding variety supported with more intensive management. The goal is to provide farmers with research-based recommendations that maximize yield while improving profitability. Stay tuned for updates as results from this project become available.

Recommended IDC materials:

• Managing iron deficiency chlorosis in soybean, University of Minnesota. https://extension.umn.edu/crop-specific-needs/managing-iron-deficiency-chlorosis-soybean#use-an-iron-chelate-product-1074263
• IDC in soybean: 4 things to know about managing iron deficiency chlorosis, University of Minnesota. https://blog-crop-news.extension.umn.edu/2023/06/idc-in-soybean-4-things-to-know-about.html