IDC in Soybeans

deficiencyIDCIronNO₃⁻plantingsoybean

Banner image of Sobyeans with IDC

Yellowing and Dark Green Spots in Soybean Fields

If you are driving through north central Iowa on an early June day, you may notice soybeans yellowing in interesting patterns. You may also notice dark green “tire tracks” that run up and down soybean fields due to previous sprayer field passes.   These are often the first signs of Iron Deficiency Chlorosis (IDC).  IDC is an ongoing challenge for growers in this region of the state.  It is due to inherent soil properties that are not easily changed, such as calcareous topsoil, which results from a calcareous subsoil that was formed when the glaciers came across millions of years ago. Basically, not something we can go back and change.

Soil pH map of Iowa 2025

What is IDC?

Iron Deficiency Chlorosis is a phenomenon caused by a lack of available form of iron to the soybean plant. Key words, “available form.” Soil test reports are a great way to start with a baseline for plant available nutrients.  In this high IDC area, iron, (Fe) often times, has high levels across wide areas.  You would think it’s most available then, and we have plenty of it. Soil test results may read iron is available to soybeans, but the combination of iron and pH need to be assessed in order to conclude you potentially have IDC issues.

Diagram of Iron+2 uptake into soybean plant

So why does this happen? As you see in the pH chart, iron availability to plants, reduces at High pH soils. Soybeans can only use iron in the form of Feᐩ².  In this part of the world, it’s more common to find iron in the form of Feᐩ³. Now, soybeans do have the ability through their roots to excrete acid and reducing agents to move Fe into the available form of Feᐩ².  Soybean varieties that tolerate IDC do this better than varieties that are more susceptible.    To learn more about IDC, ask one of our Agronomy Field Advisors! 

pH map

These are all great clues to solving your problem fields! 

The following soil conditions should help you figure out if IDC could be the root of problems in your soybean fields:

  • pH greater than 7.4 (Don’t use only pH. What does that mean? Keep reading!)
  • Excessive Free Lime 
  • EC (soluble salts) greater than one mmhos/cm. In other words, look for areas that pond in fields.

Other not-so-scientific factors are: 

  • High soil moisture
  • Excess nitrate in the surface soil - look for dark green wheel tracks across fields
  • Certain soil series that are typically calcareous in the topsoil, including Harps, Canisteo, Okoboji, and sometimes the Nicollet-Webster series  

The pH test is often sufficient for soil tests to determine whether iron and other nutrients are available. If you suspect IDC is an issue in a particular field, we suggest adding the Excessive Free Lime and the EC (soluble salts) tests, which can confirm IDC suspicions. 

How bad does it need to get before I worry about IDC?

Do you know how much of the field is affected by IDC?  Yield maps are some of the best indicators for determining affected acres.  Otherwise, if yield maps aren’t an option, ask an Agronomy Field Advisor for the next best maps.  Our rule of thumb is that if you are losing 50% or more on yield in those areas, and those areas are greater than 10% of your field, it will pay you to manage them with one or more of the following tactics. 

What to do about IDC?

1. Buy the right soybean for this type of field.

The best and easiest option is to start with a soybean that is bred to be planted in high IDC areas. These varieties won’t cost more money, just time selecting varieties and placing them on the right acres.  Agronomy Field Advisors at Liqui-Grow can help pick out the right bean for the right acre! Soybeans naturally acidify the rhizosphere (area immediately surrounding the roots), which reduces iron into the Feᐩ² form, making it available for plants to use. However, a soybean that has a better IDC rating is more efficient at this process, meaning those varieties will oftentimes thrive better in heavy IDC fields compared to soybeans that are not as tolerant to IDC. 

2. Don’t apply iron to your soil! 

As we just mentioned, there is plenty of iron in the soil, it's just not in the right form. Adding additional iron is not practical, oftentimes, it will change forms because of the soil environment and become unavailable.  If you can’t help yourself, then it’s best to use an iron chelate through an in-furrow starter on your planter. Use the iron chelate form that is most available at your pH level; anything above 7.4 is typically EDDHA, which is the strongest of the chelates, and is able to keep iron in a plant-available form when pH is above 9.0.

 

3. Reduce the amount of nitrate available in the surface soil. 

Nitrate carryover from a corn crop at the soil surface plays a large role in how bad iron deficiency chlorosis symptoms are.  Visually, scientists attribute the “green wheel tracks” to the compaction caused by wheels, which then reduces oxygen availability, resulting in the denitrification of the nitrate. The bottom line is that less nitrate means less IDC. A way to alleviate excess nitrates could be the use of cover crops. Any cover crop such as rye, wheat, triticale, etc., will uptake a lot of surface nitrate and reduce the severity of symptoms.  

 


**Bonus - Getting into the weeds:
Soybeans prefer to take up nitrate, NO₃⁻ (hence why nodulation is reduced under higher nitrate levels), and when the plant takes up NO₃⁻ , soybeans have to balance the charge. They release bicarbonate HCO₃⁻ ions, which buffer the acidification effect from the roots.  The acidification effect from the roots is what makes the iron more available. So, in other words, it's a win/lose situation. They are enjoying the free nitrogen, but they can’t utilize it because they can’t take up iron. Iron is essential for the production of chlorophyll, which is what makes the plant green and drives more growth.

4. Tile!

A great strategy to limit iron deficiency chlorosis is to reduce the amount of water standing in the field and add subsurface drainage in these areas. Soils that hold water are soils that accumulate bicarbonates. Bicarbonates will buffer the acidification effect from the soybean roots. This is the same thing that happens in the case of excess nitrate.  Reducing excess water reduces bicarbonates. An Agronomy Field Advisor can have the Excess Lime Test completed to measure the bicarbonate levels.

 

5. Plant higher populations in those parts of the field

If your planter is capable of variable rate prescriptions, planting different populations in high IDC areas can be a lot easier than a traditional planter.  It is still possible for a traditional planter to plant different populations though. The idea behind increasing populations is to pile the roots on top of each other and overwhelm the rhizosphere with acidification from roots. Typically, you need to push populations close to 200,000 or higher in 30” rows to see the impact from it. When it comes to extra seed, there is a cost, so calculating what your lost yield is worth before adding population is beneficial.

**Bonus - Getting into the weeds:
Research from the University of Minnesota showed three on-farm trials in 2021. One of the farms with an IDC “hotspot” found a 36 bu/ac advantage when using a tolerant IDC soybean variety coupled with higher planting populations (175,000 in 30” rows). This is only 1 location over 1 year, and it highlights how under the right conditions, especially in severe IDC cases, where the soybean yields may be almost zero without management.

IDC can be detrimental to soybean yields, and is also very dependent on certain environmental conditions. It’s not easy to overcome IDC, but it is possible to have good yields in those fields.  If you suspect IDC is limiting your yields, call a Liqui-Grow Agronomy Field Advisor today to learn more and take back your yield potential!