Plant Clinic Mystery: Iron chlorosis or Herbicide injury of Soybeans?

The soybean sample that was submitted to the U of I Plant Clinic consisted of a soybean plant that exhibited chlorotic symptoms on the new growth of the plant.  The older growth of the soybean appeared normal.  Pictures included with the sample indicated that there was a distinct pattern of these chlorotic plants and the pattern appeared as lateral lines throughout the field.

The plants were somewhat symptomatic of iron chlorosis.  Iron chlorosis symptoms occur when the plant is not able to take up iron or utilize iron.  Soybean varieties can vary in their response to these conditions.  There can be many causes of iron chlorosis and some of them are as follows:
Soil pH (above 7.0)
Flooding
planting in cold temperatures
planting in wet soils
lack of iron (not common)
high salt levels with higher carbonate levels
high soil nitrate levels have been found to intensify symptoms
post emergent herbicides
diseases
soybean cyst nematode

The pattern of lateral lines throughout the field raises a "red flag" that something such as tire tracks or sprayer overlap could have contributed to the iron chlorosis.

The sample was examined by Dr. Aaron Hager, U of I Extension Associate Professor in Weed Science and he stated the following based on the symptoms of the sample, further information included with the sample as well as the symptom pattern in the picture where this sample was taken:  "iron deficiency and mesotrione carryover can cause similar symptoms.  I'm not able to determine which or both might be causing these symptoms."

Further research led me to two articles, which can be found at the following links:
http://cornandsoybeandigest.com/mysteries-yellow-soybeans
http://www.ag.ndsu.edu/cpr/soils/iron-chlorosis-in-soybeans-6-30-11

Basically, it has been found that iron chlorosis can form within to wheel tracks..." When the field dries, the wheel tracks will wick water into them and be more moist than the rest of the field and will be more chlorotic."

I consulted with two Soil Extension Specialists from North Dakota State University who were quoted or authored information about iron chlorosis in the links above and here are some of their statements based on the picture of this field:

Dave Franzen - North Dakota State University Extension Soil Specialist said the following:
"Having spent half my career (almost 20 years) in Illinois north of Champaign, it is unusual to see IDC (Iron deficiency chlorosis) symptoms except in very small patches in certain varieties.  A soil sample from the area would form a basis for even considering IDC. In order for true IDC to occur the pH must be above 7. The higher above 7 it is the more IDC might be present. It is impossible to get true IDC if the pH is lower than 7. With that being said, there are areas of old lake bed sediments that before tiling were nearly always under water and shellfish left there carbonate-laden shells behind to form soil series like Harpster. I had a client who had about 80 acres of Harpster in a larger field and the pH was 7.8 . In a field such as this with the water you had and the right (wrong) variety, IDC might be possible on the scale you show. Under wet conditions, the wheel tracks will be greener than the rest of the field due to a drier soil in the wheel tracks. As the field dries, the wheel tracks become more moist compared to the rest of the field, so the IDC is worse in the wheel tracks.  A soil sample from the area and site-specific would be better on a sample per acre basis in the affected area would help to determine if IDC is even possible or if the road to diagnosis is more appropriate traveled towards the pesticide side of the argument."

Dr. R. Jay Goos, Professor, North Dakota State University stated the following:
"Iron deficiency chlorosis (IDC) occurs in soils that contain calcium carbonate (CaCO3, or "lime") in the topsoil.  Typically, that means a soil with pH levels around 7.8-8.3 or so.  Alternatively (and even better) the topsoil can be treated with 1 molar HCl (or perhaps some muriatic acid from the hardware store), and if the soil fizzes, there is lime present.The presence of lime in the topsoil on a level field is generally due to poor drainage, and a high water table in the spring.  In short...a fundamental property of the soil in question.  Farmers never discover IDC in their soybeans after years of farming a field....it is a problem that they fight almost every year.  If the farmer has never seen this problem before now, and if an examination of the topsoil does not show the presence of lime, I would say that the chances of the problem being IDC are unlikely."