18.5 Is There a Way to Predict IDC Risk?

We unpack why soybean leaves turn yellow in patches, thanks to soybean IDC (iron deficiency chlorosis) and how to predict IDC risk for management. We share the exact soil tests that matter, how to read the lab results, and where precision mapping saves money and yield thanks to IDC management.

We also discuss...

• defining iron chlorosis
• why iron-rich soils still cause deficiency
• limits of testing for DTPA iron alone
• three key predictors: pH, EC (salts), and CCE (calcium carbonate equivalent)
• why percent CCE beats a simple fizz rating
• thresholds where CCE raises severe IDC risk
• how residual nitrate can worsen chlorosis
• grid versus zone sampling for better maps
• using maps to place tolerant varieties and inputs
• practical steps to keep beans green

Tune in next time for a Tiny Byte of knowledge from GK Technology, where we have a map and an app for that!

https://gktechinc.com/

Chapters

• 0:00 Yellow Beans Raise A Flag
• 0:20 What Iron Chlorosis Really Is
• 1:18 When Soluble Iron Is Scarce
• 2:09 Three Soil Tests That Help Predict IDC
• 3:16 Reading Resulting Lab Results
• 4:20 Nitrate, Salinity, And Added Risk
• 6:00 Precision Maps To Manage IDC
• 7:12 Key Tests To Pull Before Planting

Transcript

Sarah: 0:00

And now it's time for a Tiny Bite of knowledge. Jodi, my beans are yellow. Oh no. Oh no, Sarah, I know you're not growing bananas. What's going on? They've got iron chlorosis. Yellow beans often, not always, but often can mean a number of things. One of them being iron chlorosis, meaning that plant, that soybean plant, is having a difficult time trying to extract iron out of the soil. Ironically, our soils tend to be very rich in iron. Unfortunately, iron is not very soluble in the soil. What's interesting about these yellow soybeans is they are not yellow over the entire field. Generally speaking, iron chlorosis in soybeans or in many crops actually happened in different places within a field. So it's actually a really great nutrient deficiency to try to manage from a precision agriculture standpoint. In order to do that, we actually need to be able to identify or try to predict where these areas in the field might occur. And so today, on this tiny bite, we're going to talk about some soil sampling and soil analysis methods to try to determine where iron chlorosis might occur in a field. Iron chlorosis is really interesting because our soils actually are naturally pretty rich in iron. Unfortunately, iron is not very soluble, and especially in high pH soils. And so soil sampling for iron in and to itself actually isn't very helpful. So we actually need to take a look at some other soil parameters in order to predict where and to what severity iron chlorosis might occur. There are three major soil parameters to soil sample for when trying to predict where iron chlorosis might occur: soil pH, soil salinity, and carbonates. Okay, lime. Soil pH is important because that actually controls the solubility of iron. At high soil pHs, iron is less soluble in the soil solution. Interestingly enough, one time I did a grid sampling project where I had soil pHs varying from about six up to about eight and a half. And I also ended up taking the soil, sampling that soil for the soluble iron as well, the DTPA iron. And actually those maps correlated very well. Where the soil pH is lower, there was more iron available. So it's important for us to understand what the soil pH is because you the iron will just naturally be more available with lower soil pHs. Salinity is an important parameter to also evaluate. That's important because in salinity, it's very difficult for the plants to take up the solution from the soil at all. And so it can be very challenging. Lastly, but I think what's most important for higher chlorosis management is to soil sample for carbonates, calcium carbonate equivalencies. This is lime. Ironically, lime is what we use in low soil pH situations to raise the soil pH. So, of course, you're probably going to have some higher pHs where you've got calcium carbonates occurring anyway. However, calcium carbonates can react with water and form bicarbonate. And the bicarbonate itself will actually shut down the iron uptake mechanism of the plant. So it's really critically important to get that calcium carbonate equivalency figured out.

Jodi: 4:18

Absolutely. What a great set of parameters that we can use when we're soil testing to figure out and help us predict where our RDC pressure is going to be the worst, where that potential for iron deficiency chlorosis development will be the greatest. One thing on the carbonate side is when you're getting these tests done, it's important to have in mind, like, okay, how do we define what severe is or what severe is for IDC, right? So it's going to be a combination of these things. It's going to be a combination of salinity, it's going to be a combination of carbonates. So you have to know what your salinity level is, and you have to know what your carbonate level is. And so it's really important that when you're submitting your soil test, that the lab is giving you back a number for that carbonate level. And there are labs that do measure the percent calcium carbonate equivalents. If you're not getting a number back, all they're doing is they're putting, you're taking your soil sample, they're putting some acid on it, and then they're telling you if it's fizzing or not. So you get like a low, medium, and a high reading. And that is not enough data to help us determine where exactly in our fields we're going to have the highest risk of IDC development.

Sarah: 5:33

Absolutely. I couldn't agree with that more. When I interpret the soil sample results that come back from a lab, I want to see that CCE, the calcium carbonate equivalency, in terms of a percentage. And specifically, you're getting over 5%, you've got some opportunity for some pretty severe situations. I've even worked with some soil tests that are up at 8.5%. Those beans are going to be yellow. And there's really a great need to make sure that you're managing those soybeans well.

Jodi: 6:06

One thing, too, that can contribute to that salinity level is also residual nitrate. Unfortunately, there's not a good number. There's no number that's going to say how much a residual nitrate number result will contribute to the IDC severity. So like you can't enter it into a formula to predict. But what we do know is that if you have excess nitrate going into your soybean year and you already have a lot of salinity and calcium carbonates, the nitrate is going to, it's not going to help. It's going to make it worse. So just keep that in mind too, that if you've got a lot of nitrates, it can contribute to that IDC as well.

Sarah: 6:41

Absolutely. It can certainly be very, a very conf confounding factor with everything. Now, the good news about this, if you are getting the correct soil analysis parameters evaluated with your soil samples, there's some great things that we can do to help manage iron chlorosis. And they can be implemented from a precision agriculture standpoint. You can go out and get these soil samples done in a grid or a zone management type situation. And they can be used to help that. And so you can manage the expense of raising soybeans and you can do a better job of managing that iron chlorosis. So the next time you go soil sampling to try to manage for iron chlorosis and soybeans, make sure that you are taking a look at soil pH, EC, carbonates, and you know what? Pull a nitrate too. Why not?

Jodi: 7:41

I love that. Why not nitrate? I love that so much, Sarah. Let's keep the beans green. Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that.