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/

Episode Transcript

Sarah (00:00):
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 notgrowing bananas.
What's going on?
They've got iron chlorosis.

(00:22):
Yellow beans often, not always,but often can mean a number of
things.
One of them being ironchlorosis, meaning that plant,
that soybean plant, is having adifficult time trying to extract
iron out of the soil.
Ironically, our soils tend tobe very rich in iron.

(00:48):
Unfortunately, iron is not verysoluble in the soil.
What's interesting about theseyellow soybeans is they are not
yellow over the entire field.
Generally speaking, ironchlorosis in soybeans or in many
crops actually happened indifferent places within a field.

(01:09):
So it's actually a really greatnutrient deficiency to try to
manage from a precisionagriculture standpoint.
In order to do that, weactually need to be able to
identify or try to predict wherethese areas in the field might
occur.
And so today, on this tinybite, we're going to talk about

(01:31):
some soil sampling and soilanalysis methods to try to
determine where iron chlorosismight occur in a field.
Iron chlorosis is reallyinteresting because our soils
actually are naturally prettyrich in iron.
Unfortunately, iron is not verysoluble, and especially in high

(01:52):
pH soils.
And so soil sampling for ironin and to itself actually isn't
very helpful.
So we actually need to take alook at some other soil
parameters in order to predictwhere and to what severity iron
chlorosis might occur.
There are three major soilparameters to soil sample for

(02:13):
when trying to predict whereiron chlorosis might occur: soil
pH, soil salinity, andcarbonates.
Okay, lime.
Soil pH is important becausethat actually controls the
solubility of iron.
At high soil pHs, iron is lesssoluble in the soil solution.

(02:37):
Interestingly enough, one timeI did a grid sampling project
where I had soil pHs varyingfrom about six up to about eight
and a half.
And I also ended up taking thesoil, sampling that soil for the
soluble iron as well, the DTPAiron.

(02:57):
And actually those mapscorrelated very well.
Where the soil pH is lower,there was more iron available.
So it's important for us tounderstand what the soil pH is
because you the iron will justnaturally be more available with
lower soil pHs.
Salinity is an importantparameter to also evaluate.

(03:20):
That's important because insalinity, it's very difficult
for the plants to take up thesolution from the soil at all.
And so it can be verychallenging.
Lastly, but I think what's mostimportant for higher chlorosis
management is to soil sample forcarbonates, calcium carbonate

(03:44):
equivalencies.
This is lime.
Ironically, lime is what we usein low soil pH situations to
raise the soil pH.
So, of course, you're probablygoing to have some higher pHs
where you've got calciumcarbonates occurring anyway.
However, calcium carbonates canreact with water and form

(04:05):
bicarbonate.
And the bicarbonate itself willactually shut down the iron
uptake mechanism of the plant.
So it's really criticallyimportant to get that calcium
carbonate equivalency figuredout.

Jodi (04:18):
Absolutely.
What a great set of parametersthat we can use when we're soil
testing to figure out and helpus predict where our RDC
pressure is going to be theworst, where that potential for
iron deficiency chlorosisdevelopment will be the
greatest.
One thing on the carbonate sideis when you're getting these

(04:41):
tests done, it's important tohave in mind, like, okay, how do
we define what severe is orwhat severe is for IDC, right?
So it's going to be acombination of these things.
It's going to be a combinationof salinity, it's going to be a
combination of carbonates.
So you have to know what yoursalinity level is, and you have
to know what your carbonatelevel is.
And so it's really importantthat when you're submitting your

(05:03):
soil test, that the lab isgiving you back a number for
that carbonate level.
And there are labs that domeasure the percent calcium
carbonate equivalents.
If you're not getting a numberback, all they're doing is
they're putting, you're takingyour soil sample, they're
putting some acid on it, andthen they're telling you if it's
fizzing or not.
So you get like a low, medium,and a high reading.

(05:23):
And that is not enough data tohelp us determine where exactly
in our fields we're going tohave the highest risk of IDC
development.

Sarah (05:33):
Absolutely.
I couldn't agree with thatmore.
When I interpret the soilsample results that come back
from a lab, I want to see thatCCE, the calcium carbonate
equivalency, in terms of apercentage.
And specifically, you'regetting over 5%, you've got some
opportunity for some prettysevere situations.

(05:54):
I've even worked with some soiltests that are up at 8.5%.
Those beans are going to beyellow.
And there's really a great needto make sure that you're
managing those soybeans well.

Jodi (06:06):
One thing, too, that can contribute to that salinity
level is also residual nitrate.
Unfortunately, there's not agood number.
There's no number that's goingto say how much a residual
nitrate number result willcontribute to the IDC severity.
So like you can't enter it intoa formula to predict.
But what we do know is that ifyou have excess nitrate going

(06:26):
into your soybean year and youalready have a lot of salinity
and calcium carbonates, thenitrate 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 tothat IDC as well.

Sarah (06:41):
Absolutely.
It can certainly be very, avery conf confounding factor
with everything.
Now, the good news about this,if you are getting the correct
soil analysis parametersevaluated with your soil
samples, there's some greatthings that we can do to help
manage iron chlorosis.

(07:02):
And they can be implementedfrom a precision agriculture
standpoint.
You can go out and get thesesoil samples done in a grid or a
zone management type situation.
And they can be used to helpthat.
And so you can manage theexpense of raising soybeans and
you can do a better job ofmanaging that iron chlorosis.
So the next time you go soilsampling to try to manage for

(07:26):
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 (07:41):
I love that.
Why not nitrate?
I love that so much, Sarah.
Let's keep the beans green.
Tune in next time for a tinybite of knowledge from GK
Technology, where we have a mapand an app for that.