6.5 Soil Sample the Extremes

We dig into why skipping the lowest-yielding parts of a field can be the most expensive soil sampling decision you make. We lay out a simple “sample the extremes” plan that improves variable-rate fertilizer accuracy and helps put nutrients where they actually belong. 

In this episode we discuss...
• reframing soil testing as nutrient placement, not just cost-cutting 
• why red zones like hilltops, saline spots, and drown-outs often need sampling most 
• how built-up phosphorus and potassium can hide in low-productivity areas 
• using variable rate yield goals alongside soil test results for tighter fertilizer decisions 
• choosing which management zones to sample and when to interpolate the rest 
• splitting low zones into separate mods and sampling both when causes differ 
• using ADMS to bring results back into zones and make educated interpolations 

Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that. 

https://gktechinc.com/

Transcript

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Tiny Bite Kickoff

SPEAKER_02 0:00

And now it's time for a tiny bite of knowledge.

Sarah 0:13

Hey Jody. On today's tiny bite, guess what we're doing? Oh, what's that? We're going to the extremes.

Why Sample The Extreme Zones

Sarah 0:24

What do I mean by that? We're going to talk about soil sampling the extreme zones. Oh, I'm so excited to talk about that.

SPEAKER_01 0:32

What do you mean when we're talking about soil sampling the extremes?

Sarah 0:37

Well, I've had a number of conversations lately as we are starting to prepare for the fall soil sampling season in 2026 with different people who are talking about which zones they're going to soil sample and which zones they're not going to soil sample. And some of the interesting conversations that have popped up is this concept of not soil sampling your red zone or your least productive zone out of all of the zones that you've created. And I think that's a really interesting concept. And I think we should recommend against it. I believe that we should be soil sampling the extremes, your least productivity zone, probably a middle zone, which is not the extreme. And then also your most productive zone.

SPEAKER_01 1:21

Yeah. I mean, when I think about, you know, what is the value of soil testing? A lot of times people think, oh, it's to save money on fertilizer. And I like to remember to remind people to reframe it as putting the nutrients where they are or where they need to go. What's my point with this on the extremes? Oftentimes the extreme or that red zone, oftentimes that might be hilltops, that might be saline areas, it might be areas that get drowned out frequently. If you're looking to save some costs on fertilizer using variable rate application, these places in the red zone specifically, this is where we've likely been applying way too much fertilizer and not getting much crop growth out of. And so there's a big opportunity here to get those results back and plan on not applying so much there in the

Yield Goals And Hidden Nutrients

SPEAKER_01 2:16

future.

Sarah 2:17

Absolutely, Jody. I couldn't agree with you more. So it's interesting because as I'm working with different growers, a lot of times we've already got those variable rate yield goals set up. So perhaps maybe in your lowest productivity zone, if we're talking about wheat production in the Red River Valley of North Dakota, maybe you're only going to have 10 bushels or 20 bushels for yield potential. Maybe your yellow zone is going to be 40 or 50 bushels. And maybe your dark green zone, your most productive zone, is going to be 80 or 90 bushels. And that's actually very realistic if you really think about it. And so just with those variable rate yield goals, you would automatically end up having different amounts of fertilizer needed in those areas just based on the yield goals and what each one of those production potentials would be. But what's interesting, and when you bring up that idea of soil sampling your red zone and finding accumulated nutrients there already, you might actually need even less than what that 20-bushel yield crop, for example, would require because you have that huge accumulation of especially phosphorus and maybe even potassium in that zone. So why not make sure that you're soil sampling those areas as well to really see what's there so we can make the most efficient decisions on our fertilizer applications.

Which Zones To Sample

Sarah 3:48

So soil sample the extremes. To expand this idea just a little bit farther, um, I did want to mention that normally, and I don't know how many zones you make, Jody, but normally when I'm making my zones, I kind of make a five-zone standard map. And sometimes I actually end up um increasing my zones up to six or seven zones if I need to do mod areas. You know, for example, maybe my red areas. I've got some hilltops that are sandy, and I also have some um saline areas, and they're both classified as red, low productivity areas, but for very different reasons. And so then I might mod them out. So that's kind of something that I'm doing. And then it brings up a whole nother host of questions of what zones do we actually need to sample? So a lot of times when I make my five zone standards, when I go out soil sampling, I'm not soil sampling every single zone. Um, I want to make sure that I'm understanding the extremes, though. So I might soil sample the red zone, the yellow zone, and then the dark green zone. And I would not soil sample the orange zone and the light green zone. I'll just interpolate across those. And that'll provide me enough information. But it's really important to understand what that red zone has and what that dark green zone has.

Modding Low Zones The Right Way

SPEAKER_01 5:14

When you make those mods, Sarah, are you then sampling the the both of the like the red zone and then maybe your blue mod zone too? Are you sampling both of those extremes?

Sarah 5:24

I I will because um they're gonna have different values. And so when I mod those out, I will certainly make sure that I'm getting the values from both of those areas. In that instance, I think it's worth it to increase my zone sampling efforts to that four zone. I still have that intermediate zones where I've got my, I'm not sampling my orange zone and my light green zone. So I can still interpolate across. But in order to really understand what's going on in those lower productivity areas, I do need to understand that sandy hilltop and I do need to understand that saline area because they might have very different things going on.

SPEAKER_01 6:04

And that's exactly why you you you modeled them in the first place, right? That's why you separated that those two low productivity areas. They're both low productivity, but they're low productivity for different reasons. Um, and

Using ADMS To Interpolate Results

SPEAKER_01 6:16

that's the beautiful thing about ADMS is A, you can do that. And then B, like you mentioned, Sarah, being able to interpolate the values for the soil test for those zones, like the light green or like your two, your four, um, being able to take the values from, you know, your high productivity, your medium productivity, and your lowest productivity, sample those zones, get your soil test results back, and then being able to interpolate across those areas, because the beautiful thing at ADMS is that you've got values in the background for each of those zones. So when we bring those results back in, we can easily make a really educated guess on what's happening in those areas, even if we didn't go out and sample them specifically.

Takeaways And Next Time

Sarah 7:02

Absolutely. Absolutely. So, yeah, I guess the take-home for today is make sure you soil sample that red zone, even though it's your lowest productivity zone. Having that sampling information might really help you be the most efficient with your fertilizer beyond what you even know. So, soil sample the extremes.

SPEAKER_02 7:24

Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that.