19.5 Map The Acidity, Save The Harvest

We dig into why low (acidic) soil pH unlocks aluminum toxicity, how that halts root growth, and which crops suffer first. Then we lay out a practical plan to find acidic patches with smarter sampling, NDVI, and grid-the-zone strategies, and point to lime and buffer pH for the fix.

In this episode, we discuss...
• soil pH as chemical control and pH level of 7 is neutral
• aluminum toxicity risk to crops increases below 6.5 pH 
• wheat relatively tolerant, legumes struggle with nodulation 
• stunted roots and thin stands on slopes and sandier spots 
• acidic areas are patchy and do not always follow productivity maps 
• importance of using intensive grids and how 0–3 inch sampling in no-till helps detect acidicity issues
• soil testing: pair pH with buffer pH to set lime rates 
• target NDVI-low areas and grid inside zones 
• variable-rate lime as the remediation path 

Gridding the Zone with Ag Genesis Part 1: https://www.buzzsprout.com/2297340/episodes/16692855

Gridding the Zone with Ag Gensis Part 2:
https://www.buzzsprout.com/2297340/episodes/16692855

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 Framing The Low pH Problem
• 0:36 pH Basics And Nutrient Availability
• 2:09 Aluminum Toxicity And Crop Tolerance
• 4:30 Field Symptoms And Visual Clues
• 5:23 Finding Problem Spots With Sampling
• 7:20 Zones, NDVI, And Practical Gridding
• 9:22 Lime, Buffer pH, And Next Steps
• 10:06 Quick Recap And Resources

Transcript

Sarah: 0:00

And now it's time for a Tiny Byte of knowledge. So, Jodi, what is the big deal with low soil pH? I mean, I hear people talking like down in Iowa, man, my pH is low and I got a lime. What in the heck is going on? Help me understand.

Jodi: 0:28

That's a fantastic question. And it's a question we're getting more and more often up here in the northern Great Plains and also the prairie provinces. So stepping back for a second, thinking about soil pH itself, it's basically the chemical control of our soil. So when we think about pH, it's important to remember that like seven is our baseline, that's our neutral point. And that's everything's kind of quote unquote normal. And then as we swing to higher pHs, which we can sometimes see in soil here in the valley, we can see them 8.2 to 8.3 is pretty common. Can get higher in the 8.5s. But we can also, when you kind of start to get sandier stuff, you can see pHs down to 6.5, 6, 5.5. Numbers above seven are going to be basic, and then pHs below seven are going to be considered acidic. And so what that's telling us, or what these numbers mean, or really on a practical level, is that they're controlling what in the soil is soluble and available for the plants to take up. So for those of you that have seen charts that show like the pH chart and they've got different colors and they show the pH range from, you know, zero to seven and seven to fourteen, and you've got these stripes that kind of go in and out based on the number and how each of those nutrients are, those essential crop and nutrients are available based on pH. That's what we're talking about here. As you get to lower pHs, some soil elements or some nutrients in the soil become way more available than they are at a normal pH of like seven. And then some nutrients become more tied up or no longer soluble and no longer present for plants to take up at these lower pHs. And so, long story short, when we get to pHs that are below 6.5, we start to worry about aluminum toxicity. And this isn't because, you know, the pH is introducing new aluminum. There's not aluminum falling from the sky. What's happening is that that aluminum that was tightly bound and not available for the plant to take up now is available in the soil solution for our plants to take up. And unfortunately, a lot of the crops that we grow up here in North Dakota don't like aluminum. They are not happy when they're interacting with that aluminum. And so we we run into aluminum toxicity. Some crops are better at tolerating this than others. Um, for example, wheat, small grains are going to be more on the tolerant side. Any sort of legume below 6.5, we start to worry about pH is below 6.5, it's harder for bacteria to grow. So when we think about like legumes and nodulation, below 6.5, that process becomes very, very low. And so we're starting to see reduced crop growth, reduced nodulation. Our crops just can't compete as well when they are affected by that aluminum in the soil. So, like overall, the number one concern with low pHs is that most of our crops are not tolerant to really low pHs. So 6.5, you might not see anything right away, but as we creep down into 6, 5.5, 5, 4.5, we're gonna see that the roots are going to start and explore in the soil, but then they just stop. Uh, they can't, our plants can't put on root systems because they can't grow in the presence of that aluminum.

Sarah: 3:46

That's such a great explanation about how aluminum becomes more available, um, more it's more soluble and made more available for plant takeout. And it's just so prevalent in the soil that the plants take it up readily. And it's interesting when you take a look at at roots that are affected by aluminum toxicity, they almost look like there's they reach this layer and they just become like these wimpy little things. I mean, you see a definite line where um above that maybe there's not quite as much aluminum available and the root looks normal. And then below that, um that that root looks just wimpy and and like it can't do anything. And guess what? It's not, and and your plants look terrible on the top as well. And it's interesting because you mentioned that wheat is is fairly tolerant, and it is, but at a certain point in time, not even the small grains can keep up. And we are seeing that in western North Dakota all the time. We've got had a chance to see from some of our friends out west some really interesting pictures of landscapes out there where you can clearly see where the small grain looks good and it's healthy, and then you can see the side hills or the top of the hills that are greatly affected by that aluminum toxicity, and the plants just look terrible. You can see right down to the soil in between the rows of that small grain in those scenarios where it's being affected by that low pH. So it's very interesting. So, what is the best way for us to identify where these spots are? And I think this is incredibly important for us because this soil pH issue is a perfect issue to try to address with precision agriculture. So, how do we figure out where these places are occurring in the field?

Jodi: 5:44

Yeah, absolutely. So, really the best way to identify them, unfortunately, because it's not gonna be, it's not easy, is what I'm gonna say. There's no easy button to very quickly figure out exactly where the soil pHs are. What we're finding as more and more people, at least in like Western North Dakota, are soil sampling for specifically for pH and for pH management and acidic soil management, what we're finding is that these areas that are low are pretty spotty and they don't always follow our productivity maps. In the like in the corn belt, they've been dealing with these acidic soils and managing them for the last hundred years. And it's even where the grid concept and grid soil sampling concept comes from is figuring out, you know, how can we make be more efficient in our Lyme applications? And so in general, the best way to go out and soil sample and find and identify these spots is going to be through, you know, pretty intensive soil sampling setup, one acre grids, two and a half acre grids, and then sampling at least a zero to six. And I'd say if you're in a no-till system where you're gonna have more acidity on the top, zero to three inches, than the bottom three to six inches, you may even want to consider doing a zero to three inch sample just to identify how low that pH is, where the seed is placed, because I think it surprises people more when we've got no-till. It's worse than people think. I'll just leave it there. But that's gonna be the biggest thing. And identifying it, you're going to sample it for pH. And then if you have a pH that is below 6.5, you'll want to run a buffer pH, which is the soil test result that is going to tell you how much Lyme to apply. So you need to have both a pH number and a buffer pH number to diagnose and then determine how much Lyme you should apply in order to increase your pH. And we haven't even touched that, Sarah. We haven't even talked about what to do when we have these pH, these little pH areas, but it comes down to Lyme.

Sarah: 7:47

We could talk about that in another tiny bite. But one thing I want to um make certain when we're trying to identify where these spots are, like Jodi said, some of these aren't always related to productivity areas. Many times when we were making zones for zone soil sampling, those zones are driven off of productivity data. And so they may or may not be the best identifier of where we actually need to be applying lime to remediate these areas. But one thing that you can do is if you figure out areas in a field that have less plant growth. For example, I was talking about those fields in western North Dakota earlier, where you can clearly see that the plant growth is diminished. You can use NDVI data to identify where those spots are occurring. And then once you might have that laid out in a zone, grid that zone. Go out and do that intensive soil sampling on a grid, but just within that zone. That's a really important thing to think about because especially when we're dealing with areas of the United States where we've got such large acreage fields, you know, some of those fields out west are 1200 acres in size. Are you seriously going to grid sample that on a one-acre grid? Ufda made of that's intense. And so trying to do that in a scenario where maybe we can grid a zone or identify those spots where we need more of that intensive sampling, that could be a very good option for us.

Jodi: 9:20

Yes. And do take a listen. We've got an episode where we talked to Lane Bothwell and Kurt Turner. Kurt Turner, down with Ag Genesis, South Dakota, where they are gridding their zone samples or gridding their zones to identify and make prescriptions for variable rate Lyme. And they are truly gritting the zone. And you can listen back to that episode for more tips on how to do that and how to make that work.

Sarah: 9:46

And I think we had another tiny bite about what Lyme is, right?

Jodi: 9:51

Yes. So when I say lime or calcium carbonate, if you want to know more, check back to our other tiny bites to hear more on that. Because we don't want me on my soapbox to talk about it some more, because this will get long. Um but in short, what low what acidic soils are, they are soils that have low pHs. Anything below seven is considered acidic, but we're talking soils of 6.5 pH or lower. And the problem with these fields is that they're prone to aluminum toxicity. So get out there. There is a solution.

Sarah: 10:26

Get them identified and get them taken care of.

Jodi: 10:29

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