UMN Extension Nutrient Management Podcast

University of Minnesota Nutrient Management Podcast Episode: “Liming and pH: Timing, economics, materials, and more”

October 2024

Written transcripts are generated using a combination of speech recognition software and human transcribers, and may contain errors. Please check the corresponding audio before referencing content in print.

(Music)

Jack Wilcox:
Welcome back to University of Minnesota Extension's Nutrient Management Podcast. I'm Jack Wilcox in the communications bullpen here at Extension. Liming is the topic for today, and we have four panelists with a lot of experience here to walk us through it. Could you please each introduce yourselves?

John Jones:
Thanks, Jack. My name is John Jones. I'm an assistant professor of agronomy at the University of Illinois Urbana-Champaign and the soil fertility extension specialist.

Jeff Vetsch:
This is Jeff Vetsch. I'm a researcher at the Southern Research and Outreach Center in Waseca.

Dan Kaiser:
This is Dan Kaiser. I'm a extension nutrient management specialist located out of the St. Paul campus.

Carl Rosen:
Hi, I'm Carl Rosen. I'm a nutrient management specialist on the St. Paul campus as well. And I work primarily with specialty crops but also work with some of the agronomic crops as well.

Jack Wilcox:
John Jones, let's start with you. Can you talk a little bit about the survey you did for the fertilizer recommendation support tool? What kind of variation have you seen there with lime recommendations?

John Jones:
Sure. Thanks, Jack. So the survey was really designed to send data for six specific soils out to public soil testing labs and then have them respond with what the liming recommendation would be for each of those soils along with some additional information about the soil pH test, the buffer pH test that was implemented in each state, or any other details about the liming recommendation, for example, when it was last updated.

The results were pretty interesting in terms of the variability of the state responses. And so for example, for the six soils, we had liming rates that really ranged from less than one ton or maybe below half a ton per acre of lime all the way up to over nine tons of lime per acre of effective calcium carbonate equivalents per acre. So really a large range of values that our liming recommendations would have returned for the same soil across different states.

And when we think about how liming recommendations may have been developed, there's specific crops that we focus on in our given states around the U.S. There's certain crop rotations, for example. I know Wisconsin's recommendations were always built and designed to consider alfalfa always being in the rotation within cropping systems in the state, which maybe isn't quite the case anymore. In the North Central region, for example, liming rate responses range maybe from zero depending on if the soils buffer pH was above of what the threshold that a state is recommending lime application to over 5,000 pounds of lime, an example, for one soil.

And so we really saw a large variation. And what was really interesting when following up on those results were that states just had very different research methodologies but also targets for where those liming rates were to be used within the state. Some states like Minnesota have two different regions where they're looking at providing recommendations for very different soil and environmental conditions. So a lot of variability and it was really interesting to see how we can come together of states that have similar soils and maybe try to not maybe improve liming recommendations to the degree that they were off, but get to a point where some of these similar soils make sense that we're recommending the same lime rate.

Dan Kaiser:
So there are a couple things here too I want to just follow up on that John said. And if you're getting a soil test, you're generally, especially if you're getting a lime recommendation, you're going to be getting two pieces of information. A lot of growers will focus on the water pH of the soil. We actually use water pH. I know, John, I mean, it's kind of a split, water pH and there some of the southern states use calcium chloride, correct?

John Jones:
Yes. So some of the southern states or western states use a salt solution instead of a water to soil mixture, a salt solution to soil mixture. And the attempt with that is to reduce the variability of two things. One, moisture status of the soil when it's sampled, which can affect the soil pH measurement, but also just the prevalence of salts within soils.

Dan Kaiser:
So it's one of the things that will come up every once in a while, especially if people will send stuff up far away for analysis, whether it's a salt solution or water pH it will be different. They're not the same. They don't measure exactly the same. So it's one of the things to watch out for.

Carl Rosen:
If I can just interject just a little bit because if you use the salt solution, you will get a lower pH relative to a water pH. So that's going to be the difference. It will be lower with salt, with a salt solution.

Dan Kaiser:
So your target point's going to be different if you're looking at a liming. So that's kind of the main thing with it, you can't use them the same.

And the other thing too a lot of times I'll get is people will get their soil test reports back and wonder what this buffer pH is. And it's one of the things that you'll see with buffer is that your buffer generally is going to be higher than your water pH. I mean, I've seen it with the Sikoras as of late. I mean, the numbers can be substantially higher. So a lot of people be confused and why they may have a water pH of five and a half, but the buffer is six, six and a half or somewhere higher. And it's just kind of a difference between what we call the reserve acidity, which is kind of the acidity that's not only in the soil water solution, but what's on the cation-exchange capacity.

And really what the buffer does is it tells us generally how well the soil should respond to a lime application. So if you're looking for lime, that's why the buffer pH is typically used instead of water pH is that it should give us a better indication. The issue really has been on some of the sandier soils, and I know Carl's got more experience with those, is that we've had some questions regarding in terms of the recommendations and how accurate it is, and that's one of the things that we're working on now.

So that's where I was kind of interested in some of that survey work is just to see how different we are because I have had some questions between Minnesota since we do have, I'm here kind of on the border with Wisconsin, is that the recommendations while typically the same components go into measuring the effectiveness of limestone, if you look at how a lab's analyzing that limestone for analysis, the way it's interpreted can be different. That's the struggle.

And it's interesting to hear John talk about even you look at the similar soils on how much variation there can be with the actual recommendations from state to state because it's one of the things that I'm doing now here in Minnesota is looking at our evaluation of what we have going on, and there are also some national efforts to look at some of the same things and comparing soils from across the country just to see how different we actually are.

Carl Rosen:
Yeah, I don't know if you want to go into the buffer pH in a little more detail, but the way that works is you're actually mixing the soil with a buffer and one buffer is called the Sikora buffer and the older buffer, what's called an SMP buffer. But basically you're mixing that soil to a pH of about 7.4 with that buffer, and what you're then doing is seeing how well that soil will lower the pH. If it lowers that Sikora buffer a lot, then that's correlated with more lime. If it doesn't lower it very much, then that means that you need less lime. So that's kind of the background for what that buffer pH is.

Jack Wilcox:
Dan, before we started, you were saying with lime you have to be thinking ahead, that pH changes are not instant. When's the best time to apply limestone?

Dan Kaiser:
Well, that's I think a good question because I'll get that from growers, especially can we apply lime now? Is it going to be effective? And generally what you see is it does take some time, particularly in a field setting to start see some of that decrease in pH and some of the potential, or the actual increase in pH, sorry, I was talking about acidification. That's a whole other topic we could talk about, acidification.

But when it comes down to it, I mean fall, spring. I mean, I don't know if there's necessarily an optimal time other than potentially if you start looking at soil conditions because since you're hauling tons of material out there, you really want to be into a situation where you're not getting any increases in compaction concerns. So that's one of the things why we see a lot of times fall application will see some people err towards that just because the soils are slightly drier and we don't have the compaction concerns that we would have potentially from a spring application.

I know Jeff, you brought up as we're kind of talking before we started this some growers also talking about rows that have canning crops, that when we start looking at ideal times, I think if you've got just some time and some window to think about that, if you've got a soil test that indicates that you could use some lime, I mean, it's really a good time to think about it just when it's the easiest and the most convenient, but also a situation where the soil conditions are in good enough shape to carry that applicator across the field.

What we're seeing with a lot of our current studies, and I know there's been some differences across the region, is that the first year after application we're not really seeing as big of a benefit. So you might want to consider timing with crops that maybe not or as affected by acidity to try to put it ahead of those crops where you might be getting into situations like alfalfa or soybean further down the line where hopefully then that limestone starts to react where you might see a bigger benefit for that.

So I don't think there's a straightforward answer with that, but the research has been kind of across the board and I've seen some instances from some research in Iowa where they were showing more direct change or a direct benefit really close to the time of application, but that's just really not always the case. So especially the last couple of years where we've had dry weather conditions, it doesn't surprise me at all when we go back six months after application and not see much of a change in pH in many of these fields. So it's kind of that thing that you have to start thinking ahead with lime and that it's more of a long term where you don't necessarily need an every year application. But I know certainly there's some growers that might do that.

John Jones:
Dan, that's a question that I've received multiple times. Does a low annual rate of lime lead to the same result as a, let's say three to four or five ton application immediately to try to fix a low pH issue? What's been in your experience?

Dan Kaiser:
Well, it's one of the things, John, we're looking at now. And I've got some studies out there looking at pell lime. I mean, it's kind of a question of the source and the availability of the material, that with pell lime or pelletized limestone, it can be higher cost. So certainly that's one thing that you have to factor in. I mean, usually pell lime, the material that is made from is a very pure and very finely ground calcium carbonate, so it's pretty fairly highly reactive, but it's just a question of overall economics. And I've got some studies out now, I wish I had more years in, but looking at that versus the larger rates, it's I think just a question of do you want to be applying every year or not? And I don't know Jeff or John, do you have any comments on that?

Jeff Vetsch:
Yeah, I'll get to that. When I talk about our study here in a moment, I can address that annual application versus the more traditional larger product per acre application.

John Jones:
I know from the incubation work we did in Iowa, we saw really similar results to pelleted lime applied on the same effective neutralization potential as reagent grade calcium carbonate. But that was the key in a lot of the incubation and field studies where that you still had to have the same amount of effective neutralizing potential regardless of the source. And so that was something to consider on the product price, availability.

I know we did a study in Wisconsin where we looked at annual essentially splitting a four ton liming rate into four years versus applying it just the first year, and those low rates over four years, when we start to get to even lower sub four ton rates, we're getting buffered so much that the pH is really only fluctuating a little bit. And so it required that four ton rate to get a correction pretty early in the cropping system to have an effect on yield.

Dan Kaiser:
So effective neutralizing power, I might turn this over to you Carl because you get to teach this in your class. I mean, kind of what we mean by that. We should probably clarify that before we get too far. We use ENP a lot.

Carl Rosen:
That's a good…

John Jones:
I was trying to use ENP for the Minnesota farm.

Carl Rosen:
Yeah, right. And that's a cause for confusion because each state has a different term for the same value. For example, you might be using effective calcium carbonate equivalent, and that's similar to effective neutralizing power or as John said, effective neutralizing potential. It's like all kind of the same term. And sometimes states use different measurements too because it's based on a fineness scale and it's also based on the calcium carbonate equivalent.

So usually what a lab will do is first when they're determining the effectiveness of a lime is to measure the calcium carbonate equivalent, which is relative to pure calcium carbonate. Okay? So that's the first measurement. And then they'll put it through a bunch of sieves and see what the particle size is. So obviously, a small particle size is going to react much faster than a large particle size. So you get more credit for a small size than you do for a large size. So if you have very large size particles, it's not going to be as effective as say a small size. And so you put those two together and then you can come up with what we call the effective neutralizing power or effective calcium carbonate equivalent. Those are the terms that we use.

And then for some materials, not ag lime, but if you're using say a byproduct, there may be moisture in there, so you have to take the moisture content into it. And even ag lime has some moisture, so they'll measure that as part of it as well. So that's how we come up with the effective neutralizing power.

Dan Kaiser:
Yeah, I get a lot of questions north of the metro with a lot of people using wood products, some sort of byproduct for liming and moisture. Definitely when you look at some of those numbers, it can be pretty high. I mean, if we look at normal ag lime here, if you look at our effective neutralizing power, it can be anywhere from about maybe down to about 600 to 800 all the way up to I've had some up to about 1,400 pounds of ENP per ton.

And the big thing on all those products is that ENP ratings should give you a good way to compare between products. That's generally what I tell growers. If you're looking at different products, looking at costs, it's really what you're looking at is that ENP rating to compare them to look at the overall economics. The difference in that, as Carl mentioned, a lot's fineness. I always kind of just generally assume that some of our dolomitic sources were generally lower on the ENP scale.

I mean, normally for most just normal ag lime, I consider a thousand pounds of ENP per ton kind of a standard, but the dolomitic would be more on the lower end. But it doesn't really matter because we've got some material here that I've been using for one of my field trials that has a pretty high, what we call dolomitic is magnesium carbonate, influenced by magnesium carbonate versus calcium carbonate, which would be calcitic lime with that. And I've had some dolomitic material, I would consider dolomitic that the ENP rating's around 1,400.

So you just have to have that ENP rating to make that comparison. That's really the best thing you can do. And the time it wise too. I mean, technically pell lime should react quicker, so we should see a quicker reaction. The studies that I've had the last couple of years, as John was alluding to, if you apply everything based on the same ENP of seeing pretty similar results between the two in terms of the pH change. Now, we'll see this fall now that I'm two years out on some of these studies just to see where things are at and see if that's the same or whether or not things are different.

Carl Rosen:
Right. I think as long as you're comparing it on ENP, then you're comparing apples to apples. It's kind of like the same thing when you're comparing different nitrogen fertilizers. You do it on an end content so you can compare the effectiveness that way. So it's the same thing with lime.
One other thing, I don't know if we're getting into the weeds with this, but dolomitic lime has magnesium and magnesium is an element that's lighter than calcium. So it is possible to have a higher ENP with magnesium carbonate as it would be calcium carbonate just because it's a lighter weight element than calcium. So just something to consider.

Jeff Vetsch:
The other thing I would add that you need to consider is where your source of lime is because the trucking cost is a huge part of the total application cost. So if you're in Southeastern Minnesota, you might be able to get a very good high-quality calcitic limestone with an ENP of, like Dan said, 1,400 to maybe 1,600 that's ground very fine and it might be five miles away. But if you're in South Central Minnesota, you're nearest source of one of those products may be down in Iowa somewhere where your dolomite may be a lot closer, but the quality is less. But if you balance those things based on ENP, the cost of trucking and the cost of application, that's really important to take into consideration.

Dan Kaiser:
Yeah, I think trucking is a major issue too, I mean in terms of overall costs. And you'll see fights between people saying that dolomitic is best. Some say calcitic is best. It's normally based on really what they're selling for material. I mean, on the lime side, I mean we're really looking at the ENP values, which is calcium or magnesium carbonate. I mean, the carbonate is really the big thing that's affecting the actual material. We'll talk about that a little bit more later. I'm not going to get into the weeds there because I want to cover that a little bit in terms of what's a good liming material because that does come up from time to time.

Jack Wilcox:
Let's continue along this line of economics. Jeff, is lime application economically justified? Before we started, you mentioned you and Gyles Randall, another researcher, did a six-year study. What'd you discover?

Jeff Vetsch:
Yeah, so our study was in Waseca on a nickelite clayloam soil, which is a glacial till soil. It had a surface soil water pH of 5.4 and a buffer pH of 6.0. In that study, liming did not give an economic return on investment over a six-year period in a corn-soybean rotation. But when we added alfalfa into the rotation, we did get an economic return. We put on zero to 10 tons of a dolomitic limestone that had an ENP just over a thousand. So it was anywhere from zero to 10,000 pounds of ENP. We did that once in 1998 in the late summer, and within about two years our soil pH really had not changed all that much. Even the 10,000 pound ENP rate, it had only increased about four-tenths, so it went from about 5.4 to 5.8. So we actually applied it again because we wanted to get the pH at least up to seven.

And as we mentioned earlier, we also had pell lime or calcitic pelletalized lime in lower rates. We had a two-tenths of a ton, a half ton, and a one ton that were applied twice. And then we had a treatment that was 400 pounds or two-tenths of a ton that was applied annually.

One thing to note in these glacial till soils is that you have to realize that only the surface soil is really acidic. Our surface zero to six inch depth had a water pH of 5.4, but the six to 12 inch depth was a pH near six. And once we got to 18 and 24 inches depth, our pH came to neutral and below that, below 30 inches it was actually a calcareous soil. So that definitely influences what the plants are seeing as far as the whole root mass, but clearly the early roots are experiencing that very acidic surface soil pH.

Our yield differences in soybeans, the control, we had two treatments, the six tons or about 6,000 pounds of ENP applied twice and the 10 ton treatment. They increased soybean yields, averaged over the study about two and a half bushels. And the calcite that was applied at two-tenths of a ton annually was almost three bushels. So that's still not a big yield increase when you consider the cost of applying those treatments, especially we applied twice up to 6,000, 10,000 pounds of ENP.

From a corn standpoint, our six-year average, we just barely saw significant yield increases. And some years it was not significant and it was very close to the P value averaged across years. But it was about four bushels per acre is all. And then the two ton calcite that was applied annually did increase yields a little bit, corn yields a little bit more.

So it seems like these annual treatments, even though they don't move the pH needle very much, they do seem to give a little yield response. But again, pell lime is so much more expensive. So trying to balance that right rate with getting that response.

And then the other thing that I would argue is or talk about or important is in South Central Minnesota and other areas where you've got glacial till soils, the whole field is not going to be acidic. You got to make sure you're applying only to the right spots, which means you have a good map of the pH or that you do grid sampling at a pretty good detail, or you look at your soil maps and calibrate that or correlate that with some samples that you take from certain spots in the field. Make sure you only put that lime where it's needed. It's going to have to be variably rate applied.

And the other factor is we applied it on nickelite soils, which is kind of in the upland slope of the positions on these glacial till soils, but not the highest landscape position. Often these in Southwest Minnesota, they'd probably be VESS soils. Here in Waseca, they'd probably be clarions. These eroded knolls, you may have eroded some of the topsoil and what you're dealing with in those high knolls may not be acidic. It may actually be calcareous if it's getting down to where you're farming into the parent material. So that's something else you have to think about if you're just going to use elevation as your determining factor or where to put lime. So I'll stop there and see what others have to say.

Dan Kaiser:
Well, Jeff, I've got a question. And kind of looking at, you're in Waseca, and I've always kind of considered those soils to have a higher subsoil pH. But if you look at our current area one, area two is that we split that line a lot further west. And that was one of the reasonings why I started looking at lime application. I'm just kind of curious, I mean, it probably predates all of us, well, in terms of when that split was made, but I've always wondered why that's the case because I would assume the soils you have there at Waseca wouldn't be a whole lot affected differently versus those... I mean, if you look at where the splits on the county line at Brown, Watonwan, Martin, Renville must be close to Highway 15. Anything west would be area two versus where areas where I would generally consider in area one that would have soils that probably more like area two.

So that's always been one of the things I've wondered about that because it can make a big difference, especially if you start looking at your pH going deeper in the profile and how quickly the pH increases in some of these soils.

Carl Rosen:
Yeah, I've been here the longest and I can tell you that that change had been made well before I arrived. So it's been there for a long time and maybe it does need to be re-evaluated.

Jeff Vetsch:
Yeah, Dan, I think there's a couple things that go on there. One is I think they're looking at the native vegetation of the landscape. And when they think about the native vegetation being the prairie, they kind of think of the prairie kind of out there in Brown County. But I think now you could probably move that at least back to I-35, but you might have to jaunt over, at least in Southern Minnesota when you get up in that Rice and La Sueur County because you're probably going to find some La Sueur soil, county soils that are calcareous in the subsoil, and you might find some that are acidic. But the parent material, if it was a prairie versus if it was a forest, that's going to be a factor. And then how extensive is that glacial till parent material go?

And I agree with you, I don't exactly understand why it was driven, or the line comes up and down those counties. I would think around I-35 would be a better delineation and maybe even Steele County and a couple others could still end up in the calcareous subsoil category. So it is something that if you farm in those counties along that border, taking a subsoil pH and making sure, confirming that you have either acid or calcareous subsoil might be worth doing.

Dan Kaiser:
Well, and I don't even know what subsoil means. I mean, that's the problem. It's not really very well-defined in terms of how deep you have to go. But I mean, the way I think about it generally is the Leicester series, which is our state, "state soil," that was selected because it's kind of at that transition point of forest to prairie. And that's not a bad, I think, area to kind of cut that line, which would put it more kind of Jeff around you, that New Richland area and stuff where you start getting big difference in elevation changes where to me, that's where that should change.

But that's one of the other things that I've really wanted to try to do, at least with us is define what we do mean by subsoil because I think that can vary. I think Iowa had a definition at some point for what they meant, but even that was a deeper than just six inches. So it's one of those things that's not really all that well-defined if you're ever going to use that.

Jack Wilcox:
Carl, what about selecting liming materials? Gypsum's always come up as a liming agent, but it's not. What should growers know that might be helpful?

Carl Rosen:
Well, yeah, that's a good question as well. A lot of people think that it's the calcium that's doing the liming and calcium really is just there for the ride, so to speak. It's really the carbonate that's doing all the work. And so gypsum is basically calcium sulfate and calcium sulfate is basically a neutral salt. It doesn't change pH in one direction or the other because it's calcium sulfate.

And so it's the carbonate that's doing all the work. And by that I mean the carbonate combines with acidity, which is basically hydrogen ions, and forms CO2 and water. And so that's what's happening. You're neutralizing that hydrogen ion and then replacing that hydrogen ion with calcium. But you could do the same thing with magnesium carbonate, reacts the same way. You'd be neutralizing that hydrogen with the carbonate and then replacing the hydrogen ion with magnesium. You could do it with a whole host of other... Even potassium carbonate or any other cation with carbonate will do the same thing. You're just replacing that hydrogen ion and then replacing it with some other cation in there and then that pH will go up. Because when you measure pH, you're basically measuring hydrogen ions. So when it goes up, you have less hydrogen ions in that solution, in the soil solution.

So yeah, that's basically what we're looking at when we're looking at liming materials. It's the carbonate that's doing all the work for us.

And in terms of liming materials, I mean we've kind of talked about that. We base it on the effect of neutralizing power, whether you have magnesium carbonate, which is a mixture of... Dolomitic lime is a mixture of calcium carbonate and magnesium carbonate, or calcitic lime, which has much lower magnesium in there, so it's basically calcium carbonate. Whether you have those two sources, really it just depends on the effect of neutralizing power. The only advantage of dolomite might be is if you are low in magnesium, which is not very common in most of our soils, but if you are low in magnesium, which is an essential element, you do get the added benefit of having magnesium there. So that would be the only benefit. But basically when you're looking at changing pH, we're looking at the effect of neutralizing power and comparing sources that way.

Dan Kaiser:
Yeah. And the ENP is really the critical part there. We need to just look at comparing things. So really wouldn't worry about anything else. And one thing I guess we didn't talk about was what do we need for a target pH? Because a lot of growers will fixate on a neutral pH of seven. When you talk about neutral, we usually talk about seven. If it's below seven, it's acid. If it's above seven, it's alkaline. But in most cases, most of our crops will grow fine with a pH of six, upwards to six and a half. So it really depends on the crop. There's some that'll do better, some that'll do worse. Depending on the overall pH, you just have to know that moving forward. And you don't have to necessarily pick seven. If you do pick seven, essentially it should just give you a longer time between when you have to lime.

And that's really the big thing about liming is that while it does offer some long-term benefits, I mean you may have to go one year and year, and that's just because the fertilizers we apply, especially nitrogen is acidifying. So over time, as nitrogen converts from one to the other, or converts from ammonium to nitrate, it will acidify the soil. Sulfur will do the same thing. And that's always one thing I've wondered with the addition of sulfur as much as we've had, if that's kind of increased some of these instances, as Jeff was talking about some of these, especially these hilltop areas in some of these areas that traditionally at higher pH to acidify quicker that we're seeing more lower pHs in some of those areas.

Carl Rosen:
Yeah, just one thing about sulfur, though. It's in the elemental form, reduced form. If you're using sulfate, that is already oxidized, so that's not going to affect your pH like elemental sulfur will where you're forming sulfuric acid.

Jeff Vetsch:
So Carl, like gypsum and ammonium sulfate will not affect the pH?

Carl Rosen:
No. Well, yes, it will.

Jeff Vetsch:
Ammonium sulfate will.

Carl Rosen:
Ammonium sulfate will, but it's not the sulfate that's doing it.

Jeff Vetsch:
It's the ammonium.

Carl Rosen:
It's the ammonium that's doing it. So that's why it gets a little confusing. A lot of people think that sulfur in any form is going to lower pH, but it's only in the reduced form like elemental sulfur or thiosulfate will also have a acidifying effect as well. If you use ammonium thio, that's even more acidifying than ammonium sulfate because the thio part is somewhat reduced and it's going to be oxidized in forming sulfuric acid.

Jeff Vetsch:
And Carl to that point and the reason why I brought that up was I also hear from a lot of farmers in our area that have had swine manure and had fields that have a long-term history of swine manure applications that they have very acidic surface soils. And I think it's because there's elemental sulfur compounds in that manure that sits in that anoxic tank below the ground. And…

Carl Rosen:
That's right.

Jeff Vetsch:
... it oxidizes and that's what's acidifying the soil and causing some of this more rapid acidification of the surface soil.

Carl Rosen:
Yeah, I think there's two things with swine manure. You could have some of that reduced sulfur in there just because of the way it's stored, but you also have ammonium in there as well. And usually higher ammonium content relative to other manures. So that will also increase acidity. The ammonium in that nitrification process, as Dan already mentioned.

Dan Kaiser:
And we talk a lot about yield too, and there's also some other benefits. I mean, pH is kind the master variable that controls a lot of processes in the soil. I mean, we talk about phosphorus availability being one. If you look at it, there's an optimal pH where we see optimal phosphorus availability. But when we start talking about the differences in crops, many times it's because of the biological activity that some of the microorganisms have a more optimal zone for their pH to grow in.

The other thing that does tend to come up, and you'll see this out in Western Minnesota, is talking about herbicide carryover. If you've got sensitive crops like sugar beet that the pH can affect on how quickly the herbicide will degrade over time, that can influence carryover from one year to the next. So it's a pretty complicated factor. So there might be more than just straight up I need it because the increased yield, just straight on a yield basis that might be coming into play. You might have other factors like herbicide carryover, reducing yield where adjusting the pH might benefit things.

So it's kind of an interesting thing with it in terms of what's happening that it isn't always straightforward with economics and you have to look at it over time. And that's the main thing is with just lime studies, a single year may not be enough to really completely assess what that economic benefit is going to be from that single application made one year. You've got to look at it further down the line.

Jeff Vetsch:
I'd add to that, Dan, too is the common agronomics of today's agriculture is rented land and how do you deal with that? It's something like liming. It's a challenge because if it's your own land, then just like you said, you get these other benefits and yeah, maybe it doesn't give you a return on investment this year or two years, but down the road it will. But if it's a short-term cash rental, how do you deal with that if your landlord is not going to kick in any money to cover some of that cost? That's where it gets very difficult to get a return on investment.

Dan Kaiser:
I know some of the contracts we were drawing up with some of our renters, that's kind of what we do is just look at a five-year amortization of it. So you look at kind of spreading that cost over five years or so, and so hopefully then it gives them some emphasis really to go in and look at liming because it's really not worth letting you get too low because the lower it goes, the more it's going to take to increase the pH at one point in time if somebody does have to fix it. So that's kind of the thing with it. I mean, certainly there's a good triggering point. I think John Jones, you're talking about five and a half. It's I think what I would see too is whereas you're just going to see the biggest benefit from lime application.

John Jones:
Yeah, and the field research done in Iowa usually we didn't see very large yield increases until we got to surface low pHs below five and a half. You would certainly see slow pH increases, but the yield increases just necessarily weren't there.

I would add too, at this time of the year when combines are rolling and soil sample probes are getting cleaned up and ready to get out there, sampling conditions can really start to change how pH measurements may come back and reports from the lab. I know the last few years it seemed like in Wisconsin, we saw some in Illinois, we had some very dry conditions in the fall that may have shifted our reported values of pH. So it kind of shifted them down. And so there was due diligence to agronomists and growers to look back in their records and see those pH trends over time instead of just relying on one single year where maybe that soil sampling condition was a little different than usual.

Jeff Vetsch:
Dan, I would add to that from an economic standpoint, if you have the glacial till soils where you know your subsoil is calcareous, I agree with what John said, it's your act or your go zone or when you've got to start doing something about it is probably at that 5.5, 5.4. But if you're in a soil that has an acid subsoil, that action point probably is closer to 6.0 in a corn-bean rotation.

Jack Wilcox:
Any last words for our audience?

Dan Kaiser:
Well, I think Jeff and John covered it. I mean, I think the big thing is if you're looking at trying to figure things out, I mean, a soil test is really the first step to see where you're at. And being recently down in Southeastern Minnesota, be careful where you take those samples. So specifically, you need to be so far away from your gravel roads. I know Jeff, we were harvesting the other day and looking at some of those fields with the corn is completely white because of all the limestone dust is that you need to have some planning in terms of how you do this. Grid sampling isn't necessarily a bad thing to consider because particularly in some of these areas that we see variable pHs, it will give you some of the option to look at variable rate liming. But really it's to me knowing what that overall benefit is is your crop and also having that soil test to base your recommendation on.

Carl Rosen:
Just a few other things that we never touched upon was on irrigated soils, particularly sandy soils, the irrigation water has very high lime content itself, and so sometimes you can increase soil pH without adding the lime. Just using the irrigation water is going to increase pH and somewhat neutralizes the acidifying effects of the nitrogen fertilizers.

And then the last point I want to make is, Dan mentioned this a little bit, is the biological activity is affected by liming. And one of the reasons, for example, alfalfa growers will lime is because of the association with rhizobium, very sensitive to acidic conditions. And that's one of the reasons why you get a response probably more with alfalfa than you would with corn or in some cases soybeans. So just to keep in mind that you're affecting biological activity as well.

Jeff Vetsch:
And I would add to that Carl in our study at Waseca, when we established alfalfa that first establishment year, it was the most damaging to... The low pH affected the establishment a lot. After that alfalfa was a year old, it seemed to tolerate that low pH better. So the liming effect had the greatest benefit in that first establishment year.

John Jones:
I guess my main takeaway is don't forsake soil pH or buffer pH on your soil test report when trying to just examine what's going on in a given crop or a given field. It's valuable to be considerate of soil pH levels and how they may change over time.

Jack Wilcox:
Thank you all very much. Dan Kaiser, Jeff Vetsch, Carl Rosen, and John Jones. We really appreciate it.

Jeff Vetsch:
Thanks, Jack.

John Jones:
Thanks, Jack.

Jack Wilcox:
Before we go, if you have a question or comment for one of our guests or a topic you'd like to hear discussed in an upcoming episode, please email us at nutmgmt@umn.edu. Thanks, and we look forward to hearing from you.

That about does it for this episode of the Nutrient Management Podcast. We'd like to thank the Agricultural Fertilizer Research and Education Council or AFREC for supporting the podcast. Thanks for listening.

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