Nitrification inhibitors in detail: Important information to help delay N loss
Advancing Nitrogen Smart, from the University of Minnesota Nutrient Management Podcast:
“Nitrification inhibitors in detail: Important information to help delay N loss”
October 30, 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.
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Jack Wilcox:
Welcome back to episode 12 in our special series “Advancing Nitrogen Smart”, from University of Minnesota Extension. I’m Jack Wilcox, University of Minnesota Extension communications.
Today we’re talking about nitrification inhibitors with Extension educator Brad Carlson and Extension nutrient management specialist Dan Kaiser.
Brad and Dan, let's start with some basic information first and then get into more detail. What should growers know about inhibitors?
Brad Carlson:
Well, I think the thing you have to realize is that there's two very different types of inhibitors. We've got nitrification inhibitors and urease inhibitors, and they do two very different things. And occasionally we have producers that tend to confuse the two, but we're going to talk about both in today's podcast.
And so let's start by talking a little bit about nitrification inhibitors. That's intended to delay the process of converting the ammonium in the soil to nitrate. The loss processes of nitrogen are based on, typically they're water-based, but they're also dependent on the nitrogen being in the nitrate form. And so if we can slow the conversion of nitrogen to nitrate, we can also then stave off loss. And so kind of the classic product that's been on the market for years and years is nitrapyrin, commonly available in NSERV and Instinct, and there's a few other products. I think the manufacturer's had some rebranding lately, but that's been on the market for a long time.
Dan Kaiser:
So I think we can step back though, and just when we start talking about inhibitors, I mean inhibitors don't stop the process. They slow the process. And that's kind of a key component that you need to think about is the fact that it's more of a throttling mechanism than anything else. And the way that throttling mechanism works is depending on how quickly the material will degrade in the soil, which depends on the number of things. I mean with nitrapyrin, if you look at temperature, I mean temperature really is the key because low temperature increases the persistence and the bioactivity or the ability of the nitrapyrin to affect the microbes that are or causing nitrification.
And that's one of the things that it's different with nitrapyrin is since we're affecting microbes, it's labeled as a pesticide. So you've got to think about that versus some of the other sources that aren't necessarily acting directly on some microbes in the soil is that there's some different thoughts. So with manure, generally for commercial haulers, they have to have a pesticide license to apply it, and there might be some different things that come into play when you're actually looking at using some of these products.
The other thing with nitrapyrin is it's also, the persistence is affected by organic matter and the clay content. So any situations where you get better adsorption higher, what we call, cation exchange capacity would be analogous to this. Nitrapyrin isn't necessarily impacted by the CEC, but it does persistence.
So we'll talk about this here in a moment, but when it comes to soil types, that's why it just tends to work better on high clay soils, particularly fall applications. It's really, really where you want to look at pairing the two because it's where it's going to work better. If it's in sunlight, it will decompose rapidly. If you start looking at the half-life, and when we talk about degradation, we talk about half-life or the amount of time for half the material to degrade that is if it's in the dark and in water, the half-life is about seven days. If you look at it, that's at 77 degrees Fahrenheit, you increase the temperature to 95, it's two days. So again, that goes back to that temperature component. If you put it in water in the sunlight, the half-life is about a half a day. So nitrapyrin is highly volatile. I mean, it's why we apply it subsurface to get better effects with it, and it really needs to be in with water because of the volatility of the product.
Brad Carlson:
Well, and the other point that I think a lot of people maybe don't really catch relative to all of the inhibitor products is that they are intended to affect soil processes. They don't affect the fertilizer itself. And so if they're not in the soil, then they're not doing anything. And so that's the other key thing is to remember is that you're looking at these products being at the sites where some of this activity is happening in the soil, but it's not really necessarily safening the fertilizer so much as it's affecting the soil processes which are happening where the fertilizer is. So you want it present at that spot, but it's not actually changing the fertilizer.
Dan Kaiser:
And a product like, you know, Brad, a product like ESN or polymer-coated urea, that's not an inhibitor. That polymer I mean it does slow the release of the urea into the environment, but once the urea is released into the soil, it's going to quickly undergo hydrolysis and potentially nitrification. So again, really you've got to separate the two out in terms of what they're supposed to do.
So getting back to this temperature thing, there has been some studies looking at this and looking at the amount of time it takes to get 50% degradation. If you look at just on a silty clay loam, just looking at different temperature regimes of 40, 55, and 70 degrees is that if you look at 55 versus 70 degrees, we get 50% degradation in about three weeks of the nitrapyrin. You drop your soil temperature down to close to 40, that increases out to about 90 days.
So that gets really back to when we start looking at these products is that I don't really consider these products to give me a window to apply nitrogen in September because it just doesn't effectively work. You have warm enough soils you could get into October, and that nitrapyrin is degraded down to the point where it's no longer going to be affected. So it's one of the things to consider.
Now, if you compare, say like a silt loam, there's been some data out there comparing the two, is that at those higher temperatures, you go from about 21 days down 7 days in terms of 50% degradation, and that really speaks to what I was talking about before is that the clay content and the organic matter will increase the persistence. So I mean, looking at these products is that they're again, really more tailored, particularly a product like nitrapyrin for high clay soils. And if you're looking at fall applications, it's probably going to be a better result. You're going to get more longevity than you would with some other soil types.
Brad Carlson:
And it's really not an issue of do these products work or not. I think they always work. They work, it's just a matter of do they work long enough and at the right time to have the effect that you're looking for. And so really the way you use the product and the timing and so forth is going to impact that a lot. It's not a factor of did it work or not work?
Dan Kaiser:
And we'll get some comments soon when we start talking about degradation from some industry reps with nitrapyrin talking about the longevity of it. And we know that while the degradation, it slows over time, we'll still see some persisting in the soil after five months. It's just a question of whether or not the concentration of the material is enough in the zone of application where it's still effectively controlling or delaying nitrification. And that's one of the things that you see over time is that we get to roughly about 50% degradation, and then we just really see poor control of nitrification.
So looking at the amount, the concentration that it takes to have an effect with nitrapyrin, some of the numbers I've come across is that it's active to down to about one part per million. It's one of the things though with the band application, it's a lot easier to maintain those concentrations.
We talk about NSERV a lot. The other product out there is Instinct, which is a microencapsulated version of nitrapyrin. And the microencapsulation is there to slow down the volatility of the product, to keep it available longer because again, it's highly volatile, so you've got to, especially if you're applying it on something like urea that might be surface applied and incorporated, it would volatilize extremely quickly if they didn't have that microencapsulation, but that encapsulation does cause some issues. I mean, it does slow down the release of the product, but it does affect the concentration and it's really a concentration issue.
This is no different than any other ag chemical that you apply. I mean, you put a low rate of an herbicide down, it might have some controlled benefit, but it's probably not going to be ideal. So that's one of the things you need to consider with any of these products, especially if you're buying generics, is that are you getting the concentration you need for that product to be effective? So that's really, I think, the big key when I look at a lot of these things is it's nice if they have on the label what the concentrations are so you can go in and look at that because just because you can get something cheaper doesn't mean that it's going to be as effective because the concentration of something that's cheaper might be so low that while it's there, it may have some effect, but it may not have the desired effect.
Brad Carlson:
And the nice thing about this product when it's used with anhydrous ammonia is it's injected into the anhydrous stream, and so it ends up being at the same point where the anhydrous is, and that keeps it fairly concentrated. One of the issues why we don't think we've seen great effectiveness of the product with urea is simply because when you apply urea, oftentimes you're broadcasting it, so you're spreading it out. And so you're also spreading the inhibitor out across the soil, and it just simply may not be in enough concentration to work.
Dan Kaiser:
And if you look at some of the data, Fabian Fernandez has some data where they banded it, and it does seem to be a little more consistent, but it's still not as good as just straight up anhydrous in the fall. So I mean, I look at Instinct while there might be a benefit I mean, really the bigger benefit I think with Instinct right now is with liquid manure. That's really where we've seen a bigger benefit. With urea, it's really been hit or miss. And I think a lot of it, and a lot of the questions that we've had just regionally about it is really the concentration. Does that microencapsulation, does it essentially reduce the concentration enough where we're below that effective limit? By the benefit of stretching it out could be a detriment that it's not maintaining the concentration as much as it needs to be.
The other product that's out there is DCD. This is, if you look at the Guardian, there's a few other products out there. A SuperU is the one that you can buy just directly that has DCD mixed in it. The same thing, the higher of the concentration, the better the product's going to be. DCD is interesting because DCD was first developed as a fertilizer, it's a dicyandiamide, so it's got an amide in it, which is ammonia. If you look at the concentration, the concentration of nitrogen in straight-up DCD is higher than it is with urea. So on paper would make a very good fertilizer by itself, but when they tested it, they had a lot of issues with toxicity with plants. So what they found is that if you mix DCD as a certain percentage of your total N, is that you could get some impact in delaying nitrification.
It's slightly different than nitrapyrin, but it's not a labeled pesticide, but in effect, the same thing by delaying nitrification. The issue though with DCD compared to nitrapyrin is nitrapyrin is not mobile in the soil is absorbed by the soil particles and by organic matter while DCD is mobile. And that's been one of the problematic areas with DCD in the past, particularly with the anhydrous is if you inject it in the band, a lot of times what'll happen is that the DCD will stay mobile in the soil, and it'll move deeper in the profile, and you'll have the DCD in a zone versus the anhydrous in another zone essentially where you're affecting nitrification where your nitrogen isn't at no longer.
So the benefit, I mean looking at it, it does tend to have the same mobility as urea, so in theory, it should work better with urea. The big question though is concentration. And that's been one kind of the biggest pitfalls with DCD. It's been getting enough concentration, particularly with products that are sold to be applied at the fertilizer plant mixed at the point in time before that fertilizer is going out to the field is that it's really hard to get the concentration you need to get a very effective control.
So again, getting back to this inhibitor, I mean, they don't stop the processes. The inhibitor, they slow them, and again, they're going to work better at cold temperatures. And we've talked about this before, and I don't know Brad, if you want to talk a little bit about manure.
Brad Carlson:
And we've done a podcast already on fall manure, and we talked about using inhibitors, but I guess it's just worth pointing out that the research that was done at Waseca on using nitrapyrin and manure, they found a good effect of the nitrapyrin as far as it slowing the conversion of the nitrogen in the manure to nitrate, but what they also discovered was it was not better than just simply delaying it until a soil temperature got cold.
And so again, that gets into that time period of is it long enough that it did enough that it mattered? Certainly it worked. If we're looking at trying to keep nitrogen out of the water, it was not a surrogate for just simply following better practices which was to wait for later in the year when the soil temperature got cold. That still was the preferred method to keep the nitrogen from turning into nitrate and then being subject to loss.
Dan Kaiser:
And you really want to maintain some activity into the spring, and that's really important because when it comes down to the conversion, we know there's some nitrification that's going to occur early in the spring. It's not as much, but it's something that when we look at where we get the most effect out of some of these products, it's really when we still see some impact of these products into mid to late May.
Brad Carlson:
Yeah, Dan, if you look at some of just kind of the averages as far as soil, the climate averages, as far as soil temperature and how long it's at various, when it's frozen and when it gets 50 degrees, and we also look at some of the tabular data looking at nitrapyrin and its degradation based on soil temperature and so forth, what we would expect is if you wait until the soil temperature is 50 degrees, we see that nitrapyrin and based on some of those calculations, again, this is just kind of a thumbnail sketch. It's not hard and fast, but we look at that typically being effective until about the third week of April, which is getting us into crop planting season. That's one of the reasons why it is part of our nitrogen recommendations for fall application with anhydrous ammonia in southern Minnesota.
Dan Kaiser:
The other product that's out there are what we call urease inhibitors. So this is the second class of inhibitors, and they're completely different in what they're trying to do. Urease inhibitors, if you look at it, urease mean urea. I mean the way to think about those is that they affect, essentially, they slow down where urea is split. Urea is interesting in that it's actually, we talk about inorganic fertilizers and urea being one of them, but it's actually an inorganic molecule because you can manufacture urea by combining ammonia with carbon dioxide, and the reverse of the process with the urease enzyme comes into play. It's actually splitting or going backwards on that process where it's splitting the urea molecule into ammonia and carbon dioxide. So this is important.
And then urease, when it comes down to it, the soils contain a lot of urease, and where that comes from is from the plants itself. It's in the plants, it leaches out of the residue as the plants, the residue is decaying, so it's what we call ubiquitous or it's ever-present in soils. It's going to be worse if you look at urease in high residue situations, so like continuous corn. It's why we tend to have more concerns with urea in continuous corn is because the amount of urease that's there tends to very quickly convert the urea over to ammonia which we can then come into volatility concerns, particularly if that urea is near the surface.
So what the urease inhibitors are doing, they're delaying that enzyme again from splitting the urea. So this isn't a microbial process, so it's one of the things about that is that cold will slow it, but it won't stop it. And it's one of the things I think that people think that maybe you can treat these nitrogen sources the same is that there's different things occurring, and urea, that's one of the concerns is that we get volatility of that ammonia that's generated at that first stage where that urease enzyme splits the urea. That's where the volatility comes in, where we can actually lose some of the nitrogen due to ammonia volatility.
So if you look at some of the data, there has been some data out there looking at the hydrolysis of urea. Cold, if you look at 80 degrees versus 35 degrees Fahrenheit, I mean the difference is that the study that I'm focusing on here applied 80 pounds of nitrogen as urea that at 80 degrees Fahrenheit, we saw full hydrolysis after four days. At 35 degrees or close to freezing, it was 10 days. And that's one of the things that if you apply urea on frozen ground, you can lose a substantial amount of that urea due to ammonia volatilization if there's enough moisture there to start dissolving it and if the urease enzyme is present. So that's where when we start talking about loss potential, I think it's where we tend to see a lot of failings of fall applied urea. It isn't necessarily converting to nitrate and being leached. You're losing a substantial amount potentially due to volatilization.
Brad Carlson:
When the urea molecule cracks and turns into ammonia. If that happens below the ground, it's going to get into the water, and the soil is going to absorb it as ammonium. And so if it's on the surface, it's going to just blow away. And so that's really what we're trying to avoid. And so every year we will get these situations where, for instance, and especially if it's wet, it'll be, say, middle of March, and we'll be in a little cold snap. And you'll always hear this, well, the dealers are wanting to run out there with the ground frozen and just surface supply some urea out there, and heck, later in the day or tomorrow, it's going to warm up, and it'll turn back into mud, and that'll all get incorporated. Well, typically it doesn't. It just dissolves the pearls and spreads it out then across the surface, and so that's really a situation we need to avoid.
Dan Kaiser:
If you've got a lot of evaporation coming from the soil surface, I mean even in the winter though, when it's frozen, we can have issues with volatility of the ammonia. There has been some work on this. I mean, a lot of it's been looking at winter serials because certainly looking at timing of application, there can be some issues there. And there was one study that looked at three applications of urea of the same amount with or without NBPT, which is the active ingredient in Agrotain, which is a urease inhibitor. And kind of what they found is roughly about 30% loss of the nitrogen by around the 1st of June from three applications. One was around the 1st of December, one was about the 15th of February, and the other about the 15th of April.
If you look at the loss though, the bulk of the loss, almost half of it, came in from that December 1st application. So kind of counterintuitive that some people would think that soils are frozen, they're cold, nothing's happening, but they volatilized roughly, this is about 16% or more of the nitrogen that was applied at that point in time. Where they did tend to get lower losses was from that April 15th application, and that should make some sense. I mean, if your soils aren't frozen, if you have water, urea, since it's a neutral molecule, will incorporate into the soil as it dissolves in water. We need roughly about a quarter inch of rainfall generally to effectively incorporate urea. That's what we generally like to see with surface applications is about a quarter inch within about four days after application. There's just not as much loss potential the later you go. With frozen ground, it's much more risky because you just cannot incorporate the urea. It's just going to lay on the surface.
Brad Carlson:
And then the other aspect of this, Dan, is as far as how you incorporate it, what we usually, we've got some other data that we'll maybe talk about on a different podcast, but again, if you want it a little bit deeper so that it is not ending up in the air, and so the data kind of indicates that the loss goes down to almost zero if you get it three inches deep or in essence just incorporated with a field cultivator. But when it's shallower than that, it's subject to be lost.
Again, if you use, for instance, a drag harrow, it's only an inch deep or two inches deep with a disc or something like that, we're still subject to lose it. So that's kind of our best practices. And as far as the use of a urease inhibitor is, if you're going to get a quarter of an inch of rain or if you're going to incorporate it, you don't really necessarily need it. If you're laying it on the surface and waiting for those things to happen, particularly if it's getting warmer, then we're probably looking at doing it. Since the patent's gone off on a lot of these products, the price has come down. It's just kind of, in most cases, if we're applying it on the surface, you're typically going to see farmers use it.
Dan Kaiser:
And it, again, a concentration issue. And that's one of the things with the generic. So just be careful with that if you're buying some of these generic products. There's a few of them out there that don't list their actual concentrations. They list NBPT as a component but not the concentration, so you can't figure out how much you need. I think it's roughly, you want about 1.3 pounds of NBPT per ton to be roughly effective. And we could follow it up. I can't remember if we've actually talked about that before.
But the thing about urea that it's interesting is with anhydrous, you typically can detect the volatility. If you go out in the field, smell ammonia, that's ammonia volatilizing out of the band applications. With urea, that's not necessarily the case. And the problem with urea is it's what you can't see can hurt you. And that's kind of the main thing with it is if I see it on the soil surface, if it's dry, if the granules, which a lot of its granules, we talk about pearls, but a lot of its granules, if they're still there, it's probably not as big of an issue. It's when it starts to dissolve, it's the problem.
And as Brad said is, if you don't get it effectively incorporated deep enough, it tends to, with the urease, it's there, really start kicking in if there's a little bit of moisture there, some of that hydrolysis, which kicks in some of the risk for loss. So just one of the things to consider, and it's one of the things that the biggest thing I really tell a lot of growers is ask questions of your retailer, what exactly they're applying. Don't just trust or tell you that they're getting an X inhibitor. It's nice to know what product to do a little bit of, just do a little research on it just to see if the concentration is high enough. There are a few of them out there that I question whether or not they sell themselves as having an NBPT or a urease inhibitor in it and can be an issue.
One last thing is there are some new products on the market. We talk about Instinct. Instinct's been around for a while. Again, that's micro-encapsulated NBPT. Centuro, it's pro-nitrodene. I think it's a DCD derivative. What they've tried to do with that product is make it less leachable, so it'll stay in the zone where you apply it, so it'll stay with the anhydrous. That's why it's marked for anhydrous and some liquid fertilizers.
And then the other one that's out there, there's two other urease inhibitors, Lenus is one, and I can't even remember what the other one was meant to replace. Anval is the other one. So those are the other two. The Anval we've seen just as good of results of the NBPT, but I haven't really seen anything that would set it apart from it that would say it would be better than that. So it's one of the things that NBPT, that good, that old technology, "old" still tends to work. So it's one of the things, again, ask questions and just know what you're applying because there's some other products out there which you'd just be better off saving your money on versus applying them if you're not going to get the concentrations you need for them to be effective.
Jack Wilcox:
Dan Kaiser, Extension Nutrient Management Specialist and Brad Carlson, Extension Educator. Thanks for this information on inhibitors.
Dan Kaiser:
Thank you.
Brad Carlson:
Thank you.
Jack Wilcox:
If you have a question or comment for either Brad or Dan, please email us at nutmgmt@umn.edu. Thank you for listening and we look forward to seeing you next time.
Advancing Nitrogen Smart is proud to be supported by the farm families of Minnesota and their corn check-off investment through Minnesota Corn.
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