UMN Extension Nutrient Management Podcast

A University of Minnesota Advancing Nitrogen Smart special series episode of the Nutrient Management Podcast:
“Nitrogen placement: What Minnesota farmers should know about depth, incorporation, loss pathways, and more”
May 8, 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.

Jack Wilcox:
Welcome to the first episode in our new series “Advancing Nitrogen Smart”, from University of Minnesota Extension. I’m Jack Wilcox, University of Minnesota Extension communications. I'm joined by Extension educator Brad Carlson and Extension nutrient management specialist Dan Kaiser.

Understanding how nitrogen behaves in the environment is more important than ever. And when growers have access to unbiased, research-based information, they’re better equipped to make farm-specific nitrogen management decisions.

Here at Advancing Nitrogen Smart, we unpack and examine the latest up-to-date nitrogen data to help farmers maximize their profits while at the same time minimize nitrogen loss to the environment. We cover topics that are timely and relevant for Minnesota farmers and agricultural professionals, just as we’ve been doing for the last 10 years with our in-person and online Nitrogen Smart courses.

Brad Carlson:
Well, one of the things I always talk about related to nitrogen placement is the fact that there's obviously a very heavy interaction with the type of fertilizer you're using. There's no such thing as broadcast anhydrous ammonia that would amount to just blowing it up into the atmosphere. And so really the kind of fertilizer that we're using really dictates what we can do with placement. However, there really are some nuances related to placement that we need to think about as far as within the field, whether you broadcast or you band, we need to talk a little bit about the distance from the row and some of those effects. And the depth of the fertilizer placement at the time of incorporation is also an important aspect that we're going to cover today. So I guess as I said, the consistency of the product has something to do with this, whether it's a solid or a liquid or a gas. And we also need to keep in mind the conversion pathways, how the nitrogen behaves in the soil once it's been applied. Those are all real pertinent factors related to the type of fertilizer we're using and how we place it.

Dan Kaiser:
So when it comes down to placement, particularly if we talk about situations like within row or placing near the row, I mean rate will matter significantly. And a lot of that, particularly if you're dealing with liquid fertilizers as a starter fertilizer application, the amount of nitrogen and also the amount of potash or potassium are really keys when it comes down to what we determine at "seed safe rates." Although there are no seed safe rates, you can have germination issues no matter what. So that's one of the main things to consider. And what I really worked with a lot of growers and talk to them on is really looking at limiting the amount of, particularly with a starter fertilizer application, nitrogen as low as possible. But when it comes to band applications, the rate when we start talking about placement away from the row, then things get more flexible where you can start looking at higher rates if you get about an inch of soil between where the seed is and where the fertilizer is applied. So we know that just having a buffer and having the zone right directly on the seed, the zone on the seed is really the bigger issue with that, particularly fertilizers that would form some ammonia in the seed row. So it's one of the things that you should be considering.

Brad Carlson:
And Dan, what do you think about some of these dribbles that go right above the seed, the seeds below it and has dribbled above just above the row?

Dan Kaiser:
Well, really the big issue is when the root initially develops, particularly when the radical is coming out of the seed, a lot of the issues I see with seed placement really boil down to situations where that radical is killed right at the point of time it emerges. So if you can get it away from, and you've got some soil between, where it's not, particularly if the soil, if you don't have any cracking or anything that would provide a direct pathway of the fertilizer that you could place it directly over the row. But I'd really suggest if you're looking at placement, particularly at the time of planting, to get it away from the row. So place it off to about an inch to the side because it should be sufficient, particularly with nitrogen and also with sulfur, if you're putting those two together early on, you could use a little bit higher rate, put it an inch or two to the side of the row on the soil surface is really a better option than directly over the seed itself.

Brad Carlson:
And it's worth noting here that in addition to the type of fertilizer you're using, the timing is also an aspect related to the placement of the fertilizer and that's probably bound with what you've got available for application equipment. And obviously we all know that the application methods are different depending on whether fall application is probably going to be anhydrous. And of course that's just strictly going to be knifed in. By the time we get to spring, you've got a lot more options pre-plant, but then once the crop is up and growing and we're side dressing now we get kind of hemmed in again as far as what we got available for equipment. So, it's worth at least noting that also. So Dan, one of the questions that we get frequently with urea, and there's not a ton of banding equipment out there, but strip tailors do band and there is some other banding equipment. What do you think about the differences between banded and surface broadcast and incorporated urea?

Dan Kaiser:
Well, Brad, I mean you mentioned this earlier and when we start looking at just what we deem the four Rs, so that's rate, source, timing, placement. When it comes down to interactions, we see a lot of interactions with rate and time, well, we would like to avoid rate interactions, but timing and placement, but also source timing and placement. And that's really one of the big things when it comes to urea is that we have a lot of flexibility in what we can do with it. The main issue though with urea is the loss pathways and we can actually lose nitrogen in two ways. One is through the volatilization of ammonia. And this occurs, and I don't think we're going to get into a lot of detail in this particular podcast, but it occurs at that initial step where the urea molecule is broken down by an enzyme called urease.

When that happens, ammonia gas is formed. So if that urea is too close to the surface, then that ammonia gas can be lost to the atmosphere. And there's a few ways that we can, we call stabilize this or prevent some of this from happening. And placement is one of those. And that's been one of the questions when it comes down to urea is management wise, there's a few things that come into play and really volatilization is a big key because many times a lot of growers are focusing on nitrification inhibitors, which the nitrification process happens after that volatilization can occur. So that's one of the things that we've looked at is trying to look at situations, particularly with timing of urea is looking at placement and seeing whether or not surface broadcast versus banding gives us any advantage in terms of overall loss. So Fabian Fernandez at the University of Minnesota over a number of years, looked at some different placement source and timing methods.

And what he really found when it comes to placement is that typically the subsurface band, if you look at it, I mean it wasn't a glowing, when you start talking about the overall benefit of it to be seeing roughly say that'd be about 25% of the time that the broadcast, the subsurface band was actually close to a third of the time that the subsurface band was better than broadcast incorporated. But he's also seen situations where the opposite is true. So it's not anything where it clearly happens, although if you are a strip tiller, I think that would be the best option and especially when it comes down to placement because it's one of the things that we've seen with urea is that the timing aspect really is critical. And with fall applications, we know there's a pretty significant risk for potential for loss. So the question is whether or not we can use banding.

I mean there might be some circumstances where that can happen, where banding might be better, but still really timing wise, that timing, time source interaction really is key. When it comes to urea application. We have looked at this, I mean if you look at just, this is for an example, say comparing anhydrous ammonia to urea subsurface band, Fabian Fernandez looked at this as well over a number of locations and about 38% of the time anhydrous ammonia was actually superior to urea subsurface band and you never really saw it the opposite around. And that's really one of the things we've been looking at particularly with more of a urea based system that we have in Minnesota is more growers have been looking at fall application of urea. And we've been looking at options, and it's still when we start talking about source that anhydrous ammonia really is the preferred source when it comes to a fall application.

If you look at it pretty consistently, whether, even if you do or don't have inhibitors in that, the anhydrous ammonia still tends to win out, particularly for fall application. Spring, we know that there's some flexibility, but the main thing when it comes to a situation like urea is that volatilization aspects, we want to watch that source placement interaction just to try to make sure that we're putting the urea at a situation where we can capture a lot of that ammonia that's being generated when the urea molecule is being broken down so it's not lost to the atmosphere.

Brad Carlson:
Well, I think and another aspect of this we need to look at, it's not just how often you have a problem. For instance, with fall urea, it's when you do have a problem, how big is the problem? And so if you look at that data where they found that roughly a third of the time they had problems with yield in a fall urea application and you say, "Well, it was only a third, two thirds, it was not any different." But when it was a problem, it was like almost 60 bushels an acre difference. And that's huge. I mean, I don't think anybody wants to sleep on a problem like that.

Dan Kaiser:
Yeah, and this is looking at, when we start looking at a lot of this data, we're not necessarily comparing, we're sometimes comparing suboptimal rates. So that yield difference is pretty significant if you look at the same rate of anhydrous ammonia versus urea subsurface band. So it's something to consider because we know that just when it comes down to sources that urea is going to have more questions when it comes to some of the loss pathways. And there's more concern, at least for us on a research end when we see a shift more into a urea-based system is particularly with fall application that it isn't the same. All these sources, if you look at UAN, if you look at urea, if you look at anhydrous ammonia, while the plant doesn't care where the nitrogen's coming from, as long as it's there, in the end it's that pathway by which it gets there can be an issue.

And that's one of the things in my current research I've been looking at is trying to look at more of that loss pathways to see if indeed it is some of that volatility aspect, which from some standpoint that if it's volatilizing, it isn't nitrofying and getting into the surface or subsurface waters within the state, but it's still I think, a significant loss to consider if you're a grower because you're likely looking at having to go back in with some sort of side dress application or some sort of in-season application. Then that begs the question, if you're consistently doing that, should you just be switching timing to look at focusing more on a application more at or beyond planting at that point in time if you're already doing that consistently just because the practice you have is losing nitrogen.

Brad Carlson:
Right, and it is one of the elements related to interpreting our university research sometimes I like to point out to people is the fact that when we look at averages and we've rolled, as you say, you look at an average for treatment and we've rolled all of the studies together where there wasn't a difference and there was a difference, and then the average ends up being small. For instance, one of the examples that I've given frequently is looking at fall anhydrous at the research station at Waseca is on average there's an advantage to spring application. But in reality what there is, is there's a big advantage like two out of five years and three out of five, it doesn't make a difference. And so similarly with this, sometimes we'll have, people will tell us, well, I did it and it was just fine, and it very well may have been.

And the thing is you have to realize is you get that one year where the conditions are adverse and suddenly we can have some pretty big differences there. So let's switch gears here a little bit and talk a little bit. I guess I'd like to talk first of all about anhydrous ammonia. Obviously farmers who are used to putting on anhydrous realize that really we've got two issues that need to be avoided. Obviously shallow application is a problem kind of across the board, but particularly when the soil is dry, we know that the anhydrous nature of anhydrous ammonia makes it want to find moisture in the soil. And when there's not a lot of it, particularly when you're shallow, it does have the ability of gassing off or being lost to the atmosphere. So we've got to be careful about that. But I think most farmers also can identify with making an anhydrous application when the soil is too wet and then they see that the trenches aren't sealing behind and then they can see the white smoke coming out and gassing off.

So there has been some research done on this and really kind of the sweet spot for all applications is about 16, 17, 18% moisture thereabouts. You've got kind of the least loss across the board, but in particular, the deeper you get it, the less likely it is to be lost. And the research says that if you go nine inches deep, you can pretty well get away with almost anything. However, I think we all realize that nine inches is getting awfully deep. The amount of horsepower and the wear and tear on machinery really is excessive, but we do look at wanting to get at least six inches deep to minimize those problems. Realistically, even if it's really dry, if you're down at say 4% or 5% soil moisture, as long as you're 6 inches deep, you're still only looking at about a 5% loss. I don't think a lot of people are enthusiastic about losing 5% of the fertilizer they purchase.

However, it could be a lot worse. And really you're probably still going to lose about 2% of it no matter what. And so that's kind of our BMP for anhydrous applications is looking at trying to get it 6 inches deep and preferably in that 15 to 20% soil moisture level. Now, one of the other areas, and we get a lot of calls about this, Dan, is relative to urea incorporation when we have a broadcast surface broadcast application that's made. Now, you already talked about the fact that the urea molecule breaks down into carbon dioxide and water. I think all farmers recognize that urea is water-soluble, that when it rains or you get moisture on it, the pearls just disappear. I think the thing that's important to recognize with that is that does not necessarily mean that's incorporated. So our rule of thumb related to that is we like to see about a quarter inch of precipitation and otherwise we're also looking at wanting to get it incorporated.

And so there has been some research done on this also, and very particularly kind of the BMP is get it down three inches deep. What we've found is that shallow incorporation, which is only about an inch deep and inch deep probably means using a drag hair or something like that, actually had higher surface loss initially than just simply leaving it on the surface. And that was probably because we dissolved the pearls but didn't get them deep enough to prevent them from blowing away. The loss goes down significantly when it gets down to two inches and then it gets down to zero when you get down to three inches. So I think really the take-home message for incorporation of urea is you want to use a field cultivator.

Dan Kaiser:
So one of the things I'll say about urea is when it comes down to it, what Brad said on the incorporation side is critical. So with rainfall, since urea is a neutral molecule itself, it doesn't have any charge. It won't be held by the clays and it won't react with any ions that are actually in the soil itself because that's where that quarter inch of rainfall is enough to dissolve. It's actually granules. I mean we talk about pearls a lot, but a lot of our urea is granulated more than pearl. It's really not a big difference there. But the main thing though is essentially getting it down because as Brad said, with surface application, really looking at some of the data, some of the data has shown that within the first seven or so days that we don't expect a whole lot of actual loss.

And with urea, if you can see it's really not as much of an issue if you can't. And that's kind of the problem is once it starts to dissolve, then that volatility issue kicks in because what's mitigating that is an enzyme called urease, which is in the soil itself, and it's also contained in residues and it's in a much higher concentration in residue than it is in the soil itself. So that's where if we're in a situation where you're in continuous corn, really the last thing you want to do is leave that urea on the soil surface, anything with a high level of residue because you're going to kick that process into place relatively quick. And at some point we'll likely talk about inhibitors. But generally with an inhibitor, if you can incorporate within about four days to a depth of two to three inches, you should not need any sort of urease inhibitor.

If you're laying it on the surface and you can incorporate, then it becomes more of an issue. And it's kind of what Brad was saying is incorporating it to a depth of one inch really can be worse, and that's just because we have moisture in the soil that could start that process quicker, especially if it's dry to start dissolving the urea. If you look at the numbers, the loss potential for surface application is still greater. It's just with the shallow incorporation, it kicks in a little bit sooner with that. So the big key to remember is that with urea, if you can see it, it's not as much of an issue. If you can't, then we know we are going to start to have some of these processes by which urea is converted.

Brad Carlson:
And I've had people in the past who have said, well, is a dew significant enough to incorporate urea? No, it's not. It makes the situation worse, that really, if we're getting down to the dew point at night, if you've surface supplied urea and it's just laying there on the surface, you go back the next day and you notice that the urea pearls or granules are significantly smaller than the day before, that doesn't mean that that got into the soil. It means that it dissolved and it probably spread it thin over the soil surface and probably made the situation worse. So we do need to be mindful of that. Now, another aspect that we'll probably cover in a lot more detail in a future podcast is relative to the process, the breakdown process. And it's worth mentioning, Dan said it was enzymatic. Because it's enzymatic that is not so temperature dependent as the things that are biological in nature.

And so that breakdown of urea will speed up when it is really warm. However, when it's really cold, it still is happening. I think the data indicates if you leave it on the surface, even when it's really cold after 10 days, you've really lost a large percentage of it. So what do you typically think? You mentioned if you don't have the NBPT on there, you want it in, in three days. If you got the NBPT on there, how many days you want it worked in it for?

Dan Kaiser:
So typically we would say with an inhibitor, particularly if it's NBPT, and that's the main thing to do is make sure you know what you're applying because there's a lot of nitrogen products or inhibitors out there that are sold that because they're cheap doesn't necessarily mean that they're effective. I think we could do a whole other podcast. We probably will at some point talking about this thing. But generally two weeks, I would say that you generally have good activity on many of those inhibitors. And as Brad mentioned, it is kind of a thing to kind of consider is that if it starts dissolving, I mean these processes are going to kick in. If you look at temperature, I think some of the data where we cite and use in the nitrogen smart program shows urease activity and the conversion of urea in soils that it takes roughly 4 days at, I think around 75 or 80 degrees.

If you go down to 35 degrees, it took about 10 days to convert all of that urea once it was dissolved. So I mean, really it doesn't stave it off. And that's one of the things that cold temperatures, while it will affect nitrification, you still can have volatility. And that's one of the concerns I have, particularly with late fall applications, is that people I think don't realize that you could be getting a significant amount of volatility from surface supplied urea, particularly with shallow incorporation, which now I have more concerns with situations where more growers are going to things such as vertical till that we're not getting it incorporated enough to get it where we're not reducing the losses to as little as possible.

Brad Carlson:
The other thing is, and maybe I shouldn't even introduce this, but I think it is relevant for the topic we're covering, and that is to be also mindful when it gets really, really hot. We don't have data on this, but we have visual evidence. We had an internal meeting at the SROC at Waseca a couple years ago where they had done some top dressing at a time when the air temperature was approaching a hundred degrees. They had used NBPT and the signs of burning of the leaves was extreme. And so even though they had kind of followed the practices that should have been followed for the application, when that application was made with those kinds of temperatures, clearly there was a lot of loss of ammonia off of that urea that was applied.

So Dan, the last thing I want to cover here is to talk a little bit about UAN as we're heading into the side dress time of year. Tell us a little bit because we get, every year we'll get some questions about whether farmers should be using either a urease inhibitor or a nitrification inhibitor with UAN.

Dan Kaiser:
And there's been a lot of questions, Brad, on placement options because we had a big influx, particularly as the Y-drop systems came into play of more growers interested in it because it's something that they could equip on their high-clearance equipment and go out and side dress. And a lot of that system was predicated on late season applications, which when it comes to timing, we don't really suggest any planned side dress beyond about V-five or V-six. And that's mainly because we know there's some issues and we want to make sure that the nitrogen is in a form and down close enough to the roots of the plant where when we're at peak demand, that it's there that the plant can feed off of it. But when it comes down to options, I mean really for side dress application, I think that the best option is some sort of stream injection.

There's been some work Jeff Vetch did at Waseca where they were looking at some different placement options, the wide drops, the surface dribble where it's just placed, I'm guessing, mid row. I don't know exactly how they have their systems set up versus stream injection. And that's with and without Agrotain Advanced. And one of the things you have to remember about UAN is that when it comes to a thing like Agrotain is you can only protect about half of the nitrogen because only half of the nitrogen in UAN, whether it's 28 or 32%, is in the urea form. The ammonium nitrate form, which is the other half, the nitrate, you can't really stabilize that at all. And then the ammonium is already beyond the point at which you get volatility with that. So I don't see as much of a benefit. There's some always questions with surface dribble applications of UAN, whether or not to use Agrotain, but in the end, again, you're only protecting half of it.

And with dribble applications, one of the things that is worse for volatility is spreading that material across the soil surface. So if you're applying it with flat fans, you're likely going to get more of an issue with volatility versus just a stream injection. But if you look at the data, I mean the surface dribble sometimes will equal to the stream injected. One of the things that was interesting from a lot of the work that Jeff did is that the wide drops, particularly early on, weren't yielding quite as much. And one of the questions we've had with that, particularly with the wide system, is since you're putting a band on both sides of the plant, is that, do you get greater volatility from increasing the surface area, having two bands instead of one just with a normal surface dribble application? It's one of the things, I know Brad you've mentioned before, talking to some people you know around central Minnesota is that one grower in particular went from banding, he dropped half his unit, so he was only putting one band down. But I think in general, really if you're banding, I would be as concerned about it. I mean, certainly you could use something like an Agrotain Advanced with that surface dribble application, but I don't think it's as critical.

Brad Carlson:
Well, when this method first came around, I think our reaction to it was is that's a fine method to side dress nitrogen. There were some claims made that it was better than other methods. At least the research that we've done shows that it's just as good as the other methods that you're going to use. But we haven't seen any evidence that is better than that. So I guess from that standpoint, again, if that's the way you want to apply your nitrogen, we think that's fine.

However, as you mentioned, Dan, particularly in cases where we actually saw slightly reduced yields with the Y drops, and we think that some of it was relative to doubling the surface area that the UAN was exposed to. And then some of it also was relative to side dressing a little bit early and maybe the hoses wandering around. Obviously when the plant's bigger, it's going to keep the hoses confined within between the rows. However, it's worth noting from an application standpoint, you're only talking about a week and that nitrogen doesn't really make one hill of beans difference as far as whether it's applied one week earlier or later.

Dan Kaiser:
And one of the things to think about the wide drop option is really predicated on what a lot of people talk about is water moving down the plant that's just from evap, or just water that the plant has and that soil being wet around the base of the plant. But if that soil is wetting and drying, the likelihood that you're getting enough water there to move nitrogen is pretty low because we know that, I think, what is the stat, it takes about an inch of drainage to get about six inch movement of water. So the likelihood that you're moving the nitrogen versus the nitrogen is probably just diffusing a small amount is pretty low.

Brad Carlson:
Yeah. Yeah. You're probably putting it in location of some of those surface roots, but as far as actually moving it into the soil, it's probably not going very far at all. So, well, this kind of wraps it up for our talk about placement.

I guess just to kind of finalize here as a reminder of the things we talked about, we like to see anhydrous ammonia down at least six inches deep. We like to see urea at least three inches deep. And basically the way you incorporate your nitrogen is basically the same thing as your placement. And you need to think about what is the potential loss pathway for each fertilizer when you're making your placement decisions.

Jack Wilcox:
Extension educator Brad Carlson and Extension nutrient management specialist Dan Kaiser, thank you both very much.

If you have questions for either Brad or Dan, please email us at nutmgmt@umn.edu. Thank you 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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