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Welcome to University of Minnesota Extension's Nutrient Management Podcast. Each month we bring you the latest research in nutrient management for crops and how you can incorporate the latest tips and best management practices to your farm.
Advancing Nitrogen Smart, from the University of Minnesota Nutrient Management Podcast:
“Statewide best management practices for nitrogen: A valuable resource for Minnesota growers”
May 22, 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 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.
Today we’re going to talk in-depth about Best Management Practices, or BMPs. Brad let’s begin with you. Where did nitrogen BMPs come from historically, and what issues were they created to address?
Brad Carlson:
Yeah. So really all the BMPs are is nitrogen recommendations. It's just got a statutory definition to it. In a lot of cases people are familiar with the term the four R's that's become popular over the last few years, the same thing.
The nitrogen BMPs in Minnesota originated with the Groundwater Protection Act in 1989. It was a piece of legislation. It directed the creation of best management practices for nitrogen fertilizer. The BMPs technically belonged to the state Department of Agriculture and the University of Minnesota was delegated to determine what they are. So they're co-owned. Technically they own them, but we decide what's in them.
And so they first came out in Minnesota in 1994. We have some general statewide things that we recommend, and then there's region-specific. We're not going to get region-specific today, but we do want to talk about some of the general overall practices. There certainly has been a lot of focus on this with respect to what's been going on for high nitrates in groundwater in southeast Minnesota. We're currently in the process of rewriting our nutrient reduction strategy in the state, and so there's been a lot of attention paid with how we're managing nitrogen. So we thought the timing was good to talk a little bit about what some of our general practices are.
Dan Kaiser:
That's one of the things to remember when we start talking about best management practices is that they do focus and they are general practices that should be both economic, should maximize economic productivity while, too, minimizing loss of the environment. And that's really the key is that when it comes down to a lot of these things, that they are research driven. We do have to have some research emphasis behind our best management practices that when it comes down to it is that we do integrate the economics and the environment together. And that's one of the things that I don't think it's brought out enough that a lot of people on the environmental side think we only focus on economics. And then conversely, we see the same thing from the other side where they think we only focus on the environmental aspects.
But really, as researchers, since we answer to the greater public, not only just the agricultural community, we really need to balance these two when it comes down to the recommendations. The other thing, a lot of these are generalized recommendations that should be beneficial in what we would deem as a normal year and whatever that is. But we do know these practices are good starting practices to build your nitrogen application around as we know that on average in these areas, that generally they should particularly reduce the potential risk for loss.
Brad Carlson:
It's worth noting we focus a lot on corn and our podcast is sponsored by Minnesota Corn, but we should note that there are best management practices for all of our crops that use nitrogen, but not all those crops are grown ubiquitously across the state. And so obviously our small grain best management practices tend to be focused in Northwest, Minnesota where most of that production is. Sugar beets are very localized based on processing. We have specific recommendations for potatoes and then also relative to other nitrogen-using crops like sunflowers and dry beans and pastures and so forth, and so each crop has its own.
Now really the key for all of this though and the reason why corn tends to draw all the attention is most of these other crops have issues if we over apply nitrogen. So not just simply the rate, but if we also look at bad timing or a form of nitrogen that doesn't work for the way we applied it, you can run into a lot of profitability issues. Corn on the other hand will take extra nitrogen and just ignore it and leave it in the field, and so we've not had the margin for error with corn that we've had with the other crops. And so we're catching up with respect to getting really precise on nitrogen management compared to the way we've been, for instance, with wheat over the years. You apply too much nitrogen to wheat, it ends up flat on the ground. You apply too much nitrogen to sugar beets, your sugar content goes down and you're going to not make so much money and so forth. So there's issues with some of these other crops.
So the other aspect of this I think most people are aware of is these nitrogen best management practices are also regionalized across the state of Minnesota. And so we know that there's different soil types as we move across the state just as there are different crops, but then we've also got different climatic conditions. And so for that reason, we've had separate nitrogen best management practices for the southeast, for the south central, for the southwest, west central, northwest, and then a catch all for the central. But one of the things we've been stressing for a very long time is the fact that even though that's the geographic place you live in, it may not necessarily be the correct best management practice for you where you're at.
Dan Kaiser:
It's one of the things that to me makes Minnesota interesting. I mean, I did a lot of my early research when I was doing my master's in PhD down in Iowa and I grew up in Iowa, and Iowa's boring from the aspect when it comes to soils. If you look at Minnesota, I mean, soil parent material dictates a lot of what we recommend. And it's one of the reasons why we can't do a one-size-fits-all recommendation across the state because what's inherently in the soil and some of the chemical properties, the ways at which we lose nitrogen varies from one soil to the next. So a lot of what we have for our best management practices really as Brad was talking for our regions is dictated by the parent material and also the precipitation, temperature, those types of factors, which we'll talk about here in a moment. On the parent material side, if you, again, look at Minnesota, I think all but about three of the soil orders, when we look at Minnesota, are represented. I don't think we have any gelisols, which are frozen soils, alfisols, which are highly weathered and-
Brad Carlson:
Andisols, the volcanic ones. Right.
Dan Kaiser:
So those would be the three that we don't have. And to me makes it a lot more interesting when it comes to research because it offers a much greater range in conditions that we can look at some of these things. And when it comes to parent material, I mean a lot of what ... When we start talking about differences, really it focuses in on one, how nitrogen is held in the soil. Although if we look at nitrogen, the majority of the nitrogen that our crops take up are in the nitrate form, which isn't held in any soil because it's an anion, not a cation.
Jack Wilcox:
Dan very quickly for our listeners that may not know, what is a cation?
Dan Kaiser:
A cation is simply a positively charged ion. All the fertilizers that we apply, or the nutrients that are taken up by a crop are in the ion, or some sort of ionic form. If we look at, say, potassium, which has a positive charge, that’s what constitutes a cation. And our soils have what we call a cation exchange capacity which comes from the fact that the clay layers will generate negative charge on their surface. So those positive cations will be attracted to the clay layers. Simply what it is, it’s a positively charged ion. It’s the opposite of an anion which is a negatively charged ion, which would be something like nitrate which is not held in the soil.
But when we start talking about things like cation exchange capacity, I mean that really starts to factor more in on timing aspects for recommendations where if we have something that's got a lower cation exchange capacity, we want to be applying the nitrogen closer to when the crop's actually in the field using the nitrogen versus you get to central western Minnesota, glacial till soils, high clay content, situations where fall application may work because we can maintain ... Particularly if we can maintain more than nitrogen in the ammonium form, it can be held long enough work and get to a point where there's a crop in the field.
Brad Carlson:
Well, and the other thing I guess we need to recognize is cation exchange capacity corresponds with soil texture. It's really a measure of the exchange sites on clay, and the less clay you have, the less exchange sites, the lower cation exchange capacity is. Really the key with soil texture is the coarser the soil is, the faster water moves through it. And so it's really a saturated hydraulic conductivity of the soil or how fast we could flush nitrate out of the soil. And therefore major implications on the application timing as well as in the case of sandy soil, just simply having to split apply it, because if you apply it at all pre, it might be gone by the time the crop gets to its middle stages. So there is that element.
And then in addition to that, we've also got the aspect of depth to bedrock because we've got the loess textured silty soils in southeast Minnesota, which are bad enough because they've got a higher saturated conductivity. But then in addition to that, in a lot of places you can go down 24 inches and you hit bedrock, and in that case it's fractured limestone and it goes away very quickly. So all of these are elements that play into why we divided the state the way we did originally with respect to the regional BMPs.
Now the other element that really comes into play here, and this is the one area that we're very closely re-examining, is precipitation. So if you look historically from across the state, you'll see that it's the wettest in the southeast corner and driest in the northwest corner, and there's been a very smooth gradiation of this. And so one of the areas that we'll talk about in more detail in a future podcast because it's some of the material we cover in when we do our nitrogen smart climate stuff is the amount of growing season precipitation, and particularly the amount of precipitation versus evapotranspiration, that is the amount of water that's either lost through evaporation or transpired used by the plant. And if you look at over the, well, the last 30 years, but particularly the last decade, we've been consistently wet all the way across the southern third of Minnesota, really all the way to the South Dakota border. And so while historically we divided south central and southwestern Minnesota because it was so much significantly drier in southwestern Minnesota, really for the last decade plus, it's really behaved all the same.
Dan Kaiser:
And that's one of the challenges because we know there are changes to the precipitation pattern. I don't think anybody really likes to talk a lot about climate change, but we know that especially if you look at it, 30-year normals are used a lot in our assessment of best management practices and we recalculate those about every 10 years. So the last recalculation would've been, Brad, 2020, I think?
Brad Carlson:
Yep, in 2020, yep.
Dan Kaiser:
So when it comes down to practices, we have to factor that in and look at some of these trends even though we know we have situations like 2021, 2022, 2023, which we had drought years, so we know those things are included. So really the question is, or what I really focus a lot on when I talk through some of this stuff is looking at how do you manage your nitrogen? Do you look at long-term or do you look at short-term? Because from a planning aspect, and one of the challenges with nitrogen is once we apply it, we can't take it out. I mean, we have to have a plant there to take it out. So once it's there, it's there. So the question then of a lot of these best management practices is trying to make sure that we're focusing on practices that at least don't set us up for substantial losses should the worst occur, should we get a lot of precipitation.
Or with the drought, typically we know we don't have as much of a problem with nitrogen loss because leaching loss is water based, so you don't have the water, you don't have the loss. So that's key with that and that's why we focus on that. And since the last update of the best management practices that was done around 2006, 2007, I think they were printed in 2008, we've seen it pretty substantial if you look at the trends for precipitation, which has really necessitated us to look at some of the practices, particularly in the southwestern part of the state, because as Brad was saying, we have what we call the leaching index, which essentially is the relative evapotranspiration relative to precipitation, which tended to be positive if you look at historically, if you go back 10, 20 years where we would expect some more upward movement of water over the whole growing season where …
I mean, there is some risk for leaching loss, but it wasn't quite as critical where things like fall application were less of a risk if we would see some conversion of ammonium to nitrate. So it's, again, one of these things when it comes to best management practices, they need to adapt to what we're looking at for current norms.
Brad Carlson:
And for that point, it's worth noting that because you mentioned we used 30 year rolling precipitation averages, when the first BMPs were developed and these regions were defined, it was 1994. We were using the 30-year average that was set in place in 1990. That was the precipitation from the 1980s, very dry, 1970s, very dry, 1960s, relatively wet, but as an overall, much, much drier than it has been now as we look at the 1990s, the 200s and the 2010s, which is where our 30-year average is now. We've completely moved past the whole 30 years that were used to develop those original regional recommendations.
I think the other thing we need to think a little bit about is the temperature, the soil temperature, because that does play a factor. Probably the kicker with soil temperature though is the interaction that soil temperature has with soil moisture. If we look at average air temperatures, we haven't been seeing tons of difference. I mean, Dan talks about how the climate has been changing. The big difference we've been seeing particularly in Minnesota has been warmer overnight, in the summertime. It doesn't have big implications on nitrogen management. It maybe does on how the crop grows and performs.
But when we think about nitrogen application, the one thing you do need to think about is soil moisture because that does affect field work as well as it takes a lot more energy to raise and lower the temperature of water than it does to air. And so the wetter the soil is, is going to change that dynamics of how fast it warms up and it cools down. And so as particularly we've been wetter in the fall lately, it does stay warmer later, and then it's been staying frozen a little bit longer also, and so that's going to have some implications on how we manage nitrogen into the future.
Dan Kaiser:
So one of the things about the BMPs, again, as Brad mentioned before, is there is a regional focus to this, and currently if you look at the 2006 updates, there is a big regional focus when it comes to crops. Corn is part of the majority of our BMPs across the state, with the exception of the Northwest because at that point in time, I mean corn was grown, but it wasn't where it is now, where it's displaced. That and soybeans have displaced a lot of the wheat acreage up in that area. So that's one of the things that we're looking at for this new revised update that we're working on now is going less regional focus on crops and including the crops that are mainly grown in those regions, at least some information on them in all the regions because there are some differences.
I mean, particularly I look at small grains, there's some differences in how I would manage nitrogen. I could say corn, the same thing. If you look at the Red River Valley versus the bulk of Southern Minnesota, because again, those soils are different. I mean particularly the Red River Valley, we've got shallow water tables. You look at high residual nitrates, that soil's frozen longer, so you should have less risk for nitrate movement. They're just, again, the reasons for it and it's reasons why we have separate recommendations.
One of the main things that you'll see in the regional BMPs is the fact that they do go by county line, but that's one of the main things that I think is important to remember is that, I mean, soils don't follow county lines. I mean, we had to make a delineation somewhere when these were made out. So that's what it was decided to do, use the county lines. But just because you're in one county, if you're on the edge of one, doesn't mean that you shouldn't be using the BMPs from the next county over. I mean, I think the example in that, Brad, you give is Rice and-
Brad Carlson:
Right, right. Northfield Township in Rice County, you can find limestone sticking out of the ground and that's technically part of the south central region. But if you're in that township, you really need to be following the southeastern Minnesota BMPs. Now to some extent, the new nitrogen rule that the Department of Ag has come up with is taking care of that because they've gone by soil type and they've defined parts of the state where we shouldn't be doing fall applications, and it shows that.
But Dan, the other area that we always get a lot of question about is that whole central Minnesota area. The central area was defined based on where the majority of our sandy soils are, but it's certainly not all sandy, that Stearns County particularly. There's a lot of areas that are sandy, and then there's a lot of areas that have heavier soils, and so we don't want to necessarily recommend somebody with heavy soils should be looking at, for instance, split applying their nitrogen four times or something like that.
Dan Kaiser:
Yeah, and that's one of the things, too, you look at. I mean, another example I think is like southwestern Goodhue County. You've got some soils that are probably similar to that central BMP region, but does that mean that you should be fall applying? You look at it, that temperature and precip gradient, if you look at it, really to me, I'd follow a lot of that. I mean, if you look at situations where you're getting a fair amount more precipitation at points in time, particularly when we lose nitrogen, which is April, May, and June, typically, I mean if the soils are frozen, I mean really those are key points in time, especially if there's nothing out in the field, if there's no cover crop or anything, if there's nothing there, there's nothing to capture it, if the water moves to the soil, the nitrate is going to leave.
So it is one of the things, again, while these BMPs are set in place, they aren't necessarily perfect. So as a grower, you've got to decide ... I mean, I think first I'd decide what are the worst practices and the things that I should avoid? Then look at the options that are things that would be acceptable. And then what's the best option for me? Because again, these are suggestions. I mean right now, I mean I think some of them, as we start getting into situations where some of those DWSMAs where they're requiring them to follow certain plans that they're making them up, those might change, but they are suggestions, but they are the suggestions that we know should mitigate loss as much as possible.
Brad Carlson:
And so if we think about what exactly are the best management practices, obviously everybody focuses in on rate. We're not going to talk about rate a lot here. We will talk about rate extensively in some future podcasts, but the BMPs say follow U of M rates. And it's also worth noting, I guess we maybe should have mentioned this right from the start, that BMPs are recommendations. They're not the law. It is not demanded of you that you follow them, but it is based on research. This is the way we think the best management is. All that being said, if you're grossly violating these things, you're probably creating problems that may end up resulting in some laws eventually, so we do need to be cognizant of that.
But nitrogen rates have been determined based on our current MRTN method, which uses a large amalgamation of rate trials from across the state and fits them with a quadratic plateau model, not something that anybody listening to this podcast needs to understand, but what you do need to understand is it's not average. It doesn't mean that half the sites needed more than this rate. The model does fit the majority of sites underneath the line, and so it's probably more like 80%, 20%. The thing we've always stressed with Nitrogen Smart in person or all the other types of Nitrogen Smart education we've done is there are reasons to not follow university recommendations. However, those reasons are knowable. And so you should be actually analyzing the situation and having a reason why you're making adjustments instead of just saying, well, I think I ought to do this or I'm just not comfortable with whatever. There are ways to know when situations are different than average or typical.
Dan Kaiser:
And rate is a tricky one because, again, we know if you look at our database, there's a pretty wide range in rates in terms of what maximizes yield. Yet if you look at the data, there's really no way for me to go into the database we have and separate it out by specific regions. I've tried that. I've looked at the data. I've tried to split it out to see if we could separate out specific circumstances, but the numbers come back exactly the same. So in the end, there's not a lot I can do about it. I mean really one of the bigger questions on this is when it comes to our rate recommendation is looking at all the sources of N and can we accurately credit any of that back? Certainly anything you apply in the spring, MAP, DAP, AMS, maybe some UAN in your weed and feed, some nitrogen in the starter, those are pretty easy.
What becomes more of a question mark are situations where growers are using MAP and DAP and just considering it to be phosphate, even though there is nitrogen in that is if you apply that in the fall, particularly early fall applications is how much do you credit that? So the thing that I've been wondering now is say we switched to a product like triple super phosphate, does that have it? Does it really matter to growers that aren't crediting it? That might be better because we're just putting nitrogen in the environment that might not necessarily need to be there.
But that is really key and with timing is you've got to remember some of these things that you might be applying say for sulfur, for phosphorus, that it may have nitrogen with it. So I mean then the question is based on the timing, do I credit it or not? And we'll see moving forward what happens with that because there's really no regulations saying that you have to, but from the standpoint of loss, we do know the earlier you apply it, the more potential there is for loss.
Brad Carlson:
Well, and another aspect of the whole rate thing is I think farmers who have not engaged really closely in what our recommendations are frequently will throw out the, “Well, crops are yielding so much higher than they did back when you came out with this”. Well, actually if you've been following it, you know that our rate recommendations have also increased quite significantly based on the yield data from our rate trials. And so the rate recommendations have been adjusting as yields have been increasing, not linearly because what we're discovering is in a lot of cases it's not nitrogen that's holding back the crop. And so simply adding more nitrogen doesn't mean that then you're going to hit that next yield plateau, but the rate recommendations have been increasing.
The other aspect about just our general BMPs, Dan mentioned about using all forms of fertilizer is also to be looking at whether you've got any carryover from previous legumes, particularly alfalfa, don't necessarily see big credit for other types of legumes like clovers or so forth. However, there could be something there. And as well as manure credits, I know particularly we often look at a two-year credit. Now a lot of times if we're dealing with a corn and soybean rotation, that second-year credit is moving into soybeans and then we don't worry about it. But if you got corn on corn, you do need to think about those for more than one year. But also then for that corn crop, you do need to be fairly precise. In a lot of cases you're not going to need nitrogen at all if you plow it under alfalfa. That's a pretty large expense I guess. I don't know why I would pay for that if I didn't need it.
Dan Kaiser:
And with crediting too, if you are using the MRTN approach, I get a question on what do we credit for soybeans? I mean that's all built into the recommendation since it is a database. I mean the numbers are all following soybean that's already calculated in. It's really more of a question of some of the other crops, and that's the thing that makes Minnesota challenging is because there are a lot of other crops growing out there with the canning industry that's out there and some of the other things that are growing. One of the other questions is cover crops. I mean I think we could talk about that in depth at some later date, crediting becomes difficult as well.
Sugar beet tops, one of the things, if it is tops, we do have some recommendations for that. The greener they are, the more the credit. One of the things that does come up from time to time with beets is if you're following in a field that has unharvested beets, do you get a credit from those unharvested beets? And really the answer to that is no. So really the credit comes from the tops more than the beets themselves if they are in the field. If you had to have some lay by acres where the beets are still in the field the next year, really we'd expect some tie up as those beets are being broken down. So that's one of the things that's difficult, and that's one of the things to know. And I mean that is something that you need to look into, the co-ops, particularly American Crystal and a Southern Minnesota Beet Sugar Cooperative have information on their websites and how to manage those acres and what you might be looking at the next year.
Brad Carlson:
So as far as other statewide BMPs, we talked on the last podcast about placement. So we want to make sure that we're placing the fertilizer properly. So if you're putting on urea, we like to see it either rained in by a quarter of an inch or incorporated down to three inches deep and we like to see an anhydrous down about six inches deep. Dan also had mentioned previously about in the last podcast at least about side dressing that if we get too late in the season, we don't see any kind of a crop response. And so we really like to see that side dress when the corn is in the vicinity of about 12 inches.
Typically, we see that around V 4. The latest we would ever want to go is about V 10, but that's really pushing it. From a practical standpoint, we'll cover this more when we talk about climate in more detail. You're really only talking about a difference of a week or two and the risk of losing nitrogen isn't significant. So frequently with side dress, I always recommend if the crop gets planted and the conditions are really good to just go back and put the nitrogen on, go ahead and do it.
Dan Kaiser:
Well, and one other thing too I'd bring up too, when it comes to side dress, if you are looking at side dress, a situation where you're in continuous corn, we do recommend that having some nitrogen down at planting is a good option. Whether that's something in a weed and feed or maybe a surface dribble application with the planter, it's really just to account for the fact that we know that what we deem to be really that soybean credit, I don't think really is a credit itself. What we're seeing there, why it takes more nitrogen for continuous corn is the penalty or the immobilization of nitrogen that corn residue imposes with it.
So when it comes down to it, it's why we'd recommend at least ... I mean, I like at least 40 to 50 pounds down with a lot of the studies. If you're going to be looking at continuous corn. If you're going to be looking at predominantly a side dress, and this is in a non irrigated situation, that's a whole different animal. I mean, if you've got irrigation, I mean the management is different, but you just have to be careful with that, and that's a general do for is looking at VR side dressing with continuous corn.
Brad Carlson:
So the other thing we need to be careful about is avoiding application in the fall before the soil temperature gets below 50 degrees. The loss of nitrogen is water based, but it happens after the nitrogen turns into nitrate and the conversion of nitrogen into nitrate is biological in nature, so it requires microbial activity to have that happen. And so as with anything involving life, it speeds along when it's warm and it slows down when it's cold. You and I slow down when it's cold. Just like when you eat supper and you've got leftovers, you're not going to leave them sit on the table until supper tomorrow. Bad things will probably happen, but we put them in our refrigerators, which are hopefully below 50 degrees, they're probably even colder than that, to stop microbial activity.
And so that's the reason why we recommend if you're doing a fall application to wait until it's below 50 degrees because that's the point at which microbial activity really slows down. Now, it doesn't stop, however, once we hit 50, we're pretty much always on a downhill slide towards freezing. And so every day it's getting a little bit colder on average, and so, in general, we like to wait that long.
Dan Kaiser:
Some people may say within inhibitors, too, can we go in earlier with that? And it's the same thing with inhibitors, particularly nitrification inhibitors. If you're looking at nitrapyrin with anhydrous is that the colder the soil, the better results you're going to get with it. So it doesn't give you that earlier application window because it's going to break down. It's what an inhibitor does. It breaks down over time, it becomes less effective. So you don't have that option, and it's one of the things that when it comes to anhydrous with N-Serve, looking at it, we still want to follow that 50 degree timeframe.
And then some people in some areas are using urea with Instinct, and that's just a bad practice for fall application because going back to our last podcast, I mentioned this before, is that we have volatility of the ammonia that some of the initial stages of the urea breakdown that can come into play and you're going to lose it before that nitrification inhibitor, even if it is effective, which it hasn't been shown to be highly effective with broadcast urea that you might lose it beforehand with that. So it's the same thing. I mean the inhibitors, that 50 degrees is a pretty good thing. When the soils stabilize at that point, that's generally the point we want to try to look at fall applications. You go too early, then the risk for both the inhibitor and also the nitrifications to occur becomes greater.
Brad Carlson:
So as far as some of the general don'ts, don't apply nitrogen on frozen ground, this includes MAP and DAP. We did get some reports this last year of some folks applying urea in February, bad idea. Even though the soils were relatively dry, it is completely possible to get cold and get a rainfall and then have it all wash off the field. So we really need to avoid that if at all possible, or maybe I should just say we just really need to avoid that because it should be possible to just simply not do that.
Dan Kaiser:
And a few other things to avoid would be avoid application of urea directly on the seed. This is just because, again, ammonia is formed in the initial stages of urea breakdown. I mean a lot of people focus on salts when it comes to seed safe placement. I mean this would also include air seeders. I mean, wheat, though, when it comes down to it, we know that it does tend to flex a little bit with its tillering capacity that can make up for the loss of a few plants. But with corn, that's not the case, so you want to keep urea away. And if it's broadcast and incorporated, we know we're not worried about that. We're worried more about band applications where the fertilizer is placed in a concentrated zone.
Fall application of UAN, that's a no-no. I mean some people have talked about it for residue breakdown, but really the issue with residue when it comes to breakdown is the fact that once it freezes, nothing happens. So that's really our main limiting factor. It isn't nitrogen in these fields because many of our fields have a lot of residual nitrate that once the deep freeze hits, nothing's going to happen. So if you're looking at trying to break your residue down, it's really trying to size it down into smaller particles to make it easier for the microbes to work on versus fall application of UAN because the issue with UAN, 25% nitrate, nitrate is what we lose. You can't stabilize that, so it's just a bad idea.
Any UAN application early season, even in the spring, we really want to ... Where UAN works best is really at or beyond planting just because that nitrate then is valuable because it's mobile in the soil and we can get it down to the roots quicker with that.
And then surface application of ESN is another thing. Without incorporation, I would avoid, although I know it's done in some cases. ESN, I know it's probably a future podcast. We talk about some of these products that one thing about ESN is it will float and it's better to have it with better soil contact to allow for the dispersion or the diffusion of the urea out of the ESN shells. So that's one of the things to watch.
Brad Carlson:
And I guess the last one there is if you're corn on corn, make sure you get some nitrogen on, but you already mentioned, Dan, so that's really that. I mean, the flip side of that is what if it's following soybeans? Can I put on all my nitrogen side dress? Well, yeah, in most cases you probably could get away with that. I would not wait too long and I would think about having some starter on, but I am aware of situations where people have done that. I think maybe a bigger issue is if you're following soybeans and you don't get any nitrogen applied, and for instance, you come back and apply a surface broadcast urea over top of the whole thing, that's probably fine.
Dan Kaiser:
And when it comes to side dress, I mean there's really not a big advantage to what we've seen with the research and delaying too long with a planned side dress application, unless you're in sands. I mean, obviously, with a higher leaching capacity, that would be more of an issue. Maybe some of the silt loams you might want to delay to V 3, V 4. But in many cases, if you've got heavier soils, as soon as you can roll the corn, it's a good time to get out there and start side dress application. So it gives you a wider window and that's one of the things. And when we start talking about work days is that side dress, I mean, really the big advantage there is it gives you more of a window for application that you don't need to rely on everything being down before planting so you can get the seed in first.
Brad Carlson:
So I guess just to wrap things up, we know that the recommendation table is regional, and we'll probably do podcasts in the future, talking about each of the regions specifically. We know that if you're split applying nitrogen, that that's fine pretty much everywhere you go, including on sandy soils. Sandy soils are a creature all on their own and particularly irrigated soils. A spring pre-application is good everywhere, with the exception of your coarse textured soils, which should at least be split. When we start talking about fall soils, fall application, we're really looking at primarily at anhydrous ammonia, at least in the southern half of the state. Technically, our BMPs right now do say that southwest can use urea, although the research just doesn't show that that's a good practice. So when we rewrite those, that's probably going to be coming out of there. So we're looking at fall anhydrous, probably using a nitrification inhibitor when we do the fall anhydrous.
And then in addition to that, I guess you look at that map the State Department of Agriculture has with fall application restrictions and know where that is at. And then in addition, Dan said, we're going to talk a little bit in the future about using ESN, but because of the slow release nature of that, we probably want to be a little bit careful of applying too high a rate of that. Particularly, if it's dry, there might be not enough available for the plant.
So one of the final points I guess I'd like to make, for those of you that have read our best management practices, that there's categories of recommended and not recommended, but there's also acceptable with risk. The risk part, I think a lot of people read that as it's a risk to yield loss or it's a risk to loss to the environment. That's not always necessarily the case. Actually, when these were written, it includes an economic risk, meaning this practice may not pay for itself. So in either way, some of those practices, you will get optimum yields and you will minimize loss to the environment, but you also will be investing in something that didn't matter. That's a point that I think a lot of people get confused on. We're probably going to rework the way that that happens in the future, but realize that that risk doesn't always necessarily mean that you're at risk to lose yield.
Dan Kaiser:
Yeah, and that's the big thing when you look at them. Really, the not recommended practices are those that we know that will likely increase the risk for loss of the environment, and that's the things that we want to avoid as much as possible. And as Brad said, a lot of this acceptable with risk, essentially just stuff that we know that likely won't increase the risk for loss of the environment, but may not pay for itself. So that's one of the things just to read into that a little bit. And then that the recommended practices, right now, what we have for the most part is applications as close to planning as possible. But again, moderated by the fact that we know some areas of the state, we might be able to get away with fall applications because we're not really here to try to limit what the growers can do. What we want to try to do though is to educate on things to avoid as much as possible, because really we're trying to watch out again for both environmental and economics when it comes to a lot of these recommendations.
So moving forward, these things are going to be adaptable. They have to be. When we look at these thirty-year norms and what you see now isn't necessarily what we should be doing long-term or currently just based on our environmental conditions. So it's one of the things that, it's a big job. It's something that's more of a process, not like where I can change many of my other publications without a whole lot of input. This is a process by which we have to go through public comment. So the BMPs, it's a whole different thing. But again, these things are really going to be predicated in the best of the best when it comes to practices, in terms of put our best foot forward, in terms of what we should be doing to try to mitigate risk for loss of the environment.
Jack Wilcox:
Extension nutrient management specialist Dan Kaiser, and Extension educator Brad Carlson thank you both very much.
If you have questions 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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