Variable rate nitrogen: What farmers should know
Welcome to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension where we examine and unpack data driven, research based information so you can make the best decisions for your operation. I'm Jack Wilcox at the communications desk here with Extension.
Jack Wilcox:Today, we have Brad Carlson, Extension educator, and Dan Kiser, Extension nutrient management specialist here with us. And in episode 16, we're talking all about variable rate nitrogen. Brad, talk us through variability in the nitrogen response rate.
Brad Carlson:Well, the concept of variable rating nitrogen has been around for a while, but the the big question's always been, what do you what do you actually vary it on? We know that variability across a field is very real. You know? You look at your yield maps, you see variability in yield from one place to another. We know that that variability in nitrogen response is real.
Brad Carlson:That's a much more difficult concept because it would require you to have variable rate nitrogen all the way across the field to see if there's a difference in nitrogen response across the field. The the question is, though, ultimately, if you're going to use this or do this is, can you figure out what causes it, and is it predictable? And so, you know, that that's really what it comes down to with variable rate nitrogen is can you figure out what causes variability, and is it predictable enough that you can actually utilize the information, to make it worth managing, in a way that's gonna make you profit? And and I I think, you know, the the the key here is on both sides of this as far as the yield, are you able to improve your yield and therefore increase profits, or are you able to reduce nitrogen rate and not hurt yield and reduce your input cost? And and, ultimately, that's kinda what very variable rating nitrogen comes down to.
Dan Kaiser:And one of the things that, you know, Brad, you kind of mentioned this question of what's causing some of the variability out there, and I think that's a a big question. And when it comes to how do we manage things, you know, a lot of times you look I'll just say the last fifteen years, a lot of growers will talk about managing based on zones. And what are those zones may mostly based on a lot of that's based on soil information, so soil series and, you know, some of the underlying data that's out there that's pretty easy to access. But when you start looking at just the concept of we'll just look at a soil series is, you know, in a field, if you look at a map, you've got a clear distinct boundary drawn where you go from one to the other, but it's really not that clear. And that's one of the things that becomes challenging with variable rate is what starting point or or what really information do you use to start making some of that decision on how you should be making some of those changes?
Dan Kaiser:Because, I mean, the other thing that comes into play a lot is previous management, and that's one of the things that we see more and more. It's easy to see with p and k because of changes in soil test levels. When we start looking at trying to base things on there that it's not as simple as we can use one piece of information. It's pretty complex just because, you know, we can go back to some of the things we've talked about in the past or we talk about a nitrogen smart talk on the nitrogen cycle that being that it's a biological cycle, there's a lot of other things that come into play. So, you know, the big picture is, you know, we have the technology right now to manage a lot of this.
Dan Kaiser:It's just what underlying information do we need to make decisions. And I think that's really kind of the key thing to think about is, you know, how accurate or how confident you are that some of this this information, you know, may or may not be accurate that you're using to try to make some of these variable rate decisions.
Brad Carlson:Yeah. So if you look at, if you look at data from just from you can look at the data from almost any research project that's done on farm, but, you know, if we look at particularly because we're talking nitrogen today, we've been running this long term nitrogen study, in various places across the state. We can see there's there's various subplots in in every one of these sites where we're looking at at, rate response in different parts of the field, and there's a lot of variability. There's variability, obviously, from site to site, but then there's a lot of variability just within these subplots right in the same area. And and, they can be pretty major as far as, the the range, the, you know, we see, for instance, on the sandy soils in Becker, you can see a range in in, the economic nitrogen response goes 55 pounds from the the best to the worst.
Brad Carlson:The yield range is 15. You know, similar, Morris, the the the range in nitrogen response for corn on corn is 70 pounds per acre, in in rate, and then the yield range is 14. You know, and then there's other places, where it's it's, you know, it's maybe not so extreme. Rochester, we know that we've had, kinda less, much less need for inputs in Rochester, historically. You know, similarly, our higher organic matter soils in Waseca, we don't see quite the, the extreme there either as far as the, you know, the range and the, the the required amount of nitrogen as we move across the area, but but it can be large just just within a field.
Dan Kaiser:When it comes to a lot of our nitrogen rate research is, you know, how much data do you need to base your decisions? I mean, really, honestly, when you look at variable rate, I mean, essentially, what you're looking at is just breaking a field and making just individual decisions based on that given field, based on what you know in terms of the soils or other factors that you might influence the optimal nitrogen rates. But this data, if you look at a lot of this long term nitrogen data, we have six plots that are all next to each other. And right now, the way this phase is set up, we can run what would be essentially regressions on what we considered six individual nitrogen treatment or, nitrogen response trials that are nested within each other, and it's just amazing the variability you can get. I kinda put a plug in for some of what we do with an MRTN database.
Dan Kaiser:That's why I like a larger database to try to even out some of the variabilities. I think it's one of the challenges too. We look at some of the on farm data with larger strip trials and nitrogen rate response is the amount of variability imposed by variations in the soil or some of their underlying management can really play and make a big difference in terms of what that optimal nitrogen rate is perceived to be. So I guess the you know, kind of as much as I've talked to you, I think the main thing, I think, for a lot of people to remember is, you know, it takes a decent sized dataset or database to really to look at optimal n rate. And that's kinda why we do the things the way we do them.
Dan Kaiser:But when it comes down to it, it doesn't work so well when we start looking at variable rate n. And that's one of the challenges. I mean, looking at variable rate n and trying to figure out how to segment out some of what we have for our database to see how we make some of these decisions within fields. You know, it's it's challenging, you know. I mean, I'll go back to that.
Dan Kaiser:I it if it was easy, we'd have a good answer right now, and we don't. Even with p and k, we know there's some challenges, but we just know that at least the soil test give us some indication of potential for response. With nitrogen, I mean, it I mean, you're making decisions well ahead of what you'll know what's gonna happen within a given year. And really, I mean, really environmental conditions, the amount of water falling to and being held on the the soils is really the big key when it comes to a lot of what's happening there and, I think, a lot of why we see variability within fields.
Brad Carlson:Well, it's important to remember when we're doing research, we're trying to control the the variables that that if we're researching nitrogen, we don't want other factors, whether that's organic matter or drainage or something of that sort to be impacting the results. We want the results to be strictly impacted by nitrogen rate, or whatever other one of the four r's it is where we're researching. And so we try and place our research in places where the rest of those factors, should be equal, and we're still we still will find that kind of variability, within those sites. And and so a farmer has to look at their fields where they have variability, and that's just the nature of our farm fields. I mean, there's there's, topography.
Brad Carlson:There's low spots where water ponds, and and there's areas where there's been historic, management challenges and so forth. It's important to take a look at those areas for what they are. If you're going to variable rate nitrogen, then you need to start managing those kind of based on what the factors are on-site. Does it pond? Is it subject to lose nitrogen through denitrification early in the growing season?
Brad Carlson:Is there a history of compaction? Or in other words, are we likely to see root obstruction that's that's where the crop may not actually see the nitrogen that's available? Are there pockets of sandy soils? We have separate nitrogen recommendations, for sandy soils versus our our heavier textured soils. However, we know there's also places where there's, like, pockets of that kind of soil.
Brad Carlson:Is it worth managing those separately? Are you able to variable, apply based on those conditions? And some of it comes down to how big these areas are, and and what the potential impact is. You know? In a lot of cases, you know, I mentioned before, you know, we're looking at either improving yields or we're looking at reducing inputs.
Brad Carlson:And so if there's a chance to improve yields, there's typically a chance to increase your profit by a lot. However, if you're just looking at reducing inputs, in some cases, we're really not talking about, large dollar amounts.
Dan Kaiser:You look at some of these areas. I mean, while we know there's likely gonna be some changes out there, I mean, are they large enough really where it's gonna matter? And I think that's the big thing kind of as a starting point that you need to need to look at because, you know, I could say, you know, most of South Central Minnesota, if you've got lower areas of the field that the the general likelihood is you probably be areas that might need a little bit higher on the nitrogen side due to denitrification, yet we might get situations in a year where denitrification doesn't occur. And that's kinda one of the things about a lot of these loss pathways is that really the only one you are guaranteed some loss is probably through denitrification, but still, I mean, you'll get some years where that's pretty negligible that, you know, how do you manage for that? So, you know, with the ability we have right now, particularly for side dress application, I think there's a lot of flexibility out there to, you know, at least go with some more modest rates initially in that starting point and then make some adjustments when you start knowing what the, the the situations or what the environmental conditions are gonna be within a given year.
Dan Kaiser:I mean, I think to me, the more and more I think about variable rate nitrogen, I mean, to me, that's really where it makes some sense when we start looking at it is particularly these in season options to go back in and make some adjustments. I mean, as long as you have enough out there, we know that typically, you'll say you can get half to two thirds of what you think is your your total needs. If that's out there, I mean, that should take you quite a ways into the the season, at least up through about v 10 where he gives you some time to to put some nitrogen down and look at variable rate application. But, I mean, that's really the the big issue there is, you know, a lot of these things, since we know the lost pathways are water driven, that, you know, if we don't have the conditions, there may not be really any need to go back in and or look at, variable rate application. Because they again, as I said, if this was easy, we wouldn't be having this discussion right now.
Dan Kaiser:But the more and more when we start looking at it, you look at a lot of the tools. I mean, there's been a lot of things that kind of can come come and gone off the market in terms of helping to make these decisions, and there's not one clear one out there that I would say to most growers to utilize. I mean, there might be some that would be best in some certain circumstances, but, overall, we know that, you know, there are just a lot of question marks, I mean, in terms of being able to blanket use something over every single acre across the state of Minnesota?
Brad Carlson:When we talk about where where does something need more nitrogen, you know, in some cases, the needing more nitrogen is because of the loss of nitrogen or potential for loss of nitrogen. We stress this with all the nitrogen smart materials that rate is only one of the four r's. And so, you know, it's also worth noting if you've got wet spots that are won't prone to lose nitrogen, if you got sandy soils that are prone to lose nitrogen, variable rating to just apply higher rates in there may not necessarily be the ticket. We've talked or I've talked a a fair amount in the past about side dressing and whether it pays or not. The key I think, you know, the main thing is is a side dressing is rarely worse than single applying.
Brad Carlson:It may not be any better, but it does allow you to to hedge for those losses, just simply by avoiding having the nitrogen out there when the when that loss potential happens. So that's I guess that's another thing we're thinking about is, if you need a variable rate or if you're just simply going to have a site because of wet pockets or sandy pockets that's you're just simply better off, moving to a a sidedress situation. So, you know and and as I said before, you make your money with yield, and then you just save, smaller dollar amounts through your, reduced input costs. And so the main thing with that, I guess, is are you able to even ascertain what exactly your your yield potential was out there? The hope, of course, is that you're, you're peaking your yield no matter what you do, and, therefore, you don't need to worry about whether you left something on the table or not.
Brad Carlson:But that can also be difficult, when it comes to analyzing that. You know what? If you look at, any given field and try and analyze what exactly is going on, and I know there's a there's a, yield map that I use a lot in presentations that was shared to me with by, Gary Wagner, who is one of the pioneers of precision agriculture from up by Crookston. And and what's fascinating about the specific map that he he, he shared with me, and this was many years ago. I mean, this is, like, twenty years ago that I first got a copy of this map, and we see lower yields on one side, on the west side of the field is kinda diagonal.
Brad Carlson:And then there's a band of lower yields that runs through the middle of the field. There's a couple of strips of higher, yield in between those. And at the time, Gary was was mentioning the fact that the area on the the West Side was primarily because it was along, a low area and drainage, area, and it was flooding and perpetually wet. However, the area, that cut through the middle of the field was a hillside, and and he was suggesting that that, they were looking at because of reduced yields, they were simply gonna cut their inputs, that that this lower yielding crop just simply didn't need the inputs. They were losing money, in this part of the field, so the idea was to to lose less money.
Brad Carlson:And and when I visited with Gary about this, many years later, maybe a decade after that, We were talking about that field, and I told him how much I was using this, when I disc discussed precision agriculture and and, variable rate applying and so forth. And he said, you know, funny thing is is, we were reducing our inputs in that area for a while, but then we decided we'd try and increase our inputs. And what we discovered is we could actually really greatly increase our yields in that area. Turned out that those eroded soils just simply weren't supplying much to the crop, and it had a higher nitrogen response in that that hillside than the flat areas on the top and the bottom of the hill did. And so from the standpoint of any given farmer in any given field, the challenge becomes, are you dealing with a area with reduced yield that just simply has lower potential, or are you dealing with an area that requires greater management?
Brad Carlson:And in a lot of cases, you're probably not going to find that out, you know, unless you start experimenting and playing around with it. You can use the basic science of how nitrogen behaves in the environment and the things you know about the site to maybe give you some insight, but, ultimately, you probably gotta go out there and just start messing around with some things.
Dan Kaiser:And, Brad, this is an interesting example. I mean, I like this example because it does show, you know, some things there I think that people don't always think about. Because a lot of times, I think there's this, idea that the higher yielding areas, that's where we should pour the inputs to and that's where we wanna focus on things and kinda neglect these lower areas. But, you know, looking at the corn nitrogen rate database we have, I mean, it it seems like really the opposite is true and it's kinda like this field is and we know there's some variability out there. I mean, we know there's probably some areas that would benefit to higher nitrogen rates.
Dan Kaiser:And, you know, by that too, what I'm gonna say is that even with high these higher rates, it isn't because we're getting all this loss to the groundwater. It's because the soils just aren't supplying the same level as in some of those higher yielding areas. So they just need more, and the loss isn't necessarily anymore. I mean, it's probably the same as it would be with a lower rate on some of those higher yielding areas. And that, you know, just because we have higher yields, I mean, a lot of people think those those areas really we just said need to put a lot to it, and that's really not the case.
Dan Kaiser:One of the comments here, you know, how do you make variable rate work? I think reduced inputs, if we talk about p and k, it it's pretty clear. And that's really where we're looking at because you if you're getting the same yield and you just keep applying more and more and more, it doesn't really make any sense. But with nitrogen, I mean, there might be some circumstances. And again, a lot of that has to do with some of these underlying factors that go into the nitrogen cycle that there just maybe some areas of your field that just aren't gonna produce as much, but you're gonna wanna look at some other things though too.
Dan Kaiser:And that's, getting back to a comment Brad made is that rate isn't just one of the four r's. I mean, there might be some alternative management strategies where you still can get, you know, with the same rate, higher yields in some of these areas. If, say, they're sandy or there's some other issue that might be reducing availability. So, you know, we talk about, you know, variable rate from the standpoint of rate, which, I mean, it's it's right in the name, but there's also a few other things maybe to consider with some of these if you're seeing some of the site variability. I mean, really, it's just I could say is you can kinda talk to people like me or other extension people that have done a lot of research to our general opinions, but a lot of times it's kinda what Gary did.
Dan Kaiser:You try and figure it out for yourself in terms of what's going on, and you you might find something that surprises you. So, I mean, I just, you know, don't always get locked into a single thinking when it comes to these things, particularly when it comes to why your variability's out there? I mean, it it's not simple, and you really gotta dig through in terms of figuring out what's going on.
Brad Carlson:You know, ultimately, I think a lot of farmers are looking at what's even available for for variable rate technology. And, Dan, you mentioned, fairly accurately that a lot of the stuff that we've tested and and done research on the last decade or so has actually disappeared from the marketplace. To be frank about it, there's actually not that much available right now for variable rate technology that, you know, we do see there's still some things going on with grown imagery, and so forth. I I think, really, the the thing for farmers to recognize is just because something is for sale, you can't always assume that it says, you know, that it does what it says it will. I the analogy I like using for this is, you know, there's we tend to put this stuff in the in the realm of high technology that if you're you're going into the store and you're buying your cell phone and you don't understand how the cell phone works, but you pretty well expect it to work when you buy the thing.
Brad Carlson:You know, there's a lot of faith in technology, but I think in particularly farmers and those in agriculture can relate to this. Go into, the say some of the the chemical or petroleum product section at a farm store and look at these various types of cleaners and glues and and, or or watch an infomercial on television, and it says it'll it'll stick anything together or it'll clean any stain off of something. And you probably think in the back of your head, well, I might try that, but I'm not gonna be shocked if it doesn't work. And that's kinda maybe more the kinda attitude we need to take with some of this variable rate technology is because, there's some science behind how this stuff was developed. But because there's also all these factors that are beyond our control, it's hard to know for sure if it's going to work from any given year or given circumstance to another. Probably needs to be viewed with a with a a fair amount more skepticism than I think a lot of people assigned to it.
Dan Kaiser:Well, and the other thing too is there has to be some data behind it that shows that, you know, there's some sort of measurable yield increase given whatever number these things are spitting out. I mean, we've worked a lot with a lot of these active sensors, and I always kinda chuckle because it's kinda fun to think about. I got one of them where you you turn it around and there's, like, two screws loose inside of it rattling around, but it still spits out a number at me. And the question then is what does that number mean? Because these things are kind of in the nature of what we call black box technology that it gives you a number, it spits out a recommendation, but where does that recommendation come from?
Dan Kaiser:And that's the challenge with a lot of the technology is this technology can get developed and get marketed and get pushed out to for sale a lot quicker than we can test it because, yeah, I'd like to have a couple, you know, two, three years at least where we at least have some variation environmental conditions for testing before I'm willing to kinda give any sort of comment on some of this technology because it's a really short dataset. It's it's amazing what marketing can do with a lot of this because you look at biologicals. You look at a lot of fertilizer additives. I mean, all it takes is one farmer testimonial, and, you know, that's a lot of these companies are looking for for a lot of people to start buying into this stuff. And then all of a sudden, you see the interest start to wane.
Dan Kaiser:I mean, Brad, I can think of, you know, one good example is the, is the Y Drop system. It's amazing how many I talked to growers that, you know, got into this, but a lot of them now are scaled back or they're going earlier. I mean, they're doing things, you know, not that were necessarily recommended, but, you know, they're still trying to make some of this this equipment they have work. So that's, you know, the main thing is there just has to be some testing involved. And for me, that's kinda where my confidence starts to build on some of these things if there's some data there that says that the number coming out of these things means something.
Dan Kaiser:Because you look at a lot of these these sensors, they're just an index value. There's no units to it. It's just a number. It's just it's just a plain and simple number. And if you want a number, it's gonna give you a number.
Dan Kaiser:It just whether or not that number actually means anything, whether or not you need more nitrogen is is the bigger question. So we can't always keep up with everything. We try, but, you know, it's amazing how quick some of these things come in and out of the market and as much interest they get and a lot of people buy into them. And, you know, think of one right now that are proposing, producing nitrogen on your own farm. But if you look at the technology and what is actually being done, a lot of it doesn't necessarily make sense, although the, the marketing would would claim otherwise.
Dan Kaiser:If you're looking at technology, you know, do a little bit bigger dig before you invest a significant amount into it because, you know, in the end, you might get me stuck with something that's a pretty expensive, essentially paperweight or something that's taken up space in your shop that, you bought that said it was gonna do wonders for you, but that necessarily didn't work out.
Jack Wilcox:Dan Kaiser, Extension nutrient management specialist based out of Saint Paul, and Brad Carlson, Extension educator based out of Mankato. Thank you both for being here today.
Brad Carlson:Thank you.
Jack Wilcox:Do you have a question about something on your farm? Just send us an email here at nutmgmt@umn.edu.
Jack Wilcox:Thanks a lot for listening, and we look forward to seeing you next time.
Jack Wilcox:Advancing Nitrogen Smart is proud to be supported by the farm families of Minnesota and their corn checkoff investment through Minnesota Corn.
