Predicting nitrogen rates: Factors and resources for Minnesota farmers
Advancing Nitrogen Smart, from the University of Minnesota Nutrient Management Podcast:
"Predicting nitrogen rates: Factors and resources for Minnesota farmers"
December 2, 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 Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I’m Jack Wilcox, in communications here at Extension.
Brad Carlson, Extension educator joins today along with Dan Kaiser, Extension nutrient management specialist.
Last time we talked generally about the background and history of nitrogen rate recommendations in Minnesota. Today we’re going to go into more detail about predicting your nitrogen rate needs.
Dan, what are some factors to consider when trying to look at predicting your N rate?
Dan Kaiser:
You know, one of the things that always is looked at is yield. And you know, I'm getting more yield now, don't I need more N? And that makes sense intuitively, because we know there's a certain amount of, if you grind your grain up, you're gonna find so much nitrogen, phosphorus, potassium, as well as other nutrients. And we do have some of our recommendations, especially the phosphorus and potassium recommendations are tied to what we call expected yield. I mean, not yield goal because, you know, honestly, we know that corn response to any nutrient isn't infinite, so that goes for nitrogen that generally, there's going to be another limiting factor and that's, you know, a lot of times people will look to what we call Liebig's law, the minimum, is that the amount of yield produced is directly proportional to the most limiting factor. And a lot of people just will focus on nutrients, which we can focus on a number of other things - environmental factors, I think, are one of our real key limiting factors that tend to limit things more than anything else.
So when it comes down to it, if you look at the data, especially if you look at the last 20 years is that as these corn breeding programs have bred for higher yield, what that's done is bred for higher starch production. And when we look at nitrogen, nitrogen is a key component in amino acids. And amino acids go into protein. So one of the things that we've seen is an increase in starch and decrease in protein. So if you look at grain now, the nitrogen concentration is gonna be less per bushel than it would have been 20 years ago - or even more than that actually, just because of that change in protein concentration within the grain. So it's one of the things if we look at where we're at now at 200 to 250, 250+ these yields, is that we don't necessarily need any more than we would have, you know, 20 years ago just because of some of the dilution.
So when it comes to the general efficiency, that's, I think, one of the positives if you look at our modern breeding programs, if you bred for much greater efficiency of some nutrients, I would say phosphorus might be one that would see some creep, but nitrogen isn't necessarily the case. And that's one of the things that I think, you know, looking at some of the predecessors that have come before me on the Extension side, we've really pushed a lot into that optimal fertilization realm and that yield goal or that expected yield was in the back of everybody's mind. So it makes sense that the more we have now, the more we need, but it isn't necessarily the case.
Brad Carlson:
I'll have farmers say, well, look at the guys who won the yield contest, and look at what they did. Well, you know, because this is always a factor of this package. Well, you look at what they did, but in a lot of cases, they're intensively managing a lot of stuff. Diseases, insects, you know, there's not a weed. They probably got a soil profile that resembles what you might find on a fence line. There's all kinds of things. It's not just simply a matter of, like, oh, yeah. They put on 300 pounds of nitrogen, now they got 300 bushel of corn. It doesn't work that way. There's other stuff that goes into this. And so it's just not quite that simple.
One of the things that we've worked with extensively from the university side is nitrogen use efficiency. That's important to us as far as it gives us some kind of an indication of how much of the applied nitrogen is picked up by the plant versus how much is lost in the environment. The the the big problem with nitrogen use efficiency, though, from a practical standpoint is, when we measure everything, when we measure what's picked up by the grain, what we think is lost, take water samples from the tile, even measure air to see how much might be denitrified, we don't come up with it all. And so, you know, we know that nitrogen use efficiency goes down with the more nitrogen we apply even though it may be necessary nitrogen for the crop. There's also some kind of cycling that's going on within the soil that's been elusive to us as far as getting a handle on it.
So nitrogen use efficiency, it does decrease as you apply the amount of nitrogen, but it's probably not a good number to be looking at when it comes to making decisions for just for the average farmer.
Dan Kaiser:
And NUE, nitrogen use efficiency, Brad, you hit it right on the head. If you look at all of our data, the most efficient use of nitrogen is that first pound you apply. Now, there are some circumstances where I've seen where we tend to see a slight increase in NUE up till the optimal nitrogen rate then at that point, it tends to obviously drop because you're at the situation where every pound you apply then is an increase in yield. So, that's a pretty rare case, looking at how we increase nitrogen use efficiency, it's really trying to maximize our bushels, obviously with a minimal amount of N applied, and that's one of the things with it.
In order to do that, you know, predicting the optimum nitrogen rate, I mean, again, a lot of people think that if you look at the database that the higher yielding sites are gonna be the ones that take the most nitrogen. If you look at our corn / corn and our corn / soybean data that, you know, while there is some general trend, I mean, that trend isn't strong enough to say that that the more you raise, the more you need. And if you look at the data, actually, it's interesting is that we've got situations let's just look in the, the corn soybean data where our economic optimum nitrogen rate, if you look at just say, 250 bushel yield level that we have situations where we've done that with 30 pounds, we've got situations where it's taken close to 320 pounds, so that's a pretty wide range in data. It's a site specific issue and it's an issue with a lot of these other factors when it comes to availability.
And, we've looked at trying to separate the database out, and it really hasn't been all that simple to try to look at being more fine tuned in terms of our rate recommendations based on where you're at. And it's one of the things we'll continue to work towards, but you need a lot of metadata. You need a lot of data behind it. And and when it comes to like environmental issues, if you're trying to factor those in, you need site specific information. So that's one of the things that we talk a lot about data and data collection, you need a lot in terms of doing this. And we've talked about this in the past, about maybe AI will help us try to sort out some of these issues when it comes to some of the variability in our optimal nitrogen rates, that's all dependent on whether or not you've got good data and you've got the data you need to be able to feed into that system to essentially predict a rate. It's it's it's just a lot of information and we're kind of at that point now that that might be possible to look into it, but, it'd be nice if we could look at some historical numbers. It's just a question if we've got enough information out there to be able to utilize some of that information.
Brad Carlson:
Well, one of the one of the big problems, Dan, we've talked about this a lot, is that your best soils produce your best yields. In a lot of cases, your best soils don't need as much nitrogen. And so, you know, we do a lot of, when we've done, for instance, variable rate trials, you know, I remember one trial we did, corn on corn. We had, like, 280 bushel corn with a 120 pounds of nitrogen, you know? So a lot of farmers would say, well, you can't grow that. You know, you can't grow that much corn on a corn on corn situation with that little bit of nitrogen. The great soil is a great growing season.
So we know that obviously there's there's a lot of factors out there that are very difficult to measure that go into determining the rate, and it just wasn't simply a matter of, you know, you needed to pour the nitrogen on to get that kind of a yield out there. But, you know, another factor, I guess, is worth kinda keeping an eye on, you know, we've talked about you you just mentioned the fact that the nitrogen concentration in the grain has been going down over the years. That that's not going to go down to 0.
You know, at some point, that's probably going to level off if it hasn't already, and it's it's probable that there might be some some creep then as far as the needed amount of nitrogen. But I think it's important for farmers to realize, you know, this isn't a situation where, well, we looked at nitrogen rates and now we walked away from it and and maybe in 5, 6, 10 years, we're gonna come back and look at them again. This is evaluated on an annual basis, and I know you put numbers into that database, fairly regularly, maybe not necessarily annually, but at least every year or 2, that thing gets updated. And so if these numbers start creeping upward, we're gonna find that.
Dan Kaiser:
You know, a lot of that creep really is, I think, associated with environmental conditions. If you look at the numbers because about every time I update it, I mean, we tend to see it go up the rate recommendations by a few pounds, maybe about 5 pounds. So it isn't a huge leap. It's been more of a steady increase for continuous corn than it has been for corn soybean. We started to get more information or more when Fabian Fernandez started here at the University, we just had more people collecting nitrogen rate response data. So the more data we're putting in, you know, we saw a jump and then it's it's it's been more flat lined.
And that's one of the things that we've seen over time is that more of a change from corn corn. If you looked at some of our earlier recommendations when that MRTN approach came out and recommendations for continuous corn were around a 155 pounds, which isn't a lot and it's not what I would suggest now based on our data and just what it's here. But, one thing I have done and to try to be more specific, the thing only real information I've got in the database, a lot of people think this database is wondrous and has all this information in it and it really doesn't have much that what we use for that MRTN database.
It has a set of coefficients for the the response curve and then we have a very limited amount of previous crop data and some data based on soil parent material. And I was interested in the parent material thing because if you look at historically, our loess soils which would be the silt loam soils, all those soils in the southeast around Rochester in that area, that we have seen those soils, if they have adequate moisture, they tend to have a very high mineralization capacity relative to some of the other, the poorly drained soils just because adequate moisture, good drainage, good oxygenation leads to a lot of microbial activity.
In many cases, we'd recommend less nitrogen for some of our other crops as kind of a what would almost be like a pseudo credit for those soils. So, you know, I looked at that in in some of our database since I could query it out and, you know, while there is a little bit of a difference, if you look at the corn soybean data, 138 versus 151 and this was based on one of our last updates in 2021. So it could be different now. That there might be something there, because we have seen particularly around the Waseca area, you get towards Mankato and some of those those heavier soils, a little bit higher nitrogen requirement in some of those soils. If you look at continuous corn, though, absolutely no difference. So, I mean, looking at it, that's one of the things that I've tried to do to see, oh, can we factor things in to be more precise in different areas of the state and split the state out like some of the other states that are at the MRTN approach and make different recommendations. And we just aren't there, because, you know, I've we kinda hate to say it, but it's a lack of data, and it's one of the things that I really the more sites we have, the better, when it comes to database with with any database approach.
Brad Carlson:
Well, part of the challenge beyond that, Dan, is is separating out what of that is relative to the soil itself and what's climate. Because when we get into, you know, well, like you said, the the need for higher nitrogen rates when you get towards Mankato, which is literally where I have my office, in a lot of cases, that's probably because we're seeing higher rates of denitrification because of those heavier soils. And then that rate of denitrification is gonna be just dependent on how much it rains. You know? And so it's it's a combination of the soil and the climate, but it's not necessarily the soil. It's both. And so that gets very difficult then to make a an adjustment based on on that because, again, now all of a sudden you're also trying to predict what the weather is gonna be like.
Dan Kaiser:
And that's one of the the challenges. I mean, we all know, especially, you know, if you're talking with amongst a bunch of farmers is that when it comes to nitrogen rate, it's just it's difficult. It's difficult to come up with an exact rate. We think some people think that we can come up with this exactly precise rate of what we need within a given field within a given year and there's just too many question marks with that.
The other thing I've been looking at within the database is just some other factors we can look at for adjusting rates, since we know site to site variability and economic optimum nitrogen rate is difficult to predict because of some of these loss pathways that are out there that how do we look at a site that might need more or less nitrogen? I mean, one of the things I've been playing around with the database is looking at the minimum yield since we have yield without nitrogen in all of our studies to see how that relates to our optimal nitrogen rate. And many people think that the maximum does, and it's actually more of the minimum and more of the minimum relative to the maximum, so if you look at the percent difference produced by the rate without nitrogen versus the maximum yield potential that given site, that tends to relate very well to the optimal nitrogen rate, especially within the Minnesota database.
If you if you look at it, situations where we produce more nitrogen with it or more corn without nitrogen are gonna be those situations where we need less nitrogen as a whole. And looking at that, that factors a lot of what's going on with a lot of these soil processes and feeding the feeding the plant through means that isn't commercial fertilizer. So it's one of the things that if I could get growers to put out just some small areas within fields that have no nitrogen, which, you know, the issue is with MAP and DAP, there's gonna be in AMS, there's gonna be really no situations where there's gonna be no nitrogen, so really need to look at this data with about 40, 50 pounds to see if the relationship still holds, but it'd be nice to see the consistency in that 0 N yield.
I really wanna know is that consistent enough in those areas that we could use it as a tool to help us look at where we're at and I could come up with a rate recommendation for situations that would be higher versus lower yield potential and be more prescriptive with our rate recommendation. There's still a little noise in that data but if you look at the overall correlation, it's much better And the interesting thing is you need you can overlay the corn corn and their corn soybean situations over top each other. The corn corn tend to be situations where you need more optimal N. It's just simply because it's producing less without without any nitrogen within it.
So, this might be something that we'll be looking at but the question again is that consistency and that's one of the things I don't know, because, I mean, really, it it takes some time to maybe assess what you can produce And then long term then, is there gonna be issues if any of those areas that if we cut the rate back, will there be any issues with the sites being coming more responsive and we just there's a lot of questions behind some of that with that. So there's some things to look at here, but it's I think looking at it's the best option just based on mining data out of the database that we have.
Brad Carlson:
Well, I I found it intriguing, Dan. I know Jeff Vetsch has been doing a lot of rate research in southeast Minnesota over the last several years, because of some of the the nitrate issues going on there. And and, he he had a chart, this last year looking at his his MRTN in the individual fields on where they did these rate studies and and very reliably, the the sites that needed a significantly higher nitrogen rate than than what was recommended also had a very significantly lower yield at 0 nitrogen rate. And so, it it could be a situation also where if we can reliably predict that the the field, the soils have less ability to supply nitrogen to the crop, now we know the circumstances where we need higher rates and and maybe we can just simply dial it back in most cases to recommended rates and then be able to predict the sites that actually need more instead of some of the guys who were just a little conservative and simply wanna put that amount on everywhere, just to make sure, if we can start teasing those things out. But but like you said, I think one of the things that we don't know, because we haven't been looking at this long enough, is is a is a field that has a lower yield at a 0 N rate. Is that also a a, a consistent, pattern? Did we see that year in year out, or was that just reflective of what happened climatically in that field that year? And so, you know, if we can see that predictable from one year to the next in the same fields, now all of a sudden we can start adjusting in rates. If it was climate based, now we're back to the problem of whether we're adjusting to the weather.
Dan Kaiser:
And one of the things that's brought up a lot, particularly with suboptimal rates, is this concept of mining organic matter. So that's one of the things that, you know, I guess I don't necessarily believe that that actually happens because, essentially, the corn yield is gonna adjust based on what it has available to it. So when it comes to organic matter and that, I think it's gonna stabilize at a certain point. And that's one of the things that we have in place now is a set of studies that are long term studies that where we have different rates of nitrogen, they're applied to the same plots, we're gonna be looking at this over, I think at least 10 years to see if this concept of mining organic matter actually exists. I think there's some other things that are going on, a few things I'm working on, that, might be coming into play.
But I mean, if you look at some of this data just going back to this concept of minimum yield produced, so if you look at an economic optimum nitrogen rate within the data beta, so this is all sites, if you get less than 50% yield with your check of the maximum total, I mean, EONR is around 200 pounds of N. If it's greater than 50%, the EONR drops to 140 pounds.
And I think we could what we could do with this is if you could get a good read on your soils, I could probably give you ranges within 10 pounds or 10% actually and give different rate recommendations and just see how that that generally adjusts. Because I think this is looking at, at least for us, looks good, I mean, I've looked at some data in some of the other databases, it doesn't, I was wondering if it would hold true across different states. Necessarily will hold true but at least within the Minnesota database, this might be a way to adjust some of our data to kind of get a more accurate rate across, as Brad, you're saying, across some of these fields.
Brad Carlson:
Yeah. It's an interesting concept Dan. We were talking about the the mining of organic matter. I know for years on the drainage plots at Waseca, they had a set of plots that were kept black. They had no crop grown on them. Therefore, the use of nitrogen by growing plant was essentially 0. And when you measured the amount of nitrogen that was picked up by the tile lines and the amount that was in the soil, it was a very small amount. I mean, we're talking 15, 20 pounds, something of that sort. However, if you in that same study area where you grew corn with 0 nitrogen, they were yielding 80 to a 100 bushel of corn. Well, that's you can't grow that on 20 pounds of nitrogen.
So clearly, there's some kind of a switch going on in the soil that's driving that mineralization because when the demand for nitrogen was there by that growing crop, it was mineralizing. When there was no plant growing there, it got to a certain point. It kinda quit happening. It's really it's really a strange phenomena. We haven't really been able to to to get our our hands on as far as figuring out what's actually going on.
Dan Kaiser:
And it's one of the things too with our database. I mean, I mentioned this before is about every time we add data and it does tend to increase and that's one of the things I know that if, you know, just some of the environmental groups I've talked to, I know they tend to really have some issues with when it comes to some of the water quality problems we have. But, you know, a lot of the issues I think with our increases in rates really come from a lot of our denitrification loss. And wetter soils now with some of the patterns that we're seeing, particularly if we're getting more rainfall in June, we've had, I think, a I don't know, Brad. I mean, we've we've had a few years of where we considered to have some substantial denitrification loss just based on patterns that are out there.
Brad Carlson: Right. Right. And and, you know, that that's I guess the thing we have to keep in mind with the denitrification loss is that risk is particularly high, when the soils get warm. So we know that there is some denitrification loss that will happen early in the year, but it really kicks itself in when we when we get into June when the soil temperature start warming up to to roughly, you know, 70 to 80 degrees and so forth.
And, you know, again, I mean, we said this, I don't know how many times. Can't really predict the weather that reliably, especially when you're making a rate determination in April, you know, what the weather's gonna be like in June. So in a lot of cases, I guess we're probably going to be looking at if that starts becoming a more regular situation that happens reliably, we're probably wanting to adjust to more split application or or systems of application that allow us to adjust or or compensate for those weather conditions in the growing season. However, overall, right now, we haven't seen those conditions set up routinely enough that we're kinda ready to make that jump to actually recommending that as a as a normal practice.
Dan Kaiser:
And I mean, I guess there is this notion that as we increase rates that we're getting more in loss to surface water. I mean, I I don't know if we necessarily can prove that because the optimal rate is the optimal rate, whatever it is, and we know that, you know, until you get beyond the optimal rate within a given field that we tend to see bigger issues at that point versus getting up to the the optimal rate. And that's one of the other things that we'll see some groups talk about. Well, you know, we should just be applying suboptimal rates, but looking at the gains that we're gonna have in potential for reducing loss, it's it's really not that high. I mean, we really can't gain that much by grossly under applying nitrogen because as you said, Brad, there's always gonna be something coming particularly in an annual cropping system. We're always gonna get some loss.
Brad Carlson:
Yeah, the data from Waseca on the drainage plots really doesn't show that much of a improvement in the amount of nitrogen loss nitrate loss through the tile lines when we're under fertilizing the crop. You're gonna lose some because of the nature of the soils, and and, really, it's it's fairly consistent at suboptimal rates compared to optimal rates. And so, really, the the key is to just simply get to the optimal rate, not go above that. That's where we start running into problems. Applying suboptimal rates of nitrogen, just isn't that's just not gonna solve our problem.
Dan Kaiser:
And technically, since we are dealing with an economic model, we could potentially factor in, especially if you had some fixed cost associated with mitigating some of the nitrate coming through the tile lines and factoring that in with a nitrogen rate with it. I mean, it becomes more complicated for the MRTN approach or the MRTN system is you'd be adding another factor in, but if you could put some monetary value to having to reduce that if you had to implement some practice, that could be factored into it.
So it's one of the things about the MRTN, which is nice, is that we have some flexibility should we have to do this. I mean, I think the main thing for a lot of growers is just this general question is, you know, how do you make your plan? Do you plan for the best or the worst when it comes down to it and there seems to be some reaction to the previous year's weather when it comes to making the next year's decisions. I don't think I'd go that extreme, but I think you need to start looking at, say, the the last 5 to 10 years and just, you know, look at how we see changes in some of our climatic patterns come into play in terms of just making decision if whether or not you're doing the right thing on that or you need to make some changes. Because just looking at keeping your practices all the same and not factoring all these things in, I mean, it's it's gonna cost you money in the end.
I mean, I look at situations right now like fall urea. I mean, with this is more of an issue on the retail side of retailers not carrying fall anhydrous and claiming fall urea is just as good. I mean, there's a lot of growers out there, I think, that are spending a lot of extra money going back in the next year and having to reapply nitrogen with a practice that really shouldn't be done be done in a lot of the areas, particularly south central Minnesota.
Brad Carlson:
Well, and I it gets back to one of the things that we talked about in the past, that being that your rate of application is just one of the 4Rs, Dan. That that if you're if you've got better if there's better practices as far as when you make the application and then your choice of fertilizer type, at that time, that would have been better off just simply adjusting for the, I guess, mistake, if you will, of of making bad choices in that way by adding more rate just compounds the problem. And, you know, I guess one of the things I think everybody's aware of that some of the driving the driving purpose of a lot of this this nitrogen smart work we're doing is to try and deal with some of these environmental issues. And and, you know, ultimately, we're trying to find things that are gonna work for farmers, to maintain profitability so we don't have a bunch of regulations come in place.
But, you know, you know, getting back to what you said, if if you're always planning for the worst, the worst doesn't happen the majority of the time. And so, if that's your scheme, then most years, you're gonna end up applying extra nitrogen. It's probably gonna get lost to the environment. You know, it's probably way better off to plan for the best conditions, the minimum amount you need, and make adjustments because the reasons to make adjustments are knowable reasons in most cases.
Dan Kaiser:
One of the factors I look at, when it comes to recommending split application is just really that overall benefit that you have at least with a split application of accounting for some of the things that you're seeing already. Because, again, if you're applying all your nitrogen in the fall, we don't know what's gonna happen that next year in May, June, July, you may be back in. So then it becomes more of the question, if I have that ability to split, do I just put less on in the fall then make my final adjustment as I know what factors are gonna be in the spring.
So that's kinda one of the things that, you know, more often than not the last few years when it comes if you look at, just say the we'll just look at from about, 2010 on, I mean there's been some situations where we've had seen consistently many fields growers having to reapply nitrogen just because of loss potential. So it factors more into more of a risk mitigation strategy and trying to figure out what gives you the least potential risk for losing nitrogen and looking at what options you have.
If you look at just some of the yearly variation, I mean, again, we know there's yearly variation in the trends. If we look at our MRTN database, the continuous corn has been the one with the more upward tick. Though, if you look at, just say, from about 2019 to 2023 or so, that we've actually see the rate was increasing and all of a sudden a decrease and those, we start hitting dry years and it starts to go down just slightly if you look at some of the trial averages. So we can look at trends, but again, since we're making decisions before we know what's gonna happen, that's where it becomes problematic so really the key is to try to apply something reasonable as a starting point and then, you know, if you have to make adjustments, make adjustments But once it's applied, you can't take it back so if you're already over applying, I mean, there's and you're losing a potential amount of it, it doesn't make a whole lot of sense if you're gonna go back and adjust adjust anyway at some point in season.
Brad Carlson:
Right, we know that the corn really doesn't take up a lot of nitrogen until starting roughly about the 1st week in June. Things really start taking off. If we're looking at the fact that we're planting in mid mid April, late April, early May, you know, you still got 5 or 6 weeks and on average, it's very wet that time of year. If it's too wet, you know, we could've got ourselves in trouble and just simply avoiding application to sidedress time which is again is about the 1st week of June when the soils start getting warmer, the crop starts taking off, you can actually mitigate some of that stuff. And and so it's it's something I guess that I think is worth talking about and a lot of farmers are thinking about it. We know that the the, amount of sidedress out there has has got has really increased over the last few years too.
Dan Kaiser:
Yeah. That's one of the challenges. We know it's an issue. I mean, we've had years where people have gotten caught where they can't go in and make those sidedress applications but I mean, if you've got say 75% of your expected N on, I mean, the overall risk and the time window you're gonna have is much greater. I mean, really the key is what we've seen with a lot of the data is we wanna have maximum available N between about V6 and VT.
We know that about 20% of the N is gonna be taken up, let's just say, post R3 or silking. So, if you look at the window, I mean, it's really more important that if you match your I mean, it's really easy to visually see it, so those times where we see rapid growth of the corn when we see the rapid uptake occurring. So we know that when you look at matching it, that's kinda what's critical, so that's gotta be factored in with some with some of these decisions.
Now, when it comes to changing rates, we do know that it's conceivable that the optimal rate will change from one year to the next. I mean, it doesn't mean it's always gonna increase for a particular field. I mean, it's one of the things that we've been looking at tools to try to help us adjust. We know there's some of the tools like the pre-sidedress nitrate test that work and that can work in some cases. The pre-plant nitrate test has been around for a lot longer. That's 2 foot test, but that really only works in situations where you'd expect residual nitrate.
We've got a whole the recommendations, if you wanna look at a whole decision tree in terms of making decisions. If you're growing corn following soybeans, that's generally not gonna be a situation where you're probably gonna be finding the pre plant nitrate test to be relatively effective. But I've seen situations where it's flagged some fields where we need little to no N and I've had trials on those fields that really told us that we needed no nitrogen in those fields. So, you know, looking at those tools, I mean, there's nothing out there that I'd say is perfect, but there are some circumstances where some things could be used.
Brad Carlson:
Yeah. I know one of the tools that was kinda pushed a few years ago was that basal stalk nitrate test. NRCS was really high on that, and, I guess the problem with that was is it wasn't really calibrated. I mean, you couldn't look at that number and say this was the exact amount of nitrogen I needed. But it was beneficial in terms of, if you thought that you were lacking nitrogen, you didn't put enough on, it would tell you that. And if if you put on more than enough, it probably would tell you that too. It's qualitative in nature. But there are some tools out there that can be used to, to help at least, help you build confidence in what you're doing to manage.
Dan Kaiser:
Well, the basal stalk test, I think, is a good test, but it's a post mortem test. So, essentially, you need enough years of data to give you an idea of whether or not what you're doing is over applying. I mean, if you're constantly coming back where it's it's showing excessive, that means you probably could dial your rate back a little bit. It doesn't really tell you how much, I mean, it's more of a just a tipping point at that point where it's it's plus or minus and a lot of the times you can look at your field and if you look at the leaves that are fired, if you look at from below the ground, I mean, it kinda correlates to what the basal stalk test is gonna come by. And that's one of the things that a lot of growers I mean, you like a dark green plant to towards at the end of the season, but we don't necessarily need that. We know it's okay for the plant to start cannibalizing itself. I mean, severe cannibalization becomes a problem, but we know that, it's kinda like sugarbeets, that some the plant can run out towards the end of the season, the corn plant can, and you still be at maximum yield.
Brad Carlson:
So let's talk a little bit about varying nitrogen rate. I know a lot of farmers that have attended the Nitrogen Smart program in the over the last decade or so have reported that they've kinda gone to a more pragmatic system where they don't have a set nitrogen rate. They actually are using different rates on different fields. So you mentioned, Dan, that the the carryover nitrate due to drought is one of those things that we don't normally think about carryover nitrogen, but, it can be a factor. I know we had several dry years in a row, where we were talking about that a lot.
And then, of course, one of those years that came back and bit us, it got extraordinarily wet in the spring, and we're not necessarily sure whether that carryover nitrate was still there when the crop was there. But that's at least something that can be used to change the rate, in some circumstances.
You know, some of the other stuff, though, has been a little bit more elusive as far as as, developing nitrogen credits. Particularly, we get a lot of questions about cover crops. I mean, what what are your thoughts about crediting a cover crop that was growing out there that it was grown potentially to pick up residual nitrogen in the fall and in the spring? Now we plow it under or dig it, hit it with a field cultivator and we plant. What kind can we get a nitrogen credit out of that?
Dan Kaiser:
I think rye, which is the most important or the most popular cover crop that's out there, we just don't seem to see the credit for it. And I think looking at it, I think a lot of it just because of the although that's green when a lot of times it's plowed under it, that should have a very low C to N ratio where it should mineralize N, and it doesn't necessarily show it coming back. So that's one of the things that I think is a question mark. I mean, maybe it will after a number of years. We've been looking at a lot of these system changes. They aren't immediate. I mean, it isn't, you know, a lot of people think that these things are gonna be like fertilizer than for the crop and it's just not the case based on a lot of the research I have.
Now, there might be some other research out there, but but really that's kind of the main thing is, you know, I think, you know, looking at it, manure is a big one, if you're looking at cycling, there's more going on there that we think. I mean, just an example is Waseca, we've had some studies there and then some of the areas that have been in plots for a number of years, the areas that we tend to see a higher nitrogen requirement, I think a lot of that's because of drainage and denitrification. Those areas are just a little bit more saturated. They denitrify more, but they've had some other fields around that aren't in plots like the other and they've had manure history around there. We we need less N. We need closer to maybe a 150 versus 180 in some of those those areas and, you know, so we know there's some some things out there that we probably could predict.
I think denitrification is the big one, although we can't really necessarily predict it. If you've got an area that's gonna be prone to a lot of saturation, it's probably gonna be area that's gonna need more nitrogen compared to, you know, an area that's that's better drained. And low yield potential soils or think of the other ones, there's always been a lot of interest on the research side from some of these, funding entities about specific recommendations for low yielding soils, you know, I other than the fact that I think if you look at what we talked about before the ability of the soil to produce a crop without nitrogen, I think there may be some call in those areas for a little bit higher rate just because they just don't have the capacity. You know, the question in anything you gotta temper yourself on is the fact that we just, with some of those soils, if they have moisture issues, that might cap things off as well, so it's not just as simple as we can expect, only one factor be of impacting yield.
Brad Carlson:
And I remember we had a farmer at one of the Nitrogen Smart meetings a number of years back that was farming some some sandy soils, some central Minnesota soils, and, you know, he was trying to get some better idea of what he needed for nitrogen rates on these soils. But, Dan, if I remember right, the yields this guy was talking about, I don't even know how he was paying for the seed. You know? And so it it it gets into this whole quandary of if they really are low producing soils, you know, maybe there needs to be some some really reflection on whether these areas are actually worth your time to farm. If there are pockets within fields, you know, yeah, maybe we can, do some things to adjust in those areas. But, you know, like I said in the past, you can't just fertilize your way out of poor soils. It's just there's not a lot you're gonna do about it in some cases.
Dan Kaiser:
Yeah. I think that grower is actually a non irrigated sands. So and I'm wondering if the co-op essentially was just using that recommendation so that they he didn't over apply nitrogen because he the chances are that to have him getting a crop for that crop not burning up were, you know, was was pretty low. So that's where it is. And, you know, we do see things like cation exchange capacity floated out there in terms of adjusting nitrogen rates. You know, the sandy soils would be one circumstance where we have a soil with low CEC.
I mean, you look at a lot of our sands or CECs around 5 centimoles per 100 gram versus a lot of our high clay soils, which will be in those mid twenties than that. So that will affect the ability of the soil to hold ammonium NH4. Nitrate, it doesn't really matter, although the sandier soils are gonna have better drainage, the nitrate's gonna move a lot quicker, so I think the, it's what's with an inch of drainage, is it about 6 inches in the sand versus 12 inches of the sand versus 6 in a, what we call heavier soil, so. It does impact a few things like that but it really shouldn't be anything you're basing your rate recommendation as much on. Although, you know, we do recommend more nitrogen typically for irrigated sand versus a heavier soil. But it should factor some of these other practices in such as timing and split applications when you're you're making your decision.
Brad Carlson:
Oh, cation exchange capacity has gotten thrown around in the nitrogen world so extensively in the last decade. It's you know, some of us get really frustrated with it because, in a lot of cases, it's it's a fairly complex concept that has to do with the amount of exchange sites on the clay particles, and that's going to be a factor of what the clay mineralogy is and how weathered they are, and so forth. And in general, in Minnesota, we just simply don't see a lot of differences, in our clay types here when it comes to, what it does for nitrogen management. If you're in the southern part of the United States where they have highly weathered soils, they may have heavy textured soils. That kaolinite clay that we don't have here will not hold much of anything nutrient wise and they do do base their management recommendations, on cation exchange capacity in those parts of the world.
In Minnesota, if your cation exchange capacity is high, you're dealing with a heavier heavier soil that's got more clay in it. If it's low, you're dealing with sandy soil. We do have, recommendation differences between those. You know, beyond that, I think, CEC has been grossly misused, in a lot of cases, you know, particularly in some parts of the state where we have not advised fall application. There's been the suggestion made that, well, based on your CEC, you can put a certain amount on in the fall. You know, we've kind of done away with that now with the fall application restrictions in a lot of the southeastern Minnesota. So we're not dealing with that anymore. But but, a lot of this has gotten pushed by industry. And unfortunately, I think in a lot of cases, it's just being done to confuse the growers.
Dan Kaiser:
Yeah. And one of the what I call the magical rule is that, you can take your CEC times 10 to figure out how much nitrogen your soil will hold and if you look at actually that recommendation first kinda started floating around in Illinois. And it was actually based on the amount of N as anhydrous. So, nothing about urea, just talked about N as anhydrous. And none of us on the research side really know where it came from. I mean, likely, probably somebody went and found a journal publication that looked at applying anhydrous to soils and they extracted those soils for ammonium and they just then kind of based by a factor maybe that was in that publication. But that doesn't necessarily mean that you should be utilizing that for your recommendations. Because we know that, you know, specifically sands, that we do know that we wanna break our rates out more, but if you look at actually what that soil will hold is more than 10 times CEC if you actually factor it in. I think AgVice, actually penciled, somebody at AgVice actually penciled that out. It was in a, news release they had and talked a little bit about that.
So when it comes down to it, we just don't use that 10x CEC for planning our rates, but if you look at CEC again, the soils with the lower CECs or silt loam soils in the southeast or sandier soils are ones that are likely gonna be more beneficial for a split application, but the rate wise for those splits, I just wouldn't be basing it on any particular factors.
So really, CEC itself is a general proxy for texture, so again, split applications are gonna be favored on low CEC soils. I mean, technically, a soil can hold about 290 pounds of nitrogen per 1 milli equivalent. But that's assuming essentially that a 100% of that ammonium or that would be absorbed on the cation exchange capacity, which doesn't happen, and then if you look at fertilizers like urea, you're gonna see a much greater conversion of the ammonium to nitrate immediately after application.
That's one of the reasons why this doesn't work is that our soils, when things really start cranking and we start, the ability for the soils to convert with the microbes, they're converting ammonium to nitrate. It happens at such a rapid pace where it really doesn't matter what your soil will hold because it's gonna be converted to nitrate so quickly that will not be held by the CEC. So, you know, looking at the CEC, it's not like an empty cupboard that essentially is looking to be filled. There's already other things there and there's a lot of interactions that occur. So it's just really difficult when it comes down to it to use just a general factor like CEC to base your decision on that. I just wouldn't do it. I would look at your soil types, when you wanna look at application timing more than anything else versus trying to look at what maximum rate you can apply.
Brad Carlson:
Yeah. I guess just to wrap this up, the nitrogen cycle happens. Your nitrogen is going to convert itself to nitrate naturally in the soil. Nitrate is not a cation and therefore when your nitrogen is nitrate, the cation exchange capacity has zero factor as far as what's happening with the nitrogen in the soil. So, it's just simply not a factor that's worth spending a lot of time obsessing about.
Dan Kaiser:
And one of the things too that a lot of people I mean, I hear we hear this all the time with some of the comments when we start making some general recommendation based on something, somebody will start complaining that we're just behind the times and, you know this, you know, this new fit and these these newer more advanced recommendation systems. And you break things down like CEC or, the other one's always cation balancing. I mean, a lot of that stuff, that work was done back in the fifties. I mean, it's old stuff that people are just re-bringing out. And I'm sure us talking about CEC like this and we were gonna get some people that are probably gonna comment to the contrary for this, particular podcast. But I mean, if you look at it and if you look at all the just people like me, all the scientists within the region have looked at this stuff, nobody has come up with these things that have been this silver bullet that's been able to more accurately help us manage nitrogen. So it's it's one of those things that you have to look at where this information comes from and if nobody can come up with a credible source citing a publication or some research that's done, I just kinda would stay away from it because a lot of times anymore is with the ability for people to put information out of the internet. I mean, nobody really fact-checks a lot of the things that are out there.
So in the end, it could cost you a lot more when it comes down to it with some of the things you have to do with some of these these systems for a lot of these what what are claimed as these, more advanced recommendation philosophies versus some of just the standard recommendations. And, you know, without information behind it, it just they struggle to see what the benefit is. If you can't come up with the actual piece of research that actually recommends or or shows the data behind this, why why these these recommendations are in place?
Brad Carlson:
Yeah. It kinda goes back to a conversation you and I were having before we started recording the podcast that this the the technology to be able to just put stuff out there, it's, you know, not only not only to post stuff on a blog on the internet or just simply say I think this in a chat. But, people can literally write whole books and get them published. There's no longer a publisher running quality control that says, you know, I'm not so sure about this. I mean, you could just write it up and send it somewhere and get it printed off. And and there's a lot of those books floating around out there now. It's actually kind of amazing that, some of these people don't get sued because somebody bought in whole hog and then lost a lot of money on it. But I guess that's not that's not the topic of our podcast today, so maybe it's a good time to end it.
Dan Kaiser:
Yeah. That's one of the things too. I know recently there was some comments that Dave Franzen had who was he's who was NDSU. He retired in 2024 in the summer, and he was, one of the comments there. One of the things I think I think he's going through some top ten things that he had, you know, comments he'd come across during his whole career at NDSU and one of us talking to my predecessor, George Rehm, about when Dave first started that George was pretty, just open about especially a lot of these specialty products that these fertilizer amendments and openly against them and Dave was wondering how you could make the, the argument against some of these things.
I think George’s comment was “Because I've got the data.” Now I think that's really key is you you show me the data, show me where you're coming up with this information because I'm open as, you know, just as a researcher to look at some of this stuff as long as there's some sort of data behind it, but a lot of times things get stretched so far that it becomes kind of an issue where, you know, you you tend to take something that you might just have a shred of some evidence and then stretch it a little bit too far.
Jack Wilcox:
Brad Carlson and Dan Kaiser, thank you for this information.
Brad / Dan:
Thanks
Jack Wilcox:
Seeing something on your farm that you have a question about? Send us an email here at 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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