An introduction to MRTN: Efficiencies & economics in mind
Hello and welcome back to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I'm Jack Wilcox in communications here with Extension.
Jack Wilcox:Today, we're talking about the MRTN or the maximum return to nitrogen method to figure out your optimal n rate. I'm here with Brad Carlson, Extension educator, and Daniel Kaiser, Extension nutrient management specialist.
Jack Wilcox:Brad and Dan, start us off by just telling us what the MRTN is and how is it calculated?
Daniel Kaiser:So I'll just go back a little bit of history here. The maximum return to nitrogen approach has been in place, I think, since around 02/2005, and it was put together by a number of researchers from the Northern Corn Belt getting together, at our annual meeting, when they were discussing some options and some questions that growers had when we started to see fluctuations in nitrogen price. And, I mean, I can remember, I think, it was the late nineties, early two thousand when anhydrous got extremely high that, you know, people were questioning then about adjusting their nitrogen rate based on the price of up and to the value of corn. So that's really what the maximum return to nitrogen approach is is looking at is essentially trying to target the nitrogen or have a target nitrogen application rate where you factor in the ratio of the price per pound of end of the price per bushel corn, which, you know, tends to be about point one. You know, for a lot of people planning and stuff, always wonder about what to use looking at a rate table.
Daniel Kaiser:I generally suggest point one because that's where things have have historically moderated. Although, you know, we do see stretches of time where that gets a little bit out of whack, and that it's kind of where it becomes more problematic. And this was really done because if you look back, essentially, a lot of the states were using a yield goal approach, and they were looking at some sort of efficiency factor, like, a lot of people have heard 1.2 pounds of N per expected bushel. And when you look in a lot of the data, if you pull together, that was what was seen really at that point in time around the early two thousands. You start pulling the data together that there was really no relationship between the optimal n rate in a field or the amount of n you needed to maximize yield and that maximum yield at that optimal rate.
Daniel Kaiser:So, you know, in order for that 1.2 to work, you would see a clear relationship in there. Just wasn't anything there. So, you know, that's really where, you know, we we talked about the MRT or the maximum return to nitrogen. That's kinda where things were born with a few states here on Minnesota looking at trying to be more conscious of the price when factoring in nitrogen because if you looked at, you know, what we had before, we really couldn't defend it, you know, any better than in what we have, I mean, or even worse than, you know, when it's was worse than what we have of right now with the MRTN approach.
Brad Carlson:Well, and if you look at it historically, going back to when we were using yield goal, and actually, I think we changed the term to expected yield in, like, the year 2000 about five years before we went away from that. There was a lot of controversy or teeth gnashing over what got used for that. A lot of producers wanted to say, well, my goal is to grow 300 bushels every year. I just don't do it. And of course, that created a lot of issues with, no, we need to be realistic with what that is.
Brad Carlson:But the other thing is the system we ended up with, which uses the calculator, allowed for the easy adjustment of the rate as things changed. And the way we were doing it kind of required, you know, throwing the whole thing out and starting over again every time you wanted to adjust it, and and that was getting to be problematic also. It just required a lot of work, and and people had old copies of the table and and other things. It just it was it was just was kind of a mess. The new system, while it seems complicated, in reality, it actually isn't all that complicated.
Daniel Kaiser:And really, the the thing I like about the MRTN approach is the fact that it's database driven. So it's it's real fields out in Minnesota where we collect data, and we use that data to generate a recommendation. And the more data you have, generally, a better your recommendation's gonna be. There, you know, some people I know probably are thinking, well, you know, looking at the recommendation, we make one recommendation for the state. You know, we have looked at that.
Daniel Kaiser:And looking at, you know, irrigated sands, we know that those are those are different, but most of our non irrigated soils, that in general, what we recommend, would generally work. Now we're seeing more models. I mean, crop models. I mean, we saw a few there at Albatos at maybe around Yep. Do you know it?
Daniel Kaiser:About a day we were looking at maybe around twenty fifteen to twenty twenty. Some, models come into place. Those have kinda come and gone, and, I mean, it's kinda you know, if you look at the MRTN, mean, it's database driven models at the same thing. I mean, it depends on good good data. But the only thing that, you know, I do have when it comes to crop models is just the general question on what's your starting point?
Daniel Kaiser:Because I think that's really key when it comes to nitrogen when we look talk about water quality is that we have a starting point that's not well over what that crop needs already because, you know, especially if you're fall applying, you put that out there and the crop doesn't use it. It's it's gonna be left there in the the the following fall when that crop comes off the field. And with the crop model, you know, we were looking at more adjustments in season when we know what's going on with the weather data we have, that I think that's the main challenge when it comes to when it comes to nitrogen application is the fact that a lot of decisions are being made when there's a lot of pieces to that data that go into that model that we just don't know at the point in time that decision's made.
Brad Carlson:Well, think a big part of that too is the part of the concept of the model is trying to predict when the single rate method doesn't work. And part of the whole objective of Nitrogen Smart is to talk about how nitrogen behaves in the environment and how it's lost or what happens when we get more availability and so forth. A lot of that's climatic factors and there's other factors involved too that may be a little more difficult to quantify like pests and pathogens and so forth. You know, the idea of some of these crop models is to be able to try and quantify that, predict it, and then come up with a better answer. Know, the problem always is though that you can't predict the future, so you're only gonna go so far.
Brad Carlson:I mean, if you're making a rate decision on the June, it's pretty hard to know what the weather is gonna be like on the August, you know? So from that standpoint, they can only go we can only go so far with modeling, and after that, it's still gonna require a sort of a I don't know if you wanna say a leap of faith, but more or less, have to fall back on kind of what we've seen in previous years, which is really what our research that went into the MRTN is.
Daniel Kaiser:So one of the things you'll see within the MRTN, you'll hear what we call the op economic optimum nitrogen rate, and this is the actual optimum rate for a specific field and season that's adjusted for the price of n. And that's, you know, one of the things that we'll get questions on, you know, how do I make that general, you know, plan or how do I what you know, if I look at the price ratio, how do I come up with the price ratio? And really, the best way to do it, you know kinda where you wanna market your grain at on an average, you know, kinda general what the cost per price event maybe will be for the fall or what might be look what you're buying then, or or if you've got an estimate for the spring, you can kinda start looking at making some adjustment because it's it's a challenge, you know, looking at it. And we know that that economic optimum nitrogen rate can vary from field to field. And that's really the the big thing for us is right now, we don't have specific tools to try to weigh in on how and on what that variation would be.
Daniel Kaiser:So if you've got multiple fields out there, you might have all those fields have a a separate EONR, economic optimum nitrogen rate. We just don't have a way to tell what that is, and that's kind of the thing where when we start looking at recommendations, it's a lot easier at least to have a good starting point, and that's for this this database driven approach, I think, really is valuable is that, you know, we've got at least something to kinda plan for. And then a lot of the things we talk about, as Brad said, in Nitrogen Smart is how nitrogen behaves in the environment. We start making adjustments plus or minus just based on what you know, you know, potential for losses or, you know, you know, potential for situations where a field might need more or less nitrogen from the other fields you have.
Brad Carlson:And I think to some extent, we maybe did ourselves a disservice by coming up with the EONR term because for all intents and purposes it's pretty much used interchangeably with MRTN and we end up confusing a lot of people sometimes by using the EONR, economic optimum nitrogen rate, MRTN, maximum return to nitrogen. EONR, the economic optimum, you can find that out looking backwards every year. Know, looking forwards, you know, really we're just trying to project that and so it's really almost the exact same thing as MRTN when you're looking forward and trying to determine a rate for the coming year.
Daniel Kaiser:And really the big challenge for us too is, I mean, there's still a lot of emphasis on yield. Mean, you know, growers I know are concerned as yields creep up thinking that we need more nitrogen. And we've looked at this. I mean, we know that if you look at even our MRTN data within the last ten years, we've seen a steady increase in the amount of nitrogen, recommended just based on the sites we're adding in on a yearly basis that there is some creep. Although, if you look at the data, I mean, it really doesn't relate back to the optimal yield within a given field still.
Daniel Kaiser:I mean, even some of that additional creep, I think a lot of it is is environmentally driven, yet it doesn't necessarily mean we're losing all that nitrogen to surface or groundwater. I know a lot of people would point to our MRTN recommendations as as they increase, that just means we're losing more in. And it really I don't think it's necessarily the case because if you look at it, there's more lost pathways than just lost to surface water. So one of the things that, you know, while we talk about economic optimum nitrogen rate, that's the other thing that hits too is a lot of people say, well, you just care about economics and not the environment. And we know that, you know, looking at a lot of our data that we can greatly reduce the risk for loss if we could, you know, consistently target the economic optimum nitrogen rate within a given field within a given year because we know that I mean, if you look at the increase in the amount of, you know, potential for nitrogen to be lost, it's it's it's very, very small up to the e o n r.
Daniel Kaiser:And beyond that, we're leaving a lot of nitrogen, you know, in the field almost pound for pound just because the crop isn't effectively utilizing it. So there's a really good tie in with that. I think that really needs to be known because I know there may be so many people sitting here listening to this thing. Well, you know, they just care about economics, and, you know, we have environmental issues in in some areas. And, you know, in fact, with this this approach, this MRTN, I mean, if we had some sort of estimate on a pound for pound basis, what the, you know, potential cost would be for removing any nitrate that might be potentially lost to surface water, that can be factored in.
Daniel Kaiser:So there is there is some flexibility, and that's the nice thing about an approach like this is that, you know, eventually, we could factor some of the things in to try to hone in then and maybe adjust the rates based on some of those other factors.
Brad Carlson:And and I know there's a lot of farmers and some dealers who still want to try and adjust rates upward based on what you think you're going to get for a yield because you just simply do the math and say, well, if I have an extra 40 bushels of corn, you can grind that corn up and analyze and find out how much nitrogen is in that corn and where you needed that much nitrogen. And technically, that's true. You did need that much nitrogen for that corn, but that doesn't mean you needed that much commercial fertilizer. And if if unfortunately, with this being a podcast, you know, we can't show a visual here. However, if you look at the actual data from from various nitrogen rate trials and you look at what the optimum nitrogen rate was in any given field and then you chart it against what the yield was there at that optimum nitrogen rate and you put all these together on a graph, it looks like a big old shotgun blast.
Brad Carlson:And so the problem is if you really was responding, you know, at at I mean, the old formula was 1.2 times yield, but if you even go back to a more modern, let's say, eight or even point six, that still would be a straight line. It wouldn't be a shotgun blast. And so it shows us that there's plenty of other factors beyond nitrogen rate controlling the yield or also involving the total amount of nitrogen the crop is seeing in the field beyond what you're applying as commercial fertilizer. It's the simple reason why we don't just simply multiply our bushels times some factor and come up with the nitrogen recommendation. Just the data just flat out does not support that.
Daniel Kaiser:Yeah. And one of the things too about when we start talking about the yield increase we've seen is we have seen much more efficiency in the current hybrids. If you look at the pounds of n per bushel produced, you know, Brad alluded to this. So, I mean, in terms of what we're seeing now, you know, maybe, you know, as low as point six pounds of n per bushel. I mean, if you look at, say, a 250 bushel corn crop using point six, that'd be about a 150 pounds in, which is right in with corn following or corn following soybean recommendation for the MRT at the time we're recording this podcast.
Daniel Kaiser:So, you know, looking at it, that that 1.2, think, is the main issue. I mean, I I do see some entities using it still.
Brad Carlson:Well, I've even seen 1.4 thrown out in the past.
Daniel Kaiser:And it's it's too high, based on what we're seeing. I mean, if you are in a situation like that, I mean, I would be looking at practices and just seeing why it's taking that much. We know there's some variation. Mean, we've seen some situations where that number has been as high as 2.5, but that's been know, that was 1993 or '4 Right. When we had a lot of, you know, low yields, with still people putting out regular amounts of nitrogen, you know, the low yields due to due to, extremely wet conditions.
Brad Carlson:But that had to do with nitrogen use efficiency of the crop, not with the amount of nitrogen actually in the crop harvested.
Daniel Kaiser:So, yeah, that's the thing to kinda think about with that and the fact that there's probably not one given number for that efficiency factor. So, you know, that's where again, I think the advantage is having the database and at least then we can kinda let the data drive some of the decisions that we that we make.
Brad Carlson:And and there has been some conversation industry wide about a factor called responsiveness to nitrogen. That is something that is a bit of a mystery to us because all corn is responsive to nitrogen. However, you know, we think that there's probably more to do with what the corn companies think the protein content of the grain is, and therefore the amount of nitrogen necessary to produce a bushel from one hybrid to the other, they're kind of close to the vest with that information, you know. We've kind of thrown that out there and we get a lot of kind of shrugs and hems and haws, but definitely depending on plant breeding and the the protein content in the grain, there probably will be some differences in the actual nitrogen requirements as one of the things maybe eventually that if we get better crop models, we can actually be able to tease out.
Daniel Kaiser:Yeah. And I don't think there's any way most of those companies are actually running nitrogen trials on every single cultivar, variety hybrid, whatever they're they're growing. So They could be. So I think a lot of it's it's they're either looking at grain. One of the things I think that kind of an analogy you can draw is from wheat.
Daniel Kaiser:If anybody out there is growing wheat, you kinda know you have high protein varieties and you have high yield varieties, and there's just differences in genetics in terms of where it partitions some of what it's taking up. So I said that's the challenge. And the thing about, you know, looking at on our standpoint, there's just there's absolutely no way we could ever generate a separate recommendation for all the hybrids out there because by the time we get the data, that hybrid's in and of the market. They just don't stick around too long. So that's the thing.
Daniel Kaiser:I mean, it just the MRTN, the way I view it and the way I recommend it is it's just kind of the starting point. You know, that's what we know in general where we should be around. I mean, certainly, we know there's fields that are higher and lower. I'm looking at that right now, or I have looked at that in the past for the some of our differences in their soil types across the state just to see if we could tweak some of the recommendations. So that's been, I think, the main challenge, with more growers being more technological savvy, with variable rate, they're looking for I mean, they're already looking to and some of them are already are varying their nitrogen application rates out there yet.
Daniel Kaiser:Our approach really doesn't give you a good handle in terms of how to make some of the adjustments. So I think that's the main challenge right now is with the technology we have is how do we do we adjust to some of that with the MRTN. But I think it was a good step forward because looking at profitability, and instead, I wanna make that well known that profitability in a lot of our environmental stewardship, I mean, those two tend to go hand in hand, when it comes to the the rates we have. So that, I think, is one of the things a lot of people look at essentially, you know, since I'm the one that's changing the rates on a yearly or semi yearly basis, you know, they get a little flack from some of that in terms of some of the groups when they see some of those rates their rates increase over time.
Brad Carlson:And, Dan, you already mentioned a little bit about, going back to when MRTN was first developed that I think a lot of farmers and people involved in agriculture are aware that MRTN is used kind of across the North Central Region. While we are using a similar or same methodology across the states, it is worth noting that the nitrogen rate calculator and the rates we give for our states are specific to our states, that we are doing research within our states and then therefore making recommendations based on the research in our state. There's very big differences as you go from north to south in terms of climate, west to east in terms of climate, big differences as you go from north to south in soil organic matter. So for instance, Illinois, you know, by the time you get to Central Illinois, you're dealing with a lot of 2% organic matter. It may be down to one and a half or even below by the time you get to Southern Illinois.
Brad Carlson:So even though Illinois uses this method, is it's only natural that their their rate recommendations are gonna be higher because the soils aren't able to supply as much nitrogen and and so so we use a similar methodology across the North Central Region but there's very valid reasons why despite this why you should be looking at your home state and not somebody else.
Daniel Kaiser:So, you know, what the data is based on right now, the database for corn following soybean goes back to 1990. You know, every once when I change it, I'll look at taking out some of the data and plan to play around looking at scenarios when I make edits to that database. Corn soybean hasn't been as affected by some of that older data corn corn has. It's one of the things that I think with some of the newer, more modern hybrids, particularly with some of the resistances they have, We get better in more stocks and residue out there at the end of the season, so we end up seeing higher nitrogen requirement increase much greater for corn corn versus corn soybean. That's leveled out.
Daniel Kaiser:Leveled out probably around, I would say around somewhere between '20 2005 and 02/2010, where that started to slow down that increase. I think as things kinda came in equilibrium, but right now, corn corn, I think we're if you look at as of we're recording this, we have probably around a 125 sites in the database. Corn soybean, I think close to a 170, a 175, and that's one of the things that, you know, everybody asks, is there any time you need they have enough data? The answer is no. I mean, those databases will continue to collect data, will continue to add it because the more we have, better the estimate for the MRTN.
Brad Carlson:So let's talk just a little bit about how MRTN is actually calculated. When we do a nitrogen rate trial, if you do a nitrogen rate trial, you start with zero and we know that zero nitrogen is going to produce some yield of corn and that's going to be whatever the soil is able to supply on its own. Add a little bit of nitrogen, you get a higher yield. You add more nitrogen, you get a higher yield. At some point, you're gonna maximize yield, and then the the yield's not gonna go up even though you continue to add more nitrogen.
Brad Carlson:You've maximized the yield. And so that's the response curve, for for for nitrogen. But for every pound of nitrogen additionally you add, the cost continues to go up. So that's so even though it's a certain point, the yield curve flattens out because you can't just keep dumping fertilizer on and and seeing yields go up. The price keeps going up.
Brad Carlson:And so if we combine the price and the yield, the overall profitability reaches a crescendo, and then it starts coming back down as you're no longer getting a yield increase for the amount of nitrogen that you're applying. And so that's simp that's a kind of a simple way of describing how MRTN is calculated. You just simply look at where what where we're at at the top of that chart. And and so, you know, in particular, you know, Dan, you mentioned price ratios, and there are different price ratios available depending on what you paid per pound of nitrogen. We know that price is going to be different based on what type of nitrogen you buy.
Brad Carlson:Typically, anhydrous is cheapest, and UAN is probably your most expensive. And then we also need to sort of think about your application cost. If you're split applying, you know, you got double the application cost, you should figure that out on a per acre basis and so forth. And but then also on the the grain side, it can be very difficult knowing just exactly what your corn price was. I mean, most farmers are are marketing corn.
Brad Carlson:They're contracting some in different months. They've got some for spot delivery. They've got some that they're just holding back to see what the market does. You know, it can be pretty difficult knowing exactly what the price of corn was. So for that reason, than worrying about trying to figure out your price of your value per bushel, your price of nitrogen, you know, frequently, we're just simply better off looking at those price ratios.
Brad Carlson:And so currently, we're looking at what, point zero seven five and point one and point one two five and point one five price ratios. And and you'll see a different profitability curve for those, and then you'll see a rate recommended rate window. While that looks like a big deal because it's spread by maybe 20 or 30 pounds of nitrogen, the reality is because it's on the flat part of the curve, that only represents $1 profit or loss from the maximum point. And so really, there's an awful lot of insensitivity on that part of the response curve. And so it's really not worth really getting yourself real stressed out about it when you get to that flat part of the response curve.
Daniel Kaiser:So it's looking at marginal return or what's what's called marginal return, which is essentially the return for every pound of N applied. The MRTN doesn't look at total profitability per acre in terms of total bushels produced. So that's the thing that needs to be, I think, identified with that. And, you know, again, we're looking at the point where the maximum return to nitrogen is that where we return a dollar in crop value for the last dollar invested in nitrogen fertilizer. So, essentially, we're looking at essentially where we we're looking at the breakeven point where nitrogen, you know, fertilizer beyond which we're we're actually spending more than we're getting back in terms of return from yield.
Daniel Kaiser:So that's how that's generated, and the price ratios adjust. The way they're set up now, I have them set in the if you look at go on the corn publication, I have it set for $4 corn for $30.40, 50, and 60¢ per pound of n. So that's where that that point o seven five, point one, point one two five, and point one five ratios come in because that's you know, pretty consistently, we we see things, you know, especially between that point one and that point one five.
Brad Carlson:You know, and Dan, you already mentioned this, people do tend to focus on the fact that we use economics as a determining factor in this, but the research has actually shown the best point of the environment is actually where we are most efficiently using nitrogen. And so we've got tons of data that kind of shows that, you know, that if you are most efficiently using nitrogen, you're not leaving it behind in the field. And so those those points actually cross at the same spot. And so from that standpoint and and it's it's a topic for a different day. However, the research has shown that when we use suboptimal rates of nitrogen, we lower our yields a lot, and we actually don't reduce the amount of nitrogen loss by a whole lot.
Brad Carlson:And so from that standpoint, that's really not really much of a solution as far as dealing with better environmental outcomes.
Daniel Kaiser:So I guess just, you know, kind of to wrap things up, looking at this, I mean, where do you go to get the MRTN rates? I mean, we you can get a lot of it online on the University of Minnesota Extension nutrient management section in the extension website where we have the corn publication. If you just do a web search for the corn n rate calculator, which is cornnratecalic.org, that's where you can go find the data. And the nice thing, you can kinda look at a single price or multiple price comparison to look at comparing if you have some different scenarios you wanna look at for the price event. But it's all available on the web.
Daniel Kaiser:It's freely available to anybody that wants to use it or free one, check it out and see how things compare, what you're doing compares to what we're seeing here in Minnesota.
Brad Carlson:Yeah, so cornnratecalc.org, remember there's an n at the end of corn and then we've got n rate, so you got two n's in there, cornnratecalc.org. That site used to be hosted by Iowa State. It's not anymore, so if you've had it bookmarked and you're not finding it, you may be trying to look for the old Iowa State website that's not there. It's cornnratecalc.org to find the calculator.
Jack Wilcox:Brad Carlson, Extension Educator, and Daniel Kaiser, Extension Nutrient Management Specialist. Thank you both very much.
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. 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.
