From Uncertainty to Insight: Handling Manure Nitrogen Variability

In this episode, Dan Andersen discusses the challenges and uncertainties in manure management related to the variability in manure nitrogen content. 

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Dan Andersen: 0:06

Hello, and welcome to Talkin' Crap, a podcast by Iowa State University, Extension and Outreach. This institution is an equal opportunity provider for the full non discrimination statement or accommodation inquiries, go to www.extension.iastate.edu/legal. In this podcast, we discuss insights into the science technology and best practices surrounding manure management. Our objectives are to build awareness about the challenges farmers and the broader agricultural industry face around manure and to demonstrate solutions and areas of innovation. Hello and welcome back for another episode of Talkin' Crap. I'm your host, Dan Andersen, and today we're going to be talking about manure uncertainty and the effect it has on selecting manure application rates. So one of the questions I've been having recently with myself, based on some of the data that's available in Iowa, is, why does manure always seem to get shorted on the amount of credit it provides? And as we look through maybe, sort of the system, you can come up with lots of reasons. So manure is naturally variable, and sometimes, because of that variability, we're worried we're going to have a yield hit, or we're going to see signs of nitrogen deficiency, because one chunk of manure provides more nitrogen than next, and we sort of see that under application in one part of the field. And I think we've come up with a lot of responses to this. When I look at how maybe cattle manure is used as a fertilizer, oftentimes it's a piece of the fertilizer picture, rather than being the whole thing. So in that case, we might try and say, I'm going to apply enough phosphorus for a couple of years and get some nitrogen to come along for the ride, maybe 50 pounds of available nitrogen, and then I'm going to use synthetic fertilizers to back up the rest of the nitrogen so that I make sure I get a good crop response, and I'm taking credit for my manure. But if I have this under an application uniformity from manure that place that didn't get enough manure nitrogen still looks pretty good because the commercial fertilizer made up sort of the variability that was coming through the field. The other thing we tend to see is some manures maybe get applied a little bit earlier in the fall than we typically want or hope to, and some of that is happening because, well, we don't have enough manure applicators to handle all the manure within that short window that we really want to be applying at it, and that leaves us with a lot of uncertainty to the weather conditions that might happen between the time I put that manure on and when my crop could actually use it. Is it going to be a dry fall, dry spring, or is it going to be really wet? And those make big differences in how much nitrogen we might push down in the soil profile before the crop has a chance to really take it up. In the years where it's wet, I might see this lack of nitrogen show up more than in years where it's dry and I really can take credit for all the nitrogen I put on. So I bring all that up because I don't think this is ignorance, or people saying I don't really want to use manure. I think people generally tell me, I like manure. I want to use it. But there's some challenges that are associated with trying to get the most from it, and we're trying to pick what's rational, or what should we be doing to try and use it to the best advantage of our cropping systems while handling this uncertainty. And I think that's really what we see. Farmers aren't being careless with manure they're not out there trying to put on too much or over apply. They're really trying to figure out what's the rational behavior to make sure that we are using the proper fertilizer plan and taking maybe precautions to have some insurance nitrogen out there if things aren't going according to what we expected or what's typically happening on our farm. So if we think about manure and compare it to maybe commercial fertilizers, especially commercial nitrogen, we're really talking about the same sort of nutrients, right? We're talking about nitrogen, we're talking about phosphorus, we're talking about potassium, but there's also some pretty big differences in how confident we are we're going to get what we're applying. So if you show up with commercial nitrogen fertilizer, we're really confident in the concentration of nitrogen in it. If you get buy in hydrous ammonia, we know how many units of nitrogen we get. If you buy UAN, we know how many units of nitrogen we get. If you're using manure, hopefully we've taken that manure sample, we got an analysis back to the lab, and we still don't know exactly what's in that manure, because we took maybe one liter out of a million gallon pit at the lab, they took maybe a milliliter of that sample and said, This is how much nitrogen was in that milliliter. So how well does it really represent what we're putting on our field. So I bring all that up to say that really, with commercial fertilizer, when you set your applicator control system to say, I'm going to try and put down 180 units of nitrogen, you're pretty confident you're really putting down 180 units of nitrogen. Sure, maybe it's not perfect. Maybe it has 5% error in rate, and maybe the knife to knife or uniformity across that toolbar is the same 5% but that's still really close when we're putting it down, manure systems have gotten better. We see tanks with control systems drag lines with control systems to really control the volumetric rate. But the first chunk of manure we all know probably isn't exactly the same as the last chunk of manure, maybe some of the knife to knife variabilities, or the uniformity across the back end of a tool bar isn't quite as good as we get with anhydrous because we're dealing with this natural material with chunks of solid material in it, and it's harder to get uniform distribution with that. Or maybe we just don't get it covered as good in the field, because we're putting more of that material on. And all that leads to some uncertainty challenges. So if we say, I'm setting up my control system. I have that sample. I'm pretty sure I'm getting 180 units of nitrogen. But what are we really getting? Is it closer to 140, 220, right? And all that matters at the same time. And the truth is, even if we're getting 140 or 220 or 180 that might happen if we go from a farm to farm, or even between locations in the same field, because maybe our toolbar does a much better job of covering in an area. Maybe we had that rich manure, or maybe now we're getting the poor manure, and sometimes we just don't know. So as we think about this, I wanted to start with, what are the sources of uncertainty as we're applying manure? What is causing maybe this lack of I know exactly what I put on, and there's a few things that go into it, but the first one I want to start is what's really in the tank today. When did you take your manure sample? What's happened since then? And how good of job is our agitation doing mixing it up? And I think those are all important questions, some that hopefully as we've gotten better at sampling manure, as you build the manure history on your farm, of seeing what happens when you pre sample compared to what you're taking from an as applied sample, you can sort of build up this calibration curve, or this baseline knowledge to say, Yeah, I feel like it's pretty consistent. Or, you know, at my farm, for some reason, that pre sample just is 10, 20% lower than my as applied sample, probably as I'm working those solids up and agitating them well. One of the things I wanted to talk about is asymmetry of risk. But there's other things that come into play as well. How accurate is your actual flow system? How many overlaps do you have in the field? How are you accounting for those? And then, did every knife get the same flow? Or, if we're working with solid manure, what's that distribution look like coming And while I love math, and those of you who know me probably know off the rear end of the spreader? Does it look pretty uniform? Does it look the same? Or do I see some heavy areas in the middle and lights on the edges? And you can keep doing this right? So most of us are injecting manure, if we're using a liquid manure injection system, but how well is it I love math, I want to do this without actually talking about working today in this field this year, given the soil characteristics, the moisture and maybe some of the practices that we've done. Is it a hard, compacted field that we took silage on and my injectors just aren't getting good coverage. Or is it a soft, mellow soil where all that liquid is in the ground the mass math behind it. So we've all hopefully seen a really quick, and I don't see it sitting there, pooled and All right? So I wanted to transition in this next segment vulnerable to gaseous nitrogen loss after application. And then maybe the biggest one, or one at least, that I think I hear a lot a little bit, and if I'm going to tell you, let's think of conversation about, is how available was it? You know, it's nitrogen response curve. And I know there's a few ways to think manure. It's got these chunks in it, some of that organic nitrogen. I don't feel like it's becoming available to my corn plant. It's taking time to break down in the soil. I just don't feel like it's there. And some of that's true, right? It varies from manure to manure. Some manures have a lot of ammonium about it. One is, well, it's sort of a straight line from when we're putting it on it's probably highly available. Some of those manures are a lot more organic nitrogen, and more dependent on how quickly it mineralizes, if it'll become available. And the truth is, we can say a lot about what I would have had if I put no nitrogen on up until this availability. We know it's related to the manure characteristics, that carbon to nitrogen ratio, sort of the ammonium to TKN ratio as we start. But some of it's related All right? And the next part of this is, so what does that to soils and weather. And weather can be really variable. Is it moist and hot, and we get a high mineralization rate. Is economic optimum rate, and then it flat lines, and I don't get it cool and stays cool for a while, so it's slow, or does it dry out completely in the summer and not break down? Or maybe really mean for picking our manure rate? And we can do a lot even placement in the soil might impact that availability. Am I leaving it on the surface and it really is drying out? Well, microbes probably aren't doing great in that environment. If I any more nitrogen from my corn yield. And that's probably an mix it with the soil and it stays moist, maybe I break down that nitrogen throughout the growing season more of math behind this. We actually did. I had a student, Anton, consistently. So all those things matter, and the truth is, we've kind of relied on, well, maybe one's going to be high and idealized picture in our head, not what we actually get in the one's going to be low, and those errors hopefully cancel out, and we got a pretty good estimate about what amount of nitrogen is build a little model to try and estimate this for us. And going to be there. But is that a good approach, or is there other things we can do or be thinking about to maybe try and improve what we're doing. field, but it still does a decent job of illustrating maybe essentially what he did is he built the Monte Carlo model. In the concept I want to get across. And if you do that, I Monte Carlo is kind of what it sounds like a gambling town, and think one thing you could say is, well, if I apply over the we're trying to play the odds, or a gambling scenario, and it's optimum rate, for whatever reason, I wasted the value of basically rolling the dice 1000s of times. So with each roll of the nitrogen beyond the optimum rate. So maybe that's 50 cents a the dice, his program would pick out what's the actual nitrogen pound times the 10 pounds I was over and you know, I'm talking content of the of the manure? What's the application rate that$5 an acre. IF I miss low by, let's again, say 10 pounds. you're really going to hit? How much volatilization are you Well, in that case, if I was saying it took a pound of really going to have? What's the availability going to look like? nitrogen, do a bushel of corn, 10 pounds low, I lost 10 bushels of corn, 10 times the $5 of corn. And I'm $50 an acre off, What was the seasonal weather conditions to cause losses and right? So asymmetry to maybe the risk, if I was short, that cost all those things of the sort that go behind that. And from that, it would say, Well, given the conditions that we're going me 50 bucks. If I was high, it cost me $5 so I think we're all pretty clear on what that would incentivize. Maybe, if I'm going to have in this scenario, the actual nitrogen application rate you wanted was this. Well, if we would apply to what we thought to error, I want to error to the high side. So I wanted to make another real world analogy for this sort of risk and where the was right, the average, how wrong are we? Did we put on 10 pounds too many? Did we put on 10 pounds too less? Or, lo and asymmetry of risk happens, and one is maybe picking your arrival time to the airport. Let's say you are a person who behold, were we perfect, right? So we did this over and over and likes to be to the airport an hour and a half before your over again, and you can sort of build the distribution from flight. If you're like my wife and worry a little bit about that, and that distribution says, Well, how likely is each maybe travel and making sure that things go according to of those outcomes to happen? So I think one way to think about plan, you probably try and err on the side of being 10 minutes that in your mind is it's not a asking the question of, what's early. If you are a seasoned flyer and really comfortable the right rate. Instead, it's asking, what's the rate that with the airport, maybe you err on the side of being 10 minutes you'd pick to cause the least amount of loss of income, when late, but the truth is, right, there's a big, big difference. the money, when the manure doesn't behave the way we think And we'll talk about that in just a second. And the reason I want to wait a second is because there's other things that If you are 10 minutes late and causes you to miss your plane, matter. For example, rotation matters. Crops that have a it's going to. Which is really the situation we're dealing with steeper yield response to nitrogen will have a bigger penalty for being short and therefore a bigger insurance bump in the nitrogen rate you should be picking. So one way to think about that is, well, corn, continuous corn systems, or corn well, that's a big asymmetry to the risk, right? Travel plans after corn, probably needs to error a little bit higher than in the real world. And probably no big surprise, the big result corn after soybean, right? Because that rotation effect sort of helps buffer that nitrogen miss and keep our yields more stable. In a sense, they're providing some resilience in that nitrogen response. So as we looked at the are ruined. If you're 10 minutes early, you've lost 10 minutes of data and started to say what's really happening here? One of of that was, well, uncertainty creates a nitrogen risk premium, the things that continued to show up was generally for manures, we probably wanted to aim about 10 to 30 pounds higher in nitrogen application rate. For manures where we really can your life, 10 minutes of productive time doing something predict availability, Well, let's say deep pits swine manure where it's almost all in the ammonium form at the time we're where maybe you're encouraged to apply just a little bit more applying, we probably nearly know what's in there. For some of those bedded pack manures with high C to N ratios, we're important. But you make your flight and you make whatever the much less confident in predicting what the actual nitrogen availability will be in any given year, or if we're nitrogen to handle some of that risk. And essentially, it showed injecting instead of surface applying, we really know that nitrogen will not be going into the air. We can take credit for it. So those decisions that help increase uncertainty, those connection is or the same as how we manage our gas tank, right if decisions that help decrease uncertainty, help us keep that insurance nitrogen levels low, but in general, we were probably that as manure uncertainty increases, the profit maximizing talking somewhere between 10 and 30 pounds. And other things you could do could help mitigate some of that, having to error on the high side. For example, using a program that has both you run out of gas 10 miles before your destination, commercial fertilizer and manure, because that will handle some of the non uniformity of application and help cover up nitrogen application rate increases. So if we know that some of those errors in application, essentially to provide some insurance, or maybe provide some resilience to compared to having that 10, 10 miles after you fill up with gas misses in nitrogen rate. And I want to talk a little bit more about that uniformity for our field, the ideal rate is 180 pounds for commercial across the toolbar, or a uniformity across the back end of the spreader. And the reason I want to is maybe that was the one variable where as it increases in risk or non well. I'd much rather have my tank full and make it to the gas uniformity, almost every other one says, well, just add a little bit more insurance nitrogen. With non uniformity fertilizer. If we're going to switch to manure, it says, well, coming out the back of your manure spreader, that is not inherently true. Now, the one thing that does is you do that is, well, I get to increase my application rate, and most of us station. So I think those are some examples where we see sort have probably seen that if I would go with a spreader that's trying to put on 2000 gallons an acre to a manure tank that's it how uncertainty are we about how much nitrogen we're really trying to put trying to put on 4000 gallons an acre, the uniformity across the back end of my manure tank improves. Right? Every knife is more similar. So in some ways, a of how people mitigate and manage this risk. And I think little more manure helps that problem, but it doesn't help that problem for the same reason. It's because, going to get from that manure? From that manure? How much mechanically, we've just got a better spread pattern. If we weren't getting a better spread pattern as we were doing, that oftentimes we see people trying to buffer towards the one that if we were staying the same, it would actually make the problem worse, because the rows that already had extra nitrogen, now higher should we aim? Should it be? 185, 192, 210, right? So we that we increase the rate, they get even more nitrogen, but the rows that were short, they're still short, so we're not gaining enough most of the time to make that better. And what we takes away some of that risk of something really bad happening. tended to find was that up until 30, 40% uniformity, so non uniformly, in this case, coefficient of variation from know the more uncertain we are about getting the amount of knife to knife. We were probably increasing application rate. But as we got above that, as we got to 40, 50, 60%, the rate should start coming down. Essentially, you were wasting more nitrogen And I think that's why it's rational for farmers maybe to be putting it on in a non uniform way. Then you were helping yield nitrogen in the manure, the higher we should be. But at the by getting a little more nitrogen on the plants that weren't getting it. All right, so today I've talked a little bit about, I can see why farmers might be looking at this as a sometimes applying more than what would be the recommended risk premium and trying to error high with manure systems sometimes, because we lack uncertainty. But I did want to end of the day, you're still going to ask me, Well, what's talk about, well, what's this mean in the real world? Am I out here telling people put on more manure? Well, not, not exactly. economic optimum. They're trying to come up cover up some of that I think most of us have already seen this, and that's an effect that people are trying to take. And one way I wanted to the number I should be picking then, how much insurance illustrate this is to just talk through maybe a nitrogen budget or nitrogen balance in Iowa. So these are estimates, and you can look up some of these numbers. Some of them are best guesses of risk of what happens if I'm short. what I can make. But for example, if we would look at nitrogen do I need? 2024 you can look up how much nitrogen fertilizer was purchased in Iowa. So what does this mean? Am I saying apply more manure to acres because there's this uncertainty, or there's this insurance nitrogen? Not necessarily. I think most farmers, most people, most manure planners, have already sort of figured this out and been trying to come up with plans for what to do, and probably in some cases, they are putting on a little insurance nitrogen to try and cover up the non uniformity. Or maybe we've developed cropping manure systems where we get a certain percentage of our nitrogen from manure, certain percentage from commercial fertilizer, and we're trying to figure out how to complement them. And the reason I say that maybe, maybe not is I really do believe that a lot of people have used this insurance nitrogen, or this risk premium sort of approach to their nitrogen, because it's what they see. If I go scout a field and I have this manure challenge where it wasn't supplying as much as I thought, I see yellow corn. If I had a benefit where it put on maybe a little extra nitrogen, it was more available than what I assumed, my corn is still green, but I don't really see much coming of that, right? There's not a visual response. It still looks green. And I bring that up because well, and that's sort of the feedback that people make decisions on, does my corn look sufficient in nitrogen? Does it look short? And we've probably calibrated our own recommendation for our specific field, our specific circumstance, to take that into account. And the reason I say that is you can start looking up some data from around Iowa. For example, I looked up how much nitrogen was sold basically in 2023 and 2024 so I took the fall of 23 the spring of 24 and said that probably was all to support cropping production in 2024 and in that year, I was sold about 2.5 billion pounds of nitrogen fertilizer, and I admit not all of that went to corn. Maybe urban lawns use somewhere around 36 million. That assumes that all land in urban areas is fertilized to the ISU recommendation, including driveways and houses and things like that. Or maybe soybeans get some right if we're putting map or DAP on maybe we didn't want to put nitrogen onto our soybean, but it was a long for the ride in that fertilizer decision. And maybe that was another 50 million. Another 50 million pounds, or there's hay and pasture ground that's going to take some of those nutrients, and we can start writing those off. Now, given the land use demographics in Iowa, that probably takes us down to about 2.2 billion pounds of nitrogen going to fertilizer. And this is where maybe the data gets a little more suspect or questionable, because I'm going to do some things that I think are really good, and then some things that I wish I didn't have to do. But it's the data we had. So you can look up from the NREC survey average nitrogen application rate to fields only receiving commercial fertilizer in continuous corn or in corn soybean rotations. In continuous corn rotations, they average about 200 pounds in corn following soybean, it's about 175 and those seem pretty good. And that's about 80% of our our acreage in Iowa doesn't get manure. So you can start saying, Well, that would amount to a pretty substantial amount of nitrogen, somewhere in the neighborhood of 1.85 billion pounds. And here's the part that I don't necessarily love. Well, I had 2.2 when I take 1.85 off of that, and we're left with about 350 million pounds. And that's generally okay, but taking two big numbers and subtracting them can sometimes lead to error, essentially in a calculation, because if I'm off by 10 pounds in that nitrogen application rate, or if I'm off by small amounts of acreage, it really can add up, because they're big things multiplied together. But for the sake of argument, let's say that there's 350 million pounds of commercial fertilizer that's applied to the 20% of acres that get some manure. I estimate somewhere in the neighborhood of 630 million pounds of available N, after adjusting for availability and what would be lost during storage. And here's where, you know, I can't make the perfect assumption. How much of that nitrogen is incorporated at the time of application, when's it applied, etc, etc. How much credit should farmers really be giving to that in their cropping systems? I don't know. But if we were managing it perfectly, maybe between those two we could capture almost another billion pounds of nitrogen. And the reason I do that is, if you start penciling it out, that means on manure to acres, we're probably in the neighborhood of 300 pounds of nitrogen per acre, compared to on those commercial fertilizer only acres, where we're really at, like 185. So why are we so high in the manure acres and and there's certainly lots of reasons. Maybe the timing of nitrogen application is a challenge. Maybe the people aren't trusting manure, and we're putting on a little extra because of that. Maybe there's just an error in some of this math and the numbers that I could find and that are available for us to do in Iowa, but I do think it shows that maybe we're not fully trusting that manure like we would commercial fertilizer. So where I wanted to go with this is, I think there are some things we can try and do to better credit manure. The first is, just really think about it as are we taking the credit we feel like we should deserve, or are we afraid and just saying, a little extra nitrogen, a little insurance nitrogen, is probably the easiest fix. And hopefully we're saying, Yeah, I'm crediting my manure. And I'm hopeful that you're saying I am using a little insurance nitrogen, but hopefully we can dial that back to a better number. I also think that we see some opportunities in equipment development that are starting to occur. For example, I've been working with the Harvest Lab 3000 related to real time measuring nitrogen concentrations in manure. I've used it for a couple years, and every year the calibration curves get better. The ability of that tool to predict how much nitrogen is actually my manure is improving. It's probably a tool that we can be more confident with what's actually making it out there. That tool also estimates sort of a solid content and a nitrogen content. So maybe I can make a better play at how available is my nitrogen in my manure, because I have a C to N ratio for that manure. Or we've certainly seen some of our injection equipment get more sophisticated do a better job of getting that manure underground. Understanding when I need a big slit to get the dairy manure in, or maybe when it's a little less important and it's deep pit swine manure that's getting applied at a low rate, all these So as we think about wrapping this all up and tying together things are setting us up for a system where less insurance what we've heard today, I think there's a couple key points for us. One, sometimes a little insurance nitrogen, while it is nitrogen will be needed. And I'm very optimistic for that. But rational and not reckless, isn't maybe our best approach. We should be looking for ways to address the uncertainty in our the big one is still making sure we're taking credit and doing application system and trying to make choices that really support getting the amount of nitrogen that is in the manure to be what we can with application timing to make sure that we plant available and supplied to our growing crop. So precision isn't about being perfect. It's about shrinking the penalty for trust that nitrogen really will be there for our crop the next being wrong. If we want to, if we want manure to replace commercial fertilizer, we have to make it behave more like growing season. So from my perspective, where I sit, every commercial fertilizer, not by changing the manure, but by reducing the uncertainty around it, and that goes for everything dollar spent on making more predictable is $1 you don't have that happens during our manure storage, handling, treatment and application system. So we have to make the systems work to spend putting on insurance nitrogen. Will that pay off in together to really supply that nitrogen in a predictable way every case? No, but hopefully, with the work we're doing here that we can take advantage of in our cropping systems. So hopefully that gives you something to think about. If you'd like to chat more about this topic, send me an email, at Iowa State University, the work you're doing and thinking give me a phone call, happy to chat more in depth about what it about how to optimize nitrogen in your cropping system, that is might mean for you and your farm, or how we can make better manure decisions. Thank you for joining this installment of Talkin' Crap. Be something that we'll be able to take advantage of as we move sure to take a look at the show notes on our website for links and materials mentioned in the episode. 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