Who Gets Manure?

In this episode, Dan explores the yield goal method, MRTN, and N-FACT, and how recommendations influence manure application across Iowa. He also looks at recent spatial mapping and its impact on manure management practices. 

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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/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. Welcome back to Talkin' Crap. I'm Dr. Dan Andersen, and today I will start with a simple question: Who gets manure? Now that might sound like a strange question. Most of us think of manure in terms of livestock. If you have pigs, cattle, or poultry, you have manure, and eventually you have to figure out where to put it. But what if I told you one of the biggest factors determining where manure gets applied isn't the livestock at all? It's the nitrogen recommendation we use for corn. Think about it. Every acre of corn has a nitrogen demand. If we estimate that demand at 180 pounds per acre, we'll need one amount of land to utilize the manure from the livestock operations. If we set it at 160, suddenly we need more acres. If we estimate it at 200, we need fewer. That one decision changes how far livestock manure travels, how many neighbors are involved, how much time applicators spend on the road, and even the economics of livestock production itself. For years, we debated nitrogen recommendations from the perspective of crop production. Should we use a yield goal? Should we use MRTN? Are weather-based tools like N-FACT the future? These are important questions, but today I'm going to look at them through the lens a little differently. What do the recommendations mean for manure? Because manure isn't like commercial fertilizer. If fertilizer prices go up or down, you can buy a little more or a little less. Livestock doesn't work that way. Every day, Iowa's pigs, cattle, and poultry are producing nutrients that need to be managed. The amount of manure doesn't change because we change a recommendation. It still has to go somewhere. So today, instead of asking how much nitrogen does corn need, let's ask a different question: How do our nitrogen recommendations change the way manure moves across Iowa? We'll talk about yield goal, MRTN, and N-FACT, but not as competing agronomic recommendations, but rather exploring them as tools to shape the geography of manure application, determining which fields receive nutrients, how far those nutrients travel, and what the future of nutrient management could look like. Because I think the next big innovation isn't finding a better nitrogen recommendation system; it's finding better ways to match the nutrients we've already produced with the crops that need them. So with that, let's talk some crap. All right, that was a fun little introduction, and the place I want to start on this is really when you start thinking about how much land in Iowa gets manure, how much land needs manure. There's two parts of it. There's the manure supply side. How many livestock do we have? What are the production facilities we're using, and how does that relate to both how much of that nitrogen is retained until we land apply it, but how much of those nutrients actually get land applied and credited as we do? And that's an important part of it. And I'm going to admit I've generally been a little on the the lax side on that, I use the American Society of Agricultural and Biosystems Engineering Manure Production Standard, run it through some loss algorithms for the types of storages we use in Iowa, use Iowa State recommendations for availability and loss at application, and say, yeah, that's a pretty good estimate, and I still think it is. It's a decent estimate. The truth is, it maybe is a little high? Livestock production's gotten more efficient at utilizing nitrogen, phosphorus, and potassium, turning it into things we need. But it depends on the diet and the ration we choose, and there's lots of reasons to do that. And it puts us in the ballpark, or at least pretty close to it. And I'll try and refine those numbers a little bit in the next year or so to see if it matters if if I'm okay still making those recommendations and I think there's a lot of good work in that space going on starting with the Manure Database, Manure DB, project from Minnesota to tell us what some typical concentrations are and that's not excretion but it gives us an indicator of where the industry is and maybe how it's moved. The other part of that is the demand side, or what do crops need? And I come at this from a very Midwest and especially Iowa perspective, because, well, that's where I've done most of my work in my career. And really, for us, that's mostly corn. You might see some manure put on pasture, some on hay fields, and there are times we do some of that. But the truth is, in Iowa, the majority, 95, 99 percent of all manure produced ends up going onto ground that is going to be in corn production the next year. So the recommendation tool, or the way we're relating to how much nitrogen does that cornfield need next year, really matters. And there's a long history on this, right? It's really important to supporting crop production, trying to optimize that number, and I think in the past we've heard people say farmers are just trying to get rid of manure, and that number doesn't matter to them. And I couldn't disagree more. Right? If we go back to the 70s, maybe that was true. My career, starting in the 2010s, I think farmers have always valued manure and trying to squeeze every last penny out of that value has really been my career, and I think a lot of the careers of nutrient management planners and farmers. So I think we've been moving in the right direction for a long time, and pressures of increased fertilizer prices probably keep us moving in that direction at a pretty rapid pace. So when we think about the recommendation systems, most manure plans are filled off of something called yield goal. And yield goal, it started in 1972. It was sort of a rule of thumb that got maybe formalized or standardized. That said, for every bushel of corn you anticipate growing, and there's an algorithm to figure out what your yield goal or amount of corn you think you might produce is, we need 1.2 pounds of nitrogen, and then they'd have something they call the legume credit. These days we might call it more of a rotation effect, or even the exact opposite of this, a continuous corn penalty. But you'd encourage that in there, and for most of Iowa, that worked out to if you had soybeans before corn, you're probably taking credit for 50 pounds of nitrogen per acre. Again, that really isn't a credit. Soybeans tend to remove more nitrogen from the soil than what they fix from the atmosphere, so it's not a credit for that. But it's probably more related to if I had grown corn instead of soybeans, I'd have all this residue from that corn. Maybe get some tie up maybe that residue keeps soils a little cooler, a little wetter, slows mineralization. So really, it's maybe more of a continuous corn penalty rather than a credit. But in either case, we sort of recognize this effect that said, hey, if I had soybeans the year before, apparently I don't need as much nitrogen to get to the same yield or a better yield from having soybeans. So let's adjust how much nitrogen we think we need some to that point. And that system from '72 until the mid '90s, early 2000s, probably was predominant, right? It was the method that most people used. And if you look back at that method, it didn't say, "Well, you actually need 1.2. It said, "Chances are you need a little less than 1.2, and this is a good starting point. And if you had soybeans or a legume before, maybe you needed one pound of nitrogen per bushel of corn you grow. If we move ahead, in the mid 2000s, Iowa State and many of the land grant institutions in the Midwest, but I think of Iowa State and John Sawyer as a pioneer of this, came up with this idea of maximum return to nitrogen. So how do we figure out when the next pound of nitrogen we apply will make just enough corn that make that next bushel, so I can pay for the nitrogen fertilizer I put on. And man, if I could predict that number, wouldn't the world be nice? Because I'm always going to apply at the optimum rate because I'm going to put on fertilizer until it just pays for itself, and then I'm going to say, well, that was enough, and the way they did that is they did yield trials on lots of farms, ideally as many as possible. In this case, as many as possible was probably something like 20 farms a year, and they kept doing those for a little more than a decade, 15 or 20 years, and they made a response curve. So, if I had continuous corn and I put on this amount of nitrogen. How did I compare to if I had put on no nitrogen, and can I find that optimal spot? Or if I had corn following soybean, sort of same procedure. So making a curve that said as I put on more nitrogen, how much extra yield do I anticipate getting, and trying to identify the spot where the nitrogen just paid for itself. And I think that method made a lot of sense to a lot of people. It was really trying to dial in fertilizer recommendations to be a business proposition. How do I hit the right rate as often as possible? And I learned a lot from it. And I still think about what they were doing and how it changed our recommendation system. Going from well, it probably always takes a pound to hey, it doesn't always take a pound as we start to hit that maximum, really, where does this taper off when we don't get enough yield response from putting more on? Was a pretty big conceptual leap, but I think as they did that, we started to learn a few more things. One, corn yields continued to go up, and if you live in Iowa, you might think, well, what's the best guess of how much corn I'm going to make next year? And it's probably about 2.4 bushels more corn per acre than I grew the previous year. Because when we look at trendline yield history in Iowa, it goes up a little more than two bushels an acre a year, and we've done that for close to 100 years now. Right? It's been as consistent as clockwork. It doesn't mean we always grow two bushels more, right? Because weather matters a lot. But as a

general rule of thumb: 9:39

That trend has been pretty consistent, and we can see it pretty heavily in the data. And if you think back to that first methodology, that yield goal, it would have said, "Well, as you're growing more corn, you probably need more nitrogen. And it doesn't take a lot of thought to say, "Well, if I grow more corn, I'm definitely harvesting more nitrogen in that grain. How could I not need?" More nitrogen, and there's reasons, right? Maybe the soil makes it up more. We get more nitrogen mineralization from the soil, but generally, more you harvest, more weed removal, and we'll have to think about how is that nitrogen getting replaced, right? And as people started to see this and recognize this trend and look at maybe some of the maximum return to nitrogen data, they started to say, is there a trend in how much nitrogen we need per acre in terms of change with time, and they saw that it was trending up, and that made me think about it a little bit differently, and maybe that means we could predict how much nitrogen we need next year based on where we were and how much extra yield we think we're going to get this following year, and then there's a weather factor, and maximum return to nitrogen just based on how they're collecting the data, they average it all together. They were saying that sort of for average conditions, this is how much nitrogen you would need, which means on average it's right, and in any given year it's it's wrong, right? Because the weather's different, and we didn't have that average year. Still a great leap forward, and we saw some rules of thumb start to develop, like if we get more than a certain amount of rainfall in May to June 15th, may we need a little more nitrogen? And that takes us to where I think we are today, where Iowa State is using something called N-FACT. You've heard Mitch come on the the program in the past and talk to this, but it's an online tool that's really combining two

things: 11:17

lots of on-farm yield trial data, and then some modeling to come up with a recommendation system, and to me that's really powerful. When we look at sort of what we learned from MRTN, it said data is good, right? With more data, we can start to make informed decisions. We can see what general response trends are, and almost all those trials were on university farms. So the N-FACT system, the Iowa Nitrogen Initiative system said it said, wouldn't it be great if we could take this to the people and start doing a lot of these trials on farm, and by doing that we see greater variation in yield, greater variation in soil conditions rather than using the same university fields over and over again, and I think the data they've given us from those on farm trials is really strong, and there's a few things that jump out to me when I look through all the data that's been collected this far. Sites that have higher yield tend to need more nitrogen. How much more? For every bushel of corn you anticipate growing, I the data says on average we need about half a pound, 0.55 pounds per bushel more nitrogen per acre. So going back to that sort of yield goal effect of saying yeah yields a driver on this now it's not one it's not 1.2 it's a little under six tenths a little more than half a pound right so good efficiency in what they're seeing there but it's nice to have on farm data that says that it also says maybe the state average for pounds of nitrogen per bushel of corn you grow at optimum is nine tenths. Now, does weather play a role in that? Absolutely. Wet years, dry years, how much soil mineralization I had all make a difference. And to push the the analogy a little further, or talk to what N-FACT does, there's two parameters on there: spring rainfall compared to average, summer rainfall compared to average, that help us take into account that year-to-year variation. So a really strong, really powerful tool. Now you might be saying, I don't know what the weather's going to be next year. Good news, neither do I. I don't know that we'll ever be able to predict the weather that well. As I sit here in 2026 and look at the weather so far, I can say, man, it's been wet. And and given what we know, staying consistently wet for that long really helps soil microbial activity, especially if the soil is warm, it is. So if it's moist, so that near field capacity, a little under field capacity where microbes are active, we're probably mineralizing a lot of nitrogen, and that's again what we're seeing this year. But that tool, that N-FACT tool with some of their simulation model, gives us a way to start taking credit or accounting for that. Now I'm not going to dive into those details too much. We'll try and do that in a future episode because what I really wanted to talk about here was how does how do those differences change how much land we need for manure in Iowa? How does it impact maybe how far we're hauling manure or what different parts of the state look like? Okay, so if you remember, I had a student on Cain Bynum not that long ago, who was looking at how do we draw circles around livestock farms to represent where manure is going. And what I'm going to talk about next really comes from some of the work that we've done. You can look at the show graphic that goes with this to sort of see where we've gotten to, trying to interpret some things, make some differences of it. But I had him say, if we know all the facilities in Iowa where they are, if you can download that from the Iowa DNR database associated with the manure storage, we can make good estimates of how much manure there is. What does that mean for how much land and where manure is getting? So we used each of those three methodologies: yield goal, MRTN, and N-FACT, and we drew a circle around the farm, and I'm going to give you some areas, noting that those areas don't receive manure every year, but they're areas that, based on the cropping pattern in that region, that county, I would anticipate would be in a manure plan. And I say that because it could be in corn this year and getting manure. It could be in soybean, not getting manure this year, but as it rotates to corn next year, getting manure. And then to try and make the map look right, I did have to cheat a little bit, and we don't farm every acre in Iowa. I know some places it might feel like it, but it varies around the state. And my acreage is actually going to include roads, non-use, non-farm areas because I was trying to make the circle radius right, and and I can try and fix that for you. But as we think about maybe where we're at and trying to give some comparison of some numbers, if we were doing manure on a yield goal basis in that sort of radius that where manure would be covered or within the envelope of where we're probably hauling manure, I'm looking at about 8 million acres, which means really probably somewhere around three and a half million acres of land should be getting manure if we're using the yield goal. Now, the good news is, if you look at the census of ag that we do, it says roughly in Iowa three and a half million acres of land get manure. So that estimate's working out about where I anticipate it should be or think it should be. If we would switch suddenly and say, what would happen if we use MRTN? And I'd like to tell you this MRTN number is what would have been on the website if you ever looked at the old tool. How much nitrogen do I need? Used MRTN, it spits a number that wasn't the number I chose to use here. We saw that it was trending with time, so I was running a time trend correction. So the number I'm going to say how much nitrogen we needed, that tool probably spitter out around 145 pounds of nitrogen. If you're in corn following soybean, I'm going to use more like 165, just because that's what the trend line to how that was changing with time says we would have done. And sort of that trend line, if I'm looking at Iowa, it says that overall in that circular radius I would have needed about 10 million acres. So as we start thinking about what does that mean for corn, well, I would have needed somewhere around four, four and a half million acres. So about a million more acres than if I was filling it out relative to yield goal, right? So a fair amount more land. If we jump ahead, sort of, and do the same thing with yield goal, me making all the best corrections I can. I'm not going to detail them here, but trying to really think about what do the on-farm trials tell us? What does the tool tell us for if when the modeling says how do we adjust for different parameters like yield or rainfall or soil organic matter, right? And if I do all that, it looks to me like I would need somewhere in the neighborhood of 3.5, 3.75 million acres of land that would be in corn to be receiving manure. So more similar to yield goal than what that trended MRTN number looks like, which is really kind of interesting. It tells us that maybe yield goal has some validity. It's maybe a little low, but it put us in the ballpark. And as long as we think we could do a little bit better than that algorithm that was invented in '72, we're probably at least in the in the realm of where we should be. Now, what was really neat to me about this, and you can start looking at the show graphic to see it, is we could start saying now that we know where the livestock facility is, we know how much nitrogen each acre of corn ground would need in those areas. We can draw a circle and color it. Is this area going to get manure? Is it not going to get manure in terms of how would anticipate people most wanting to fill out their yield goal manure plan? Now I don't actually know if the farm owns that field or not. So real world decisions are more complicated than this, but it gives a pretty good representation. So on that handout, if you take a look at it, and I really hope you do, we colored all the areas that we think probably would be in a manure plan tan, and it really gives you some perspective on how far manure is moving and really what this means. And I think the big thing that jumps out to me when I first start looking at it is, man, there's a lot of farms where manure doesn't have to move very far, and you might be like Dan, I knew this. I've heard you talk before, and you say things like, on average, liquid swine manure in Iowa is moving one mile plus or minus a mile. It stays pretty close to home. You didn't need to make me a fancy map to say something that you've said before, and well, I agree with you. I didn't need to, but don't we like looking at fancy maps? I tease. The map is still helpful in some ways to me, right? Because it starts showing where do farms potentially compete for land, and that might be related to what does land price do in that area, right? If we're competing for manure application land, it might drive prices up. Or we might look in regions where there's a lot of overlap, and we might start saying, well, those regions have to start thinking about how do we move manure further? Who's moving the manure? Is it some with liquid manure? Is it someone with solid manure? Do we have solid manure options there where some of that poultry litter could get loaded, hauled further off, and we don't have to think harder about what happens with liquid manure? And what I really love about this map is it puts me in a position to really start talking intelligently about those decisions, because when we look at some of the counties in Iowa that get manure heavily utilized in them, those conversations should be happening, right? They should be starting to happen, and we didn't really have great data to facilitate them. And I think this puts us in a position to help do that, rather than saying, "Hey, this county has more manure than they can put in a manure plan, we can start saying yeah, but look, there's some large poultry facilities here. We know that those large poultry facilities tend to be trucking manure 40 to 60 miles. That gets it out of the county and where someone else can use it. We don't have to be treating liquid manure in that area, right? So I think it's really exciting for me to be able to put data behind that discussion. And then the last place that I wanted to think about this data is: we hear a lot about water quality these days, and how much of that is nutrient management. How much of that is, we need to find a way to more fully utilize cover crops? What's happening in different areas? How do we compare watersheds? And one of the things that always comes out of those discussions is we need a good framework for areas that are getting manure, areas that are getting commercial fertilizer, and the reason I say that is oftentimes manure gets a disproportionate number of finger points at it, and whether fair or unfair, if we don't have data to help people understand, is it really manure? Is there manure in that watershed? How much is it accounting for? It's hard to talk about it from a science or data perspective. Now the good news is, since we colored pixels, we could break it up by watershed of various sizes. And in the bottom right there, we did it in a HUC eight watershed, so hydraulic unit code size eight, to sort of say these are the watersheds that have a fair amount of land receiving manure. These are watersheds that don't have a lot of land receiving manure, and we're really hopeful that that will help people with modeling in the future. So, still a work in progress, but I really wanted to highlight where we are, get you to start thinking about what do these agronomic decisions that we make mean for manure, how far we're moving manure, and hopefully I did that for you at least a little bit today. I think it's an interesting area. It sets us up for understanding what farms might do nutrient treatment. Where might infrastructure to help us transport manure make a lot of sense? Where might reduction in friction related to manure trading or manure sales make a lot of sense? And we finally have data that's geolocated to really help us understand how farms are moving manure. So I think that's really exciting. Hopefully, helps push the conversation forward and gives you something to chew on as you think about what am I going to do not today, but in the next decade to help us all use manure better and take advantage of that fertility supply it offers. So, with that, thanks for tuning in today. Thank you for joining this installment of Talkin' Crap. Be sure to take a look at the show notes on our website for links and materials mentioned in the episode. For more information or to get in touch, go to our website www.extension.iastate.edu/immag/. If you found what you heard today useful or it made you think, we hope you subscribe to the show on your podcast app of choice. Signing off from a job that sometimes smells but never stinks, keep on talking crap.