Talkin' Crap

The Power of Manure Timing: Enhancing Nitrogen Efficiency

• Dan Andersen • Season 1 • Episode 8

Share episode
Dan Andersen is joined by Jake Willsea, a graduate student at Iowa State University, to discuss his research on in-season nitrogen application management using the 360 Rain irrigation machine. Jake analyzes long-term studies from the University of Minnesota and shares his findings about side-dress and fall nitrogen. Find show materials here.


Dan Andersen:

Music. 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/diversity/ext. 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 in areas of innovation. Hello, and welcome to this installment of Talkin' Crap. I'm your host. Dan Andersen, associate professor and extension specialist in the ag and biosystems engineering department at Iowa State University. T his week, I have Jake WilLsea, a graduate student at Iowa State University, joining me. Jake, could you tell us a little bit about yourself?

Jake Willsea:

Sure. My name is Jake WiLlsea and I'm a grad student. I'm originally from Michigan, and I came out here to pursue my masters. For my project, I'm working with a company called 360 Yield Center and a piece of equipment called the 360 Rain, which is a high, high clearance automated irrigation machine. And we're looking at that from really three different perspectives. We're looking at it from a nitrogen management perspective, as a methane reduction tool and also an irrigation tool. So we want to see each side of that and how we can use that to our advantage for crop production. That sounds great.

Dan Andersen:

It's definitely an interesting piece of equipment. I think you're really working hard to understand each of those three things. And today we get to focus on that in season nitrogen application management perspective. And you've been putting together a few things for us on that. And before we dive into the sort of review and where you're at on that, I want to do, to do just a little bit of a review of the nitrogen cycle and especially how it's relevant in what we're seeing for results and what we expect to see. You want to take a shot at the nitrogen cycle in terms of manure and how it moves through soil.

Jake Willsea:

I can give it a try. So really, the nitrogen cycle, the important part of it is how these different forms of nitrogen are going to be moving. So in cases where you're going to be losing, mostly losing your nitrogen, so you'll either lose it through the soil, typically, nitrate will be lost through the soil, through leaching, because it moves very well with water. Now, a lot of your swine manure is high in ammonia or ammonium, and so you can lose that to the atmosphere through volatilization. So we're just trying to really cut down on all these different pathways for loss so that we can keep the most on the field for crop use.

Dan Andersen:

Absolutely. And I think you nailed it. When we think about that nitrogen cycle, there is that gaseous form ammonia, and we talk about manure application methods, we're really concerned about getting the manure in contact with the soil, into the soil quickly to minimize that. But after that, it's all about nitrification and turning it into nitrate. And you focused on leaching there, right? And that's the one we think about most often in Iowa. We hear about nitrate concentrations and tile lines, and that's a result of some of that nitrogen making it to nitrate form and leaching with water moving to the soil. And then there's some denitrification that can occur, and that one's certainly harder to measure and harder to get good estimates on. So the leaching one makes a lot of sense to think about. One other thing I wanted to touch on before we move around is sort of that leaching aspect, and how wet and dry years can make a difference in that. Certainly you don't get to pick your weather year. It is what it is, but is there a big difference in how much nitrogen we might lose in some of those years?

Jake Willsea:

There definitely is. If you're not having water moving through the soil, you're not going to be losing nitrogen due to leaching. So if we have a dry year like we did last year, a lot of our leashing effects will probably be minimal. That's not to say that other other pathways for losses aren't working either, but in a wet year, you'll tend to see a lot more nitrogen loss and probably a yield hit if you're applying earlier in the year when you have all that rainfall that it needs to hold up to perfect.

Dan Andersen:

I think that hits it on the head. That's one of the things that's a challenge about this. Is we can say what things are like on average and what we think is going to happen, but the weather of any given growing season, any year, really has huge impacts on what actually happens and what we actually see, and how we have to work to interpret some of those results. So one of the things you've been doing to get us started on understanding what the potential value from in season nitrogen application was, was really focused on some literature reviews, and you looked at two things, but think I'm really interested in starting with a review of some work you did from Minnesota studies. Can you tell us, sort of what they did for a study, and then what you've been doing with that data?

Jake Willsea:

Yep. So I looked at a study out of the University of Minnesota. It's a very long term study out of Lamberton, Minnesota, which is one of their extension stations. The studies range from 1960 to 1996 and so I looked across the entire range of those studies, using the maximum yield of those studies as really the baseline, or the normalizer, so I could normalize everything to the max yield. That way I can adjust for the changing trend line yield across years.

Dan Andersen:

So in each year, you picked out whatever treatment had the maximum yield and said that's 100% of the yield we could achieve. And every other yield got normalized to that. So it was 50% or 90% of that maximum.

Jake Willsea:

Yep, exactly. So across all of those years, I compared fall, spring, and side dress. They had different nitrogen rates at each of those different timings. They also looked at different fertilizer types.

Dan Andersen:

So can you tell us anything about what they meant when they said side dress. Was all the nitrogen applied in season? Was it a split application? What was happening there?

Jake Willsea:

Side dress was a broadcast application of whatever fertilizer they were using at that time, and it was all in June. So whenever the weather allowed in the month of June, they would apply it .

Dan Andersen:

Perfect. And the fertilizer types here, they were all commercial fertilizers. These weren't actually with manure, but nitrogen is nitrogen in some sense. So I think using them as a baseline for understanding and especially one of the things we're interested in rates and different rates and how that impacts this, and that's hard to do with manure, so we often could find data with commercial fertilizers, but much harder to do with manure.

Jake Willsea:

Right, right.

Dan Andersen:

Okay, so what have you learned from that? What's it showing you?

Jake Willsea:

Well, across all of those years, there was a relatively tight grouping between spring and side dress, which it makes sense, because compared to the length of time between a fall and a spring application, about six months, there's a lot more time, a lot more opportunity for losses there. But between a spring and a side dress application, there's only about a month and a half that you're really going to be losing. So a lot of those values were pretty similar. But in general, the closer we got to the planting season, or the closer we got to crop use of that nitrogen for application, the better.

Dan Andersen:

And for those of you listening along, we're going to have a plot of this data in the show notes, so you can take a look at that for yourself. But it is an interesting graph. I think, it's like Jake said, there's a bigger difference between fall and spring than there is between spring and side dress, right? And it makes sense from what he said, it's just exposed to more water, more weather conditions and potential for loss. When I look at the graph, it looks like one of the things that we see is, as we get to higher rates, all the yields get to the same level. Is that true? At least pretty close.

Jake Willsea:

Yeah. So once you get to a certain point, even if you apply in the fall, but you're really applying a really high rate of nitrogen, you're going to be hitting about your maximum yield.

Dan Andersen:

So, when we think about this, it's not like changing season changes what our yield potential is. It just changes the amount of nitrogen to get to that yield that we might think about or need. And another way you and I have talked about that is sort of what efficiency or how effective is that nitrogen for us at influencing corn yield. And I think you decided that spring was going to be our standardizing number. Is that true?

Jake Willsea:

Yep. So I decided that we would look at it from spring is going to be our baseline, and we wanted to see what the power is with this nitrogen, if you apply it in seasons other than spring. So we looked at for a fall application, we saw that it has about 78% of the actual power of 100% in the spring.

Dan Andersen:

of nitrogen. If I'm putting it on the fall, on average, I'm getting about eight tenths of a pound of nitrogen that I put on, effectively causing yield, and the other two tenths is, who knows where?

Jake Willsea:

Yep, exactly.

Dan Andersen:

And then what'd you see if they were side dressing?

Jake Willsea:

For a side dress, I saw it was about 113% so 13% of a yield increase, or a increase in power of that nitrogen.

Dan Andersen:

So moving it more in-season, it improved our nitrogen use efficiency. It didn't necessarily lead to more corn, but it let us make it a fertilizer application decision that would be a little bit lower, because there's more more nitrogen that we're actually taking advantage of or capturing, presumably, because we're not having as many losses. Did you do anything to try and understand if you could relate it to the potential for loss, or it was all related to loss.

Jake Willsea:

So, I looked at this in terms of rainfall, because this is all based out of the same experiment station in Lamberton. I could found historical data from that location, and categorized years into either a dry year, an average year, or a wet year. So a dry year was anything that was more than one inch below average for November to June rainfall, and then a wet year would be greater than one inch over the average.

Dan Andersen:

And can you tell us why you picked that November to June rainfall? What's the choice there? Why'd you pick that ?

Jake Willsea:

So November to June rainfall is the amount of extra rainfall that the nitrogen would experience if it was applied in the fall versus side dress.

Dan Andersen:

So that rainfall is really an indicator of potential for loss, either through leaching or denitrification. Okay. So what you find when you group those together into those three classes?

Jake Willsea:

So I found that in wet years, as you might expect, there was a much higher potential for loss. We saw that it was about a 0.1, so a 10% reduction in your yield for a wet year. Compared to a dry year, you might have about a 5% yield loss if you applied in the fall versus side dress, but it could be anywhere from 5% to no change at all. So in wet years, overall, we're seeing that there's a lot more potential for nitrogen loss and yield loss due to that nitrogen deficiency.

Dan Andersen:

Perfect. I think you really pointed out one of the harder aspects of this. Well, you can group these and you got statistical differences between the groups. There's still a lot of variation that just occurs because of maybe soil conditions or weather conditions. There are particular timings of rainfall. So it's it's easier for us to say, well, we can group it. We see these statistical differences. But when you try and make a fertilizer decision in any given year, that's a little bit more challenging. We can say, in general, we see this, or we know that wet years, as you pointed out, probably are riskier for nitrogen loss, and we tend to see that that did indeed at this Minnesota site cause that change. But if we were going to try and say, Well, what does this year look like, it's hard to make that determination. Is that fair?

Jake Willsea:

Yeah, that's fair, and that's something that I really do like about this Minnesota data. It's all from the same location. So by doing that, you're cutting out some of the variables like different soil types or different locations. And I think that's a real benefit of having that. But if we want to be able to do this on a large scale, we need to take a look at different sites and different weather conditions, which can be more of a challenge to analyze, but it's important to look at.

Dan Andersen:

Perfect and you've been giving that a try as well. That was one of the things we said is, does this site actually represent Iowa, or does it represent the Midwest? Right? So I think you did a summary of some Midwestern data. Could you talk us through that? And is there any differences between what you did for the Minnesota analysis or this, this Midwestern data?

Jake Willsea:

Yeah. So I looked at about 20 different sites for the Midwest overall. And again, this data ranges from back in the 60s all the way to about modern day. So I got a good range of years and weather conditions and locations, and by doing that, we found a very similar result as we found in Minnesota, but with some more variation, and that variation might be to due to the fact that it's different weather conditions, but it could also be the soil and different temperature effects that you might see in different locations throughout the Midwest. But in general, we found again, that fall application had the least effect or the most opportunity for loss compared to a spring or a side dress application. So when possible, you should strive to get that nitrogen on later in the season, if you can.

Dan Andersen:

Perfect. And I think that's that's fair, right? Soils are really important. We hear this talked about in Iowa. I know I've done a fair amount of work at Nashua, and one of the things I'll say is Nashua soils seem flashier than some of our other research sites, and that's code for me that I don't really understand why it seems more sensitive to timing, but it does, right. And I think trying to get a handle on that variation, it's encouraging that you saw a similar curve and got similar results. But your mileage may vary. The soil that you have, the weather that you experience, makes a big difference. For instance, as we go from the western Corn Belt, where it's pretty dry and you don't see much leaching, or to the eastern Corn Belt, where it's more humid, more precipitation, we're going to see that difference in potential for loss and drainage and and the Minnesota site sort of bears that out for you when you group it by years. But looking across a lot of sites, it gets more complicated. This is Talkin' Crap, so it's important that we hit on the manure notes of this and and all the studies that you looked at, unfortunately, were commercial fertilizer. Is that true?

Jake Willsea:

That's true. Yeah.

Dan Andersen:

So then we're gonna try and think about, what does this really mean for manure, and how do we place it in a manure context, right? And I think there's been a few studies out there. One that I really like is one that Aaron Sassman did here in Ames. He worked with John Sawyer, and it was a comparison where they put on anhydrous ammonia and liquid swine manure at two different times, either in October or November, and then with the manure, they had some Instinct rates that were used into it. So Instinct is a nitrification inhibitor. As Jake pointed out, that nitrate really is the form we're worried about moving in the soil with the water, it's very soluble. Nitrate carries a negative charge, so it doesn't like to stick to Iowa soils. So if you make nitrate and water moves through soils, nitrogen tends to move with that water. Nitrate is is a product. It's a nitropyrin that helps reduce the rate that ammonia gets turned into nitrate, so trying to hold it in that ammonium form longer. But I think what was really interesting to me in that John Sawyer study is when you compare his anhydrous ammonia and liquid swine manure, anhydrous ammonia early and late, had very little yield difference over the years he looked at and this was done back in 2011 to 2013 whereas that manure showed a lot more seasonality, the early manure suffered more yield loss at the same rate of nitrogen compared to that late manure. And I think there's a couple things we can think about this. When you work with anhydrous ammonia, you're putting it in a band. It's really basic. It stays in that little band, and it's not conditions that favor microbial activity. When we talk about manure, on the other hand, we're still putting it in a band. But manure is like eating cake for a microbe, right? It's got all the good stuff in it, nitrogen, carbon, and it really encourages microbial activity and gives us more chance to turn it into a nitrate. So that shouldn't come as too much of a surprise. I know I did a lab study where we incubated some soils and we hit them with different fertilizer types, and in my study, manure was very similar to urea and how quickly it nitrified, which I think makes a lot of sense. We're putting it on in that ammonium form. It does kind of resemble urea, except it comes with a fair amount of water. We also did anhydrous ammonia in that and we saw the same sort of effect as John Sawyer had, that that ammonia took a little longer to nitrify, and that was based on we periodically leached the soil. So every week we came through and we leached all the nitrate we could to try and see what was coming off, but saw a same, similar effect, at least with that. The other thing I want to point out with that John Sawyer study that I found really interesting is he was really doing it early in a late manure, so about a month difference in timing, and he hit it with nitropyrin, that Instinct product. And in that study, at least, the nitropyrin performed really well for him. Using nitropyrin early was almost equivalent to delaying that manure application until soil conditions were 50 and cooling, which I think is really encouraging. I know oftentimes we're stressed in the fall, and it's hard to get all the manure generated in Iowa, that 16 to 18 billion gallons of liquid manure applied in our timely window, and people sometimes feel like they have to start early. But at least in that study, he saw that nitropyrin was as effective as delaying that manure application. Jeff Vetsch, up in Minnesota, has done a similar study that was in southern Minnesota, so I think soils that really resemble the Des Moines lobe, and he saw almost the same results. Definitely, anhydrous ammonia was less sensitive to timing than that manure was manure application being delayed certainly helped improve yields. But again, he saw really positive results from adding instinct to that manure to try and help delay nitrification. So all very encouraging. And both of those studies occurred roughly in the same period, 2011 to 2014ish. Up at Nashua, Iowa, I've had the opportunity to do some similar types of studies. In this case, we were doing early manure, late manure and spring manure. And one of the things that we saw was that in wet years, even delaying that manure application wasn't as good as waiting till spring. But in the dry years that we had, they were very similar, right? It didn't matter what time we put it on, basically, fall was as good as spring. So the weather conditions in those years make a good difference. And when we talk about this and give you some insight into why we think it's important, we're not saying that fall application can't work. It certainly can. There are years where fall application will yield similar or better than Spring application for various reasons and and we saw those the last couple years when it was extremely dry at Nashua, and part it was probably related to compaction of equipment moving through the field when our springs are still dry, but at least a little wetter and no potential, or very limited potential, for nutrient loss. But I think at least when we talk about manure and and how it's working, and compared to other fertilizers, it's more like urea than it is like anhydrous ammonia. So having to think a little bit more about timing and being careful with that is really important to us. Now, I get told all the time by my friends in the manure industry that I talk about timing a lot, but I recognize there's challenges with moving to spring. I think it's important for us to pursue we see great fertility reasons to do that. I think with your project here, you're finding out that there might be some other reasons, especially related to greenhouse gas production.

Jake Willsea:

Yeah, definitely. So this is something that I'm hoping to get into maybe a different day on this podcast. But I think the potential for emptying your manure storage right before it gets too warm in season, so right before the hot months of the year, can really cut down on your greenhouse gas emissions, rather than if you're storing it all over the winter,

Dan Andersen:

Perfect. And we'll definitely have you back to try and talk about that and ways to potentially monetize it. But what I was hoping to get some insight from you and have a little discussion about is we know there's challenges with trying to move from fall to spring. Could you talk about a couple that you think and why the 360 rain might be interesting, exciting as an opportunity for that?

Jake Willsea:

Yeah. So one of the main challenges that you see with a spring application of fertilizer or manure would be the weather conditions. So a lot of the time in the spring you'll have wetter field conditions, and so it's a lot harder to actually get out in the field and apply that manure. Some years, even farmers are delayed in their planting. So if they can't get out and plant, they're definitely not going to find time to go out and spread fertilizer.

Dan Andersen:

And that's something that really was highlighted this year with 2024 is weather season. We were coming in relatively dry. We thought maybe we hopeful it'd be a nice spring, and then it seemed to rain enough just every day that we really didn't get. At as much production as we want it done in terms of getting out in the field and getting things done. And that's a really sensitive time. We know that corn needs to get in the ground to start collecting that heat energy, that solar radiation, and any delay can be difficult to handle. Sort of in the same vein, there's a compaction concern in spring versus fall and and we know that compaction is related to soil moisture, and springs tend to be wetter in Iowa, so that's just one of the challenges if we do try and move towards spring, you might have to deal with some more compaction issues, and trying to understand that, especially with tanks, is is difficult. The other thing I think, that we probably want to talk about there is some people have been trying to side dress manure, often with a tank or a drag line, and that can be successful, but the window is pretty short, and if that weather isn't cooperative at that time, we don't want a yes or no answer. And certainly we can side dress with commercial fertilizers and make that up, but with manure equipment, it's historically been hard to come up with what that solution is. The 360 Rain gives us a little bit more flexibility than maybe trying to dry line over standing corn. Why is that?

Jake Willsea:

Right. So in in a drag line system, you can really only fertilize up until V4 and then if that that hose drags over the corn after that, then you can do some permanent damage. Now, with this 360 Rain, it lays down the hose in a way that it won't drag over the corn. When it's making turns, it'll lay it down behind it, and it's a very controlled process. The other benefit for in season application is the clearance. So there's a 10 foot, 10 foot high boom on this machine. So it can even go out while the corn is fully grown 10 feet high. Now, as it's driving through, it'll it has these Y drops on it that'll drop the manure right at the root level. So you can still get that on the surface right at the roots, instead of applying it over top, like you might be forced to with a center pivot system.

Dan Andersen:

Perfect.I think that was one of the things that Thanks for having me. really excited me about the machine, is I like the idea of side dressing manure. I thought it, thought it was great. And then seeing the weather conditions that we've struggled with sometimes in the possibility of getting that done, and thinking about what it would take to manage risk in that system to make sure my storages never got too full. How much manure could we really do that way? I had concerns, and I think one of the things that's exciting about this is it alleviates at least some of those concerns. It offers the possibility to keep side dressing later, so if I missed that ideal window, as long as I had some nitrogen up there, didn't get nitrogen deficient, I could still get my nitrogen applied that as manure, rather than having to give up and switch to something else. Now, as we think about what we talked about today, or heard today, certainly, Jake's work showed that timing is important. I think there's a large body of research out there that has shown that fall application, you only get somewhere around 80% of that nitrogen that you're applying compared to a spring application. And that's real value that could be in your pocket, right? That's a savings of 20% if you can move from fall to spring on what your fertilizer bill might be for nitrogen, and if we think about side dressing, maybe even more potential benefit. That doesn't mean it's the right fit for everyone yet at this time, but it's certainly something that we're exploring and offers a lot of possibilities. One of our concerns is that the equipment to make that happen can be a little expensive, and what does it take to capture enough value to do that? How do we get that piece of equipment through enough acres, or make sure that we're reliably getting it done, so that we are getting the crop yield that we're hoping for and anticipating with never being behind on nitrogen delivery to the crop. But I think it's an exciting area where technology can make a lot of difference, and we're starting to see innovations where it's becoming more and more practical without having to rely on irrigation equipment that hasn't necessarily been practical or usable in Iowa, because we don't really need irrigation. So with that, thank you for your time today. It's been great to have you Jake and talk through some of these issues. And to the rest of you. Thanks for joining in. 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.extensiono.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.