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Welcome to University of Minnesota Extension's Nutrient Management Podcast. Each month we bring you the latest research in nutrient management for crops and how you can incorporate the latest tips and best management practices to your farm.
Hello and welcome to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I'm Jack Wilcox in the Extension Communications bullpen.
Jack Wilcox:Today we'll talk about the complexities of manure nutrient availability. I'm here with Brad Carlson, Extension Educator from Mankato and Extension Manure Nutrient Management Specialist Melissa Wilson from St. Paul.
Jack Wilcox:Brad and Melissa, explain where that complexity in manure nutrient availability comes from.
Brad Carlson:Of course, the premise of our podcast here is we're talking about nitrogen. It's our Nitrogen Smart podcast series. But, really, manure is kinda complex when it comes to that because there's all kinds of nutrients in manure. There's obviously nitrogen, phosphorus, and potassium. But in addition to that, there's micronutrients and and, you know, then there's a lot of stuff in there that adds complexity to manure management, you know, not the least of which is water, which involves a lot of weight, which, you know, kinda adds to the complexity of the economics.
Brad Carlson:You know? There's not a lot of, I've always said there's there's the economics of hauling water up and down the road isn't really good. But but, there's carbon in there, of course, which can involve tying up some of the nutrients that are either in the manure or otherwise and on-site and so forth. And so, you know, manure is is complex when it comes to that. And so in addition to that, of course, when we put on fertilizer, it's a standard chemical product, and we know exactly how much of each of those nutrients are in there.
Brad Carlson:And with manure, we're not always quite so sure.
Melissa Wilson:Yeah. I think the heterogeneity is one of the biggest factor manure that makes it so complex. You might pick up a handful of manure from one area of a storage, and it's gonna have completely different NPK than grabbing a handful from another area. Say you had a lot of sawdust in one area versus urine in the other area. So the complexity is also in the heterogeneity.
Brad Carlson:Yeah. And and and mixing it up and trying to get it to be a little more consistent, of course, not only for the sake of developing a management plan, but when it's applied out on the field, we, you know, we need consistent nutrient availability out in the field in order to be adequately fertilizing our crops. And so it it... Particularly, like, with solid manure, as you alluded to, Melissa, it can be pretty challenging, you know, especially if you're using a a high carbon bedding source you referenced using sawdust like in in poultry or maybe some dairies are still bedded with sawdust. But also, like beef manure, if you're bedding with cornstalks, grabbing a representative sample or getting it mixed up, really good can be pretty tough.
Melissa Wilson:Speaking of the availability and all the different species you mentioned there, the availability really does differ based on species as well. We know our bovine species, the dairy cattle, beef cattle, sheep, goats, etcetera. Just the way their digestive gut works oftentimes means that the nitrogen from the manure will release a lot more slowly than something like our swine manure or poultry litter, etcetera. So those things really affect availability of it as well.
Brad Carlson:Right. And, you know, we focused or just mentioned a little bit about the whole bedding situation. It's... It it it... Again, it it adds that level of complexity that, not only do we have a different situation with bedding where cattle are gonna have, you know, typically a deeper type of a bedding.
Brad Carlson:Hogs, in a lot of cases, have no bedding at all. They're indoors, and they don't need to worry about the climate, and so we don't bed them. You know, poultry is, you know, somewhere in between there. But then you've got the whole issue of how their digestive systems work as well as then what they get fed, you know, because your arominent animals are gonna get fed some pretty high carbon sources. They're gonna get hay.
Brad Carlson:They're gonna, you know, they're gonna get long chains of carbons in their diet versus your nonruminants of your poultry and your your your swine are are not going to get those kinds of feeds, and and that, of course, is gonna make a difference on what's coming out the back end also.
Melissa Wilson:And then to make things more complicated, how you apply the manure is gonna affect how everything breaks down in the soil as well. Putting it on the surface, you might see more gaseous losses. Nitrogen's gonna convert to gas, ammonium in particular. Getting it incorporated might preserve some of that ammonium, but, you know, that includes soil disturbance.
Brad Carlson:There's gonna be... Obviously, how you apply the manure, is gonna vary a lot from farmer to farmer, but an individual farmer probably doesn't change up how they're applying manure a whole lot. In a lot of cases, they kind of got their method, whether it's their own equipment or they're having it done from a custom applicator. You know, most farmers know exactly how they're going to be applying their manure, how they're gonna be handling it. So at least from that standpoint, it allows you to develop a management plan without having to worry about having a lot of curveballs thrown into it.
Melissa Wilson:Yeah. That's true. Yeah. I would say, though, if people are considering maybe some of the low disturbance application equipment that's starting to come out, just making sure that manure is covered as much as possible and making adjustments to the equipment if needed to get it incorporated is kind of one of your best bets for preserving nitrogen. We've seen, like, people over years have moved to double disc where it basically dribbles it on the surface and throws soil over the top.
Melissa Wilson:That's great. Even removing more from, like, sweeps and knives to the disc injectors. But sometimes if you're just opening the the slot for the menorah to go into, it might kinda spill over onto the surface. So if you have closing wheels on that, that can help reduce some of the ammonium losses too.
Brad Carlson:And how much time the... Because of the components of the manure and particularly the amount of nitrogen that may be in the ammonia form or being evolved as ammonia, which, of course, is subject to being basically evaporated and blown away with the wind. You know, laying it on the surface can be a bit of an issue. And so, you know, historically speaking, most manure... You know, if I went back to, like, when I was a child, most manure was just simply put on the surface.
Brad Carlson:Incorporation happened sometime. You know? In a lot of cases, it may have been weeks or even months. You know? The the the real concern was just getting the manure applied and getting it out of the farmstead.
Brad Carlson:It wasn't so much about the nutrient availability, but we know a whole lot more now about the interactions between the climate and manure and the nitrogen. With the cost of fertilizer, the cost of nitrogen, it really kinda makes it imperative to be managing manure in a way that tries to retain as much of that nitrogen as possible. I know, you know, going back in my career, there seemed to be an awful lot of concern about manure odor. I don't wanna say that that doesn't exist anymore, but a lot of the best management practices that were put in place to try and minimize odor were actually pretty beneficial for respect of trying to retain as much nitrogen as possible also.
Melissa Wilson:Odor is definitely one of the reasons why here in Minnesota, I think a lot of people were pushed to incorporate. I know sometimes here in the cities in the fall, if you get the right wind blowing from the right direction, it smells like manure here too, and I'm always thinking, well, that's nutrients getting back out on the soil.
Brad Carlson:Yeah. And if I look at some of the charts, you know, if we look at, like, swine manure, if it's if it's injected and immediately incorporated or or sweep injected and so forth, you're looking at 70 to 80% nitrogen availability in a lot of cases, maybe even higher. I don't know if if you've got newer research that indicates that, Melissa. But but if you leave it lay on the surface for, like, four days, you know, you've lost, like, half of... Or more of the nitrogen is just simply blown away in the wind, and so it could be pretty significant.
Melissa Wilson:The ammonia losses with swine manure can be pretty high. I think on average, we see most samples come back, like, 75% ammonia out of the total nitrogen. So especially leaving that on the surface, the best thing you could do is get that covered up. That's just one of the things we like to point out with these disc injection systems. If you're not closing that area or that slot where the manure is being placed, that's where the ammonia losses can come from.
Melissa Wilson:And that is why we see a bit of differences, like, from that 70 to 80%. The more you close it up and get it covered, that's more like 80% availability then because you haven't lost as much. And the 70% is usually when there's a little bit maybe kind of access to the to the air.
Brad Carlson:And I don't know if we've got good research on it, but I guess intuitively, if you're applying manure, for instance, on a field that's corn on corn and you're dealing with a lot of corn residue, that residue could be interfering with getting good coverage over top of that manure also. So I think that's something at least to be to be wary of. You know, if you're injecting it and just flat out going below the ground, not such a big deal. But if you're trying to use some kind of, like, double disc closers, and you're applying it on cornstalks, you do need to be kinda concerned about whether you're actually getting the soil thrown on top of the the, manure and whether you're getting it at all. You know, I think another thing that we we need to pay attention to and...
Brad Carlson:Is the fact that phosphorus loss in particular comes from the surface. And so if we end up with a lot of runoff, water runoff from rainfall, particularly speaking, we can lose a lot of phosphorus also, and that's a pretty major water quality impediment. And so, by simply incorporating the manure into the ground, we can prevent a lot of that phosphorus loss too.
Melissa Wilson:There is actually a study out in Ohio that, you know, they had a lot of phosphorus issues going into Lake Erie, and they switched to doing a lot more no till because, you know, we always thought a lot of the phosphorus comes from sediment. And so initially, phosphorus levels did decline that were kind of ending up in Lake Erie, but then they did start to increase, and it was because manure application was now happening on the surface rather than having incorporation because they switched to no till. And they started seeing a lot more dissolved phosphorus ending up in Lake Erie, which is more of a pollutant than kind of that phosphor... Or the soil bound phosphorus. So even if you're doing no till, maybe Right.
Melissa Wilson:Kind of doing some incorporation once every couple of years can really with that.
Brad Carlson:You know, and historically, we've talked a lot about phosphorus doesn't leach, and it has a lot to do with the... With phosphorus chemistry and its interaction with the soil. It doesn't have necessarily so much to do with the water. And so if it's laying on the surface and it interacts with water, it will dissolve in water and and wash away. And so that is...
Brad Carlson:You know, that's just definitely something you gotta be careful of. And, you know, I... And I think even, you know, beyond the beyond that runoff on the surface and some of those no till situations, there also is concern about macropore flows, about, you know, kind of permanent cracks and root channels and wormholes and the fact that water could move really quickly into some of those... So those large pores in the soil. Things that we would define as being good soil health, actually ended up being a bit of an impediment as far as water quality because it allowed water to infiltrate fast enough that there wasn't adequate interaction with the soil to bind the phosphorus to it.
Brad Carlson:So let's talk a little bit, Melissa, about best practices as far as doing surface application. Maybe don't see so much of people just broadcast and surface applying. I still see some of it because for some farmers, it kind of matches with their application practices. They may have tillage equipment. You know, it may help them with with with the tractors being spread out, and and...
Brad Carlson:Well, we know you can surface supply really fast if you're not worrying about incorporating. And from that standpoint, it doesn't take quite so much horsepower either. What exactly is that nuance as far as how much time and and the amount of nitrogen we can lose with with... When we get the Manure incorporated.
Melissa Wilson:Gas losses happen within the first twelve hours, and it's like... It kind of decreases pretty rapidly within that twelve hours. That's why we say getting it incorporated as soon as twelve hours or getting it injected is kind of your best bet for preserving nitrogen. And then it just slowly, continues to release over time. So it's really critical to get it kind of incorporated into the soil as quickly as possible, but it gets to the point where if you don't incorporate it within, you know, four days, then pretty much most of the ammonia has been lost.
Melissa Wilson:We have some data that shows that if you surface apply it, and there's a difference between liquids and solids, 10 to 25% of your ammonia is gonna be lost if it's a liquid that's surface applied, and it's higher for solids. 15 to 30% is gonna be lost if you just surface apply it. And the difference between being that liquid does soak in versus the solids just sit right on top so that ammonia is more exposed. Of course, that can fluctuate though if you put liquid manure on the surface of a very wet soil. It's not gonna incorporate or it's not gonna infiltrate nearly as fast as if it's a drier soil or if you have a crust or something like that.
Melissa Wilson:But incorporating it within a few hours, you might lose one to 5%, and that's regardless of whether it's solid or liquid. Injecting it's anywhere from zero to 3%. And then if you're irrigating, which we don't actually see too much of here in Minnesota right now, it's a little more prevalent down south. You might actually lose, you know, 30 to 40% of it, but you can kind of imagine having a high ammonia liquid flowing through the air, especially if you're irrigating. It's probably warm conditions that's really gonna drive ammonia losses.
Brad Carlson:And what about poultry manure? Because we see a lot of that gets delivered at kind of at harvest time. You see the piles on the edge of the field, and the crews are kinda moving around, you know, with the the, the surface spreaders and the front end loaders to to load those things up. And so in a lot of cases, that stuff is getting, fanned out on the surface and then by a commercial applicator, and then the farmers gotta come back and work that stuff in. Same thing, or in some cases where that's been composted, if we already kind of lost a lot of that nutrient?
Melissa Wilson:That's a... It depends. One good scientist answer. Right? One of the things is, like, it's got so much nitrogen, but actually only a small fraction of that is ammonium. It's roughly 25% on average.
Melissa Wilson:So if you're piling it up, like, they'll have obviously some ammonia losses from a surface. But if that develops a nice crust from rainfall and that sort of thing, that kind of blocks some of that ammonia losses. But, yeah, like you said, if you're spreading it out or just moving it a bunch of times, the ammonia losses can potentially be high over time. One of the things I joke about is, like, one of my first experiments, we went to get some turkey litter. So there's a pile outside the barn.
Melissa Wilson:We were digging it into our containers, and these white plumes kept coming up. And I thought it was just like... It was kind of a cold morning, so I just thought it was like steam coming off the piles. And then I accidentally got too close to the pile and took a big whiff of one of those, and no. That was straight ammonia.
Melissa Wilson:It felt like it singed my nose hairs off.
Brad Carlson:Not fun.
Melissa Wilson:It goes to say that, like, goes to show that even though it's not a high proportion in poultry litter, the ammonia, it's it's still a lot just because there's that much total nitrogen in there.
Brad Carlson:So a recommended practice for most farmers is probably then to be in touch with the, commercial applicators and to be kinda ready to be out there, digging that stuff in, as soon as it's getting applied.
Melissa Wilson:Yeah. I think for poultry litter, we say that you get 70% availability if you get it incorporated within twelve hours. Goes down to 55% if it's between that twelve hours and four days. So you do lose some of it, and then it's down to 45% if you do not incorporate that. And that's mainly because most of the ammonia's gone, but there is a good fraction of it that's still in the organic form that's left.
Brad Carlson:Let's shift gears now and talk about, knifing it in. So, we don't see as much of the old straight knives. I know thirty years ago, there was an awful lot of that stuff, but that's still out there. I mean, you know, the the the sweep injection ends up having a lot of extra horsepower because you're moving that much more surface. There's a lot more disturbance going on.
Brad Carlson:So there still is, you know, people that knife manure on, still is a fair amount. You know, what's what's the best practice for knifing it on?
Melissa Wilson:Like I said, a lot of people have moved the discs, which is very similar, just less horsepower because it's actually rolling. In those cases, our low rates are probably gonna soak in pretty well. So the swine manure, etcetera, that's gonna soak in pretty well and not remain on the surface. But when you have pretty high rates like dairy manure that just... It's so much volume of liquid that it takes longer to soak in.
Melissa Wilson:So that's kind of what I was talking about before. If you have some closing wheels or something on the back end that can help kinda cover that up or kind of pinch off the top part, that's kind of your best case scenario for reducing the ammonia losses.
Brad Carlson:Well, and I I know there can be a lot of issues with... Not just with compaction, but just simply with kinda what you do to the soil structure if you're applying too wet. But when you're... If you're injecting manure and it's too wet, a lot of cases, that manure doesn't go down the way you want to. It it...
Brad Carlson:For one thing, the slots tend to stay open and end up finding a lot a lot of a backup on the surface too.
Melissa Wilson:Yeah. We've even seen that with some of our, like, heavier soils where just... It's not that it's not closing. There's just such big clods summing up that they're not kinda resealing behind it.
Brad Carlson:Right. I mean, that's one of the reasons why there's a lot of preference to get that put on in the fall. It allows the freezing and thawing. I mean, freezing and thawing doesn't go real deep, but the top six inches freezes and thaws back and forth several times in the fall, several times in the spring. It helps loosen a lot of those clods up as opposed to those spring applications.
Brad Carlson:You're just kind of hoping that you have ideal conditions when you're putting it on if that's the case. So there was a lot of movement towards sweep injection again thirty years ago. I don't see so much of it anymore. Again, it's just... I think it's just a horsepower issue.
Brad Carlson:I think everybody's kinda decided that the double disc closers and laying it on the surface and the double disc closers just simply have so much less horsepower and equipment wear and so forth. We just don't see that much sweep injection anymore. Obviously, there's some of that equipment out there. If that's what you got, it's not just a simple thing to say, oh, I'm just gonna sell my equipment and go buy new. That being said, we just don't see that much of it anymore.
Melissa Wilson:I guess I should say that the double discs that band... Or dribble on the surface and then throw soil up over, we basically treat that as broadcast with immediate incorporation,
Brad Carlson:Right.
Melissa Wilson:Just in case you are wondering how to deal with that for your nitrogen availability factors.
Brad Carlson:A trend that we saw years ago, it's still out there some, was, using the the airway, equipment. Particularly, we were seeing that in no till situations where farmers wanted to do luminaire application. They didn't want, you know, have a a full width, disturbance of the surface because they had a long history of of either no till or strip till. Also saw some of that for pasture applications. You know, something that gets a little bit undersold is, where we do have, pastures.
Brad Carlson:Those pastures do respond very positively to fertilizing them. And so this is a way to get that accomplished because, obviously, you know, just surface supplying fertilizers in a pasture is is sort of a guessing game too as to whether or not that ends up getting down to the plants or not. You've done some research on airway stuff.
Melissa Wilson:No. I haven't.
Melissa Wilson:No. I haven't been able to get my hands on one because
Brad Carlson:I hear... I thought you did. Oh, wow.
Melissa Wilson:I don't know that they're really sold that much anymore, at least when I was last in the market for one. But our colleagues over in Wisconsin have used one, and they've basically found that the the airway system, it's it's supposed to help increase infiltration for liquid manures. But the high rates that they were using, so this is, like, 20,000 gallons of dairy manure, for instance, it still just wasn't enough to increase infiltration enough to reduce ammonia losses. The surface applied was pretty much the same as the airway applied, but the injected manure was way lower ammonia losses than the other two. So that's probably one of those things again, and it kinda depends on the rates if it makes a big impact.
Brad Carlson:I I was personally at a demo one time, and this is a while ago, where they were doing an an manure application from swine farrowing barns in pasture and in some grass pasture where beef cattle were. I mean, I was really scratching my head as far as what act... What actually was probably the amount of nitrogen being applied. Now given the fact it was grass pasture that probably wasn't going to get a, for instance, a broadcast urea application to fertilize it. They probably were alright with whatever it ended up being, but it can be...
Brad Carlson:That could be pretty difficult to predict just given what that circumstance is. Yeah. Alright. So we'll just kinda wrap things up here. So, you know, there's...
Brad Carlson:When we... When it comes down to doing a manure management plan, you've got your manure analysis, and you've got the amount of nitrogen that's in it. It really comes down to if if we want to be making a plan based on manure, to the amount not just available in the manure, but also how we're applying it. And so we need to account for whether we're surface applying it and the amount of time between in the application and the incorporation. We need to worry about whether it's injected, and whether it's sweep or whether it's it's knife injected, although that difference isn't huge.
Brad Carlson:And there's gonna be some differences also in liquid and solid. So, again, it's kind of a complex system, but for most farmers, they kinda know what they have personally as far as manure and what they're doing as far as application practices. And so while from a big picture standpoint, it's complex, most people are able to kinda get narrowed in on where they actually need to be themselves.
Melissa Wilson:I agree. I also think it's probably healthy to question if there's anything you could be doing better, though, too. And thinking about preserving nitrogen is... Especially in these days with how expensive fertilizer is, is how you're gonna get the best bang for your buck. Remember, you you paid for this nitrogen in some shape, way, or form, whether it was fertilizer or with the...
Melissa Wilson:You brought in feed, whatever it might be. You know, why pay for it twice by letting it be lost and then having to buy more fertilizer again? So Yeah. Trying to keep the nitrogen on your farm is always always good.
Brad Carlson:You know? And it's really not necessarily a a topic that that we kinda had for today, but I think it's worth mentioning in this context. There's at least one tool available for determining if you put enough nitrogen on the the basal stock, nitrate test, which would involves going in late season. It's too late now. You know, the date we're recording this is kind of...
Brad Carlson:We... We've hit physiological maturity for our for our corn plants. But if you think that what you're doing is not applying enough nitrogen, you can go in and sample some of the the the stalks at the bottom of the corn plants and have them analyzed. And it it won't it won't allow you to get real precise, with where you're at, but it will definitely tell you if you're underfertilizing or overfertilizing. And I think in this particular case, that can actually be a tool too.
Brad Carlson:So, that's something we'll cover in more detail in another podcast, but I did wanna throw that out there that in this circumstance is something we can at least be thinking about.
Jack Wilcox:Thank you to Brad Carlson, Extension educator, and Melissa Wilson, Extension manure nutrient management specialist. Thank you both for being here.
Brad Carlson:Thanks.
Melissa Wilson:Thanks.
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.