Manure sampling and testing: Variability, guidelines & safety for your operation
Hello and welcome back to Advancing Nitrogen Smart, the special podcast series from University of Minnesota Extension. I'm Jack Wilcox in communications here at Extension.
Jack Wilcox:Joining us as always, we have Brad Carlson, Extension educator. And also today we have Melissa Wilson, Extension manure nutrient management specialist.
Jack Wilcox:Today we're gonna talk about manure sampling and testing. Melissa, how do farmers with manure know what they're applying?
Melissa Wilson:Well, one of the best things to do obviously is test your manure. One of the things that I've learned in my time working with manure is that it can be very variable, particularly because we're dealing with urine, we're dealing with feces, we're dealing with all of it that's kind of mixed together into one thing. Then if you're dealing with liquids, there's settling that happens so you end up with different nutrients kind of at these different levels in your manure. So sampling is always best and right now our recommendations are to sample it especially if you have a new barn sampling annually for the first three years is best to kind of get a baseline manure standard analysis and if it's pretty consistent, then you can probably go every three to four years after that but if there's any big changes, you add more water to it, there was a pipe leak, you change your feeding situation, all of those things might change it and then you'd kinda wanna get that baseline of three years again.
Brad Carlson:And I think it's important to realize that sampling is one of the few ways to really get a handle on it. In my years working previously as a county educator, I wrote a lot of manure management plans and particularly, you go back like twenty five years ago plus, very few farmers actually had manure test values and we were writing all those plans based on book values. And it was pretty rare when they actually got a test in that it was really close to the book value. And so the book value is just kind of a, it's an average and the variation can be pretty wild from there. Sampling is really the only way to get specific with your own operation as far as how you're handling manure, also it gets more specific on how you're feeding, how your water is being handled, how much air exposure there is from the manure because there can be evaporation.
Brad Carlson:It's possible to lose ammonia off of that depending on what's going on and so forth. And so testing is important, then as you point out, Melissa, testing is also a way to find out if something's going on that you didn't expect. If you suddenly get an anomalous value, you know, like you've got water leaking or something of that nature, that's a good way to find that out and get on it because I definitely have worked with farmers who had their numbers suddenly, you know, the test values dropped and they're like, what's going on here? Well, it's being diluted out by fresh water. And so so that's that's important to to get a handle on those things.
Melissa Wilson:I kinda have two stories. First one is that we've been working with labs across the country a bit, particularly here in the Upper Midwest. And we got a bunch of manure samples data, manure sample data from them. And looking at our swine manure, the middle 50% of all samples, kind of that middle average range, range anywhere from 30 pounds of nitrogen per 1,000 gallons of manure up to 60. So it really goes to show, like, you could be pretty far off if you're using that average, you know, 50 in the middle there, but you could be at 60 or 30.
Melissa Wilson:So it's really important to make sure you're sampling your manure.
Brad Carlson:And I guess just a little bit more about what the state rules say about this. If you're establishing a new operation, a new barn, you're required to sample for the first three years to establish sort of a baseline. From there on out, you really only are required to sample every three to four years, just from a matter of requirement, from a matter of recommended protocol, I think we talked about if in that first year you started having water leaking or something else is going on, it would have been nice if you'd have been sampling it annually. So that's kind of our recommendation. But then also anything that really changes with your operation.
Brad Carlson:And obviously, if you change up your manure handling, if suddenly you're doing liquid solid separation, obviously, now you don't really know what you got. If you're changing your pumping schedule drastically, if you've been pumping annually and now you're gonna start pumping twice a year, you know, that's going to change. But then also think on the livestock side, if you're changing your feeding, if you've got dairy cattle and you're changing your bedding, you should be thinking about taking a new sample in the swine side. If you're changing your supplements, if you hired a new nutritionist and they've changed a lot or if you've got a different feed company coming in. There are going be a lot of things that can make those numbers change, and so it's important just to stay on top of that.
Melissa Wilson:Well, it leads into my second story. So I had a farmer come up and talk to me after a talk, and we had been kind of discussing these possible changes in manure. And he said in his hog barn, he went from kind of old school waters, and they kind of leaked and dripped a lot, to one of these wet dry feeders. And he ended up having to change his manure handling because he was applying something like six, seven thousand gallons per acre before when it was more diluted. And then now he was down to applying like 3,000 gallons per acre.
Melissa Wilson:So he went almost in half just because there was so much less water in his manure. So again, another reason it's really good to test your manure in your specific situation.
Brad Carlson:Yeah. And would see that kind of a thing with there was a couple of swine operations that I worked with years ago that were farrow to finish, and so they had farrowing barns and then they had finishing barns and manure was all going into one place. And, you know, in a lot of cases, those smaller operations stopped farrowing and they just focused on finishing and that changed what was in the manure pretty drastically at that point. So let's talk a little bit about about the actual taking the sample and and when to do it. You know, there there's been a couple of different theories on that.
Brad Carlson:I mean, obviously, farmers are taking that sample because they want to know what they're applying. They wanna know what the rates should be. You know, the kind of the issue with that is the timeliness of taking the sample and getting it submitted for laboratory analysis and getting the results back and then being able to still use those numbers for this year's application. What's been your experience with that, Melissa? Because I find most farmers have just kinda thrown up their hands and said that that it's just too difficult to get that all done, realizing that if they end up with some value that they weren't anticipating, the best they're gonna do is correct for it the following year.
Melissa Wilson:Yeah. There's kind of two schools of thought. The one is to sample before you apply, and that you kind of have to take spot samples. So whether it's you have a big stack and you're trying to take, you know, handfuls from all over the stack, mixing them up and putting them together and then sending it out. Or for liquid, if you have like a big PVC pipe that you stick down into the liquid or a big cup that you have on the end of a pipe or something that you can try to get some spot samples and then sent and they get them back in time.
Melissa Wilson:But those cases, none of that manure is mixed as well as it is. Like when you're going to apply it, you'll be agitating it if it's a liquid or when you're loading it out if it's stacked manure, like you'll be able to grab handfuls from kind of all different depths of the pile. So the before application, the pros are you get the results back in time to make decisions if there is a difference than you're expecting, but the con is that you're not necessarily as accurate as when it's really well mixed. So applying or doing it at application when everything's mixed really well, you probably get more realistic results, at least more consistent results but you kind of have to use the results that you get back after the fact to make adjustments or make adjustments for the next year. So it's kind of more for planning for the next year then.
Brad Carlson:Well, and I think it's worth noting, and and farmers will have a better feel for this with their what kind of has happened historically with their own operations. But even if you're sampling at application time, if you're pulling samples, there can be some differences between the the beginning and the end, particularly if you're using some sort of bedding that's gonna be heavier and difficult to to agitate and mix into the mix into the solution. And so I know a lot of farmers also will will grab a sample at the beginning, the middle, and the end just to to kinda see what's going on there, and then they'll potentially be adjusting their rates as they as they apply just kinda based on what that's looked like over time. You know, you talked a little bit about this, Melissa, but what's your preferred philosophy as far as grabbing those samples? Does I mean, will anything do?
Brad Carlson:I know there are some sampling tubes out there for going into slatted floors or stick into the inspection hole and pull from the column of manure. What's been your experience with these things as far as how accurate they are and how much variability there can be?
Melissa Wilson:I think the biggest thing is to make sure either it's well agitated and mixed or, well, in any case, I think it's grabbing lots of small samples and mixing those together from different areas of the thing. We know with our liquids, like a lot of phosphorus will settle out to the bottom, which is one of the reasons why you see differences when you're pumping out from the beginning to the end. With our even our solids, don't see quite as much stratification so to speak but rainwater can affect things if you've had a lot of rain. It can kind of pull nutrients to the bottom, etcetera. So making sure you're getting samples from all different depths if you can, whether it's liquids or solids, is kind of the best bang for your buck and making sure it's really, really well mixed together.
Brad Carlson:I know from my experience working with farmers and manure testing and sampling, and I was involved with, again, twenty five years ago, we were doing a lot of manure spreader calibrations, probably had a lot more smaller operations with a smaller number of cattle in those days, with outdoor manure, kind of the whole, it was just in the lot, and then they cleaned the lot out and they put it in a pile. A lot of bedding with cornstalks can be very difficult getting a representative sample if there's a lot of course bedding in there, like like cornstalks and so forth. I guess, you know, ultimately, you've just kinda got to to do the best you can with that. I mean, you can't grab a probably not gonna to take something and start cutting pieces of cornstalk and shoving it into the sample jar. Doesn't work really well, but you also have to recognize that that's in there.
Brad Carlson:Furthermore, if you're routinely cleaning a outdoor lot out and then just putting it in a pile, recognize that what's out the what's out on the edge of the pile is gonna be different than what's on the the deeper interior of that pile. It's going to be more composted towards the middle, and you're likely to have lost some ammonia on the outside of that thing. So there's going to be some some differences in that respect also. You know, I think the the one area that tends to be quite consistent in my experience tends to be a lot of the poultry manure. Some of those facilities are still composting their their poultry litter, particularly if there's a lot of sawdust in there because that can otherwise cause some other issues when it's applied with the high carbon content.
Brad Carlson:But the composted stuff also tends to be fairly well mixed, and then a lot of the the commercial poultry facilities are supplying that information in advance. So when you buy that manure, you're you kinda know what you're getting. Those I feel fairly comfortable with. However, there's always some poultry manure that's getting cleaned out of the barns kinda right before it's getting hauled out in the fields. And so some of those situations, also have to be a little bit careful with with whether you've got a representative sample too because poultry is extensively bedded with sawdust, and and sawdust can actually be kind of a nitrogen robber out in the field if there's too much carbon out there.
Brad Carlson:So so you do have to kind of pay attention to that also.
Melissa Wilson:Yeah. Especially with poultry litter that's a little more fresh, so to speak. Any time there's cake out that has high nitrogen content because it has a lot more of the feces and whatnot coming from the birds versus stuff from the edge of the barns where the birds are not feeding or drinking, it's not quite as thick or dense there, so that's definitely gonna be a little bit different than a well composted manure.
Brad Carlson:And most of the places you're going to send the sample to will provide you with a sampling container. So obviously you're going to fit that manure or squeeze it into that container as best as possible. However, also realize that you probably should be cooling it. Probably don't want to take it in the house and put it in the refrigerator in the house, but hopefully there's some kind of shop refrigerator or barn refrigerator you can put that in to cool it down because remember, it's going to have to go through the mail in most cases. I mean, maybe you're close enough, you could drive it to the lab, but but most people are gonna put it through the mail.
Brad Carlson:So we've heard horror stories. This again goes back years ago before people really got a hang of it, of, producers, supplying their own jars and putting it in glass. That will, can build up gas pressure and actually blow up. And and, it you know, if a creek gets cracked in the mail, that's a problem too. So obviously, you wanna be using plastic.
Brad Carlson:You wanna make sure you screw the lid on tight. The post office is not gonna be real happy nor are your neighbors if they had manure leaking out in the mail and getting on the rest of the mail.
Melissa Wilson:I think there's actually an example when I worked in Maryland of a farmer who got banned from the mail for a little bit because manure leaked all over one of the trucks.
Brad Carlson:And I've also heard stories about these sample containers showing up in the laboratory where they had gotten excessively hot and they had built up gas pressure inside and when they opened the lid, it kind of blew manure out of the bottle all over the place and of course they don't really appreciate that. They are in the in the business of testing manure, so they expect to be exposed to manure, but I don't think they really want a blowing out of the top of the bottle all over everywhere.
Melissa Wilson:Well, just for that practical reason, you don't want a blowing up in anyone's face, but also it's literally changing the nutrient content if it's doing that too. So you wanna keep it cool to help diminish all of those changes that are...
Brad Carlson:And a lot of those places, in addition to supplying you with a sample container, they're also supplying a box to mail it in. So, it's easy enough to, put it in the jar, seal it up nice and tight, probably put a Ziploc bag around the jar and, seal that up tight in case the jar leaks, put it in the box, tape that up, and then put the box in the refrigerator. And we always recommended mailing them on a Monday. I think given kind of what most people's experiences with the US Postal Service these days, that's even more poignant than ever, that you would like that to hopefully get to the lab yet within a day or two and not be sitting somewhere in a sorting facility where it could be getting pretty warm.
Melissa Wilson:That might be a good reason to even freeze the manure ahead of time to give you a little more time too.
Brad Carlson:Correct. And and and so hopefully, they're receiving that within a couple of days of when you dropped it in the mail. I mean, from that standpoint, I know myself personally, I know exactly when the mail gets picked up at my local post office, and I live in between two towns, and in one town it's being picked up at 03:15 and the other one it's at 03:30. And so, you know, if you drove them into town, if they came out of the fridge and you drove them into town, you probably could get them on the truck within ten minutes of when the truck shows up every day and avoid it sitting around for longer too, and that would buy a little bit also.
Melissa Wilson:One of the things that I always like to bring up when we're talking about manure sampling is safety. There are certainly hazards with being around manure storages. Obviously, liquid storages, you don't want to fall in and drown, but there's a lot of hazardous gases that can be formed as well. Unfortunately, we hear every year of a death that happened in some state or another, even some here in Minnesota, where someone was overcome by manure gases. And some survive and some do not.
Melissa Wilson:So it's definitely something to consider. Minorum gases can be very dangerous.
Brad Carlson:And remember, sulfide is heavier than air. So it will settle if if there's no way of it mixing and it'll basically be in a layer and that layer will be deprived of oxygen. And so it may not always I mean, you know it's gonna smell because it's manure, so you're probably not clued off just simply by the smell. So really, you do need to be careful with that. I know another aspect, we're not really going to go down this road extensively about talking about inhibitors, but the smell of nitropyrin can be pretty overwhelming too.
Brad Carlson:There was originally some talk about mixing instinct into a manure pit and then agitating it, I think most people found they didn't really care for that either. Really agitating the pit when there's animals in there is a little bit risky as far as what you're gonna put off too. Mean, if it's a curtain sided barn and it's open, you might get away with it, but I think we all recognize that that's not good for the health of anything else either if we're giving off a lot of hydrosulfide or ammonia, Those are things that you don't wanna be breathing in. So, Melissa, do you do you guys have some you know, thinking about the podcasts are fleeting. Of course, I suppose anybody can go back and listen to this podcast as many times as they want, But what what else do you have available for resources?
Brad Carlson:And I know particularly a lot of livestock operations have a lot of employees. So if if you wanted to just show some some quick tutorials or have folks incorporate that into their some of their training materials, what do you got available for that?
Melissa Wilson:We do have some sampling videos for liquid manure as well as another one for solid manure on our website, so you should be able to find it at manure.umn.edu. I know a very creative website. On our manure website, we have different resources for sampling and educational stuff on like what is the sample. When it comes back, what does it mean? That sort of thing.
Brad Carlson:I know from my experience, there's a number of options relative to where the samples can go. It's worth producers understanding that the state of Minnesota actually does lab certification for manure testing, and so that there is a list of labs that have submitted samples or consented to be part of the evaluation program, and therefore have been certified. Department of Agriculture has that list, so that is available. I mean, for the most part, most of the samples in Minnesota are only going to a couple of places. And you know, the the other thing you do have to realize is if you are looking at or or choosing to send it to a lab that is farther away, you know, kind of remember what we said about that whole transport time as far as it going through the mail that that you run the risk of that.
Brad Carlson:And I know, Melissa, you've seen some issues with some of those labs in further places as far as how they report the results too.
Melissa Wilson:Through my program and just some things that I do working with manure and different labs across the country, we've found some interesting differences in how they report it and oftentimes it's related to the regulations in their state. For instance, in Maryland, they tie all of their like soil samples is just one example to a kind of a standardized scale rather than reporting the actual parts per million and that's just because that's how their soil testing recommendations are. So you might see differences in the different states. Another one that you might see is that when reporting like phosphorus or potassium, most of the labs here in Minnesota will report those on a total phosphorus as P2O5 basis to be similar to fertilizer or potassium as K2O basis. Again, to be similar to fertilizer but not all labs in every state do that.
Melissa Wilson:So you might need to make that conversion if you send it off to a far off lab.
Brad Carlson:Yeah, for the most part, you're probably the one area that you're going to be most interested in is the nitrogen component in the manure. That's the area that most of our manure management plans are written to nitrogen. Some of them are written to phosphorus, of depending on the circumstance. But from the nitrogen standpoint, there's really three different numbers that you might be getting on that report. One being the total nitrogen, one being the that would include the the organic fractions, and then the other would be ammonium and nitrate.
Brad Carlson:What have you found, Melissa, as far as the usefulness of those three numbers and then using calibrating those numbers versus an application rate?
Melissa Wilson:So I guess I wanna point out two things. You might get, there's two different kinds of nitrogen tests for manure. One is total nitrogen, so it might be called that total nitrogen. Another is TKN which is total caldol nitrogen. For all intents and purposes, they mean the same thing for us because technically total nitrogen includes, I believe nitrate, but total calval nitrogen does not.
Melissa Wilson:Or I might have that reversed, but one of them includes nitrate. But the thing is with manure is there's not very much nitrate in most manure types. So that might, you might get two different numbers if you send in a compost which does have nitrate in it, but for most manures you could do the same test and you get back very similar numbers. So just know that those are slightly different tests. But both are for total nitrogen or total caldol nitrogen, it does include organic fractions and the inorganic fractions.
Melissa Wilson:As far as thinking about an application rate here in Minnesota, right now we're basing it off just a total nitrogen rate and then we have a fraction of that that might be available based on how you apply it or animal species versus in other states and will probably moving be moving in this direction as well. Some will look at the organic fraction of nitrogen and the ammonium fraction and then they have kind of two different ways of calculating how much available nitrogen there might be. So you would see how much you think might mineralize from the organic fraction in a year and of the ammonium based on how you're applying it, how much will be left after you apply it. Because, right, if you blow it on the surface, you're gonna lose a lot more ammonium. If you inject it or incorporate it pretty quickly, you'll lose less ammonium.
Melissa Wilson:So kind of adding those fractions together is probably what we'll be doing in the future.
Brad Carlson:Well, and I've had producers want to look at that total nitrogen and then the the ratio of the organic and inorganic as as a gauge as far as the total availability. I mean, you've got plenty of had plenty of experience with field, just simply field research where you applied known nitrogen levels, total nitrogen levels, and then looked at the total availability in the field. Do you think it's wise for producers to be worrying about that inorganic to organic ratio in the manure or just simply go off the book values and assume it's gonna behave kind of on an average way?
Melissa Wilson:I think everything is always based on an average way, right? Because especially with manure, just the year and how things are changing based on the weather is going to change things. So everything is based on averages. But knowing your fraction that's the inorganic portion is always important particularly if you're applying it in the fall. If you have something that's highly ammonium, like there's a higher fraction that's ammonium compared to the organic, you're definitely gonna wanna wait until soil temperatures are cooler to apply that just to reduce the riskiness of it converting to nitrate versus something that has a much higher component that's in the organic fraction.
Melissa Wilson:It's gonna take longer to break down, even first to ammonium and then to nitrate. So those are a little less riskier to apply. Still think you should apply them when the soils are cool. Don't get me wrong. But it's a little less riskier than something that has a lot of ammonia in
Brad Carlson:Well, and the other thing is, of course, is we expect to see some pretty big differences there based on whether it's swine or dairy manure, of course. But we have different recommendations for the percent available for those two species also. It it it's it's it's almost like, you know, when we talk about just nitrogen rate overall and we say, we don't take a soybean credit because soybean the fact that you're growing and following soybeans is already factored into our recommendation. You know, similarly, the percent available when we're talking about swine versus dairy, it's already factored into that, that that that's what it already you know, we already expect it to be that way. So from that standpoint, it's probably not worth spending a lot of time worrying about it.
Melissa Wilson:Yeah. And we found that with our swine manure, it can be anywhere from seventy, eighty, sometimes even 90% ammonium coming out of the barn versus the dairy manure, it's closer to fifty fifty. Yeah. That's one of the reasons why it's kind of baked into those availability factors already.
Brad Carlson:And I know you already mentioned this once, but again, it's worth noting that most of the way calibrate our fertilizer applications, our P and K are based on the nonexistent oxide molecules of those fertilizers, P2O5 and K2O. So from that standpoint, just make sure that your results are in those, our representatives, P205 and K20, just to make sure that you're getting a good number as far as what you're actually applying there for P and K. Don't get confused by any use of just straight P and straight K.
Melissa Wilson:Yeah, and like I said, most of the labs here in the Midwest are reporting on the oxide basis, but if you start sending them out, I know labs we worked with on the East Coast were reporting it as percent P and percent K, so you had to make the conversion then. So it's just a warning.
Brad Carlson:It's kinda like The US still using the British measurement system. Recently read a I was reading the this was great bedtime reading, though, The 100 year anniversary publication of the American Society of Agronomy. It's really good because after five pages, you feel like really going to sleep. But but there was some discussion in there how the society was trying to push for for getting rid of the the p two zero five and the k two o back in the late sixties and early seventies, and they just had to drop it because it just people weren't just weren't using it. And, you know, it's it's kinda like like us switching to the metric system in The US.
Brad Carlson:Everybody's just so so comfortable using going the other way even though technically it's more complicated. That's that's just simply what we know. And so, again, I think it's it's just an important for producers not to get confused by that if they if they encounter that. So there's other stuff, Melissa, that's going to show up on the manure test report. How useful is any of the rest of that?
Melissa Wilson:So usually you'll find moisture content or total solids. That's pretty much on every manure analysis. That can be useful again when we were talking about like dilution. If you're starting to get way more solids than you expected or way fewer solids than you expected, maybe there's a water issue or a lack of one. Otherwise, you probably have to pay for some of these other tests if you want look at micronutrients or even the secondary nutrients.
Melissa Wilson:Sulfur, for instance, is becoming more and more important. Do note though that when they measure sulfur, it's total sulfur. So that's not necessarily available sulfur. It's actually kind of difficult to measure available sulfur in manure just because manure is so brown and it doesn't do the test well for sulfur.
Brad Carlson:Well, my experience, if you're applying manure, you're probably applying adequate amounts of sulfur and therefore you don't need to worry about how much is in there and then supplementing it with commercial sulfur fertilizer anyway.
Melissa Wilson:Yeah, that's fine if you're applying it every year, but then people might want to know how much they have just if they're doing a rotation. Yeah. As as far as other things, pH and electrical conductivity might be on there. You can maybe ask for those to be measured. People might be interested in doing the electrical conductivity for salts if you're in a more dry, arid region.
Melissa Wilson:But here in Minnesota, it's generally has not been an issue.
Brad Carlson:I remember twenty five, thirty years ago, people used to talk about that and worry about it, and we never we never saw any issues, and the climate averages indicated it's gotten significantly wetter even since then. So I I just don't see how the salt content in manure has any relevance on on on anything.
Melissa Wilson:Yeah. The other thing you could potentially measure for if you have a lot of bedding, you might want to look at the carbon to nitrogen ratio because that might indicate, again, if you have a lot of sawdust in your manure and you have a high c to n ratio, it could indicate if you might kind of rob your soil of nitrogen early in the season after it's applied. But that test is also a little bit difficult with manure because they sample a very small amount and you might have cornstalks in your manure which are very big things. So sometimes it's a little hard to get a decent C:N ratio, but it is something that you could potentially get analyzed.
Brad Carlson:There was some talk back about, oh, I don't know, maybe ten, fifteen years ago, some discussion about using the copper sulfate foot baths in some of the the livestock facilities and ending up with too much copper showing up in manure, but I really haven't heard any conversation about that now in a while. Did did you know, is that something that a farmer needs to be concerned about?
Melissa Wilson:So I have not heard of it being an issue here in Minnesota, but there are issues down south with some sensitive crops. So my colleagues from North Carolina are looking into it in peanut production, actually. The the copper is becoming an issue in peanuts. So it could be an issue if you have really sensitive crops to it. Have not heard of an issue here in Minnesota yet.
Jack Wilcox:That was Melissa Wilson, extension manure nutrient management specialist, and Brad Carlson, Extension Educator. Thank you both very much for being here.
Brad Carlson:Thanks, Jack.
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.
