The Value of Manure Sampling

Join Dan Andersen and Jake Willsea as they discuss the importance of manure sampling for effective fertilizer use. They highlight different sampling methods for liquid, slurry, and solid manures, review the benefits of pre-sampling and sampling during application, and examine the economic value of manure tests. Find show materials here. 

Transcript

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Music.

Dan Andersen  00:06

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/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 back for another 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. Joining me once again is Jake Willsea. Nice to see you again, Jake. 

Jake Willsea  00:56

Thanks for having me back. 

Jake Willsea  00:57

We ll, I think the most important part is just understanding what's actually in the manure. So if you're using it as a fertilizer, how can you delineate the different types of nutrients that are in that fertilizer and use that to your advantage? 

Dan Andersen  00:57

And today we're going to be talking manure sampling 101 - what, when, how and why, it matters. So this episode's gonna be all about manure sampling and the best practices for following how to get the information and actually do something useful with it. I think the data we have from around the state is that we're doing a really good job of sampling. I think lots of people are doing a good job trying to take advantage of the information they generate. But of course, there's always room to try and do better, try and learn some new nutrient management techniques and and get a refresher on what's going on. So that's what we're going to be trying to cover for you today. So I think where we want to start is just some basics of manure sampling. And Jake is a grad student, works with me, doing a great job, and he studied up on manure sampling here really quick. We've had him dipping a few samples out of some manure pits as part of his project. So now that he's done that a few times, we're ready to call him an expert and see what we have to talk about here today. So when we talk about manure sampling, Jake, what are some some things that you learned in that you think are important recommendations for us?

Dan Andersen  02:10

Absolutely, I think that's, that's the rationale. But behind what we're doing, right? There's two parts of it, really, there's dipping the sample so that we're legal and you're submitting it to DNR. But then there's the part of, hey, I want to use it as a fertilizer. I want to get the most out of my manure. How do I make a decision to do that? And the first step in that process is really making sure we we get a good sample. And there's lots of types of manure around the state. There's lots of types of manure around the US, right? So when we think about some of them, we have liquid manure, slurry manure, solid manures, and we probably want a little bit different sampling techniques for each of them, 

Jake Willsea  02:40

Definitely. 

Dan Andersen  02:40

So when we think of, let's start with slurry, manure, right? It's what we tend to have the most of here in Iowa, swine manure hanging out in a deep pit. There's a couple methods we can take for sampling. Could you walk us through a couple?

Jake Willsea  02:51

So really, when it comes to sampling, you want to look at, how are you going to apply this manure? And then your sampling method will change depending on what time of the year or how what portion of this manure are you going to apply. So if you're going to be applying the full slurry, or the full all of the manure, then you're going to be wanting to take the whole agitated sample. But if you're only going to be taking from the top portion and maybe leaving some of the sludge in the bottom, then you would want to avoid agitating it completely, so that you don't have a sample that doesn't represent what you would actually be applying. 

Dan Andersen  03:30

Absolutely. I think that's a good point. When we think about slurry manures, we're generally going to try and agitate at the time of application so we can get as many of the solids out as possible. But that isn't always the strategy that we're going to use is, for instance, if it's summer and we're putting manure on an alfalfa field for a dairy farm, probably aren't going to agitate. We're just going to take the top so we have more liquidy water and and you really want to get a sample of what you're putting on, what is, what's really going to be the manure that we're using? So sometimes that might mean the top, sometimes it might mean trying to get a sample of the whole profile. And there's some options for how to do that a little better, and chances to try and improve that. But it really is, it comes down to trying to get as representative of a sample as you can. So you mentioned that if we wanted the whole sample, we really want to agitate when we sample. That may not always be practical. Certainly, it's easy to dip off the top. If we dip off the top from a manure pit to slurry store, we're not going to have quite as high as solids content, and that changes a little bit about how we might think about using the results. I think the good news for me, at least in deep pit swine manure, the majority of the nitrogens in the ammonium form, and ammonia is really soluble, and that's good when we're just dipping off the top, because, well, since it's soluble, it'll still be there, right? It's not associated with the solids. If we wanted a good number for phosphorus, that might not be such a good approach. So if I wanted to sample it, let's say a deep pit, and it wasn't a situation where I could agitate the manure before I got a sample. What do you recommend? What do

Jake Willsea  04:52

we do? One I one ideal condition would be that you sample as you're pumping out and right before you apply. Yeah, so as it's in your tanker, you could pull out from that tanker, as it's just been pumped out, and test it from there. That would be one method that I would use. 

Dan Andersen  05:08

Yeah, I think that's that's a really good approach, right? So especially if we're not putting on a full nitrogen rate with our manure, that's a great option for us, because we'll get to know what we really put on. Whatever happened to that manure between the time we would have sampled and applied, it's already accounted for. We actually got the manure. And since we're going to come back and put more nitrogen on anyway, we can really tailor the recipe to say I got this amount of nitrogen from my manure, now I just need this much more to hit hit that goal I was shooting for. The other thing that you can sometimes try and do is probe the whole pit to get a profile. And that might look something like a PVC pipe with a tennis ball on the bottom, or a racquetball on the bottom. Lower that pipe down to the floor of the pit. Pull a cord on that racquetball or tennis ball tight to trap all the manure inside the pit, and then lift it up and carefully put it in a bottle. If you're me, it's a good idea to normally have a grad student hold the bottle for you, rather than holding it yourself, because it can sometimes get a little messy. In all truthfulness, put it in a five gallon bucket, and then pour from the five gallon bucket. And if you're going to do that, if, depending on the size of the storage, how big the pit is, probing from a couple places in the pit, can be a nice idea. Even if we don't do that, since the majority of nitrogen is in a soluble form, oftentimes we'll get a pretty good sample for nitrogen just by dipping from the surface. I normally think that's somewhere in the neighborhood of 90% of the nitrogen. So when it comes time to apply, you'll be a little bit higher than that. If we're doing something like solid manure, oftentimes we think solid manure - it's solid manure, it all looks the same. But that isn't really the case, right? So if we think about our bedded, packed beef barn, it might be a lot sloppier manure next to the feed alley, the feed bunk, a lot more dry in the sort of that area they use as a bedded pack. And we want to try and get a mix of where those two are. So for cleaning it out at once, it's what percentage of the manure do I think is coming from that alley area, what percent is coming from the bedded pack, and trying to sample that accordingly. And sometimes that can be really easy to do. Other times, if you've been cleaning out the barn periodically throughout the year, putting it into some sort of stockpiling facility, man, it can be hard to get back to some of that older than manure that's not very accessible and and you sort of get a sample where, where you're going to get it from. I think the good news is, you pointed out earlier that there's really two approaches, right? It's that pre sample, and I'm going to adjust my nutrient management plan as I go, or I can sample during application and see where I'm at and and typically with solid manures, we're not trying to get all our nitrogen needs from from that manure. So sampling at the time of application, putting a sheet down potentially, so you can both check the rate that you ended up putting on if you don't have load cells on your on your spreader, and then taking a few samples as we go from start, middle, and end can sort of give us a feel for where we're at. So I wanted to talk a little bit more about why the timing of sampling matters and how you might use that. So pre sampling, sampling beforehand, sampling at application, two different strategies. I think both have some uses.

Jake Willsea  07:55

Yeah. So pre sampling, I think, has the main advantage that you're you can tailor your nitrogen rate to the rate that you tested before you sampled. Now, in the case of a sampling during application, you're not able to fine tune it as much, but you can go back later and see how much you actually applied. And then if you want to go back after that and put on some commercial fertilizer to make up for maybe if you you undershot your nitrogen rate, then you could go make up for it at that point. But the advantage to pre sampling is that you're able to get a pretty accurate representation of how much is actually going to be going on in the future. 

Dan Andersen  08:35

Perfect. And I think that sums it up really well. So the real risk that we're running if we don't pre sample is if we overshoot the amount of nitrogen we wanted to get on. There's no tool to take nitrogen away, right? So that's the one risk. But if your goal is to be short of nitrogen, not to have that be your full dose, you still have the opportunity to tailor so I tend to, I often put some research plots out where we're trying to do full rates of manure and no other fertilizer sources. I think if you're doing that strategy, pre sampling is almost necessary, right? For me to try and say I'm going to hit this target rate, or at least get close to that target rate, and not overshoot it, I have to have a good idea what's there. The other thing I wanted to point it out, point out is that while that pre sample is nice, it's nice to have that one year value, there's really a lot of information to be gained from what did it test last year and the year before? And how are we trending with time? Every growing season's a little different. Every year the manure pits a little different. And all we're trying to do is figure out how to best balance those two things to really integrate into our cropping decision. And unfortunately, there's no perfect this isn't a commercial fertilizer with a perfectly known composition. If I go take a one liter bottle out of a million gallon pit. It's a pretty small sample, and it is what it is, and you take it to the lab for analysis, and they're going to take a mL out of that one milliliter, that one liter bottle, and all of a sudden we have a really small amount representing something really large. And a bad sample can can throw that off a lot. But if you have sort of that history with the barns run or what your manure typically is and you see a sample that you're like that looks really funny compared to what I've ran before. You can readjust, or say, I want to try again and see what happened. And if it comes back way off again, you can say, well, it must be more real this year. I trust it a little bit more and start thinking about the reasons. Why did I install new waters that limited water wastage in the barn, or did I change a ration somehow, or did something change in a management strategy of what I'm doing? But I think those are both really good points for us.

Jake Willsea  10:27

And I think that's definitely an advantage of sampling every year. So a lot of people might want to just sample every every two or three years, but really, some minor changes can have a pretty drastic effect on the actual composition of the manure.

Dan Andersen  10:40

Absolutely. And there's some great tools out there. I know, Minnesota recently put out a manure database that can let you look at what people have sampled from lots of different manure pits. But there's nothing like home cooking, right? There's nothing quite like understanding it at your barn. And certainly the database gives you a great reference point. Things you can say, how do I compare to many of these other facilities, but your barn's a little bit different. It has different water quality for the animals because the the well area that you're in, your water wastage is probably inherently a little different because of how you wash things. And giving those that database specific to your farm really provides a lot more information. And I know your manure management planner probably would be glad to help you sort through some of the details in there, because there can be a lot to be gleaned from it, at least at certain times. 

Dan Andersen  11:26

All right, so one of the things that I wanted to hit on today is, what's the value of actually taking manure test? How much economic value do we think think that it provides? And I know I had a student, Kelsey, who did a really nice job for me a few years ago, start thinking about value of a manure test and what it's worth per acre and how we can use it to make a better decision, and it's really dependent on fertilizer prices. If you go back a few years, fertilizer prices were quite a bit higher than they are today. Today, I think we're hanging around 30 cents per pound of nitrogen as we film this podcast, but that means there's still substantial value. So I often say things like a deep pit in Iowa from a swine finishing barn will average somewhere around 52 pounds of nitrogen per 1000 gallons. On the other hand, if I see a sample that tests 85 I'll say, yeah, that's within the expected range. And if I see a sample that tests 40, I'll also say, yeah, that's within the variance that I expect. So tailoring in on that. I mean, that doesn't sound so bad at first, but all of a sudden you're off 15 pounds of nitrogen per 1000 gallons. It's 30 cents a pound. Be off by 15 pounds. That's about $5 per every 1000 gallons of just nitrogen that you're either short on or throwing away and and I think when we think about how people respond to that, you're worried about being short just from the risk of yield drop of corn. So oftentimes we'll say, Well, I don't want to be short, a little more, more is probably better. And while that covers up some of the sins of not knowing, right, it can make sure that we get the yield that we want. There's some water quality implications.

Jake Willsea  12:54

Yeah, definitely. And one thing that I would say is you're better if you pre sample to be short, and then you can actually be more precise with your actual nitrogen application. So if you have a time of year or a certain year where your nitrogen is expensive, you want to make sure that you have that right on the nose.

Dan Andersen  13:18

So when we've been talking so far, oftentimes we've been saying, the nitrogen, the nitrogen. Why are we focusing so much on nitrogen when we think about manure sampling?

Jake Willsea  13:26

Well, I think of nitrogen, from a crop perspective, as being really the driving factor in corn production in Iowa. So if you're short on nitrogen, that'll have major implications. A lot of the fields around here are less dependent on phosphorus than they would be on nitrogen, so that's really where our main focus is. 

Dan Andersen  13:43

Yeah, and I think they're less dependent on that yearly application of phosphorus, because phosphorus loves to stick to soil particles, right? So we can use a soil test to really understand phosphorus in a way that, as of yet, we haven't really found the perfect soil test for nitrogen, just because it is so flashy, it is so mobile in the soil, that it's really sort of that year to year management, whereas phosphorus and potassium both stick to soil reasonably well. We can use some soil tests to help us out. What are some keys to taking a good soil sample?

Jake Willsea  14:12

Just like getting a manure sample, it's good to have a representative sample. So you want to take a lot of samples from good representative areas in your field. So you want to avoid some of maybe the odd spots, the small potholes in different areas that maybe are not representative of your field as a whole. So you want to make sure that you're going to good spread out areas that can give you a picture of what your whole field is like. 

Dan Andersen  14:37

Absolutely. And if you're required to do a manure management plan for the DNR, they're going to want to soil sample for every four acres of your field. So as you start thinking about, how do you break it down? That's sort of the going guidelines that I think are a good starting point. I know some people will grid a lot finer than that trying to catch things like potholes. When we're applying manure, we're probably not going to vary rate apply over the pothole, and that might not be as good of information for us to catch, but we can think about zones in our field, and I think that's what you were getting at for us. If you have a part of the field that was historically a feedlot, an open beef feedlot, chances are it's probably going to have a pretty high nutrient content concentration. It may not be representative to the rest of the field. Or if a field has a strong manure history, and it was a 40, and all of a sudden, you got a chance to buy that 40 from the neighbor and stack two fields together, and they didn't use manure. Well, those fields can be vastly different in making sure that we're getting those soil samples so that we can understand sort of where the line is and tailor our nutrient decisions are really important. How do how do we sort of use those two things together? How does the manure test sort of interplay with those soil samples and what we can do to make some decisions.

Jake Willsea  15:42

Well, if you're able to get an accurate soil sample and an accurate manure sample, then you're really able to fine tune how much you're actually going to apply on each area of the field. So that's that's really what we're looking for, is just to hit the right rate at the right time.

Dan Andersen  15:58

Absolutely. So I think we've talked about you. You helped me out with our other podcast on the March Madness of manures. And I think this is a great time to sort of think back to that. So if we have a deep pit swine manure, we're probably testing 50 pounds of nitrogen per 1000 gallons, maybe in that 15 to 20 pounds of P2O5, per 1000 gallons. And you start thinking about, what does that nitrogen to phosphorus ratio look like, right? And turns out, if you're in a corn soybean rotation, that's probably pretty close to enough phosphorus if we're putting on a nitrogen rate for corn. So we're not in a situation where we'd expect to build up much phosphorus in our soil. So if we start to see a field that's well, that looks a little low, it's testing low for phosphorus, and we're like, I want to build that up, knowing that might say, well, I need to change something about my cropping system, and you're like, well, that's the manure I got. It's the only one. So what am I going to do? Right? And I think your choices end up being something like, well, you can buy commercial phosphorus and say, I'm going to put on commercial phosphorus every so many years to make that up. But there's some other things you can try too. One of the ones that I contemplate, or at least think about, a little bit more, these days, is throwing an extra year of corn in the rotation. So rather than corn bean, corn beans rotation, I love and fully support. What if you go corn, corn beans, and then get back to your corn continuous year, your rotation of alternating every year. And the advantage of doing that as well, I get an extra manure application. I get to throw an extra dose of phosphorus on, and maybe that's enough to tide me through and keep me in that sort of optimal zone. With some of the other manures, we might think about it exactly the opposite way, right? So when we talked about poultry litter, one of the things we talked about was really high phosphorus in that manure. So if you wanted to get full value from that manure, you better be looking for fields that need phosphorus, and soil tests are the key to that, right? So if you see a soil test, and you can interpret it as sitting in that optimum zone or a low zone. You can be like, That's the field I want to get my poultry manure to this year. And I think that's, that's sort of the interplay. And one of the questions we we debated about there is, is there a best manure? And I think the answer we came to is probably not. It depends, which is the the answer that everyone in extension likes to give. It depends, but it really does. It depends on what your goal is, what you're trying to achieve. I wanted to come back to a little bit on your sampling during and sampling, presampling, and how that comes down to your strategy. And thinking about this in terms of phosphorus, is there an advantage to pre sampling if you're trying to manage for phosphorus?

Jake Willsea  18:18

Well, in terms of phosphorus, you're going to have a lot lower losses during the year. So there's really not as much of a risk to sampling after or during your application. So if you're going to sample during application and then apply that phosphorus can stay around for a few years, so you're not really you have, you have more of a buffer, more of a safety zone in terms of sampling there. 

Dan Andersen  18:45

Absolutely, and that was the word I wanted you to use, was buffer. That's the way I think of it too, is there's just a safety buffer where it's not trying to be right every year, it's trying to be right, on average over the course of a few years, if you're off a little bit, one year, you'll catch it on some soil sampling and be able to correct for that. Certainly, sampling is important. I think one of the things you pointed out is building that library is important, but building that library up by season is also important. So oftentimes we're entering fall here, we think about it as a heavy manure application season. But if you are applying manure in spring, having that database that says this is what I average in spring, this is what I average in fall, is really useful, just because barn management is vastly different by season, evaporation potential is different, the amount of heat stress animals undergo is different, their water consumption is. So when you think about this, and we're entering this age of of data here and trying to sort out what some of these things could mean or could could tell us, that's definitely something that we have the opportunity to collect a little bit more information about and try and use to make some better decisions. What's your last best sampling tip for us?

Jake Willsea  19:44

My last best sampling tip. I would say the last best sampling tip that I have for you is just make sure that you're doing it consistently. So as long as you have a good representative sample, you're able to add value to that manure and really return that to your to your farm. it's

Dan Andersen  20:01

That's what  all about. I agree completely. It's about trying to use that to make it a better decision. And information really is power. I know sometimes it can be confusing to try and make sense of it all, but it really is a process, right? One step at a time, making sure that we have that information, so that if you're using consultant, if you're trying to do it yourself, you can help make and fine tune where we're going from here. So I wanted to take thank you for your time today, Jake, it's always a pleasure to talk to you and have a chance to talk about manure. And thank you all for listening. If any of you have any questions or topics that you would like us to talk about on future episodes, feel free to shoot me an email. We're always happy to try and address what's on your mind with that. Keep on spreading. 

Dan Andersen  20:39

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.