Manure Systems and Carbon Footprints

Dan Andersen delves into carbon neutrality in livestock production, and the impact manure emissions have on a carbon-neutral system. He also looks at current practices, like anaerobic digestion, that are already being used to reduce methane emissions, as well as practices being considered for the future. Supporting materials for this podcast can be found here. 

Transcript

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Dan Andersen 

Hello, and welcome to Talkin' Crap, a podcast by Iowa State Extension and Outreach, where 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. 

Dan Andersen 

I'm Dan Andersen, associate professor, and extension specialist in agricultural and biosystems Engineering Department at Iowa State University, you may know me better by my Twitter handle @drmanure, and if you don't check me out there. Today's episode is going to be about carbon footprinting of swine finishing operations, and talking about the impact that our manure system has on our carbon footprint. 

Dan Andersen 

Before we get to that, let's hear today's manure fact. During manure storage, some nitrogen is lost as ammonia to the environment. The amount of nitrogen lost is dependent on the type of system we're using, environmental factors, and really the diet that we're feeding the animals. So, there's lots of things that make it complicated, but in all manure system, some nitrogen is lost. Our goal from a sustainability standpoint is trying to minimize the amount of nitrogen that is lost, and especially different forms that are lost. When we look at swine production systems around the state of Iowa, there was a great paper from 2014, written by Liu  that did a review of all swine manure management systems in the United States. And that article suggests that deep pit swine finishing barns lose about eight pounds of nitrogen per pig per year. Barns with a slurry tank and drain pit lose about seven and barns with a recharge pit and a lagoon lose somewhere in the neighborhood of 13 pounds of nitrogen per pig's space per year. I bring that up because the manure system that they chose essentially has a pretty big impact on how much nitrogen we're losing. And one of the things that we saw happen in Iowa as we went from 1990 to today is a lot fewer lagoon systems, a lot more deep pit systems. And when you look at the amount of nitrogen they're losing, well, we've almost cut in half the amount of nitrogen that is lost in the air. That's nitrogen that we now get to deliver out to our fields used as a fertilizer and actually add value to our farm and I think that's been a pretty big driver. Now that we're here, I think the next question is, what do we do now? How do we keep improving our manure systems so that we have less nitrogen loss to the environment, less negative environmental impacts, and just as importantly, can save that nitrogen in our manure so that we can better capture it and utilize it as a fertilizer? 

Dan Andersen 

There are several things we can do to try and reduce ammonia losses. And while I'm not going to be able to talk about them all today, I'm going to talk about impermeable covers. Impermeable covers are basically a sheet of plastic that you pull over the manure storage that keeps air from going in and gases from leaving. So, impermeable is just a fancy word for it doesn't let gas move through it right and if it doesn't let gas move through it, it also isn't letting liquids move through it. Because of that, it's pretty hard to implement on a deep pit barn where we have a slatted floor, the manure falls through those slats and into a storage below. If you think well, I'm going to put a cover on that. Well, now the manure is not falling into the storage, it's falling onto this cover, and we didn't make any progress on the solution. However, on the manure systems where the manure stored out of barn, we can think about putting that cover over the top of the storage, the manure goes through a pipe underneath the cover, it still gets into the storage, and we get some added benefits. We keep rainfall out of that manure storage, so we don't get dilution in, in rainy years. In 2023, here that probably didn't matter as much to us. But there are a few places that have had substantial amounts of rainfall this year, and, and historically, I will we'll get a little more precipitation, then we get evaporation potential. So generally, we'll add some water to our manure if it's our department or storage. The other thing that it does really well is it helps hold ammonia in the manure. So, nitrogen, the manure is present in two forms organic nitrogen, and the mechanical nitrogen and ammonia co nitrogen can be ammonia that can turn into a gas and leave the manure or ammonium and the pH, and the amount of nitrogen really controls how much ammonia there is.

Dan Andersen 

When we think about reducing those ammonia losses, one of the best practices we can do is basically catch it and not let it leave, right. So, if we have that plastic covering on the manure surface, then it's not going up into the air. And we start thinking about what a deep pit farm might have to do to modify to be a facility that can use a cover, well, we're going to have to modify that deep pit, so it turns into probably a drain system, where we periodically move manure from that that pit that we're using as a temporary storage to an out of barn storage, we put a cover on the storage. And there's a couple of things we have to do right we have to spend some money to modify our current deep pit to be a drain pit. We have to build the new out of barn manure storage, and then we have to put a cover on it and unfortunately right now that gets pretty expensive. For instance, just putting the cover on alone is probably something like $70,000 worth of value cost at 4800 head facility. If you want to think about how much nitrogen I'm saving, it's probably in the neighborhood of 4 - 4.5 pounds of nitrogen per pig per year. And that works out to about $6,000 worth of fertilizer value. But that means to get there, we probably need our cover to last 10-12 years. Permeable covers probably could last that long if the weather really cooperated and we didn't have anything go wrong. There will be some maintenance expenses, some upkeep of fixing them when they get leaks, things like that. But generally, that's probably a little bit longer than we'd be looking for to get it to pay back. 

Dan Andersen 

However, there are other things you can do to try and capture value from those impermeable covers, right, we might do something like say, they are really good at reducing odors, they might reduce odors from the facility by 80-90%. And maybe that has value or if our facilities large enough, we might be able to think about capturing methane underneath that cover, cleaning and putting in the pipeline, or burning it for electricity. And in some cases that can offer some value as well. But just on fertility alone, there's probably not enough savings to justify a cover today. But as we move forward and put more pressure on how circular are we that might change. 

Dan Andersen 

If you're interested in learning more about practices that help reduce ammonia loss from manure storage, as Iowa State has a tool called AMPAT, the Air Management Practices Assessment Tool. If you Google that, it'll come up to a great website that looks at some of the things we can do in barn, in manure storage, and at application help reduce some of those ammonia losses. 

Dan Andersen 

All right, with that we're gonna move into what I really wanted to talk about today, pursuing carbon neutrality in livestock production. For livestock production, improving circularity, reducing nutrient loss to air and surface waters, making sure that we're protecting our soils has long been a hallmark of pursuing sustainability. We recently added limiting greenhouse gases to that list. And I think we're seeing a lot of areas where that's evolving and changing from day to day. Achieving carbon neutral livestock production requires implementing strategies to reduce greenhouse gas emissions from the farm and any other emissions that you have need to be offset by implementing some other practices wherever generating a credit. In carbon footprinting, there are basically three emission scopes that we talk about or think about. Scope one emissions are greenhouse gas emissions from the operations that are owned and controlled by the livestock producers. So, the hallmark case for this one, at least for me, and most of my systems, is emissions from the manure, right? So, scope one emissions would be enteric fermentation, methane emissions that come from the animal, and then methane and nitrous oxide emissions from the manure storage facility itself. This category could also include emissions from the combustion of propane, which is often used to heat livestock buildings, or fuel use to power equipment and tractors that might handle emergency and mortality, compost, or anything else that we're doing on site. 

Dan Andersen 

Scope two emissions are indirect emissions resulting from the generation or purchase of required acquired electricity, steam, heating, and cooling. Typically, livestock farms would have fans, and those fans run on electricity. So, the amount of carbon dioxide generated from burning fossil fuels is really our scope two emissions, along with any other power we use for electric motors in for instance, the feed delivery system. Scope three emissions are indirect emissions in the value chain, including upstream and downstream emissions. And I'm not going to talk too much about downstream emissions, but an example of this would be greenhouse gas emissions resulting from feed production, including raising corn and soybean meal, grinding, and delivering that feed to the production facility. And if you really did want to think about downstream, it might be moving the livestock products, the milk, meat, or eggs to a processing plant, and then eventually to the store. So, the categories can get pretty big, pretty quickly, I'm going to try and give you a little more breakdown of what those things might be and what we can do about them. 

Dan Andersen 

So, those scope one emissions, which were the direct emissions from the livestock facility, our biggest area of impact right now generally is manure management. And what we're trying to do is implement efficient management practices to minimize nitrogen emissions as nitrous oxide, which is a really potent greenhouse gas, and then carbon emissions as methane. One practice that is getting a lot of attention is anaerobic digestion systems. They convert manure, or at least some of the carbon in manure into biogas, which can be used for energy production. Other options could include things like aeration, acidification, frequent manure removal from the barn for land application, or diet modifications. Right now, most of those techniques primarily focus on reducing the methane emissions. I did mention nitrous oxide, and it is important different systems have different levels of nitrous oxide emissions, but we're still at the early stages of developing management practices that can substantially change those. Another scope one emission is enteric fermentation. Methane is produced during digestion in fermentation in the animal's digestive tract. We think about this more for ruminant animals than non-ruminants, but non ruminants do generate some methane from enteric fermentation as well, just generally much lower amounts. So, what people are working on is developing feeding strategies that reduce enteric fermentation from dairy cattle or pigs. And there's a lot of things that people are doing, there's products such as Monensin, or adding seaweed, that have been suggested. And what those do is disrupt the microbial community in the animal gut, and hopefully turn more of that energy into acids that are absorbed by the intestines rather than being lost to methane. So hopefully, we get livestock performance improvement along with just this general reduction in methane fermentation from the animal. 

Dan Andersen 

One big area that people have worked for a long time and continue to work is feed efficiency, enhance feed efficiency by utilizing improved nutrition strategies, formulating diets that are better balanced for what the animal is needing, or by using feed additives. Improved feed efficiency reduces the amount of feed required to produce a unit of meat, milk, or eggs and that lowers the associated emissions from feed production. So, it's something that in scope one our feed efficiency impacts maybe what some of our scope three emissions are, but I'm gonna put it under one because it's something we directly get to do at the livestock facility. Things we've seen people really do in the long term, and that have provided some improvement are improved grinding, which increases digestibility makes our feed conversion efficiency better and helps us out in the long term. And then the final place that I think a fair amount of work is going is in just genetic selection of animals. When you look at how we bred animals, how we've improved genetics over time, they've often got animals to give more milk or to finish faster. And that's a good start, we might have to start thinking about swine breeds or genetic lines with higher feed efficiency and lower emissions, right. So is there a way to select for both at the same time that is a little more robust, rather than just picking one variable and working there. Genetic improvement can help reduce mines production environmental impact over time. And really, it's been one of the key environmental efficiency gains that we've seen over the last 20, 30, 40 years. When I think about scope two emissions, those were really emissions that come from power plant while we're buying power. And things that we can do on farm really focus on either energy efficiency, or making sure our power comes from a renewable source. So, in terms of energy efficiency in swing production facilities, that might be looking for energy efficient equipment, and optimizing our heating, ventilation, and lighting systems. Optimizing our system there reduces energy consumption, and with that, we get reduced associated emissions. Examples might be switching to LED light bulbs; we've seen that become really popular in poultry housing facilities. It might be a fan staging to increase fan efficiency or installation of variable frequency drives on fans to improve performance. 

Dan Andersen 

The other place that we've seen some work is on just generating renewable power. So that could be incorporating renewable energy sources such as solar panels, wind turbines, or even biogas systems to generate clean energy for powering our barn or farm. Renewable energy can oftentimes significantly reduce carbon emissions. But at many livestock facilities, the amount of energy we're using is relatively small relative to some of our other sources. But it can be a way that we sell credits back to the grid, right? If we're generating more renewable power than we need, we can take some credit for that and use that to offset some emissions that we haven't gotten rid of. And then our scope three emissions and to me that was really related to the emissions that come from feed production. So, one aspect of that is nutrient management, optimizing nutrient management practices to minimize the release of nitrous oxide during crop production, or recycling our manure better, so that we don't have to buy as much commercial nitrogen fertilizer, which is relatively energy to produce. The other place is thinking about what feed ingredients we're using. So, selecting feed ingredients from different agricultural practices can lower our carbon footprint of the supplied feed ingredients, a choice that we often make is balancing the amount of DDGs in the swine ration versus the amount of soybean meal and how that might impact it. I'm not going to delve into that, because that gets out of my area of expertise. But there are plenty of people who are thinking about that and thinking about how do we adjust these in our ration to lower the carbon footprint score the feed, and overall, the carbon footprint score of a pig. 

Dan Andersen 

And all that's great to say, when it comes down to practice. Every one of these factors needs to be balanced with price and our availability to do it. We don't live in a vacuum. I certainly recognize that. These things happen in small steps, and I think it's important for us to start thinking about them planning for them. But that doesn't necessarily mean implementing, I'm going to be carbon neutral tomorrow, right? It's small steps about what are the things I could be doing or looking into to get us there as an industry. 

Dan Andersen 

The final thing that we can do if we can't get those scope one, scope two, and scope three emissions down to zero is looking to carbon offsetting. And effectively what carbon offsetting is, is looking for practices that offer carbon storage. And using that to compensate for any remaining emissions, we couldn't get down to zero. That could involve activities like supporting reforestation, using either trees or grassland to soak up some carbon, stored in the material, stored in the soil, and taking credit for that. It could also be generating renewable energy, beyond what we're using at the farm, and selling those credits to someone else, or claiming those credits, right, in the market to show that we're now offsetting whatever we had coming from our facility before, so that we've become cleaner. I'm not going to give you every carbon emission. But if you look at the handout for this webinar, which you can find on our resource page, I do have some information on where some of the carbon associated with swine production is coming from. So, if we think about a deep pit storage system, it emits approximately 192 kilograms of carbon dioxide per head per year. That's less than some other facilities. If you had a lagoon system for manure storage, you might be double or two and a half times that number can get pretty high, but it is a good start. Another place is enteric fermentation. And while we don't know exactly how much methane any pig will generate, because it's associated with the diet, a good general rule of thumb is somewhere around one and a half kilograms per headspace per year from a swine finishing barn are about 42 kilograms per animal per year. Now, I want you to note that that 42, it's a little under 50. That's about 1/5 of what it was coming from the manure. So, when we talk about enteric fermentation, yes, it can be important, it can matter. But it's still much much smaller than focusing on that manure system. Another place that we could look at is barn heat. Jay Harmon, here at Iowa State University, did some work looking into how much propane we're really using per pig space to heat a barn, he came up with an estimate of two gallons per pig space per year. That works out to somewhere in the neighborhood of 11 kilograms of CO2 per headspace per year. Again, much much smaller than what we're talking about with the manure number, or even that enteric fermentation number. Barn electricity is a little harder to estimate as it is dependent on our barn ventilation system. Are we a naturally ventilated barn or we tunnel a ventilated barn, or we something else entirely? But again, Jay, along with Mark Hanna, in a 2016 publications surveyed some different Iowa facilities and estimated that we used somewhere around 25 kilowatt hours per pig space per year, you can look up roughly what it takes to make power in terms of nitrous oxide emissions and CO2 emissions. In the state of Iowa, we do pretty good, right, since we have a fair amount of wind, but we do burn some coal and other fuels like natural gas to make some of our electricity. It works out to somewhere in the neighborhood of half a kilogram per kilowatt hour, or 13 kilograms per pigs base per year, roughly the same amount of carbon that we make for heating, right and so but the same amount of carbon that results from heating our barn, results from trying to keep our pigs cool as well. Again, it matters but relatively low compared to maybe some of those other sources. 

Dan Andersen 

When I looked at feed production, I took the easy road route, I found a paper Benavides from 2012. And they gave me a general estimate of about 0.4 kilograms of CO2 per kilogram of feed and a swine diet. That paper goes into much more detail, it talks about how different diet rations might impact that, it looks at DDGs versus distillers grain or versus soybean meal, and how that could impact it. But for just a general rough estimate, I'm going to use that 0.4, we need to know roughly how efficient our pigs are at turning feed into a pound of live gain. I'm going to put us at about two and a half. And if you start thinking about doing that, assuming 2.2 turns a year, raising pigs from somewhere around 25 to 280 pounds sold. That works out to somewhere in the neighborhood of 265 kilograms of CO2 equivalents per head per year, or bigger than our manure actually impact right, so that feed side is important. It's really hard. And then we do have to move a few things around I have to move feed to the farm, I have to move pigs from the farm to my facility, right, so I have to bring nursery pigs in, take finishing pigs out, how far you move, that stuff does matter. But just generally thinking that I'm going to move it in the neighborhood of somewhere like 100 miles, I might be looking at 12 kilograms to bring the feed in and I'm moving pigs out I might be looking at five kilograms of CO2 per year. So overall, what does this really tell us? So, if I look at where I'm at for carbon footprint, add those numbers up. I'm about half a ton of CO2 per pig space per year for swine production in Iowa. If you start thinking about that on a take home meat that might be three kilograms of CO2 per kilogram of meat or three pounds of CO2 per pound of meat that we generate. There are a couple of caveats to this. I didn't look at how much CO2 is associated with generating the piglets. If we really were going to carbon neutral system, those piglets would have zero carbon footprint, because we've looked at how to remove the carbon footprint from them, just like we'd be looking at how to remove the carbon footprint from finishing pigs right now. So, where this leaves us is that roughly half of all our CO2 emissions from our production footprint are associated with feed, then somewhere in the neighborhood of 35% of them are associated with manure, and the rest is associated with electricity and moving stuff around that we'd have to think about as a whole energy system. And what that really means to me is, the feed side is important, right? It's the biggest part of our footprint, it's something that we have to think about. But it's also a hard area to make big improvements really quickly. There isn't some magic thing we can do to eliminate nitrous oxide emissions, while we're making corn or to cut out all the energy use, we have from each one of our field passes to grow that corn to harvest it. So that's really a big hard problem to work on. 

Dan Andersen 

On the other side, we have manure, and we do have some things about manure that we have practices we could implement, we could think about those impermeable covers or anaerobic digestion, or aeration of the manure, or acidification of the manure where we can really do this one thing and make a big impact on our emissions from the farm. Will it get us to carbon neutral? No, of course not. Right? It's going to take a whole system's approach to do that. But we can do this one thing and make a big chunk play. So, when we see a lot of interest in manure right now, I'm not here to say, if we got rid of all manure emissions, it is going to change what we think of humanity's greenhouse gas emissions. It won't. We're probably somewhere between 2 and 5% of all anthropogenic greenhouse gas emissions. Right, we are a small chunk, but we are a chunk we can look at and say, we know practices that would improve this, we know practices that could work. The hard part is trying to find a way to make those practices cost affordable. And, and developing carbon markets have really helped bring that to the forefront and brought new practices that for a long time, we might have said yeah, it's hard to make it pencil out at a facility. And instead, now we can look at it and say, if these markets are going to be stable, there might be opportunities here. And from a manure standpoint, I think that's really interesting. It gives us a lot to look at think about how we're going to continue to build new facilities, and then how do we design and modify existing facilities. 

Dan Andersen 

So, just a quick summary of that. It's important to note that achieving carbon neutrality in livestock production is going to require a combination of strategies, and the feasibility of implementation can vary depending on lots of things: farm size, farm locations, available resources for the livestock species, the importance of mitigating those carbon emissions for a value-added product, or the development of actually carbon markets that would pay for these reductions. Regular assessment, adaptation and improvements are necessary to ensure ongoing progress towards a goal of carbon neutrality. I'm not saying this to say let's get to carbon neutral tomorrow, but I do think it's time for us to start thinking about what might work on our farm, what are some options we have, and how can we value add to our farming system by doing that? 

Dan Andersen 

So, if you have any questions or comments, I'd love to talk to you more about what some of the options are, how they might fit on your manure system, feel free to give me a call 515-294-4210 or send me an email at D as in dog, S and Samuel A is an apple at iastate.edu (dsa@iastate.edu). Thank you for joining this installment of Talkin' Crap. Be sure to take a look at our 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, Iowa Manure Management Action Group, which you can find at www.extension.iastate.edu/immag/. If you found what you heard today useful, where it made you think we hope you'll subscribe to the show on your podcast app of choice. Signing off from a job that sometimes smells, but never stinks, keep on talkin' crap.