Where phosphorus comes from and where it goes

Show Notes

Across the Great Lakes region, we see vegetable farms with very high levels of soil phosphorus. In this episode, Natalie Hoidal interviews four ecologists who study nutrient leaching in freshwater ecosystems to understand how much it matters for vegetable farms to have high phosphorus levels in their soils, and what we can do about it. 

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The Vegetable Beet
Episode title: Where phosphorus comes from and where it goes
Ben Phillips (00:14):
Welcome to the Vegetable Beat. My name is Ben Phillips, and I work with Michigan State University Extension.
Natalie Hoidal (00:20):
And my name is Natalie Hoidal, I work with the University of Minnesota Extension.
Ben Phillips (00:25):
How are we doing this, Natalie?
Natalie Hoidal (00:26):
So this podcast is brought to you by the Great Lakes Vegetable Producers Network. It was kick started by the North Central Integrated Pest Management Center, and our license for Transistor is held by the University of Minnesota Extension.
Ben Phillips (00:38):
And you can listen to this episode and all the rest at glveg.net/listen. Enjoy the show.
Natalie Hoidal (00:54):
After recording the first episode in this series, a conversation with Dr. Elsa Sanchez and Thomas Ford about phosphorus and salt buildup in the soils of vegetable farms, I had a conversation with three freshwater ecologists at the University of Minnesota, Christy Dolph, Jacque Finlay and Brent Dalzell. I had some questions about how much it actually matters, from an ecosystem perspective, if we have phosphorus loading on vegetable farms, especially if those farms don't make up a huge portion of the landscape and if they're using good practices like strips of perennials, cover crops and other practices that should reduce erosion and surface runoff. I share the numbers from Pennsylvania soil tests discussed in the last episode and some anecdotal soil tests from the upper Midwest and asked Christy, Jacque and Brent to weigh in. Here's Christy.
Christy Dolph (01:43):
I mean, it's funny. I mean, I think those are high numbers, but I think because we're so focused on what's happening to the phosphorus, my first questions are what's the hydrology of the vegetable farm? Is it tiled? And the fact that there's strips that are there.
Christy Dolph (02:02):
Basically the thing with phosphorus, it's like what you're putting on is how I'm starting to think about it. What you're putting on, on a regular basis, then is it readily going to be lost either through soil erosion or through like overland flow or a lot is being lost potentially from stream banks because the hydrology of these regions have been altered so much that the stream banks are eroding a lot. So in some ways, if these farms have ways that are trapping phosphorus, it could be good. Then there also could be really high flow events where all that trapped phosphorus is then going to be exported across the land. That's just what I started thinking about as what does that different type of landscape mean for how the phosphorus is actually going to get out to the waterways? And if it's not tiled, that's a lot different than the farms that we typically are talking about.
Natalie Hoidal (03:03):
I guess I'm curious, there is this assumption that it's fine because phosphorus is immobile in the soil. I don't know. It's not actually immobile, but like we think of nitrogen as move it all over the place. Farmers are kind of like, oh, phosphorus is immobile, so it'll just stay there. I'm curious if you have some general principles, like in sandy soil there's more risk, or this many feet from a stream, or it seems intuitively the further you are away from a stream or the more buffers you have, the less it's going to move around. And I'm curious if there are some general rules about how far do you need to be to reduce the risk, or what characteristics do those buffers need to have?
Christy Dolph (03:52):
With something like riparian buffers, the concern that people are starting to see is that those buffers also get saturated for phosphorous over time and then start to leak. I think we don't necessarily have a super great handle on-- your questions are so good. Cause how wide of a buffer or wetlands will store phosphorus to a point, and then they will probably start to leak it when they become saturated. That's the problem with phosphorus is one, I think it's really not immobile. It's really moving a lot across the land, and some of the work that we've done in Southern Minnesota, half of the phosphorus sometimes in these systems is coming from dissolved phosphorus. It's actually phosphorous that one way or another is reaching out of these systems. It's not bound to the soil. It's now dissolved in water, and that's a pretty hefty component of what's ending up in the rivers. And there's different pathways for that. The breakdown of decaying vegetation can release phosphorus. You can also get, once the soil reaches a certain phosphorous level, it can only hold so much, and the rest is going to become resolved.
Christy Dolph (05:18):
I think so I guess the crux is there are things you can put on the landscape that will change how it moves and probably hold onto it for longer. What I keep circling back to in my mind is this thing with the Turkey manure, because that's still an ecological rift. That turkey manure, that's still phosphorus that was mined from somewhere, like Africa came here to fertilize crops that were fed to turkeys. Now we've got the turkey manure and we're putting it on the land. It's still not actually a closed loop. So we're still getting a lot of excess phosphorus on the land of which a good part of it is going to ultimately be lost to the surrounding environment. So part of it, I think definitely the inputs has got to be a thing.
Christy Dolph (06:16):
And then the transport is the other piece. But what I struggle with so much with phosphorus is you can't permanently, unless like Jacque' saying, maybe we can mine it from our environment, but once it's out there, eventually it's probably going to mobilize. That's why it's always like stabbing me in the heart because it's not like nitrogen, we can't subtract it from the system once it's out there. And there are things you can do to alter how quickly it will be done, transported to waterways, which I think Jacque is saying, we don't know enough about how that works. But it's frustrating because a lot of those practices even will eventually start to leak phosphorous. They can only hold so much. I don't know. That's not very helpful. I wish there was like a silver bullet of like the riparian buffer should be 50 feet wide. You're good.
Natalie Hoidal (07:09):
Yeah, no I think the key is figuring out how to reduce phosphorous inputs, but then for the farms that already have so much phosphorous, it's like, what do we do in that situation?
Speaker 1 (07:22):
Yeah. This, this idea that phosphorus is a mobile is there's really kind of been a change in paradigm in the last center of decade or so. I'd say even 15 years ago, I would've told you the same thing, and we're just realizing that once these systems get saturated, it's not as mobile as nitrate. But to say it's immobile I think is not fair, but that's probably taken a while to work its way into the collective consciousness of growers. At best it's temporarily immobile sometimes, and there's a lot of growing body of literature that shows that things that we think of being good for agriculture, like no-till practices, they're good for sediment, but they can actually result in slight increases in phosphorous export in the right conditions.
Natalie Hoidal (08:27):
Is that because the phosphorus is not being working into the soil, and so it's more to surface?
Speaker 1 (08:31):
Yeah. It'sthose really organic phosphorous, rich, organic residues. They decompose, and it's not bound to any stationary phase. And there's enough of it, it's just ready to go. This idea of the more organic inputs you can add, the better. Right? And just build up soil organic matter. I can see how you could talk yourself into thinking that was the right practice. But if you were to phrase that in terms of fertilizing a field and turn it into those numbers, I'd think a lot of people would probably be pretty astounded at what they were doing and know just because it's in a mulch, it doesn't change the fact that you're putting on 10 times what you need to, and something like that.
Speaker 2 (09:25):
The relationships are messy, but you can see if you want to relate runoff, like field runoff, concentration to any one factor Bray or soil test phosphorus. Those are usually the strongest results that you see. Maybe above a threshold, you start to see a pretty linear, but noisy relationship between what you see in runoff and that sort of excess phosphorus. Those things are fairly well developed or could be developed, and then sort of when do you get runoff is the really hard part because it involves soil and climate and all these other things.
Natalie Hoidal (10:11):
After my conversation with Christy, Brett and Jacque, I reached out to another ecologist, Chip Small, who has been working on quantifying the impacts of nutrient loading in urban agriculture in the Twin Cities on the broader watershed. While he is looking at urban systems, his research has some important takeaways for farmers.
Chip Small (10:39):
I'm Chip Small. I'm a faculty member at the University of St. Thomas in St. Paul, Minnesota. I'm an ecosystem ecologist. So my background is thinking about how nutrients cycle in ecosystems, and I've studied phosphorus in streams in a tropical rain forest in Costa Rica. I came to Minnesota 12 years ago to work on a project on the Great Lakes. So we looked at nitrogen and phosphorus in the Great Lakes and some of the other bodies of water that flow into it. And then for the past decade, I've been at St. Thomas, and I have gotten more and more interested in urban ecosystems. And one of my colleagues, Adam Kay, had started a campus research garden, and I started collaborating with him and thinking about how do these questions that I've been working on in other types of ecosystems?
Chip Small (11:32):
It's really the same processes, right? The same processes are happening and you can apply the same lens to ask these questions in something that's more practical, and in some ways it's a lot easier to talk to your parents about what you're doing when it involves gardens than maybe Great Lakes or tropical rainforests. So that's sort of how I got into this. It's been a great way to plug students and research undergraduates, and it's been a lot of fun, and I think it hopefully led to some useful information.
Natalie Hoidal (12:06):
Yeah. Nice. So one of those useful pieces of information was a study that you published in 2019, and this is really the study that got me thinking about this topic. A lot of people know that there is a lot of phosphorous loading in like at least kind of small scale organic farms. I think we're starting to see that trend is bigger, but didn't really know what that meant. Kind of assumed, oh, phosphorus is immobile, so maybe it doesn't matter. And you published this study from Twin Cities urban farms and gardens, where you estimated how much phosphorus was actually entering the watershed from those gardens. And I'm wondering if you can give some background on that study for the listeners and talk about what you learned.
Chip Small (13:00):
This was, this was kind of the first phase of our big project that we've been working on for the past six or seven years. So we started just with a survey. We created an electronic survey. We distributed it through, through different garden listers, through community councils and any venue that would share it. And we got responses from about 145 different gardeners, both backyard gardens and a few urban farms and community garden plots across St. Paul and Minneapolis. And so we asked questions like how large is the area that you garden? What are your management practices? What do you do for soil amendments? What specific type of soil amendments do you use? How much do you apply every year? What crops do you plant? What are your typical yields?
Chip Small (13:54):
And we based that survey on a similar survey that my colleague Genevieve Metson had done in Montreal, that was part of her dissertation work. So she had done a previous phosphorous budget for urban agriculture in Montreal, and we adapted that for the Twin Cities. And we found kind of similar results. On average, people are applying a lot more nutrients as compost, and in particular phosphorus, then what the crops are able to take up. Oftentimes, it's nitrogen, that's going to be the limiting nutrients, and if you're adding enough soil amendments to give your crops enough nitrogen, you're probably adding way too much compost. And so from our survey data there somewhat back of the envelope calculations, but on average people are, the median, is most people are putting 40 times more phosphorous on their gardens than the crops are able to take up.
Chip Small (14:53):
So the question is what's happening to the rest of it. And then we were able kind of a second phase of that same study. We were able to go out to a subset of those gardens and collect soil samples, measure, plant available, phosphorus in the soil, and then compare that to soil from their lawns as well. And the garden soil was quite high, typically 80 parts per million was the Olsen phosphorus plane available phosphorus. It was also correlated with the age of the garden. So the longer they had that garden in operation, the higher the plant available phosphorus was, which is again, is consistent with it, just building up over time.
Chip Small (15:38):
So that was sort of the foundation for a lot of our work. And then we've built on that with, with additional experiments at our research garden, at the university of St. Thomas, looking at what fraction of the phosphorus and compost is actually being recovered by crops under like normal conditions when people are putting a lot of compost on the gardens. And then what are kind of strategies to optimize that? We're in year six of a study to try to really target compost applications and see how high we can get that minimizing phosphorous loss and maximizing uptake by crops without sacrificing yields. This study, the survey study that you're referring to is, was sort of the impetus for kind of the experimental work that we've been doing since.
Natalie Hoidal (16:37):
Yeah. Nice. So I think when I first read that study, my reaction was like, oh, well, like it's just backyard gardens. People in gardens are probably like adding way more fertilizer than a farmer would, but then when I saw the actual rates in the soil, like 80 Olson was kind of like, oh, actually, that's what we're seeing on farms too, to some extent. So maybe this is actually really applicable in terms of some of the conclusions that you're drawing.
Chip Small (17:06):
I think so. And I've first got interested in this question. I got to be part, part of a sustainable phosphorus workshop at Arizona State University, I think it was 2011, and heard from a couple of researchers who had worked with both in the fertilizer industry and with organic farms and where there's some awareness that this is an issue with organic farms. If you're fertilizing using manure, again, you're adding a lot of phosphorous relative to nitrogen. And there's a challenge. How do you recycle a non-limiting nutrient, right? On the one hand, there's, there's been some scientists have argued that phosphorus could become a limiting nutrient for global agriculture in the next century. And on the other hand, we have too much of it where we don't need it locally.
Chip Small (18:08):
So especially when you have a lot of phosphorus in your soils your plants can't live without it. And yet, typically what they need is some of these other nutrients. So how do we recycle those nutrients when the stoichiometric balance, the ratio of in, into [inaudible 00:18:29] there's just some mass balance problems there. So if we're talking about scaling up urban agriculture as cities are trying to keep more organic waste out of landfills and producing more and more compost, we need to think about how do we use that without inadvertently creating pollution issues.
Natalie Hoidal (18:52):
Yeah. So I already asked this to Christie and Brent and Jacque, but I want to ask you this question about how mobile actually is phosphorous in the soil? We don't talk about it as being mobile when we talk about nutrient management, but as someone who studies it, I'd love to hear your take on that as well as this concept of legacy phosphorus that you talk about in some of your work. Can you explain that?
Chip Small (19:21):
So the mobility question is really interesting because it's true. Phosphorus is tends to be sticky. It binds to soil. It's less soluble than compared to nitrate, which is extremely soluble. It kind of just goes wherever the water goes. And so in a lot of cases, a lot of conventional agriculture systems, a lot of the phosphorus loss off of farms is due to soil erosion. There's phosphorus, that's stuck to these soil particles that are moving into the Minnesota River or wherever, but there's a limit to how much phosphorus soil can bind. And it depends on the mineralogy, the clay content, and the pH and the redox conditions and all that. The chemistry gets to be complicated, but regardless, it can only hold so much.
Chip Small (20:11):
And so if you're putting on excess phosphorus year after year after year, eventually you're going to reach a point where the soil is saturated. It's holding on to all it can, and any excess phosphorus it can leech out either be lost via runoff or via leachate. And so in our garden experiments, we have lysimeters, just buried leachate collectors, really low tech bottles with funnels with tubes that we can pull the water out, measure that dissolved phosphorus and calculate how much phosphorus is escaping from these experimental raised bed garden plots that we have. And it's not a huge percent, again, most of that phosphorus is just building up, but in some cases about as much as leeching out as is actually being recovered by the crops.
Chip Small (21:05):
So that's a problem if we can't just assume that the phosphorus, the nutrients that you put on your garden as compost are recycled. Really what's recycled is what's recovered by the crops, and then the rest is building up. And some fraction of that is leeching out. We've also done some studies, just digging soil cores down below our raised bed garden. So into the native soil, and we see elevated phosphorus up to a meter below these garden plots. So we know it's kind of slowly moving its way down through the soil now is that a huge problem? It depends on the scale on the grand scheme of things right now, there's probably other sources of phosphorus that are going to be larger than urban gardens, but we're currently doing some watershed runoff modeling with different garden scenarios to show what are the situations where this could be really important from an urban watershed budget?
Chip Small (22:00):
And in some cases it might be the other question you asked was about legacy phosphorus and that's just this issue of phosphorus building up in the environment, so you can have kind of a reservoir of phosphorus that might be causing problems for a long time in the future, despite what your current management actions are. So, for example, in lakes, I'm doing some work in urban lakes. And sometimes we do a lot of work to try to reduce phosphorus moving into urban lakes, but there's a lot of phosphorus in the sediment of that lakes. It's called internal loading phosphorus coming out and causing algal blooms. And so that's a legacy phosphorous problem. And the same is true in soils, as well. So phosphorus just builds up in soils or along hydrologic flow paths. And it could, it could cause issues for decades or centuries into the future.
Natalie Hoidal (23:03):
Yeah. Thanks for explaining that. I think that's a really difficult concept, especially for like maybe beginning farmers who don't have a lot of background in soils and like nutrient calculations and stuff. I think often people will put a ton of compost on their beds, and it looks really good. The plants look really good, and so it must be a good thing, right? And maybe 10 years from now, you start to see the plant health effects, and it sounds like it could potentially be even longer before you start to see the environmental effects of that.
Chip Small (23:38):
I think so. And the environmental effects I would argue are probably more like an aggregate, right? Like it's something that we should as a community of people who are gardening and farming need to be thinking about. What you do as an individual in your backyard, isn't going to make or break, it's not going to tip the balance into causing unification problems in some lake probably, but collectively, if everybody's doing that, which is kind of what we're seeing from the survey data, right? Most people are putting way too much phosphorus. Then we need to be smart about that. And it's not to say that you should never add a lot. There may be situations where you're starting a new garden where it makes where you're trying to build the soil.
Chip Small (24:25):
And it makes sense to be having a lot of inputs. You're trying to build up that organic matter. So I would say, and I'm not an extension agent, but I would say that makes sense. As long as you're intentional about what you're doing, but I think there's a lot of cases where, like you said, it just feels like the right thing to do. You're in the habit of adding a lot of organic matter year after year after year. And once you have your soil at a place where you want it, then it might be time to change strategies and say, okay, now I just need to keep a certain amount of nitrogen. Maybe you can add that nitrogen through a cover crop alfalfa or something, and you don't need to be putting in a bunch of new phosphorus each year.
Natalie Hoidal (25:14):
Yeah. Those are good points. There are plenty of farms and gardens that are nutrient deficient still. So this is not a blanket statement. Yeah. Also your point about it being kind of a community effort, I think is really important. I guess that brings me to this last question of, I think sometimes even when you do have enough nutrients in your soil, it can feel kind of scary to do nothing. I think that's true across like human experience, right? Doing nothing is always harder than doing something. And so sometimes adding a little bit of something can feel almost like an insurance policy. And you're doing some work in these plots that are already pretty saturated with kind of different levels of compost, even applying nothing. Can you just talk about what you're finding in those trials?
Chip Small (26:11):
Yeah. You know, this is so we started six years ago. These garden plots had been going for about five years at that point, and already had fairly high organic matter content, but from that point we started different experimental treatments. We were adding one of two types of compost, either composted cow manure or municipal compost, and either at a higher level to meet the crop nitrogen demands, which means they're getting excess phosphorus. And even that higher amount is still lower than what most people are putting in their gardens or lower amount to meet the nitrogen or to meet the phosphorous demand, and then we're adding some extra inorganic nitrogen. We also have plots that only get synthetic fertilizer to meet the nitrogen and phosphorous demand. And then we have control plots where we've added nothing, no soil amendments for six years.
Chip Small (27:05):
And it took a few years, but finally, we're starting to see slight decreases in the crop yields, in the control plots that have gotten no soil amendments after like five or six years. But my bet would be that most people could take one or two years off from adding any soil amendments. And you probably wouldn't notice any decreases in yields. And even in these control plots, the soil phosphorus is still pretty high. It's come down maybe five or 10% over that many years, but that's the legacy phosphorous thing, right? There's just so much in the soil, and it's going to take a long time to use it all up. So what happens if you don't add anything eventually that nitrogen's going to run out first and that's what's going to limit the crops. But the good news from this experiment is these targeted compost applications are working really well.
Chip Small (27:57):
The crop yields are doing fine. The amount of phosphorus and nitrogen that we're losing from leachate is pretty low. And so it's a high fraction of what we're adding is getting recycled into the crops. I think the take home message is, if we're intentional about what we're doing, if gardeners, farmers get their soils tested and add soil amendments based on what the data say that the soil needs that crop yields are probably going to be fine. And you're going to be minimizing your losses of nitrogen and phosphorus to the environment.
Natalie Hoidal (28:40):
Yeah. That is good news. And I think that's what we expect, but it's always really nice when you see your expectations actually play out in reality too. So that's encouraging. All right. Well, thank you so much.
Chip Small (28:55):
All right. Thanks, Natalie.
Ben Phillips (29:03):
I enjoyed the conversation with Christy and Jacque and Brent. They seem like they know a lot about these systems, and they come at it from a different different perspective that we don't hear as often in the ag community, and I thought that was an important perspective to hear. And I guess the one takeaway that I took that is lodged with me now is how phosphorous is mobile. And at some point in the line of farm education, it got associated with immobility.
Natalie Hoidal (29:41):
Isn't that funny? It's so drilled in prosperous is immobile.
Ben Phillips (29:45):
Yeah, and that little factoid is immobile in our brains too. Cause it's like a very hard thing to then change your mind about having heard it kind of drilled in so many ways. Yeah.
Natalie Hoidal (29:59):
Yeah. It was funny to hear like all of these ecologists, so unequivocally say phosphorus is mobile. It's like, oh, okay. That's a total game changer.
Natalie Hoidal (30:11):
I think what Christy said really stuck with me, and it's so obvious, but this idea of phosphorus being an ecological rift and just sort of imagining like it's mind from Morocco, it's brought to fertilize up crops, it's fed to livestock, it's then added in the form of manure. And I knew that, but to hear her explain it that way was, I don't know. That was very helpful for me.
Ben Phillips (30:35):
Yeah. I thought that was interesting too. Because as she was talking before she got to that point, I was just thinking like, okay, so we're stuck with it. How do we get it back to its source, so that it's not essentially a contaminant in a new place? And there's no easy answer to that. The easiest answer would be to not put it on, if you don't need it. That would be the easiest answer. And then I think it was Jacque then shared that one of the, perhaps it was Brent, shared that one of the problems is literally every fertilizer everywhere that comes marketed in different ways, especially it's a smaller growers, it's got a phosphorus component. Like all of them. Small or large. There's never not phosphorus in it. It's very rare.
Natalie Hoidal (31:19):
Unless it's like blood meal or something super specific.
Ben Phillips (31:22):
Yeah. Yeah. There's a few in the conventional world, there's a few good examples of like nitrogen only and potassium only fertilizers, but by and large phosphorus comes linked with a lot of things.
Ben Phillips (31:35):
You just kind of get it as a byproduct and it's tough. It's like always being pushed. But then I think Christy had mentioned something about trying to mine phosphorus where it ends up, which in our case, in the Great Lakes, is in the Great Lakes. And I'm just kind of picturing like these, I don't know, would that look like some kind of phosphorous recovery factory in Toledo or something that's just like harvesting algae. I'm just thinking, what would the impact of that be then? We'd still have have more phosphorus to then be used again. Or sent back to Morocco. Like what is it? The more we started talking about phosphorus, the more I think of it as a forever chemical in some ways. There's like some benefits just like there are benefits to stuff like PFOS, except that it also ends up in places that we don't want it. And there are some downstream effects that are undesirable.
Natalie Hoidal (32:36):
Yeah, there are definitely comparisons to be made with single-use plastics containing.
Ben Phillips (32:43):
Right. Right. And then your fourth guest Chip was talking about legacy phosphorus too. And like what is the effect of it now being in the environment when we perhaps didn't need it to start with, and now it's here. It's not where we put it. It's moved. So what are the responsibilities behind that? Oh man. A lot of great. This was a good one. This is like a hard candy that you can just suck on this one for a while.
Natalie Hoidal (33:06):
Yeah.
Ben Phillips (33:06):
And he also mentioned how doing nothing is really hard to do.
Natalie Hoidal (33:11):
Yeah.
Ben Phillips (33:12):
To be like, okay. I don't need that.
Natalie Hoidal (33:13):
Stopping is the hardest thing.
Ben Phillips (33:15):
It's so tough, especially when a nice, like two inch layer of compost looks so great. Yep. So great on a bed. Some popular YouTubers are really good at showing like the bed preparation and this liberal compost edition and like these cool little hand drill machines that mix it in. It's like, that's the perfect, that's what I need.
Natalie Hoidal (33:39):
Yeah. I've been talking more about like Instagram farmer celebrities in my outreach. Because there are so many accounts where these like farmer celebrities are saying that they're adding eight inches of compost every year, and their beds look so beautiful. And you can't compete with these like beautiful Instagram farm images, but that is being portrayed as the goal. That's a really hard like cultural force to move around.
Ben Phillips (34:11):
Lets do a question that I started thinking about over these first two episodes at how it appears that among most vegetable growers, organic matter is a key little metric that's easy to latch onto as it be. It's just easy to latch onto. And the way to get it is to essentially incorporate manures, incorporate cover crops, incorporate composts. And especially as it relates to manures and composts, it seems it's always a multi nutrient analysis, and if you're trying to do some of the fertilizer math that would meet your nitrogen needs, you're always going to oversupply phosphorus. It got me wondering, is phosphorus always linked to organic matter? Are there organic matter sources without phosphorus? I feel like that should be the new frontier. What are those? Maybe they're obvious and I'd sound like an idiot even asking the question.
Natalie Hoidal (35:09):
Yeah. I mean, cover crops are an obvious example, right? Like that's a great way to add a lot of nitrogen to your system without adding more phosphorus.
Ben Phillips (35:18):
I suppose, unless there's already phosphorus there.
Natalie Hoidal (35:21):
You know what I mean? Right? So you're not adding it. You're just like recycling the phosphorus up there, and hopefully then eventually your crops will pull it out.
Speaker 8 (35:29):
Yeah. A legume cover crop would definitely augment that system to have more nitrogen, and more stable nitrogen as well.
Natalie Hoidal (35:37):
Yeah. In my outreach, I've started doing comparisons of like taking a common composted manure and saying, okay, I'm growing half an acre of spinach. So this is how much I would add to meet my nitrogen needs. This is how much I would add to meet my phosphorus needs. This is how much I would add if I'm also using a cover crop and sort of doing a cost comparison, and almost every time, at least because the organic, the approved compost of manures that we have access to in this part of the Midwest are quite expensive. Like in almost every scenario using a cover crop to meet your nitrogen needs and then like just using that composted man to meet your phosphorous needs is substantially cheaper, and then you don't get all this excess phosphorous and potassium too. So I think sometimes including an economic analysis in there too can help to make the can help make it more appealing maybe.
Ben Phillips (36:35):
Yeah, no, that's an interesting approach. Yeah. Sometimes a pocketbook argument is a lot more effective. Cool, Natalie, good job on that.
Ben Phillips (36:46):
That concludes this episode of the Vegetable Beat. If you'd like to check out all of our past episodes, head on over to glveg.net/listen, bye.

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