Episode #213
Jennifer Pett-Ridge: Carbon Cycling on Organic Farms

Soil scientist Jennifer Pett-Ridge joins Linley to discuss the powerful role agriculture can play in both carbon sequestration and carbon cycling. She explains that carbon cycling and storage are complementary, not opposing processes, and that organic farming practices with their focus on organic matter (om = carbon! otherwise known as sugar/ plant food!) are perfectly positioned to be great tools for drawing down atmospheric carbon. Excellent practices like over cropping consistently improve soil carbon by keeping the “carbon flywheel” spinning year-round. Pett-Ridge stresses the importance of place-based solutions, noting that climate-smart practices vary significantly by region. She encourages farmers to collect and share data, viewing every farm as an ongoing experiment. The most promising systems incorporate diversity—from cover crops to complex rotations, creating what she describes as “healthy soil” with rich microbial communities.

Our Jennifer Pett-Ridge interview has been edited and condensed for clarity:

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Linley Dixon interviews Jennifer Pett-Ridge in California, January 2025

Linley Dixon 0:54
I was wondering if you could just start with that overarching theme of, in your experience, is there potential for annual crop farmers to sequester carbon, or are we more just thinking of how to keep carbon cycling on our farm, and that might be the best we can do?

Jennifer Pett-Ridge 1:13
That’s a great question, Linley. Thanks for having me here to talk about it. I think that those two things that you just brought up, you want both to occur. It’s funny that maybe in the last 10 -15 years, our thoughts about soil carbon and how it comes to reside in soil and persist for longer periods of time and maybe even accumulate, have really changed.

Jennifer Pett-Ridge 1:43
There was a seminal paper published in about 2011 and we went from really thinking about soil carbon as something that is…We use the word “recalcitrant,” meaning that it’s kind of nasty and just hard for microbes to eat – stable or sequestered. There are a lot of words that we actually try to avoid now, because we found that the carbon that’s really old, that’s lasted for thousands of years in soil – and we use c-14 dating to tell us that – that carbon is actually made of sugars, amino acids and really yummy stuff that microorganisms should love to eat.

Jennifer Pett-Ridge 2:27
That’s why I’m, long story short, saying it’s important to keep carbon cycling and turning over, and that that flywheel is actually part of growing the stock of carbon in soil. Those things are not mutually exclusive. It’s one thing.

Jennifer Pett-Ridge 2:45
You brought up, can we increase soil carbon in our annual croplands? I want to absolutely just clearly say, yes. There is really good evidence that we can do that, and it does take careful management, because the standard across the US – and I know we’re here in California and you’re in… sorry, you’re down in Arizona, is that right?

Linley Dixon 3:11
Southwest Colorado.

Linley Dixon 3:12
Southwest Colorado, forgive me. In a lot of the US and sort of the Corn Belt, the standard is actually that we’re losing carbon. We’re not even at a flat baseline. But that can be stopped a couple of ways. I think the first one that a lot of folks think about is no-till. When we looked at the literature really carefully on no-till, there’s so much variability from site to site that it doesn’t reliably cause soil carbon to increase. What I guess it does is kind of holds the line. It prevents a lot of loss – and certainly erosion loss. But what we saw as really consistently having a benefit is cover cropping.

Linley Dixon 4:04
So, putting a crop in the winter time and having photosynthesis happening all year long, is just causing that flywheel to spin more of the time. There’s other techniques too that we can get into, but I should probably stop there and let you have a chance to say something more.

Linley Dixon 4:23
Yeah. I’d love to dive into that no-till thing, because it was really traumatic as an organic farmer to go to DC last year. We were lobbying for organic practices in the Farm Bill. It was like this overarching statement that every representative we met with – because it was a bunch of organic farmers, and we divided and conquered – we all came back together and said, “Everybody’s saying organic cannot be climate-smart, because we use tillage.”

Linley Dixon 4:52
So, no-till was what was working – this concept of no-till in Washington. I took some time to look at some of the research too. I don’t know if you agree with what I found, but they were showing like higher carbon sequestration, maybe in the top layers, and not so much in lower layers. They were not looking at, in my opinion, full cost accounting, cradle to grave of these farming practices. Supplying synthetic fertilizers on the surface, not really incorporating them. Made it so that the soils had greater cracks in them, and the fertilizers were going down to the drainage tiles more readily. So, you’re having algal blooms. I was just like, “We need to take a deeper look at these systems.”

Linley Dixon 5:39
Some of the concerns I always have are these point measurements, as opposed to full cost accounting. I’m just wondering if things like that come up in your research, but also, are any carbon markets working to… I worry that they just take these point measurements like, “Well, how deep are you measuring?” All these things. Just kind of throwing a big bag of worms at you.

Jennifer Pett-Ridge 6:05
I resonate with so many of those comments. I love that no-till has been embraced by very conventional farmers. The organic farmers I talk to as well aspire to be able to do, maybe not no-till, but at least less tillage. That nobody wants erosion. Nobody wants to disrupt those wonderful mycorrhizae and the things that happen; the aggregates that form when we don’t till.

Jennifer Pett-Ridge 6:38
But I hear you – organic farming is really hard. You got to get real weeds. If you’re not going to put on some sort of chemical to do that, tillage has a place. But I’ve also learned it’s not black and white. There’s really wonderful farm tillage that happens that’s kind of one turn or uses modified plows that are much less destructive and don’t just pulverize all of the aggregate structure. So, that’s my comment on no-till.

Jennifer Pett-Ridge 7:09
You talked about a couple of other things. You talked about carbon markets and accounting. Absolutely, I’m with you that we can’t just take point measurements, we can’t take just measurements at the surface and really understand the entire system. No, there is not a carbon market right now that I think is really doing a good enough job. Of course, you could collaborate with Indigo, Nori, or Verra – these voluntary market places – and probably get paid for particular practices right now.

Jennifer Pett-Ridge 7:49
I think that in another five years, we’re going to have a much more reliable marketplace with what they call, ‘measurement, reporting, and verification’ standards that are more well agreed upon. But the sticky thing right now is the measurement. Those point measurements, just like you said, they’re hard to do at anything below maybe 20 cm. They are hard to do often enough. A single field, you might need 15 measurements in a hectare. That’s cost prohibitive for most growers. For an academic or a researcher like myself, that’s our bread and butter.

Jennifer Pett-Ridge 8:35
But we are actually pretty excited and working with some companies, but also some research groups that are looking at much more low-cost ways to do soil carbon monitoring. That ranges from cool spectroscopy approaches to really cheap sensors that you would put on the soil surface and might even be biodegradable so, we’re not putting garbage in our fields. But these kinds of systems where we are monitoring, not with a single point measurement, but with at least multiple times over multiple season and multiple years. That’s, what I think, is going to be important to get our heads around this and get to a place where we feel comfortable to have a carbon market.

Linley Dixon 9:24
I talked to a farmer from Vilicus Farms – they are dryland grain farmers. They have pretty complex crop rotations, a lot of perennial strips in their grain production, and many different crops, sort of their carbon goes up and down in their rotations. They tried to apply for some carbon markets because of all the farmers are just like, “Wow. These guys really are doing a lot right.” They were told their farm is too complex to measure.

Linley Dixon 10:01
I think it’s funny sometimes, because I feel like you could get really good…there’s kind of a debate in the organic versus the regenerative thinking that organic is systems based and regenerative is outcomes based. We’re going to measure it to improve it. I just have concerns that…you could take in a bunch of hay, and you could get really amazing carbon increases on your land. But I’m like, “Let’s look at the system as a whole.” The skeptic in me just always worries that taking soil measurements, even if we could get them really accurate, we’re not actually accomplishing our goal of sequestering carbon overall in the system.

Jennifer Pett-Ridge 10:43
Yeah. This is a big issue we’ve faced. We’ve published some papers on this. It sounds really nerdy, but we talk about systems boundaries. Let’s say compost as an example. If you have a soil that’s, let’s say, starts with 3% carbon, and you truck in a bunch of compost from some other place, and you start adding it year on year on year. Yeah, your carbon is very likely going to go up. You’re adding carbon. You got to be screwing up to be not seeing your carbon go up if you’re adding carbon.

Jennifer Pett-Ridge 11:19
But first of all, is that carbon causing a net drawdown from the atmosphere? Are we benefiting the overall climate? Not necessarily, because you’re just kind of moving it from whatever that other farm was where the compost was made – it probably would have biodegraded over there. Now it’s just biotegrating on your field. Maybe you’re adding a little carbon in the process, but if you just draw the system boundaries at your fence line, you’re not really accounting for the broader system.

Jennifer Pett-Ridge 11:51
Now, if your goal is simply to increase the organic matter in your field so that your crops grow better, that your soil health is higher, great. That’s your goal. From a carbon marketing perspective, our goal is more global, that we’re trying to actually help the climate by removing carbon dioxide from the atmosphere. We’re trying to kind of restore the carbon cycle balance of the planet. That’s kind of just moving deck chairs around in the Titanic. It’s not actually like helping the overall system.

Linley Dixon 12:24
Do you feel like some of these – you said within five years – you’re going to feel better about them? Are there some systems that you’re excited about that are maybe taking a bigger…?

Jennifer Pett-Ridge 12:33
Yeah. I say that largely because, A, I think it’s it is a solvable problem. B, I just see a lot of people working on it, and there was actually federal investment, but maybe that’s going to slow down. Maybe I’ll need to extend to eight years that we’ll see actually some progress. It is hard to move policy, but I truly believe that growers are pragmatic. They are soil scientists at heart, whether or not they have a degree. Every grower that I’ve talked to, whether they’re conventional or organic, is interested in retaining their soil, stopping erosion and improving the health of their soil because they know how important that it is for the health of their production systems.

Jennifer Pett-Ridge 13:32
I think that’s why I’m optimistic that we will move forward in terms of making those measurements. Probably they won’t get made down to a meter deep, which is what I would love to see. We won’t get it all, but I think that we will make progress on the next five years.

Linley Dixon 13:50
Your studies in switchgrass, is that something that’s going much deeper? Is that something you feel like we should be incorporating in our farm production?

Jennifer Pett-Ridge 14:00
Yeah. That’s one reason why I do think that deep soil is important – because there are mostly perennials, but even some annuals. We’re working on sorghum these days and it has really deep roots. If we distribute root carbon throughout a greater volume, we just have more chances to accumulate that carbon. Also, the microbes that are down deep; they’re less of them, they’re a little sluggish, they’re not degrading it and causing the loss as fast. It’s sort of a simplistic understanding still, but we do see accumulation when we get roots that are further through the profile.

Jennifer Pett-Ridge 14:46
But that’s actually not the only reason. There’s some great work that came out of Kate Scow’s lab at UC Davis, where they looked at these long, long-term trials of no-till and different kinds of amendments. They said – just what you said a few minutes ago – that what was happening at the surface is not necessarily reflecting what happened at depth in the soil. You might be actually accumulating carbon in that upper 10 cm to 15 cm and losing it from deep soil. That is obviously something you’re not going to know unless you start making those measurements with depth.

Linley Dixon 15:24
One of the questions after your presentation that was asked you used the word ‘carbon flux.’ I’m wondering if you could describe why ‘flux’ not ‘flow’? What does it mean to you? Maybe to just describe what you’re talking about. I think organic farmers have this intuitively, that they are trying to keep nutrient cycling. That’s their job to keep things going. But I’m just curious if you could dive into that term a little bit more, and what your thoughts are.

Jennifer Pett-Ridge 15:24
Oh, sure. It’s just a nerdy, sciency word. I think it’s almost exactly the same thing is flow. But what is important and has been a through line in my career is, we tend to talk about pools – and those are static. If you think about the size of the bathtub is sort of a static thing. But if you’ve got the plug open and the tap on in the bathtub, it might stay full, but there is water moving through that system. There’s water coming in and there’s water going down the drain.

Jennifer Pett-Ridge 16:34
Now, instead of talking about water, what if that was carbon and the bathtub is your field. That carbon is coming in and it’s leaving both through loss of CO₂ and methane, because there’s decent composition, there’s a certain amount of dissolved carbon that actually just drains down into aquifers. It might even have a little bit of erosion that takes carbon off site. So, the point is that you’ve got flow happening.

Jennifer Pett-Ridge 17:02
Every time the plants grow and they put roots in the ground or there are flows coming out of the roots, there’s roots decay into micro-organisms, things are coming back into the atmosphere eventually. That’s a very moving vision of what I talked about earlier – that flywheel of carbon entering and then leaving the system. A little tiny bit of that carbon might kind of get stuck and stay in the bathtub, as it were. We can talk about the ways it gets stuck, but really, it’s that flow that’s happening. It’s super healthy in terms of providing nitrogen and providing phosphorus for both the plant and the microbes they depend on.

Jennifer Pett-Ridge 17:47
That’s, in a way, a new thinking for me: to not want to just increase the size of the bathtub over time. Increase the pool size, but just make sure that the flow is happening all year-round, which is coming back to cover crops. That’s why I love them. We think that they really seem to work. The data suggests they work in terms of increasing soil carbon below ground.

Linley Dixon 18:13
Have you ever looked at that debate? I know some of those minimum till annual organic farmers looked at keeping the cover crops on the surface. They had trouble keeping that flux – that flow – going, because they weren’t incorporating, they weren’t tilling that cover crop in. I don’t know if you have looked at any of the…

Jennifer Pett-Ridge 18:32
Super interesting. I have not. I want to be honest that I haven’t looked at that nuance. Our analysis of cover cropping was tied to a report that I helped lead called roadster removal. We were looking at how to remove CO₂ from the atmosphere. We were just trying to make decisions on what to encourage across the entire nation, which, of course, is hard because there’s really different climates, soils and farming practices. That’s where we came down to… It just looked like every time we looked at cover cropping generically, it was beneficial.

Jennifer Pett-Ridge 19:12
But I think that you’re right. There are so many nuances of how you do the cover cropping that probably need additional study that I don’t know enough about, to be honest. When I talk to farmers in Nebraska, the way that they are transitioning from their cover crop into their cash crop, is very different from the farmers here in California, than farmers that I’ve talked to in North Carolina. It depends on your climate, on how wet your soils are, and then, a certain amount of tilling that material in does seem to need to happen – whether it happens every year or every few years. Again, there’s different practices in different places.

Jennifer Pett-Ridge 20:01
I remember even the different crops, because they were like, “Well, then the rodents loved this stuff on the surface. For our melons, we had all these mice bites.” It’s just very complicated. Phil Foster said it worked when he then added plastic on top of the those, because that traps the moisture and helps it degrade. So, there’s all these trade offs that we have to figure out.

Jennifer Pett-Ridge 20:23
When Phil first told me about that, he came to talk to our group. They were using this term, I think they called it ‘plastic mulch.’ I was like, “Okay, sorry. What is plastic mulch? You guys are organic. Why would you use plastic? That feels like it breaks some fundamental rule.” But no, it really works, because it helps warm everything up and everything degrades better. That was a big eye opener for me.

Linley Dixon 20:55
The second half, I want to nerd out on like where the long term storage might happen. But just keeping on the theme of policy. I’m curious if you have thoughts. Some of the climate-smart money, I was just like, “This is so climate dumb,” when I read some of where the money went. One of them was growing a cover crop to produce a liquid fertilizer. They harvested it, and then I was like, “Why are we just using that fertility in place?” It seemed like, again, the full cost accounting wasn’t being done.

Linley Dixon 21:30
I’m curious if you have thoughts about certain practices that we should be funding. There’s trade-offs with everything. I don’t know if you’ve been following SGMA in California – growing cover crops needs water. These things are so complicated. Do you do you have faith that maybe we’ve got some systems that we’re just like, “Yes, this is a climate-smart practice. We should be promoting this across the board.”?

Jennifer Pett-Ridge 22:02
Let me just say, I’m a big, big believer in place-based science and policy. I think that is very difficult for the USDA – for the Farm Bill – to prescribe single policies that are going to be good across the nation. I laud them for trying. I think that, in general, cover cropping is a good thing to encourage. I think the Conservation Reserve Program (CRP), where you put land aside…I support those ideas.

Jennifer Pett-Ridge 22:42
In general, encouraging head rose, encouraging some perennials on a landscape – even if you’re growing annuals – like just getting some trees, some hedges and some deep roots back in that landscape, getting those prairie strips back in the landscape. There’s probably a list of maybe half a dozen things that I think are just great across the country.

Jennifer Pett-Ridge 23:04
But then, when you get into the weeds, sorry to talk about weeds, of course, but to get into the details, we really need place-based data and solutions. What’s right for somebody in the San Joaquin Valley might be something that’s different than in the northern part of the Central Valley, than in the Central Coast of California. We are just in a very different space, both in terms of what we grow, but also our climate, than folks in Colorado, than folks who are in Indiana.

Jennifer Pett-Ridge 23:42
You brought up SGMA. A big project that we’re leading right now is, how do we increase soil carbon, take it out of the atmosphere in a water-limited reality? SGMA is taking potentially millions of acres out of production in California because there’s no water. If all of those acres are just left bare, that is terrible for our climate, it’s terrible for our air quality, because there’s a lot of dust, for erosion, for many, many reasons.

Jennifer Pett-Ridge 24:22
I think that some of the language around how having just a cover crop on the landscape takes water away from the main crop, or even just takes water, we really need to look at the data on that, because the data don’t support the idea that cover crops steal from your cash crop. Especially in our California and Mediterranean climate, where we do get our rainfall in the wintertime, often you can have either an annual or a perennial cover crop in place that is supported by just natural rainfall and need irrigating.

Jennifer Pett-Ridge 25:03
That’s just putting roots in the ground that are going to hold that soil. They’re going to hold the nitrogen, and keep it from leaching off site. I do think that carbon and water management can be integrated. They don’t have to be opposing forces. In Colorado, the story might be different. You don’t have quite a Mediterranean climate. There’s changes in when rain is coming that maybe I haven’t thought deeply enough about, but I can tell you what I know for California. Again, place-based answers. That’s where I live, and that’s kind of what I know most about at this point.

Linley Dixon 25:46
That makes a ton of sense especially with the confusion around, is cover cropping good or bad, or just leave it on the surface, incorporated, all of that. Like you said, it is so place-based. I’m thinking of Vallis Gates Farms again, where the norm is chem fallow for wheat, because you pretty much need to take a full year off of wheat production, which is the crop that’s subsidized. That’s what everybody wants to grow.

Linley Dixon 26:12
In order to get enough water, because it’s all dryland farm, they only really use crop insurance if you’re following these practices, which are like a full year of absolutely bare soils. This is thought to conserve water. That’s what we’re subsidizing, and that’s what our crop insurance is favoring. That’s why this organic farm just they’re not going to herbicide and keep bare soils in it. The things didn’t support what they were trying to do there – both our crop insurance and subsidies.

Linley Dixon 26:42
It just makes you realize how important scientists that know about local agriculture, their role in actually influencing policy, and that’s so counter intuitive to what we’re taught. I even at EcoFarm, I saw a scientist on a panel who was like, “Well, I’m a scientist, so I shouldn’t have an opinion here.” And it was just like, “No, you absolutely need to speak up, because you probably have the most informed opinion that we should all be listening to.”

Linley Dixon 26:42
I’m curious if you have thoughts about how to encourage scientists to speak up when they see a policy is going the wrong direction. How do we kind of create more activist scientists? Because I think we really need them right now.

Jennifer Pett-Ridge 27:32
You’re absolutely right that the traditional academic disciplines we’re very taught to sort of stay in our lane and be just very evidence-based. I think everyone is realizing that just publishing a paper in a peer review journal that somebody has to pay to even access, that is not a way to influence growers or policy. It is just staying in our little bubble – staying in the ivory tower.

Jennifer Pett-Ridge 28:03
That’s why I love to see…the number of extension specialists seems to be, I don’t know if it’s growing, but I’m engaging more and more with those folks. I just feel like there’s such a critical spot to sit in between that research university life and knowledge base, and actually direct engagement with farmers. I just met a guy at UC Santa Cruz who’s playing that role. I know UC Merced is hiring someone, and UC Davis has tons of people.

Jennifer Pett-Ridge 28:35
We have a family farm out in Nebraska. When I was out there last, I was talking to the farm manager, and he said, “I just do whatever my extension agent tells me to do. He’s gives me the recipe, and I do it.” I was like, “Wow, you’re putting a lot of trust in that person, but great, they have a lot of influence, and hopefully they’re good.

Linley Dixon 29:00
The important thing is to make sure they’re good.

Jennifer Pett-Ridge 29:02
Yeah, right. Hopefully they know what they’re doing. But translating that to policy, I will tell you I don’t have an answer for you, yet. That seems stickier. That path between research and growers, I think that the extension folks are the answer. But getting the evidence-based information into the hands of USDA and those Congress representatives that you said you met in DC, that is proving hard.

Jennifer Pett-Ridge 29:36
I have several colleagues who’ve done…we call them details. Just little temporary assignments in Washington and engage with USDA. The officials there are desperate for information. But like all of us, they’re super busy, they got a lot on their plate. They can’t read literature. How do they know which academic to trust and which…? Because we all have a little bit of bias. That’s just how we made. I wish I you had a better answer for you, but I feel like that is a piece that we need to work on – developing a better flow from the academic and grower-informed world into policy making.

Linley Dixon 30:19
I’m afraid what we have now is they have the ear of the scientists from the big agricultural companies or the chemical companies that those guys do get a seat at the table [inaudible 30:33]. The huge microphone that they have, we’re trying to at least get a small voice in there and it’s really challenging. There was a Nature paper that came out, and it was talking about how organic farming is bad for the climate, because we have lower yields per acre, and therefore we need more land, and all agriculture is inherently worse than native ecosystems. Therefore, organic is bad for the climate.

Linley Dixon 31:01
It was just like, “Okay. I think we might be cherry picking again – one piece of data. Do we need to look at the bigger picture here?” Is there something that comes to mind to you when you hear about that study – the conclusion that was made?

Jennifer Pett-Ridge 31:13
Yeah. I think again, that’s a problem of a lack of systems thinking. Just like in a lot of areas to do with energy use that we don’t measure all of what we call externalities – the things that are difficult to measure, usually. That happens in agriculture. When we add in organic fertilizer, it takes an enormous amount of fossil fuel to make that inorganic fertilizer. So, there’s that cost, but it’s off farm. There’s the negative effects of that inorganic fertilizer, both in situ, and the loss of nitrous oxide, which is a very potent greenhouse gas, but that seepage of usually nitrate into waterways and the algal blooms.

Jennifer Pett-Ridge 32:03
Again, all those are off farm and difficult to measure, because they’re…anytime something moves into the hydrologic cycle and is affecting a river or the Gulf of Mexico, how are you going to really measure…who’s at fault or who caused what? So those systems level analyzes often don’t get done. They don’t get funded. They take very interdisciplinary science, but encouraging as much as we can of that kind of thinking to think about, “Okay, well, organic agriculture may not be producing as much, but last time I checked, we’re using 30% of our corn to feed cows. That we have more than we need.”

Jennifer Pett-Ridge 32:47
We have more calories than we need being produced at least in the United States. It’s not true in every country, but we’re putting a lot of that into our gas tanks. Food security is a real issue globally, but at least in this country, we have enough. We need to stop wasting food more than we need to produce an extra 5%, 10%, 20% on every acre of land. I think if we produced what we produce in a more sustainable manner, I’m perfectly fine with lower yields. That’s my perspective.

Jennifer Pett-Ridge 33:28
JP, you mentioned cows and confinement – feeding them corn. Do you feel comfortable enough talking about a better way to produce animals? Or do you feel like confinement we just shouldn’t be eating animals. There’s kind of that debate in climate science.

Jennifer Pett-Ridge 33:45
It is big [inaudible 33:50]. It’s not an area that I have real expertise in. I have friends who have very, very strong opinions about: if we took cows out of the landscape, we could transition so, so many acres back into forest, and into ecosystems that are absorbing carbon. We could even potentially get paid to do that. So, there are landowners, particularly in the southeastern US where the land values are pretty low, that are barely making money running cattle, and potentially could be getting paid much more in terms of carbon credits if they took the cows off and started growing forests.

Jennifer Pett-Ridge 34:36
That’s a interesting idea, but the problem is that we do just still have a lot of demand for meat protein. If we started doing that in the US, does that mean we cut down more forests in Brazil or in Southeast Asia or elsewhere? Those trickle-down effects are really scary. Again, I’m starting to wade into areas that I don’t really have data to support, but it’s a tough issue. I’ll just be straight with you, though. I’m not a vegetarian, and I’m not a completely anti-cow person, but I do think that there are a lot of inefficiencies in the way that we… particularly the whole pathway from corn to cattle in this country – the way that occurs.

Linley Dixon 35:25
Then putting a lot of these really large confinements in the desert, where it does require a lot of water. We’re talking about draining aquifers and things. Climate issues are inherently global. Again, it goes back to place-based. Then you talked about, “Well, if we implement something in the US, what does that mean for what then happens in Brazil?” Could you maybe talk about anything hopeful that you feel like is happening in terms of working together internationally on some of these issues?

Jennifer Pett-Ridge 36:00
I want to come back to the area that I actually have expertise in, because I feel most comfortable in talking about carbondioxide removal. That’s a topic that I’ve really worked hard on in the past several years. There is international agreement that even if we did our darndest to decarbonize – to stop using fossil energy as much as we can – we’re just not going fast enough. We probably even can’t get all the way to zero, because there’s just too many industries. Farming is one of them where we produce greenhouse gasses that we don’t have a way to avoid.

Jennifer Pett-Ridge 36:38
We got to actually figure out how to vacuum some of that extra greenhouse gas, or CO₂ out of the atmosphere. I just see that as such a big win for agriculture, because we know that carbon is actually organic matter. Organic matter is half carbon, and so there’s nitrogen, phosphorus and water holding capacity and diverse microorganisms and all these other, what we call ‘co-benefits.’ They come along with that carbon.

Jennifer Pett-Ridge 36:38
All across the world, nations have agreed that, “Yes, we need to focus on this. That agriculture is a big place to focus.” The carbon that we put back in our soils gives us so much benefit locally. Even if the climate benefit is very diffuse and very hard to even get wrap your head around, it has these immediate benefits in terms of our soil health. I see that in Europe. I see that in developing countries, in the Global South. I was in Africa this past summer, and it resonated in all sorts of places in South Africa and elsewhere. Kenya is very involved in this.

Jennifer Pett-Ridge 37:53
I’m enthusiastic that managing soils in more – pick your favorite word – healthy, regenerative, whatever you want; no-till, whatever term you want to use, is something that seems to be just globally appreciated. I see marketplaces developing that are encouraging it. Not in every country, but the biggest amount of carbon dioxide removal that’s actually being paid for internationally, is adding mostly bio char, but adding amendments to soils.

Jennifer Pett-Ridge 38:32
Most of that’s happening in Europe, but it’s something that can happen anywhere. On the horizon, there’s a lot of discussion about adding crushed rock – what they call ‘Enhanced Rock Weathering’ – which is really kind of just like lime additions, but slightly different. But that’s another approach that I think in five years time we’ll be talking very seriously about, and could be benefiting soils and production across the world.

Linley Dixon 38:58
Is this like…I’m in Colorado with very young soils, so maybe that wouldn’t benefit me as much as more aged soils. Or what is the idea here?

Jennifer Pett-Ridge 39:06
No, not necessarily. The idea is that you take, typically, basalts, so they’re all calcium or magnesium silicates that naturally weather. When they are weathering and breaking down, they naturally take molecules of CO₂ from the atmosphere. There’s a lot of chemistry involved – they create bicarbonate that then ends up kind of washing out into the oceans. But it’s a net removal of carbon from the atmosphere. In the process, there’s not enough data yet, but a lot of folks are seeing benefits to their crop production. In the same way that managing pH through liming often is. Many, many soils benefit from a little lime addition.

Jennifer Pett-Ridge 39:54
Now, you’re absolutely right that your particular land in Colorado there might be more or less benefit than somebody in a more highly weathered or less, that’s always going to be true. But again, it’s a technique that’s right now seen as, on the whole beneficial with not too many downsides. That’s kind of what we go for, right? It’s something that’s net positive.

Linley Dixon 40:21
You got asked a question about biochar at the conference. You said it seemed to be more effective in tropical soils. I was curious if you could elaborate on that. Biochar is kind of a really sexy thing right now. [inaudible 40:33] do it in a pretty cold soils?

Jennifer Pett-Ridge 40:36
Again, I don’t see a lot of downsize for biochar. Unless you got a batch that was made that, just for whatever reason, had a lot of strange hydrocarbons or something in it, which I haven’t seen literature on it. I really just think it’s either a net neutral or a net positive in almost all soils to be adding biochar. It’s, again, back to those systems boundaries, that if you take biochar that was made off-site and you maybe made it from trees, or you made it from corn stove, or whatever you made it from, and you add it to your site. Do we at the system level call that a net carbon increase, because that biochar is going to probably stick around for a long time in your site? Well, you kind of just moved things around on the landscape.

Jennifer Pett-Ridge 41:28
Some folks have seen, though, that when you add biochar to a soil, that the productivity of that land actually increases. We’re not entirely sure why that is, but some folks think it has to do with those… Biochar when you look at it in a microscope, kind of looks like pumice. What I mean by that, it’s got a lot of surfaces. It’s just got a lot of little, kind of crevices and holes. Each of those, if you can imagine, has a little potential to react with an ion like nitrate, ammonium or phosphate. A lot of those are things that we want – do we want to hang on to?

Jennifer Pett-Ridge 42:04
So if what that biochar does is, it takes a pretty inert material, but creates just a lot of surface area to grab good things that we want to kind of be slow-released so that plants can get at that ammonium but not all in one day – kind of over a long period of time – then I think of it as, in a way, kind of a…it’s not a fertilizer in itself, but if it allows the system to have time to access those nutrients and it stretches out that process. I wonder if that’s the benefit.

Jennifer Pett-Ridge 42:43
I have little data to support that – not enough – but the carbon itself that’s in the biochar is really pretty inert. It is in such a cooked, pyrolyzed form that it’s not really interacting. We actually see very, very little decomposition. But it’s that surface reactivity that seems to have the beneficial effect that people have measured in some systems.

Linley Dixon 43:15
When you’re speaking, tell me if this makes any sense. It seems to me that it might be more beneficial, say, if you’re applying fertilizers, and you know how they say at most only a third are taken up, and the rest kind of wash away. It might be great at holding on to what you’ve applied. I’m curious if you’re an organic farmer and you’re thinking about that cycling, and you’re growing your cover crop in place, and it’s a diverse cover crop, so the nutrients are kind of breaking down over time. Is there any concern that biochar might lock up something that you need, that might be readily available.

Linley Dixon 43:48
Does it have different applications for a farm that’s applying fertilizers that are readily available versus a traditional organic system, where the breakdown of organic matter over time is what’s feeding your crop?

Jennifer Pett-Ridge 44:02
I think that’s an interesting hypothesis, and I can’t tell you that I’ve seen anybody really study it.

Linley Dixon 44:07
I gotta go back to grad school.

Jennifer Pett-Ridge 44:08
You do. I think that a lot of the organic farmers I engage with are functionally in grad school. Too bad they’re not getting it to get an official degree because they deserve it. But there’s some great studies – not enough, but a couple – on what we call co-composted biochar. Where folks have actually mixed biochar in with compost, or it’s been part of a like a municipal industrial composting system.

Jennifer Pett-Ridge 44:42
What I think that does is it, it charges up all of those exchange sites in the char, it gets all those great nutrients absorbed, and then when you add it, you got some compost that’s actually just providing nutrients instantaneously through microbial action, and then you got that more slow-release kind of fertilizer effect that’s coming from the char. That’s a guess. I would really love to see somebody test that in a really careful way. But I I’ve not seen real downsides with char additions, with and without compost. I don’t know a ton of farmers that do it. It goes back to policy. It’s not something that’s been encouraged, but I think could be.

Linley Dixon 45:28
Do you think that the applications and tropical soils are because of so much leaching from all the rain that it’s just the capacity to hold on to it? It might be why it’s working there so well?

Jennifer Pett-Ridge 45:43
Tropical soils, on the whole, have a very different net charge. This is, again, kind of in the weeds and soil chemistry. But the types of ions that are held, that are bound well in tropical soils are very, very different than in the temperate zone, and it has to do just simply the amount of weathering. They are at the far end of the weathering spectrum.

Jennifer Pett-Ridge 46:09
The soils are so old they’ve lost a lot of… we call them a short-range order, but they’re the types of minerals that are really grabby, that are good at holding on to ions. So, you’re kind of left with mineral phases that are mostly clays and iron oxides that are not as good at hanging on to some of those nutrients that are so important to our plant growth. So, in some ways, it’s adding that char just, again, kind of rebuilds that ability to hang on to those important ions.

Linley Dixon 46:46
I’m very aware of our time. I’m wondering – we did get a recording of our presentation. I know that farmers are most excited, usually about the fungal highways, and some of those items you presented in our talk. So maybe it makes sense, since you have a flight to catch to do a two-parter. The second part can be just like, “Let’s wonk out on the life in the soil – what it’s doing.” You can talk about [inaudible 47:15] and nutrient exchange stuff like that that farmers get really excited about. Does that make sense?

Jennifer Pett-Ridge 47:20
Yeah. I’d be happy to do that.

Jennifer Pett-Ridge 47:22
Okay. Do you have any kind of final thoughts on the political aspect of…? I know that so much of what we’re doing, farmers want to be involved; they want to be stewards. A lot of times, we’re told something’s great, and then we find out later, it’s not. Maybe the role of the farmer. Do we need more farmers on the land? Can we be involved in the processes? Involved in the politics?

Jennifer Pett-Ridge 47:58
What is in the future you see, if we’re really going to create an agriculture that helps with climate? Can you see it out? Can you envision…? Does it look like, maybe just machines on the land, and it’s like, everybody’s kind of removed, they’re in cities, and it’s all automated. In the realm of anything possible, do you kind of a vision of where we need to be going?

Jennifer Pett-Ridge 48:23
Here’s, I think what I would ask of the farming and grower community is…I made that little comment earlier about, you’re all as much soil scientists as I am. What’s different is the collection of data. I would encourage growers to collect as much data year on year as they can: as they can afford, and as they can afford the time to keep track of it. Or collaborate with a soil scientist or with your extension agent to keep data on how much you’re producing, what your soil chemistry looks like, what you’ve added, how much you’ve added year on year. Try to keep that information per field.

Jennifer Pett-Ridge 49:15
I know that’s hard. That’s what scientists’ bread and butter is. But what we find when we go to engage with a grower is that history is kind of all in their head, and it’s not written down. It’s not in a digital fashion. That personal history is super, super important. I always interview a grower if we’re if we’re going to go work in a new site.

Jennifer Pett-Ridge 49:43
But being able to look at how things are actually changing year on year on year, when you add compost, when you do this, when you add fertilizer, whatever it is you do, is the only way we’re going to be able to collect enough information to truly kind of get a sense of what are the right practices. You mentioned that sometimes you’re told to do something, and then all you learn later on, that’s the wrong thing to do. The reason for those kind of ups and downs is because we just don’t have enough information across enough different climate and soil contexts.

Jennifer Pett-Ridge 50:24
I have been nagging the state of the California with some of their Healthy Soils Program. They’ve been collecting data from farmers for a decade now, but they haven’t made it public. They haven’t shared it back out. That is what it’s really critical: that all of that information gets collected, but then it becomes publicly available, so that we can not point to the one farmer who didn’t do a good job, but to understand across all of many hundreds of farms what seems to be working.

Jennifer Pett-Ridge 50:58
Because I do think that every farmer is actually, every year, carrying out an experiment. The piece that is, I’m not even going to say it’s missing, because most farmers actually absolutely know what their production level is, but there are a couple of other critical pieces of information that I would love to encourage that folks collect.

Linley Dixon 51:17
What comes to mind when you’re talking, ‘is too complex to measure’? Our systems at the farms that I visit, they’ve got pigs, chickens, vegetables and greenhouses and so it seems overwhelming. So, collecting data, but like, what data? We do need help and guidance in that process [inaudible 51:42]… do you want these complex farms as anything that you could use, or is it too complex to know what’s going on?

Jennifer Pett-Ridge 51:50
Well, let me just say this. Aidee Guzman who spoke in our session at EcoFarm; she’s done some wonderful work in poly cultures here in California, these are farms where they sometimes have a hundred different crops growing on a single acre – which is mind boggling – but she sees significant increases in soil carbon and really significant increases in the diversity of the mycorrhizae, but also just the total microbiome organisms.

Jennifer Pett-Ridge 52:26
I call that healthy soil. Those are my metrics. That diversity that you’re talking about, whether it’s in the number of different crops or having the pigs and the compost and the till, all of the things, I think those always have a net positive benefit.

Linley Dixon 52:48
Thank you, JP. We’ll do part two when we find the time. I really appreciate it.

Jennifer Pett-Ridge 52:53
Alright. It was great to talk to you, Linley. Thank you.

Linley Dixon 52:55
Have a good flight.

Jennifer Pett-Ridge 52:56
Alright. See you.

Jennifer Pett-Ridge 52:57
Bye.