Unearthing the Secrets of Soil Carbon Sequestration with Doug Collins – Episode 014

In this episode of “The Evergreen Thumb,” we delve into the fascinating world of carbon sequestration, exploring how gardeners in Washington State can play a crucial role in environmental stewardship. Our expert guest, Doug Collins, sheds light on the significance of healthy soil in capturing and storing carbon, emphasizing the impact of gardening practices on this process. From the role of plants in soil carbon sequestration to practical steps for listeners to enhance soil health in their gardens, we uncover the secrets beneath the surface. Join us as we sow the seeds of knowledge on soil science, guiding our audience toward sustainable gardening practices that contribute to a greener and more climate-resilient future.

• Carbon Sequestration
• Gardening and Farming to Sequester Carbon
• The Essentials of Carbon Gardening – Horticulture
• The Basics of Soil Biology – Episode 12
  

[00:00:00] Erin: Welcome to episode 14 of the Evergreen Thumb. My guest today is Doug Collins and he’s here to talk to us about carbon sequestration. Doug Collins is an extension professor and soil scientist with WSU’s Center for Sustaining Agriculture and Natural Resources. Doug has a Ph. D. in soil science from Washington State University and an M.S. in plant pathology from Montana State University. He focuses on managing and monitoring soil fertility on diverse organic vegetable farms, composting systems, and evaluating soil quality in different vegetable cropping systems, including organic reduced tillage. Doug is also interested in soil variability across landscapes and biological indicators of soil quality.

He has also consulted on composting, organic waste management, and soil health in the Dominican Republic and Colombia, and currently serves on the board of Washington Organics Recycling Council and the Washington State Department of Agriculture’s Organics Program.

All right, first off, it is time for the February gardening calendar.

In planning, it’s a good time to tune up your lawnmower and your garden equipment before the busy season begins. This can include cleaning up and sharpening tools and things like that. It’s a good time to have soil tested and determine the nutrient needs. For more information on soil testing, you can contact your local extension office and they can usually provide a list of laboratories in maintenance.

It’s a good time to repair winter damage to trees and shrubs. Uh, it’s a good time to start thinking about seed starting and cool-season vegetables. Um, you could start, uh, with winter sowing, uh, in milk jugs or in a cold frame. It’s getting close to time to incorporate cover crops. You want to make sure that cover crops are incorporated into the soil, um, at least six weeks before planting.

It’s time to trim ornamental grasses before new growth emerges in the spring. Um, in the east side of the Cascades, it’s time to prune and train summer-bearing and fall-bearing raspberries. Uh, it’s also time for prune and train grapes and take cuttings. Prune fruit trees and blueberries. Basically, it’s a good time to prune all of those, uh, fruit-bearing, uh, plants and, uh, shrubs and trees while they are still dormant.

In Western Washington, it’s a good time to prune and train trailing blackberries. If you didn’t do it last summer, uh, again, prune raspberries, deciduous summer blooming shrubs and trees, uh, in higher elevations. Uh, wait until April, uh, to do that pruning. In propagation, you can start container gardens, like, with herbs like chives and cilantro and parsley.

Plan for herbaceous perennials you want to add to your garden this spring. Um, some suggestions are astilbes or peonies and enemies. If the ground is warm enough, it’s a good time to plant asparagus. You can also start, uh, warm season crops like peppers, cold crops like cabbage, Brussels sprouts, cauliflower, broccoli can be started indoors in a greenhouse.

Um, snowdrops. If you have snowdrops on your property, you can move and divide those as the blooms begin to fade. Where the soil is dry enough and workable. Um, and you’ll know when the soil is workable. If you squeeze a handful of the soil, um, no water runs out of it. Um, it’s not frozen and it’s not saturated with water.

If you try to, uh, work in soil when it’s too wet, it will compact the soil. It’ll break down the soil aggregates and compress some of the, the air out of the soil. So make sure that the soil is dry enough and workable. And you can start to plant things like peas and sweet peas. Um, if it’s above freezing, you can plant new roses for pest monitoring management.

Um, don’t treat unless a problem is identified, and if you have trouble identifying what the problem is that you think you have, please contact your local extension office, get in touch with your local master gardeners, and they can help you identify the issue you’re having so that it can be treated appropriately.

Uh, you can use delayed or dormant sprays of for fruit and deciduous trees. Remove cankered limbs from fruit and nut trees for control of diseases such as anthracnose and bacterial canker of storm fruit and eastern filbert blight. Control moles and gophers with traps. Box elder bugs are emerging from hibernation.

They are not harmful but are a nuisance. So don’t be afraid of them, but you can remove them from your home with a vacuum or a broom and a dustpan. Um, in Western Oregon and Washington, monitor for European crane fly and treat lawns if damage has been verified. For houseplants and indoor gardening, you can make your own potting soil for starting seedlings in pots or flats and use clean or sterile commercial mixes if that works better for you.

Uh, it’s also a good time to sterilize your pots if you reuse pots for seed starting. And in central Washington, um, you can gather branches of quince, forsythia, or flowering cherries to bring indoors and force for early blooms. That about covers it for February. If you have any questions about any of these tasks that I’ve mentioned, please be sure to contact your local Master Gardener program.

You can find that at mastergardener.wsu.edu. All right. Now let’s get to Doug and soil carbon sequestration.

Doug, welcome to the show.

[00:06:01] Doug Collins: Thanks Erin.

[00:06:03] Erin: So to start off, why don’t you tell us a little bit about yourself and what you do and, um, how you got into soil science?

[00:06:09] Doug Collins: Sure. Yeah. My title is extension specialist and soil scientist, and I work at the Washington State University Puyallup Research and Extension Center in Puyallup, Washington, and I focus primarily on diversified organic cropping systems and also do a fair amount of work with composting and composting research and education. And especially with, I guess, with both of those, we were looking at soil, soil quality, um, you know, the impact of different management practices on soil health.

[00:06:47] Erin: Okay. So, um, since we’re talking mostly about carbon sequestration or today, uh, can you tell us a little bit about what that is and why it’s important to gardeners?

[00:06:58] Doug Collins: Sure. I guess sort of taking a big, um, picture view or a long view. Um, over the last about 800,000 years, uh, carbon dioxide concentrations in the atmosphere were below 300 parts per million.

They did go up and down quite a bit, but they tended to be, you know, below 300 parts per million for that long expanse of time. And in the last 6,000 years, uh, levels were around 280 parts per million in the atmosphere. Then you can see these steady levels of CO2 starting to change sort of gradually between 1750 and 1850 with the start of the Industrial Revolution, and by 1870, humans were really starting to admit significant CO2 into the atmosphere reaching around five gigatons annually by 1950. And currently, we’re over 35 gigatons of CO2 emitted annually, and atmospheric CO2 has reached 420 parts per million.

And so this atmosphere, this increase in atmospheric CO2 tracks really closely to the human emissions of CO2. And there’s no doubt that these increases in CO2, which is a greenhouse gas, it has, it reflects heat back to the atmosphere, to the Earth’s surface, and other greenhouse gases such as methane and nitrous oxide have led to an increase in surface temperature, and then also droughts, um, and more severe weather in general.

Most of that, uh, increase in CO2 came from burning fossil fuels, but it’s also estimated that as much as a third of the surplus CO2 has come from agriculture. and land management practices. So in other words, the soil has been a source of atmospheric CO2. Soils contain carbon and this carbon can be released into the atmosphere.

So soil carbon sequestration is the idea that perhaps we can put some of that carbon back into the soil.

[00:09:00] Erin: What constitutes healthy soil? I guess is a first good place to start.

[00:09:05] Doug Collins: Okay. Yeah. Um, healthy soil and, and is, the definition of sort of healthy soil or quality soil, and those are pretty similar, um, the short definition is the capacity of soil to function.

So in terms of whether a soil is healthy or it has good quality, you have to kind of put it in the context of what you’re expecting that soil to do. If you want the soil to be, you know, a place where you put a foundation to build a house or, um, support, you know, a fence post or something, you’re going to be looking at different attributes, um, then you are, if you’re looking for that soil to produce a forest or to produce, um, agriculturally.

So in our context, a lot of the times we are talking about, um, the function that we’re interested in, you know, in agriculture is going to be that the soil can provide healthy plants, um, and it can do so continually, right?

Because another definition to be aware of is productivity. So you can have a very productive soil, and when we talk about productivity, we’re usually talking, we measure that in terms of like bushels per acre or, or tons per acre.

So like how much can we get from the soil? And you can get a very productive soil, but that doesn’t necessarily mean it’s healthy if it’s, if you’re degrading that resource over time, or you could also be degrading the surrounding environment. So if we put down a lot of nutrients. Uh, to increase productivity, then those nutrients can be moved off of the, um, off the local site into waterways, into groundwater, and then they, they cause negative effects on those, on those natural resources, and so we certainly wouldn’t call that a healthy soil.

So, the main thing is kind of what is the, you know, the capacity of soil to function. We often require many different functions from soil. So, like producing healthy plants, but also cleansing, so cleansing, um, water. So, we want the water to be able to infiltrate into the soil. That’s a function that we look for from soil, um, you know, to hold nutrients, to re-release nutrients to plants.

[00:11:11] Erin: All right. So, um, for listeners who are interested, um, episode 12 is, um, an episode I did on kind of a brief overview of soil biology and, um, how it is a function of soil health. I encourage you to check that one out if you want to go a little more in-depth into that. So, my next question is, how does healthy soil contribute to carbon sequestration?

[00:11:34] Doug Collins: Yeah, a lot of your listeners have probably heard of soil organic matter and that is, organic matter is 55 percent carbon, um, more or less. So, they’re, they’re not interchangeable, um, carbon is a big part of organic matter, but organic matter includes um, other elements that are bound to carbon, such as hydrogen, oxygen, phosphorus, nitrogen, sulfur, potassium, and calcium.

So, when we talk about the organic matter, those are, are, are compounds that were, or, you know, were usually were derived from living material. And they’re brought into the soil, but it’s more than just the carbon. It’s like these other elements that are also bound to the carbon. So, they have weight, they have mass.

And if we’re measuring the organic matter, we’re going to measure those as well. We can also just measure directly the carbon. Um, so they’re, they’re not interchangeable, but you can usually derive one for the other, one from the other, um, based on that kind of what percentage of organic matter is carbon.

So again, as your listeners know, or probably have heard, like building organic matter is a great way to achieve healthy soil, and this is definitely related to the biological component, the organic matter, the carbon is like a, is a food source for a lot of the organisms in the soil and organisms mediate a lot of these important functions that we talked about earlier. So feeding that biology, um, with carbon, with, uh, organic matter. It’s a great way to promote healthy soils.

[00:13:08] Erin: Okay, so for the home gardener, what are some practices that they can use to facilitate carbon sequestration?

[00:13:16] Doug Collins: As I mentioned previously, it’s estimated that one-third of the surplus carbon in the soil has come from agricultural activities, and a big part of that is tillage.

So as soils are disturbed or tilled, that kind of, well, it exposes organic matter to being decomposed by, by bacteria and fungi. It gives them, it provides more of this food source. So instead of the carbon remaining in the soil, it basically like speeds up the engine and it becomes it, it basically becomes decomposed and is emitted as, as CO2 into the atmosphere.

Tillage really increases that the speed of decomposition by, by, um, making those materials more available to the microorganisms that, that do that decomposition. So, I would say, you know, for the home gardener, reducing tillage is important. Adding amendments to the soil is going to be helpful.

Compost Uh, and then cover crops are great. Anything that, you know, is going to cover crops or, or, or plants in general, just having like something growing is through the process of photosynthesis, plants take carbon out of the atmosphere. And then some of that carbon is going to be deposited below ground, just in the root biomass and then roots are also kind of, um, leaking carbon sugars that are feeding the microbes.

And then some crops are kind of like the biomass is left on the soil or turned into the soil and then you’re putting, you’re putting carbon directly into the soil. Other crops might, you know, drop some leaves, and provide input that way. Uh, if we’re growing like if you’re growing kale or something, you’re basically taking almost the entire above-ground biomass off to eat, but you, you’re also leaving behind the roots. So, I would say like a mix, you know, getting like a cover crop is a crop specifically grown to, um support the soil.

So growing cover crops like the idea is generally to take that biomass and put it into the soil to build organic matter. And you also get some benefits while the cover crop is growing from weed suppression, weed competition, and then again, like just having that root in the soil, leaking sugars, and putting carbon like directly underground.

So, there’s this relationship between, um, plant roots, roots, and good bacteria, uh, you know, that really tend to colonize what we call the rhizosphere. The rhizosphere is that area of the soil that’s very close to the roots. You know, within millimeters of the roots is the rhizosphere, and so we see a lot of, we see a different microbial environment, like, in that rhizosphere, like, right next to the roots than you do even just a couple millimeters away from the roots.

And that is due to roots kind of, like, feeding that native um, those, those microorganisms, uh, through, through leakage. So we have other, we have other, uh, relationships between plants and microbes, which are more symbiotic where they’re like, literally the microbe is inside the root or, you know, inside a structure that, that the plant builds to host the microbes, so rhizobia are an example of that, where there’s a really tight symbiotic relationship, but there are these other relationships that aren’t necessarily at that cellular level where um, we know that plants are like feeding microbes, um, by, by having some, you know, leakage of, of sugars. Cause plants are this, you know, they’re this amazing organism that’s actually bringing like carbon and sugar into the, um, environment and so, so other, other organisms are benefiting from that.

[00:17:10] Erin: So does that process continue for a time even after you cut the aerial parts of the plant? So, like, if you’re cutting it at the soil level as opposed to ripping them out?

[00:17:17] Doug Collins: That is a great question. I don’t think you’re going to get, like, I think when you cut the above ground, you’re going to stop photosynthesizing for the most part, depending on the plant, you know, if it’s a perennial that sort of is in its life cycle, okay with being chopped off and it’s going to start growing again from the root. Um, then you’re going to see photosynthesis starting again when conditions are right on, you know, I guess, like, think of mowing the lawn or something.

Um, there’s a lot of perennials in the lawn and, and we, we cut that down or, or if it’s a pasture, we have animals graze it and then we try to leave a little bit of it so the, the plant has can, can continue to photosynthesize, but for some annuals and a lot of cover crops or annuals, we let them like, especially in a no-till situation, we would let that cover crop grow until it flowers, and then we would probably mow it, or there’s other ways to try to terminate that cover crop at that point, um, usually trying to prevent it from making seed. But, um, you know, it’s going to, if it’s already kind of gone into that flowering stage, and it’s an annual, we cut it down, it’s not going to grow back, so at that point, it’s kind of going to die, or, or senesce, and then at that point the roots are going to become part of the soil organic matter.

[00:18:44] Erin: Right, okay. Um, so are there specific gardening practices besides, uh, no-till cover crops that will help with sequestration?

[00:18:52] Doug Collins: I, yeah, I mean, adding organic matter, um, which you can do through compost or, or other materials, you know, I don’t know how much this is an issue for gardeners. I think it’s very site-specific, but just avoiding soil loss is important.

Um, and that can happen through wind or water or erosion. So yeah, that’s kind of the number one thing with soil quality that we sometimes forget to mention is just keep the soil where it is, you know, don’t, don’t lose your soil.

[00:19:23] Erin: Right. Yeah, that is one of the things I talked about before about healthy soil is that’s, you know, keeping live roots in the ground to help prevent erosion and leaching of nutrients and, and things like that too.

[00:19:35] Doug Collins: Exactly. Yeah. Um, you know, perennials, perennials are great for soil quality. Uh, cause you, you remove that disturbance element. Um, you know, I mean, a lot of the things that we want to grow and eat are not perennials, so, um, we just, you know, we try to improve the production, but, but yeah, I think soil quality under perennials tends to be a little bit better because you don’t have that disturbance element.

[00:20:04] Erin: So are there particular plants that, um, maybe are better or more effective at capturing carbon than others?

[00:20:13] Doug Collins: I, you know, anything that’s really a fast-growing plant is probably, um, going to be, uh, the best choice, I think. Um, but like I said, also perennials are, are really good. Um, because they are holding, you know, like a perennial is holding a certain amount of carbon.

Uh, this is going to be more true with a tree. Uh, it’s going to hold quite a bit of carbon, especially a fast-growing tree, like in that first couple of years is really going to sequester, um, quite a bit of carbon. So like that, like the highest, best purpose for a tree, like if it’s especially in the early, early years is probably just to leave it where it is and let it, let it grow.

Um, but. For annuals, I think having a good rotation with some cover, like we do, like some cover crops are pretty fast growing and we like those. I like those because I don’t like weeds, and so I think a good fast-growing cover crop is, is great for suppressing weeds, but it’s also going to probably add the, you know, the most biomass to the soil.

Um, this question kind of also gets to this concept, um, about how stable is carbon in the soil and, you know, ideas around, around this have, have evolved, um, over the last two decades significantly, I would say, and the, um, what, what people, what most people, uh, understand now is that the location of the organic matter in the soil is really important in terms of how stable that organic matter is and a couple of places that we can find organic matter are associated with one, one would be associated with the mineral components of the soil. So like if you think clay, clay is the smallest particle size of minerals in the soil and the clay has a lot of organic matter and sorry, the clay has a lot of surface area. And organic matter can attach to that surface area. So like the more clay there is in the soil, the more opportunity there is for organic matter to kind of adhere to those surfaces and they form what we call organo-mineral complexes.

So it’s this mineral component, the clay, which is like coated in organic matter, and so that’s mineral-associated organic matter. Another type of organic matter is particulate organic matter. So, this is maybe newer organic material that was just put into the soil. And it’s just kind of floating around as small particles of organic matter that are getting progressively smaller as things sort of chew on them.

Um, we can also have organic matter inside of soil aggregates. And aggregates are these naturally formed stable conglomerates of soil, which are going to be composed of minerals and organic matter. And you can have mineral associated and you can have pom inside of that. POM is particulate organic matter.

You can have that inside of the aggregates. And that material is pretty stable as well until that aggregate breaks apart. Um, so like the most stable component is this mineral-associated organic matter. And the evidence shows that the organic matter that’s the most likely to associate with those mineral surfaces is organic matter that has been derived from biological activity. So, like bacteria, right?

It’s the waste products from the bacteria or it’s the cells of the bacteria themselves that is the most likely to actually attach to those mineral surfaces. And so, what that has led people to, to, uh, hypothesize is that the best materials to, um, sequester organic matter, sequester carbon in the soil are going to be the things that microbes like to eat.

And so, this is called high-quality litter, and it is material that has a low carbon-to-nitrogen ratio. So, it’s got more nitrogen for every, um, atom of carbon. And so in the world of cover crops, like that would be legumes, you know, things like, um, peas or clovers or vetches, they tend to have a low carbon to nitrogen ratio compared to like a grass, um, which is going to, you know, have, have more carbon, less nitrogen, so low seed in ratio and then low on the low on the phenol and lignin content, so more woody stuff is not the most palatable or the most desirable or the most energetic material for a microbe, so it’s going to be slower to be decomposed by those organisms and then sort of less likely to go to the mineral associated organic matter.

So this is a theory that basically, you know. Says putting high-quality materials into the soil is more likely to create that mineral-associated, but another element of that is that the amount of clay in the soil is going to, you know, set an upper threshold on how much mineral-associated organic matter you can have in a soil. So if you’ve got a really sandy soil. There just isn’t a lot of clay in there, so there’s less potential for forming mineral-associated organic matter.

[00:25:54] Erin: That makes sense where we’re at, because I’ve got, um, a lot of the Master Gardeners in our area are on the coast, where they have very sandy soil. Um, but even here where I’m at, I’m in, uh, um, the Chehalis River Valley, and so we have, we’re not, we’re on a shelf up above the river, but it’s really fast draining, very compacted…soil with no, no clay, hardly at all. So, I mean, is, is clay, um, necessary to fill, to form those, the mineral?

[00:26:26] Doug Collins: associated? Yeah, it is kind of by definition. Um, you know, I mean, when you say minerals, we’re talking about the, the inorganic material in the soil. So, you know, in a volume of soil, you’re going to have probably 50 percent of that volume is going to be minerals. Um, and that’s just like, think about. Rocks, you know, broken down, weathered rocks is essentially where those minerals are coming from. And then the, almost the other 50 percent of the soil is just going to be air space or porosity, which can be filled by air or water. So maybe 25 percent filled by water, 25 percent filled by air and then there’s going to be a small amount of organic matter, like one to 4 percent or, or sometimes a lot higher than that. So yeah, and then that mineral component.

We can further break that down just by size, and that’s what we call your soil texture. So that can be, the texture is just looking at what’s the percentage of those different size components and so sand is the biggest size of mineral components, silt is in the middle, and then clay is the smaller stuff.

So silt, you know, probably has the ability to, the surfaces of silt can react and maybe get some organic matter. On a surface area, just mathematically surface area is so much higher with clay that it, you know, the amount of clay is really going to drive like that surface area calculation.

[00:27:57] Erin: Okay. So kind of back to what you’re saying about cover crops and the, um, the carbon to nitrogen ratio would using inoculants for some of the, with some of those cover crops have an impact on that ratio or is it just the, the volume of plant material?

[00:28:15] Doug Collins: No, that’s, that’s a great question. Yeah, we, so inoculants, um, are generally used with legumes.

Um, and what is exactly in the inoculant would be, uh, specific species of rhizobia, which are a genus of bacteria that are able to form a symbiotic relationship, um, with legumes. And it is a good idea generally to coat the, the legume seed with rhizobia, um, before planting them, you know, if you’ve grown a lot of legumes and you’ve done some inoculation, you, you might not see a difference um, but if it’s new, you haven’t grown legumes for a while or, or the soil is really degraded, um, you’re likely to see a big difference by, um, getting some inoculum and putting it on, on your seeds. A lot of clover seeds are sold with a coating and those coatings, um, tend to have the rhizobia in them. So that’s one thing, um, to look for with the clovers in particular.

[00:29:22] Erin: And, um, is it true that a lot of those, uh, rhizobia are species specific to the various legumes? So, if you were to buy an inoculant separate, you want to make sure it’s for the right species of plant. So, a vetch versus a clover.

[00:29:38] Doug Collins: Exactly.

Yeah, I mean, some of them will say like they’re pretty general. I think they put a mixture of species in, in each one, but you want to make sure that it says a little usually say like for vetch and peas, you know, and you just want to make sure that it’s going to work for your particular species. And what that does again is just you know, the plant’s probably still going to grow well even if you don’t inoculate, but if everything is working well, we get a lot of what we call nodulation on those roots and so these nodules form when the rhizobia bacteria kind of infect the roots, almost like a pathogen. They infect the roots, they enter the root, then the plant will form this nodule, and inside of that nodule, and these nodules are macroscopic, so you can, you can dig up a root and tend to be able to see them.

Um, and so you can assess, you know, you can dig up a plant and, and sort of see the, the level of, of nodulation. Um, or see like, do I have any nodules? You know, if you don’t have any nodules, that’s probably a sign that, yeah, I should have, should have put some inoculum in there. And then, uh, you know, you’re, but even without the nodulation, you’ll still see growth of the plant, especially if there’s available nitrogen, um, in the environment.

Um, And I think, I think that if there’s excess nitrogen, that can even reduce nodulation. So, you know, the, the plant might be growing fine and not be nodulating a lot. Um, and that could be because it’s, there’s plenty of nitrogen in the environment or the, um, or you didn’t have the rhizobia weren’t, weren’t present. So you might still get growth and, and, you know, still have, like, it’s, it’s going to have. The C to N ratio is maybe going to be affected a little bit, like a nitrogen content might be affected a little bit if you don’t have good nodulation, but it’s probably still going to be a different C to N ratio than a grass would be. And grasses change too, they change their C to N ratio as they’re developing, as they’re maturing. So if you’re talking about, for example, like a cereal rye or a triticale or a wheat cover crop. Early in the year, like early in the spring when those plants are pretty small, kind of below knee-high, they are going to have more, uh, nitrogen relatively in them. Um, but then what happens is they sort of stop taking up nitrogen and they just keep growing. And so as they get taller and more woody, they might have the same nitrogen, but they have a whole lot more carbon associated with them. So the, the biomass increases, but the, the nitrogen concentration kind of stays the same whereas with the legume, they’ll continue to get bigger and bigger and bigger, and the, the nitrogen concentration will, will stay the same. The nitrogen content will go up with the biomass.

[00:32:27] Erin: So what are some challenges or opportunities, uh, in gardening for soil sequestration?

[00:32:34] Doug Collins: Yeah, you know, well, um, this whole idea of organic matter, you know, when we look at, at sort of natural soils, we do see some variability, but probably most are around that, like one to 4 percent organic matter. Um, there are soils, if a soil is greater than 20%, we call that an organic soil. And you can find those in like peats, and you know, those occur naturally, like really high organic matter. But then when we look at soils that are sort of in the backyard or, um, container grown areas, um, urban farms, you know, there’s a lot, a lot of urban farms out there these days. You can find really high organic matter, like, you know, 25%, it’s not unusual. Uh, and so that’s good, I think.

 Uh, there, some issues can arise when we get too much organic matter. And those have to do with oxygen. So, if you, you know, like this organic matter is just really good at holding water. If, if you’re not allowing the water to drain, or if for some reason the water isn’t draining well, then the, um, that really high organic matter soil can just become kind of waterlogged and then there’s no, um, porosity for oxygen and, um, air, you know, air exchange and roots need to have air exchange. So that’s one issue. Um, they, um, ironically, they don’t aggregate very well. So that’s kind of also related to that drainage because minerals are actually a really important component of aggregates, forming aggregates.

So I guess, you know, the take home there is you can have too much of a good thing, but I, would be hesitant to put a number on it because I see, you know, some really very successful and productive operations that are growing like almost 100 percent compost or like a compost sand mixture or something like that, so I think that is an opportunity. I think it’s an interesting area of research. And it’s, um, it’s an area, like there, there’s an area of research called anthropogenic soils, which is looking at, at soils that are, are highly influenced by human activity. So, I think we see opportunities for, for those, for creativity and, and, um, for sort of testing some of the boundaries or perceived boundaries and with anthropogenic soils, And another component of that is urban soils. So soils that may have been degraded by, um, human activity, uh, you know, what can we do to turn those into, uh, more productive areas and, you know, adding organic matter is kind of like the first on that list.

[00:35:17] Erin: So how does soil sequestration or I guess carbon in the larger sense tie into broader environmental stewardship efforts?

[00:35:29] Doug Collins: Well, I think like as, as we talked about, um, you know, just increasing soil quality in general um, is really good and adding organic matter is a great way to improve soil quality. So, specifically for sort of like environmental stewardship, we look to some of those functions that we look for from soil for like cleansing water, infiltrating water, storing water. Um, that’s another issue in urban environments, right? It’s like there’s no permeable surface, everything is paved, and so where water hits that pavement and it just starts to run, and so it’s really important to have soils be a part of that urban built environment so water has a place to go. And then a lot of that water is pretty, you know, it’s carrying with it contaminants that we don’t want to go into the surface water bodies.

We know that those contaminants can have negative impacts on, uh, fish populations, the material that comes off of tires has recently been found to be really toxic, uh, to salmon and other fish species. So, you know, can we create built environments using soil, using this natural resource that are going to be able to capture some of that material and, and provide filtration, infiltration, and then also filtration. So grabbing it and then cleansing it as, as we let it go. Um, so yeah, I think it’s just, you know, it’s natural that, that soil carbon is going to be, is going to be part of that solution or, or, you know, for, for, uh, gardening or urban audience.

[00:37:21] Erin: That kind of ties into our next episode, which is about rain gardens and I know that’s one of the things is that helps does help filter and infiltrate the water through the soil, that will be episode 15.

So, um, are there any misconceptions or hype around soil sequestration that we should know about?

[00:37:42] Doug Collins: Of course.

Yeah, there is, uh, there’s definitely some disagreement about the potential for sequestering carbon in the soil through management practices. On the one hand, there are efforts such as what’s called the four per mil, which states that if we increase by four parts per thousand or 0.4% a year, the quantity of carbon contained in soils, we can halt the annual increase in carbon dioxide in the atmosphere and so that that’s a French program that’s, you know, kind of promoting this idea that all we need to do is increase carbon, soil carbon concentration by 0.4% and that will counteract this, you know, surplus carbon dioxide. So the soil is the answer. We need to just get more carbon into the soil.

Um, other researchers take issue with that, um, and they say that cultural, economic, and physical barriers mean that soils face dim prospects as major carbon sinks. And some of the obstacles that are pointed to are, you know, the lack of farm-based investments. So, you know, first of all, if we’re going to do that 0.4 per mil, this is probably going to go beyond gardeners. And we’re, we’re looking at like big acreage of farms and there is a lot, right? There’s a lot of agriculture acres. And so you can kind of like do the math out that way and be like, Oh, all we need to do is, you know, add all this organic matter to these vast agricultural acres, in the world. And, you know, and there’s plenty of that in the, in the US as well, but, um, you know, how, like, what’s the investment that’s going to be provided to farmers to do that, you know, to really change the way they grow? So like how, like, how are you going to convince them to grow cover crops or whatever it takes to increase that even like, and that’s no small amount, either 0.4%, you know, that, that’s pretty impressive, um, level of, of building soil, organic matter.

Limits and verification; so say you can get them to get farmers to grow and just sequester carbon for the sake of it. How are we going to verify that that’s actually happening? Um, this gets there’s issues with that to get back to, you know, the questions about stable carbon. So, like I said, you can have carbon that’s sort of in aggregates, right? And, and if we break those aggregates up, then it can quickly decompose.

So like some of that verification may be, oh, because we’re growing a perennial or, you know, like something like alfalfa. So it’s in the ground for a couple of years, and during that time, things look really great. There’s lots of carbon there. But then if you come out of alfalfa and you till it up, you know, how much of that carbon do you lose?

Technical assistance, so, you know, who’s out there to help farmers do this. Resistance to government regulations. So, like, again, any program that’s going to pay somebody to do something, and then you are going to have to verify that that’s actually happening. Like, you’re basically talking about a government program, government regulation.

[00:40:45] Erin: And convincing a lot of farmers to completely change the way they’ve been doing things for generations.

[00:40:48] Doug Collins: Right. And then sort of the last obstacle is just this concept of, um, warming feedback loops. So, in the current temperature regime, we can try to model, like, you know, adding this amount of carbon to the soil, adding this amount of biomass to the soil will result in, you know, X increase of soil carbon over the years but that’s under like the current temperature regime. And if we start to add a degree Fahrenheit or a degree centigrade to that current temperature, that actually increases decomposition rates. So you get more biological activity in the soil, more decomposition. And so we call that a feedback loop. So there’s more increase in temperature, which increases decomposition rates, which increases CO2 in the atmosphere, which increases temperature. And so that, you know, the idea that sequestering carbon in the soil, um, is based on, on maybe a certain climate regime. And then as that climate warms, it can be, the math may not work the same in terms of now things are actually, decomposition rates are happening faster.

[00:42:08] Erin: So what kind of ongoing research is happening in this area and sequestration say in Washington?

[00:42:16] Doug Collins: I mean, I think, you know, a lot of those, I think the verification is definitely, um, a hot topic. There’s, there’s research going on in terms of that. Like, I think if we were able to confidently, I mean, that’s kind of almost the first step to any kind of program that might support farmers for where, where sequestration became like a driving force in agriculture.

In addition to, you know, running a profitable farm and, and selling what you’re, you know, marketing, what you’re, what you’re growing and things like that, if you want to add on top of that, this idea of, um, oh, now we’re going to, you know, compensate you for, for putting carbon into the soil. So I think, um, verification programs, there’s, there’s quite a bit of research into that. And that involves a lot of modeling, like I, you know, I talked about, like sort of the feedback loops problem, so there’s going to be an element of modeling. So you can get some data, but then you have to take that data and kind of like that might include what’s the texture of the soil, right? Like how much clay is in the soil?

What’s the climate at that particular location? What are the practices and how much biomass is that putting into the soil? And then what does that look like in turn? Like what’s your current level of organic matter? How close are you to like a threshold maybe of maximum organic matter? And what is the potential?

The whole idea of verification is an important one, and I’m not an expert on the, on the other kind of policy programs, but I think that’s also coming government support or regulation, um, to promote good practices. I mean, there’s a lot of voluntary stuff already out there, like programs that help farmers grow cover crops or, you know, help with, um, compensation for the, for growing cover crops or for doing other, for organic amendments there are some, already kind of voluntary programs that one can enter into that will provide some support. In terms of the gardening specifically, I think this area of anthropogenic soils is pretty exciting. And, um, you know, I, again, like on an acre basis, there’s fewer acres in cities, and so if we’re talking about, you know, increasing soils by a certain percentage, that will always require us to look at larger farms.

But in the gardening space, there are a lot of benefits to locally grown, um, produce, the, you know, just having more green space, uh, in cities makes a, makes a better environment, uh, helps reduce the heat island effect. So, um, it cools, you know, like having plants, it, it, it cools the, um, the city and you might be able to reduce transportation, um, for produce, um, closing nutrient cycles. There’s a lot of nutrients in cities like either from organic waste or, um, and then, and then can we, you know, figure out how to kind of recycle that back into the food chain more locally. It’s hard to move those materials. They’re heavy and expensive to move, so.

[00:45:41] Erin: All right. So are there any final thoughts that you’d like to add about um, soil health or carbon sequestration?

[00:45:48] Doug Collins: I don’t, I don’t know. I mean, I, I think in Washington in particular, there seems to be a lot of interest. Um, I think, I think it’s important that we, we give people good tools to work with, good systems to work with. Uh, you know, I mentioned a little bit about organic waste.

Uh, so I think being able to reduce waste, like, that’s an area where we see, um, both carbon and nutrients kind of ending up in the wrong places, you know, despite, I don’t know if you’ve ever been to like an event where there’s composting happening or, you know, people are trying to separate waste. It’s rare to see an example of where that’s going very smoothly. And I think that’s something that comes back to each individual, um, you know, to take the time to do that. Uh, I mean, obviously in your own home, like making sure that. Um, we’re separating waste and, and trying to make sure those wastes are, are being composted or, or entering the right, the right chain. So, in Washington, this is going to become more and more prevalent. You know, some cities already require composting food waste, but this is coming like, uh, at a larger scale in Washington. And it’s going to take a lot of, of education, a lot of, of changing, um, behaviors at the individual level.

And I think that, that’s, it’s, um, it’s an area that, that Washington can kind of set a good example for, I think, the rest of the country. So that’s one thing just on kind of a societal level. And then, yeah, I think gardening and, you know, educating others, like trying to get as many people to do this as possible on any scale, um, is going to have an effect, uh, and so we can get carbon, you know, into the soil through compost, if it’s, you know, made well and we’re able to continue to eliminate more contamination in compost, which is mainly in the form of plastic, right? So, like, that’s just human decisions about where things go in the waste stream. And then gardening and farming practices that promote soil health also are going to increase carbon sequestration in the soil.

[00:48:12] Erin: Okay. And so, and the key ways to protect your soil health would be no-till?

[00:48:17] Doug Collins: Yeah, um, reducing disturbance, um, keeping the soil covered, and that can be with cover crops, um, having a diversity of plants, uh, diversity of plants, and then, you know, along with that would be like root systems, um, so feeding the soil that way, providing organic matter into the soil through other amendments.

[00:48:46] Erin: Okay. Thanks so much for joining me today. That was a good conversation.

Doug Collins: Thanks, Erin.