My thoughts are that we aren't ready for a carbon sequestration label, because we don't yet know enough about the sequestration effects of individual on-farm practices to honestly claim that they consistently result in carbon sequestration. And measuring actual C sequestration on individual farms over short time frames is not technically feasible. It's really important to understand the difference between simply adding carbon to a soil and actually sequestering it. Sequestration means that the added carbon will remain in the soil for a long time. In the climate change research community, 100 years is often used as a minimum. Sequestered carbon has been stabilized against decomposition, usually by interacting chemically with reactive mineral surfaces, such as the surfaces of clay particles, or by being locked up inside soil aggregates where low-oxygen conditions or sub-micron pore spaces protect the carbon from decomposing microbes. Note that an increasing organic matter % on your soil test reports does not necessarily mean C is being sequestered. If you add 40 tons of co mpost per acre containing around 10,000 pounds of actual C, the vast majority (and perhaps all) of that C will be returned to the atmosphere as carbon dioxide as a result of microbial respiration. But if you did soil tests before and immediately after the compost application (assuming the compost had been incorporated) the results would show an increase of around 0.75% in the organic matter level. There's no doubt that soils can sequester carbon and that this can help mitigate climate change. The devil is in the details. There are scores of scientific papers published annually on this topic, but the results are inconsistent and extremely variable. We have a lot more to learn before we can say with confidence that such-and-such a practice will consistently lead to C sequestration. Once we get there, not only will we be able to make legitimate claims about our farming practices and climate change, but we may also get paid for the carbon we sequester. This idea has been around for a long time, but hasn't been widely implemented for all the reasons described above.
I was intrigued by this researcher's (Derek Lynch) article which says "On the Prairies, farm soil carbon levels have stabilized or increased over the past few decades, largely as a result of adoption of no-till cropping, which avoids disturbing the soil while growing a crop. In Eastern Canada, however, most estimates suggest that the intensity of crop production (especially reduced use of forage crops) is causing soil carbon levels to decline. This situation is made more challenging by the fact that in higher moisture regions such as Eastern Canada and British Columbia no-till cropping does not enhance soil carbon." https://theconversation.com/how-soil-carbon-can-help-tackle-climate-change-116039?fbclid=IwAR23h06SVMDf6cB0lvwqYnhYt_UKFk0Vgap14mURhMM6SuDbZbH2eCgehb0
Wouldn't a growing tendency of soil carbon on a given farm be indicative of successful carbon capture? If soil C % is increasing year after year simple logic suggests that carbon is being sequestered. Or am i missing something? I understand that an annual soil C check will not say much but a multiannual tendency has to be indicative of carbon being carried over from one year to another.
You're absolutely right that a long-term increasing trend in soil C is indicative of sequestration. But it's also important to consider the source of the C that's being sequestered. For example, consider a farm where this is happening as the result of really great soil management: cover cropping, minimal disturbance, good crop residue handling, careful nutrient management. There is minimal reliance on off-farm inputs. This farm could legitimately claim to be sequestering C in a way that mitigates climate change, because the C going into the soil was fixed by photosynthesis from the air above the farm. Now consider a farm with a heavy reliance on compost imported from off-farm sources - a common scenario among farms participating in this community. Where I live, in the Canadian Maritimes, a lot of the commercial compost is made from bark and wood chips from the forest products industry, and chicken manure from the confinement poultry industry. Here we have a zero-sum game: the farm importing the compost gains carbon, but at the expense of the forest soils where the chips came from, and the grain fields that grew the poultry feed. In my opinion, it would be disingenuous for this farm to claim that it was making a genuine contribution to climate change mitigation.
Great stuff as always, David. I think you're last one is a good one, though farmers who use the deep compost mulch systems have seen C increases above what can be attributable to the compost applications by leaving roots in and constant photosynthesis (I'm specifically talking about singing frogs who have tested this). This is not achieved through cover croppping exactly but constant cropping in this way can have similar effects no?
Sorry, "your last one" not "you're." It's 4 am...
David, I absolutely see your point. I think small-scale growers could do a better job in nutrient management and producing more of their own fertility. And yes, Jesse, if I remember right, they were saying they calculated that only 1/3 of their organic matter increase could be attributed to direct compost/amendment application. So, I think there is a middle ground here... We, ourselves, have used quite a lot of compost to establish our bed system on about 3/4 acre. I see us using 1/3 the amount next year, and even less after that. But, it makes me wonder what a world of vegetable agriculture would look like if growers adopted this approach, it'd take a high-functioning composter in every region! Not a bad thing when you think about all the good soil building material being lost to the waste stream. That said, the compost we use is coming from recycled wastes that, just a few short years ago, went to the dump. Further, most of it's current use is non-edible annual flower landscaping or to bury dead cows in. My point being, I think the line here is pretty blurry. In my particular case, though I'm importing it, I think of it as putting the carbon to better use. With so much valuable soil building material being "thrown away" there is a lot of value in diverting those waste streams to benefit soils. Read Farmers of Forty Centuries, the East's small scale farms were masterful at taking wastes the community generated and using them for fuel or fertilizer. Thinking long-term, that's a great strategy. Small farms as digesters of waste streams and turning them into good food. Indeed, production farms must import something to produce enough food for enough people to make economic sense. We, as growers, could be a little more mindful of where those inputs come from, for sure. Further, there are some smart people able to assess a farm/lifestyles C footprint. Maybe striving to be net-positive, including increase in OM, is a little more accurate? Pete Seeger's banjo inscription read, "this machine surrounds hate and forces it to surrender" How about, "this food surrounds carbon, and forces it to sequester"?
Jackson, our compost is similar. It's waste (mostly from horse and hay farms) so in that way we are putting it in a potentially more stable and beneficial place (the soil). Good point on imputs too. Cover crop seed itself comes from potentially carbon wasting tillage systems, so... Also, "this food surrounds carbon and forces it to sequester" is my favorite no-till quote to date.
Jackson, I first read Farmers of Forty Centuries back in the 1970s, and in fact re-read it just last year. It's a great book, and I don't need to be convinced of the value of returning the waste stream to farms. But that's not really what this thread is about. It's about a proposed C sequestration labeling scheme, which I think is premature because C sequestration is a complex and nuanced topic, and there's a lot we don't fully understand yet. I would hate to see another label that might just be greenwash bullshit. There's good news and bad news arising from all this attention to climate and soil carbon. The bad news is that research is pretty consistently showing that as soils get warmer it becomes harder to increase organic matter levels, mostly because microbial activity scales positively with temperature over warming of a few degrees. That's one reason why tropical soils typically have low organic matter. So it looks like carbon sequestration is going to become more challenging even as we need it more and more. The good news is that there has been a real renaissanc e in soil organic matter science over the last 15 years or so, as interest in SOM has spread beyond soil science departments and into the world of climate science, meaning a lot more talent and research money has been devoted to it. Interestingly, a lot of what we thought we knew about SOM has turned out to be incorrect, and the new understanding has important implications for practical soil management on the farm. This would be an interesting and relevant topic for a future podcast.
Apparently we're not the only ones having this discussion. The website Cover Crop Strategies just posted a story about an effort, headed by a consortium of environmental organizations and food companies, to establish a carbon credits market for farmers based on practices like cover cropping and no-till. Part of the plan includes development of measurement and monitoring techniques for soil carbon that are accurate, repeatable, and practical - which is exactly what we're currently lacking. You can read the story here: https://www.covercropstrategies.com/blogs/1-covering-cover-crops/post/307-carbon-credits-by-2020-for-no-till-cover-crops-it-could-happen-this-time?utm_source=omail&utm_medium=email&utm_campaign=weekly&utm_content=ccs&oly_enc_id=5467H7030934H1Z
Wow good article, David. And the author notes as you said, measuring carbon sequestration is complicated. I agree with you about the podcast--I think this would make a fascinating conversation.
Perhaps there could be other slogans/ marketing copy that spark valuable conversation and spread understanding about no-till that don't have to involve the complexity of measuring carbon sequestration? I've been trying to brainstorm, but haven't thought of anything that great. Something like No Till = No Kill, our food teams (or teems?) with life. Or maybe: this food builds soil? Or use "regenerative agriculture" terminology? I don't know, marketing is NOT my strength. But I have been thinking about it nonetheless...
Of course you’ve read it, David. And you’re right, waste streams are sort of beside the point here. With regards to labeling, I’m not sure I could be convinced a label is a good idea. One thing I like about or work here is that we recognize the importance of a handful of basic principles and strive to enact them as often as possible on our farms. Sometimes we fail from stupidity. Sometimes we break them for good reason. Farms that enact these principles relatively well begin to look wildly different from one another based on crops, bio-regions, available local resources, etc. Labeling could dampen that sort of diversity of approach. Sure, there are a few CSA folks I get to geek out with about what I’m learning, but I think what’s more important than consumer education about no-till (which I feel should be more focused on cooking skills) is making ecological farm choices easier for farmers, beginning with better study. I, myself, already feel like I’m poorly e quipped in what I need to know about soil health, biology, and management. How do you appropriately label something the scientific community says we know so little about, anyway?
And, David, understand that I genuinely look forward to your contributions to these threads. Serious.