Compost: Johnson-Su Method
The how & why of the "bioreactor" that grows LOTS of fungi for soil restoration.
As you may have seen over on @soilissexy instagram, I recently had the pleasure of making some compost cylinders with soil friends here in Austin.
Our cylinders are inspired by the Johnson-Su composting methods, named after husband-wife collaborators: David Johnson and Hui-Chun Su. Today I want to tell you all the details about the Johnson-Su design, how our cylinders differ, and why.
First, a couple new things: the substack name has changed from Rhizos Field Notes to Soil is Sexy. This is to create some continuity as most of those following along here come by way of @soilissexy online.
Based on your feedback in a previous survey (thank you!) I expect to create a variety of content in 2023 ranging from science communication on microbial life, practical advice for improving soil health with technical explanations, BTS look into projects I’m working on in my business, Rhizos LLC, plus the occasional personal blog as I account my experiences in this work. You can always respond to newsletters with topics you’d like to see discussed!
Lastly, for those wanting extra details, I’ve created a section just for you titled “The Grit”. When you see a worm icon, like the one above, know that there is more information waiting for you in the The Grit section after the main post!
Now let’s get to it…
Backstory on Johnson & Su
I was inspired to find that David Johnson came to his career in science later in life. He had been a custom home builder for most of his professional years. At the age of 51 he decided to complete his undergraduate studies and eventually his masters and PhD in molecular microbiology.
I love hearing stories like this. I think we’re actually better scientists when we have experience in other professions. Western science can be so dogmatic and reductive, to have decades of experience adulting in other fields is bound to make us more well rounded and less hardheaded.
As Dr. Johnson tells it, he had been tasked with a research assignment to explore different methods of making a beneficial compost out of the abundance of manure produced by a dairy CAFO (consolidated feed lots). He says his wife, Hui-Chun Su, became motivated to help him because she was sick of him coming home covered in cow manure - ha!
Dr. Johnson had been using a classic windrow method which required a lot of turning and inevitably coated him in the stink of the (mostly anaerobic) byproducts of the compost materials. Together, he and Hui-Chun developed a no-turn, static method that ALSO kept the pile oxygenated. Not only was the scent of their relationship saved, but so too was the fungal biomass of the compost!
Every time we turn a compost, it’s like a destructive tornado to the fungal communities - they just get torn apart and it takes a lot of time and energy to restore their population. However, most compost piles would go anaerobic without being turned. Which is a real conundrum because anaerobic conditions, like turning, also suppress beneficial fungi. Furthermore, low-oxygen conditions breed pathogenic organisms and can quickly become combustible at certain temperatures. All this to say, the aerobic part of this static aerobic method is essential.
Somewhere along the way (from what I can tell), Johnson & Su’s methods evolved from this dairy manure research project and into a system more specifically focused on yielding fungally-dominant compost.
The system has been dubbed the “Johnson-Su Bioreactor” - which sounds a lot more complex than it is!
Today, most Johnson-Su Bioreactors are built using nothing but carbon-rich inputs like leaves and woodchips i.e. the foods fungi love most.
How I came to be interested in this method:
I started my microscope practice in 2019, and by my estimation have evaluated hundreds of compost samples and several hundred more soil samples to date (aiming for my 10,000 hours 😉)
The first time someone asked me to look at a sample of their Johnson-Su Compost (Feb ‘22), it blew my hair back!
I was having a field day measuring all the fungal hyphae. I had heard of this composting method, but it wasn’t till seeing it on the microscope that it really got my attention. Since then, I’ve been telling anyone who will listen about the Johnson-Su Bioreactor and sending them a video of Dr. Johnson building one (I link it later in this post).
I evaluated several other composts from various Johnson-Su Bioreactors this past year and I’m pleased to report that the trend of blow-your-hair-back levels of fungi has continued.
An Important Exception
The only exception has been samples from systems that incorporated a significant amount of high-nitrogen feedstocks like beer grain, manure, or green waste.
People often add these inputs to “speed up” the process of decomposition. Though this may technically increase the rate of materials breaking down, from what I’ve observed it actually disrupts and delays the progress of biodiversity in the compost.
Dr. Johnson has also experienced this saying, “I tried at the beginning.. adding nitrogen to the system to speed it up [and] it failed”.
He also adds this really interesting point:
“I saw that.. [by] allowing the system to fix its own nitrogen….you start developing the community of microbes that can do that”
He explains that metagenomic data of bioreactor compost reflects significant amounts of free-living nitrogen-fixing bacteria - how ‘bout that!!
Remember, the main point of a bioreactor is to yield high fungal biomass for our soils that are deficient in fungi (just about all of ‘em!) Adding everything but the kitchen sink to such a system for the sake of speeding or “suping” things up isn’t advised here. (Every now and then we’ve gotta put our hustle culture and bro science aside to consider the big picture and be intentional.)
Our J-Su Inspired Compost Cylinders
We built three cylinders each with a different “recipe” or ratio of input materials.
Our methods differed a bit from the Johnson-Su protocol in the following ways: slightly smaller size, different approach to central air tunnels, no automated irrigation, and the use of a plastic pallet instead of wood.
For the details on these differences, head to “the grit” section at the bottom of this post!
However, I believe we’ve maintained the principles of the design, and that’s what’s most important!
Principles of J-Su:
Static/Undisturbed: bioreactors are meant to remain in their location for ~12 months. This allows for fungi to grow their hyphae and eventually sporulate in high numbers.
Aerobic: beneficial fungi respire like you and me and need oxygen to thrive. The aeration of the bioreactor is passive (instead of forced through turning) - the use of air tunnels and a pallet to raise the composting cylinder off the ground allow air to infiltrate from many sides.
Moisture: A relatively high and consistent moisture content of ~70% is encouraged to support a high rate of myceliation. This is achieved through the practice of soaking starter materials and automating watering. Additionally, using a weed cloth (or something similar) on the exterior can prevent moisture loss to evaporation which is especially important in hot and/or arid environments. Keep in mind, this layer should still allow air to infiltrate. Also, to maintain its integrity and purpose throughout the process, the material used for evaporation loss should be resistant to decomposition or degradation in the elements.
Primarily Fungal Foods: diverse, high carbon inputs will naturally support diverse, high fungal outputs!
Worms: Dr. Johnson recommends adding ~100 worms to the bioreactor once temps are 80F or lower. Technically this is optional, but why the heck not! The addition of worms will only improve the rate of decomposition and positively impact the biodiversity of microbial life.
For a tutorial from Dr. Johnson himself:
Now, What?!
How do you know when the bioreactor is “done” and ready to be used?
Some inputs will degrade faster than others. For example, some bioreactors made mostly of leaves may take only about 9 months to fully degrade, while wood chip based piles take closer to 12 months or longer. That may seem like a long time, but keep in mind a little solid compost goes a long way as a liquid, especially when it's so concentrated with beneficial biology.
To know when each of our bioreactors are ready, I plan to look at…
Texture: depending on my end-use (TBD), I may be looking for a very fine final compost or okay with a chunkier blend; the interior parts of the pile can look very different than the exterior layer, so it may take some poking around to really assess the fineness.
Biology: collecting a sample and putting it under the microscope is a sure fire way to know if the compost is “ready” for the restoration site. I’m mostly interested in the fungi:bacteria (F:B) ratio and only plan to harvest some compost when the ratio is significantly higher than the site I’m attempting to restore.
How do you go about using it?
I plan to…
Make an extract! To use as a soil drench to really get those fungal spores into the soil. The process of making an extract, when done thoughtfully, is not very disruptive to biology - there’s just enough pressure to “knock” microbes off the surfaces of the compost material and into water that can then be used as a soil drench.
For high clay or compacted soils, ideally an extract is applied into soil cores. If not, we risk the extract just kind of sitting at the surface and baking off 😕
After being used for an extract, the remaining solid materials can be used in a number of ways: applied like a top dressing or mulch, used to make a compost tea, used as an input to inoculate the next bioreactor or other compost pile… what else?!
Concluding Thoughts
There are dozens of ways to compost, and I don’t think we’re meant to compare them to one another to attempt to identify THE BEST method. So please don’t mistake this post as a claim that the Johnson-Su Bioreactor is the only worthwhile composting method! Rather, it's one of many exciting ways to do something meaningful with organic waste and helpful for our soil health.
I love that the bioreactor is low-maintenance and that it reliably yields fungal biomass. However, it is not a particularly useful composting system for food scraps, so I won’t be giving up any of my other modes of decomposition. You know what they say, “variety is the spice of life!” 🌶️
Thanks for reading this deep dive! What do you think? Do you have any lingering Q’s or curiosities?
With Love,
Andie
For those with maximum curiosity, this new section is for YOU, have at it:
Grit 1 of 3: What is it about the J-Su Bioreactor that allows for significantly more fungal activity compared to a static compost process?
Feedstocks: firstly, most “static compost” is actually made up of a lot of green waste to begin with, while the bioreactor is entirely made up of fungal foods. Though the fungi are provided undisturbed time, they may not have the resources to really proliferate in a static compost like they do in a bioreactor. Now, would a static compost that’s largely made up of carbon-rich foods yield higher fungal biomass - I can say with near certainty that it would, but that’s just not often how they’re built.
Heat: by design the bioreactor is not meant to be thermophillic, at least not for long. Dr. Johnson advises that IF bioreactors reach thermophillic temps (over 130F) they should only do so for about a week. My understanding is this is to preserve biodiversity of the organisms in the reactor. Static composts are often made-up of substrate that has already gone through a thermophillic process. After the heating phases, are there enough resources left to support the restoration of beneficial organism groups? Or did breakdown happen so fast not only is there little biodiversity left, but also little to no nitrogen left in the system to support ongoing microbial activity? With these characteristics, if such a substrate is left to sit in a static pile it can’t be expected to restore itself without further inputs, it will likely just go dormant.
Sporulation: this is the biggest game-changer for me. In a Johnson-Su Bioreactor, as fungal foods decompose and fewer food types become available, well-established fungi of various kinds will slowly become less active and sporulate. In many other composting methods, the fungi are likely sporulating in short desperate spurts between the heat cycles, and producing nowhere close to the amount of spores in a bioreactor, because the fungi are not well-established due to the heat and disruption (turning).
Grit 2 of 3: What was the rationale behind your differences in the Johnson-Su design?
Size: we opted for 4’ tall instead of 5’ tall because we didn’t want to have to use a step stool to check on them. This way, they’ll be monitored more closely as we can see them and touch them while standing on the ground.
“Chimneys”: the recommended method for air tunnels is to create ~6 chimneys using pvc pipes, which are removed after 24 hrs. However, we chose to make one large cylinder in the center using hardware cloth and do not plan to remove it. We did this because it seemed like a waste of money to purchase enough pvc for all three cylinders (which were being built simultaneously, not consecutively), just to pull them out after 24 hrs and have to store the pipes. We could have made small cylinders out of hardware cloth to mimic the pvc pipe size, but that would have taken way more time than making one large cylinder for each. However, we honored the observation that’s been made that the material needs a source of air within 12” or less.
Irrigation: consistent moisture levels ensure consistent rates of decomposition. Automated irrigation is a great way to ensure moisture is being maintained. However, between cost of irrigation materials and no pressurized water source (just a gravity fed rainwater harvesting tank), we decided one of our teammates whose at the site several times a week will hand water. If someone wasn’t going to be at the site so regularly we would have taken measure to automate irrigation in some way.
Pallet: most people use a wood pallet because they’re easier to come by and then add a weed barrier cloth over the top after cutting out holes (in the cloth and the pallet) for where the air tunnels are inserted. The weed barrier ensures the wood pallet doesn’t start decomposing and give out! We were fortunate to find plastic pallets that already had plenty of air space so no extra step of cutting into it.
Grit 3 of 3: Why is the compost raised up on a pallet - wouldn’t you want it exposed to the soil organisms belowground?
I love the instincts contained within this question. In theory, yes, we want to find ways to work with nature and providing an avenue for local microbes to migrate into our compost is a good thing. However, one of the critical principles of this particular composting system is aeration. Raising the pallet off the ground significantly improves airflow for the whole cylinder, which in turn supports the overall microbial activity. Without this factor, we’re not maintaining the integrity of the Johnson-Su design, and therefore not maximizing the fungal biomass of the end compost. It’s kind of a matter of pros and cons on this point, for example I’ve seen composting systems that make contact with the ground and incorporate aeration pipes horizontally, but this often requires some type of forced aeration source like an electric blower.
Sources:
How to Build Your Own Compost Bioreactor. California State University Chico. https://web.archive.org/web/20221126085603/https://www.csuchico.edu/regenerativeagriculture/bioreactor/bioreactor-instructions.shtml
^This link has been broken since the year turned to 2023, however I’ve listed an archive link here. I’m not sure how long access with this link will be good for, so I’d recommend “printing to pdf” to save these instructions from Dr. Johnson himself.
Compost & The Promise of Microbes. (2018, April). Eco Farming Daily. (https://www.ecofarmingdaily.com/build-soil/soil-life/soil-microbes/compost-the-promise-of-microbes/
Diego Footer. (2020, October 28). The Benefits of Johnson-Su Bioreactor Compost | Dr. David Johnson [Video]. YouTube.
Do you have freezing winter temperatures? If so, do you protect the bioreactors from freezing and how?