By Pam Gunnell, future Ecovillage resident
Those of us at the Friday morning demonstration garden working bee last week were treated to a demonstration by Mark Tupman of how to make a Johnson-Su bioreactor composter. The name comes from the inventors of this method of making compost, Dr David Johnson, a molecular biologist and research scientist at the State University of New Mexico, and Hui Chun Su Johnson, his wife, and collaborator on this project.
Most of us, I’m sure, were already enthusiastic makers and users of compost, that miracle of microbial magic that turns veggie scraps, prunings, leaves, dust and dirt, pet hairs (in fact, just about anything organic you’d otherwise send to landfill) into a dark, crumbly, sweet-smelling addition to soil that produces the strongest, greenest and most healthy-looking veggies (and anything else we grow).
So, no need to extol the virtues of compost making, I’m sure.
However, most of us probably think of compost simply as a way to apply nutrients to the soil, thus feeding the plants. However, as Mark pointed out, the primary function of compost is to enhance the diversity and numbers of beneficial microbial lifeforms to the soil, especially around the plants’ roots. It’s the bacteria and especially the fungi, that exist in and around the roots that supply many nutrients to the plants in exchange for sugary exudates that the plant produces through photosynthesis.
As Mark explained, compost is really a probiotic, packed as it is with untold millions of microbes. And those microbes also provide food for whatever microbes already exist in the soil because, like all life on earth, everything eats something else.
The result is an overall greater abundance and species diversity of microbes. The more microbial life we have in the soil the greater the stability of the ecosystem and the greater the health of the plants we’re trying to grow. When we plant different species together, plants can ‘borrow’ nutrients they might be lacking from the microbes surrounding the roots of their neighbours.
These are Mark’s instructions for constructing the bioreactor / composter (with a few extra tidbits from an interview with David Johnson by Diego Footer on a Youtube series called ‘In Search of Soil’):
- Start with an old wooden pallet, and lie it flat on the ground.
- Find six or so lengths of white drainpipe that, preferably, will fit into the spaces between the slats of the pallet. If they’re too wide, either cut out some circles in the slats to accommodate the pipes or cut away the edges of the slats where you want the pipes to go so that they do fit in the spaces between.
- Cut some 1-2cm diameter holes along their lengths.
- Leaving the pipes aside temporarily, find a length of wire mesh about 1.5m wide that’s sufficiently flexible to bend into a circle that will fit easily on top of the pallet. See the photos below.
- Cut the wire to the length you need, leaving the horizontal wires sticking out at the end where you cut it. Then bend the wire into a circle and secure it using the sticking-out horizontal ends of wire.
- Now push your lengths of pipe down into their holes inside the wire circle. They should stand more or less upright, and you can keep them from falling over too much by packing organic matter around them in step 8.
- Cut a length of woven poly weed-mat that’s about 20 cm longer than the circumference of the wire circle and about 50 cm wider than the height of the wire circle. Wrap it around the inside of the wire, overlapping the edges and folding the top to the outside to hold it in place. It’s possible to sew the weed-mat to the wire, but not really necessary since it will be held in place by the organic matter inside the circle.
- Begin to fill inside the wire circle with your prunings, leaves, etc. Start off with the coarsest material such as twigs and stalks, gradually using finer material as you go up.
- Water the material in as you go and make sure it’s packed around the pipes, but don’t press it down. The idea is to encourage as much air into the pile as possible.
- You can add rock minerals, but this isn’t strictly necessary.
- Unless you’re going to hand-water the pile, fix up a circle of brown dripper pipe on top of the pile (connected to a tap, obviously, and preferably a timer).
- After 24 hours or so you can remove all the pipes. The composting material will hold together, partly because the microbial life will have created webs and structures that begin to bind the material together.
- After that, you have to let nature take her course. It can 12 months or more for this type of compost pile to work. You should NOT turn it, mix it or add anything but water.
Advantages and Disadvantages
- You don’t have to turn it or mix it, ever. Given time, this enables the fungal community to dominate the compost, which is really beneficial to the soil and our plants. In a normal compost pile, however, where the material is turned or mixed, the fungal hyphae are broken up so the bacteria and other life forms get the upper hand. It also means that the system stays relatively cool, which encourages worms and turns the pile into a vermicompost system. In a normal, turned compost pile, the pile heats up after it’s turned, killing whatever worms are there are present. They come back only when the system has cooled down again.
- You don’t have to worry about proportions of ‘brown’ to ‘green’ organic material: everything just goes in (including kitchen scraps and anything you’d put in any compost bin), just as any natural ecosystem doesn’t rely on human intervention to get the proportions correct.
- Because you don’t have to add anything to the organic material mix, free-living microbes will produce whatever nutrients are in short supply within the mix. They’ll be present in the finished compost and, therefore, in your soil when you apply the compost.
- The system is aerobic which encourages the proliferation of beneficial bacteria, fungi and other microbial life. The more beneficial ones there are, the less space there is for pathogenic ones. An aerobic system doesn’t smell bad and doesn’t encourage flies.
- It’s a very easy, non-labour-intensive way to make compost. Other aerobic systems I’ve worked with have required three or four separate compost bays to be constructed, the plant material to be cut relatively small, and the semi-composted material to be moved / turned from bin to bin over time. The advantage of that method was that it produced great compost in just a few weeks, but it probably wasn’t so dominated by fungi. The Johnson-Su method enables large quantities of organic material to be used, and we will certainly have a lot from all our veggie gardens and community gardens.
- The only disadvantage I can see with the Johnson-Su method is that it takes a long time to work, the longer the better since the microbial content increases over time. The way to make this work for us will be to have a number of these bioreactors on the go at any one time. I wonder whether the essentials of how it works would be the same if we built the more conventional compost bays, piled everything into them (one at a time), and didn’t turn them. I know the Organic Garden in Margaret River makes compost heaps this way, leaving them for about a year. I assume they must, therefore, be fungaI dominated, but don’t know for sure.
Many thanks to Mark for showing us how to make the Johnson-Su bioreactor and for alerting us to the many benefits of enhancing the microbial content of our soil. There’s so much to learn about this, so many Youtubes to watch, books and papers to read. I hope we still get time to actually get out in the garden!