With more attention to detail and a few extra tools, compost can be made fertilizer-grade where a little bit goes a long way. What we’re talking about here is not the SAM (stacked, aged manure)that I described a couple articles ago. In working with commercial farms, I have learned to use different terms in describing the very best compost. Most people react negatively to the idea of paying fertilizer prices for something called compost, and it requires education to get them to understand what they’re buying is fertilizer quality.
In the mid-20th century the Lubke family in Austria first developed what has become known as Humus Compost. Dr. Lubke became internationally famous when, shortly after the Chernobyl nuclear disaster, he was able to demonstrate much lower radioactive contamination on his family’s farm produce than was found in immediate surrounding areas. The system of creating humus compost was then brought into this country primarily by Edwin Blosser, who established Midwest Bio Systems to build the turners and other tools needed. Today they support a network of composters around North America.
The production of humus at the tail end of a composting process requires careful assembly of ingredients at the beginning, coupled with gentle but thorough turning at precise intervals based on testing. Along with balanced levels of green and brown organic material, humus composters also add clay and often other raw minerals as well as microbial inoculants. The finished material resembles soil rather than what we would usually picture as compost.
While there is nothing about this process that cannot be duplicated at a small scale, it is a knowledge-intensive process and requires precise timing and labor availability. Most small farmers and gardeners will find it makes more sense to purchase this material from a commercial operation rather than trying to duplicate it themselves.
Fortunately for the do-it-yourselfer, Dr. David Johnson, working at the New Mexico State University, came up with a very doable smaller scale method to achieve similar results to humus compost. In fact, reported results from the use of the end product have possibly been more dramatic than the use of the Lubke process. This process is now widely known as the Johnson-Su bioreactor, named after Dr. Johnson and his wife.
A Johnson-Su bioreactor is fairly easy to build and use. I believe this is probably one of the best returns on investment the home gardener or small farmer can make.
To build a bioreactor you will need the following materials:
- 6’ wide woven landscape cloth, enough for one piece 13’ long and two 6’ x 6’ squares
- 1 standard, sturdy shipping pallet approximately 40” x 48”
- 1 piece of concrete wire (re-mesh) 6” x 6” x 10 gauge 5’ wide x 12½’ long
- 4, 10’ lengths of perforated bell-end 4” septic drain pipe
- Pipe glue
- A roll of tie wire (commonly used for tying rebar)
- Approximately 12’ of ½” landscape water hose with a tee leading to a garden hose attachment
To build the bioreactor, it is helpful to create a jig for the spacing of the pipes. Place a screw exactly in the middle of a thin piece of plywood about 3’ x 3’. Hook a tape onto the screw head and draw a circle on the plywood at 143/16” for a final diameter of 28⅜”. Then, using a carpenter speed square and a straight edge, mark out five evenly spaced points around the circle, 72° apart. Using a section of your 4” pipe for a guide, draw 4” holes at the five marks on the inside of the 28⅜” diameter, and one hole exactly in the center of the circle. Using a drill and a jigsaw, cut out these holes so that a four-inch pipe loosely fits inside.
Place this jig in the center of your pallet and adjust clockwise/counterclockwise to avoid, if possible, cutting any of the pallet slats completely in two. If this is not possible, you may need to screw a block of wood in place underneath to hold up any slat that gets cut completely. When you have the jig in the best possible place, transfer the hole markings to the pallet and cut out with jigsaw.
Cut your four pipes 6’ from the non-bell end; then glue the remaining sections together for two more pipes. Cut off the extra bell ends to end up with six 6’ sections. The sections will go vertically in the holes of the pallet. You may wish to bend a hoop out of light-gauge rebar to tie the pipes together at the top and keep them in place. Alternatively, they could be moved around and repositioned vertically as you fill the bioreactor.
To create the outside frame, tie ends of your 12½’ re-mesh together securely with the tie wire. Do not skimp on this part since there will be considerable pressure outward on this ring. Line the interior of your re-mesh hoop with the larger piece of landscape fabric. Fold over the wire at the top and bottom and sew into place with tie wire. It is helpful to cut the tie wire at an angle to create a sharp point. When working with re-mesh and tie wire, be careful of the sharp ends. I recommend eye protection and gloves.
Using a few staples or small nails, fasten one 6’ x 6’ section of landscape fabric across the top of the pallet. Cut out the holes with a scissors or knife. When this is complete, center the fabric/wire ring on the pallet and fasten down temporarily with a few screws in the corners. The ring is likely to slightly overhang the pallet on at least two sides. Where it overhangs, fold up the bottom landscape fabric and tie into the re-mesh with tie wire to seal off the bottom.
When the bioreactor is complete, place it where it can remain undisturbed for at least a year. You should be able to conveniently reach it with a water hose for adding moisture.
The bioreactor can be filled with any material that you would ordinarily put in a compost pile. The same rules apply that we have mentioned before (see June) for mixing higher carbon/nitrogen ratio with lower. For best results, you should run all coarse materials through a shredder before filling the reactor. Materials should also be uniformly moist before filling.
Unless you have a spot next to a retaining wall or ramp of some sort, everything will have to be lifted up 5’ and dumped into the bioreactor. Five-gallon buckets can work well for lifting material into the reactor. Ideally, the reactor will be filled in one day, so you will want to have the materials located before starting to fill the reactor. A full-size Johnson-Su model as described here will hold nearly eighty 5-gallon buckets of shredded material. If that seems too large for your purposes, the reactor will work fine shortened down to 3’ to 4’ tall.
About twenty-four hours after filling the reactor, the material should have settled together enough that you can remove the pipes without the holes collapsing. This should be done sooner rather than later to facilitate optimal flow of oxygen through the pile. Also, at the same time, install a water drip line a few inches inside the perimeter of the cage. Form a circle out of 1/2” landscape piping, connecting both ends to a tee with a garden hose running to the outside of the frame.
Drill 1/₁₆” holes in the bottom of the hose 4”-5” apart, and 6” apart on the inside of the ring for spraying toward the middle. This irrigation should be run approximately one minute every day except during extended periods of rain. Of course it must be shut off during freezing weather. The easiest way to do this is to set it up on a timer.
Monitor the pile for moisture occasionally. This is made easier with a probe moisture meter. The material should stay uniformly wet, above 70% moisture, but not so wet that it oozes out the bottom.
After the initial heating of the composting ingredients is over and the temperature drops below 80°, add a couple handfuls of small earthworms known as red wigglers. These could be purchased, but you can often find them under and around partially decomposed existing compost piles, or dig around the edges of a barnyard. After everything is complete with worms in place and irrigation line working, cover the top of the bioreactor with another piece of landscape cloth and tie down to the re-mesh.
For the next year, the only thing that needs to be done to this system is to monitor the moisture, making sure the bioreactor does not dry out. At the end of the year, you will have a fertilizer-grade compost useful in many applications.