To Trommel or To Drum

So far this week we have spent  2 days harvesting compost from worms (vermicompost) and we will probably spend another 2 days. The harvesting includes general maintenance.

Let’s refer to Farmer Al’s talk  on “Compost: the new rage in sustainability” and specifically to the slide comparing vermicomposting and thermophilic composting.  Both composts have their advantages and disadvantages  but vermicompost is richer from a biological point of view (more humus-like compounds, more microbial diversity, rich in phytohormones). The two approaches are not mutually exclusive and will be  used in the future in sequence to take advantage of the unique features of each.

There are basically two types of vermicomposting systems: one consists of  ground based beds or windrows  (placed outdoors or indoors in a stable) and the other is an  automated raised continuous flow system usually installed indoors. In a future blog we will discuss why the ground based windrow system (considered low technology) was chosen by Frog Hollow Farm and MLF Soil Consulting.

We have four worm beds located outdoors in the paddock area of what used to be a stable. The beds are about 5 feet wide, 100 feet long and one foot high. We have three beds inside a stable , each  3 feet wide,  6 feet long and about one foot high. The indoor beds are protected from the elements and are used for experimental purposes. We keep a mother stock of worms in a manually operated continuous-flow system called a Wigwam; the Wigwam worms are used to house “pure” worms (Eisenia fetida) obtained from reputable commercial farms.

The worm beds are built using local materials: shredded Frog Hollow Farm boxes, fruit residue, horse bedding. The worms take a minimum of  2-3 months to produce vermicompost from these materials in the spring and summer months. Vermicomposting continues during the winter months but at a slower pace because of lower ambient temperatures.

Three worm beds were ready this week for the harvesting of vermicompost. Ideally, we would like to separate quantitatively all the worms from the vermicompost and use the separated worms to start a new compost bed. The earth-worm harvesting equipment we use is called a trommel (see You Tube video “Extracting earthworms from vermicompost bed at Frog Hollow Farm”): the vermicompost is passed through a piece of equipment with rotating screens set on a slope with a cone shaped unit at the end. The cone shaped funnel at the end is a smooth metal surface. As the trommel rotates, the vermicompost particles are screened and collected along the length of the trommel. At the trommel end, the worms  adhere to the metal surface and drop off into a collection tray. The trommel is rotated by a small electric motor. The vermicompost has to shoveled into the trommel as it is rotating.

After harvesting with the trommel, a lot of the worms but not all are separated from the vermicompost and are used to seed a fresh bed. The vermicompost is used to amend the soil around trees and tomato plants and of course contains significant numbers of worms. This situation results in an amendment that is more productive than commercially produced vermicompost. The residual worms produce more compost using organic material present around the tree or the tomato plant.

The harvesting of the worms from outdoor vermicompost beds using a trommel requires low capital outlay, is easily managed and recycles the worms on the farm but it is labor intensive.  Several workers participated in the operation (Andreas, Manuel, Cesar, Benito, Humberto, Aurelio) and also Marlene (farmer-assistant-in training) and we needed a front loader.

Some interesting worm factoids.  Worms produce a compost that contains more diverse microbes than thermophilic compost probably because worms operate at a much lower temeperature (60-95 F). Also, because the temperatures are lower in vermicomposts, a lot of the phytohormones are more stable. However,  it has also been shown that worms (Eisenia fetida)  decrease dramatically the populations of coliform bacteria during vermicomposting and other bacteria (Serratia, Salmonella). It also appears that worms decrease the total biomass and affect the species diversity  during vermicomposting and this helps the microbial community to use the available energy more efficiently. This suggests that using different starting materials, it is possible to tailor specific vermicomposts to specific problems on a farm (based on work done by J. Dominguez, M. Aira, C.A. Edwards, M. Lores).


Author: Christophe Kreis MLF Soil Consulting PhD, Molecular Biology/Developmental Biology, University of British Columbia, Canada. Christophe is co-founder of MLF Soil Consulting with his wife Monique. He started his career in basic medical research and after various positions in academia and industry Christophe slowly returned to his first passion Soil Ecology and Microbiology. It is his belief that human health is tied intimately to soil health through the production of healthy food. For this reason MLF Soil Consulting is committed to help farmers improve the management of their soil through composting, vermicomposting and biological analysis of microbial soil life.



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