Terra Preta in School
Albert-Einstein-Gymnasium Hameln: From the school garden to the Terra Preta garden - schoolchildren discover biochar
The garden plot used by the school garden consists of two adjacent parcels in the "Abendfrieden" colony, which is located near the grammar school. The two teachers in charge are also involved in the board of the allotment garden association.
With the start of the gardening season in March 2021, two pyrolysis ovens were delivered (see image above) and the students were introduced to how the oven worked. The first steps were taken with the conversion of wood pellets. Since kindling can also be used in the stove, two students came up with the idea of getting discarded pallets and using them to make kindling. They dragged several sacks full of kindling and thus supplied the pyrolysis ovens with fuel throughout the garden year. The charcoal produced was trimmed in small pieces at the beginning, later senior student councilor Hänel organized a small knife shredder with which the charcoal could be shredded very well, because the pieces of charcoal should fit through the mouth of the earthworms. The students learned that beneficial bacteria colonize the earthworm's gut. Recently there has been consideration of buying a roller shredder that can shred tree cuttings into pieces the size of a thumb. After drying, one would have a second source for self-made fuel. A discussion ensued about the chemical-physical processes involved in the production of charcoal. Sagawe reports that the charcoal was examined for any polycyclic aromatic hydrocarbons (PAHs) it might contain. The values were below the detection limit. Always provided that uncontaminated dry material is used. The students were given detailed instructions on how to use the stove. It is important that the furnace is tipped onto a stone surface or into a metal container without water after the pyrolysis process has ended, in order to avoid scalding from the formation of steam. The controlled extinguishing with a watering can only takes place afterwards.
The pyrolysis process is adjusted with a special ventilation control so that a smokeless flame is created. Measurements by a chimney sweep showed that only extremely small amounts of carbon monoxide were released. "They can cook with you for hours," he says. And so crepes and popcorn were eagerly made and eaten.
Before the Terra Preta was spread on the beds, soil samples were submitted to the Agricultural Testing and Research Institute in Hameln for testing, so that the development in the following years can be better assessed.
Then it was about the production of the biochar substrate. The students learned that you need at least three things to produce a Terra Preta: 1. Soft green material, 2. Charcoal (at least 10%), 3. Lactic acid bacteria for fermentation, to which dung can also be added.
The students learned that fermentation under largely airtight conditions emits far fewer greenhouse gases than is the case with normal compost. In the beginning, the material was mixed in round mason's tubs and then simply placed upside down on the ground, this ensured airtightness and after eight to 10 weeks the Terra Preta was ready when the material smelled nutty, mushroomy. It was then distributed to the first beds, mulching was used to feed the soil organisms.
In the beginning, lawn clippings were used as material, until the realization prevailed that many insects were also sucked in and killed. Leaves and other green garden leftovers were then used. After the coffee grounds from the staff room were promptly treated with lactic acid bacteria, they no longer grew moldy and were also used. As a second method, the children then built fermentation towers from old pallets and lined the inside with PE film. A small problem arose: when asked whether the material should be 80% or 100% airtight, I gave the recommendation: Use 100% dense material. We had to learn that this material is extremely stiff and difficult to work with, but the children managed it anyway. These towers are given a floating lid so that the material is always largely shielded from oxygen. These containers are equipped with wide flaps at the bottom so that material can be removed after a while and new material can then be added from above. Two towers were built, which allow the accumulating material to mature in peace.
At the Environment Day in September, the garden opened its doors to visitors, and the students explained to the visitors the Terra Preta principle that was newly applied in the garden.
Setting up a Terra Preta separation toilet was considered next. Urine is largely sterile, diluted with water and spilled in the garden. The solid substances are then processed in the fermentation towers. It turned out that the small square room separated from the garden shed, which houses tables, benches and kindling, used to be the toilet. This function is now to be restored so that a circular economy can then be demonstrated in the school garden: growing food, eating it, digesting it, excreting it and feeding it back into the cycle. The pupils were shown the central component of such a toilet: the large oval is divided in two: at the back for the solid waste, at the front the liquid is collected and drained off via a hose. A small house is already there as alternative accommodation for benches and firewood, currently only as a kit - that is the construction project for the coming year.
The knowledge acquired through practice in the summer was theoretically underpinned by two teaching units of 1.5 hours each: A basic lecture on Terra Preta with a Power Point presentation and a short lecture on the Bec Hellouin permaculture garden: by creating hill beds and mixed cultures that complement each other support, by integrating small fruit trees and berry bushes, stable biotopes were created, which result in high fertility. In this way, vegetables worth 57,000 euros are produced annually on 1,000 square meters. The garden group would like to go there for a visit.
Three short films and a documentary were shown on the following topics: 1. Biodiversity of soil life from "Good Food - Bad Food" by Coline Sereau 2. The importance of cooperation between fungi and plants (ARD) 3. The use of biochar in cattle farming Bauer Unkelbach (ARD) 4. "The Rediscovery of Terra Preta" ZDF, 2011, approx. 45 min. This film shows the rediscovery of Terra Preta as an ancient cultural technique of indigenous peoples in Brazil and the attempt by German companies to patent this process. Rainer Sagawe was able to report that these patenting efforts were declared null and void by a patent court with the result: "The Terra Preta is free", free for use by everyone and every woman, for the fertilization of the soil, for the preservation of biodiversity and for Creation of CO2 sinks.
Due to the corona pandemic, the topic could not be taught to the extent that would have been desirable, but it was still possible to convey the essential content and arouse enthusiasm. The garden group already has plans for developing this theme further in the coming year.
Rainer Sagawe, Hamelin, December 2021
– This project was financed by the Bingo-Umweltstiftung, Hanover.
