Ecological Soil Reactivation

Ecological Soil Reactivation and Forest Fire Protection: How to Produce your own Biochar for Terra Preta

In deforested regions with depleted soils farmers are particularly challenged to create and store enough humus to be able to start the reforestation process that will, eventually, protect the land from bush fires, droughts, and desertification. Achim Ecker, living in ZEGG, has experimented with creating Terra Preta for some years. Now he has found a brilliant method to produce biochar and Terra Preta to assist in the challenging South European climate.

Almost 20 years ago I bought 7ha of land in Alentejo, Portugal which was called “Retumbana-Nova”. It has a common border with Tamera. The land had an old rammed earth farm house in ruins with the roof broken in, that we refurbished and enlarged. Now there is a beautiful energy, we are autonomous for water, and have a natural building holiday house that we rent out to visitors.
The barren land, with only some old cork oaks and one Eucalyptus tree after years of drought, called me to reforest it. My inner vision was a dense forest of high grown trees on all slopes. We started to reforest the land with about 30,000 trees over the first 15 years using all kinds of ways and species.
'We' are my colleague, Arnold Schonhardt, and myself, Achim Ecker, living at ZEGG in Germany. We partner the land and reforestation effort. As first we could not irrigate, and only about half of the trees survived the very tough and dry summers of Alentejo. The soil is depleted and consists of acidic clay soil with humus washed down to the valleys. The winters are very wet and drown the plants and the land for a short time, with normally most of the water running off due to the deforestation. We started building a water retention lake and some ponds to keep the water on site about 2002. Winters are difficult ecologically also, with frosts down to -7°C which limits the choice of trees to reforest.
Now, after all this planting, a forest is growing and I need to prune the fast growing species to leave space for the slower ones. As the danger of forest fires is great during the first critical phase of reforestation, we need to get all dry material out of the growing forest. The idea is to prune the trees to a height of about 2 m so a fire would not catch the branches.
The bigger parts of stems and branches give excellent firewood. And the brushwood I pulled to piles and cut it in short pieces so the piles would be more dense and rot with the water trapped inside. However, after years of doing so the piles are still growing in height and in number and the danger of fires grows as well. The times of drought are too long for real composting to happen and the winters too cold for much soil activity. Maybe later, when a good forest cover will be established and the soil organisms have settled in again and grown in numbers, it will work. For now it does not rot fast enough to help build soil, leave alone prevent fires. Terra Preta soils do both, and may spark the change to a soil that is capable in the future to really rot organic material without dangerous build-up of dry organic material on the surface.

Making Biochar for Terra Preta
For two years we have been experimenting with Terra Preta at ZEGG on sandy soils with very promising results. In Portugal I was lacking biochar to be able to start. I read an article by Ithaka Institute about the Kontiki Kiln that gave me the idea to try the Open Earth Kiln. It is a circular cone hole in the ground about 1.5 m deep with about 50° angles and an opening of about 2 m. I could not try it at ZEGG where I live and work, as the sandy soil would give in and not keep the form. But in the rock and clay soil of Alejanto, the hole will be stable for many firings. So I had an excavator make 8 holes in different locations and started firing the first one.

The article read: "In this method you take care to build a strong initial bed of flaming embers at the bottom of the hole in the ground, gradually, layer by layer you can add combustible material such as wood, food scraps, bones, leaves and straw while maintaining a smoke-consuming fire front. The burning pyrolysis gas consumes most of the oxygen drawn into the pit by the flame and therefore protects the pyrolysis zone, while the earthen walls keep air out from the sides and below. The fire itself is so effective at excluding air that the underlying layers outgas and char instead of burning to ash. After a few hours, by the steady piling and outgassing of fresh biomass, one or more cubic meters of biochar accumulate that can then be quenched by water or by a 5-10 cm thick layer of soil, sand or manure, (from: Kon-Tiki - The democratization of biochar production; Ithaka Journal.

From the basic principle of smokeless fire (Kon-Tiki - The democratization of biochar production; Ithaka Jounal): If you layer a wood pile loosely, with enough small branches in the upper layer, and light it at the top, nearly all the resulting wood gas will pass through the overlying flame front and burn so there is only a clean, smoke free combustion gas. Radiant heat from the flame chars the wood beneath layer by layer. Air is drafted in from the sides of the pile, but is updrafted into the flame and consumed in combustion. Under the nearly oxygen-free fire front the char is mostly preserved. As the pyrolysis reduces the wood chunks to smaller pieces that pass down through the loose pile, fresh layers of wood are continually exposed to off-gassing heat below the fire front. By observing the flame and the onset of ash build up on the outer layers of the charred wood you can determine the right moment to quench with water or smother with dirt, and instead of producing ash alone, you may retain close to a fifth of the wood as charcoal.

At first I was skeptical and did not believe it would work. I pyrolyzed the old piles which were surprisingly dry for the rainy season and burned in a way that gave me respect of forest fires here in Alentejo. I felt that what I did was so very right. It took about 2 hours until I could see how the embers grew and the hole started filling up. The fire became really hot and I could start to add green fresh prunings. With green material added it would smoke for a moment, but only short and then return to smokeless combustion. This first hole I quenched with water from a hose and let it run into the side of the hole so it would fill up from the bottom up so the steam would purify the biochar further.
The third time around I had a hole where I did not have water so I quenched with soil and was surprised how easy and quick it worked. The thin layer of soil became warm but not hot, and did not even dry up completely. Of course I had to wait some days before I could uncover and remove it.
I realized that instead of being carbon neutral like with rotting or burning, the brushwood becomes carbon negative or carbon sequestering. I could even find pyrolyzed pine needles as biochar sticks in the heap. The brushwood does not have to be dried or shredded (which would use energy!). This makes this method the most energy efficient and least work intensive. It is a pity to loose the heat, but in the Alentejo you would not need so much heat anyway and the idea to install a district heating with an expensive high-tech pyrolysis burner seems a bit of a joke.

Using Biochar
The biochar should not be added to soil directly as it is nutrient hungry and would take nutrients from the soil to charge up. I use it in the compost toilet where it charges up with Nitrogen, Phosphorus, and lacto-acid bacteria. It can be used in the compost bucket to prevent smells and I started adding it in the form of biochar dust to clay plaster as surcharge material. I used it in one place in the house where the wall keeps moist and the room smells a bit wet and moldy. There the plaster keeps falling off every few years. I cannot predict what will come, but it was good to work with this mixture and it stuck and the smell disappeared. There are many other possible uses and entrepreneurial possibilities for biochar!
Now I need many people peeing onto my biochar to charge it with nutrients so I can use it on the land. The funny thing is that once I started and by now fired 5 holes and made about 5m³ of biochar, the transport and handling it started to spread it all over the land as parts drop off the wheelbarrow and shovel. So the carbon age has started in Retumbana-Nova in Alentejo.
Now freshly inspired returning to ZEGG I will have a kiln built so I can move it to where the brushwood is. As we started collecting urine at ZEGG from waterless urinals, I thought of using the urine as quenching liquid and have the biochar charged up immediately. As biochar is really expensive in Germany at least from responsible and sustainable resources, after 4 firings the cost of building the kiln should be returned. This will speed up the carbon age at ZEGG as we could use it as litter for the horse stable, for plaster in humid places and of course as we have done already in Terra Preta soils.
Since 2013, we are experimenting with TP soils and are more than astonished by the good results. As ZEGG stands on purely sand soils, our efforts of creating humus by mulching and lately adding clay are limited as rains wash out both humus and clay. TP soils could offer a solution here of the most stable soil building.

We hope that Achim will write about the waterless urinals in the next newsletter. If you need more information, write to [email protected]


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