A short history about spreading 10 tons of rock powder and 5 tons of biochar

Our blog has been a little quiet during the the beginning of this year as we were fully focussing on implementing our first pilot. Since 1st of January we were working on taking our idea to the field. In this blog post we want to take some time to share our intense but successful first weeks of this year. At this point we also want to take the opportunity to thank everyone who supported our mini-crowdfunding campaign last year. Thanks to you we even passed our funding goal by 100€!

Returning to our pilot: The first challenge we had to overcome was finding a pilot area where we could apply our three pillars of carbon farming. Luckily this was very easy as we onboarded our first carbon farming partner already in December 2021. When we presented the Woonderlands method to Paula and Valter from PRETATERRA, they did not hesitate one moment and offered to implement our first carbon hub on their property. Since 15th of January we have been on their farm in Timburi, São Paulo State, supporting the implementation of a 2ha agroforestry system. Knowing the location, we were able to take the next two crucial steps: Getting biochar and rock powder to the farm!

In regard to rock powder, we identified various possible sources throughout Brazil. In fact the organic institute of Brazil has created a map were they show a variety of certified sources for rock powder in the country. We are currently analyzing those sources and will share a map of carbon removal suitability of these rocks in a future post. Just next to the farm of PRETATERRA, the company REMINER was the closest source of rock powder. They produce this powder based on residues from the production of gravel stone and other building materials and give it an extra grind to accelerate weathering and accessibility of nutrients to the plants. We will visit the facility later this month to take a close look at their mining and production processes. Even though their material was not optimal in terms of carbon removal potential we picked it due to the low delivery distance. Using the equations from Renforth 2012 we conservatively calculated a potential 0.5 tCO2 that will be removed through the application of 10tons of our rock powder (see equation 5 of the paper and compare our rock powder properties). After an LCA according to Lefebvre et al. 2019 we were happy to see that even with this non optimal material we will potentially remove significantly more carbon than we emitted through the application, with at least 80% of the removed CO2 representing net removal. 

In regard to Biochar we made the discovery that the Brazilian market is still in its infancy. Throughout Brazil we identified only two biochar producers that work with a certified pyrolysis process. Moreover, these two producers were located at a distance and sold their products at a price that did render a collaboration for the pilot unfeasible. To keep the carbon footprint as low as possible, we opted for using the leftovers from a nearby charcoal producer in Piraju. He delivered 5 tons of eucalyptus char in a somewhat diverse texture, with some parts more chunky and others more powder like. We are aware that vegetable charcoal is not the same as biochar and that both materials show different permanences in the soil, however, for this pilot case the material was just fine, and the procurement brought interesting insights about the Brazilian biochar market. With a carbon content of 75% and a 100 years permanence of ca 50% of this carbon, we have captured additional 6.8t of CO2 in the soil of our 2ha agroforestry system.

 

Getting to the final part, the spreading, we have used a small Massey Ferguson Tractor (MF 4300) with a 2 ton limestone spreader attached. We loaded two shovels of biochar and two shovels of rock powder for each spreading session. As only one tractor was available we needed to disconnect the spreader for each loading which resulted in each loading session taking between 20 to 30min time. The actual spreading of one load (1.5t rock powder with 0.2t of biochar) took only 15min. Optimally a second tractor would be used to load the spreader. After some initial challenges regarding the spreaders disc rotation and tractor speed we found a good setting that allowed us to spread the material mix on 4 agroforestry lines per load. Spreading consumed about 3.5l/h of diesel. As we have spread after an extended time without rain we noticed that the spreading resulted in the creation of a serious dust cloud. Thus, an application after a rain event or with a slightly humid material may be recommended, however, in terms of carbon removal through enhanced weathering this does not reduce the impact. Luckily, just after the spreading it started to rain, this way incorporating the rock powder into the soil were we want it from a nutrient perspective. Currently we are waiting for the soil to dry up again so that we can start implementing the agroforestry system lines and plant the beautiful avocado, teak, banana and mahogany seedlings which have just arrived. 

To get a better impression of the pilot check out our video from Timburi and follow us on Instagram. To learn more about carbon farming and how you can create a carbon hub with us, get in touch.

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