What does a farm intern do over the winter months to keep herself busy until the beginning of spring fun begins? Other than dream of crop rotation designs and new vegetables to try I also had the opportunity to attend an all day conference about biochar! Biochar is a very old concept that is only recently getting new attention for its carbon sequestering capabilities. The biochar story begins in Brazil when anthropologists discovered what they termed as “terra preta” or dark earth. When they tested the soil they found that it had very high levels of charcoal that had been buried thousands of years earlier. The impact of the charcoal made the soil more efficient in retaining water and nutrients and it can still be seen in the soil today.
One major question I had going into this conference was what is the difference between charcoal and biochar? Hugh McLaughlin, a scientist at Alterna Biocarbon, answered that question for me. It was explained that charcoal is fuel that is used to cook and is made at around 300 degrees Celsius. Biochar on the other hand is a soil amendment and is made at 600 degrees Celsius. The key difference is the amount of mobile vs. resident matter. When you heat the biomass (woodchips, organic waste, manure, crop residues), to such a high temperature it becomes extremely stable and also creates a very porous structure. Good biochar should have high cation exchange capacity and absorption capacity – these are what make the biochar so beneficial to the soil. The main benefits of biochar are (1) improved moisture dynamic, (2) improved nutrient retention (N, P, K for example), (3) improved microbe survival during drought, and (4) improved plant – microbe synergisms. So, the idea is that biochar will keep carbon in the soil, rather than in the atmosphere, whilst simultaneously leading to improved soil health and larger crop yields.
The process of making biochar involves collecting your biomass (referred to as feedstock) and lighting it on fire in a sealed container with very low oxygen conditions. Ideally the feedstock you use is coming from your farm or very near by, or else it kind of defeats the whole carbon saving notion. There are many different devices to make biochar – ranging from homemade “TLUD” (Top Lit Up Draft) Ovens, to much larger scale kilns and retorts. Click HERE for instructions on building yur own TLUD. They did a biochar making demonstration at the conference using homemade TLUDs. There are also more and more companies that are selling biochar on the web. The most reputable companies mentioned at the conference (in which the biochar has been tested and approved) were Soil Reef, Encendia and Colorado Biochar. It was also emphasized that testing your biochar is really important before using it. Now that there is a market for it, there are companies using left over wood scraps from construction sites as their feedstock. Bad biochar can actually do soil more harm than good – so it is important to know the contents of your char.
Once you have your biochar – you need to charge it. There are no nutrients inherent to the biochar, so the most common way to charge biochar is to combine the char with compost in a 50:50 ratio. You can add the char to the compost in the early stages of the compost and let it go through the process of composting. You can also mix it with finished compost and let it sit for about 2 weeks – this process is referred to as “weathering the char”. Compost is great but the benefits only last so long, the idea with biochar is that it absorbs the nutrients and makes them available to the plants for a much longer period of time. When you are ready to apply it to the soil, you can just add it by hand and mix it with the topsoil. Application rates range from between 1-10 tons per acre depending on your soil needs.
There is still a lot of research to be done in this field to determine the lasting benefits of biochar. But there are certainly a lot of exciting prospects and research projects being done. One farmer at the conference brought his own biochar to give out to fellow farmers as long as they promised to report back their experience with the char. The community of biochar users is still relatively small and there remains a need for more information on the use of biochar on small and large scales. I am happy to report that we have a bag of this precious biochar to experiment with this season at the farm. We will continue to report on our findings and hopefully will have some record yields!