Here Darryl advocates plantation forests with regular planting and harvesting of trees after their vegetative growth phase, around 25 years in his example. The harvested material would then be made into biochar and amended into these forest soils to increase soil carbon and growth rates of subsequent plantings.
On one hand this sounds like rotational or holistic grazing where fields are divided and livestock intensively grazes (fells) and manures (biochars) the soil, and is then moved on. Thereby allowing enough time between grazing for fields to recover, and for plants to benefit from the manures and spend more time in the vegetative growth phase sequestering more carbon.
Only, this is basically clear felling whereas rotational grazing is more like forest thinning if I understand it correctly. If only we still had dinosaurs to thin and manage our forests for us, or alternatively robots that were economically viable.
One issue I see with the clear felling apart from the ecological, diversity and hydrological problems it creates – is the subsequent seedling growth stage where you aren’t maximising canopy area in order to maximise photosynthesis and carbon sequestration.
One solution may be thinning and forest management, and he does mention thinning but never delves into the details.
That brings me to one of the issues he mentions about the cost of making biochar commercially and that made me think about my field Terra Preta interpretation of how the Amazonians might have made it buried in soil, but again that’s clear felling, and probably wouldn’t pass the EPA…
I also wondered what a biochar retort might look like in place around a standing tree… just for fun.
I also wonder if something similar can this be done as a polyculture or as or in combination with a food forest at scale while increase ecosystem diversity and at the same time sequestering carbon through management.
But, no doubt “scale” and “performance” is the issue, and commercially it comes down to what is “economically viable” under the “carbon market” rules and can be done today.
His comment on subsoil carbon is interesting: “It’s more expensive to monitor it and measure it, than it’s worth.”
Add 1.5% biochar to a 3.5% (0-100mm sampled) soil organic carbon soil, wait 9 years and it begins to positively prime. Clearly they didn’t add enough to reach a tipping point faster, or depending on your perspective and availability, adding biochar to low carbon soils is a long-term investment. I assume it was surface applied as the study is paywalled.
Paywalled: Biochar built soil carbon over a decade by stabilizing rhizodeposits : Nature Climate Change : Nature Research
David talks about his biochar experiments and that got me thinking…
Recently I watched a great talk about the negative priming effects of pyrogenic carbon on soil organic carbon that you may find interesting:
Extrapolating from Silene’s results, when biochar concentration is high enough (~3%) there should be a halving of soil organic carbon (SOC) priming, and this should cause a doubling of SOC sequestration and effectively grow high carbon content Terra Preta soils faster. This correlates well with other research I’ve seen by David Johnson.
What the biochar is doing is interesting. I’ve hypothesised that microbes change metabolic strategy in the presence of enough carbon and in particular high electron transfer biochar, as recently biochar has been shown to increase electron transfer within soils.
So in addition to nutrient sorption, biochar may be acting as a sort of microbe electricity grid, and moving their metabolism from one of oxidation to reduction as they get their energy from the grid, thereby facilitating more SOC sequestration.
If this is the case, to facilitate this we may want high electron transfer biochars that have large surface areas that are effectively many aggregate soil capacitors, which made me think of Robert Murray-Smith’s recent videos in which he creates his own graphene inks for batteries and capacitors, and has been recently been talking about his strange capacitors.
I know from other research that the most productive soils long-term are those that are most connected ecologically, not fungal dominated, though that helps up to a point, and creating these connected soils is important if we want productive systems. This electron transfer effect that biochar has may be one small part of the puzzle along with plant roots, mycorrhizal fungi and other interconnected ecosystems we’ve yet to discover.
Also, if I calculated correctly, in Silene’s video, 450C carbon-13 tagged biochar soil appears to respire at a rate about 13x slower than SOC, so it’s not going to stay around forever.
Microorganisms need electrons for everything they do. If they consume nutrients or spew out methane or expel carbon dioxide – for any living, biological process – they need electrons.
Amending the soil with pyrogenic carbon – known as biochar – brings high definition to the electron network. In turn, the electrons spur conductive networks and growth.
Lehmann and the members of his laboratory had struggled to understand why microorganisms thrived in the presence of biochar. The group removed soil phosphorus, making the environment inhospitable. They ruled out water and nutrients. They discarded the use of biochar as a food source because microorganisms cannot consume much of it. Through Sun’s background in environmental chemistry, the scientists found that microorganisms may be drawn to electrons that the biochar can transport.
Other research has shown that long-term ecosystem succession is caused by an increase in the connectivity of the ecosystem, and as carbon builds in soils this aids that process.
Dan talks about no till (minimum till) harvesting techniques and living mulch trails.