Biochar, The Soil Capacitor

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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.

Cover Crops May Increase Soil Microbial Biomass 3x More Than Compost

Three to six times more microbial biomass carbon and nitrogen depending on soil type.

These results provide evidence that carbon (C) inputs from frequent cover cropping are the primary driver of changes in the soil food web and soil health in high-input, tillage-intensive organic vegetable production systems.

Fresh is best.

Cover cropping frequency is the main driver of soil microbial changes during six years of organic vegetable production

New Slow-release Nitrogen Calcium Phosphate Fertilizer


Researchers have used nanoparticles to create a a fertilizer that releases nutrients over a week, giving crops more time to absorb them (ACS Nano 2017, DOI: 10.1021/acsnano.6b07781).

They attached urea molecules to nanoparticles of hydroxyapatite, a naturally occurring form of calcium phosphate found in bone meal. Hydroxyapatite is nontoxic and a good source of phosphorous, which plants also need.

In water, the urea-hydroxyapatite combination released nitrogen for about a week, compared with a few minutes for urea by itself. In field trials on rice in Sri Lanka, crop yields increased by 10%, even though the nanofertilizer delivered only half the amount of urea compared with traditional fertilizer.

Slow-release nitrogen fertilizer could increase crop yields | Chemical & Engineering News

They should call it UreaCa! Geddit?

Alternately you could just use fresh plant litter or cover crop residues that leach nitrogen over two weeks and also feed soil microbes carbon. Or faba bean that will release it over three years[1] and build soil carbon so eventually you don’t need to add any.

[1] Carbon and Nitrogen Release from Legume Crop Residues for Three Subsequent Crops
Abstract | Digital Library

[2] Formation of soil organic matter via biochemical and physical pathways of litter mass loss : Nature Geoscience : Nature Research

Soil Priming – Let’s Get This Party Started.


The priming effect, i.e. the increase in soil organic matter (SOM) decomposition rate after fresh organic matter input to soil, is often supposed to result from a global increase in microbial activity and competition due to the higher availability of energy released from the decomposition of fresh organic matter.

However a new study suggests that:

The chemical structure of added compounds on the priming effect is much larger than the effect of energy-content.


Different substrates resulted in different priming effect but appeared to stimulate the growth of similar bacterial groups. This suggests that the added compounds stimulate different enzyme systems within similar bacterial taxa.

Priming of soil organic matter: Chemical structure of added compounds is more important than the energy content