Soil Organic Carbon: keystone to sustainability in a changing world


Build Soil Organic Matter with Brown-rot Fungi

Spatial Heterogeneity of SOM Concentrations Associated with White-rot Versus Brown-rot Wood Decay. – PubMed – NCBI

The brown-rot fungal wood decay resulted in higher concentrations of soil C and N and a greater increase in microbial necromass (i.e., 1.3- to 1.7-fold greater) than the white-rot fungal wood decay. The white-rot sets were accompanied by significant differences in the proportions of the bacterial residue index (muramic acid%) with soil depth; however, the brown-rot-associated soils showed complementary shifts, primarily in fungal necromass, across horizontal distances. Soil C and N concentrations were significantly correlated with fungal rather than bacterial necromass in the brown-rot systems. Our findings confirmed that the brown-rot fungi-dominated degradation of lignocellulosic residues resulted in a greater SOM buildup than the white-rot fungi-dominated degradation.

Adding Carbon to Soils increases Microbial Nitrogen Use Efficiency

… and that in the short-term carbon through microbial form immobilizes already available N, potentially making less available for plants or loss through leaching.

The belief that adding high-carbon mulch locks up nitrogen may yet have some merit, not necessarily in the mulch, but in the microbes!

From Short-term carbon input increases microbial nitrogen demand, but not microbial nitrogen mining:

Although C input promoted microbial growth and N demand, we did not find indicators of increased N mobilization from SOM polymers, given that none of the soils showed a significant increase in protein depolymerization, and only one soil showed a significant increase in N-targeting enzymes. Instead, our findings suggest that microorganisms immobilized the already available N more efficiently, as indicated by decreased ammonification and inorganic N concentrations. Likewise, although N input stimulated ammonification, we found no significant effect on protein depolymerization. Although our findings do not rule out in general that higher plant-soil C allocation can promote microbial N mining, they suggest that such an effect can be counteracted, at least in the short term, by increased microbial N immobilization, further aggravating plant N limitation.


IMAGINE IF… we could fix the climate by fixing the soils – Soil C Quest 2031


Plant roots 5x more likely than leaves to turn into soil organic matter

Plant roots are five times more likely than leaves to turn into soil organic matter for the same mass of material.

This among other findings from Stanford researchers.

Improving how land is managed could increase soil’s carbon storage enough to offset future carbon emissions from thawing permafrost, the researchers find. Among the possible approaches: reduced tillage, year-round livestock forage and compost application. Planting more perennial crops, instead of annuals, could store more carbon and reduce erosion by allowing roots to reach deeper into the ground.

Soil holds potential to slow global warming | Stanford News


Humification Theory [Rant]

“Soil organic matter (SOM) derives from dead plant parts in the litter layer”
“A fraction of SOM persists because it can resist decomposition.”
“The process which converts litter into resistant or “recalcitrant” soil organic matter
was called humification”
The product of humification = presumably ‘stable’ organic matter = is called humus

I don’t believe in humification theory. There, I’ve said it. I cringe every time I hear the word humus.

Biochar isn’t even that stable in soil. Unless it’s buried where oxygen doesn’t reach it deep deep in the profile. Something fungi can do with it by embedding it inside soil microaggregates where it won’t be oxidized or access by other organisms. But carbon cycling in soils doesn’t stop there.

I’m not the only one that questions it. Here is a video summary of a paper by Johannes Lehmann and Markus Kleber from 2015, and there are others I’m too lazy to link to.

How is carbon stored in the soil?
Thomas Fester

Here are some slides from a talk about the paper, a talk I wish I could find, and the scientific paper from Nature.
However even Johannes Lehmann the co-author of the paper uses the word humus in the following talk on soil carbon two years ago around the time the paper was released. It’s so engrained in people and our language that I believe it will be around long after the “stable” humus is.


No doubt I’m bound to use the word humus to confuse myself and others too, just a heads up then… 🙂


Soil Carbon Mineralization Limits.

A new study titled Is the rate of mineralization of soil organic carbon under microbiological control? suggests that:

  • the rate limiting step in SOC mineralization is abiotic (physical rather than biological).
  • that mineralization of SOC may be a two-stage process: firstly, non-bioavailable forms are converted abiologically to bioavailable forms, which, only then, undergo a second process, biological mineralization.

I’ll speculate and say that mineralization is perhaps limited by dissolved organic matter in the form of complex carbon structures that are produced by weathering, oxidation, and detritivores that break apart plant litter. Liquid compounds that tend to be lost when composting.

Compounds that are probably why wet climates and seagrasses sequester the most carbon.

Why drying and wetting of these compounds leads to CO2-Bursts.

Compounds we should be trying to keep in the soil profile doing good, and not in aquifers or waterways creating algal blooms, like we really need to with this recently discovered underground molten lake the size of Mexico!

That depending on the complexity of the carbon molecule as it gets passed down the soil carbon continuum food web it may be more than a two-stage process, with more than one in both the physical and biological realms based upon chemical energy and chemisorption of the carbon compounds.

*shrugs* Just my guess, I suck at chemistry.

Chemisorption:Screenshot from 2017-05-21 12-34-28.png


Add 1.5% Biochar to a 3.5% SOC Soil And Wait 9 Years.

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 compost it. I assume it was surface applied as the study is paywalled.

Screenshot from 2017-05-21 07-29-17

Paywalled: Biochar built soil carbon over a decade by stabilizing rhizodeposits : Nature Climate Change : Nature Research


Diverse aboveground biomass for the soil organic carbon win

Now this is interesting:

“the rhizosphere priming effect was positively correlated with aboveground plant biomass, but surprisingly not with root biomass

  1. Grow diverse aboveground biomass
  2. Chop and drop
  3. Mulcho profit!

In a meta-analysis of 31 studies, researches show that the rhizosphere enhances soil organic carbon mineralization by 59%[*].

That woody species are best, then grass, then crops.

[Me: *So long as it’s fed from the above ground biomass litter.]

Sounds like C:Nhoosing Your Mulch? Think of the Fungi to me, and photosynthesise as much as you can be!

Don’t forget plant and mulch diversity in this mix, as Plant litter diversity increases microbial abundance, fungal diversity, and carbon and nitrogen cycling.

Another interesting study today suggests that soil fungal community is mainly influenced by plant community composition, distance between communities, and rainfall.

So go diverse and you can’t really lose.

Diverse ecosystems in connected communities.


Biochar, The Soil Capacitor

Work With Nature

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.


A Mechanistic Breakdown of Negative Priming of Soil Organic Carbon by pyOM

Silene DeCiucies

Cornell SIPS


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