The Soil Carbon Sponge

Interesting talk. Regarding too many trees, I saw this today in my news: Billions of gallons of water saved by thinning forests | NSF
I will reserve my judgement on until I can find the paper they refer to. 🙂

I have read previously that during drought water stressed trees exhale more carbon than they consume. I recently read that _any_ amount of selective logging harms freshwater fish diversity, and I assume the same with large fires and extra water run-off. The carbon from fires is also washed down hill and collects in troughs and the land becomes nitrogen and phosphorous deficient.

On soil carbon; the highest natural soil organic carbon recorded that I know about so far is in a protected bay in Sweden growing sea grass. When the grass dies it gets buried in the anaerobic sediment and stays there a long time aided by the bay being well protected from nutrients being washed out to sea.

Roots sequester on average five times more carbon than aboveground biomass litter.

From other research I’ve read, plants with long, thin, and deep roots sequester the most soil carbon over the whole soil profile. And the deeper the roots go, the longer the carbon is sequested and the more energy is required by microbes to utilize it. Ultimately the dissolved organic matter may be washed out of soil profile and end up in rivers and the ocean where it is consumed by bioluminescent cyanobacteria, apparently these are the most abundant carbon fixers of the ocean, and the carbon eventually ends up in sea monsters.

A 600 farm Victorian soil carbon study found rainfall was by far the biggest factor for soil carbon, something like 80%, followed by soil bulk density and pH, all pretty much irrespective of land management practice. So anything to improve those especially in compacted surfaces will help. I’ve seen one study show compost teas improve soil bulk density and water infiltration, but so do water treatment practices like Puricare that oxidize bore water prior to irrigation. Another Victorian study showed subsurface manuring with a C:N below 25:1 was most effective in reducing bulk density and improving pH so long as there was enough soil moisture for the microbes to break the material down. A preliminary microbiome subsoil manuring study found it’s the nutrient ratios that matter, not whether they’re organic or inorganic, and that most microbes are in the soil, they just need the right mix to begin cycling it.
There’s data showing bacterial and fungal abundance increase linearly up to at least 4% soil organic carbon, with fungal diversity tapering off at 3%.  Microbial diversity has also been shown to determine nutrient cycling and soil testing with Solvita CO2 test can determine respiration.
The SoilKee Renovator has been shown to increase nutrient cycling through oxidation and increased dissolved organic matter at the initial expense of soil carbon by bringing strips of pasture roots and soil to the surface.
Small predators like arthropods are also important for soil carbon sequestration, however Regenerative Farming has become a real buzzword for larger animal management practices. Most studies I’ve read show they are only appropriate in context with appropriate rainfall, soil moisture and existing soil carbon. David Johnson has shown that about 3% soil organic matter is needed before plants put more carbon into the soil than they take out, and that optimum plant productivity happens at a fungal to bacterial ratio of about 3:1. This is because fungi and plants and higher carbon life forms being eukaryotes require more carbon to build their cells as opposed to prokaryotic bacteria.

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