Natural Sequence Farming – The Untold Story of the Australian Landscape

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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.

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

Key to speeding up carbon sequestration in the ocean discovered

Scientists at Caltech and USC have discovered a way to speed up the slow part of the chemical reaction that ultimately helps the earth to safely lock away, or sequester, carbon dioxide into the ocean. Simply adding a common enzyme to the mix, the researchers have found, can make that rate-limiting part of the process go 500 times faster.

On paper, the reaction is fairly straightforward: Water plus carbon dioxide plus calcium carbonate equals dissolved calcium and bicarbonate ions in water. In practice, it is complex. “Somehow, calcium carbonate decides to spontaneously slice itself in half. But what is the actual chemical path that reaction takes?” Adkins says.

Studying the process with a secondary ion mass spectrometer (which analyzes the surface of a solid by bombarding it with a beam of ions) and a cavity ringdown spectrometer (which analyzes the 13C/12C ratio in solution), Subhas discovered that the slow part of the reaction is the conversion of carbon dioxide and water to carbonic acid.

“This reaction has been overlooked,” Subhas says. “The slow step is making and breaking carbon-oxygen bonds. They don’t like to break; they’re stable forms.”

Armed with this knowledge, the team added the enzyme carbonic anhydrase — which helps maintain the pH balance of blood in humans and other animals — and were able to speed up the reaction by orders of magnitude.

Key to speeding up carbon sequestration discovered | EurekAlert! Science News

That makes me wonder about the chemical limitation of carbon sequestration in soils.

Leaf particles cause nitrous oxide hotspots in large pore soils

“The leaf particles act as tiny sponges in soil, soaking up water from large pores to create a micro-habitat perfect for the bacteria that produce nitrous oxide.”

Not as much N2O is produced in areas where smaller pores are present. Small pores, such as in clay soils, hold water more tightly so that it can’t be soaked up by the leaf particles. Without additional moisture, the bacteria aren’t able to produce as much nitrous oxide. Small pores also make it harder for the gas produced to leave the soil before being consumed by other bacteria.

Every time you till, what are you creating? Large pores.

Decomposing leaves are a surprising source of greenhouse gases | MSUToday | Michigan State University

Why microbes sometimes fail to break down organic carbon in soils

A new study has found that:

In oxygen-starved places such as marshes and in floodplains, microorganisms do not equally break down all of the available organic matter. Instead, carbon compounds that do not provide enough energy to be worthwhile for microorganisms to degrade end up accumulating. This passed-over carbon, however, does not necessarily stay locked away below ground in the long run. Being water soluble, the carbon can seep into nearby oxygen-rich waterways, where microbes readily consume it.

Tests found that, in contrast to the layers where oxygen was available, leftover carbon compounds in the sediment samples where sulfur had been used for respiration instead of oxygen were mostly of the sort that requires more energy to degrade than would be liberated through the degradation itself. Making these carbon compounds of no use, then, to growing microbes, and had remained within the deeper sediment layers.

Shunned by microbes, organic carbon can resist breakdown in underground environments, Stanford scientists say | Stanford School of Earth, Energy & Environmental Sciences