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.
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.
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.
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.
Comments and Questions 6 20 2017
My only experience with weed mat, was pulling one up, and finding stinky dead earth beneath
Now it sounds like this person’s plastic weed mat caused the soil below it to turn anaerobic due to either a lack of air penetrating the mat or retaining too much moisture which then excluded the air from entering the soil. When this happens the soil begins to anaerobically digest and produce alcohols, phenols, and gasses such as methane, the scent of sewer gas.
Not ideal plant growing conditions!
However there can be benefits when using plastic weed mat in the right conditions that does let air and water through, as the mat can help keep the soil moist, especially in drier regions. Weed mats can also warm or cool the soil depending on how much sunlight they absorb or reflect. They can also help prevent erosion. But the main reason people use it, is because the mats also reduce weed competition for plants planted into or near the weed mat. Reduced competition for water, sunlight, and for nutrients.
However the biggest problem with plastic weed mat when growing and assuming the correct mat was chosen for the conditions, is that if left on for extended periods, the soil often tends to breed plant pathogens. This happens when soils are not amended with a high carbon source such as plant leaf litter, plant exudates, or an organic mulch.
In soils that are kept moist and aerated and warm the microbiology and fauna become more active and will chomp through organic matter like there is no tomorrow. In doing so there is an increase in soil carbon respiration in the form of carbon dioxide and methane along with other gasses. This increase in respiration can actually help increase plant growth by providing carbon dioxide concentrated around the plant leaves. The increase in microbiological activity also increases nutrient cycling and plant available soil nutrients. However if the plants aren’t putting the carbon back into the soil via their roots, exudates, or plant litter when they die – then over the long term the soil community suffers.
When there is a lack of high carbon input that organic mulch provides to soil organisms, competition for that soil carbon increases. And the less soil carbon, the less complex organisms will survive. This is particularly important for fungi that rely on the carbon because they are made up of more carbon than other microbiology. Worse, the fungi that do survive the hostile conditions are often those that are plant predators able to fight for the carbon needed in order to survive because they now lack competition. As a result those predators infect plants and reduce yields or even kill them, and so gardeners and farmers search for solutions to their fungal problems in the form of fungicides. As a result fungi get a bad name. The same happens to nematodes.
However for short season plants like seasonal crops in Kevin’s example, this may not be much of a problem as the plant may be ready for harvest before the predators have overcome a plants defences, and he’s adding organic matter every year.
To conclude, when organic resources are plentiful, everyone’s happy and works in symbiosis, and when they’re not happy it’s war. Not quite extremophile Star Wars, but certainly localised Planet Wars, and eventually those wars include us higher order carbon beings in Human Wars that result from desertification and a lack of resources.
Plastic mulch is also plastic. Did you know that most sea salt already has microplastics in it after a little over 100 years of plastics use?
The Technical Potential of Soil Carbon Sequestration