I'm a biologist and I just completed a PDC. I'm absolutely enthusiastic about learning more about forests. forest gardens, land regeneration and C farming. I'm trying to understand what kind of soil management is more effective in terms of both food production efficiency and C sequestration so as I'm able to compare forests vs praeries and forest gardens vs pastures vs crops so as I can take rational and well informed decisions about land use and management according to both aspects (C and food).
I'd be very grateful if someone could send links or recommend good technical bibliography (books, research articles...) on C farming and C absortion in all kinds of soils (crops, pastures, forests, forest gardens, praeries...) under all kinds of managements (no management (wild), organic management, conventional management...).
There seems to be lots of literature and debate and so far I have the impression that there is no consensus on what kind of management is more effective in terms of C sequestration (some say that pastures, if well managed, are better, others say that forests are better...) . Is my impression correct, or there is some degree of consensus? I'd be grateful if you expose your own points of view on the topic too.
Welcome. We seldom have consensus and I can't see that happening on this particular topic anytime soon. Some of the best stuff I've seen concerning adding organic material and carbon to grazing land, is through crowd grazing, where large numbers of animals consume the bulk of the grass in a short time and they trample the rest into the soil along with their manure. This regenerates quickly, with an increase in soil depth over time.
In some parts of the world forests grow better, in other parts, grass grows better, so it may be appropriate to proceed based on which grows best in the location where the carbon sequestration is desired. I don't think there is a "one size fits all" solution.
The closest to consensus that I've gathered is that you will maximize carbon sequestration by minimizing soil disturbance. So straight up annual crop fields seem to be regarded as the least effective way to sequester carbon (although many people demonstrate an ability to draw more carbon into their crop field soil than others), beyond that you've probably got to consider your specific location. I am partial to the notion that some savanna type mix of grasses, shrubs, and trees maximizes the amount of biological activity throughout the year and that seems to correlate to the amount of carbon that is fixed into the soil
I was reading another thread regarding sheep and carbon sequestration. I didn't see this mentioned but my understanding is that not only does grass become animal, and animal poo, and some methane, but when the grass is grazed the root die back leaves (how much?) carbon in the soil as root exudate. The stuff that binds soil aggregates and feeds microorganisms. I think that's where the real action is, but just my gut feeling. Anyone have science on this?
Carbon is durable in the soil because it is either stable chemically (char) anoxic (peat) or incorporated in something that is managed. The natural history of carbon is to cycle in and out of the atmosphere, so we are working against nature to incorporate it.
But we have allies in the soil food web. They can make stable sticky compounds, fungal hyphae and slow growing microbes that contain complex molecules, which are carbon-rich. This is like sheep planting their own forage through droppings, they colonize and maintain an underground kingdom. Everything we do "up top" is just their harvesting scheme to get more juicy carbon. If my soil is 7% organic matter, that is way more carbon in the soil than in even a large tree up on the surface, including the roots. So I want not just high organic matter, but deep soils. Essentially I want to turn B horizon into A horizon, and C horizon into B as I add more depth. See the graph on the bottom, we are trying to get the most carbon into the "stable humus" category, and to do that we need all the guys on the right, and we feed them with the readily decomposable material.
So in my opinion, whatever you can do to churn readily decomposable material through the system will gradually accumulate as humus. The more you can deliver, the faster the kinetics. All the stuff I do to optimize the mineralization and earthworks and everything else just set up a carbon farm, which I can use to generate the soil life. How often you deliver it depends on the crop. Trees are once a year, grasses I can deliver several times a year, as mentioned above and below the surface. Some places trees give important gifts in minerals and shade and windbreaks that offset the loss in only annual biomass. It really is dependent on climate and management intensity. I'm kind of splitting the baby and doing silvopasture to get elements of both. Later on I can thin the trees or let them fill in. The consensus here is in VA is that silvopasture with approx 40' gaps gives the most grass biomass per acre per year, and tree biomass on top of that.
I don't think minimizing disturbance is a goal at all, there is a healthy amount of disturbance, which will advance those horizons deeper, but annual total disturbance is undesirable.
Standing on the shoulders of giants. Giants with dirt under their nails
Companion Planting Guide by World Permaculture Association