Short term carbon is the fast moving carbon and long term carbon is the slow moving carbon. To put fast and slow moving carbon into a commercial analogy, think of cash flows versus capital.
Cash flows keep you in business, just like the fast moving carbon that keeps you in business too. Think of the slow moving carbon as really part of your capital base, just like cattle yards and buildings.
The cash flow aspect
The fast moving short term carbon makes money for you because it feeds all the life in the soil that keeps the soil productive AND feeds sheep and cattle. Remember cattle are 18% carbon, with all this carbon coming from the fast moving carbon. It is the faster moving carbon that builds larger root systems in plants so that they can access more moisture and nutrients to grow. It is central to plant energy reserves that determine how well plants can come out of dormancy. The ability to respond to isolated small falls of rain is especially important in dry years when getting something to grow is critical.
Ground cover is fast moving carbon as is organic matter that supplies nutrients to plants.
The capital aspect
Humus in the soil is long term carbon which is the by-product of microbial activity (consumption).
This slow moving long term carbon is important for a different reason. It provides long term resilience by holding resources. It is essential for increasing the “storage” of both water and nutrients in the soil for plant growth.
A lot of literature uses the terms “organic matter” and “humus” very loosely, as if they were the same thing, which they aren’t. Organic matter is the raw material for humus.
Humus helps hold water in the root zone. Because humus is smaller in particle size than clay, it has a greater water holding capacity than clay. Smaller particles have a higher surface area to volume, which increases holding capacity. This also explains why sand, which has large particles, has a poor water holding capacity.
Because humus is highly charged, it will aggregate many particles into stable aggregates. This leads to better soil structure and it is resultant pores that hold extra water containing the soluble nutrients like nitrate nitrogen.
Also, humus is the habitat for long-term populations of microbes.
The cation exchange capacity (CEC) is a measure of soil fertility and quantifies the volume of mineral elements that the soil can hold and make available for plants to use. Humus has a higher CEC than clay particles, so is better at keeping nutrients in the paddock.
How to reduce carbon flows & cash flows
Management that leads to a reduction in carbon flows from any rain that falls, also reduces cash flows.
Sheep shutting down carbon flows after rain (Photo: Patrick Francis)
The above photo was taken after 30mm of rain. This is a grazing operation that will be out of production soon. The question has to be asked, when should carbon flows be harvested? When possible, pastures should be rested for a short period after rain to maximise carbon flows into the paddock, like in the foreground. In other words, graziers need to let sheep and cattle only harvest the surplus, not the means by which a usable surplus is generated.
Moribund pasture bringing in little carbon after rain
Letting animals over consume plants when they are trying to grow is one way to reduce carbon flows, however, when perennial grasses are not exposed to grazing, they become moribund. Moribund grass introduces a lot less carbon than grass correctly grazed.
Capitalising short term carbon
It is very hard to establish a figure, but it would appear that about 2% of long term soil carbon leaves the system each year i.e. flows back to the atmosphere. It also appears that about 2% of carbon flows find their way into the long term pool.
All businesses have to maintain capital infrastructure. Think of carbon flows as maintaining the pool of long term soil carbon. If carbon flows are really well managed, this can lead to a capital gain if more carbon moves into the long term pool than moves out. Of course, there is a limit to how much long term carbon the soil can store.
When I ran the “financial analogy” past Ruaridh Petre, he responded by broadening it further, “Life on earth is an economy that runs on carbon. The more busily plants and microbes trade carbon molecules, the more prosperous the ecological economy becomes. Also, you’ve got to use carbon to store carbon.”
Erosion is an immediate reduction in earning capacity, because it removes both short term and long term carbon.
Next week's discussion: "Edible shrubs provide more reliable carbon flows"