Carbon Sequestration

Increasing your soil microbes increases carbon sequestration. Carbon is stored in the soil as “humic materials” i.e. C,N,P,K etc.; rich organic matter which is the soil organic carbon or sequestered carbon in the soil. ­­­­­

The formation of humus, the final stable carbon, is a stepwise process. All organic carbon in soil comes from plants, either directly or via digested plant material. It starts with plant material being digested by soil microbes, or in the case of brown manure, being predigested by animals and further digested by microbes. The breakdown process begins with soil fungi and bacteria. As these microbes are fed carbon, they multiply. If fresh carbon stores are not utilized, they become attached to soil particles and become stored, therefore, less available as food sources. As microbes die, if they are not immediately cannibalized, their remains also become part of the more recalcitrant humic material.

Slowly, this humic material, which is as much as 80% the bodies of dead microbes, builds up. We measure it as soil organic carbon (SOC) and it reflects the carbon sequestered in the soil, but it also contains all the minerals and other plant nutrients. To increase SOC, the fresh organic matter required to feed the microbes and in turn the plant via the microbes, there needs to be an excess of the minimum required for a low microbial population. If there is an excess, the microbial population increases, and their dead bodies will increase the humic matter, in return increasing carbon sequestration. If it is not adequate, the soil microbes will be stimulated by the plant to mine the stored organic matter, which will decrease the stored carbon. It is not surprising that scientists have compared the plant/microbe/soil fertility index to economic models. A rich soil, like a rich man, has money in his pocket and money in the bank, for soil the currency is carbon.

This system is very much like our agricultural complex. There is fresh food, which we utilize within days, food we freeze or can, which requires freezers and can openers to access, and food stores (our sequestered carbon) that we maintain in silos as protection against disaster.

How do plants farm soil microbes?

Source: How Plants ‘Farm’ Soil Microbes and Endophytes in Roots

UPDATE: Dr. White sat down with Dr. Fitzpatrick and Jeff Lowenfels to discuss rhizophagy. Click here to view the webinar. (Jan. 15, 2021)

A summary of James F. White’s presentation at BioFarm, 2020 (Nov. 12, 2020). 

The rhizophagy cycle is an amazing process recently discovered by James White’s laboratory at the University of New Jersey, by which root tips “ingest” bacteria and absorb nitrogen and phosphorus and other nutrients from them.

The microbes pictured here in roots are called endophytes because they can live inside plants. The bacteria are attracted to the root tip by root exudates. They then enter the root where the cell walls are dissolved using superoxide, allowing nutrients to leak out to the plant. But the plant does not kill the microbes instead the microbes stimulate the formation of root hairs, which are escape routes for the microbes.

After ejection from root hair tips, bacterial cell walls re-form. The bacteria fatten up and are soon ready to acquire soil nutrients and become another meal for the plant.

Source: How Plants ‘Farm’ Soil Microbes and Endophytes in Roots

Not only does rhizophagy provide mineral nutrients, it is also the stimulus for formation of root hairs, which are critical to the establishment of a healthy root as can be seen in this photo of a plant root with and without endophytes.




What is “priming” and how does it affect your soil?

Priming is currently a hot topic as it affects whether the fertilizer you are using is effective. For instance, when you prime a pump, the water you add allows the pump to start pumping water. If there is not enough water, you just wasted the priming water.

This is exactly what happens in your soil. When the microbes in the soil are fed nutrients “primed”, by the plant or amendment, it wakes them up and they start growing. But, whether they can continue to grow depends on the continual supply of nutrients. If there is enough balanced organic matter in the soil, they are fine. If not, the microbes will work hard to harvest some of the stored carbon, nitrogen and phosphorus in the soil. And instead of storing carbon in the soil, their labors will produce CO2.

A key point is “balanced” nutrition available in the fresh organic matter which is most available to microbes. Like us, if microbes do not have access to one of the key nutrients, e.g. N, P, S, K, Mg, Mn, B, etc. they cannot thrive. Clive Kirby’s group in Australia has demonstrated that by balancing the ratio of key nutrients in fertilizer regimens to bring the ratio of fresh organic matter to a C:N:P:S ratio of 10,000:261:32:48 they increased yield and substantially increased the stored soil carbon.

Source: Coonan, E.C., Kirkby, C.A., Kirkegaard, J.A., Richardson, A., Amidy, M. and Strong, C., 2020. Microorganisms and nutrient stoichiometry as mediators of soil organic matter dynamics. NUTRIENT CYCLING IN AGROECOSYSTEMS, 117(3), pp.273-298.