How healthy plants create healthy soil
NOTE- This is a consolidation of a webinar that was produced by John Kempf from Advancing Eco Agriculture. I cannot say enough good things about the work that John is doing in the field of regenerative agriculture. But I view this particular short webinar to be the best and most concise outline of what happens in our soils- to a greater or lessor degree- when we properly understand the principles and relationships between soil, biology and plants. Many who first stumble on this world are confused by the various players and their roles. John has simplified this complex realm beautifully here, and his insightful words are worthy of broader exposure.
How healthy plants create healthy soil
The general thinking with regards to our gardens and soils is that you need healthy soils to produce healthy plants. Healthy soil is made through the use of compost, manure, cover crops and mineralization, all which contribute ultimately to healthy plants. This concept is certainly not entirely incorrect, though it is incomplete. It is actually healthy plants that can produce healthy soils through the process of photosynthesis.
It is the process of photosynthesis that sees plants sequester carbon dioxide from the air, produce sugars and produce carbohydrates. Once produced, the plant sends a significant proportion, perhaps the majority, of these carbohydrates and sugars down into the soil as root exudates to build organic soil matter. This is the central driver of building healthy soil- it is the plants, not soil, that is the engine that drives soil health. Without the plants, you would have nothing more than decomposed rock particles- sand.
Why is this important? When we understand that it is healthy plants that drive the ecosystem, we will focus on growing very healthy plants, rather than very healthy soil. Growing healthy plants is the pathway to developing soil health. If we focus exclusively on building soil health, and expect plant health to be a secondary outcome, we can get to the same place, but it will take a couple decades, rather than 3 or 4 years. Rapid responses in achieving better disease and insect resistance, better crop yields and better quality all happen much more quickly when the focus is on plant health first.
This allows you to build soil health very quickly. How does this work? This is called the biological cascade. The first stage is where we have plants at full capacity photosynthesis. It is very possible that we will never have plants at 100% capacity, because we have limiting factors from inadequate carbon dioxide, inadequate water, inadequate light, or inadequate nutrition, such as manganese or nitrogen, magnesium, sulphur etc. Most outdoor plants are at 15-20% photosynthetic capacity. Although it is unlikely to ever get to 100%, it is quite possible to get to 40, 50 or 60% capacity, particularly when we have weather supportive conditions.
So when you have achieved 60% capacity, that means you have 3 x’s the photosynthetic production, 3 x’s the photosynthates, or the sugar production in each 24 hour photoperiod. When that happens a significant portion of the sugars move down through the plant and out through the roots as root exudates in larger and larger concentrates, and this results in a very aggressive increases of bacterial populations and bacterial digestion in the rhizosphere. These carbohydrates and sugars feed the bacterial populations, and their colonies proliferate in the presence of this abundant supply of food.
We know that if we have a plant operating at 20% photosynthetic efficiency that during the framing stage- as opposed to the flowering stage, as much as 70% of the total photosynthate production in a 24 hour period can move out through the root system as root exudates. This is obviously higher with a plant that is at 60% photosynthetic capacity. This is a threefold increase, which does not necessarily correlate to a 3 fold increase in yield. You will get some increase in yield, possibly as much as a 30% increase, but you move a much larger quantity of sugar into the rhizosphere and into bacterial digestion.
This bacterial digestion produces what is called a mineralization response in the soil. Bacteria consume these sugars that are root exudates, which are largely carbon, hydrogen and oxygen, along with carbohydrates and enzymes. But what is not present in root exudates in any appreciable quantities is minerals- there are very low levels of calcium, magnesium, copper and zinc etc present in the exudates. And yet, bacteria need these minerals to form their own bodies. As the bacteria consume these carbohydrates, they then go out and extract these minerals from the soil mineral matrix and incorporate these into their own cells. As the life of bacteria is very short- often measured in hours, they eventually perish, and these microbial cells are now incorporated back into the root systems taking the nutrients back with them.
When plants start to absorb these microbial metabolites- which are the minerals now in a bio available form, they can access this abundance of nutrition and their growth systems become very efficient. They produce more energy than they need to sustain themselves, and they begin storing the excess energy in the form of lipids- plant fats and oils. We can see this in the plants when we have leaves that produce the very waxy oily sheen on the leaf surface, this also helps them to become very resistant to airborne pathogens.
Now if there is strong photosynthesis, along with good biological activity, then you have the ideal conditions to create high lipid production in the plants. The excess lipids are then transferred out to the rhizosphere- as was previously the carbohydrates and sugars. When we now have lipids moving into the rhizosphere, something very interesting happens. Because bacteria are not able to digest lipids, this triggers very strong fungal digestion. We get increasing colonization of mycorrhizal fungi and other types of beneficial fungi in the soil profile that begin consuming the lipids.
Fungal digestion is quite different than bacterial digestion. When fungi begin to digest something, they digest it, metabolize it and break it down over and over again, until it reaches a point where it cannot be broken down any further. Only at this point do the fungi release these digested lipids back into the soil profile and this process is called humification. The fungal digestion of these lipids along with the digestion of other high carbon compounds is what results in the formation of stable organic matter. An important component of the humification process is the formation of glomalins- as group of compounds that 'glue' together the soil particles, giving the ever so essential soil structure to our soils.
Whether we are referring to glomalin, or any of the list of various compounds that aggregate soil particles and produce a very stable organic matter, this is a result of fungal decomposition of healthier plants that have a higher concentration of lipid content. So you want to produce healthy plants that have the highest fat content possible- the highest lipid content.
It becomes very clear that if you want to build organic matter quickly, having a higher fat content plant is very important. The interesting point of this whole cascade is photosynthesis- once you increase the plants photosynthesis, all the rest of this happens automatically, happens on its own. Accelerating photosynthesis is the key to hacking the system-we can speed up the entire process.
This is also why increasing photosynthesis involves the strategy of cover crops, as with these, you have increased the amount of plant canopy that is photosynthesizing and exuding the valuable sugars and lipids into the soil.
When we really focus on plant health, we get our biggest soil response. This response is bigger than adding compost, or soil inoculants, because photosynthesis is the engine that drives the entire process.
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