WEDNESDAY, JAN 25, 2023: NOTE TO FILE
Module 3-4
The soil microbiome and the nutrient cycles
As we have seen, microbial life has existed on this planet for around 3.8 billion years and has been the driving force of evolution, changing the gaseous composition of the atmosphere, laying down minerals as sedimentary rocks and creating the soil that is the basis for all life as we know it. Humans have known about microbial life for hundreds of years, but recent developments in research technology (e.g. ‘batch sequencing) are revealing the full extent of microbial involvement in maintaining life on the Earth and their crucial role in the functional cycles of the biosphere. In Module 1 we looked at the overall picture; in Module 2, we looked at aerobic and anaerobic microbes based on their relationship to oxygen; but microbiologists are now finding remarkable microbes that rely on other chemical processes for respiration and energy and can even switch nimbly from one process to another according to the elements available. The greatest (theoretical) grandmother of all life on Earth, fondly called LUCA (Last Universal Common Ancestor) was most likely such a creature with remarkable flexibility for survival, nimbly switching between processes for extracting energy from a wide range of organic and inorganic elements, which is no doubt why all life as we know it has descended from her with such a broad range of specialisations and commonalities. Paradoxically, it was life itself that saved planet Earth from the sterile fate of our neighbours Mars and Venus and it is life itself that will make the most crucial contribution to resolving the current biosphere crisis: biodiversity loss, desertification and climate change.
Thanks to our microbial cousins, mineral nutrients attached to electrically-charged particles in the soil (called cations) can be liberated and made available for uptake by plant root systems. Plants use these nutrients to create the enzymes, vitamins, essential oils and proteins they need. They also use them to create complex compounds we experience as taste and aroma. The compounds in plants like onions and garlic are obvious, but the expertise in organic chemistry exhibited by plants is astonishing. The odour of Elderflower blossoms, for example, requires a combination of nine chemical compounds, all of which have been manufactured by the tree from the basic nutrients it acquired from the soil, and brought together in exactly the right combination to produce the smell. Plants have a remarkable agency we have poorly understood; they are the absolute masters of organic chemistry on this planet, but it’s also clear that soil is the basis for all health as the compounds in plants are our source of essential minerals. Food is medicine only if we have a healthy soil microbiome, the soil bacteria and mycorrhizal fungi that provide the mineral nutrients to plants. Everything is connected.
At present, our industrial agriculture is destroying the bacteria and mycorrhizal fungal networks and impacting on our health. We have a recipe for a catastrophe and reducing pesticides alone is not enough to regenerate soil; we have to ensure that our farming methods transition from inorganic nitrogen fertilisers to agro-ecological methods that restore the symbiotic relationship to produce the organic nitrogen plants need to build proteins as well as the other nutrients.
More information on pedogenesis (soil creation), plant health and its influence on our own health can be found in the following talk by Dr Walter Jehne, soil microbiologist and campaigner for ecosystem restoration as a solution to the biosphere crisis. This is not an obligatory part of the module material, but is excellent additional, in-depth information for participants with a particular interest in agriculture.
["A new generation of soil studies powered by modern microscopes and imaging technologies has revealed that whatever humus is, it is not the long-lasting substance scientists believed it to be. Soil researchers have concluded that even the largest, most complex molecules can be quickly devoured by soil’s abundant and voracious microbes. The magic molecule you can just stick in the soil and expect to stay there may not exist.... Indeed, the existence of humus is probably one of the few soil science facts that many non-scientists could recite.
What helped break humus’s hold on soil science was physics. In the second half of the 20th century, powerful new microscopes and techniques such as nuclear magnetic resonance and X-ray spectroscopy allowed soil scientists for the first time to peer directly into soil and see what was there, rather than pull things out and then look at them.
What they found — or, more specifically, what they didn’t find — was shocking: there were few or no long “recalcitrant” carbon molecules — the kind that don’t break down. Almost everything seemed to be small and, in principle, digestible." As Wikipedia notes, "recent work suggests that complex soil organic molecules may be much less stable than previously thought: “the available evidence does not support the formation of large-molecular-size and persistent ‘humic substances’ in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds.″
Non-scientists traffic in belief-based thinking. If the data is telling those who will listen that 'humus' is as imagined, then those who would rather know than believe change the story they tell. Believers do not.
As noted in the introduction (which uses 'humus' seven times), "It suffices to state that without humus, the soil has no life, thereby rendering the soil infertile," and of course if adding industrial fertilizers to a soil seems to work, it is because the soil is humus depleted due to conventional agricultural practices. Oh, and to all you mathematician types out there, 2+2=5.]
Module 3, lesson 5
