Triumph of the Microbes
by Gary Kline
I was mistaken. Let me say that right up front. But I’m glad that I was wrong, and this is good news. As a biologist I always wanted to cheer for the primacy of the biological dimension (as opposed to the physical and chemical) being responsible for soil fertility. But I couldn’t.
Dr. Albrecht had taught, through his writings, that certain chemical elements were ultimately responsible for fertility; i.e., calcium, magnesium, potassium and sodium, in a certain ratio, which largely controlled that fertility. Those four elements were dependent on an electrical property or negative charge on tiny particles of clay and humus known as colloids or micelles. I prefer the term colloid, a discussion of which would require another article.
Those four key chemical elements in their active state are positively charged and are known as cations, which are drawn to the larger negatively-charged colloids as if by a magnet. These colloid particles help to hang onto the cations so they are not drained away by water passing downward through the soil. The four major cations (along with several others to a lesser extent) are thus held in place for plant roots to pluck off as needed for their nourishment, and the plant does this using the tiny hydrogen cation, which it sends out like cue balls to dislodge the nutrient cations.
The hydrogen ion, however, is not a nutrient in its rogue, cation state and causes acidity when present in large amounts in the soil water and occupying most of the negatively-charged sites on a colloid. When the hydrogen ion changes places with the nutrient cations, that’s an exchange, known as a cation exchange, and the amount of cations a given colloid can hold is known as its cation exchange capacity or CEC. In general, humus has up to triple the capacity of clays.
So colloids great and small (in their charge) are like reserve gas tanks, and what you want for feeding plants is a large tank able to hold or holding a lot of cation nutrients that are either naturally present or supplied by you in the form of various fertilizer materials high in those key mineral elements. Organic matter in the form of leaves, straw, insect bodies, manure, etc., that naturally recycles or is deposited by you, contains only low levels of minerals. As Solomon points out in his book The Intelligent Gardener, you generally can’t get to full nutrient balance piling on organic matter. Indeed, you can throw the balance way off. Solomon found this out in Oregon (too much potassium, too little calcium) and Tasmania (too much magnesium, too little calcium) with rather severe effects on his health.
Besides feeding roots, the cation minerals feed microscopic organisms (microbes) of various kinds that help in decomposing organic matter, and also mining rock particles to release additional minerals and organic compounds for plant roots to take up. But the four major cations also have a chemical and physical effect on the soil and loosen or tighten it, and thereby create more (or less) suitable air and moisture conditions to foster microbe growth. In turn, expanding microbe populations (given enough nutrients) further prepare and modify the soil to assist plant growth. They help make good soil, otherwise known as good tilth.
Albrecht was right. The four major cations (chemicals) largely govern soil fertility and thus plant growth. But there’s more to it. After careful study, I had to reluctantly conclude that soil fertility was not about microlife, the “soil food web”, or having a “live soil”. These were all agents and ancillary to the soil’s nutrient mineral composition. Let’s not forget, soil starts out as rock. No getting around that. Fertility proceeds from the primacy of the minerals rather than the biota or biological dimension. You have to have enough of the necessary minerals for it to all work correctly. Rotted vegetation (or humus) can bring about a high CEC or large tank, but it’s the cation minerals that fill the tank (or not) that dictate fertility, and thus plant yield, but also crop nutrient density. Trace elements in tiny quantities are also necessary to obtaining complete and full mineral balance in the soil and plant.
Organic matter (or humus) and microbes certainly make their indispensible contribution to soil fertility dynamics and to soil make-up or structure. However, by themselves they don’t cause fertility to rise very high in the absence of necessary minerals in the right amount, balance and complete array needed to produce the highest quality food. Microbes and organic matter are of secondary significance. But that was until biochar.
Biochar, as exhibited in the Terra Preta case, is a very different matter when it comes to the prominence of microbes and organic matter (but not without some minerals) in the creation of high soil fertility. Here is where biology and the microbes clearly triumph.
My mistake, early on, was thinking that Terra Preta’s incredibly high and extremely durable fertility (which we know is owed to the use of biochar) must be due to biochar being a “super-colloid”, possessing an extremely high CEC, and enabling it to hang onto minerals and other nutrients against heavy rainfall-caused leaching. But this isn’t so. Biochar has a rather low CEC compared to rotted organic matter, so something else has to be involved that explains Terra Preta hanging on to its fertility for centuries while nearby native soil remained forever comparatively infertile.
When I first read about biochar several years back in an Acres USA article, I was mystified and perplexed, almost to the point of disbelief. The author made a big point of the charcoal in Terra Preta soils always being accompanied by pottery shards (pieces), and implied that there must be some necessary synergy between the pottery shards and the charcoal discovered through the wizardry of the native inhabitants in the distant past. It now appears that was largely mistaken speculation (like mine), but certainly it couldn’t be argued that this ancient, human-created soil was not still highly fertile. The pottery used by Amazonian natives was made of clay, but the clay was baked, so probably had little to do with the soil’s incredible fertility. Maybe biochar was made inside clay pots, or they were simply thrown into a rubbish heap when broken and later got scattered about.
What I’m learning is that Terra Preta soil is a very unusual and exceptional phenomenon where the biology primarily accounts for the fertility; and furthermore, that the biochar enables the microbes to not only hold the nutrients, but to grow and expand that fertility and to keep it self-renewed. That is truly amazing, and it, once again, points to a magical triumphal role for microbes (no doubt with assistance from earthworms). I was wrong about biochar being a “super-colloid”, but its effect (thanks to fostered biological activity) is much the same as a high CEC colloid.
So how does this sensational synergy work if it doesn’t rely on a high CEC or a “super-colloidal” property of biochar? In a word, it is due to the micropore structure of biochar, although other factors are involved as well. The micropores create millions of catacombs invisible to the eye, which harbor, protect and foster numerous kinds of beneficial bacteria and fungi, thus enabling them to flourish, given moisture and sufficient food or nutrients starting off and in the vicinity for moving into.
These micropores, or their walls, thus create a vast amount of surface area in a very tiny space on a given chunk of charcoal. In essence, this provides the basis for a “coral reef”, enabling microbes to thrive in a protected niche environment, and it is in their bodies, living and dead, where much of the nutrients needed by plant rootlets are held. More are brought in by the spreading mycorrhizal mycelium and free-form nitrogen-fixing bacteria; or something like that. Keep in mind, Terra Preta type soils are exceptions.
It’s this stable, very long-term habitat that provides a different substrate than does decomposing organic matter (and even resistant humus) that tends to rot away into CO2 and water, eventually, though some portion of humus remains in soils longtime. Clay, on the other hand, while having generally a much smaller CEC than humus, persists for eons. However, it too can degrade and become worn-out or depleted of minerals, and conversely loaded-down with non-nutrient hydrogen ions. Thus, soil acidity really means non-fertility.
But now a new concept of synergy is emerging (at least in my knowledge) having to do with the combining of clay and decaying organic matter for the creation of true humus. Steve Solomon revealed this to me in The Intelligent Gardener, and states that there is no real humus in the absence of clay in its make-up. Thus, a compost heap made without clay-containing soil (a.k.a. dirt) as a component never becomes that holy grail of organic soil-builders because it melts away into CO2 and H2O, rather than being made into highly complex and resistant true humus. Incidentally, probably the best way to employ biochar in gardening is to charge it with Sea-Crop and/or diluted urine, and run it through your compost (along with some clay), plus a fertilizer blend, such as the BLO Compost Fortifier mix.
Actually, I had some prior inklings that true humus consisted of a combination of decomposing organic matter and clay. One of these reference sources came from Harnessing the Earthworm by Dr. Thomas A. Barrett back in the forties, wherein he talks about earthworm castings being a combination of mineral soil and dead organic matter comprising humus, and this being the actual origin of topsoil all over the world. A light went on. Humus isn’t simply a form of pure organic matter, but combines inorganic and organic matter. So, mineral-augmented organics was on the right track more than we knew.
We know that earthworms are as interested in the bacteria growing on decaying organic matter as they are in that organic matter itself as food. We also know that in the ground, earthworms ingest mineral soil as they build tunnels. They come to the surface for organic debris, but also to deposit their excreta (castings), which are generally very rich in a number of minerals compared to the surrounding soil.
This richness is largely due to the earthworm’s ability to free-up minerals from soil particles as these pass through the worm’s intestinal tract. In the process, the minerals and organic matter (surely including some clay) are thoroughly intermixed, inoculated with bacteria, digestive juices, etc., and excreted as a superb fertilizer. This is real humus, but is not so good as Terra Preta soil. Just add biochar?
© 2013, Gary L. Kline
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