By Herwig Pommeresche
The term “soil humus content” refers to the totality of all the organic substances present in the soil. It is often expressed in terms of carbon content percentage, as carbon is the basic building block of organic material. But this definition is insufficient as it only reveals the sum of all the carbon atoms contained in the soil. How much of that is valuable compost, living soil biota, liquid manure, or other organic substances is not clarified. A relevant quote comes from M. M. Kononova’s treatise, “The Soil’s Humic Substances – Results and Problems in Humus Research” (1958):
“The history of humus research is rich in incorrect approaches to clarifying important questions, which has led to contradictions and confused ideas about the nature of humic substances, their origins, and the role they play in forming the soil and determining its fertility.”
But if we primarily understand “humus” as referring to the abundance of organic substances present in the soil, we overlook its mineral content. The proportion of minerals has increased in cultivated soils during our era in comparison with past eras in which consistently humid heat promoted the formation of organic soil material over huge swaths of forest for thousands of years.
The ratio between the organic and mineral portions of the material has shifted, to the detriment of the soil.
Incidentally, this is a particularly strong example of the importance of using the right terms with the right meanings: the word “mineral” is here used correctly to refer to everything from rocks, gravel, and sand to the very finest mechanically ground particles – it has absolutely nothing to do with NPK fertilizers or other salt ions.
One small calculation is sufficient to get an idea of the significance of plant roots in the soil: “The formation of root hairs greatly increases the root’s surface area. Rye (Secale cereale) has about 13,000,000 roots with a surface area of 235 square meters, and 14,000,000,000 root hairs with a surface area of 400 square meters in 1/22 of a cubic meter of soil (…) The surface area of the underground portions is thus 130 times as large as that of the above-ground portions” (Jurzitza 1987, 28).
One single rye plant has the equivalent surface area of an entire garden in direct contact with the soil in which it grows. What this soil is made up of has to be crucially important.
Annie Francé-Harrar (1957) wrote the following about how healthy soil should look for plant roots to be able to optimally carry out their work:
“Ideal soil should have the following composition: 65 percent organic material, 20 percent edaphic organisms, 15 percent mineral substances. (…) But this kind of abundance of organic material exists hardly anywhere on the planet any more, the highest concentrations being in untrodden corners of tropical jungles, but never in our growing soil. But it is possible to restore the organic-inorganic balance in growing soil within a practical timespan through systematically employed humus management.”
These recommended ratios also provide a target to work toward in systematic humus management. But she was already well aware of how difficult it is to put this into practice:
“But this (…) means a radical agricultural revolution, much larger than the one triggered by Liebig in his time” (20).
How does humus form?
Topsoil formation is very much a classic case study in the movement of living material from the waste material of living things into plants, of the descent of living material into Mother Earth.
It’s also a study in the soil, of its many functions, of its conversions and storage until its reappearance in the world of above-ground organisms. The bulk of the soil material first becomes clearly visible as nutrient-forming chlorophyll, but that chlorophyll would never exist without the work of the countless organisms in the soil.
The same species of bacterial symbionts appear in almost all animal and plant organisms, the lactic acid bacteria. In fact, soil probes from all over the world, even if the soil in question is only slightly fertile, always contain large quantities of lactic acid bacteria. The soil contains more of them, and of better varieties, the more fertile it is. This is further evidence that the cycle of living material takes place in the topsoil through the mediation of bacteria.
The remnants of biological processes on the surface, processed by countless species of small creatures, are first processes into precursors by budding fungi species, predominantly yeasts and molds, and then passed along to the bacterial symbionts in the soil. According to the most recent research, these symbionts—lactic acid bacteria in this case—can be directly consumed and digested as food via endocytosis by plant root hairs (Rateaver and Rateaver 1993), and they leave all kinds of organic material behind after they die, especially in the fall.
These particles, as well as the bacteria themselves (i.e., the living material in the soil bacteria), are a prerequisite for the formation of high-quality soil: topsoil that is aerated, loose, water-retaining, capable of biological tillage (Sekera 2012), safe from erosion, and fertile, the result of the functions of the edaphon, as outlined by Henning (2011).
The adhesiveness of the microorganism residues cements the inorganic mineral substances of rock erosion into soil crumbs. In contrast to the views of agrochemists, it is this alone that deserves the name “humus” in the biological sense: a conglomeration of organic and inorganic material. And this means that it is completely impossible to describe humus as a dead, chemical substance!
Humus formation is a sort of “organic predigestion” for plants; and at the same time, humic soil serves as a pantry of living nutrients during the growing season, when plants can grow only if supplied with sufficient warmth, water, and sunlight.
Otherwise, however, the parallels between animal and plant digestion are unmistakable. In both cases, microorganisms serve as an intermediate station, as “nutrient facilitators,” and in both cases organic or inorganic material can be extracted as needed from the nutrient substrate and used to build cells and tissues.
Edaphon: The “Residents” of the Humusphere
Just as the water has plankton, there is also “the plankton of the soil,” as Raoul H. Francé so singularly described and illustrated the term “edaphon” for us in 1911. The whole fertility of the humusphere depends on this edaphon, and it contains the entire existential basis of our life on this planet. The biosphere carries out its own cycle via its own living beings.
Under the heading “Ein Buch mit vielen Siegeln” (“A Book with Many Seals”) in “Mensch und Umwelt,” J. Filser (1997) writes:
“Microorganisms in the soil can contribute to the nutrition of a plant or strengthen its resistance to pathogenic organisms or the effects of environmental damage. [. . .] They represent a biological potential that promises a wide variety of useful applications in protecting our resources in agriculture and forestry. [. . .] Thus far, only a limited portion of the soil microflora has been cultivated and examined in more detail. We are not even aware of an estimated 90 to 99 percent of soil organisms.”
Edaphon: Plankton of the soil
Just as plankton provides the basic conditions for all further life in the hydrosphere (i.e., in the water) the edaphon provides the basic conditions for all further life in and on the soil.
But it’s possible that even larger quantities of proteins are hidden within it than in plankton! A comparison accentuates this point: the average human biomass in the United States is 18 kilograms per hectare. On the other hand, the average biomass over the same area of insects, earthworms, single-celled organisms, algae, bacteria, and fungi is about 6,500 kilograms. That’s more than 350 times as much!
To break it down more specifically, that’s 150 kilograms of single-celled organisms, 1,000 kilograms of earthworms, 1,000 kilograms of insects, 1,700 kilograms of bacteria, and 2,500 kilograms of fungi (Gaia 1985, 150).
And what’s the breakdown in our gardens? In a 1,000-square-meter garden, 1,000 kilograms of edaphon lives and works in complete silence, without disturbing the neighbors, all year long.
The biomass of the earthworms alone—who represent a part of the edaphon—can be determined by any interested layman by collecting and weighing them. In sandy soil beneath conventional barley, I’ve found 9 grams per square meter of surface area (to the depth of a spade), 49 grams beneath conventional pasture, and 840 grams in my own biologically cultivated garden soil. Per hectare, or 10,000 square meters, that comes out to 90, 490, and up to 8,400 kilograms of living biomass respectively. And that’s just the earthworms?
The ideal for fertile growing soil is (Francé 1911, 1995): 1 kilogram of living biomass or edaphon per square meter of garden or field soil. One kilogram of living cytoplasm per square meter corresponds to 1 metric ton of biomass per 1,000 square meters, or 10 metric tons per hectare. Ten hectares of cultivated field soil thus come with 100 metric tons of living biomass in the form of the edaphon beneath the ground—and that’s without even considering what can be achieved above the ground. That comes out to the weight of one thousand hogs or two hundred cows!
For readers who are farmers: these numbers reveal how much “livestock” you have hidden on your farm, without ever seeing or noticing it. If you converted this quantity into actual livestock, how much would you have to supply them with on your farm in terms of feed, stalling, ventilation, weather protection, and eventual excrement disposal? How about veterinary costs, consultation, and researching?
This is only hard for us to conceptualize because we have neglected it in the models we use to teach and think about agriculture. If you think about these numbers in the context of the new, still unfamiliar “plants can digest protein” model, you quickly recognize the new possibilities that they reveal for our agricultural practices.
About the Author
Herwig Pommeresche was born in Hamburg in 1938 and has lived in Norway since 1974. He received a degree in architecture from the University of Hanover. He has spent many years active as an architect and urban planner in Norway. After finishing his studies in architecture, he became a trained permaculture designer and teacher under the instruction of Professor Declan Kennedy. Alongside other permaculture experts, he served as an organizer of the third International Permaculture Convergence in Scandinavia in 1993. He later served as a visiting lecturer at the University of Oslo. Today, Herwig Pommeresche is seen as a pillar of the Norwegian permaculture movement. He also serves as an author
and a speaker.
Herwig Pommeresche is a holder of the prestigious Francé Medal, awarded in 2010 by the Gesellschaft für Boden, Technik, Qualität (BTQ) e.V. (founded in 1993) in recognition of his contributions to organic methods and ways of thinking and to the preservation and improvement of the humusphere.