Can humus save humans?
Economics start with photosynthesis.
– Abe Collins
I feel like getting naked and running though the streets, yelling eureka, eureka! By George, I think I’ve got it. And I wasn’t even looking. It all began a few days ago, when I started on a post about creating soil from scratch. A radical notion in its own right, to be sure. So let’s begin with the story there.
Growing new topsoil
Human future depends on the future of earthly soils. The most meaningful indicator for the health of the land, and the long term wealth of a people, is whether soil is being formed or lost. If soil is being lost, so too is the economic and ecological foundation of society.
– Christine Jones (paraphrased)
I won’t dwell again on the dire facts of soil loss around the world. We all know it’s a serious problem. What is not so clear to many of us is that the major efforts out there attempting to counter this trend merely hope to slow down the rate of loss. The option of growing new soil and actually coming out ahead is only considered by a few maverick soil scientists and small groups of farmers who’ve finally had the courage to forgo conventional ag advice and forge their own path. Most gardeners are familiar with soil-building, but this generally involves robbing Peter to pay Paul, as manures or leaf mold are imported from elsewhere.
The process that forms soil from weathered rocks takes thousands of years. But new soils can form quite rapidly from the soil that’s already there, provided the natural sequence is unimpeded. Here is how it happens:
- In order for new soil to grow, it must be living.
- In order for soil to be living, it must be covered.
- In order for soil to be covered, it must be periodically disturbed.
It makes sense, doesn’t it? Only living things can grow. For soil to grow, it must be a thriving community of microorganisms, fungi, insects, and worms. These need to be sheltered from weather extremes and kept moist. A ground cover of live plants and decomposing plant litter protects the living soil by buffering temperature extremes, improving water infiltration and slowing evaporation.
To flourish, these ground covers need to be fed. This is where soil disturbance comes in. Nature brings in herbivores on the hoof who trample decomposing plant material into the ground, pushing it into the root zone. They break up the soil crust and aerate it, making it more permeable to water. And they crush old dried stalks so that sunlight can reach new growth.
As the herbivores graze and chew off the tops of the grasses, part of the root system dies back and feeds the soil organisms. Intermittent grazing creates cycles of root die-back and regrowth that provides a rich feast for all who inhabit the soil community. And there are a lot of hungry mouths! It is said that a teaspoon of good soil contains almost as many tiny denizens as there are people on Earth.
Well fed soil microorganisms then produce the gums and sugars that build crumbly, porous soil texture which provides spaces for roots, passageways for small invertebrates, and room for rain. Since these gums and sugars need to be continually replenished, a steady supply of food — decomposing plant roots and litter alongside water, air and minerals — must be coming their way.
This simple and elegant process begins to produce new topsoil within the year, with dramatic results reported in three years. The higher the biomass and turnover of plant roots, the faster new topsoil will form.
Here is the recipe for growing new soil:
- seed or plant perennial ground covers known for extensive, deep root systems
- graze or slash new growth intermittently
- then disturb the soil by working decaying plant material into the root zone, whether by hooves, hoes, or disks
- since high levels of biological activity are required, avoid pesticides, herbicides and fertilizers known to harm soil life
- on drylands, predigestion of plant matter (either in ruminant stomachs or via composting) is essential; without adequate moisture old plant matter oxidizes rather than rots
Now I understand why lawns take so much fussy effort. Without the third step — intermittent disturbance — the grasses need to be constantly propped up by chemicals and aerating machinery, while at the same time, the chemical brews depress soil life.
The miracle of humus
Feeding soil life depends ultimately on photosynthesis. Powered by sunlight, plants synthesize nutrients out of water and CO2. They use these nutrients for their own growth and maintenance, and share the surplus by exuding the rest through the roots. This carbon-rich fluid is used in turn by mycorrhizal fungi and other micro-critters as they turn plant remains into humus.
I admit to being woefully misinformed. While the term ‘humus’ does commonly refer to the dark, fertile, friable stuff compost eventually turns into, the real miracle is the substance soil scientists call stable humus. This dark colloidal gel consists largely of water and carbon in many permutations (humic acids, humins, etc.), tightly bound to clay and metal hydroxides. Greatly resistant to further decomposition, it plays an essential role in providing soil structure, increases the ability of soil to store nutrients resistant to leaching, buffers acids and alkalis, binds toxic heavy metals, and can hold the equivalent of 80-90% of its weight in water. It can last in the soil for centuries and perhaps longer, sequestering water and carbon for slow release.
Stable humus is used up en masse by plowing and high nitrogen fertilizers. On the other hand, its formation can be encouraged by following the soil growth generative sequence, and by the addition of chopped roots of grass species (to restore mycorrhizal fungi) or black carbon (biochar). Rotational grazing where feasible optimizes conditions for photosynthesis and humification. And how can we tell we are getting somewhere? Soils with high humus content feel sticky to the touch when rubbed between the fingers.
The soil solution
It would be awesome enough to have access to a simple process that grows new topsoil, and to become skilled in aiding humification to keep these soils highly fertile over the long term. But it gets better.
Is your area plagued by drought and desertification? Is the local aquifer steadily depleting? Did you have endless days of 115°F heat last summer? Are you worried about food security? Maybe your region’s lands have suffered from declining rainfall or salinization. I have some truly good news for you. Growing soil with high stable humus content is the healing treatment for all these ills.
Nature works on the principle that waste (of some) equals food (for others). Civilized humans in our unsapiential wisdom work hard to turn what could be food into waste. We’ve been doing it with human manures for some 150 years, with animal manures for a few decades, and as it turns out, we’ve really done a number on water and carbon, the very stuff of life, spewing them into the air while soils go begging.
After the oceans, the soil is the Earth’s largest carbon sink. But humus depleting agricultural practices have caused soils to lose both water and carbon to the atmosphere where these otherwise life-giving substances do mischief in high concentrations. Perhaps there are enough of us now who appreciate the value of humus-laden soils, ready to turn things around. Here are a few quotes I have pulled from the work of Dr. Christine Jones, Australian soil scientist who has been working with farmers and ranchers for many years to successfully regenerate the soils under their care and sequester large amounts of carbon and water at the same time.
Photosynthesis is a cooling process. Lack of green cover on the land greatly increases heat absorption, causing a dramatic increase in evaporation. Water vapour is a greenhouse gas of greater significance for global warming than CO2. Lower rainfall can also result from groundcover loss.
Of the estimated 3060 gigatonnes of carbon in the terrestrial biosphere, 82 per cent is in soils. That’s over four times the amount of carbon stored in the world’s vegetation… If only 18 per cent is stored in vegetation, why all the emphasis on biomass, rather than soil, as a carbon sink?
1% carbon increase in grasslands and cropsoils in Australia would offset the entire “legacy load” or total rise in CO2 over the last 50 years. Carbon sequestration of farmlands can be higher than that of tropical forests.
Soil loss and soil destruction spread far and wide as domination-based civilization claimed larger and larger portions of the planet. When we fan out, bringing about soil gain and soil regeneration wherever we go, we’ll know that our metamorphosis into viable human earthlings is well underway.
What do you think? Leave a comment below.
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