I began teaching a Soil Management and Conservation course in
Lorain County Community College’s new Sustainable Agriculture program two weeks ago. (This is its first semester. Come join us in creating a vibrant forum for learning and applying sustainable agriculture principles to the NE Ohio region.) Roughly speaking, the class is divided into three units: What is Soil?; How Does Soil Work?; How Do We Work with Soil? These first few sessions have given me a chance to revisit just how amazing the scale of time on the planet is. As Wes Jackson put it in the opening of
New Roots for Agriculture, the world has been around for a long time and it's only gotten interesting in the most recent sixth of that time, that is, 750,000,000 years ago!
Every week we get out of the classroom and do a hands-on lab. In these early weeks we are very simply trying to understand what soil actually is. When you pick up a handful of dirt, what is it you hold? Air; water; minerals; literally billions of beings eating, breathing, excreting, and breeding; the shreds and wisps of the innumerable beings that have come before, metamorphosed into that mysterious and all-powerful thing called humus; the kaleidoscoping whirlwind of electrical charges passing like gifts from one point to another.
How disorienting and reorienting it is to know that the principal elements of soil – and hence of us as well – are produced not in the furnace of our own sun, but were forged in suns far different and far away, that our own origin originates in the end of another place in another time.
Today, we did two simple tests to gauge the texture of soil. (Try them out yourself.
Here are the instructions.) Texture is a measurement and description of the relative percentages of the three kinds of inorganic particles in soil – sand, silt, and clay. Sand in our everyday lives is one of those very things that signifies the small, the inconsequential, the overlooked. Sand in-between your toes after a trip to the beach. What portion of a moment is one grain of sand passing through the throat of an hourglass? “Innumerable as the sands of the Ganges.” Yet when we enter the world of soil, sand looms large as boulders, big as houses. Silt is middling, and clay is the smallest particle. If “O” is a grain of sand, then clay is the period at the end of this sentence.
Here in northern Ohio we are a people of clay.
Bacteria and fungi eat rock, lick by enzymatic lick. They unlock electrons and tiny molecules of silicon and magnesium and aluminum float away from “parent rock” into microbial gullets and out into the great whirling energetic ferris wheel that is life, rising up perhaps some millennia later into the sky to seed a cloud and then down again after an eon or two to the bottom of the sea. But nothing eats rock like a glacier, and here in northern Ohio, one of these great white land-leviathans crept further and further, pulverizing under the sheer scraping weight of its belly a quantity of rock in a relatively short period of time that bacteria and fungi could never have hoped to digest. It was these minute particles left behind that became the fertile matrix for a resurgence of plants, animals, and soil in the wake of the glaciers’ retreat.
We also talked about soil horizons, the characteristic profile that soil forms as it is created. Typically, as one scrolls down such a profile one goes through decomposing organic matter to topsoil rich in biological activity and then to subsoil rich in minerals and poor in humus and eventually down to bedrock, solid and immutable (or are there some patient intrepid microbes down there? Lick. Lick.) However, here in northern Ohio, where once this was the bottom of a glacier and then after that the bottom of a lake, dig and dig and dig and you are likely to only encounter the frustratingly dense and sticky clay that every gardener around here wrestles with.
In 2008 I had the luck to travel to Patagonia, making my way down down down to El Chalten near Tierra del Fuego. I camped and hiked through an amazing landscape of alpine plant hummocks like living boulders clinging to near-bare rock; brilliant mosaics of lichens and barren fields of scree; and forests comprised of one and only one tree --Nothofagus, the southern beech – tall and stately in sheltered areas, scrubby and contorted in open places. Finally I climbed up and onto the serene alien beauty of a glacier. Light refracted into varying shades of turquoise through its undulating twenty-, fifty-, hundred-foot walls. The group I was with balanced our way up ridges with crampons on our feet and gloves on our hands lest we shred them on the knife-sharp crystals of ice.
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| For a sense of scale, the face of the glacier was well over 100 feet high. |
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| Me climbing up the side of one of the "ripples" on the surface of the glacier in the picture above. |
The glacier lay in a trough of its own making between imposing blackish-greyish-red cliffs and one could see along the seam between glacier and mountain where boulders had been knocked off the side and embedded in the icy flow. More subtle and more fascinating was the dust, blown or washed off the mountains, that coated the glacier to varying degrees. The “dust” ranged in size from pin-point to quarter-sized. Being blackish-greyish-red, each speck absorbed the heat of the sun and, like innumerable little heaters, melted the surrounding ice. The smaller pieces pock-marked the surface. The larger stones and boulders “carved” their way deep into the glacier, tunneling down into the blue deep heart of it. Ultimately all this “sweating” results in a glacial lake that bleeds out into a rushing glacial stream. Strange world, where black stones burrow like moles through white ice and emerge into a blue lake that pours out into a milky white river. The milky whiteness of these rivers (note the color of the glacial lake in the picture above) is from all the mineral particles they carry, reflecting light back out of its currents. Like all flowing waters carrying minerals from mountaintop to ocean bottom, these shining rivers carry suspended in them specks of the mountain their parent glacier is bringing down bit by bit.
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| If you look closely a the dark gray "rock" to the right of the center light-gray boulder you'll notice it is actually ice covered in dust. |
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| Everything but the immense bluish rock forming the horizon is actually rubble crusted over the glacier. |
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| The strange tunnels formed by heated rocks and flowing water on the glacier's surface. |
Once upon a time, this too was a glacial place. (I was sad to learn recently that A Place on the Glacial Till by Thomas Fairchild Sherman is out of print. Those of you from Oberlin, Lorain County, or northern Ohio, should go to your library or find a copy online. It is an invaluable place-book, lovingly cataloguing all the horizons of this particular bit of land.) As our own glacier ebbed away, how much dust sweated and burrowed its way down off its flanks, slipping off the great white body into the lake that once was over all of this land? Sherman writes that in most spots around here one would have to dig twenty to fifty feet through clay to hit bedrock, and under the Cuyahoga it would be 500 feet! Over millennia, it was minute clay particle by minute clay particle, drifting through the chilled milky waters and settling at the bottom 500 feet down, that shaped this land. As you grapple with the clenching heavy mud of it all in your own garden or farm field, imagine that you are at the bottom of a bone-shivering cold body of water and looking up you see nothing but a sky of shimmering white, the winking patient tumbling of innumerable bits of mountains making their way across eons to lay at your feet.
I demonstrated one of the soil texture tests for my students and then asked them to replicate it at home. First soil is dried and then pulverized. As I rubbed the dirt between my fingers and palms, I said, “What other processes that we’ve talked about does this remind you of?” At one end of Wes Jackson’s great line of time, I am a glacier, grinding to dust the massive and unbroken expanse of bedrock. At the other end, though, I am also a tiller passing through a field, taking all the complexity imbued in healthy soil by the powers of time, physics, chemistry, and biology over millennia and reducing it to a uniform and simple dust. I placed the pulverized soil into a bottle and then poured water into it. After shaking the mixture thoroughly, the goal of this test is to measure the percentages of different size soil particles – sand, silt, clay – as they fall out of suspension. On the one hand, we have the shimmering descent of mountains through a glacial lake. On the other is a freshly tilled field after a heavy rainfall, muddy puddles and ponds pooling here and there. Within a minute, the heavy sand particles have settled out into a sludge at the bottom. A few hours later the silt particles will rest as well. Clay -- the clay of our fields that resists our shovels and follows us into the house to the annoyance of our non-gardening partners – is so fine that it may take days before it fully settles out of the water.
“Now,” I asked the students as we watch the chocolatey water swirl and the larger particles settle, “when this test is finally done and there is a layer of fine clay on top, how well will plants grow in this newly configured soil?” Clay is clay, the same as what terracotta pots are made of. Imagine how well a plant’s roots would penetrate such a thing. When our glacier receded back to Canada and the glacial lake drained away and the sun finally graced the mucky sticky clay of the lake bottom, it took millennia for plants and animals to churn up that uniformity and impregnate it -- life by life -- with their own corpses broken down cell by cell, electrical bond by electrical bond, into that mysterious and all-powerful humus. Ask any gardener around here about making the mistake of working their soil when it is too wet, and they will readily shake their heads and groan. “Concrete” is what they’ll mutter, usually followed by a curse. When the puddles and pools dry up in the tilled fields all around us, little by little the work of millennia has been undone. Little by little microbes and fungi and earthworms will resume their endless churning complexifying work, but it will take other millennia more before the soil returns to what it was yesterday, and will we even be here to see that return?
