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How Your Soil Got to Be What It Is Today

The pasture on the hill is nothing like the one in the valley. Travel to the east, to the west, to the north, to the south. The soil changes with each mile, with each step of your journey.

There’s a reason, or five or six for those changes, and those reasons play into our management decisions. In the early 1940s, Hans Jenny figured it out a way to describe those reasons with a formula:

s=f(cl, o, r, p, t,…)

Someone with a sense of humor named the equation “Clorpt”. What Hans Jenny was saying with Clorpt was that soil is a function of climate, Screen Shot 2013-05-20 at 2.55.49 PMorganisms, relief, parent material, time and something else.

See the soil or different soils on your farm as soil individuals, formed differently through the function of Clorpt can help you understand your soil’s potential. Then you can manage your soil and help it “reach its potential”.

Parent material is the raw material for our soil. There are so many sources for parent materials, and that makes it all the more fun. Parent materials may be rocks that break down, releasing their mineral make up. It may be layers of sand and other soils along a river, laid down over years of floods. It may be windblown dust, loess, settled in one place. Or it may be a tumble of glacial materials, rolled over miles before leaving behind rounded rocks mixed in with soils.

There are so many sources for different parent materials, and they aren’t even the whole equation. They’re just one part of it.

Another factor is climate. Climate’s effects on soil formation are mostly due to precipitation and temperature. Water moving through transports all sorts of nutrients, in and out of the soil. The temperature affects the rate of reactions in the soil. It impacts plant growth and microbial activity, as well as biochemical reactions. The warmer it is, the more activity you can expect to see.

Time is a third piece of the puzzle.  Time lets the processes of weathering carry on. Plants grow, adding organic matter. Rain falls, moving minerals through the soil, adding acidity, or washing soil from the surface. The longer the soil or parent material sits in one place, the more it takes on characteristics that distinguish it. The soil develops more character as it gets older, just like us.

Relief or topography plays into the idea of time. Slopes are not conducive to long periods of soil formation. Soils on hillsides often end up in the valleys, especially when they are left bare. That means there’s not a lot of time for them to age, not enough time for the chemical and biological activity that can enrich them.

There’s also the way the slope faces. Slopes facing the south receive more sun, and have a longer growing season. They might build up more organic matter and be more fertile than soils on the northern facing slopes. You might even see this on smaller scales in little undulations in your pastures, comparing the slopes that hold snow longer with those that shed their winter coats earlier on.

The final part of the function is organisms. It’s the earthworm and dung beetle, and the nematode and paramecium. It’s the mole and the gopher, burrowing through the soil, and the plants growing there.

Soils forming under grasses will have thick layers of rich dark soil, from the addition of plant roots every year. Soils under deciduous forests will have much thinner layers of organic-rich soil. The leaves on top will share some organic matter, but it stays close to the surface.

The other key organism is us. People shape soils building roads and homes. And we change them by farming them.

The choices that we make when we manage land are part of the soil formation equation.

We can improve soil quality. I’m not sure about claims to add a foot of topsoil in a year. Here’s a list of activities that happen in the time it takes to build an inch of topsoil. It’s a pretty long list, more along the lines of a century or a millennium, not a year. That’s just something to think about when you consider different tools and practices to improve your soil.

When we understand our soils for their different textures, slopes, “ages”, and parent materials, we can manage them to their full potentials. When we manage soil well, we are a key part of Clorpt, and our land thanks us.

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Rachel Gilker
Rachel Gilker
Rachel's interest in sustainable agriculture and grazing has deep roots in the soil. She's been following that passion around the world, working on an ancient Nabatean farm in the Negev, and with farmers in West Africa's Niger. After returning to the US, Rachel received her M.S. and Ph.D. in agronomy and soil science from the University of Maryland. For her doctoral research, Rachel spent 3 years working with Maryland dairy farmers using management intensive grazing. She then began her work with grass farmers, a source of joy and a journey of discovery.

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