Ten misconceptions about soil

Dr. Pat Megonigal, a biogeochemist at the Smithsonian Environmental Research Center (SERC) in Edgewater, Md., recently curated an exhibit called Dig It! The Secrets of Soil, which was on display at the Smithsonian National Museum of Natural History. His soil research at SERC focuses on wetlands and tidal marshes, and the effects of sea level rise and climate change.

Megonigal said there are a lot of misconceptions about soil, “which is amazing, because one-third of the planet is soil, and it’s 100 percent of what we deal with in our everyday lives, as opposed to oceans.” I spoke to him recently about these misconceptions. Below, he refutes 10 commonly held beliefs.

1. Soil is sterile. Just yesterday my son’s science teacher told him this, which couldn’t be further from the truth. A handful of soil has more microorganisms in it than there are people on the planet. It’s full of microbial life.

2. Soil is fully understood. We know less about the soil beneath our feet than we do about the surface of the moon, because it’s microscopic.

3. Soil doesn’t have anything to do with climate change. To the contrary. That black, partly decomposed plant material on the surface of the soil is carbon. We call that very young coal. When we do things to disturb the soil, that makes it turn into carbon dioxide. There’s twice as much carbon locked away in soils as there is in the atmosphere.

4. Soil is solid. Really, soil is half empty space, which is what distinguishes it from rock. The space between soil particles is where things can live—including microorganisms, worms, roots of plants–and where there is space for water and air. The organisms need oxygen and water.

5. All soil is brown. If you ask people to describe soil, they’ll probably miss the colorful layers. People think it’s red or brown, but soils come in every color of the rainbow, although purple soils are rare. Most have hues of red, yellow and orange, and then you get black from organic matter. The more unusual colors—blue, green, purple—you’ll find in wetlands or from some unusual minerals. They also have a lot of texture. Run your hand over soils, and you’ll find some are smooth, some are bumpy, some have huge rocks in them.

6. Soil is a minor part of the ecosystem. I look at the world as a complicated machine. You have to understand the parts to understand the whole. Soils are the most important piece. Plants, microorganisms, water, all come together in the soil, and what happens in the soil dictates what happens in the ecosystem. People think of soil as brown or orange stuff that you track into the house, but we need to think of it as much bigger, because virtually everything we touch has some connection to it. Food is the best example.

7. Soil is straightforward. The environment of the soil is complex. It has many layers, including a rich surface layer and then all these other layers of different colors and textures. If you know what you’re looking at, it reads like the pages of a novel. It tells you information such as the history of the land and what the soil is made from.

8. Soil is only found in certain areas. Soils are found everywhere—in wet places, in dry places, in urban areas, in the gutters of your house. It takes relatively little soil for a plant to grow.

9. Soil isn’t useful; it’s just dirty. Michelle Obama’s done a wonderful job showing how you can use the soil in your own backyard. So many things come from soil: food, vitamins, wood, minerals, pigments, water, even the clay used for kitty litter.

10. Soil is either good or bad. There’s no “good” and “bad” soil. Even soil in the desert supports desert plants. There are over 20,000 types of soil in the U.S., distinguished by texture—how much sand, silt, clay, organic matter is in it. If you want to grow wetlands you want it to be almost all clay. “Loam” is a word that tells a farmer or gardener that the soil has just the right balance of sand, silt and clay.