15 Things You Didn't Know About Soil

Billions of invisible bacteria and other organisms live in just one handful of soil. bluedog studio/Shutterstock

Some people think the new frontier is artificial intelligence. Others say it's space exploration. Julia Gaskin thinks the new frontier is much closer to home. In fact, she thinks it's right under our feet, in the soil that supports the plants we depend upon for food.

Gaskin would know. She's a soil scientist at the University of Georgia (UGA) who pulls people together to find sustainable solutions to soil problems and then trains Extension agents in those techniques.

"There's a lot of stuff about soil we don't understand very well," she contends. "I think there is so much potential for us to be better partners with the soil and help suppress plant disease and get plants healthy, less stressed and more productive."

Solving soil problems is important because soils support 95 percent of all food production, and by 2060 humans will ask the Earth's soils to produce as much food as we have consumed in the last 500 years, according to the Soil Health Institute.

Yet in the last 150 years, the world's soils have lost half of the basic building blocks that makes soil productive. The Soil Health Institute produced a 60-minute documentary about soil health that explains the status of global soils and features what innovative farmers and soil health experts are doing about it.

Gaskin — whose official title is sustainable agriculture coordinator and extension specialist at UGA, but she proudly prefers "soil nerd" — shared her take on soil with Mother Nature Network. She's just fine if you find some of this info nerdy or even a little quirky. What she really hopes you'll take away is a better appreciation of what's going on in the ground that will help you improve the health of your soil and, consequently, the plants in your landscape.

1. Soils are one of the most biodiverse ecosystems on the planet

There are many more living organisms in the soil besides worms. You just can't see the others as easily.
There are many more living organisms in the soil besides worms. You just can't see the others as easily. Alf Manciagli/Shutterstock

We know there are earthworms in soil because we can see them, although most people may not know there can be as many as 50 in a square foot of healthy soil. But, Gaskin points out, there's another world of microscopic organisms that live in the soil that we may not be aware of because we can't see them without special tools. Even under a microscope, they are too numerous to count.

In their book, "Teaming with Microbes", Jeff Lowenfels and Wayne Lewis write that "a mere teaspoon of healthy garden soil contains a billion invisible bacteria, several yards of equally invisible fungal hyphae, several thousand protozoa and a few dozen nematodes."

"We don't think about them because we can't see them," Gaskin said of these microscopic organisms. "The soil ecosystem is one of the most biodiverse and most productive ecosystems on the planet."

2. Plant roots give back to the soil

Grass growing in healthy soil with roots
Plants don't just take nutrients from the soil. They secrete energy back into it, too. ER_09/Shutterstock

This amazing array of microscopic life exists because plant roots do much more than take up nutrients. Plant roots give back to the soil through photosynthesis, a process by which sunlight is converted into chemical energy that fuels the plant. Plants secrete, or exude, some of this energy through their roots into the ground. A simple analogy is human perspiration, write Lowenfels and Lewis.

These microscopic organisms live in an area of the soil called the rhizosphere, which extends about a tenth of an inch from the plant roots. The numbers and diversity of the organisms that occur in the rhizosphere are something soil scientists like Gaskin are still trying to fully comprehend.

"We're starting to get a clue about how many different species are in the soil, but we honestly don't know what everybody is doing down there," said Gaskin.

3. There are more than 20,000 types of soil in the U.S.

The broadest classification of soil is an 'order.' The smallest classification of soil is called a series, or type.
The broadest classification of soil is an 'order.' The smallest classification of soil is called a series, or type. Rita Meraki/Shutterstock

"I think one thing that is fascinating to me about soil is how diverse they are," said Gaskin. "I think people don't think about what is underneath their feet."

Scientists who do think about these sorts of things classify soil by its different characteristics, just like other scientists classify plants and animals based on their characteristics and behavior.

"There is this whole language for classification of soils," said Gaskin, pointing out that the broadest classification is an "order," of which there are 12. Among these soil orders, in the United States alone, there are more than 20,000 different series, or types, of soil, which is the smallest classification unit.

4. The largest U.S. soil type is in prairies

Prairie soils are the most extensive type of soil in the U.S.
Prairie soils are rich ecosystems, thanks to the annual dieback of the grasses, legumes and more. windcoast/Shutterstock

Prairie soils, Gaskin added, are the most extensive type of soil in the United States. Called Mollisols, they cover 21.5 percent of the country's land mass.

"That makes sense when you look at the United States and how big the old prairies would have been," she said. "They would have stretched from a bit west of the Mississippi out until it got too dry towards Wyoming and Colorado and all the way up through Minnesota and down into Texas. That's a huge land mass. And these deep, dark soils formed because for thousands of years the grass would put down deep roots, it would get really cold and the foliage and the roots would die back. That turnover created a lot of soil organic matter, which gave the soil that deep dark brown color that people associate with good, fertile soil."

Something else that contributed to the quality of the soil in the prairies was that the prairies were not a monoculture of grass. Instead, they consisted of grasses, grains and a diversity of flowers and legumes. There's an important lesson here for home ornamental gardens. "Anytime you have that kind of diversity, you have a more diverse community of micro-organisms," said Gaskin.

5. Soils can have beautiful colors

Healthy soil isn't just brown. It can be pink or even blue, too.
Healthy soil isn't just brown. It can be pink or even blue, too. Kae B Yuki/Shutterstock

Healthy soils aren't always dark brown. They also can have beautiful shades of blue and pink. "I have seen soils when you get down two or three or feet that have a blue color. Some even have beautiful a beautiful pink color. Colors tell a soil scientist how the soil was formed and how water is moving around in the soil," explained Gaskin.

The blue soil she saw in New England was a silty soil from which iron had been leached and that had been wet for many years. The ones that were pink were on the Coastal Plain of North Carolina where some of the organic compounds moving through the soil had interacted with different clays. She thinks an interesting exercise for gardeners would be to dig down into their soil to see how the color of their soil might change. A grayer layer, for example, many times can be an indication of where the water table ends up being because that area has been depleted of iron compounds that cause red or bright orange colors.

6. Digging busts up everyone's home

Think before you dig in the garden. Do you really need to till the soil, or are the beds good enough as they are?
Think before you dig in the garden. Do you really need to till the soil, or are the beds good enough as they are?. Syda Productions/Shutterstock

Gaskin urges gardeners not to get too caught up in the numbers of microbes in the soil. Instead, she believes gardeners should think in more practical terms, such as the implications of the traditional gardening practice of breaking up the soil for spring planting and applying chemical fertilizers.

"When you go in and plow up the ground or rototill it up, you're busting up everybody's house. It's like you're breaking up the cabinet and the refrigerator," she said. Instead of tilling to create what looks like the perfect garden on top of the soil, she cautions gardeners to think more strategically about preserving what's happening underneath the soil's surface.

"If you're going to transplant tomatoes or peppers, or anything you can transplant, if you've left a pretty decent bed there from last year, you may be able to just transplant right into the garden and put some organic fertilizer in with the transplant rather than till it all up and make it a perfect-looking bed. If you're growing lettuce or carrots, things that have tiny seeds that need a prepared seed bed, you can't do that. That's when you make that good seed bed."

7. Busted-up homes release carbon dioxide

You can learn your way to a green thumb with online tutorials. (Photo: zlikovec/Shutterstock)

Good soil contains something else we can't see: tiny pores woven through the aggregates of sand, clay, silt and other matter that make up soil. Those pores are home to all of those bacteria, fungal hyphae, microbes like nematodes and protozoa and larger creatures like earthworms. Tilling not only breaks up these homes, but it releases a lot of soil organic matter into the air as carbon dioxide.

"Especially in the South, we have a hard time maintaining that organic matter anyway, so we need to do everything we can to preserve what we have," Gaskin advises.

8. Healthy soil takes hundreds of years to form

It may take hundreds or thousands of years to form new soil.
Good soil takes time. patruflo/Shutterstock

It takes a long time to restore soil that has been destroyed through carelessness or less-than-optimal gardening practices. "I have heard it takes a thousand years to form an inch of top soil," she said.

Just how long "depends on where you live and the parent material there — whether you are working in old marine sediments or you are trying to weather a piece of bedrock. Soil types vary quite a bit, but don't despair. You can greatly improve degraded soils over three to five years and make them much more productive."

9. Be patient when trying to improve your soil

You can improve the quality of your soil in three to five years, but patience is key.
You can improve the quality of your soil in three to five years, but patience is key. Cora Mueller/Shutterstock

Gardeners typically try to improve the organic matter in their soil by adding mulch and amendments. While that won't take hundreds of years, it will take more than one growing season of amending the soil to make significant improvements.

"I think that when we are talking about restoring our soil and bringing it to a healthy balance, we need to have some patience and add amendments gradually over time. Our goal to get the soil to where we want it to be should be in a course of three to five years, not instantaneously. I have seen people who think, 'OK, I've got this cruddy soil, and I am going to put four inches of compost on it and turn it in.' If you think about the compost and organic matter as being the base of the food chain, a kind of ultimate food for the microbes in the soil, it would sort of be like you eating three or four bacon cheeseburgers at a sitting. Things in the soil just can't deal with that much that quickly."

10. Cover crops benefit the soil — in more ways than one

green clover covered in snow
Clover is a great choice for a winter cover crop because it can thrive even in snow. Rashid Valitov/Shutterstock.com

Scientists are learning more and more that keeping a living root in the soil provides a healthy habitat for soil microbes. Gaskin is a big proponent of planting cover crops to achieve that goal. The roots exude food for the micro-organisms, and the pores in which they live create channels for rain to penetrate and moisten the soil.

"There will be a lot going on down there if we keep something growing as much of the year as we can," she advised. Because gardeners typically have something growing in spring, summer and even into the fall, cover crops are most frequently grown in winter. These include clovers, winter peas, cereal rye, oats and mixtures of various other species.

Cover crops also keep rain from damaging the soil. Rain hits the soil with a huge amount of force, about 20 miles an hour, according to Gaskin. When that happens, the rain drops splash up soil particles and cause a crust to form on the surface of the soil. This process also seals off all the pores the microbial matter has created for oxygen and rain to get down to the root zone where the plants need the moisture.

"If you have a mulch like a cover crop, or you put mulch on top of the soil, you are breaking up that force of the raindrops so you will get a lot more of the rain going into the ground where you want it, less erosion, less crusting and it adds carbon to the soil."

11. Meet soil's natural rototiller — the earthworm

Earthworm in the dirt, closeup
Earthworms work their way through your soil as natural-born tillers. Maryna Pleshkun/Shutterstock

Compost is a very stable form of organic matter and is a great amendment because over time it will enrich the soil and hold down weeds — something organic herbicides are not good at. But, as difficult as it may be, Gaskin says to avoid the natural inclination to till or otherwise incorporate compost into the soil. Think of earthworms as nature's rototillers. They will pull it down for you, she said.

12. Old agricultural practices didn't do soils any favors

Old agricultural practices such as over-plowing led to soil loss through erosion.
Old agricultural practices such as over-plowing led to soil loss through erosion. Andriy Solovyov/Shutterstock

Gaskin thinks the greatest harm humans have done to soil has been though recent agricultural practices that have increased erosion — "recent" as measured against the timeline of human existence.

"I'm looking out my window on the UGA Campus in Athens from the Plant Sciences building, and all I see is trees," said Gaskin. "If you had stood here in the 1940s or earlier, you would not have seen a tree. It was all cotton fields, and farmers were plowing every year. There was a lot of bare soil, and with the slopes we have around here they could lose an inch or more of top soil in a year.

"Those old agricultural practices, which date back to the early 1900s, would have been organic practices then. But it was a totally different technology. They went out to the prairie and broke the prairie. Then it dried up and blew away. The Natural Resource Conservation Service, which was originally called the Soil Conservation Service, was voted into existence because one of those dust storms made it to Washington, D.C. So, erosion from constant plowing that depleted the soil organic matter is probably the biggest impact that we have had on the soil."

13. Georgia's red clay is a subsoil exposed by erosion

Georgia's famous red clay in places like Providence Canyon
Today, we can see Georgia's famous red clay in places like Providence Canyon because of many years of erosion. Vadim Fedotov/Shutterstock

Another result from constant plowing can be seen in Georgia's famous red clay, which gets its rust color from oxidized iron. The clay is actually a subsoil, Gaskin pointed out. "Georgia lost its top soil in cotton farming," she said, "a good foot of top soil, maybe more. There are people who have done studies who say there is as much as 10 feet of those top soil sediments in the state's stream bottoms."

14. Soils have a huge impact on water quality and quantity

In parts of the Appalachians, rivers often have a tea-colored tinge due to soil.
In parts of the Appalachians, rivers often have a tea-colored tinge. Aspen Photo/Shutterstock

Soils have had a huge effect on the whole ecosystem, including water quality and quantity, Gaskin said. In the southern Appalachians, streams often have a tea-colored tinge. That's because the soil there is sandy, shallow and full of mica. Also, tannins and organic molecules from decomposing leaves easily move through the subsurface and into the streams. In the Piedmont, which is heavy in clay with red oxides, streams can often have a muddy appearance, especially after rains.

As you go down into the Coastal Plain you get the black water rivers. That's the same process. The sandy soil near the ocean doesn't filter out the organic tannins and other organic compounds that are created from decomposing organic matter. Soils can affect the quantity of the water in the streams because deep, heavy soils in the Piedmont allow streams to quickly rise after a rain but leave them slow to recede since subsoil water moves slowly through these deep soils to the stream.

Streams in areas with more shallow soils, such as those found in the Ridge and Valley area in northwest Georgia and eastern Tennessee can jump up in a flash after a storm but dry up in summer because the soil and the subsoil aren't deep enough to store subsoil water and release it slowly.

15. You don't have to be a soil nerd to appreciate good soil

Gaskin doesn't think you need to share her passion for soils. Though she hopes you'll find facts about soil interesting enough that you'll better appreciate what is under your feet. If you'll do that, she's convinced you'll be able to use that information to become a better-informed and more effective gardener.