Soil is so complex it’s often referred to as a "superorganism". There isn’t one soil but thousands of Soils.
Each one of those different soils has physical, chemical, and biological properties that make it unique. You probably learned in school that soil was composed of particles like sand or clay and that it also contained lots of microorganisms.
And then you went on to talk about more interesting things, like the universe and planets. Because everyone thinks soil is boring. But is it?
Here are 10 facts we bet you never knew about the soil under your feet...
1. Lichens break down rock in the first step toward soil
They work both physically and chemically. A lichen is a complex of fungi and algae. Fungi are unable to gain energy through photosynthesis so they partner with algae (green or blue-green which is commonly called cyanobacteria, who can photosynthesize).
The fungus is in control and farms the algae for the carbon necessary for fungal growth. The lichen matrix attaches to rocks with the fungal hyphae. There are 17,000 species of lichen worldwide, according to Robert Lucking, curator at the Botanical Garden in Berlin, Germany.The freezing and thawing of the hyphae cause expansion and contraction, expanding the tiny crack in a rock until an environment is created that supports plant life. In other words, soil. Lichens also secrete oxalic acid, which dissolves minerals and acts as a chelating agent to dissolve minerals from the rock substrate. As long as we have fungi, algae, and rocks, we’ll have the mineral components of soil.
2. There are 70,000 different types of soil in the United States
There are 5 soil forming factors taken into account to determine soil type by the USDA. They are:
- Parent material
- Living organisms
- Landscape position
These do not factor in human activity on the land. Whether or not a farmer is using chemicals makes a difference in the long-term on soil type. That soil may retain the same name but when one farmer uses conventional and another regenerative farming it changes the characteristics of that soil. The loss of living organisms is the major change for a conventional farmer. Can that loss be reversed? Yes.
3. There are 12 Soil Orders in the world
A Soil Order is usually defined by a single dominant characteristic. It could be vegetation, the type of rock (parent material), a specific climate, or the amount of weathering to create a soil Profile. The World Soil Map is a joint effort of the FAO and UNESCO.
It would be helpful if the Soil Orders were broken down further into Soil Types. Which ones are good for agriculture, for forestry, which are bogs, desert soils – but the countries of the world each have their own system to define their soils. Comparing an agricultural soil in the USA to one in Buganda or France is like comparing apples and oranges.
Farmers and ranchers know their soils in far greater detail than Soil Order. It is an “on the ground” or indigenous knowledge. It is also a knowledge that identifies changes in soils at the local level, affecting crops grown and the health of consumers. Soil definitions are as much a definition of the culture as they are an explanation of the physical, chemical, and biological characteristics.
4. Soil is 45% mineral, 25% air, 25% water, and 5% organic matter, on average
That 5% is critical for plant growth because it contains the microbial community, humic and fulvic acids, and the organic matter that sustains microorganisms. The mineral content of soil is not plant soluble and microbes convert minerals into plant soluble nutrients. The microbes need water and air to survive and the make-up of the microbial community is dependent on many external factors. If the soil is too wet only anaerobic bacteria can thrive. If the soil is too dry all microbes will idle until conditions are right for them to thrive.
5. Plants change the pH in the rhizosphere for optimum growth
Your soil can be anywhere from 5.5 to 11 but if you have an active microbial community your plants will thrive. The plants put out exudates that feed the microorganisms necessary for optimal health at that stage of the plant’s growth.
The microbial community is dependent on the plant’s needs. Microbes break down the soil minerals for the plant. With the plant-microbe partnership the soil in the plant’s root zone (rhizosphere) becomes the optimal pH for that specific plant’s growth.
6. More than 1,000 different earthworm species aerate the world’s soils
All worm species excrete what we call “worm castings.” They are high in plant soluble nutrients and beneficial microbes from the digestive processes in the earthworms guts. A healthy earthworm population can consume 2 tons of dry matter per acre per year. But they’re picky eaters, worms prefer a diet higher in greens than browns so put a little extra manure or grass clippings in your compost for greater worm activity. Earthworms are classified by the part of the soil where they dwell most of the time.
Litter dwellers are found most often in decaying vegetative matter, such as leaf litter and compost. Most litter dwellers are not adapted to freezing temperatures so they are found mainly in warm southern areas. But because they are adapted to living in decaying vegetative matter, they are the worms commonly used in worm bins for vermicomposting.
Subsoil dwellers create vertical burrows that can be up to 5-6 feet deep. They cap these burrows with crop residue and their castings. They eat significant amounts of soil and this is the worm species that leaves a mound of excrement on the surface of the soil. Nightcrawlers are subsoil worms that are often found on the soil surface after a heavy rain because they’ve gotten flooded out of their burrow. Robins benefit if they can tug them out of the soil. Earthworms have bristle like organs that help them cling to slippery surfaces and hold onto the soil when a Robin is tugging on them. Sometimes the worm wins.
Topsoil dwellers live in the top 2-3 inches of soil and create horizontal burrows. They eat mostly partially decomposed organic matter that is already in the soil. They ingest large amounts of soil and microbes, leaving their worm castings in the root zone of most plants, a natural fertilizer.
Earthworms are very beneficial for soil health. Their burrowing aerates the soil, allowing quick water infiltration. Their burrows are fertilizer filled pathways for plant root systems. Earthworms create greater soil porosity, leading to better soil tilth and less compaction. Their castings are highly stable and create aggregates of soil and organic matter.
7. Deep tree and plant roots break up the parent rock under your soil
There is a roots deep in soil continual creation of soil through the physical action of roots and the chemical action of microbes. We will never run out of the basic material for soil but it needs to be converted to plant soluble form by microbes.
Many farms do not have the microbial community necessary to convert soil minerals into plant soluble nutrients.
8. Soil with high organic matter holds a lot of water
That water is made available to your plants through osmosis. For every 1% of organic matter you add to your soil you increase the plant available water per acre by 16,500 gallons, according to a report by the National Center for Appropriate Technologies. That equates to about 1.5 quarts of water per cubic foot of soil for each 1% of soil organic matter (SOM).Compost isn’t the only component in organic matter. There are also billions of microorganisms that break down the SOM and store water. Tilling destroys the balance of your soil, dramatically decreasing the number of microorganisms, and the water available to your plants during a drought. The microbial community is an integral part of your soil. Plant residue supplies SOM to the microbes, who work with your plants to create a balanced soil.
9. The time needed to complete the plant nutrient cycle
Plant photosynthesis creates carbon – 50% of which goes to the plant’s roots. A plant signals microbes that it needs certain nutrients through root exudates; sugars and carbohydrates that microbes need to live. The microbes take up the exudates and give the plant nutrients it has stored in its body or has access to in the soil. The plant takes up the nutrients and transmits the nutrients where they are needed in the plant. Then the cycle begins again. This nutrient cycling takes 3 seconds, according to Dr. Elaine Ingham.
10. Microorganisms create soil aggregates by secreting glues
Bacteria create soil micro-aggregates by secreting sticky polysaccharides, which also serve to protect the bacteria from desiccation. Fungi, specifically arbuscular mycorrhizal fungi, secrete a glue called glomalin that makes the soil aggregates larger and more stable. The concentration of these aggregates is related to how much of the time the soil has growing plants and no-till management of the fields.
It takes approximately 3 days for microorganisms to repair the soil if they are given a chance. That means no tilling or adding synthetics. Adding humic acid as a soil amendment helps give the microorganisms a kick start. Microorganisms might not be in your tilled field right now but they are in ditches, field edges, your lawn, and flower borders.
We are surrounded by microorganisms; bacteria, fungi, nematodes, and millions of other microscopic creatures. A few are harmful but most are useful. When we accumulate enough of the good microorganisms in our soil, they protect crops from disease and pests.
There are many more soil health facts. Check out our website to see how complex the world is beneath our feet. Microorganisms are the foundation of the soil food web but it extends from bacteria to nematodes to moles to coyotes to humans. We are an integral part of the soil food web. We have the ability to be the biggest disruptor or the greatest regenerator of healthy soil. How are you farming? Let us know your farming practices. We are always interested in learning something new.