Planting Seeds - Food & Farming News from CDFA

What is Soil? From Dirt to Dinner

By Lucy M. Stitzer


Life on earth would not survive without soil. Whether we live in a city apartment or on the farm, our lives depend on this seemingly mundane piece of earth. Yet it is not boring and dull at all – it is full of minerals, water, air, organic matter, and microscopic creatures that give life to almost all the food we eat. Let’s take a few minutes to better understand and appreciate our living soil…

What is Soil?

It is a natural body on the land surface of Earth, made up of minerals and organic matter. Soil has many jobs, including:

  • Providing our plants with the minerals and nutrients needed to give them proper nourishment which then keeps us healthy
  • Holding in moisture, preventing flooding, giving us groundwater, and keeping water intact for crops to grow
  • Modifying the atmosphere by providing a massive carbon sink for the Earth’s CO2 cycle by emitting and storing CO2, water vapor, and other gases
  • Purifying the water as it enters the ground
  • Providing a habitat for everything, from groundhogs and gophers to bacteria and fungi
  • Recycling nutrients so they can be used over and over again
  • Finally, it is also the foundation for photosynthesis, which is needed to grow our food

Soil vs. Dirt

Soil is found in layers with the “litter zone” on top. This layer is what we can see and where we find matter, like twigs and leaves. After that, there’s the topsoil, the subsoil, and rock fragments and bedrock at the bottom. That is a lot more than just a pile of dirt!

The most important layer is the topsoil, where all plant growth takes place. But it is a long, slow process. Because it is made from crushed rock and decaying plants and animals, it can take thousands of years in colder climates and hundreds of years in hot, wet climates to make just one inch of topsoil. Crushed rock is the time-consuming part.

Think of the rich, dark soil that was formed by the glaciers when they came down across North America and other parts of the world. A combination of glacial pressure, wind, rain, and basic weathering broke down the rocks into smaller fragments. As they break down, the minerals from the rocks dissolve into the earth.

Take a look at the soil in your hand, rub it between your fingers. Those shiny particles could be crushed rock from the glaciers millions of years ago.

Soil is also formed by decaying roots, old plant material, and living organisms, which help break it down.  As dying material degrades into the soil, it provides nutrients for vegetation, as well as enriching the microbiome. These microbiomes are arguably the most important part of the soil.

The Soil Microbiome

When you hold soil in your hand, what you can’t see with the naked eye are the billions of bacteria, fungi, protozoa, and other microorganisms. These are known as microbes and, this collection is commonly referred to as the soil microbiome.

Microbes act like a fertilizer. They help plants change nitrogen from the air for growth and maturity, absorb phosphorus for health and vigor, and can protect a plant from fungal disease, like botrytis, or gray mold. This is the fungus we see most on our spoiled, inedible strawberries.

A diverse microbiome is an essential ingredient to healthy food and nutrition and is responsible for the micro and macro ingredients for our daily 5-7 servings of fruits and vegetables, protein in wheat, and healthy animal feed for our protein. The more microbe diversity in your gut, the healthier your gut and overall immune system. A spoonful of soil? It is generally thought that by working in the garden, you inadvertently ingest soil – and healthy microbiomes for your gut.

Ever wonder how some plants grow in dry conditions? Microbiomes! The microbiome in and around the roots of that plant helps it survive amidst drought and heat. Scientists can isolate these microbes and apply them to crops with drought conditions. For example, the company Indigo Ag has developed microbial-treated seeds for wheat to increase plant health in the face of water stress.


Soil health is the key to human and environmental life and health. With its layers and microbiomes, it is our most precious resource. Next time you put your shovel in the garden, thank all the little creatures, minerals, and nutrients that are providing us with our life.

Some Fun Topsoil Facts:

  • One earthworm can digest 36 tons of soil in one year – that is equal to five elephants!
  • There are over 70,000 kinds of soil in the U.S.
  • Five tons of topsoil spread over an acre is as thick as a dime

Link to story on Dirt to Dinner web site

This entry was posted in Uncategorized. Bookmark the permalink.

One Response to What is Soil? From Dirt to Dinner

  1. Pingback: Agriculture… à la carte – Your Weekly Ag Update – LearnAboutAg@Home!

Leave a Reply

Your email address will not be published. Required fields are marked *