Life in soil

In just one teaspoon of soil, there can be more microbes than there are people on the planet. That’s before you even count the miles of fungal hyphae also living there. 

The microbes, fungi and creatures that live in soil do the important work of eating dead plants and animals. There are also some soil bacteria that eat actual rock. It’s this array of soil-living organisms that enables energy to flow between rocks, animals and plants, and they play a vital role in the carbon, nitrogen and phosphorus cycles, which underpin life on the planet. 

In fact, this blanket of life supports everything on Earth, including us, so it’s worth getting to know the creatures that crawl, creep, wiggle and weave their way through our soils. 

What is soil?

Up close, soil is a maze of mineral grains, organic matter, air and water, plus a whole host of living organisms, including microbes, plants, fungi and invertebrates. Soil sits on top of the bedrock and can be anything from centimetres to metres deep. 

Most soil life lives in the top five centimetres, so it is here where you will see much of the weird and wonderful biology that makes soil one of the most biodiverse environments on the planet. 

The underground life of plants

You might think of plants as living above soil, but a lot of a plant lies beneath the soil’s surface. This underground network of plant roots helps to physically bind the soil together. 

Microbes rule the soil world

If you look closely at soil with a microscope, you can see a vast array of tiny, mind-blowing bacteria. They sit between all the gaps in the soil grains, and flow through these openings and worm holes when it’s wet.

Microorganisms can shape the soil structure. They alter how much water it absorbs and change its pH and mineral composition.

The diversity of these soil bacteria is vast. There are microbes that attach to plant roots and help them to absorb nitrogen - an important nutrient for plant growth. There are microbes that breakdown organic material in the soil. There are even microbes that shape the soil chemically through decomposition and by weathering the rock and soil with chemicals. 

As they eat, they are also eaten. Microbes are a food source for many nematodes and other microbes such as amoeba and protozoans. 

Fungus in soils

Fungal mycelium weaves through the tangle of mineral grains, air gaps and organic material in soil. Fungal hyphae may be small and operating at the microscopic scale, but when connected as a network they become one of the biggest organisms in the world, living right underneath our feet. 

Small but mighty soil invertebrates

There is a vast array of invertebrates living in soil. These small creatures are vital for soil health as they eat living or decaying matter and turn it into soil. They can also eat one another, making for some quality soil drama.

There are extraordinary numbers of invertebrates living in soil. Just looking at mites alone, in 100 grams of soil there can be as many as 500 mites from around 100 genera.

All of these invertebrates bring organic materials into different layers of the soil. For example, there are earthworm species that live on the surface of the soil eating leaf litter, earthworm species that live in the soil itself, and earthworm species that make deep burrows, only emerging to the surface at night to drag leaf litter into their burrows. 

How is soil made? 

Soils are shaped by the rock beneath them. Rock is turned into soil as it’s weathered by wind, water and ice. Rock-eating bacteria also break down rock, releasing its minerals, which then become part of the soil. 

These minerals shape what life can live in that soil. The soil’s grain size and how close they are packed together influences what can live there, along with the soil’s pH and the nutrients available.

The living and non-living parts of soil are interconnected

Everything influences each other in the soil. The minerals and the soil structure influence what creatures, fungi and plants can live there and those same creatures, fungi and plants in turn shape the mineral and structure of the soil. 

Soil life can survive dry times

Without rain or moisture, soil can become completely dry, making it very difficult for life to survive. Fortunately, soil life has adapted remarkable ways to live through these dry spells. One example of this are worm eggs, which can survive in dry places because they are laid in a cocoon that prevents them from drying out. 

Tardigrades, also called water bears or moss piglets, love to live in watery environments but also have a remarkable ability to survive when their home dries out. Around one millimetre in length, they can be found in moss clumps or wet soil and can be seen under a microscope. Tardigrades can survive for up to 30 years in dry conditions by tucking in their legs, shrinking into a little ball and drying out.

How to look after soil life

Like us, most of the life in soil needs something to eat, water and oxygen. You can look after soil life by keeping soil covered with either plants or mulch, as this helps to keep the soil moist and gives soil life something to eat. Not disturbing the soil will also help life establish itself and thrive.

Reducing your use of chemicals, including fertilisers and pesticides, will also be of great help to soil life, as chemicals can leave residues and too much fertiliser can overload the soil ecosystem with nutrients.