THE SOIL, A WORLD IN ITSELF
We walk, run, and jump on it. We use it to build roads, houses, and schools. We grow plants on it to feed ourselves. Soil is the foundation of life on Earth. It is a mixture of elements, both inert and living, and it is a memory of a constantly changing structure.
Soil covered of sphaignum, image from Audrey Thériault
The soil’s recipe
Is a hardwood floor considered a soil, or potting soil or rock ? The answer is no. There are many criterias that must be met in order for something to be called a soil. First, wood floors and rocks are solid. Soil is said to be unconsolidated, meaning it is malleable and made of detachable pieces [1].
Than, soil is the work of time. It is formed gradually under the influence of climate, underlying rock, living organisms, topography and groundwater [1]. It contains water, gases such as oxygen, organic matter such as decomposing roots and mineral matter such as silica and iron. There is also dissolved elements, such as ions in water. Garden soil certainly contains these elements, but is not considered soil because it is not actively alive.
Soil is alive and dynamic; it is an ecosystem in itself. Small animals create tunnels in it, microorganisms transform matter and plants structure the soil with their roots. All this life eventually dies and nourishes the soil. Soil is a recycling factory for nutrients such as nitrogen and phosphorus.
Roots can be seen in the top few centimeters of this soil. Image from T2 Environnement
This soil has orange and grey traces. This is a useful clue for determining the soil type. Image from T2 Environnement
Life beneath our feet
Life in the soil is most concentrated in the top few centimeters [2]. It is where roots take place and where we find countless organisms, including earthworms that create tunnels and fungi that spread throughout the soil. Living organisms are essential in the soil. They work to transform matter to make it accessible to others. Each living organism plays a role in nutrient cycling. It’s no surprise that 1 g of soil can contain thousands of different bacterias and a network of fungi several kilometers long [3]! Lets say, the environment and living organisms both transform the soil over time.
Leaf litter on the ground, image by T2 Environment
The soil as history book
Canadian soils are much younger than others. They are between 6,000 and 17,000 years old [1]. In comparison, some Australian and African soils can be up to 250 million years old, while others, such as those in Iceland, are even younger than the Canadians! Here, glaciers covered the land for a long time. The soils we walk on today only began to form after the last big ice melt. This unique feature gives us a significant advantage. Compared to those in the tropics, our soils are young and therefore much more fertile. The oldest Canadian soil is in Alberta. It is 720,000 years old. [1] Why such a big age difference? This particular location was ice-free, which gave it a head start.
If you dig into the soil at home, you can see history. Soil is composed of several successive layers that tell us about its life, like the growth rings of a tree. Like an archaeologist, the deeper you dig, the further back you go into the past of ecosystems.
A glimpse into history is possible by analyzing the layers of soil and rock. Image from Audrey Thériault
Soil is complex; it is alive, changing and an history reminder. Given its importance in all our lives, it is an entity that deserves our attention. Soil feeds us, sometimes even provides us with shelter and allows us to move around. Let’s not take it for granted!
[1] Krzic M. and al. (2021). Digging Into Canadian Soils: An Introduction to Soil Science. Pinawata, Manitoba. Canadian Society of Soil Science. https://openpress.usask.ca/soilscience/
[2] Bardgett, R. D. (2005). The biology of soil a community and ecosystem approach. Oxford University Press.
[3] Paul, E. A. (2007). Soil microbiology, ecology, and biochemistry (3rd ed). Academic Press.
