Soil Processes

Watch this to unpack soil-forming processes for Higher Geography (and why mud really matters)

Did you know that in one handful of healthy soil, you will find more life than the amount of people that live on planet Earth?

Soil is the most incredible stuff but we never talk about it. Everything we eat can be traced to the soil beneath our feet. It feeds us, it sustains us. Soil, and the microbes it contains, allow
our ecosystems to breathe, function and prosper.

Without the cycle of carbon capture, store, and transfer, below us,
Life as we know it on the surface, would not exist.

So let's look down for a change, at the ground beneath our feet, and explore the processes that make it so perfect.

You might want to put your wellies on.

This is thinkfour.

Process one, humification.

This is simply the process whereby humus is made - an organic material of decomposed plants and animals.

Warm, fairly dry conditions encourage quicker decomposition rates.

Soil biota and vegetation are also two important factors that influence the process of humification.

Invertebrates such as worms are its engineers. They break down and mix the organic matter as they forage and feed, aerating the soil aiding decomposition.

Deciduous vegetation provides an abundant leaf litter that sustains the production of humus and its inhabitants. The deep roots also recycle nutrients, promoting new plant growth and biota activity at the surface.

This harmonious relationship is what soil scientists call the nutrient cycle.

Our second soil forming process is leaching.

It is a natural process by which water soluble minerals such as iron and aluminum are washed from A horizon to the B. When minerals are washed from the A horizon, we call it eluviation. When they are washed into the B, we call it illuviation.

Leaching is most associated with Podzols as it promotes the formation of an Iron Pan.

When precipitation is greater than evapotranspiration, leaching intensifies. So, it’s no surprise to find that Scotland has its fair share of podzols!

The chemistry of parent material is a key factor influencing this process.

Parent material is the bedrock that soil has formed on top of. Soil is intrinsically linked to the characteristics of its parental base – just like the genetics between children and their parents.

A common rock lying beneath Scottish podzols is Granite, an acidic rock because of its mineral, silica.

But how does this influence the process of leaching?

Well, as rainwater filters through an acidic soil, it too becomes acidic and breaks down iron and aluminium into more soluble particles making them easier to eluviate.

Therefore, without the acidity of its parent rock, Podzols would not form their characteristic iron pan.

Our third and final process is gleying, the water logging and deoxygenation of soils.

It is the process that gives Gleys their characteristic blue/grey horizons.

Gleys love the west of Scotland and blanket most of the Outer Hebrides.
I know I am in a Gley when I feel the slow ingress of water into my boots!

But what factors contribute to my soggy socks? The answer - relief and drainage.

Gleys form when the angle of a slope is between 0 and 5 degrees. This slows the movement of the water throughout the soil. For this reason, Gleys are found in the boggy landscapes that skirt our hills.

The way in which the biosphere manufactures itself from these competing factors and processes is truly amazing. It really does shape the foundations of life on our planet.

So never let anyone tell you that it is just ‘mud’.

It is something much more precious. It is the product of a beautiful interplay between climate, biology and geology. It is quite possibly the most important stuff you have ever talked about.

Thanks for watching; this was thinkfour.