What is soil made of and what does it do?

Soil provides physical support, moisture, air and nutrients, but what is soil really? It has been called "A medium for plant growth", but this is just some academic talking. Too often, the textbook view of soil present only the scientific view of components and contents - like some kind of cookie recipe: "Take 2 cups of sand, a cup and a half of organic matter..." and so on.

So, in real terms then - "What is soil?" And what that makes it more than just 'dirt'. I prefer to say that Soil is a Living System, but I want to be clear what I mean by that. Soil is made up of both mineral and organic particles of various sizes. These include sand, silt, clay and humus. There is also air water and a myriad of living organisms. So the first aspect of this living system is that there needs to be a balance between the proportions of these components.

In other words, any answer to the question "What is soil?" must lead to a better understanding of this balance. Soil is a living system because this balance is not entirely fixed, but results from a range of dynamic interactions. It is also a living system because it contains so much life. In terms of both biomass and biodiversity, a good friable soil can be compared with a rain forest or coral reef. The only real difference being the lack of National Geographic film-makers hanging about.

Lastly, soil is a living system because it behaves in many ways as if it were alive. Don't misunderstand me here, I am not saying soil is a living organism, just that it seems to behave in ways that are Like those of a living organism. For instance, under certain conditions, soil will deposit iron and other minerals as nodules that vary in size from pebbles to boulders. This process can be likened to that of excretion, since it doesn't simply occur at random , or as a coating over soil particles. Nodules form in specific places and the process of deposition continues only there (on the surfaces of existing nodules).

Also, if you take the trouble to use a good soil testing service to monitor the condition of your soil, you may sometimes find yourself wondering if you have made a mistake. By this I mean that you can get a soil test, apply the recommended amendments, 12 months later test again and see either less change that you expected, or something else quite unexpected. With experience you will come to realize that no matter how good the science - sometimes soil will just seem to do whatever it 'wants'. Don't worry about this, as my old soil science lecturer once said: "Most things will usually work themselves out in the wash".

New! Comments

Share your thoughts about what you just read! Leave us a comment in the box below.