The mysteries of soil

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By John Colwill

I used to call it dirt. Some people still do. But dirt is such a dismissive word for something that is amazingly complex and truly wonderful.

Dirt is what we get on our clothes. In our gardens, parks, paddocks and nature reserves we have soil. Soil is not, as we are sometimes led to believe, just bits of broken down rock. It is so much more and as we humans continue to breed unabated, its role in our food producing future is becoming increasingly important.

Some of the world’s best scientists may well be working on brain surgery or rocket science but the most important of them are engaged in studying soil. If soil were no more than bits of broken down rock you would think they would have figured it out a long time ago. So why haven’t they? Well the short answer is they did – work out the relationship and characteristics of bits of rock that is.

What they are studying now is what lives between the bits of inorganic material and that is remarkably complex, truly amazing and the subject of new scientific papers published on an almost daily basis.


I would love to be able to detail all this complex life but I’m just an amateur gardener with an interest in the subject whose views on what’s under my feet have changed dramatically and as a result, so too have my gardening habits.

Let me give you a few examples. I thought I knew about the role of a group of fungi called mycorrhiza. These are fungi that have formed a close, mutually beneficial, relationship with plants. These fungi spread out from the root, harvest water and minerals from the soil and deliver them back to the plant.

In exchange the plant gives them energy in the form of sugars. That’s the simple version but it seems these fungi are capable of doing much more than that. They can also change the formulation of minerals into a form the plants can use, even extract minerals out of a soil which according to soil tests doesn’t have that mineral in it. But the really surprising discoveries are about the presence of the messenger molecule RNA. This allows these fungi to pass information from plant to plant.

One study showed that a fungus could even act as a memory, or notebook as the researcher called it. The study showed that in an area where crops had been grown before, when a new plant was put in the ground and the fungus plugged into it, the fungus passed on information about growing conditions and any problem the plant was likely to face. Another study showed that a fungus attached to two different plants could relay messages from one to another. It seems that these fungi invented the internet long before we did.


In a few grams of a good soil there are literally billions of bacteria. Most are busy feeding on organic material, breaking it down until such a stage that the fungi can take it in. Recent discoveries have made us reconsider the role of bacteria and plants. It seems the bacteria can also feed plants. One paper that caused much excitement showed that one bacteria is able to harvest nitrogen from the air in the soil and turn it into nitrate before giving it to the plant. That’s fertilising, albeit on a micro scale. It’s discoveries like these that have led to an increasing number of products coming onto the market containing specific bacteria in suspended animation form, loosely referred to as plant probiotics. There certainly will be many more in the future as the technology improves.

As a result of discoveries like these I now tread far more lightly on the soil. Before I do anything, I ask myself “What effect is it going to have on the soil life?” and if there is any doubt – I don’t do it. Surprisingly, one of the most common garden practices is also one of the worst things we can do to our soil. It’s called digging. Digging dries and kills, smashes up fungal systems and destroys natural air and water channels. It’s all bad news. Ban the spade I say!