Symbiotic relationships and fertility – Fungi.

With the boom in plantation forestry, silvaculturists noticed that some trees grew well in some areas but not in others, even though the soils were identical. Chemical analysis couldn’t explain the difference. Finally it was discovered that a fungi, at the time dubbed mycorrhiza, was causing the difference. It was colonising the root tips and increasing the plant’s ability to absorb nutrients over a wider area. In some cases it formed extensive networks of fibres extending well beyond the normal root system. Since then we have discovered many other fungi that share the same relationship with plants. While we know a lot about plants and insects, we know very little about fungi.

Biologists estimate we have only identified and classified around 12% of all the fungi species. Because soil is actually a living microcosm, peak fertility will not come from chemicals alone. Fertility is the result from a variety of organisms interacting within a favourable environment.

a collection of red spotted toadstools

We still have a lot to learn about fungi. Some can extend the ability of plant roots to get nutrients.

So far we have focused on the chemicals. Let’s move on to the biologicals.

You can’t go down to the garden shop and buy a bag full of beneficial organisms for your soil. Even if you added a kilogram of worms, without the vegetable content in the soil, they will starve and die out. However there is an easier way to add these beneficial organisms.

I had a small hobby farm just out of Melbourne. There was a small enclosure close to the house that was sheltered but too small for grazing and the soil was not very good either. At the time I was working for a subcontractor for Melbourne’s parks and gardens. Each day one of the grounds contractors would dump about 75 Kg of lawn clippings. As an experiment, I asked him if I could have them all for about six weeks. I simply dumped them in rows and covered them with polythene to retain the moisture. The following spring, I planted six black currant bushes in one row and two red current bushes in another.

The bushes grew well, possibly extremely well but I had never seen a current bush to compare them to. What I did see was a huge yield of currents only in the top half of the bushes. We were swamped with currants. Being ignorant of currants, I assumed this was normal for currents. We also noticed our free range chooks were consuming less feed but the eggs were rich orange yolks and plentiful. I never connected the two until several weeks later when I was collecting the last of the season’s currents and flushed out several fat hens from the currant bushes. The reason we had no currants below 1 metre high, was the chooks were eating them! I wonder what our yield would have been if it wasn’t for the chooks?

Although I added no chemical fertilisers to that enclosure, the grass clippings had decomposed into compost and enriched the tired soil with both chemicals and organisms from the composted grass clippings. Many trace elements can be present in soil but are in an insoluble form. The fungi and other organisms that colonise the soil can break down these insoluble compounds into soluble ones, releasing the trace elements and nutrients for plants.

The role of fungi is a relatively new area of study for science. We think it aids plants by extending their root systems ability to extract nutrients. In some cases the fungi extracts nutrition from the plant but in many cases we don’t know what the fungi gains from the plant however the fact that the plant and the fungi exist and flourish better together would indicate there is some mutual benefit for each other – a symbiotic relationship. There are even predatory fungi that trap nematode worms.

We see fungi only when they fruit, forming fruiting bodies like mushrooms and toadstools. What we never see is the vast network of filaments that exist below ground, often extending hundreds of metres in all directions, that is the real fungi, supporting that fruiting body. There is a lot more to be discovered yet.

We might know how all the organisms work together to increase the soil’s fertility but there is no doubt that introducing your own composted material will boost your soil. The compost you buy in bags from the garden store is sterilised, usually with super heated steam, so although it is high in humus, it has virtually no micro-organisms. Making your own compost is best.

To make your own compost is very simple. Vegetable scraps can be buried directly in the soil that is later to be used as a garden. Alternatively create a compost heap by forming a low wall on three sides of a rectangle and throw all your grass clippings and vegetable scraps inside. In dry climates, it pays to water the heap every so often, the organisms perform best in a damp environment.


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