Image of a Ciliate in organic gardening

A Ciliate under the microscope

The three main protozoa of interest to us as organic gardeners are amoebae, ciliates and flagellates. Ultimately they all serve a similar purpose by releasing the nutrients bound in the soil food web by the bacteria and fungi. Their presence has the remarkable ability to keep the web in balance – making the whole cycle self-regulating (actually that regulation goes further than that, because of all the other aspects of the soil food web, but without the protozoa we’d be soon over run with bacteria!)
All the protozoa require moisture to move around and exist, without it they will enter a dormant state ready for the right conditions to arrive.
In order of size, largest first, we have the amoebae, these move around by filling their pseudopodia with cytoplasm – they essentially squeeze their whole being in to one or more “false feet” moving themselves around. Think water in a rubber glove…. Using this cytoplasm they can surround bacteria and absorb them by releasing enzymes to break them down, eventually releasing any waste as they travel.
Moving on to ciliates – these move around by beating very fine hairs that cover their body, they can use this method to both propel

themselves forward or for pulling bacteria in toward their “mouth” – Ciliates primarily consume bacteria but can also feed on fungi and themselves if the size is right.
Finally the smallest of the protozoa are flagellates. Their primary form of locomotion is by means of one or two long hairs, or flagella – again they consume bacteria as they move around the rhizosphere if not preyed upon by the larger ciliates or a passing nematode. However as they are much smaller they have an advantage in that they can move around in much tighter areas, essentially hiding themselves whilst being able to access bacteria more easily.

Why do we need protozoa in an organic garden?

An average protozoan can eat 10,000 bacteria a day – after this the waste that is excreted is plant available nutrient. So while the bacteria are unlocking the nutrients from the organic matter and holding them in the rhizosphere, the protozoa are then going on to release these minerals back in to the soil – as we already know that fungi and bacteria crowd around roots looking for food, it makes sense that these newly released nutrients are right where they need to be!

Image of an Amoeba on a dark field

An Amoeba under the microscope on a Dark Field

 

How can we add more protozoa in to the soil food web?

Firstly I’d say by not digging, that way you don’t break up the path ways the soil food web sets out for itself. If you follow a no dig (or no till) technique you’re likely to be adding compost and mulches at the surface and relying on the worms to bring this down – the worm castings that they produce will increase your bacterial and protozoa population. If you’re container gardening or practising indoor cultivation you can purchase worm castings and add them manually. But for me, the ultimate method is to add a well produced, balanced compost tea – this will add a diverse range of life in levels that far outnumber a straight input like worm castings alone including bacteria, fungi, protozoa and nematodes

Photo Credits:
Amoeba and Ciliate microagua