So far we have dealt with basic soil organisms, however there is a whole network of interactions taking place at a microscopic level. So let’s move up the food chain and concentrate on the one of the predators.
Protozoa – Flagellates, Amoebae and Ciliates
Using the aqueous solution, these single cell animals move through the soil, consuming large quantities of bacteria, soluble organic matter and sometimes fungi. In the process of feeding upon bacteria, left over nutrients, including nitrogen are released in to the soil solution, becoming available to plants. This is because the concentration of carbon to nitrogen in their cells is much lower than bacteria (10:1 as opposed to bacteria starting around 3:1). In simple terms, this consumption releases ammonium and is the basic principle of nutrient cycling through microbial interactions.
Flagellates and Amoebae are true aerobes, meaning that they must have adequate oxygen to breath and survive. Under a microscope Flagellates can be very active indeed, with a long probe that whips out and sucks in food. Protozoa can be a lot more difficult to find, as they move slower and surround and smother their prey, with their large ‘foot’ before consuming. Ciliates are facultative anaerobes which means that they can survive in low oxygen conditions and can be seen moving around very fast, using their hair like cilia to provide the thrust.
Although in a mature, healthy and diverse soil community we may like large numbers of protozoa to help increase plant food availability, it should be understood that a sample with a high soil moisture content may be an indication of less than ideal soil conditions (flooding) and therefore high numbers of ciliates can indicate anaerobic conditions and the potential presence of harmful organisms.
Simon runs Mind, Body & Soil and is Cofounder of SoilBioLab. He specialises in services and solutions for soil fertility management. You can follow him on twitter @peat_free or email him at simon@mindbodysoil.co.uk