Microfauna are the smallest of the soil fauna and are less than 0.1 mm in size, and so need a microscope to be seen. The two most important soil creatures are the nematodes and the protozoa. Nematodes occur widely in soils, particularly in sandy soils. They depend on a thin film of water around particles for their movement. Some species are parasites and can be a problem for agricultural crops such as potatoes. Protozoa are small and variable in shape. They are major consumers of bacteria. They are well suited to life in soil because they slide over surfaces relatively easily, feeding on soil particles, roots and thin water films in the soil.

Bacteria in the soil.

There are three main forms of microflora in soils: bacteria, fungi and viruses. Bacteria are tiny organisms composed of single cells and without a distinct nucleus. They are extremely numerous in soils with billions in just one gram of soil and many thousands of species also within a single gram.

Bacteria take part in some of the most important transformations in soils including weathering of rocks and minerals, breakdown of organic matter, and many aspects of nutrient cycling.

Fungi are also very common in soils, taking the form of spores, globules and filaments. They depend on living and dead matter in the soil for their carbon and energy. Toadstools and other fungi have extensive roots spreading out through the soil. They are important in the decomposition of organic matter and also play an important part in stabilising soil aggregates. Very importantly, mycorrhizal fungi play a major part in securing nutrients for plant production and many plants are dependent on such relationships.

Viruses are the smallest and simplest multiplying entities in the soil but, perhaps because of their small size, rather little is known about them. All are parasites, i.e. they live off other flora and fauna. A range of plant, insect and human viruses can be found in soils. The conditions in soils that most influence the numbers of viruses are moisture, the surface of soil aggregates and structural units and the rooting system of the plants. We know relatively little about the viruses in soil and also about many of the other tiny organisms. The fact that many are extremely small and are out of sight below ground means that the full importance of many of these creatures may yet remain undiscovered for some time.

Source: www.soil-net.com

The soil is an ecosystem in which millions of living creatures live and interact. There can be more creatures in a teaspoonful of good quality soil than there are people in the entire planet earth, i.e. more than 6+ billion - that is amazing! Not only are the numbers of creatures large but there are also many different types of creature. This is partly because the soil is the source of many different types of food for these creatures and is also the source of their nutrition and water. The soil can also offer a range of habitats, for instance the badger's sett, the rabbit warren, the earthworm channel, numerous pores where the small creatures can exist and develop.

Rather little is known about many of these organisms and about their many functions. It is so much easier to learn about creatures that live on the surface of the earth and can be readily seen, for example elephants, blackbirds, bumblebees, butterflies, than it is to learn about the soil creatures many of which live underground all their life. We live in a time when we are using the soil much more intensively than ever before to try and keep food production apace with needs of the fast growing population. We need to develop a much better understanding of the soil ecosystem. The soil ecosystem has been declared by some scientists as the last great biotic frontier.

There is a very huge range of organisms in the soil varying in size from protozoa which require the strongest of microscopes to see them, up to large burrowing animals such as badgers and rabbits which live part of the time in the soil and part of it on the soil surface. Not only is there this large range of size but there is also wide variation in what they use the soil for. Soil organisms can be classified in several different ways: by size, feeding habits, burrowing activities. The most usual way of classifying soil organisms is according to size, in particular, separating them into macrofauna, mesofauna, microfauna and microflora.