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Soil Animals

What are soil animals and what are the main types?

Soil animals are an extremely diverse group of organisms. Soil animals are grouped roughly according to their size, into three groups. The first group is the microfauna. These are the smallest of the soil animals ranging from 20 - 200m. The main soil animals in this group are protozoa. The mesofauna is the next largest group and range in size from 200m - 10mm. The most important animals in this group are mites, collembola (or spring tails) and nematodes. The macrofauna contain the largest soil animals such as earthworms, beetles and termites. Generally, the most common soil animals are protozoa, nematodes, mites and collembola.

Why are soil animals important?

Soil animals perform several functions in soil that make them a vital part of all ecosystems, including agriculture. Soil animals are involved in:

  • degradation of organic matter and mineralisation of nutrients,
  • controlling populations of pathogens,
  • improving and maintaining soil structure and
  • mixing organic matter through the soil.

How do soil animals affect decomposition of organic matter?

Soil animals contribute directly to nutrient cycling in soil when they release mineralised nutrients in their excreta. However, most of their contributions are indirect, by:

  • grazing on the microbial biomass, which alters the rate at which organic matter breaks down
  • fragmenting organic matter and increasing its surface area for attack by microorganisms,
  • controlling the grazing pressure of nematodes on microorganisms,
  • mixing soil and organic matter and
  • introducing microorganisms onto fresh organic matter.

How do soil animals affect soil structure?

Soil animals have an important role in the formation of soil structure. Soil animals improve soil structure by forming channels and pores, concentrating fine soil particles together into aggregates and by fragmenting and mixing organic matter through soil.

What do soil animals need to survive in soil?

Soil animals are found in almost every environment on earth, including Antarctica! Different species require different conditions to grow and survive but all soil animals, require sufficient carbon and nutrients, moisture, oxygen and an optimum pH and temperature. The optimum pH and temperature levels vary between species. Some organisms do not survive dry or very cold conditions, but they may leave eggs in the soil that hatch when conditions become more favourable. Other soil animals remain in the soil in an inactive state and become active again when conditions become favourable. Larger soil animals such as earthworms may live deeper in the soil when there are unfavourable conditions near the soil surface.

microfauna

microfauna

Mite

Earthworm

Springtails

Refer to "Soils are Alive" newsletter Volume 1 Number 1: "Mites in your soil" by Dr Graeme Osler

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