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Life in Soils

More living matter and diversity grow below ground level. Fertile soils provide an ideal medium for the healthy growth of many lifeforms. Most plants obtain water and esential nutrients from soils. Many small animals including worms, mites and ants live in the leaf litter and surface soils. A small number of large animals including wombats and rabbits burrow into the soil to make their family home.

Fertile soils are teaming with invisible microrganisms. Soils are an ideal home for, bacteria, actinomycetes, algae, protozoa and fungi. Many plant roots and microrganisms form special interactive relationships. In the rhizosphere surrounding plant roots, exudates containing food for microrganism are exuded by the roots encouraging prolific microbial growth. The microbes help the roots to absorb nutrients.

 

Organic matter

 

 

Soil organic matter is the decaying remains of plants and animals and consists of carbon compounds.

Small soil animals and microrganisms continually break down soil organic matter into gaseous CO2, water and minerals. The decomposition of organic matter releases essential mineral elements into compounds available to growing plants. Nitrogen, phosphorus and sulphur are important plant nutrients continually added to the soil by the decomposition of organic matter.

Fertile soils are dynamic ecosystems with growing plants continually adding organic matter to soils and lifeforms continually eating and converting the dead plant remains into compounds available to new growing plants. There is a continual cycle of elements without the build up of large amounts of dead plant material. The accumulation of peat in swamps and the ancient formation of coal and oil are excemptions to the rules of decaying carbon cycles.

Soil organic matter

Organic matter is made up of partly decomposed plants and humus. On the soil surface is a layer of leaf litter. Many small animals, especially insects and worms eat the fallen plant material and deposit faeces deeper in the soil. Many microorganisms feed on organic matter. Bacteria live in the film of water surrounding clay particles and preffer to eat soluble compounds, especially sugars. Fungi preffer to live in large pore spaces and feed on hard to decompose organic compounds including cellulose, lignin and plant fibres.

\soils a healthy, fertile feeling.

A healthy soil contains 10% or more organic matter in the top soil and the sub soil may only contain 0.5% .

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Microbes

 

Soils are an ideal medium for microbes to grow in. Bacteria prefer to grow in the thin layer of moisture surrounding clay particles and fungi grow better in large soil pores and can survive in dry conditions. Bacteria have a diameter of approximately 0.001 mm and fungi filaments about 0.005 mm. In comparison clay particles are less than 0.002 mm.

Microbes need a continual supply of organic food to grow and growing plants provide leaf litter to the soil surface. Different microbes eat different plant materials. Bacteria generally prefer smaller and more soluble molecules and fungi feed on tougher woody material containing cellulose and lignin.

A gram of healthy soil contains up to 3,000 million bacteria and 500,000 fungi plus actinomycetes, algae and protozoa.

Microbes generally grow faster in fertile soils similar to the ideal conditions for plant growth. The soil needs to have adequate moisture, aeration and good drainage. Most microbes need similar inorganic nutrients to plants. Nearly all microbes differ from plants and cannot manufacture organic material by photosynthesis and need a supply of organic matter to grow on.

Healthy soils with dynamic microbial ecosystems are able to break down many organic pollutants at a faster rate than in sterile mediums. Organic pollutants may be broken down by chemical or microbial actions.

SMALL SOIL ANIMALS

 

MESOFAUNA INVERTEBRATES

Most small soil animals are found in the leaf litter and top 10cm of soil. Good soil aeration is needed for optinum growth and waterlogging greatly reduces the survival of animals.

Phylum Annelidia,

Class Oligochaeta, Order Lumbricus

Earthworms, Segmented roundworms

European earthworms – Oligochaeta

Australian earthworms – Lumbricidae ?

Phylum Nematoda, Nematodes, Eelworms, hookworms, , Non segmented roundworms

Phylum Mollusca, Class Gasteropods, Slugs and Snails

Phylum Arthropoda

Class Arachnida

Order Pseudoscorpianes, small and nonpoisonous, eight legs

Acari, Soil mites, 0.1 to 1mm, ticks

Araneae, Spiders

Class Crustacia,Slater Pillbug Sowbug – Isopods

Class Myriapods

Diplopoda, Millepedes, 2 pairs legs a segment, eat decaying plant litter

Chilopoda, Centipedes – 1 pair legs segment, are carnivorous, eat small soil animals and have poison fangs.

Class Insecta, three pairs of legs

Springtails – Collembola, Wingless insects, 0.5 to 2mm

Beetles – Coleoptera, Eggs, Grub (larva) & pupa (chrysalis)

Fly larvae – Diptera

Cutworms – Lepidoptera moths and buterflies

Wireworms – Elateridae larvae

Ants

Termites, Common in tropical soils

Cockroach

Thrips – Thysanoptera

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