THELIVINGSOIL

Functions of soilSupport plant growth

Regulate water flow

Absorb and transform pollutants

Habitat for living organisms

Soil Quality

Objective:

Soil organisms:• Who are they and what do

they do?• How do they contribute to

soil quality?

VEGETATION

• Vegetation - Additon of Organic Matter (OM).

• Prairie ~ OM added to upper 2 ft. of soil due to fibrous root system of grass plants.

Ap

A

AB

Bg

VEGETATION

• Forest ~ OM added to upper 4 “ due to yearly leaf fall to surface of soil.

Prairie - Border Biotic Factor

• Prairie - Border soils (oak savannahs) have the influence of the prairie and forest ~ due to changes in vegetation over the past 8000 years the soils have been both under prairie and forest.

Soil Organisms: sizes and abundances

Organism Length or (diameter) mm

Abundance (arable systems)

Bacteria (0.001) 3,000,000,000 / g Fungi (0.005-0.020) 50 meters / g Protozoa 0.010-0.200 100,000 / g Nematodes 1-4.5 7,000,000 / m2 Earthworms 20-200 950 / m2 Potworms 10-50 65,000 / m2 Isopods 3-18 ?? Centipedes 5-80 ?? Millipedes 5-50 ?? Symphylans 2-15 4,500 / m2 Pauropods 0.5-1.5 5,000 / m2 Diplurans 2-7 30 / m2 Proturans 0.4-2 1,000 / m2 Springtails 1-7 100,000 / m2 Mites 0.1-3 250,000 / m2

Size classification of soil fauna

•Microfauna (<0.1mm diameter)–Occupy water films and existing water-filled pores•Protozoa, nematodes

•Mesofauna (0.1 – 2mm diameter)–Occupy existing water- and air-filled pore spaces

–Able to break free from surface tension of soil water•Potworms, microarthropods

Macrofauna (2-20mm diameter)

–Able to alter soil structure•Earthworms, macroarthropods

Bacteria

• Microscopic, single-celled

• Up to 3 billion/g• Autotrophs,

decomposers, plant symbionts, pathogens

Fungi

• Up to 50 meters/g

• Decomposers, plant symbionts, pathogens, predators

•Thread-like hyphae; some form visible fruiting bodies (mushrooms, bracket fungi)

Protozoa• Single-celled

animals• 10,000 -

100,000/g• Feed on

bacteria, fungi, decaying organic matter, other protozoa

Nematodes

• 1 - 4.5 mm• Up to 7

million /m2 • Bacteria

feeders, fungus feeders, predators, plant roots, parasites

Isopods• Crustaceans• Feed on decaying plant residues

Myriapods• Centipedes – predators• Millipedes – decaying plant residues• Symphylans, pauropods

Springtails

•1 - 7 mm•Up to

100,000/m2

•Fungus feeders, decaying OM, some plant feeders

Mites•0.1 - 3mm•Up to

250,000/m2

•Decomposers, predators, parasites, plant feeders

Earthworms

• 2 - 20 cm• 10 - 950/m2

• Many introduced species

• Decaying organic matter

• Different ecological types

Anecic Earthworms

•Medium to large size•Dorsal, anterior pigment•Permanent vertical

burrows•Forage for plant

residues on the soil surface

•e.g. Lumbricus terrestris

Endogeic Earthworms

• Small to medium size• Unpigmented• Horizontal burrows

in topsoil• Feed on dead plant

roots and other buried organic matter

• e.g. Octolasion tyrtaeum

Epigeic Earthwor

ms

• Small in size• Red-brown pigment• Weak burrowers; do not inhabit

mineral soils• Forest litter, compost• e.g. Eisenia fetida

Role in Soil Processes

•Soil formation and soil structuring

•Nutrient recycling and retention

•Population regulation

Role in Soil Formation Fragment and humify organic

residues and mix into mineral soil

Soil formationFormation and

stabilization of aggregatesFormation of pore spaces

Nutrient Availability

•Symbiotic associations

–Rhizobium and legumes

–Mycorrhizae and most plants

Nutrient Availability

•Nutrient mineralization from organic matter pools

•Biological nutrient pool

Live weight of soil organisms in annual cropping systems. These are maximum recorded weights and estimates.

Kg per hectare Bacteria 3,500 Fungi 1,750 Protozoa 175 Nematodes 75 Earthworms 1,100 Potworms 400 Other invertebrates <10 Total weight: 6,000 – 7,000 kg/ha

Population regulation