Soil organic matter Soil organic matter and soil organisms

Soil biomassSoil biomass

(living organic matter) =(living organic matter) =

• living plants

• and animals

• and micro-organisms.

Humusthe slowly decomposing residue of soil

organic matter

• chiefly fibrous vegetation, decomposed gradually by active micro-organisms into a black, colloidal material that coats soil particles.

• it has a high CEC.

Organic matter levels in the Organic matter levels in the

soilsoildepend on how much fresh material is added,

compared with the rate of decomposition. It is stable when these two processes are

balanced. This is determined by

• climate• soil type• and cultivation

Most topsoil contains between 1- 6% of organic matter, subsoil contains less than 2%.

Soil composition

macro-organisms- macro-organisms-

( (small animals and predators)small animals and predators)

• insects, • ants,• beetles, • mites • and spiders

macro-organisms- macro-organisms-

(herbivores and detrivores (herbivores and detrivores))

• rabbits • mice• springtails• ants• beetles• grubs

• woodlice• earthworms • slugs• millipedes• snails

Micro-organismsMicro-organisms• detrivores, predators or parasitesdetrivores, predators or parasites (nematodes, protozoa and rotifers)

Soil floraSoil flora (growing things) include• Roots of higher plants,• algae,• fungi (mushrooms, yeasts and moulds),• actinomycetes• and various bacteria

Earthworms Earthworms

– 10 common species– 10 common speciesresponsible for refining dead plant remains (their main food source) and other organic matter. active when conditions are favourable:

• adequate moisture• pH 6-7 • soil temperature (around 10ºC)

Slugs, snails, arthropods (such as millipedes, springtails, and mites and nematodes) play an important part in the decomposition of organic matter.

BacteriaBacteria• single celled organisms existing in clumps

or colonies.

• Most are heterotrophic, getting their energy from the carbon in organic matter;

• they are present in soils in large numbers and play a major part in the decomposition of organic matter, minerals and other substances.