Soil colloids are particles between 0.2 and 1 micrometer in diameter that remain in suspension in soil solutions rather than settling due to their small size. There are two main types of soil colloids: organic colloids derived from decomposed plant and animal residues, and inorganic colloids composed of various clay minerals from non-living sources. Colloids are the main site of chemical activity in soil.

1. Soil Colloids
• Colloid: A particle, either mineral or organic,
with a diameter of 0.2 to 1 micrometer (μm)
• 1μm = 1/1000 mm
• = 0.001mm
• = 0.0001 cm µm.
• Because of their small size, colloids go into
suspension in a solution—they float around
for great lengths of time without settling out.
• Seat of chemical activity in the soil

3. Types Soil Colloids
• Organic colloids – decomposed residues
of plants, animals and microbial remains.
Materials from living things.
–Humus – stable product of organic
matter decomposition.
• Inorganic colloids – made up of clay
minerals of various kinds. Materials from
non-living things.