Soil colloids are the chemically active portion of the soil. They contain positive and negatively charged ions. They are tiny particles that aide in the adhesion of the soil Colloids can be either organic or inorganic, and determine the physical and chemical properties and the fertility level of the soil. The organic colloids are in the form of humus and the inorganic colloids are clays.
Phyllosilicate Clay Minerals
Phyllosilicates are a group of minerals that includes micas and clay. According to Louisiana State University, they consist of thin layers of repeated structural units, which are the dominant clay minerals in the soil in temperate regions. These types of colloids help to bind the soil together and prevent the weathering and washing away of nutrients. These colloids give the soil the appearance of large cracks when it begins to dry out.
Oxides are in the form of aluminum and iron oxides. They are either crystalline or amorphous, which refers to the shape of their atoms. Amorphous means there is no set arrangement of atoms, and crystalline oxides have an orderly, repeating pattern of atoms. Oxides are common in low-fertility soils in tropical and subtropical climates.
Amorphous minerals are those with randomly arranged atoms. Allophane and imogolite are two types of amorphous minerals. These are the clays that form volcanic ash. These substances have a low cohesion property, are easily dispersed and have a low water content.
Organic colloids, or humus, are the smallest of all organic materials. These colloids have been broken down to the smallest point possible. Organic colloids, often referred to as compost, are used in soil additives and quickly absorbed by plant life. They help the soil retain its moisture and oxygen levels.