What Are the Advantages of Colloids in the Soil?

Cation Adsorption

• Cations are positively charged particles. Some nutrients, including potassium, magnesium and calcium, are cations. Colloids often have a negative charge, which causes them to "adsorb," or hold, positively charged particles. Cations in soil solutions can exchange with those on the surfaces of colloids, allowing colloids to hold nutrients in the soil, rather than having nutrients leach out of the soil with water. Nutrients held by the colloids are slowly released into the soil solution, where they are available for plants to use.

Anion Adsorption

• Anions are negatively charged particles. Phosphates, nitrates and sulfates are some of the important anionic nutrients. Positively charged colloids will adsorb these nutrient anions, keeping the nutrients in the soil and available for plants to use. Anion adsorption does not happen to the same degree as cation adsorption because most soils have fewer positively charged colloids -- but it still plays a crucial role in soil fertility.

Moisture Adsorption

• Colloids also adsorb water molecules. Water molecules are held by either the cations adsorbed to the colloid, or by the colloid particles themselves. Water affects both chemical and physical properties of the soil, including temperature, oxygenation and the effectiveness of the adsorbed nutrients. Having water molecules held in the soil, of course, helps make moisture available for plants to use.

Groundwater Protection

• Soil colloids help to prevent groundwater contamination from organic compounds, including pesticides. Colloids hold onto the contaminants, slowing or stopping their movement through the soil. If movement is stopped, the contaminants never reach the groundwater. Slowed movement allows microbes in the soil more time to break down the contaminants and render them harmless before they reach the groundwater.

Soil Structure

• Soil colloids can stick together, creating clumps known as floccules or aggregates. The colloids sticking together helps to give the soil structure. In soils with few to no colloids, like sand, the soil has very little, if any, structure. On the other hand, soils with a high proportion of colloids, like clays, are much more structured. Soil structure is a determining factor in whether a site is suitable for construction or road building.