4.3 Soil Formation & Erosion

Sand, Silt, Clay (Particle Sizes)

The rock portion of soil is made of three particle types ordered from largest to smallest: sand > silt > clay; particle size affects permeability, porosity, and water retention.

Soil Texture

The percentage of sand, silt, and clay in a soil, which determines how well the soil holds water, drains water, and supports plant growth.

Porosity

The amount of pore space in a soil; sandy soils have high porosity (larger pores), while clay soils have low porosity (tiny pores).

Permeability

How easily water flows through a soil; soils with high porosity (like sand) drain water quickly, while clay-heavy soils drain slowly.

Water Holding Capacity

A soil’s ability to retain water; soils with low permeability (such as clay) hold more water, while highly permeable soils (like sand) hold less.

Soil Fertility

A soil’s ability to support plant growth by providing nutrients, water, and a suitable structure; increased by organic matter, humus, decomposers, clay content, and basic (higher pH) soils.