Earth's Systems and Resources - Environmental Science - page 27

Soil Properties
Soil is classified based on the properties of pH, texture, color, and structure. Soil texture affects the other prop-
erties, including porosity and permeability. Soil porosity is the amount of open space between each soil
particle, the ratio of void space to total volume. Water, air, or other gases fill these pore spaces. More pore
space means a high water-holding capacity and, therefore, a higher porosity. Conversely, lower porosity means
a lower water-holding capacity. Soil permeability is the ability of a liquid to flow through the soil. Larger
particles have large pore spaces, allowing water to pass through more easily. Clay is considered to have low
permeability because it's hard for water to flow through easily. Sand has a higher permeability.
Soil Texture
Soil texture is used to describe grain sizes in soils. It is divided into three main groups:
• Clay is classified as having very fine particles and low permeability (water does not pass through easily).
Particle diameter is less than 0.002 mm.
• Silt has fine particles, but they are larger than those of clay. Particle diameter is 0.002 to 0.05 mm.
• Sand particles are larger than those of silt, so water passes through relatively easily. Particle diameter is
0.05 to 2 mm. Sand is not conducive to plant growth or crop growth unless the plants' requirements for
water are low.