All About Soil

All About Soil

4.7A

Soil can basically be separated into 5 main parts:

1. Humus2. Clay3. Silt4. Sand5. Gravel

Humus: A dark, moist soil composed of bits of dead, rotting insects, animals, leaves, roots, sticks, and food.  Humus adds nutrients to the soil which plants need to grow and live.

Clay: A soil that holds water.  When wet, clay feels slippery and slimy.  It is made of particles that are smaller than 0.004 millimeters.

Silt: Soil that looks like fine grains or tiny pieces of rock.  Particles classified as silt measure from 0.004 millimeters to 0.006 millimeters.

Sand: Soil that is coarse and drains quickly.  Sand particles measure from about 0.006 millimeters to 2.00 millimeters.

Gravel: Visible rock particles, sometimes referred to as pebbles.

Soil Profiles

• A soil profile is a view of a cross section of soil.

• Most living material exists in the top section, or topsoil.

• Plant roots often extend into the second layer, called the subsoil.

• The bottom two layers consist mostly of rock.

Characteristics of Soil Horizons• 0 Horizon-located on surface, mostly O.M. (organic materials)• A Horizon-Called Topsoil, good amounts of O.M. and minerals.• B Horizon- Known as Subsoil, Less O.M.• C Horizon- Mostly parent material, does little for plant growth.

Soil Texture

Soil texture is the relative sizes of the different soil particles.

Major Soil Texture Classes

• Sand is the largest particle.

• Silt is a medium-sized particle.

• Clay is the smallest particle in size.

Characteristics of aSandy Soil

Characteristics of a Silty Soil

Characteristics of a Clay Soil

Soil Structure

• Sand, silt and clay particles combine with one anther to form cluster called aggregates.

• The way in which aggregates or clusters are arranged is referred to as soil structure.

Soil Structure Categories

Modified from a presentation by Carrie Nagle, Mecklenberg Public Schools.