Introduction to Soils

Soil Horizons

100

 It’s the very top layer of soil. Made mostly of organic material

O Horizon- Organic matter 

200

Beneath all other soil layers – the bottom of the soil profile. Contents unweathered bedrock such as sandstone, granite, or limestone.

R Horizon -Bedrock

300

Below the B Horizon; just above the bedrock. Partially weathered parent material; little to no organic matter.

C Horizon -Parent Rock  

400

Just below the O Horizon (if present).  mix of minerals (sand, silt, clay) and organic matter (decayed plants and animals).

A Horizon -Top Soil 

500

Below the E Horizon- Contains minerals like clay, iron, and aluminum that have leached down from upper layers; low in organic matter.

B Horizon- Subsoil

Factors of Soil Formation

100

earth moving, overuse, compaction is known as 

Human Activity

200

Plants, animals, insects and microbes affect soil formation 

Biological Activity 

300

Affected by glacial ice, wind, water, gravity, volcanic deposits and organic deposits 

Parent Material

400

Mature soils are generally productive but become less as they continue to age

Time 

500

Soils position in a landscape influences soil development mainly be affecting water movement

Topography 

Physical soil properties

100

Indicate certain physical and chemical characteristics. Due primarily of two factors: 

Humus and Iron compounds present

Soil Color 

200

Size, shape, and arrangement of soil particles and associated pores determine the ability of the soil to retain water

Water Holding Capacity

300

Refers to the total depth of parent material or soil layers. Classified by the following:

−Deep: 35 inches or more

−Moderately deep: 20–35 inches

−Shallow: 10–20 inches

• Very shallow: 10 inches or less

Soil Depth 

400

Refers to weight of oven-dry soil with its natural structural arrangement (NO WATER)

Soil Density 

500

Refers to the arrangement of soil particles. Classified by these 3 main types

Structureless, With-structure, Structure-destroyed

Soil Structure

Components of soil

100

 sand, silt, clay

Mineral particles

200

 moisture that supports plant and microbial life

Water

300

 oxygen and other gases in soil pores

Air

400

decomposed plants and animals (humus)

Organic matter

500

microbes, insects, worms, fungi, etc.

Living organisms

Soil Particles

100

particles are the largest, ranging from 0.05 to 2.0 millimeters in diameter.  

Sand 

200

particles are intermediate in size, falling between 0.002 and 0.05 millimeters in diameter.

Silt

300

particles are the smallest, with diameters less than 0.002 millimeters.

Clay 

400

This soil particle holds water better than sand but not as much as clay 

silt

500

used to determine the textural name of a soil by mechanical analysis

Soil texture triangle