Soil BasicsAP Environmental Science

SOIL ≠ DIRT

What is soil?a complex mixture of organic and inorganic components full of living organisms whose actions help keep it fertile (can be considered its own ecosystem)

Composition of Good Quality Soil

Soil Formation1. weathering – processes that break down

rocks, turning large particles into smaller particles

a. physical weathering- rain and windb. chemical weathering- water or other substances interact with parent materialc. biological weathering- rock broken apart by living organisms2. erosion – movement of soil from one area to

another3. deposition and decomposition of organic

matter

Five Factors Impacting Soil Formation1. Climate: temperature and rain (ie: soil forms

quicker in warm environments)2. Organisms: Activity of earthworms, plants,

etc. mix soil and add organic matter3. Topographical relief: The effects of hills and

valleys (ie: steep slopes have more runoff and erosion and less leaching and accumulation of organics)

4. Parent material: Type of rock influences soil properties

5. Time: Forming soil takes time; all the factors above change over time

Soil HorizonsO horizon: organic or litter layer A horizon: inorganic mineral components and humus (topsoil) E horizon: loses some minerals and organic material through leaching B horizon: collects and accumulates minerals from above C horizon: weathered parent material R horizon: unaltered parent material  

Soil TextureParticle Diameter

Sand 0.05 – 2 mm Silt 0.002 – 0.05 mm Clay less than 0.002 mm

 Loam: relatively even mixture of three particle sizes 

Soil Triangle

Soil Texture by Fractionation