UNIT 5 WEATHERING AND WATER PART 2 SOIL.

Soil-solid earth material altered by physical, chemical, & organic processes so it can support rooted plant life.It is growing medium for food.Purifies organic waste.100 years to form. Soil lose to erosion.

• 1. Composition of soil.• Mineral grains.• Water held between porespaces.25% air.Organic matter both coarse &fine.Bacteria: gram can contain 2 billion bacteria, 30 million fungi.

• Rock material: sand, clay, & silt.• Soil thickness reflects balance between rates of

soil production & rates of downslope soil movement.

Soil Production

• 2. Factors of Soil Formation• a. climate: temperature & precipitation.• Greater rainfall amount, more rapid rate of both

weathering & erosion.• b. Organisms: native vegetation, weathering is

dependent of plant growth. • Plant & animal activity produces humic acids that

are powerful weathering agents.• Plants can physically as well as chemically break

down rocks. Plants stabilize soil profiles, animals tend to increase erosion.

• c. Parent material: chemistry, mineralogy, & grain size.

• d. Topography: ground slope, elevation, & aspects of slopes.

• The steeper the surface slope, more likely any eroded material is to be transported out of the system.

• Erosion rate = f(S)

• LEARNING OBJECTIVE:• Recognize the major components of soil and list

the most important factors in soil formation.• Explain how soil varies with depth.

• Soils on flat surfaces, such as floodplains or plateaus, tend to thicken through time due to weathering rates being greater than sediment transport rates.

• d. Time • 3. Additions to Soils• a. Atmospheric inputs: precipitation, dust,

deposition• b. Surface inputs: floods, tidal exchange, erosion,

land-water movement.

Soil Development

• c. Interior inputs: litterfall, root turnover.• 4. Soil Formation• Decomposition of organic matter.• Weathering of rocks : Freeze, thaw, drying,

wetting, fire.• Chemical weathering.

Soil Profiles