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 pore spaces. 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