5.2 Soil

Characteristics of Soil Soil is the part of the regolith that supports the growth of plants Regolith covers nearly all of the Earth’s land surface Composition Texture Structure

Characteristics of Soil continued… Composition Structure 4 main components Mineral Matter Broken down rock Organic Matter Humus (decay remains) Water Air Soil particles usually form clumps that give soil a certain structure Determines how easily it can be cultivated & susceptible it is to erosion Affects how water penetrates the soil

Characteristics of Soil continued… Texture Refers to the proportions of different particle sizes Based on the % of clay, silt, & sand in soil Influences the ability to support plants. Sandy soils = drain & dry out quick Clay-rich soils = drain slow Loam soils = best for plant growth & retain water best

What type of soil consists of 10% clay, 60% silt, 30% sand? https://www.youtube.com/watch?v=-KNcUNGaou0

Soil Formation Most important factors of soil formation are Parent Material Time Climate Organisms Slope

Soil Formation Parent Material Source of the mineral matter in soil How does PM influence soil Source of the mineral matter in soil Soil that forms on bedrock is called residual soil Soil that forms on unconsolidated deposits is called transported soil Look at fig. 12 pg. 135 2 ways Chemical Makeup Affects soil’s fertility ( types of plants the soil can support) Rate of Weathering / Rate of Soil Formation Unconsolidated deposits = partly weathered (more SA) TS develops more quickly than RS

Soil Formation continued… Time / Climate Organisms / Slope Longer forming = thicker Climate has greatest effect on soil formation Temp. Amt. of Precipitation Types of organisms in the soil Plants are main source of organic matter Animals & microorganisms also contribute Fungi, bacteria (help to decompose) Variations in slope = different soil types

Soil Profile Soil varies in composition, texture, structure, & color at different depths Soil horizons (Surface > A > B > C > PM ) Soil Profile (all the soil horizons) A Horizon Topsoil, mainly organic matter (ex. Loose leaves). Lower part of A is a mixture of mineral matter & organic matter B Horizon Subsoil, Fine clay particles, Lower limit of plant roots & burrowing animals C Horizon Partially weathered parent material. Resembles PM

Soil Types 3 common types of soil are pedalfer, pedocal, & laterite Pedalfer usually forms in temperate areas with > 63 cm of rain each year (Eastern USA – forested areas) Pedocal are found in drier western USA (Grasses & brush vegetation) Laterite form in hot, wet tropical areas (Deeper in the soil) (When dried = very hard & waterproof) Soil in tropical rainforests lack nutrition Garden in TRF or TN?

Soil Erosion Water, wind, & other agents move soil from place to place Rain Human activities that remove natural vegetation (farming, logging, construction) have greatly accelerated erosion Depends on soil characteristics, climate, slope, & vegetation Wind erodes soil more slowly than water Ex) 1930s Dust Bowl

Soil Types are determined primarily by the climate of where they form. Location Contains Color Pedalfer Temperate, wet Eastern US Iron oxide, aluminum clays Red-brown Pedocal Dry Western US Calcite Gray-brown Laterite Hot, humid Tropics Iron oxide, aluminum oxide Orange red

5.3 Mass Movement

Triggers of Mass Movements The transfer of rock & soil downslope due to gravity Saturation of surface materials w/ H2O, slopes, removal of vegetation, earthquakes Earthquakes Dramatic triggers – aftershocks - landslide Removal of Vegetation Plants = more stable slopes due to root systems binding soil & regolith (Ex. Landslide) Oversteepened Slopes MM become more likely when a slope > 40 degrees Water = heavy rain / rapid melting of snow Ex) Mudslides / Mudflows

Types of Mass Movements Classified based on the kind of material that moves, how it moves, & the speed of movement Rockfalls Rocks/rock fragments fall freely through air (steep slope) Slides Rockslides Slumps Downward movement of a block of material along a curved surface – slower travel speed Flows Mudflows - Earthflows Creep SLOWEST type of MM (few mm/cm per year) Ex. Freeze-thaw cycles