Soils: Chapters 1&2
Soils are crucial to life on earth
The many functions of soil can be grouped into six categories
Formation of Soils From Parent Materials
Physical and chemical weathering break down rocks and minerals
Characteristics of Rocks and Minerals
Rock types:Igneous Rocks
composed primarily of minerals of light-colored:
Granite containing Potassium feldspar,
In general, dark-colored minerals contain iron and magnesium and are more easily weathered
Therefore, dark-colored igneous rocks such as gabbro and basalt are more easily broken down than granite and other light-colored igneous rocks
Conglomerate - rounded particles
Thinly bedded siltstone
Granite on left, Gneiss on right
Weathering: is the name given to processes that change the surface material of the Earth as a result of exposure to the effects of water and the atmosphere.
Erosion means the removal of material from one position on the surface of the Earth to a different position, again by the effects of water and the atmosphere.
Monument Valley, AZ
Mechanical Weathering Processes
abrasion - refers to the breaking and grinding away of solid rock by collisions with moving particles.
pressure release - expansion of rock as they are brought close to the surface forming sheet joints.
biologic effects - plant roots, burrowing animals, mining.
Chemical Weathering: changes the composition of rocks
reactions in the atmosphere:
Salty water can help the formation of salt crystals that can grow and dislodge sand particles. Also, slightly acidic water can dissolve the cementing material in sandstone.
Four Basic Processes of Soil Formation
Consider: changes that might take place as a soil develops from a thick layer of loess parent material in a climate conducive to grass vegetation
Soil Architecture & Physical Properties
Soil physical properties closely influence....
Soil scientists use the physical properties of the soil horizons in classifying soil profiles and in making determinations about soil suitability for agricultural and environmental projects
Three major factors influence soil color:
Soil Texture (details)
Knowledge of the proportions of different sized particles in a soil is critical for understanding soil behavior
A thin section of a loamy soil.
40x scanning electron micrographs of quartz sand (left) and feldspar (below)
Influence of Surface Area on Other Soil Properties
Soil Texture Classes
Loams are a combination of sand, silt and clay particles.
Structure of Mineral Soils
Soil Structure relates to the arrangement of sand, silt, clay and organic particles in soils
Types of Soil Structure
Most soils exhibit some type of aggregation and are composed of peds that can be characterized by their:
Principal Soil Ped Shapes
Making a Soil Monolith