18 a Flashcards
Soil Colloides
◦ Tiny particles of clay and humus with negative
charge
◦ Attract cations necessary for plant growth
Cation Exchange Capacity (CEC)
◦ A measure of fertility
◦ Ability of colloids to store or exchange cations
w/ soil solution
◦ High CEC – High fertility
Alkalinity
◦ High base cations
◦ Linked to salinity
Acidity
◦ Accelerates chemical weathering and nutrient depletion
Soil Taxonomy
A Basic System of Soil Classification for Making and
Interpreting Soil Surveys (1975, revised in 1999)
Recognizes 12 orders and five other hierarchical categories
Diagnostic Soil Horizons
Regions with distinctive qualities (color, texture, structure, etc.) identifying soil taxonomy.
Soil Orders of the Soil Taxonomy
Oxisols, Aridisols, Mollisols,
Alfisols
Laterization
A leaching process in humid
and warm climates (oxisols).
Salinization
A process that concentrates
salts in soils in climates with excessive POTET rates (aridisols).
Calcification
A process that produces an
illuviated accumulation of calcium carbonates in continental climates (mollisols
and aridisols).
Oxisols
Tropical soils in hot and humid areas.
Very mature soils; lacking distinct horizons.
Iron (reddish) and aluminum oxides (yellowish) dominate.
Low CEC and fertility due to eluviation of colloidal material and laterization process.
Limited agricultural potential.
Aridisols
Single largest soil order in the world (~19% of Earth’s land surface).
Lack of organic matter.
Pale, and light soil color.
Infrequently but easily leached due to lack of colloidal structure.
Salinization common due to high POTET.
Calcification also a concern.
Mollisols
Grassland soils (World’s best
land for agriculture).
Dark, organic layer 25cm thick.
High CEC, high fertility.
