EAS 430 Soils Flashcards
Soil definition
A dynamic natural body composed of mineral matter, organic matter, gases and living organisms in which plants grow.
Factors Influencing Soil Formation
- Climate - Temperature & precipitation
- Living Organisms - Animals (humans too), Plants, & Microorganisms
- Parent Material - Physical & chemical properties of geologic materials
- Topography - Landform, slope & aspect
- Time - Duration over which climate and living organisms have influenced parent material
3 important soil properies
texture, structure, color
soil texture
proportion of sand, silt & clay
soil structure
aggregation of sand, silt & clay into secondary structures called aggregates
soil color
insight into organic matter content and other soil properties
sand
portion of soil texture measuring 0.05 - 2 mm
[ADD composition]
silt
portion of soil texture measuring 0.002 - 0.05 mm
[ADD composition]
clay
portion of soil texture measuring < 0.002 mm
[ADD composition]
granular
description of soil structure with high permeability
blocky
description of soil structure with moderate permeability
platey
description of soil structure with low permeability
massive
description of soil structure with low permeability
components of macroaggregate
micro-aggregates (plant and fungal debris, silt-sized aggregates, clay microstructures), particulate organic matter decomposed by saprophytic fungi, and mycorrhizal fungal hyphae. Pore space and organic binding agents.
A-horizon
surface horizon.
Mineral horizons that formed at the surface or below an O horizon and (1) are characterized by an accumulation of humified organic matter intimately mixed with the mineral fraction and not dominated by properties characteristic of E or B horizons (defined below) or (2) have properties resulting from cultivation, pasturing, or similar kinds of disturbance.
Ap - Plowing or other disturbance
O-horizon
organic horizon. On the surface, but can be buried.
Layers dominated by organic material. Some are saturated with water for long periods or were once saturated but are now artificially drained; others have never been saturated.
Oa - Highly decomposed organic material
Oe - Organic material of intermediate decomposition
Oi - Slightly decomposed organic material
B-horizon
subsoil. Horizons that formed below an A, E, or O horizon and are dominated by obliteration of all or much of the original rock structure 11/ and by (1) illuvial concentration of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in combination; (2) evidence of removal of carbonates; (3) residual concentration of sesquioxides; (4) coatings of sesquioxides that make the horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons without apparent illuviation of iron; (5) alteration that forms silicate clay or liberates oxides or both and that forms granular, blocky, or prismatic structure if volume changes accompany changes in moisture content; or (6) any combination of these.
Bh - Illuvial accumulation of organic matter
Bs - Illuvial accumulation of sesquioxides and organic matter
Bt - Accumulation of silicate clay
C-horizon
Horizons or layers, excluding hard bedrock, that are little affected by pedogenic processes and lack properties of O, A, E, or B horizons. Most are mineral layers, but limnic layers, 10/ whether organic or inorganic, are included. The material of C layers may be either like or unlike that from which the solum presumably formed. A C horizon may have been modified even if there is no evidence of pedogenesis.
E-horizon
eluviation layer. O-A-E-B-C.
Mineral horizons in which the main feature is loss of silicate clay, iron, aluminum, or some combination of these, leaving a concentration of sand and silt particules of quartz or other resistant minerals.
Used for horizons with significant loss of minerals.
idealized soil proportion of solid, liquid, and fas
45% mineral
25% water
25% gas
5% organic matter
water properties
polar (local positive and negative charge)
hydrogen bonding
field capacity
wilting coefficient
