Chp 12 Soils Flashcards
What is soil
Is a component of the landscape; regolith overlays the bedrock below
What is in soil?
-Inorganic material
-organic matter (<5%)
-air (50% of pore spaces)
-Water (50% of pore spaces)
What is loam
Loam is about 20% clay, 40% sand, and 40% silt
What determines the type of soil at a place: climate, parent material, topography, biology + time.
-geologic factor: source of the rock fragments that make up soil is parent material, which may be either bedrock or loose sediments
-climate factor: temperature and moisture are the climactic variables of greatest significance on soil formation
-topographic factor: slope and drainage are the two main features of topography that influence soil characteristics.
-biologic factor: soil is about half mineral matter and about half air and water but the organic matter gives life to the soil and makes it more than just ‘dirt’
-time factor: most soil develops with geologic slowness—so slowly that changes are imperceptible within the human lifespan
Soil Water: Gravitational (free), Capillary (cohesion), Hygroscopic (adhesion), Combined (soil minerals)
-gravitational water: results from prolonged infiltration from above and sinks through interstices toward the groundwater zone
-capillary water: remains after gravitational water has drained away, held in the soil by surface tension—the force exerted along the surface, caused by cohesion of water
-hygroscopic water: consists of a microscopically thin film of moisture bound to soil particles by adhesion
-combined water: the least available of all, it is held in chemical combination with various soil minerals
Gravity pulls soil water downward:
Leaches and transports dissolved nutrients (eluviation) and deposits them at depth (illuviation).
Three major Soil Properties: Color, Structure, Texture (sieve shaker determines proportion of sand, silt, clay).
-Color can provide clues about a soil’s nature and capabilities.
-standard colors are black, brown, red, yellow, gray, or white
-in most cases, color is the result of stains, imparted by metallic oxides or organic matter, on the surface of soil particles
-Structure refers to the individual particles of soils that aggregate together (peds)
-the size, shape, and stability of peds have marked influence on how easily water, air, and other organisms move throh the soil
-classified on the basis of shape:
-spheroidal, platy, blocky, or prismatic
-Texture refers to the various sizes of individual particles
-gravel>sand>silt>clay
Soil chemistry: Colloids - suspended particles → Cation exchange - soil nutrients
-COLLOIDS: soil particles that are smaller than about 0.1 micrometer in diameter.
-inorganic colloids consist of clay in thin, crystalline, platelike forms created by the chemical alteration of larger particles.
-organic colloids represent decomposed organic matter in the form of humus.
-when mixed with water, colloids remain suspended indefinitely as a homogenous murky solution
-colloids have remarkable storage capacities-> they influence the water holding capacity of a soil
-CATION EXCHANGE:
-colloids carry a mostly negative charge on the surface, this attracts swarms of nutrient cations and prevents them from being leached from the soil
-common cations: magnesium, calcium, potassium (essential for soil fertility)
-some cations are bound more tightly than others. Cations that bond more strongly may replace those that bond less strongly. THIS is cation exchange
Soil Profiles and Soil Horizons: these reflect soil depth and the amount of time that soils had to form.
-four processes deepen and age soils:
-addition (ingredients added to soils)
-loss (ingredients lost from the soil)
-translocation (ingredients moved within the soil)
-transformation (ingredients altered within the soil)
-the 5 soil forming factors influence the rate of these four processes
-soil tends to have more or less distinctly recognizable layers, called horizions, each with different characteristics
-O horizon: surface layer of lose and partly decayed organic matter
-A Horizon: mineral matter mixed with humus
-E Horizon: zone of eluviation and leaching
-B Horizon: accumulation of clay, iron, and some aluminium from above
-C Horizon: partly altered parent material
-R Horizon: unweathered parent material
Laterization (hot, moist):
named for the brick-red color of the soil it produces. The processes associated with this regime are typical of the warm, moist regions of the world. Most prominent in the tropics and subtropics, in regions dominated by forest, shrub, or savannah vegetation
-characterized by rapid weathering of parent material, dissolution of nearly all minerals, and. speedy decomposition of organic matter
-minerals are leached out rapidly leaving behind iron and aluminium oxides and barren grains of quartz sand
Podzolization (wet, cool)
named after the gray soil that it produces. Occurs in regions having a positive moisture balance and involves considerable leaching. However, it occurs primarily in areas where the vegetation las limited nutrient requirements and where the plant litter is acidic, such as in mid- and high-latitude locales with a coniferous forest cover
-in these cool regions, chemical weathering is slow, but the abundance of acids, plus adequate precipitation, makes the leaching very effective
Gleziation (wet, cold)
constricted to waterlogged areas, normally in a cool climate. The poor drainage that produces the waterlogged environment can be associated with flat land, a topographic depression, a high water table, or various other conditions.
-prominent around the great lakes
-decomposition of organic matter proceeds slowly because bacteria are inhibited by the lack of oxygen in waterlogged sites.
-in such anaerobic environments, chemical reduction takes place. Reduced iron is more easily carried away so over time the iron poor soil turns gray.
Salinization (hot, dry):
in arid and semiarid climates, it is common to find areas of poor drainage. Intense evaporating water leaves behind various salts in or on the soil surface, sometimes enough to make the surface brilliant white.
-salts are mostly chlorides and sulfates of calcium and sodium. These are highly toxic to most plants and soil organisms—soil bears little life other than a few salt-tolerant shrubs and grasses
