Chapter 6: Soil Ecology Flashcards
Give three ways in which rocks are formed.
Igneous rocks: rock formed from cooling magma
Sedimentary Rocks: layers of sediments in lakes/oceans put under tremendous pressure which consolidate into rocks
Metamorphic Rock: when either Igneous or Sedimentary are heated and put under pressure so that they transform into new rock
Give four ways parent material may be broken down or added to soil.
- Mechanical or Chemical Weathering
- Climate: temperature and rainfall
- Biotic factors: organisms
- Topography: slopes, runoff, rate of erosion
How does chemical weathering of parent material occur?
when rainwater containing dissolved carbon dioxide becomes carbonic acid and dissolves rock
What is the difference between till and loess?
Till is parent material added by rivers or glaciers
Loess is parent material added by wind
What role do biological growth and decomposition play in soil formation?
it helps break down parent material and affects the accumulation of humus (organic material in soil)
What role does climate play in soil formation?
it determines the rate of weathering of parent material and decomposition of minerals and organic matter, the leaching and movement of these which develops the soil layers
What role do biotic factors play in soil formation?
it is responsible for the organic matter in soil and the color of the surface and it influences the nutrient content in soil
How does topography affect soil ecology?
it determines how much water enters the soil, the rate of erosion and the downhill transport of soil material
How do young and old soils compare in terms of their fertility and why?
Young soil is more fertile because old soil has had long-time leaching of nutrients without replacement from fresh minerals
Characterize each of the soil horizons.
O: surface layer resting on a mineral layer composed of freshly, partially decomposed organic material that has not been mixed into the mineral soil (Oi: litter layer, Oa: humus layer)
A: accumulation of humus, loss of clay, inorganic minerals, and soluble matter by eluviation (leeching), minerals dissolved by water then readily available to plants
B: zone of extensive illuviation (deposit of minerals from A horizon
C: primarily weakly weathered material that resembles parent rock, little affected by soil forming processes
R: unweathered parent material or bedrock
What is the difference eluviation and illuviation, and in what soil horizons does each typically occur?
Eluviation is the loss of minerals/organic molecules through leeching (A horizon)
Illuviation is the deposit of the material that has been leeched from higher horizons (B horizon)
What kind of information can be gained from soil color?
what it is made of, presence of oxides, indicators of good drainage, aeration
How is soil color normally determined?
Standardized color charts; Munsell color charts
Characterize each of the following in terms of soil texture: gravel, sand, silt and clay
Gravel: particles greater than 2mm
Sand: 0.05-2mm, feels gritty to the touch
Silt: 0.002-0.05mm, feels like flour
Clay: must be seen with microscope
Give two important properties of the soil controlled by clays.
- Plasticity: the ability to change and retain shape when pressure is applied
- exchange of ions between soil particles and soil solutions used by plants
How does soil depth differ from one place to another?
Native grasslands: several meters deep Forests: relatively shallow Deserts: very shallow Bottom of slopes, level ground & alluvial (outwash) planes: very deep Ridge tops and steep slopes: shallow
What is meant by the terms “field capacity” and “permanent wilting point”?
Field Capacity: maximum amount of water soil can hold following drainage of gravitational water
Permanent Wilting Point: point where soil dries out to a point at which plants are unable to absorb enough water to replace that lost by transpiration
How do field capacity and permanent wilting point relate to available water capacity?
Available water capacity is the amount of water retained between the field capacity and the permanent wilting point
Give three factors that play a role in determining soil moisture regimes
Texture: intermediates are best
Amount of organic matter
Topographic position: affects movement of water on surface and within soil
What is soil moisture regimes?
the ability to retain moisture against drainage
With respect to soil drainage classes, what type of soil marks the beginning of wetlands?
somewhat poorly drained soils
What are micelles and what role do they play in soil chemistry?
Micelles: particles and complexes of clay and humus that hold ions
They affect the mobility of ions; prevent charged nutrient cations from leeching
Describe the structure of a clay molecule.
aluminum, silica and oxygen arranged in a complex tetrahedral fashion
What are isomorphous substitutions?
the substitution of one element in the arrangement without changing the structure
