ESS 210 Exam 1
Terms in this set (60)
What do soils do? Think ecosystem services.
Principle factor in hydrologic cycle.
Source of biodiversity.
Decomposition - "Natures recycling system"
What are the five soil forming factors? Be very familiar with these and how each individual determines or influences how a soil forms.
Parent material - comes from weathering of bedrock, accumulation of particles by wind, rain and ice. Residuum - Parent materials left behind. Bedrock that soil develops on can strongly influence the type of soil.
Time - Chemical/physical/fertility changes
Topography - Can effect formation, depth, age and amount of water received. Effective precipitation - proxy for age differentiation among soils.
Biota - Life, carbon cycle, detritus.
Climate - Temperature, precipitation and native vegetation all play a role here.
What are soils made of/what is their composition?
47% Mineral, 25% Water, 25% Air, 3% Organic Matter
Soils formed by material carried by gravity
What is the definition of a pedon?
Smallest 3-D body of soil that allows determination of all soil properties of that soil.
What is the definition of a profile?
Vertical section of soil explosion all layers of soil. (Soils vary in number of layers and their thickness) a 2-D vertical cross-section of a soil through all horizons.
What is the definition of a horizon?
Different in properties from the layer above and below it. A soil layer that formed parallel to the land surface during the natural development of the soil body.
Unconsolidated material above solid bedrock.
The A and B Horizons together of the single one of these that overlies the C horizon at a site.
The solid rock underlying unconsolidated surface material.
Define Mottling and what it means
Indicates drainage issues, the darker the soil, generally the more organic matter; the lighter the soil the saltier
Explain what colors mean in soils
Red means that the iron is oxidized and not hydrated, yellow indicates hydration and sometimes oxidation, gray indicates chemical reduction caused by wetness and lack of oxygen.
Spectral color of the rainbow, amount of yellow to red.
Ligtness or darkeness of the hue 0-black and 10 - white.
Brightness or purity of color. 1 - high grey low purity 8 - low grey, high purity
Mixture of different colors. Bright colors mixed with greys (low chroma) indicate drainage problems.
Explain 5 YR 5/6
Hue, Value, Chroma
What is a soil texture
Percentage of sand, silt, and clay in the soil.
What are the SUDA textural size classes?
Sand .05-2mm diameter
Silt .002 - .05 mm diameter
Clay <.002 mm diameter
What is soil structure?
The arrangement of soil particles into aggregates
Transported by river waters (alluvial Fans)
Define Marine Deposits
Soils produced by ocean waters
Soils transported by lakes
Define Eolian Soils
Also known as loess; wind blown silt from glaciated areas
Define Glacial Till
From Unsorted Glacial Ice
Define Glacial Outwash
From sorted Glacial Ice
Why is knowing a parent material important?
Often, knowing the parent materials characteristics are transferred to the minerals above it.
What are the Structural Classes
Structureless / single grained and massive
Why is structure important?
It helps to determine drainage of soil, aeration of subsoil, influences erosion, rooting medium
What is bulk density?
The mass of a dry soil sample per unit of bulk volume as compared with the mass of an equal volume of water.
What factors affect bulk density
Soil depth, OM Content, texture, structure, and traffic increases.
What are the typical values of bulk density?
What is soil porosity a measure of?
it is a measure of how much of the soil is open space.
What changes porosity?
Bulk density & Texture
What is pore size distribution and what is an optimal one?
Macropores > .06 mm
Micropores < .06 mm
Best to have a 50/50 mix
What is the relationship between porosity/bulk density and structure/texture?
The higher bulk density is, the less porous it will be. The more clay contained in soil the more porosity.
How does organic matter, Bulk density, and structure vary with depth?
A horizon has the most organic matter,
B horizon has the highest bulk density,
C horizon is massive structureless.
Granular exists at A horizon, Block like, prizm like, and platy are in B
What is the difference between gravimetric and volumetric soil water content?
Mass of dry soil is used in gravimetric. volume of soil is used in volumetric.
What are some of the unique properties of water?
High specific heat
Expansion at freezing
Slightly positive and negative ends.
Attraction of water to itself
Attraction of water to other substances or surfaces
The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension.
What is the concept of Soil Water Potential?
The work water can do as it moves from present state to free pool
What determines the energy potential of water?
What are the four components of soil water potential?
What is field capacity?
The greatest amount of water held against gravity when the Soil Water Potential is -10 to -33 Kpa
What is the permanent wilting point?
The amount of water held too tightly that plants cannot extract it. -1500 Kpa
What is gravitational water?
water drains freely through soil when the soil water potential is 0-(-33) Kpa
What is plant available water?
water in large micropores that can be extracted by plants when soil water potential is between -10 and -1500 Kpa
How does plant available water differ between soil types?
Loam has the largest amount of Plant available water.
How does water move in soil?
Water moves from high Soil Water Potential to low SWP
How does water move in saturated and unsaturated conditions?
Water in saturated conditions are mainly under gravity.
Water in unsaturated conditions are mainly influenced by adhesion and cohesion.
What causes flow constraints in the soil?
Water flows slower in fine textures versus compacted soils.
What controls infiltration and percolation?
Infilatration - Soil type, thickness, origninal water content, precipitation characteristics.
Percolation - Percolation rate controls infiltration rate.
Why is infiltration and percolation important?
When rainfall exceed infiltration surface ponding and runoff occur.
What is soil consistence or soil consistency?
Soil consistence - Soil science term for the degree to which a soil can resist rupturing.
Soil consistency - Engineering term for the degree to which soils resist penetration.
How is soil consistency and soil consistence measured?
Soil consistence - Unconfined compression test.
Soil consistency - Using the standard proctor test.
Why is soil strength important?
Cohesive soils are stronger
How do we measure soil strength?
Unconfined compression test.
What is liquefaction?
when a wet solid gets jarred and begins to behave as a liquid.