Components and Functions of Soils
entisols
"baby" soils that have NO horizons
The two "subgroups" within the silicates
1) quartz 2) clay-forming minerals
Functions of Soil (6)
1. Medium for plant growth 2. Regulates water flow - primary filter of water as water moves into streams and rivers 3. Habitat for a wide variety of living organisms 4. Recycler of raw materials/organic matter, 5. Modifier of the atmosphere 6. Engineering medium
In a loam soil, what is the average percentage of the pore space that is filled with air?
50%
In a typical mineral soil in optimal condition for plant growth, approximately what percentage of the pore space would be filled with water and what percentage would be filled with air? 25% water & 75% air 25% water & 25% air 90% water & 10% air 50% water & 50% air 10% water & 90% air
50% water & 50% air
If we are looking at the total soil volume, pore space is ____% of the total volume, therefore, the air and water filled space would be ___% each of the total volume.
50%, 25%
Which of the following pH values represents a neutral condition? 5.0 6.0 1.0 10 7.0
7.0
The ___-horizon is dark due to the organic matter leaching from the organic horizon.
A
Which conatins more organic matter, A or B horizon?
A
Which contains more sand and silt, A or B horizon?
A
Soil horizon
A distinct layer within a soil profile that is generally parallel to the soil surface that is differentiated based on properties and characteristics of layers adjacent to it
Soil
A dynamic natural body having properties due to the combined influences of CLIMATE and BIOTA as modified by TOPOGRAPHY acting on Parent Material over TIME.
sandstone
A sedimentary rock formed from quartz particles and shale, which is formed from silicate clay minerals.
Metamorphic rock
A type of rock that forms from existing rock through the application of high pressure and/or temperature
List the 5 master horizons in order from top to bottom
A, E, B, C, R
Surface soil and _____ usually refer to the same layer within the soil. regolith parent material solum A-horizon B-horizon
A-horizon
Name the major components of a typical, moist surface soil and give the percentage of each component by volume.
Air (20-30%) in pore space Water (20-30%) in pore space Mineral (45%) weathered from parent material Organic Matter (5%)
_______ are found in areas that have a fair amount of effective precipitation and may support trees in some ecoregions and grasslands in others.
Alfisols
The ___-horizon is actually an accumulation of elements such as clay, salts, carbonates and some types of oxides.
B
This horizon may have an accumulation of clay.
B
Which contains larger aggregates, A or B horizon?
B
Which is more compacted, A or B horizon?
B
"Subsoil" is generally equivalent to which soil horizon?
B-horizon
An Introduction to Soils lab student has taken soil samples from an A and B horizon, but neglected to label the bags. Once in the lab, bulk density (Db) was measured and the student found the Db for soil bag 1 was 1.55 g/cm3 and the Db for soil bag 2 was 1.22 g/cm3. Of the soils, which do you suspect is the soil from the A horizon?
Bag 2 - The B-horizon tends to have more mass per volume than the A-horizon.
In the formation of igneous rock, why does "extrusive" magma, called lava on the surface, result in smaller particles (i.e., fine)?
Because it cools rapidly so that the crystals have less time to grow.
In the formation of igneous rock, why does magma that cools beneath the Earth's surface, called "intrusive", result in large particles (i.e., coarse)?
Because it cools very slowly so that the crystals have time to grow.
How can we can roughly estimate how "resistant" it may be to weathering based on the elemental composition of a mineral?
By knowing that, for the most part, bases (e.g., Ca, Mg, K) are easily weathered from minerals, leaving the more resistant ions and elements in the soil.
The ___-horizon is unconsolidated parent material that may also have an accumulation of salt.
C
_____ acts as a glue in the soil.
Clay
Feldspars, amphiboles, pyroxenes, and micas are all ________ minerals.
Clay-forming minerals
The ___-horizon is basically a bleached horizon that's usually found in old soils and in areas with high precipitation.
E
Which is better for landscaping purposes (i.e., plantings), subsoil or topsoil?
For the most part, there are fewer nutrients associated with subsoil, therefore it is not nearly as good for landscaping purposes as topsoil.
________, like table salt (NaCl) and sylvite (KCl), are very soluble and ionize readily in water.
Halides
Arrange the following mineral groups in order of most to least soluble: sulfates, halides, phosphates
Halides Sulfates Phosphates
_______ is a plant essential nutrient, but is not a base cation and is not easily lost from the soil.
Iron
Why is the A horizon darker than the B horizon?
It contains more OM
Are ultisols found in grasslands?
No, ultisols are considered soils of forests.
Pedosphere
Outermost layer of the earth that is composed of soil and subject to soil formation processes.
The ____-horizon is the rock material which may or may not be the actual parent material.
R
Are spodosols found in Texas? Why or why not?
Spodosols are soils of cool climates, therefore they are not found in Texas.
soil pedon
The smallest volume of what can be called a soil, 3 dimensional section, ranges from 1 to 10 square meters, used as a way to "section" soil for describing it
What is the modifying soil forming factor?
Topography (relief)
soil solum
Upper horizons of soil in which most roots are contained, usually consists of A and B horizons (sometimes part of C horizon)
Which of the following is not considered one of the five major factors influencing soil formation? Parent materials Topography Climate Living organisms Valence state
Valence state
______ soils shrink and swell depending on how wet or dry they are.
Vertisol
soil profile
a 2D vertical section through a soil showing its succession of horizons and extending into the parent material
Aggregate
a collection of soil particles and OM that are bound together by some organic material such as roots, fungus, or hyphae
Ultisols are generally older, so they have few base cations remaining, making them _______.
acidic
The major components of the typical moist surface soil are mineral matter, organic matter, water, and _____. carbon dioxide rock air primary minerals humus
air
The pedosphere interacts with the _______ through gas exchange and through the exchange of energy in the form of solar radiation
atmosphere
Of the following elements, which is not a plant essential base cation? a. Mg2+ b. Fe2+ c. Ca2+ d. K+
b
For the most part, ______ (e.g., Ca, Mg, K) will be easily weathered from minerals, leaving the more resistant ions and elements in the soil.
bases
Why does the B-horizon tend to contain more clay than the A-horizon?
because clay particles are so small that they tend to be leached into the B horizon from the A horizon, leaving more sand and silt in that A horizon
A rough relationship between where the ecoregions lay and coverage of soil orders exists due to regional differences in ______.
climate
One of the active factors in soil formation is _____. weathering climate parent material time topography
climate
Precipitation is an example of _____ activity in the formation of soil.
climate
The soil solum is the parts of the soil that are actually affected by
climate
What are the active soil forming factors?
climate and biota
Water is flowing through a soil with a granular structure and encounters a soil with a platy structure. Water flow is likely to ___ once it reaches the platy structure.
decrease
Why are clay forming mineral silicates more prone to weathering than quartz silicates?
due to the bases that are part of the mineral composition of clay forming minerals
In regard to igneous rock, finer grains are indicative of ______ rock, while coarser grains are indicative of _______ rock.
extrusive, intrusive
These mineral types are the most prone to weathering.
halides
Regolith
heterogeneous, unconsolidated material above the bedrock or R horizon that extends from the top of the A horizon all the way down to the bottom of the C horizon
In aridisols, there is a ____ concentration of base cations due to the lack of rainfall.
high
Oxides consist of iron and aluminum oxides and __________.
hydroxides
Rattlesnake Mountain, has an intrusive feature formed during the Oligocene in the Big Bend region. This is a(n) ___ rock type.
igneous
Rocks are assemblages of minerals and there are three overarching types:
igneous, sedimentary, and metamorphic
Apatite is relatively _______ in its native form and therefore has little ability to provide phosphate to plants.
insoluble
Of the eight elements that are the most prevalent in the Earth's crust, which four are considered "essential" nutrients, needed for growth and reproduction?
iron (Fe) calcium (Ca) magnesium (Mg) potassium (K)
Water flow will likely slow somewhat once it encounters a soil structure that has _____ aggregates with a tortuous path.
larger
Once water encounters a restrictive layer it primarily will continue a _____ flow.
lateral/horizontal
The A-horizon has ____ mass per volume than the same volume in the B-horizon.
less
The A-horizon is generally _____ compacted than the B-horizon.
less
If we were to take the limestone from around San Antonio and apply high pressure and/or temperature we would have a ______________ rock called marble.
metamorphic
As a soil ages, especially in warm wet areas, _______ will be the "ultimate weathering product", that is, this is all that remains in the soil when it is very old or senile.
oxides
These mineral types are the least prone to weathering and will be the ultimate products in a senile soil.
oxides
These minerals are the most resistant to weathering.
oxides
In the Earth's crust, what eight elements are the most prevalent?
oxygen (O) silicon (Si) aluminum (Al) iron (Fe) calcium (Ca) magnesium (Mg) sodium (Na) potassium (K)
Both precipitation and temperature will be active in the weathering of ______ material to form soils.
parent
What is the passive soil forming factor?
parent material
If a student digs up a three-dimensional soil monolith that is a total representation of the soil, this is considered a(n) ____.
pedon
A student cuts down through a soil and exposes all of the horizons for study. This would be an example of a(n) ___.
profile
Name the primary silicate mineral that is resistant to weathering and dominates the sand and silt fractions of most soils.
quartz
Of the two "subgroups" of silicates, _____ is extremely resistant to weathering and dominates the sand fraction of the soil.
quartz
In aridisols, there is not a lot of differentiation within the soil column due to the lack of _______.
rainfall
Igneous rock
rock material that is formed from the cooling of molten magma and depending on the rapidity of hardening, the size of minerals will be determined
Sandstones are good examples of _________ rocks.
sedimentary
vertisols
shrink-swell, clay-rich soils that can cause instability of structures
A subgroup of these types of minerals are prone to weathering due to the concentration of base cations found in the structure.
silicates
Soils as a medium for plant growth provide all of the following except _____. nutrients physical support water silicon & aluminum oxygen
silicon & aluminum
The A horizon generally has _______ aggregates than the B horizon because there's less clay in the A horizon than in the B horizon.
smaller
State the general characteristics necessary for soil to support plant growth.
support nutrients and water
The soil solum consists of _____. : surface soil only subsurface soil only surface & subsurface soil A, B, & C horizons
surface & subsurface soil
Earth's permeable near-surface layer that runs from the tops of trees down to the bottom of our groundwater, where rock, soil, water, air, and living organisms interact and where we see the recycling of nutrients and these complex interactions regulate the natural habitat and determine the availability of life-sustaining resources, including our food production and water quality.
the critical zone
the part of the Earth's environment in which humans interact, where "rock and life meets"
the critical zone
effective precipitation
the precipitation that actually infiltrates the soil and percolates down through the soil profile (i.e., the horizons)
Sedimentary rock
type of rock formed through the deposition, cementation, and hardening of deposited materials or the evaporation of water
limestone
type of sedimentary rock consisting of CaCO3 (calcite)
Carbonates have carbonate ions (i.e., CO32-) as one of the chemical constituents and are somewhat soluble in _____ acids.
weak
