Soils Test 1
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Major functions of soils in the ecosystem?
- 1. Recyler of Raw Materials
- 2. Medium for Plants
- 3. Regulate H2O supply
- 4. Habitat for Soil Organisms
- 5. Modifier of Atmosphere
Organic and inorganic matter with very small particle size and a correspondingly large surface area per unit of mass.
The capacity of a soil to return to its original state after a disturbance
A layer of soil, approximately parallel to the soil surface, differing in properties and characteristics from adjacent layers below or above it.
The more or less stable faction of the soil organic matter remaining after the major portions of added plant and animal residues have decomposed. Usually dark in color
The uppermost layer of an arable soil to the depth of primary tillage; the layer of soil sliced away from the rest of the profile and inverted by a moldboard plow.
- A soil separate consisting of particles less than 0.002 mm
- A soil textural class containing more than 40% clay, less than 45% sand and less than 40% silt
What three ways is the word mineral used in soil science?
- 1. as a general adjective to describe inorganic materials derived from rocks
- 2. as a specific noun to refer to distinct minerals found in nature such as quartz and fieldspars
- 3. as an adjective to describe chemical elements, such as nitrogen and phosphorus, in their inorganic state in contrast to their occurence as a part of organic compounds
Difference between mineral and organic soils?
- Mineral soils are predominated by weathered, inorganic materials.
- Organic soils are formed by decayed plant and animal residues.
- considers soils as a natural entity, a biochemically weathered and synthesized product of nature.
- soil genesis and development, profile formation, classification and description are studied.
Study of soils from the standpoint of higher plants. Emphasis on the role of soil in plant production.
- The combination or arrangement of primary soil particles into secondary particles, units or peds.
- Classified and characterized on basis of size, shape and degree of distinctiveness into classes (v. fine to v. coarse), types (platy, prismatic, columnar, blocky, etc.) and grades (structureless, weak, moderate, strong)
Soil structure v. soil texture?
structure is the way the particles are arranged together, while texture is the relative amounts of different sizes of particles
- The aqueous liquid phase of the soil and its solutes, consisting of ions dissociated from the surfaces of soil particles and of other soil materials.
- A more accurate name than soil water, because it contains hundreds of dissolved organic and inorganic substances.
Dispersion is caused by what elements?
- Sodium (this causes serious situations involving water movement and plant growth)
- K - to a lesser extent
- Dispersion is encouraged by high pH values
What elements are flocculating agents?
aluminum, hydrogen, magnesium or calcium
How can you reduce electronegativity?
- 1. Lower soil pH (replacing ions by hydrogen or aluminum will result in a lower pH)
- 2. Replacing the adsorbed ion with a di or trivalent ion such as Ca2+, Mg2+, or Al3+
- 3. Replacing the adsorbed ion with an ion of a smaller size
If a soil has a large quantity of quartz, what can that tell you about its age?
It's an old soil
If a soil has a lot of K, what does that tell you about its age?
It's a young soil
How old is a soil with a lot of Al or Al and K?
It's somewhere between young (K) and old (quartz)
How do you calculate the surface area of a sphere?
- divided by
- diameter of its smallest sphere
- should be in cm2
What did we use hydroflouric acid for in the mineral staining exercise?
To etch the sand particles
What did we use the sodium colbalti nitrate for in lab?
To stain sands and determine the amount of K in soil (it turns yellow)
Materials that contain hydrogen, calcium and aluminum are good at what?
Will clays be dispersed or flocculated in well-drained soils?
Dispersed means what?
Particles will be in suspension
Particles will settle out
The surface area of clay has a lot of (positive or negative) particles?
- This means positive charges will be attracted
What elements are the best choice for leaky ponds?
- Ca and Mg
- (HCl lowers the pH so quick that fish die, aluminum isn't so healthy)
The clay of a soil consists principally of what products?
the insoluble end products of the chemical weathering of the primary minerals from the silt and sand fractions of the soil.
T/F: The negative charges of clay surfaces store the nutrient anions liberated by the chemical weathering of silt and sand particles and also the nutrient cations that are added as fertilizers.
False. Clay stores cations (not anions)
Principal functions of clay in a soil?
- storage of plant nutrients and moisture
- cementation of groups of particles into soil aggregates
In what three ways may clay be characterized?
- 1. according to the amounts of moisture it will retain under different moisture stresses
- 2. according to the amounts of exchangeable cations it will hold
- 3. according to the energy with which it retains different cations
sand and silt consist of primarly what products?
discrete primary minerals
Sand and silt are too small to be i.d.'d by crystal shape, color, and hardness. How do we identify them?
Optical, by refraction, diffraction, the rotation of polarized light and fluorescence under ultraviolet light. We stained them in lab.
Where in the state would you find older soils?
Ozark uplift, you'll find quartz and various clays
Where would you find newer soils in MO?
Along the MO River
Do soils derived from loess and glacial till contain many non-weathered primary minerals?
The capacity of a soil to maintain its productivity under heavy cropping over a long period of years is associated primarily with what?
The percentage of nutrient containing minerals principally in the silt fraction of the soil
Size of sand particles
2.0 to 0.05 mm
Size of silt particles?
0.05 to 0.002 mm
Size of clay particles?
0.002 mm and less
Mineral fractions of soil, other than gravel and stones, divided into groups according to size are known as
Particle size analysis (or mechanical analysis) can be done by sieving and sedimentation. When would you use sedimentation?
With particles less than 0.05 mm.
What does Stokes Law of Sedimentation do?
- It relates the rate (velocity) that a particle will fall in a liquid to the size of the particle.
- (A particle falls in a viscous medium with an increasing velocity until the downward force is just balanced by the frictional resistance, after which the particle falls with a uniform velocity.)
You can use decantation, pipette sampling or the hydrometer to perform a quantitative separation by Stoke's sedimentation method. What did we do?
Used a hydrometer
During the sedimentation process, sand falls first (it's the heaviest). What were we left with after 40 seconds, and again after two hours?
Silt and clay after 40 seconds, clay after 2 hours
- textural class name for soil having a moderate amount of sand silt and clay
- Sand (23-52%) Silt (28 to 50%) Clay (7 to 27%)
How do you adjust your hydrometer reading for temp?
- For every degree above the reference temp, add 0.2 to the observed reading.
- For every degree below the reference temp, subtract 0.2 from the observed reading.
considers soils as a natural entity
considers from the standpoint of plants. emphasis on soil is its role in plant production
haven't been chemically altered
resulting from the decomposition of a primary mineral
a vertical section through all of the horizons and extending into the parent material
the unconsolidated matle of weathered rock and soil materails on the earth's surface
organic and inorganic matter with very small particle size and correspondingly large surface area per unit of mass
soft, friable, weathered bedrock that retains the fabric and structure of parent material but is porous and can be dug with a spade
upper and most weathered part of the soil profile (A, E & B horizons)
the uppermost layer of arable soil to the depth of primary tillage
- capacity to produce a specified plant or plants under a system of management
- expressed in yields
- the aqueous liquid phase of soil and solutes (aka water and dissolved salts)
- better term than soil water, because it contains more than just soil.
usually dark in color, organic matter after decomp
capacity to function within natural or managed boundaries, to sustain plant and animal productivity
relative proportions of various separates in a soil
capacity to return to original state after a disturbance
a layer of soil, approximately parallel to the soil surface, differentiated from adjacent layers above and below
quality of a soil that enables it to provide essential chemical elements in quantities and proportions for the growth of specified plants
If a soil has a pH of 6.0 what is it classified as?
If a soil has a pH of 7.0 what is it?
If a soil has a pH of 8.0, what is it?
How is the soil a modifier of the atmosphere?
- It can produce dust in the atmosphere
- evaporation of soil moisture is a major source of water vapor in the atmosphere (affects temp, composition and wx patterns)
How does the CO2 level and moisture percentage of air in soil pores compare with above ground atmosphere?
- Soil air generally has a higher moisture content than the atmosphere
- relative humidity of soil air approaches 100% unless it's very dry
- CO2 is usually much higher and O2 lower than those found in the atmosphere
The amount and composition of air in the soil is largely determined by what?
The amount of water in the soil
What happens to the air to water ratio from the surface to subsoil horizons?
Compared to soil surface layers, subsoils tend to contain less organic matter, less total pore space and a larger proportion of small pores (micropores) which tend to be filled with water rather than air.
What are the four major components (by volume) of a representative loam surface soil? Which components are more easily changed?
- Mineral (45%), Organic (5%), Water (20-30%) and Air (20-30%)
- Water and Air are most easily changed
unconsolidated and partly weathered materials accumulated by disintegration of consolidated rock in place
Poorly sorted rock fragments detached from heights and carried downslope (gravity)
organic deposits (peats)
unconsolidated soil material consisting largely of undecomposed or slightly decomposed organic matter accumulated under conditions of excessive moisture
alluvial deposits formed where a stream or river drops its sediment load upon entering a quieter body of water
fan-shaped alluvium deposited at the mouth of a canyon or ravine where debris-laden waters fan out, slow down and deposit their burdens
material transported and deposited by the wind and predominantly consisting of silt-sized particles
the irregular ridges much glacial till is deposited in
- material deposited in lake water and later exposed by lowering the water level or elevation of the land
- fresh water - comes from glacial lakes
- mainly in N. part of U.S.
conical hill or ridge of sand or gravel deposited in contact with glacial ice
long smooth cigar shaped low hills of glacial till with long axis parallel to the direction of ice movement
a narrow ridge of gravelly or sandy glacial material deposited by a stream in an ice-walled valley or tunnel in a receding glacier
5 major soil-forming factors on soil profile development
parent materials, climate, biota, topography, time
made from molten lava
weathered products of other rocks
both igneous and sedimentary
what types of rocks are most commonly found in southwestern Missouri?
sedimentary, mostly limestone and shale
List three examples of the physical weathering process?
shrink-swell, erosion-deposition, plant roots, earthworms, microbes
what types of weathering process usually dominate in arid areas? humid areas?
- arid - physical processes dominate
- humind, tropical areas - decomposition and recomination are most prominent
Examples of solubility changes in chemical weathering reactions?
- hydrolysis (water on microline)
- dissolution (gypsum dissolving in water)
- acid reactions (when carbon dioxide dissolves in water, the carbonic acid produced hastes the dissolution of calcite in limestone or marble)
examples of structural changes in chemical weathering reactions?
- hydration (ex: hydrated oxides of iron and aluminum)
- oxidation-reduction (Iron is oxidized from Fe (II) to Fe (III)
- Complexation (oxalic acide forms a soluble complex with Al from muscovite, destroying the structure and releasing dissolved ions of K)
eluviated horizon in the soil profile?
- E is the zone of max. eluviation
- eluviated = washed out
illuviated horizon in the soil profile?
- B is the zone of maximum illuviation
- illuviated = washed in
- organic layer in various stages of decomp
- (found in forested or forest/prairie)
top most mineral horizon - dark colored
- zone of max eluviation (washed or leached out)
- Lighter in color, not found in prairie
- zone of maximum illuvation (washed in)
- deposition of colloids, soluble minerals and particles to an underlying soil
- clay and aluminum oxides accumulate here
Unconsolidated, non weathered materials (usually parent material)
consolidated rock, with little evidence of weathering
How do you know the difference between master horizons, transition horizons and subordinate horizons?
- Master horizons - capital letter
- Transition horizons - combination of two capital letters
- Subordinate horizons - small letters after major horizon designation
- (subdivisions of subordinate horizons have numbers after small letter)
inherited soil properties
- color, texture, structure
- young soils get more inherited properties
aquired soil properties
clay accumulation, organic matter, drainage characteristics, etc.
- reaction of a chemical with water to form a chemical compound
- look for the dot in the product line - it says water is a part of the structure
- changes the solubility
- it's a reaction between mineral and water - water molecules split into their hydrogen and hydroxyl components and the hydrogen often replaces a cation from the mineral structure
- look for OH
- weathering is accelerated by the presence of acids, which increase the activity of hydrogen ions in water
- (look for acids: H2CO3; HNO3; H2SO4)
- Iron, Manganese, or Sulfur minerals expecially susceptible
- loss of electrons (oxidation), gain of electrons (reduction)
- water saturation means more reduction because you're pushing out the air
- water dissolves minerals by hydrating the cations and anions until they become dissassociated with each other and surrounded by water molecules
- look for combos to be split
- organic acid dissolution
- look for 2K+
Five soil forming factors?
- Parent Material
Limnic or sedimentary peat
includes anything that isn't moss, herbaceous or woody peat (excretions from earth worms, microbes fit here)
Types of alluvial (flowing water) deposits
- Flood plains (aka river bottoms - fertile because the water brings in new parent materials)
- Terraces (old flood plains no longer under frequent flooding)
- Alluvial fans (occurs when changes elevation)
- Deltas (extensions of flood plains, occur where two rivers or streams intersect)
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