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What are the five factors of soil formation?
Climate, organic matter, parent material, topography, and time.
Soils are used for what 5 things?
Construction, wildlife habitats, crops, fiber, and water shed.
What are the majority of minerals in a soil?
Aluminum, hydroxyl, and silicon.
What are the percentages of soil components?
Pore space 50% (Air:20-30%, Water: 20-30%) and soil solid 50%(Minerals: 45%, organic matter:5%).
What is a soil profile?
A vertical cross section of the soil exposing the various horizons.
What is a soil horizon?
A layer of soil approximately parallel to the soil surface, differing in properties and characteristics from adjacent layers below and above it.
What is an A horizon made up of?
Mostly surface minerals and sometimes organic matter.
What is an E horizon made up of?
Eluviation, it is a leached soil. Light in color.
What is a B horizon made up of?
Accumulation of clay, iron, and aluminum oxides.
What is a C horizon made up of?
Parent material, least weathered.
What is R horizon made up of?
What is an O horizon made up of?
Decaying plant residue (organic matter).
What are the soil horizons in order?
A, O, E, B, C, R.
What are the physical types of weathering that can effect soil?
- 1. Freeze/thaw
- 2. Heat/cool
- 3. Wetting/drying
- 4. Grinding action
- 5. Action of organisms
What are the types of chemical weathering that effect soil?
- 1. Solution
- 2. Hydrolysis
- 3. Carbonation
- 4. Hydration
- 5. Oxidation-Reduction
Define soil structure.
The manner in which soil particles are assembled in aggregate form.
What are the 6 different types of soil structure?
- Prismatic and columnar
- blocky, angular and subangular
- Granular and crumb
What types of factors affect soil structure formation?
- Clay and organic matter
- Particle orientation
- Shrinking and swelling
- Root forces
- Ice crystals
- Animals and insects
- Cementing agents
How do you calculate Bulk Density?
Mass/volume or g/cm^3
True or false: Bacteria are generally found in soils at numbers near 10^8 or 10^9 per g of soil.
What clay is made up of two silicon sheets and one aluminum sheet, is
high in shrink/swell properties, and has a cation exchange capacity of
60-100 cmol (+) per kg?
Soil organic matter and clay particles are both considered to be
colloidal. Between __________ is the generally accepted maximum diameter
for a soil colloid.
When present in abundance, which soil component contributes the most to the soil's cation exchange capacity (CEC)?
organic matter or humus
A 2:1 clay that is naturally high in potassium, exhibits minor
shrink/swell properties and would exhibit moderate CEC would
Name something that is classified as microflora.
Bacteria, root hairs, algae, fungi, actinomycetes, cyanobacteria, etc.
True or False: Autotrophic microorganisms obtain carbon from atmospheric CO2.
The fungal/root interaction so important to water and nutrient uptake in many plant species is:
True or False: Al+3 replacing Mg +2 or Si+4 replacing AI+3 in
the structure of a 2:1 clay mineral results in an increase in cation
exchange capacity and that process is called isomorphous substitution.
False! The valence electrons need to be the same size or smaller to replace the mineral.
Soil water content (by weight) at field capacity is 38% and at permanent
wilting point is 24%. The plant available water (by weight) of this
soil would be ______.
If the bulk density is 1.3 g/cm3, what is the plant available water percentage by volume (14%)?
Multiply the plant available water percentage (weight) by the bulk density to get the plant available water percentage (volume). 18.2%
How many inches of plant available water is held in 18 inches of soil (use information from the last two questions)?
Multiply the plant available water percentage by the amount of inches it is held in to get the amount of water available to plants in that amount of space. 18.2*18"=3.3"
If a soil has 3.3" of available water for plants, what type of soil would it be? a) Sand b) Sandy Loam c) Silty Clay Loam
c) Silty Clay Loam
A microorganism that gets its energy from organic carbon and uses O2 in respiration is classified as an:
Where do autotroph organisms obtain Carbon?
CO2. Energy from light or chemical oxidation or the atmosphere.
Where do heterotrophic organisms get their Carbon?
They get their Carbon from other organic carbon. Energy from oxidation of organic C.
How do aerobic organisms breath (respiration)?
They must use oxygen (O2).
How do anaerobic organisms breath (respiration)?
They use oxidized compounds that are not oxygen (O2).
What are oxidation-reduction reactions?
The transfer of electrons from one atom to another, changing the oxidation number of both.
How does the oxidation number decrease?
When the electron acceptor accepts an electron it becomes reduced. Thus, the oxidation number decreases.
How does the oxidation number increase?
When the electron donor gives up an electron it becomes oxidized. Thus the oxidation number increases.
True or False: Bacteria and fungi can be potentially devastating to crops, but strict
pH requirements for rapid growth minimize their numbers in most soils.
An organism that lacks a nucleus and membrane bound organelles is ________________.
A soil contains only the following exchangeable cations on the cation
exchange sites (in cmol (+) per kg): Ca=21.5, K=2.0, Na=0.5, and Mg=3.0.
H=3.0. What is the CEC of the soil?
30. Learn how to calculate base saturation.
If all of the CEC is associated with mineral particles, then what is the soil texture
of the soil with a 30 CEC?
-1/3 to -15 bar (-33 to -1500 kPa) is the range of water potential for:
Plant available water
Which of the following is not a benefit of soil microorganisms?
Increased soil pH.
What is a major factor contributing to poor or deteriorating soil aggregation through lower aggregate stability?
Loss of organic matter.
What is the soil moisture potential (pressure) at permanent wilting point?
The attraction of water molecules to other surfaces (e.g. xylem tissue, window pane, or a clay particle) is called:
Of the six major cations likely to be found in large amounts in acid soils, which are considered “acidic”?
H and Al
Which of the following descriptions most accurately represents a “B” horizon?
A horizon in which materials (such as iron and aluminum oxides) have accumulated due to leaching from the horizons above.
________________ describes a soil composed primarily of silt-sized particles that was transported by wind.
Which of the following equations best represents a dissolution reaction (solution)?
A) CaCO3 + H2CO3 à Ca(HCO3)2
B) 2Fe2O3 + 3H2O à 2Fe2O3∙(3H2O)
C) NaCl + H2O à Na+ + Cl- +H2O
D) 2FeO (ferrous oxide)+ O2 à 2Fe2O3 (ferric oxide)
C) NaCl + H2O à Na+ + Cl- +H2O
(this multiple choice question has been scrambled)
The bulk density of the A horizon of a soil consisting of 25% sand, 35% silt and 40% clay would be _____________ the bulk density of C horizon.
What is a benefit of having clay in a soil?
Increased water holding oapacity
True or False: Activities of microorganisms and plant roots generally reduce soil aggregate stability
According to Stoke’s Law, which soil separate measured for texture would fall the fastest?
The long-term effect of tilling (mechanically mixing) a soil on bulk density would be?
It increases bulk density by promoting microbial growth which decreased organic matter content
What components make a flooded B horizon in a soil become darker over time (more grey or bluish)?
Manganese is reduced from oxidized forms in the absence of O2
What is the typical range of bulk density for mineral soils?
1.1 – 1.6 g/cm3
Glacial till is an example of which type of parent material?
Platy, prismatic, blocky, granular, and massive are all examples of:
What is the size range for silt particles?
0.05 – 0.002 mm
two soil profiles, both from granite parent material. One is formed
under warm, semiarid grassland and the other in cool, humid pine
forest. Which soil would be most likely to develop an “O” horizon?
The soil of the cool, humid pine forest.
What is one disadvantage of single-grained (sandy) soils?
Lack of water holding capacity
What are the percentages of each component of an ideal soil?
45% Mineral, 5% Organic Matter, 20-30% Water, 20-30% Air
Rainfall, freeze-thaw cycles, types of vegetation, and leaching are all effects of which factor of soil formation?
and carbon dioxide accumulate in soils to different concentrations than
atmospheric levels. In which soil horizon would lower molecular oxygen
(O2) concentrations generally be measured?
A cube of soil 10 cm on a side weighed 1910 g after oven drying would have a bulk density in g/cm3 of (the particle density of the soil particles is 2.65g/cm3):