NRES 201 Exam 2 Study GUIDE
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School
University of Illinois, Urbana Champaign *
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Course
201
Subject
Geography
Date
Dec 6, 2023
Type
Pages
4
Uploaded by MateEnergy10704
Review Questions for Hour Exam 2 (Fall 2023)
Soil Physical Properties
·
How does the hydrometer method determine soil texture?
Hydrometer determines texture based on how fast particles settle.
·
How do bulk and particle densities differ?\
Bulk density includes organic matter, pore space, and soil soilds
·
How does bulk density affect root growth?
Bulk density restricts movement of the roots, and soil is more compact with root density because roots
cannot penetrate
·
What are the effects of soil compaction on particle density, bulk density, and percent pore space?
Soil compaction indicates higher bulk density and decreases total pore space
·
How is percent pore space calculated from bulk and particle densities?
Soil Porosity = ( 1 - (Bulk Density ÷ Particle Density) ) x 100
·
How do macro- and micropores compare for soil air and water movement?
Macropores drain freely and allow easy water movement
·
Why is tillage more detrimental to aggregate stability for Mollisols than for Oxisols?
Oxisols have higher hydrous oxide content which means they’re less depended on organic matter
Soil Organic Matter
·
What is soil organic matter and what are its functions?
Biomass, residue, humus: higher nutrient availability, allows soil to respond better to pH changes
·
How does residue decomposition vary with C/N ratio?
Higher c/n ratio decreases decompostion
·
How do soil orders vary in organic matter content?
fine textured soils have higher organic matter content:
Histosols, mollisols, entisols, alfosols
·
What effect has synthetic N fertilization had on soil organic matter levels in the Morrow Plots?
Increase organic matter depletion, increase residue carbon inputs
Soil Water
·
How do polarity and H bonding affect the properties of water?
H20 forms by covalent bonds, creates a vshape
·
What causes capillarity?
Molecules rise due to adhesion pulls itself up, cohesion water molecules attach to other water molecules
·
What affects the height and rate of capillary rise in soils?
Height increase with pore diameter,
·
How does water flow in relation to potential?
Water flows from high potential to low
·
What are the four potentials that determine the energetics of soil water? Which one is most
Important?
Matric (most important), osmotic, hygroscopic, gravitational
·
How is soil water classified with respect to saturation, field capacity, the wilting coefficient, the
hygroscopic coefficient, and oven-dryness?
·
How is gravimetric water content calculated?
=Wet weight - dry weight/dry weight
·
What two factors cause infiltration, and how do infiltration rates compare for fine- versus coarse-
textured soils?
Matric and gravitational potential, fine texture slow infiltration - coarse is fast infiltration
·
What distinguishes saturated from unsaturated flow?
Saturated is based on gravitational flow, unsaturated is based on matric flow
·
Why and how is water flow restricted in stratified soils?
·
How does water move by vapor equalization?
Moves from high humidity to low humidity
·
How do texture and organic matter content affect soil water availability?
Fine texture soils have more water availability and soils with organic matter content have higher soil
water availability
The Hydrologic Cycle
·
How has water management changed over time, and what is the major use today?
Adapt environment to culture: more tillage and irrigation
·
How is water balance estimated for a watershed?
·
How do foliar interception and runoff compare for a deciduous forest versus a corn field?
·
How does cover cropping help to increase soil water storage?
Cover cropping prevents evaporation, protects surface soil structure
·
What is water use efficiency, and how does it compare for arid versus humid regions?
plant dry matter produced per unit of water much lower for arid regions because evaporation
·
How can evaporation and transpiration be controlled?
Weed control, dry land
·
What are furrow, basin (flood), sprinkler, and drip irrigation? Which is most efficient, and why?
·
How do surface and subsurface drainage differ? Which is more important in Illinois?
·
How does soil type determine the agricultural need for tile drainage?
·
How does subsoil permeability affect tile spacing and depth?
Soil Aeration & Temperature
·
How are soils aerated?
Soils are aerated by different ways such as tillage, digging holes/poking holes to promote gas exchange
within the soils and the air above it. Aeration supplies O2 for respiration and removed CO2 and other
toxic gases thru mass flow and diffusion
·
How and why does soil air differ in composition from ambient air?
·
What changes occur when a soil is waterlogged?
Produces methane, hydrogen sulfide, ethylene, oxygen gas decreases, redox potential decreases
·
What is redox potential (
E
h
), and how does it relate to soil aeration?
When you lose/gain electrons. (oxidizing gains electrons, reduction gives election) important for soil
aeration because of microbial activities, mineral solubility.
·
How does soil temperature affect aeration status?
Low temperature limits activity, high temps stimulate O2 and CO2 production.
·
How do plants adapt to poor soil aeration?
Plants adapt to poor aeration by closing stomata which reduces photosynthesis. This limits their growth.
·
What are the two fundamental requirements that define a wetland soil?
Saturated near surface and O2 depleted from plant and microbial growth
·
What are three properties that can be used as hydric soil indicators?
Hydric soils are histosols and have periods of saturation that deplete O2 and lower redox. 3 properties
are organic matter content, gleying chroma, and nodules.
·
How does frost heaving occur?
Large pressures from water expanding when freezing. Liquid water below frot line expands in frozen
soils, causing stones and plants and fence posts. Can cause cracks in foundations
·
How effective is solar radiation for heating the soil?
Main source of heat for soils
·
How is soil heating affected by albedo and aspect?
Albedo is the radiation reflected by and surface and aspect
·
How do growing plants cool the soil?
Vegetation covers the soil from sunlight and creates insulating effect
·
How does evaporation cool a wet soil?
Evaporation cools soils because it consumes large amounts of energy, which means it losses heat
·
What can be done to manage soil temperature?
Practicing prescribe burning to heat the soil and mulch to cool them.
Colloidal Properties
·
What are the two sources of negative charge on clay minerals?
Ionic adsorption:
-
pH independent: isomorphous substitution (ionic substitution in the structure for Al3+
-
pH dependent:
·
Classify the following as 1:1, 2:1, or 2:1:1 clay minerals:
- Kaolinite
- Montmorillonite
- Vermiculite
- Illite
- Chlorite
·
Is this a 1:1 or 2:1 clay mineral, and where is the isomorphous substitution?
- (Al
2-x
Mg
x
)Si
4
O
10
(OH)
2
·nH
2
O
montmorillonite (Mg for Al)
- Al
4
Si
4
O
10
(OH)
8
no substitution, kaolintie (no swell)
- [K
2-x
(Ca,Mg)
x
](Si
4-y
Al
y
)Al
2
O
10
(OH)
2
·nH
2
O
(Al for Si) (illinite)
- Mg
n
(H
2
O)
6
(Si
4-x
Al
x
)(Al
2-y
Fe
y
)O
10
(OH)
2
·nHO
vermiculite (Al for Si) (Fe for Al)
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·
Is cation-exchange capacity (CEC) directly related to unit-layer charge?
CEC is not directly related. It is sum cations that can be adsorbed.
·
For what kind of soils would hydrous oxides be an important source of CEC?
Oxisols, ultisols, not present in illinois soil
·
How is CEC measured?
Measured by ammonium saturated soils and sulfuric acid to find the CEC. This is measured in
milliequivalents/100 grams
·
Which cation is held most tightly to exchange sites? Which is held least tightly?
- Ca
2+
2
- Mg
2+
3
- K
+
4
- Na
+
5 (less tight)
- H
+
1 (most tight) due to ionic radius
·
Which type of soil colloid is highest in CEC?
- Clay minerals
- Hydrous oxides
- Organic matter
·
Which type of soil colloid is highest in anion-exchange capacity (AEC)?
- Clay minerals
- Hydrous oxides
- Organic matter
·
What is the source of positive charge for AEC?
·
How does soil acidity affect CEC and AEC?
·
How does soil weathering affect CEC and AEC?
·
How are nonpolar organic compounds retained in soils?