Final Exam Flashcards
(108 cards)
1
Q
Brunisols
A
Less developed forest soils
Related to luvisols and podzols
Dependent on soil texture
2
Q
Brunisol Great Groups
A
Melanic
Eutric
Sombric
Dystric
3
Q
Basic Great Groups
A
Melanic
Eutric
4
Q
Great Groups with Ah
A
Sombric
Melanic
5
Q
Acidic Great Groups
A
Sombric
Dystric
6
Q
Great Groups without Ah
A
Dystric
Eutric
7
Q
Podzols
A
High precipitation
Highly acidic soils, enhanced weathering of primary minerals
Strong leaching = sandy
8
Q
Podzolic Diagnostic Horizon
A
Illuvial Ae above B B >10cm thick 7.5 YR or redder Coarse texture Coastal forests and areas
9
Q
Podzol Great Groups
A
Humic
Ferro-Humic
Humo-Ferric
10
Q
Humic
A
Organic Matter forms Bh
A lot of organic matter production
11
Q
Ferro-Humic
A
Bhf
Not as wet, not as dry, some organic matter, some Fe, not as dark, more red
12
Q
Humo-Ferric
A
Bf
Dry
Less intense weathering
13
Q
What soils do Eutric soils become?
A
Gray Luvisols
14
Q
What soils do Melanic soils become?
A
Gray-Brown Luvisols
15
Q
What soils do Dystric soils become?
A
Podozols
16
Q
Types of space in soil
A
Pore Space
Solid Space
17
Q
Pore Space
A
Gas or Liquid Void
18
Q
Solid Space
A
Mineral particles Organic matter (disregard
19
Q
Interactions of Solid Space and Pore Space
A
Open spaces called pores, pores fill with water (soil water), soil porosity influences soil water movement
20
Q
Macropores
A
> 0.08mm
Water drainage
Habitat for arthropods
Gas exchange
21
Q
Micropores
A
<0.1mm Water storage (where bacteria are)
22
Q
Porosity
A
Doesn’t change
Volume of the pores divided by the bulk soil volume
Total percentage, doesn’t tell if micro or macro pores
23
Q
Bulk Density
A
Soil Mass/Soil Volume Measured oven dry Changes as pore space changes - compaction increases bulk density Surface Soils = 1.1 - 1.4 Subsoils = 1.3 - 1.7
24
Q
Factors on Bulk Density
A
Texture
Aggregation
Surface
25
Texture and Bulk Density
Finer textures = lower BD
26
Aggregation and Bulk Density
More Aggregates = lower BD
27
Particle Density
```
Mass of particles divided by the volume of particles
Typically 2.65 g/cm3
Used with BD to caluculate porosity
Porosity = 1-BD/2.65 x 100
Influenced by structure and texture
BD increases, Porosity decreases
```
28
Adhesion Water
```
Water attracted to solid surfaces
Held by strong electrical forces (low energy)
Little movement - held tight by soil
Exists as film, unavailable to plants
Removed by drying in oven
```
29
Cohesion water
Water attracted to other water molecules
Held by H bonding
Major source of water for plants
Greater energy than adhesion water
30
Gravitational Water
Water under the influence of gravity
Moves freely due to gravitational forces
Greatest energy
Exists in macropores
31
Potential Energy
Systems tend to change from a state of high energy to states of low energy
Behaviour of an object within a system is dictated by potential energy
32
Water Potential
Way to measure current energy state of unit of water
| Water Behaviour
33
How does water flow in soils?
Upward and downward
Drier to wetter
Low concentration to high concentration
34
Soil Water Potential Types
```
Matric Potential
Gravitational Potential (usually 0)
Osmotic Potential (usually 0)
```
35
Matric Potential
Major force
Adhesive forces
Cohesive forces
As soil dries, decreases (negative number)
36
Soil Water Classification
Unavailable to Plants
| Plant Available
37
Unavailable to Plants
0 to -10 kPa
| -1.5Mpa to -100Mpa
38
Available to Plants
-10 kPa (field capacity) to -1500 kPa (Wilting point)
39
Sandy Textured Soil and Water
Low available water
| Large pores that cannot hold cohesive water, mostly gravitational
40
Clay Textured Soil and Water
Low available water
| Small pores mostly under wilting point
41
Loam Textured Soils and Water
High available water
Even pore distribution
Lots of capillary water
42
Volumetric Water Content
Volume of water in a given water of soil
| Amount of water
43
Gravimetric Water Content
Easiest, most used way
Mass of water in a given mass of soil
[wet soil (g) - drysoil (g)]/drysoil (g)
44
Infiltration
Water entering the soil from precipitation
45
Infiltration is affected by:
Structure
Texture
Existing Water Conditions
46
Infiltration Rate Behaviour
Highest when soil is very dry
| Decreases as soil becomes wetter
47
Effects of Soil Structure on Infiltration
Well aggregated granular and single grain have rapid flow
Subsurface structure has moderate
Massive structure and Platy have slower infiltration
48
Preferential Flow
Deposits surface chemicals to deeper soil layer
49
What affects saturated flow?
Soil texture, structure, existence of preferential flow channels
Moisture status of the soil
50
Calculated Hydraulic Conductivity
Rate at which water moves through a material
Saturated flow
Pore size decreases, Kstat decreases
51
Unsaturated Flow
Matric forces at play
| Moves from wet to dry
52
Aerobic Soil Respiration
Plant roots, soil bacteria and fungi
| Conversion of O.M. create gradients of oxygen and carbon dioxide
53
Anaerobic Soil Respiration
Bacteria can use compounds other than oxygen for respiration
| Preferable compounds are nitrate and ferric iron
54
Carbon Cycle
Conversion of soil carbon to carbon dioxide and methane
| Loss of carbon from the soil
55
Nitrogen Cycle
Conversion of soil nitrate to nitrous oxide and nitrogen gas (anaerobic)
Loss of nitrogen from soil
56
Colloids
Particles less than 1 or 2 micrometers
Very large surface area
Very reactive chemically (cation exchange, ionic double layer)
57
Components of Colloidal Fraction
Crystalline silicate clays
Non-crystalline silicate clays
Iron and Aluminium oxides
Humus
58
Building Blocks for Crystalline Silicate Clay minerals
Silicon Tetrahedron
| Aluminium octahedron
59
Crystalline Silicate Clay Minerals
Pure form have no charge, changes at sheet edges and has negative charge
60
Isomorphic Substitution
Tetrahedron - Al for Si
| Octohedron - Mg for Al or Zn for Al
61
Kaolinite
Bonding between layers are hydrogen bonds
No interlayer swelling
Little isomorphous substitution => lower negative charge
Lower surace area
1:1 sheet
Bonding between layers is hydrogen bonds (Strong)
62
Montmorillonite
```
2:1 clay
Extensive isomorphous substitution
Cations and water exist between unit layers
Swelling
Bonding between layers in cations (weak)
```
63
Illite
```
Isomorphic substitution (Si replaced by Al in tetrahedral sheet, Al substituted by Mg or Fe in octahedral sheet)
Charge deficiency is balanced by the potassium ion between layers
```
64
Cation Exchange Capacity
Colloids have large amount of negative charge, attract positive charge (cations)
65
Importance of CEC
```
Fertility issues
Acidity & liming rates
Pesticides
Contaminants
Base saturation
Chemical behaviour in soils
```
66
Common Soil Cations
Ca, K, H, Na, Mg, Al
67
Origin of Cations
Parent Geological Material
| Additions
68
Parent Geological Materal
Soil minerals
| Released through weathering
69
Additions
```
Atmospheric deposition (wind erosion, ash particles, cosmic dust)
Fertilization
```
70
Fate of cations
Added/released to the soil
Switches between soil solution and plant biomass before being leached out of the soil (only leached out of soil from soil solution)
71
Rules of Cation Exchange
Cation Selectivity
Cation Equivalence
Ratio Law
Complementary Cations
72
Cation Selectivity
Large cations are held more tightly than small cations
73
Cation Equivalence
High charge cations are held more tightly than low charge cations
Al>Ca>Mg>K>Na
74
Ratio Law
Any one cation can replace any other if its concentration is high enough (all are reversible)
75
Mass Action Rule (part of ratio law)
Al will always win when 1 to 1
| H will win when up agains 1000
76
Complementary Cations
The combined influence of charge equivalencies ion selectivity and complementary ions drive the exchange at cations
Lower charge gets knocked off easier
Generally cation with largest ionic radius and lowest hydration energies that absorb more strongly on the permanent charge sites
77
Quantifying CEC
Measuring positive charges of cation, quantifying amount of positive charges supplied by soils
78
Measuring CEC
1. Known volume/concentration of NH4
2. Replace all cations in soil with NH4
3. lush with K
4. Measure NH4 in leachate, NH4 concentration = TCEC
79
CEC and Fertility
CEC measures the total ability of a soil to retain cations
| Does not provide information about what types of cations are retained
80
Calculations using CEC
Base Saturation
| Percentage affects uptake by plants
81
Base Saturation
Measure of base cations located on exchange sites
82
Sources of Acidity in Soils
```
Carbonic and other organic acids
Accumulation of OM
Oxidation Reactions
Plant uptake of Cations
Free Al
Human Activities
```
83
Carbonic and Other organic Acides
Dessolved CO2 in rainwater
84
Accumulation of OM
Carboxyl group (COOH)
85
Oxidation Reactions
Microbial usage produces H
86
Plant Uptake of Cations
Removal of base cations
87
Free Al
Weathering
88
Human Activities
Acid rain is important one
89
Mineral Weathering and Aluminum
1. Weathering of Aluminum releases it into soil
| 2. Reaction of Al with H2O creates excess H in soil
90
Acid Rain
Fossil Fuel combustion creates NOx and SOx
| Dissolve in rainwater to produce nitric and sulfuric acids
91
Fertilization
Intentional
| Unintentional
92
Intentional Fertilization
Adding acidifying agents to alkaline soils
93
Unintentional Fertilization
Oxidation of Ammonium to Nitrate
| Removal of base cations by harvesting plants that took cations out of soil
94
Pools of Acidity in Soils
Active (Small/Reactive)
Exchangeable (Large/Reactive)
Residual (Largest/Unreactive)
95
Active Acidity
H in the soil solution
| Determines solubility of many substances in soil
96
Exchangeable Acidity
H &Al associated with colloidal cation exchangesites
97
Residual Acidity
Associated with structural H and Al in physillicate structures
Slowly released by weathering
98
Base Cations
Ca, Mg, K, Na
99
How do base cations act as bases?
Exchange places with H in solution
100
Leaching Losses of Base Cations
Acidifying processes continually add H with cations lost to leachingB
Gradual increase in soil pH as H dominates
101
Buffering Actions
Carbonate Buffering
| Aluminium Buffering
102
Carbonate Buffering
pH>8
Ca exchanges with H and Al
CO3 reacts with free H and Al
103
Aluminium Buffereing
pH<5
Al absorbs OH
Resists rise in pH
104
Soil Nutrients
Macronutrients
| Micronutrients
105
Macronutrients
Inhibited by low pH
106
Micronutrients
Inhibited by high pH
107
pH effects on Plants and Soils
Excess H = leaching loss of soil nutrients
Direct tissue damage
Change in soil bacteria
108
ALuminium Toxicity
Blocks Ca from entering into plants
Binds with Phosphorus in ATP
Restricts cell wall expansion
