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RENR 210 > MIDTERM 2 > Flashcards

MIDTERM 2 Flashcards

1
Q

What is a thin section analysis?

A

Historical technique
Soil cast in resin then cut into thin sections (<0.01mm width)
Allows light to penetrate and see details through it
See rocks/ceramics

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1
Q

What is a scanning electron micrograph?

A

Modern technique
Soil encrusted in thin layer of gold
Bombarded with electrons, the reflection of which produces the image
<0.01mm - 1um
for the examination and analysis of micro- and nanoparticle imaging characterization of solid objects

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2
Q

What is the importance of porosity>

A

Water movement (infiltration)
Water availability (amount stored for plant use)
Root growth (easiest growth through pore space – decreased resistance)

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3
Q

What is porosity/VS/VP?

A

Porosity(%) = pore space: the relative proportion of a volume of soil that is filled by air and water
VP: volume of pores (air and water)
VS: volume of solids (mineral and organic)

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4
Q

What is soil bulk density?

A

Density = mass per unit volume
Bulk density = mass of soil per unit of volume

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5
Q

What are 3 factors affecting bulk density?

A

Porosity: increased porosity = decreased bulk density
Texture: increased clay = decreased bulk density
Organic matter content = increased ogm = decreased bulk density

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6
Q

What is field capacity?

A

-33kpa

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7
Q

What is wilting point?

A

-1500kpa

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8
Q

What is the hygroscopic coefficient?

A

-3100kpa

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9
Q

What are the water potentials?

A

Superfluous (gravitational) water = 0 to -33
Available water = -33 to -1500
Unavailable water = -1500 to -3100
Hygroscopic water = -3100 to solid

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10
Q

How do sandy soils affect FC, WP and AW?

A

Sandy soils: low porosity and large pores
FC = low WC
WP = very low WC
AW = low

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11
Q

How do clay soils affect FC, WP and AW?

A

Clay soils: high porosity and fine pores
FC = high WC
WP = high WC
AW = low to medium

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12
Q

How do loam soils affect FC, WP and AW?

A

Loam soils: range of pore size
FC and WP = low to medium WC
AW = high

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13
Q

How does Ogm affect WC and storage?

A

increases both

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14
Q

What is infiltration rate?

A

= rate of movement of water into soil pore space

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15
Q

How do soil structures affect infiltration rate?

A

Coarse soil increases it, fine soil decreases
Granular: rapid flow, small round peds
Blocky: moderate flow, angular peds
Prism: moderate flow, salt crust, osmotic potential is high
Platy: slow flow, horizontal peds

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16
Q

Macro vs meso vs micro water capacity

A

Macro/transmission pores = 50um, drained at FC
Meso/storage = 0.5-50um, available water holding capacity
Micro/residual pores = <0.5um, mostly unavailable water

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17
Q

What is hydraulic conductivity?

A

measure of how easily water can pass through soil or rock: high values indicate permeable material through which water can pass easily; low values indicate that the material is less permeable
Darcy’s law
High K to low: coarse sand > organic matter > Bt (blocky) > Ae (has plates, slows water movement)

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18
Q

Ground water vs water table vs vadose zone vs capillary zone

A

Ground water: saturated zone

Water table: upper limit of the groundwater

Vadose zone: zone of unsaturated material above the water table (surface to groundwater)

Capillary fringe: zone of capillary rise (ground water seeps up from a water table by capillary action to fill pores)

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19
Q

What are the 3 types of weathering?

A

Physical: disintegration, freeze/thaw cycles
Chemical: decomposition, molecular changes (water is universal solvent)
Biological: decomposition mediated by organisms, done by enzymes and organic acids

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20
Q

What are the 5 primary minerals?

A

Quartz: SiO2 – silicate framework (sand)
Muscovite (white mica)
Biotite (black mica)
Feldspar: Na, K, Ca, Mg are the base cations, bonded to a silicate framework
Albite (Na feldspar)

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21
Q

What soil texture is a primary mineral?

A

sand and silt

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22
Q

What primary minerals are most to least hard?

A

Quartz>feldspar>micas

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23
Q

What soil texture is a secondary mineral?

A

clay
Soil separate
Particle size is <2mm
Textural class
Secondary mineral
Component of the colloidal fraction of soils (soil colloid)

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24
What are colloids?
a homogeneous mixture consisting of ultramicroscopic particles of one substance dispersed through a second substance. Colloids include gels, soils and emulsions: the particles don’t settle and cannot be separated out by ordinary filtering or centrifuging like those in a suspension Particles <1-2um behave as colloids Total SA ranges from 10-1000m2g-1
25
What is the structure and function of colloids?
Internal and external surfaces have electronegative or electropositive charges (negative charge is dominant) Each micelle adsorbs (passes through membrane of cells) 1000s of hydrated Al, Ca, H, K, Mg, Na ions (enclosed within several water molecules)
26
What is the cation exchange?
occurs when ions break away into the soil solution and are replaced by other ions
27
What is the ionic double layer?
negative charged micelle surrounded by a swarm of cations
28
What are minerals?
composed of different elements, impart properties to soil
29
What rock types are there?
igneous, metamorphic and sedimentary (different types have different types of minerals in them
30
What is mineral soil?
decomposed rocks
31
What are the 4 components of the colloidal fractions?
1. Crystalline silicate clays: phyllosilicates = aluminosilicates (dominant colloid in AB soils) 2. Non crystalline silicate clays (amorphous) – for instance, allophane and imogolite that are both present in volcanic soils 3. Fe and Al oxides: fe adna Al atoms connected to O2 atoms and hydroxyl (OH) groups: may be either amorphous or organized in crystalline sheets – mostly present in more weathered soils (ex. podzols) 4. Humus: OgM – functional groups R-OH
32
What are the building blocks of silicate clay minerals?
Silicon tetrahedron – silicon and oxygen with silicon being the central cation Aluminum octahedron – hydroxyl and aluminum (central cation) Clay = 2 tetrahedral sheets outside a octahedral sheet (2:1 or 1:1 = 1 of each)
33
What is kaolinite?
Secondary clay mineral (phyllosilicate) Non expanding clay (no shrink swell) 1:1 Common in old soils (AUS) Silicate framework (hydrophilic) Hydrogen bonding between layers and no interlayer swelling Little (low) isomorphous substitution – poor fertility D spacing = 0.72nm Good for construction (bricks), ceramics and magazines glossy coating 2-4 CEC
34
What is d spacing?
the distance from the top of one platelet to the top of the next platelet
35
What is montmorillonite?
Silicate framework (theoretical unsubstituted) Extensive (high) isomorphous substitution Water and cations exist between unit layers – interlayer bonding by cations (weak to no bonding) High level of shrink swell with wetting 2:1 secondary clay mineral (phyllosilicate) Common in young soils (AB) 1-2 nm d spacing No attraction between the platelets – water can get into the interlayer and cause swelling (interlayer expands and contracts) Good for nutrient retention, increases CEC, can be used in construction for sealing pipes, irrigation and wells 80-160 CEC
36
What is illite/chlorite?
2:1 Some (medium) isomorphic substitution but charge satisfied by potassium Fine grained mica Low shrink swell Illite: forms in potassium rich environments (calcareous soils) Chlorite: lots in AB cause of magnesium rich PM (calcareous soils) Lots in AB because of potassium rich PM and calcareous soils Cation bridging 20-40 CEC
37
What are the 2 sources of charges?
Isomorphous substitution (permanent charge) 2:1 and 1:1 clays Not pH dependent Hydroxyls (OH-) or other functional groups (non permanent charge) releasing/accepting H+ ions pH dependent Common source of charge on: organic matter, iron and aluminum oxides and non-crystalline silicates
38
What has more CEC?
OgM and increased fine texture
39
What is cation exchange capacity?
a measure of the total negative charges within the soil that adsorb plant nutrient cations such as Ca, Mg, K, etc. – it is a property of a soil that describes its capacity to supply nutrient cations to the soil solution for plant uptake Modifies chemical behaviour in soils Increased CEC = increased fertility Decreases with increasing weathering
40
What is base saturation?
degree to which exchange sites are occupied by Ca, Mg, Na, K (influences pH of soil and are plant nutrients) – increases with increasing sediment geology
41
What does CEC do?
Diffuse ions in solution – free in solution Outer Sphere complexes (exchanged with ions in solution) Inner Sphere complexes represents atoms that are covalently bonded with mineral structure – only released through weathering
42
The ease of cation replacement depends on what?
Valences (primarily): higher valence cations can replace cations of lower valence Ion size: cations with smaller hydrated radius have greater replacement power Relative amount: high concentration of Na can displace Al Li
43
What is anion exchange caused by?
caused by protonation of hydroxyl groups – increases with decreasing acidity (excess H+) and increases with weathering
44
What are the 4 principles of ionic exchange?
Reversible reactions Charge balance Ion selectivity (3a) = concentration
45
What is the optimal pH for ag soils?
Optimal pH = 6.5 for agricultural soils (increases nutrient availability and allows microbes to thrive better) In ag soils, affected by microorganisms (fungi and bacteria) and available nutrients
46
How do you adjust pH?
lime/limestone
47
What is soil reactivity?
48
What are the affects of aluminum on plants?
Very toxic to plants Can acidify soils under certain conditions because it reacts with water to form aluminum hydroxide (releases hydrogen into the soil) Releases 3 H
49
Active vs exchange vs residual activity
Active activity: H in soil solution, measured with a pH meter Exchange activity: Al and H on exchange sites, measured by extraction (with CaCl2) Residual activity: Al and H bound (trapped - might be released with some weathering) in non-exchangeable forms on clay surfaces, non-measurable
50
Increased CEC affects what?
Increased CEC = increased pH = increased retention = more deprotonation (loose H = increase space to hold nutrients) = more negative charges on soil particle
51
Leaching leads to what?
Leaching = eutrophication – doesn’t go to crops and therefore they can’t retain nutrients
52
What is soil reactivity?
the ability of certain elements or ions in the soil to be replaced or exchanged with other ions in the soil solution (most common: Ca, Mg, K, Na)
53
What is the soil buffering capacity?
the soils resistance to changes in pH when an acid (such as hydrogen ions, H) or a base (Hydroxide ions, OH) is added to the soil – measures the soils ability to maintain a relatively stable pH level even when external acids or bases are introduced Higher with higher base saturation and CEC High in chernozem, medium in luvisol, low in brunisol
54
What are some consequences of soil acidity on plant growth and soil health?
Nutrient availability Microbial processes Restricted plant diversity Soil erosion
55
What are some soil acid forming processes?
carbonic acid, acids from biological metabolisms (decomposition), oxidation of N, oxidation of S, plant uptake, acid rain
56
What is acid rain caused by?
sulfur dioxide and nitric oxide combine with water and oxygen in the air to for sulfuric acid and nitric acid (increase of H) – due to high population, industry and vehicle traffic Not too much of a worry in AB as we have calcareous soils (alkaline) Slightly more in edmonton, calgary and fort mac
57
Salinity and sodicity promote what?
***salinity promotes soil flocculation ***sodicity promotes soil dispersion (deflocculation)
58
What is electrical conductivity?
concentration and composition of all dissolved salts (over 4dS/m = plants suffer osmotic stress)
59
Where are salt affected soils in Canada, what are the most common and how do salts move?
30% of canadian prairie region considered saline (salty – solonetzic soils) Due to natural or anthropogenic activities Most common salts in AB are NaCl and MgSO4 Salts move by leaching or capillary action
60
Why is a salt crest bad?
makes hard for water infiltration and seed germination to occur
61
What are some ways of fixing salt affected soils?
leaching, improved drainage, gypsum application and amending with organic matter

RENR 210 (3 decks)

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