Lecture 13-15 Flashcards
1
Q
What are the 4 phases of soil formation?
A
Bedrock begins to disintegrate
Organic materials faciliate disintegration
- appearance of OM
Horizons form
- appearance of A horizon
- Parent material and C horizon
Developed soils support thick vegetation
- A, B, and C horizon
2
Q
What is the O horizon?
A
OM layer on the top
Also known as LFH horizon
- L = litter
- F = fiber material
- H = humus (relates to the decomposition state of the litter)
3
Q
What is the Ah horizon?
A
Enrichment of humus
4
Q
What is the Ae horizon?
A
Depletion of humus and particular soil minerals (clay minerals)
The e represents eluviation (washing away)
5
Q
What is the B horizon?
A
There is a huge variety
However, mainly minerals
6
Q
What is the C horizon?
A
Soil particles and bedrock material
7
Q
What horizons is the topsoil made up of?
A
LFH and Ah horizon
8
Q
What horizons is the transition layer made up of?
A
Ah
9
Q
What horizon is the subsoil made up of?
A
Horizon B
10
Q
What horizon is the weathered/solid bedrock made up of?
A
Horizon c
11
Q
What are the 4 soil forming processes?
A
Additions: precipitation (with included ions and solid particles), OM, human processes (fertilizer, grazing,), feces, etc.
Transformations:
- OM –> humus
- Primary minerals –> secondary minerals, hydrous oxides, clays, ions, H4SiO4
Transfers downward: humus compounds, clays, ions, H4SiO4
Transfers upward: Ions, H4SiO4
- upward direction of ions is from capillary action from water table (groundwater rises and carries dissolved ions, some of these ions may be left behind within the soil profile)
Removals: ions, H4SiO4
- due to human activity (harvesting, etc.)
- leaching to groundwater
- erosion
12
Q
What are the 5 soil forming factors?
A
Parent material
Climate
Organisms (including humans)
Topography
Time
13
Q
Parent material
A
Substrate from which the soil starts to develop
There is residual parent material (such as rocks) but also transported parent material
Chemical and mineralogical composition of the parent material influences degree of weathering and soil chemistry
14
Q
What is residual parent material?
A
Bedrock
- can be igneous or sedimentary
Igneous
- Canadian shield mostly formed of igneous rock types
Sedimentary
- more prone to weathering
- Saint-Lawrence lowland is mostly sedimentary rock
15
Q
What is transported parent material?
A
Parent material that was transported by water, gravity (landslides), ice (glaciers), and wind
16
Q
What parent material do water transported rocks and minerals form into?
A
Can be deposited in:
- Lakes = lacustrine
- Streams = alluvial (fluvial)
- Oceans = marine
17
Q
What parent material does gravity transported rocks and minerals form into?
A
Colluvial
18
Q
What parent material does ice transported rocks and minerals form into?
A
Can be deposited By
- Ice = till, moraine
- water = outwash lacustrine, alluvial, marine
- wind transpored = eolian
19
Q
What parent material does wind transported rocks and minerals form into?
A
Deposited by wind = eolian
20
Q
How are floodplains created?
A
Floodplains are created when the high flow recedes (high flows have a lot of sediment and OM transport)
21
Q
What happens to soil growth when there are a lot of flooding events?
A
Soils grows upwards rather than downwards
- layers refer to flooding events
Example deltas
22
Q
What are moraines?
A
Transported by ice (glaciers)
Glaciers flow down from mountains into valleys
Mixture of fragmented rock that is transported down
Frontal moraines –> glaciers are pushing earth forward
23
Q
What is a glacial till?
A
What has been lying below a glacier
Glacier eroded the rock below it
Important in regions that were covered by ice sheet during last glaciation (example Saint-Lawrence lowlands)
24
Q
Dust as parent material (eolian)
A
Dust plumes can be transported across the Atlantic ocean and deposited on the Amazon rainforest
Dust becomes parent material
Important role as fresh parent material and nutrients in old and higher weathered soils such as Hawaii
25
What is a loess?
Transport of dust that is so intense that it creates a parent material similar to alluvial plain
Created during the last Ice Age
Very fertile soil since it has good soil hydrological properties (good at providing water for plants)
Provides habitats for birds
26
What are the factors that make climate an important soil forming factor?
Precipitation and temp.
27
How does temperature and moisture impact clay content?
The higher the soil moisture, the higher the temp. --> the more clay content you can find since weathering processes of primary minerals into secondary minerals are accelerated
28
Explain the transition of soil properties/type according to climate
Polar desert --> little chem. alteration
Tundra: Appearance of illite-montmorillonite
- cold and dry = no soil dev. and very little chemical interactions
Taiga: formation of 1:1 clay minerals
- precipitation and temp. increases slightly --> smectite and kaolinte formation
Tropics
- higher precipitation and temp. --> development of deep tropical soils
- top layer called oxisols because dominated by iron and aluminum oxides
- formation of sesquioxides
29
How do organisms influence soil-forming factors?
Vegetation
Soil organisms
Human activities
30
How does vegetation impact grasslands?
Thick Ah horizon since grass vegetation has a very dense and thick rooting system. When they die they add a lot fo OM to the soil and into deeper soil layers
Absence of Ae horizon
CaCO3 closer to surface
31
How does vegetation impact forests?
Rarely water limited, therefore thin Ah horizon and leached Ae horizon (more prec.)
Thick B horizon
Higher output pathways --> higher rates of decomposition (because higher moisture/higher erosion and leaching)
- erosion, leaching, and decomp. of SOM is higher in forests than in prairies since it has more precip.
32
How does vegetation impact deciduous ecosystems?
Higher CEC
Higher pH (less acidic)
- Because litter decomposes much quicker in deciduous forests (thereby reusing the cations that are stored within the litter)
- Coniferous trees shed waxy needles that decompose much more slowly
33
How did earthworm invasion impact soil profile in New Brunswick?
Disappearance of F and H layer
Mineral and humus layer became well mixed (Ah horizon)
34
How do humans impact soil-forming factors?
Changes vegetation cover (grasslands and forests are converted to agricultural land)
Drainage of wetland and peat soils
Addition of fertilizers to soil
Atmospheric deposition of pollutants (acid rain, N deposition)
Transport of soil for agricultural purposes
35
How does topography impact soil-forming factors?
Determines drainage class and accumulation and removal of material
36
Explain the erosion, accumulation, and soil moisture on a hill
On a slope: A and B horizon much more shallow since it is eroded away
- restricted drainage
- luvisols
On the top of the hill:
- water table is deep (does not influence as much soil formation)
- free drainage
- gleysols
At the bottom of a hill
- water table is much higher, therefore has an influence on drainage
- more diverse and complex soil horizons
- poor drainage
- organic soils
37
How does time impact soil-forming factors?
Slow impact of processes on parent material leading to steady state
Where soil-forming factors have changed through time, age of soil may be important explanatory factor, rather than present-day conditions
That is why it is important to have geological knowledge of the area you are working in
Examples: Montreal
- soil developed when the glaciers receded 10 000 years ago and left behind glacier till which become the substrate of soil development
38
Explain soil development over time on Loess
Fresh loess deposited:
- relatively unweather loess
As time goes on
- beginning of accumulation of CaCO3 + CaSO4 at the surface
- that layer begins to deepen
- formation of A horizon that progressively deepens as well
- LFH horizons (more vegetation)
10, 000 years
- A horizon
- Bt: accumulation of clays
- Bc
- Ck
Soil grows in both direction (addition on the top and transformation downwards)
39
What are the benefits of factorial approach to soil formation?
Reduces complex, spatially-variable soils to simple environmental relationships
Allows predictions of soil types in the field and properties, base don easily measured factors
Allows easy mapping of soils, from easily determined factors
40
What are the limitations of factorial approach to soil formation?
Often assumes factors are independent when they are frequently inter-dependent
Over simplification: tends to ignore processes which are the real explanation
Soils are often polygenetic (have formed under differing soil forming factors)
Factorial appraoch is a concept most applicable in temperate regions
(since non-glaciated areas differ)
41
Why do we classify soils? What is the problem with soil classification?
To help communicate information
To make predictions
To establish inter-relationships among soils and their envr.
However, soils are a multi-property body, with great spatial and temporal variability, particularly with respect to soil moisture but also in other properties
- Horizon borders are often blurred
42
What are the categorical levels of soil classification?
Order: properties that reflect envr and soil forming processes
Great Group: subdivision of order reflecting difference in dominant processes
Subgroup: differentiated by content and arrangement of horizons
Family: differences in texture, minerology, climate and chemistry
Series: detailed features of the pedon differentiate subdivisions of the family
43
What are the three mineral horizons in the Canadian System of Soil Classification?
A, B, and C followed by lowercase suffixes
Connects parent material with soil
44
What are the four organic horizons in the Canadian System of Soil Classification?
O, L, F, H
O horizon is further defined by suffixes
45
A horizon suffixes and description
Ah: accumulation of SOM (h stands for humus)
Ae: removal of clay, SOM, iron, or aluminum (e stands for eluviation)
46
B horizon suffixes and description
Bh: accumulation of SOM
Bf: accumulation of iron and or aluminum
Bss: presence of slickensides (smooth clay coating caused by stress in clay soils)
Bv: vertic horizon caused by turbation (mixing) of material in high clay soils
Bt: accumulation of clay
Bn: strong soil structure and sodium accumulation
Bg: mottling and gleying due to water saturation
Bm: slight colour or strucural changes from the parent material
47
C horizon suffixes and description
Cca: accumulation of Ca and Mg carbonates
Cs: accumulation of soluable salts
Ck: presence of orginial Ca and Mg carbonates
Css: presence of slickensides
Cg: mottling and gleying due to water saturation
48
R horizon description
Consolidated bedrock
49
W horizon description
Water layer
50
O horizon suffixes and description
Of: composed of fibrous materials of readily recognizable origin (f stands for fibrous material)
Om: organic materials in an intermediate (or mesic) stage of decomposition
Oh: organic material which is highly decomposed (in a humic state) (h stands for humus)
51
L horizon description
Leaf litter, ready recognizable
52
F horizon description
Partially decomposed leaf and twig material (folic material)
53
H horizon description
Humic material
Decomposed OM with no original structures
54
What are the 10 soil orders of the CSSC
Brunisols
Cryosolic
Chernozemic
Gleysolic
Luvisolic
Organic
Podzolic
Regosolic
Solonetzic
Vertisol
55
Regosolic soils description
Occus in every ecozone but are rarely dominant in the landscape
- 2% of the surface in Canada
B horizon is absent (or only has limited dev.)
- only consists of A horizon
Form on young materials, fresh alluvial deposits, post volcanic eruptions, sand dunes, mass wasted slopes, dry and cold conditions
56
Brunisolic soils
Forms under mixed forests
- widely distributed in Canada (14%)
- Saint-Lawrnece lowlands, Northern qbc, regions of central provinces, as well as BC and Yukon
Brownish Bm horizons
- slight colour or structural changes from the parent material
- not yet chemically altered a lot (slight changes in colour and chem. composition)
- clearly distinguished from B horizon
A stage of an evolutionary sequences that begins with parent material and ends with Podzols or Luvisols
Medium fertility
In ecozones where mean annual precip. <700 mm
The parent materials are derived from igneous rocks and typically have moderately or highly acidic pH values
57
Luvisolic soils
Develop beneath mixed deciduous and coniferous forests (one of the three orders for forested soils)
- Usually in the south
Parent materials are rich in base cations such as calcium and magnesium --> high fertility
- used for farming purposes (good for crops)
- Ap (Ah horizon) --> p stands for plow
- agricultural soils: A horizon straight line because it is promoted by farming practices
Neutral or alkaline pH values although some acidic luvisols are found in eastern Canada
Eluviation and illuviation produce Ae and Bt horizons
- seen by presence of Ae and Bt horizons
- Ae = strong eluvation, washing out of humus and clay minerals into deeper layers
- These materials accumulate into deeper layers which creates Bt horizon and sometimes Bh horizon
58
Podzolic soils
Develop beneath coniferous forests (acidic needles) and on sandy parent materials
- Norther qbc, BC
- 14% of Canada
Means annual prec. >700 mm
Low to medium fertility depending on acidity
- the more acid, the less fertile
Intense chem. weathering in the upper part of soil
- Al, Fe, and other ions are weather away from topsoil into deeper layer
Metals ions form complexes with the org. decomp. products (called chelates)
Develop in cool and wet climate --> have rich LFH horizon
LFH horizon
A horizon (light pale layer): eluvation of bases, oxides, clays
B horizon: illuvation of oxides and clays
C horizon: loss of base to water table, acc. of oxides and clays
59
Horizons in podzolic soils
Ae: a lot fo elivation and washing out of materials (pale colour)
Darker colour: a lot of OM eluviated into this horizon from the trop
Reddish colour: eluvation of iron and Al oxides that accumulate and create the colour
Bfh: mineral horizon, very enriched in humus, OM material
- Bf is a lyer with strong acc. of iron and Al oxides
60
Vertisolic soils
Very high clay content (>60%)
Little dev. of horizons (large amounts of smectice)
Shrinking and welling upon drying and wetting
- diagnostic feature are cracks
Occuring primarily in cool subarid grasslands throughout the Prairie ecozone
0 0.3% of surface area in Canada
Parent materials were deposited in lakes that existed during the retreat of the last (Wisconsian) glaciers between approx. 17000 to 9000 years ago
Has Ah horizon with OM
Bv: v stands for vertic (means that it is very high in clay and quite fertile)
61
Gleysolic soils
Influence by the presence of water
- When O is preset, Fe is oxidized and has reddish colour
- Water saturation leads to depletion of O -> iron is reduced into Fe2 and takes on a blue-grey hue
High water table and develop in the vicinity to rivers and lakes
- water table can rise up and create situations where there are anoxic pockets
Diagnostic Bg (g for gley) horizon develops
Medium to high fertility
- depends on the soil in the vicinity to the body of water
62
How do gleysoils influence N and P pathways?
P is often found to rion oxides. When iron is reduced, P becomes mobilized and can be transported away from the soil into the body of water
Nitrates in anoix conditions become reduced and lost into the atmosphere
Therefore, gleysols can reduce the input of nitrates in freshwater bodies but can promote P in waterways
63
Organic soils
Prominently found in Hudson bay lowlands
- 9% of Canada
Composed largely of OM including peat, bog, and muck soils
Commonly saturated with water for prolonged periods
Low to medium fertility depending on drainage and nutrient availability
Associated with landscape positions where water accumulates and saturates the soil
- ex. acc. of water in topographic low points
Cooler climates slow decomp. of OM therefore OM can accumulate more
Develop because input of OM is higher than output through decomp.
64
How is peat soil formed?
waterlogged, anaerobic, cold conditions leading to slow rates of OM decomp.
65
Why are peatlands important in terms of carbon?
Important since huge carbon sinks
However, because they are good for vegetable production, they are drained.
- OM begins to decompose (since exposed to O)
66
Cryosolic soils
Usually found north of the treeline
- 28% of Canada
- North
Ah horizon is lacking or very thin (a lot of enrichment of humus)
Cryturbation is common --> ground circles, polygons, stripes
- Diagnsitc feature: strange features forming. Organic horizons translocated in deeper layers since melting and freezing of ice moves soil layers around and disturbs layers
Mean annual temp <0 (cold conditions, often develop in permafrost landscapes)
Fertility ratings are not applicable because they are dominated by ice or permafrost
Cryosols may be found in association with other soil orders (eg. organic soils of gleysoils)
Weak chem. dev.
LFH and Ah horizons are underlined by thick ice layer
These soils are strongly disturbed by climate change when ice melts
67
Chernozemic soils
4% of Canada
- Prairie
Black earth
Well to imperfectly drained soils
OM accumulation
- thick surface layer
Majority of carbon input occurs below ground through the dev. of extensive root networks of grasses
High fertility mostly because they have relatively high pH??? (rich in base cations,P, and large amount of SOM)
- very limited leaching of bases
- neutral pH???
Dissolved salts from topsoil often precipitate in the upper C horizon (Cca)
15-30% of the original soil carbon was lost after converstion of the nature Prairie to agriculture
68
Solonetzic soils
Found in the Prairies where it is dry (high evaporation leads to acc. of salts)
- 1 % of Canada
Associated with salinity and alkalinity
Very hard B horizon when dry and sticky mass with low permeability when moist
Variable fertility
Distribution of salts throughout soil profile
- usually not useful for crop prod. because pH is high due to acc. of salt minerals
- Salinization promoted by irrigation with groundwater (groundwater is rich in irons since in contact with parent material).
- The combination of groundwater irrigation and high evaporation leads to acc. of salts in the soils
Salinization when dissolved salts migrate to surface in areas with high evapotranspiration
69
What is soil erosion?
Naturally occuring process that affects all landforms
Refers to the wearing away of the topsoil by physical forces of water and wind or through forces associated with human activities (tillage, cattle grazing, tree harvest)
Topsoil which is high in OM, fertility, and soil life is detached, moved, and deposited elsewhere
Reduces the productivity of corlands and natural ecosystems and contributes to the pollution of adjacent watercourses, wetlands and lakes
70
What is soil creep?
Slow downslope movement of soil particles in response to disturbances
- Movement of topsoil and subsoil
Slow process
Expansion/contraction with wetting/drying
71
What are landslides and earthflows?
Rapid mass movements when soil strength is exceeded by gravity, usually heavy rainfall
All of a sudden, a large mass of soil moves
Often in the tropics due to heavy rainfall
72
What is fluvial erosion?
Erosion by running water
- Caused by overland flow of water that moves on top of the soil (does not relate to subsoil)
By far the most important form of erosion
73
What is aeolian erosion?
Wind removel of surface layer
Requires the absence of protective vegetation cover, dry soils and strong winds
Occurs usually in dry soils
74
What are the 3 processes of fluvial erosion of soil?
Raindrop impact and splash
Creation of overland flow
Deposition
75
Explain the draindrop impact and splash
Raindrop hits bare soil unprotected from vegetation
Impact and subsequent splash leads to the destruction of the soil aggregates and topsoil structure (detachment)
Soil aggregate is destroyed and smaller particles can be moved away by flowing water (transport)
Particles can be deposited elswhere (deposition)
76
What are the 3 types of overland flow erosion?
Sheet erosion:
- A whole area is eroded simultaneously
- Can be observed in the environment
- Caused biggest damage to agricultural systems (since it multiplies over the years and affects large area)
- Can lead to burial and suffocation of crops
Rill erosion
- Certain locations (rills) experience more erosion
- Creation of channel -> surrounding water will flow and accelerate erosion
- Areas around are spared from erosion
Gully erosion
- Creates deep channels called gullies
- From strong precipitation
- Excessive rill erosions
77
What is Horton overland flow (HOF)?
the tendency of water to flow horizontally across land surfaces when rainfall has exceeded infiltration
78
What are the two factors that overland flow is affected by?
Vegetation cover (prevents splash impact)
Soil infiltration (determined by soil structure --> presence of SOM)
79
Compare the interception, overland flow, and infiltration in a vegetated forest, a forest without litter or humus, and unimproved pasture
Oak hickory: same interception, low overland flow, high infiltration rate
Forest w/out litter/humus: same interception, higher overland flow, lower infiltration
pasture: no interception, high overland flow, lowest infiltration
80
How is soil erosion measured?
Collect soil downslope in troughs: measures weight of particles deposited in it
Measure loss of soil against stable surface (tree root)
Radionucleotides: using radionuclotides from old nuclear explosion to estimate soil erosion
81
What are some problems with measuring soil erosion rates?
Large temporal and spatial variability
Labour-intensive and expansive
Difficult to scale-up from small plots to drainage basins and landscapes
Of little predictive value (only gives measurement from one pt in time)
82
What is the Universal Soil Loss Equation?
A = R x K x LS x C x P
where,
A=erosion rate (tons ha^-1yr^-1)
R=rainfall erosivity
K=soil erodibility
LS=combination of length and slope of field
C=crop type
P=conservation measures applied
83
What are the two factors of rainfall erosivity (R)?
Rainfall intensity: affects creation of overland flow by exceeding soil infiltration rate
Rainfall energy: ability to splash soil particles downslope and destroy soil aggregates
- gravitation energy: height from which the raindrop is coming from and size of the raindrop
84
Explain the distribution of rainfall erosivity in the world
Lowest in desert and arid regions
Highest in humid regions and North East since has more rainfall intensity occuring (exceeding infiltration)
Monsoon in Asia also causes high rainfall erosivity
85
What is soil erodibility (K)?
Potential of soil to become eroded
Depends on soil textures since it determines the water infiltration rate
Combination of:
- Soil infiltration rate
- Ease of detachment of soil particles
- Ease of transport of soil particles
86
What is the order of soil infiltration rate of sand loam and clay?
sand>loam>clay
87
What is the order of ease of detachment of soil particles of sand silt and clay?
silt>clay>sand
Silt is detached the easiest due to bonding strength
Clay size fraction is dominated by clay minerals which have highly charged surfaces that bind to SOM that form aggregation which prevents the small particles from detaching
Sand particles are big and not as easily transported away
88
What is the order of ease of transport of soil particles of sand silt, gravel and clay?
clay>silt>sand>gravel
89
What soil texture has the highest soil erodibility values (K)?
Silt loam
90
What are the factors that affect the slope-length factor (LS)?
Longer slopes mean greater cumulative overland flow from upslope, leading to faster movement and greater capacity to erode and carry soil
Steeper slopes mean faster overland flow and greater capacity to erode and carry soil
- the steeper the slope, the higher the LS factor
91
What is the soil erosion equation used for?
Predict erosion raets for individual fields
Devise conservation measures to ensure that erosion rates are less than that regarded as intolerable
A, R, and K defined, farmer can change slope angle, field lengt , crop type or conservation practice
92
What does a crop (C) value and conservation (P) value of 1.0 represent?
Bare soil, no conservation
93
What are the envr effects of accelerated rates of soil erosion on site?
Reduced water availability
- increases surface runoff (reduces water for plant growth)
- removes finer particles (clay, OM) leaving sand and gravel particles which have lower available water capacity
Reduced soil fertility
- leads to loss of fertilizers, especially N and P, by overland flow
- removes smallest particles (clay, OM) which have highest available nutrient content and CEC
Reduces rooting depth for plants (shallower soils)
Gully creation
- loses agri. land
- increases accessibility costs of farming
Greater energy costs
- for ploughing and tillage
- for seeding and fertilizer needs
94
How does soil erosion promote a positive feedback loop?
Exposure of lower soil horizons by erosion --> decreased infiltration rates --> increasing overland flow --> less vegetation --> more surface layer removal --> more erosion --> exposure of lower soil horizons -->
95
What are the envr effects of accelerated rates of soil erosion off site?
Sedimentation of eroded soil in river channels, dams, reservoirs
Leads to eutrophication of water bodies (rivers, lakes)
- N and P transported and adsorbed to eroded soils
- pesticides transfer from land surface to aquative system through erosion
Deteriotation of water quality and higher water treatment costs
Increased frequency of flooding
- greater surface runoff and channel volume may be reduced by deposited soil
- larger amount of HOF --> accumulates downstream in smaller channels --> increases frequency of flooding
96
What is a conservation method developed for agriculture in loess plateau regions?
Terraces because they limit soil erosion, retain water during dry season
97
What are some strategies to reduce fluvial erosion rates in agricultural systems?
Change crop type or planting/harvesting schedules (C)
Protect soil surface and increase infiltration rate
- add OM (K)
- change tillage practices (no till or less intense ploughing) (K)
Change length and angle of field by creating terraces or ploughing parallel to slope (LS)
Reduce grazing densities to allow grass cover: 25% grass cover is critical in reducing erosion rates (C)
98
How is contour ploughing beneficial?
Crops parralel to slope will slow down water movement downhill
Plant and remove crops layers at different times decreases erosion rates
99
What can wind erosion be caused by?
Creeping of larger particles
saltation of medium sized particles (airborne for short amount of time)
suspension of smaller particles of clay and silt size fraction
100
What are ways in which wind erosion can be controlled?
Maintain soil moisture
Cover soil
Reduce tillage and timing of tillage
Create barriers
101
What are shelterbelts?
Rows of trees planted in between agricultural crops to break up wind and prevent wind erosion
They are barriers that can prevent soil erosion from wind
102
How does erosion impact food security?
Soil erosion cuases SOM to deplete (lowers fertility of crops)
There is a decline in agricultural production which leads to food insecurity
Food insecurity leads to more intensive agricultural practices which leads to more erosion
