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EnviSci Year1 > LEC.103 Soils > Flashcards

LEC.103 Soils Flashcards

(106 cards)

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1
Q

What is soil (very simply)

A

The outermost layer of Earth

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2
Q

Is soil a renewable source?

A

No, its non-renewable hence requiring sustainable use and management

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3
Q

What are some of the provisioning ecosystem services of soil?

A

Foundation of food production, raw materials for construction such as bricks, clay, peat, foundation of production of biomass, home to bacteria which produce antibiotics, provides fresh water

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4
Q

What are some of the regulating ecosystem services of soil?

A

Important part of climate regulation, contribute to air quality regulation, soils store large amounts of carbon, filters water contribution to water purification and waste treatments, stores water which mitigates flooding

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5
Q

What are some of the supporting ecosystem services of soil?

A

Key parts of nutrient cycles for many different macro and micro nutrients, supports organisms which photosynthesise, key in the process of soil formation

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6
Q

What are some of the cultural ecosystem services of soil?

A

Important component of recreational and other outdoor spaces, preserves archaeology.

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7
Q

What is the difference between the moon and Earth that meant volcanic impact materials formed into soil on Earth but not on the moon?

A

Earth as the presence of water, air, and life that altered the same volcanic and impact materials found on the moon into soil.

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8
Q

How are mineral soils formed?

A

Weathering of rock masses to unconsolidated and often transported material.

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9
Q

How are organic soils (e.g. peat) formed?

A

Plant material

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10
Q

What type are most soils (organic/mineral)?

A

Most soils are a mix of mineral and organic.

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11
Q

Physical weathering mechanisms?

A

Onion layer, freeze-thaw, erosion, hydraulic action/abrasion, thermal, mechanical, biological

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12
Q

Chemical weathering mechanisms?

A

Hydrolysis, carbonation, hydration, dissolution, oxidation and reduction

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13
Q

Rock becomes soil when____?

A

organic matter is incorporated

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14
Q

Inputs of organic matter to soil?

A

Dead plants and animals.

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15
Q

What does soil organic matter do?

A

Supplies nutrients and alters the physical nature of soils.

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16
Q

Soil forming factors: parent material. How does the parent material affect the soil?

A

The initial rock can have a large influence on the soil - the breakdown, particle size, etc. Glacial tills can be heterogeneous and unstratified.
Variation in plant communities leads to differences in soil organic matter - changes Earthworm activity.

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17
Q

Soil forming factors: climate. How does climate affect the soil?

A

Precipitation, temperature. Impacts the weathering processes, carbonates accumulating if theres low rainfall. Acidic soils in humid areas due to intense weathering, rainfall causing soil erosion/deposition of chemicals into soil. Cold climates have much slower weathering than warm climates.

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18
Q

Soil forming factors: Organisms (living). How do organisms affect the soil?

A

Micro-organisms decomposing organic matter and forming weak acids, leaving H+ to break down minerals. Soil varies depending on the type of vegetation cover.

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19
Q

Soil forming factors: Relief. How does relief affect the soil?

A

Topography modifies water and temperature. Soil on steep slopes tend to be thinner. Landlocked depressions receive more runoff, greater production of vegetation but slower decomp. Water logged - peat. Slopes facing the sun are warmer this can affect the breakdown of organic matter.

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20
Q

Soil forming factors: Time. How does time affect the soil?

A

Soils change over time as they weather, weathering duration varies on climate, soils form very very slowly so slowly that it makes them non-renewable.

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21
Q

Processes of soil formation?

A

Mixing, additions, removals, transformations, translocation

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22
Q

Soil forming processes: mixing. How does it work?

A

Soil animals, plant growth, gravity, shrinking and swelling due to water content changing, freeze-thaw

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23
Q

Soil forming processes: translocation. How does it work?

A

(vertical movement) - gradients in water potential and chemical concentrations within the soil pores, materials can move up or down the profile, biological activity may also cause gradients in the chemical composition of the water and air filled pores of the soil.

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24
Q

What are soil layers called?

A

Horizons

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25
Why do soil horizons develop?
Result of the soil forming processes acting on the parent geological materials over time.
26
Overview of what soil is made of?
Soil solids - mineral and organic Pore spaces - air and water
27
Inorganic components in soil?
Mineral particles, primary minerals (little changed from og rock), secondary minerals (altered by interaction with air and water)
28
Organic components in soil?
Living organisms, dead and decaying plant and animal remains, humus (humic and non-humic substances.
29
Function of organic matter?
Supply nutrients, maintaining structure, water storage, heat absorption, deviation of chemicals, main source of energy for soil organisms
30
Decomposition is a continuous process - what is required?
Regular additions of organic matter.
31
Water in soil?
In pores, regulates soil aeration, soluble constituents and the water make soil solution, soil solution is critical medium for supplying nutrients and water to plants, direction of transport (gravity/evaporation).
32
Air in soil?
Regulated by the moisture content, plants need O2 for respiration and organisms for decomp of OM, lack of O2 will impact biochem rxns, a well aerated soil is ideal for growth of plants
33
What is meant by a 'well aerated soil'?
Rapid exchange of soil air and atmospheric air.
34
What is the Munsell soil colour chart used for?
Classifying soils by colour which can indicate to their composition.
35
What are the three major factors influencing soil colour?
Carbon, water, chemical
36
How does carbon influence soil colour?
OM dark brown-black
37
How does water influence soil colour?
Moisture darkens colours, water also changes O2 levels in soil which directly impacts the chemical factor of soil colour.
38
How does chemicals/chemistry influence soil colour?
Different minerals different colours. O2 levels high soils more red, O2 levels low soils more grey blue. Certain minerals give it distinctive colours.
39
Why does soil have texture?
Proportions of different sized particles in a soil
40
Sand?
coarsest fraction 0.5-2mm, soil feels gritty sandy soil have very open structures with large pores water drains easily, low in nutrients, often lack OM
41
Silt?
0.002-0.06mm air spaces and water channels ae more restricted than in sandy soils fertile, fairly well drained and holds more moisture than sandy soils easy to cultivate, except in dry conditions, but easily compacted
42
Clay?
very large specific surface are (particles are tiny) massive capacity to adsorb water and other substances. coheres in a hard mass when dry flakes or plates tiny pores make water and air movement very slow
43
Five fundamental surface phenomena?
1. Water is retained as thin films on the surfaces of soil particles. 2. Gases and dissolved chemicals are attracted to, and adsorbed by, mineral surfaces. 3. Weathering is a surface phenomena. 4. Particle surfaces and the water films between them tend to attract and aggregate. 5. Microorganisms tend to grow and colonise particle surfaces.
44
What are the fundamental surface phenomena greatly affected by?
Specific surface area (SSA)
45
The greater the SSA the greater the ability to retain ___?
Water
46
The greater the SSA the greater the capacity to retain ____ and ____?
Nutrients and pollutants
47
The greater the SSA the _____ the weathering is, releasing its constituent elements into ___?
more rapid, solution
48
The greater the SSA the greater the propensity for forming a ______ soil?
Cohesive
49
Soil relativity increases with?
Decreasing particle size/increasing surface area
50
Lab analysis of soil particle size methods?
Sieving, sedimentation, laser diffraction
51
Non-lab method ('feel') to determine particle size?
Ball and ribbon.
52
Ball and ribbon - sand?
Won't form a ball
53
Ball and ribbon - loamy sand?
Form a ball but not a ribbon
54
Ball and ribbon - sandy loam?
Gritty, non-cohesive ribbon
55
Ball and ribbon - silt loam?
Smooth, dull appearance, crumbly ribbon
56
Ball and ribbon - clay?
Smooth, shiny appearance, long and flexible ribbon
57
What determines soil structure?
How individual soil granules aggregate and therefore the arrangement of soil pores between them.
58
Some of the factors soil structure is dependent on?
What the soil developed from, environmental conditions, clay, organic materials, management
59
What will happen to soil structure under most forms of cultivation?
It will decline
60
Granular soil?
Crumby, found where roots have permeated the soil, each individual particle does not fit together with each surrounding ped because the shape of each ped is roughly spherical
61
Block soil?
Irregularly shaped blocks, each block ped can be broken into smaller aggregates
62
Platy soil?
Thin flat, orientated in a horizontal direction, common in compacted soil
63
Higher density soils have?
Poor organic content and a wide range of tight packing grains
64
What plays a large role in pore formation?
Biota
65
Macropores allow for the easy movement of?
Water and air
66
Macropores are commonly found in what type of soils?
Sandy
67
What are macropores large enough to accommodate?
Plant roots and small organisms
68
In well structured soils what tends to form the macropores?
Interped spaces
69
What is a pore called when its formed by a living organism?
Biopore
70
What are micropores usually filled by?
Water, surface tension holding water onto particles
71
Why don't micropores allow for significant gas movement?
Too small
72
What type of porosity dominates in fine textured soils
Micropores
73
Why are root redevelopment and microbial activity at low levels in soil with micropores?
Poor aeration.
74
Nutrients are available in soil in the form of?
Cations and anions
75
Where are micronutrient deficient soils particularly prevalent?
Middle East, N Africa, SW USA, Australia
76
Why are calcareous soils micronutrient deficient?
High pH and predominate CaCO3 contents
77
pH of soil in the field?
Testing kit, hand held meter
78
pH of soil in the lab?
Solution with water, then test
79
Why is pH important in soil?
Chem and bio rxns dependent on soil pH, influences solubility and therefore the availability of nutrients.
80
How does soil act as a buffer zone between atmos and groundwater?
Clay minerals and OM adsorb ions, molecules and gases.
81
What is CEC? (cation exchange capacity)
Sum of total cations that soil can adsorb as 'exchangeable'. Rapid and reversible. Dependent on total negative charge density.
82
What is a high CEC value (>25) indicative of?
a soil has a high clay and OM content and can hold alot of cations
83
What is a low CEC value (<5) indicative of?
a soil is sandy with little or no OM and that it cannot hold many cations
84
In neutral soils what are the main exchangeable cations?
Ca2+ Mg2+ K+ Na+
85
What does soil acidification result in?
Cations being replaced by protons and Al ions
86
What would lead to soil acidification being permanent?
If basic cations are leached out of the root zone or removed by harvest.
87
3 methods to neutralise acidity?
Liming with limestone or dolomite (replaces the protons and Al with Ca). Addition of gypsum (reduces Al toxicity). Addition of OM (reduces Al toxicity)
88
Why is the nutrient content of soil different from the nutrient bioavailability?
Precipitation, complexation, REDOX
89
Define decomposition
the gradual disintegration of organic matter
90
Define nutrient cycling
the conversion of inorganic nutrients to organic nutrients (immobilisation) and back again (mineralisation).
91
3 methods of measuring soil organic matter?
Loss on ignition - weigh before and after heating Soil organic carbon (SOC) - combustion and measurement of CO2, catalyst to help high temp, gas chromatography to measure CO2. Walkley black - chemical oxidation
92
The distribution of organisms in soils influences and is influenced by ___?
the pore distribution
93
Soil communities?
Assemblages of species populations that occur together in space and time.
94
Microbes?
Very diverse group, perform vast array of functions Bacteria tend to be anchored to the side of soil particles Soil microbes decompose organic matter - carbon for growth and energy, nutrients for growth Important side effect of converting organic nutrients into inorganic nutrients that plants and other organisms can access
95
Fungi?
Over 140,000 known species of organisms Fungi form thread like hyphae which come together to form mycelia Fungi grow from the tips of the hyphae and digest organic matter externally by absorbing it into their mycelia Mushrooms are the most easily recognised fungi Mycorrhizal fungi form mutualistic relationship with plants and help it take up nutrients
96
What happens to ammonium in soil?
Plant uptake, nitrification, mineralisation in warm moist soil
97
What happens to nitrate in soil?
Plant uptake (must be reduced back to ammonium), denitrification (reduction to gaseous forms)
98
What is humus?
Combination of resistant materials from original plant tissue, compounds synthesised as part of the microorganisms' tissue which remain as the organism die
99
Functions of humus?
- holds water and nutrients - sticks together & helps establish and maintain a strong crumb structure & thus reduce soil erosion - provides some nutrients (N & P) as it is slowly decayed by microbial activity - buffers effects of pesticides - creates good soil texture for growing plants - coats the sand, silt, clay particles making them dark (the darker the colour, the greater the amount of soil humus present).
100
What is the function of microbivores?
Eat microbes. Influence decomposition, can cause nutrient enrichment as they don't use all the nutrients they ingest.
101
Examples of ecosystem engineers?
Earthworms, ants, termites.
102
Rhizosphere?
Area around roots. Biological and physio-chemical properties are very different from those of the bulk soil.
103
What is soil quality?
- Soil quality is a measure of the condition of soil relative to the requirements of one or more biotic species and or to any human need or purpose - Soil quality reflects how well a soil performs the functions of maintaining biodiversity and productivity, partitioning water and solute flow, filtering and buffering, nutrient cycling, and providing support for plants and other structures.
104
What is soil health?
state of a soil meeting its range of ecosystem functions as appropriate to its environment.
105
Soil health depends on ____ and can be improved via ____?
soil biodiversity, soil management
106
What are some factors of a soil that is considered healthy?
- Has high organic matter - Does not erode - Has lots of biological activity, especially earthworms - Has fast infiltration (water pass through quickly) - Has minimal compaction - Has sufficient levels of nutrients

EnviSci Year1 (8 decks)

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