Soil formation and chemistry Flashcards by Andrew Jeavons

Why is soil important? (general areas)

Climate
Ecosystem
Pollutants
Water
Health
Plants

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Why is soil important for ecosystems?

hold 1/4 of the worlds biodiversity

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Why is soil important for dealing with pollutants?

water filtration system

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What can be present in one teaspoon of soil?

1 billion organisms
10,000 species
10 kilometres of fungi

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Why is soil important for plants?

95% food production (CWR)
Building materials
Clothes

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Why is soil important for water?

400mm can be stored in 1m
1.5 Olympic swimming pools per hectare
60% water return

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What is soil composition by volume?

45% mineral
5% organic
50% space (air/water)

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What is soil composition by mass?

0% air
18% water
80% mineral
2% organic

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What 5 things is soil formed by?

Parent material
Climate
Topography
Time
Biological

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How is soil formation affected by parent material?

original weathered bedrock transported from elsewhere, usually by wind or water

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How is soil formation affected by climate?

amount, intensity, timing and type of precipitation that degrades ecosystem into soil

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How is soil formation affected by topography?

slope and aspect affect the angle of the land and position toward/away from the sun that soil will be exposed to

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How can time affect soil formation?

the amount of time it takes for four factors to interact with each other

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How can biological factors affect soil formation?

Plants, animals, microscopic organisms, and humans interact with soil in different ways

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What is pedigenesis?

process of soil formation

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What 2 ways can pedigenesis be?

ex-situ
in-situ

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What is ex-situ pedigenesis?

gravity downslope
Colluvial

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What is colluvium?

loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rain-wash, sheet-wash, slow continuous downslope creep

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What is ex-situ pedigenesis?

transported and deposited material

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What would earths early soil have been like?

simple structure
poor at holding water
lack of nutrients or soil biota

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What is the progression to form present day soil?

Not much for first few bn yrs
Stramatalites (first algae/ cyanobacteria)
Mosses (465 Ma)
Proper soil development with biota (420-400Ma)
Lichens
Vascular plants (DOM)

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What did the development of lichens allow for?

rock to be broken down so nutrient cycling

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What are some key parent materials?

Granite (acidic)
Basalt (basic)
Sandstone
Mudstone and shale (clay material)

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What will soil be like in an area with active glaciation?

No soil due to scouring of rock by overlying ice

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What are the 2 main soil groups?

Organic Mineral

How can you tell the organic layer in soil?

Dark black layer in the soil

What are the characteristics of organic soil?

Saturated soil or low temp Low nutrient level Low pH High rainfall

Why is organic matter content so high in organic soils?

As the conditions aren't favourable for decomposition and detritivores

What is the organic matter content cut-off for organic soils?

>30%

What is alluvium?

loose unconsolidated soil or sediment which has been eroded and reshaped by water and then deposited

What is eluvium?

weathered material at or near the source

What are Lacustrine deposits?

Clay deposits originally at bottom of lake but the lake in no longer there

What is till?

unconsolidated material deposited by glacial ice

What is ablation till?

Till that falls onto the top of the glacier from surroundings so doesn't experience any or little erosional processes

What is basal till?

rounded sub-glacial material that is heavily eroded due being dragged along bedrock

What is outwash?

Unconsolidated, sorted material deposited by meltwater from a glacier

What is an outwash plain?

Accumulation of sediment in front of a end moraine flat consisting of sand and fine sediments

What will marine deposits be like?

Shell, reef and other bits previously at bottom of ocean which has been uplifted

What is eolian deposits?

Volcanic ash

What is podzol?

A type of soil with string leaching leading to a poor top soil

What are peaty soils important for?

Carbon storage

What is leaf litter?

Matter which isnt decomposing: Leaves, needles, twigs, moss etc

What is humus?

Rich organic material of plant and animal origin in stage of decomposition

What can the O horizon consist of?

Several O-layers

What is Histosol?

Usually more than 30% organic matter Poor drainage Cold soil

What will the organic matter content of a mineral soil?

<30%

What will happen to soluble minerals in the soil profile?

Readily leached (Ca, Mg, Na)

What minerals will tend to accumulate in the soil?

Oxides (Fe, Al, Si)

What does black colour soil usually mean?

Organic matter/ reduced iron Manganese (purple-black)

What does a red soil mean for composition generally?

Iron - oxidised (hematite)

What does a yellow soil mean for composition generally?

Iron - oxidised (geothite)

What does a grey-green soil mean for composition generally?

Glauconite

What does a white soil mean for composition generally?

calcium and magnesium carbonates Gypsum soluble salts

What is a soil profile?

vertical cross section of layers of soil in a given area

What can the soil profile be sub-divided into?

soil horizons

What are soil horizons used for?

classifying soil types

What are soil horizons based on ?

colour texture roots structure rock fragments

What is the order for the master soil horizons? (top down)

O A E B C D/R

What is the A horizon?

Topsoil/ biomantle of horizons

What are the characteristics of the A horizon?

Some humus Darker colour than deeper layers Usually mixing by biota Highly productive

What is the B horizon?

subsoil

How might some organic matter reach the B horizon?

Leaching

What is the E-horizon?

Eluviation

What will the B horizon be rich in?

Clay and minerals (Fe, Al)

What are the characteristics of the E horizon?

Lighter colour than adjacent horizons Poor mineral and clay content Larger soil particles than A or B

Why does the E horizon have poor mineral and clay content?

leaching (loss water retaining plant nutrients to water table)

What is the C horizon?

weathered regolith

What are the characteristics of the C horizon?

Large rocks/ lumps partially broken bedrock Least affected by weathering Devoid organic matter

What is the D/R horizon?

Bedrock horizon

What are the characteristics of of the D/R horizon?

No rock or boulder just continuous bedrock Colours those of original rock

How many soil classes are there?

What is Andosol?

Volcanic soils

What is Cambisol?

Young soil (brown soil)

What is Fluvisol?

young alluvial soil

What is Gleysol?

Water saturated soil

What is Histosol?

Organic soil

What is Leptosol?

Shallow poorly developed soil (rocky)

What is Regosol?

Arid eroding soils Mountain soils

What is Podzol?

acidic soils (usually upland coniferous forest)

What are the key features that affect soil chemical processes?

Texture pH Porosity Water content Cation exchange capacity

What type of system can soil be thought of as?

Collodial

What is a colloid?

mixture of particles ranging between 1 and 1000 nanometres

What is the surface area of colloid like?

large surface area

How active the colloid soil?

most chemically active

What are the subcategories of soil texture?

Sand (<2mm) Silt (not needed) Clay (<0.002mm) Colloid (<0.001mm)

How do you usually find colloids?

Clay (inorganic) Degraded organic matter

What other name can be given to clay mineral structures?

phyllosilicates

What does the structure affect in clay minerals?

chemical processes- cation exchange (retention and loss of nutrients)

What 2 types of sheets can cay minerals be aligned in?

Tetrahedral Octahedral

What are 1:1 and 2:1 clays?

1:1- 1 layer of tetrahedral to 1 layer of octahedral 2:1- 2 tetrahedra layers to 1 octahedral

What does arrangement of the clay layers?

reactivity in the soil

What is cation exchange capacity?

amount of cations a soil can adsorb

What is cation exchange capacity the sum of?

sum of negative charges on soil particle surfaces

What is anion exchange capacity?

amount of adsorbed anions

What is the structure of tetrahedral sheets?

1 silicon 4 oxygen

What is an example of a 2:1 clay?

Mica

What can affect how well cations are attaches to anion in clays?

Physical size of cation Negative charge of clay soil or organic matter Lower pH Competition with other cations Temperature

What clay will have the highest cation exchange and why?

Vermiculite- sweet spot of gap which allows good negative charge site exposure

What is porosity?

volume of soil voids that can be filled with water/air

What is bulk density?

weight of dry soil per unit volume

How can trampling affect measuring carbon stock?

actual carbon stock the same but bulk density higher

What can pH as a variable be referred to as?

the master variable

What is the pH range for most soils?

5.5-8

What are the acid producing processes?

Respiration Mineralisation of organic matter Leaching Nitrification Oxidation of sulfur Rain (5.6 pH) Plant uptake of cations

Why do we can about soil properties?

Nutrient retention - crop growth Pollution retention Water holding capacity Carbon storage