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Materials Identification > Soil components > Flashcards

Soil components Flashcards

1
Q

percentage of mineral matter in soil?

A

45%

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2
Q

percentage of air in soil?

A

25%

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3
Q

percentage of water in soil?

A

25%

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4
Q

percentage of organic matter in soil?

A

5%

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5
Q

four major components in soil?

A

mineral
organic
water
air

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6
Q

mineral components

A
  • inorganic materials derived from rocks

* extremely variable in size and composition.

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7
Q

primary minerals

A
  • formed at high temperature and pressure, under reducing conditions without free oxygen.
  • mainly present in soils as sand (quartz), feldspar and silicates (discrete and chain)
  • crystallized from igneous rock formed from molten lava.
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8
Q

secondary minerals

A
  • formed at low temperature and pressure through oxidation.
  • weathering product of primary minerals,
  • usually present in soil as clay particles.
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9
Q

most common elements in soil

A
  • highest quantities are O, Si, Al, Fe, C, Ca, K, Na and Mg

* Oxygen is the most prevalent - comprises about 47% of the Earths crust by weight and more than 90% by volume

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10
Q

elemental composition of soils

A
  • Oxygen 49%
  • Silicon 31%
  • Aluminum 7.2%
  • Iron 2.6%
  • Carbon 2.5%
  • Calcium 2.4%
  • Potassium 1.5%
  • Sodium 1.2%
  • Other 2.6%
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11
Q

weathering

A

• Breakdown and changes in rocks by biological, chemical, and physical agents can result in synthesis of new (secondary) minerals of great importance in soil (e.g. clay minerals).

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12
Q

see pp for

A

weathering processes and responses

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13
Q

chemical weathering consists of what 5 things

A 
hydration
hydrolysis
dissolution
carbonation
oxidation-reduction
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14
Q

hydration - chemical weathering

A

water molecules bind to a mineral e.g. transforming hematite into ferrihydrate
see pp for equation

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15
Q

hydrolysis - chemical weathering

A

water molecules split into their hydrogen and hydroxyl components and hydrogen replaces a cation from the mineral structure e.g. transformation of feldspar to kaolinite
see pp for equation

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16
Q

dissolution - chemical weathering

A

water can dissolve many minerals by hydrating the cations and anions e.g. dissolution of gypsum
see pp for equation

17
Q

carbonation - chemical weathering

A

When carbon dioxide dissolves in water (enhanced by microbial and root respiration) the carbonic acid produced hastens the chemical dissolution limestone into soluble hydrogen carbonate
see pp for equation

18
Q

oxidation-reduction - chemical weathering

A

minerals that contain Fe, Mn, or S are especially susceptible to oxidation-reduction reactions.
Fe(II) oxidized to Fe(III) forming – colour change to red-brown and change in valence and ionic radius destabilizes crystal structure of the mineral.

19
Q

biological weathering effects

A
  • the break-up of rock particles by roots
  • the transfer and mixing of materials by burrowing animals and
  • the formation of organo-mineral complexes (soil biological processes produce organic acids that can solubilize Al and Si ions)
20
Q

particle density

A
  • () is mass of solids (Ms) per volume of solids (Vs).
  • = Ms/Vs
  • mean particle density is 2.6-2.7 gm/cm3.
  • Soils with a high content of iron oxides and various heavy minerals have a particle density of 5.2-5.3 gm/cm3,
  • Soils with high organic matter content can have a particle density as low as 1.3 gm/cm3.
21
Q

bulk density

A
  • (b) is the mass of solids (Ms) per total soil volume (Vt).
  • b = Ms / Vt b= Ms / (Vs + Va + Vw)
  • Vs=volume of solids; Va=volume of air; Vw=volume of water
  • Bulk density is always smaller than particle density.
  • Since pores constitute half the volume, b is about half of , namely 1.3-1.35 g/cm3
22
Q

size of soil particles

A

• mineral particles in soils vary enormously in size. Sieved for size fractions.

a) particles < 2-mm diameter holes - the fine earth (consisting of sand, silt, and clay particles),
b) that is retained on the sieve (> 2 mm) - the coarse fragments (gravel, cobbles, and stones).

23
Q

see pp for

A

comparison of soil particles

24
Q

particle size determination

A
  • Sieving - Stack of sieves, larger mesh size at top
  • Soil on each sieve turned out onto paper.
  • Back of sieve brushed onto paper and weighed.
  • wire brush used (for coarse sieves) and nylon brush (for fine nylon sieves).
  • Results expressed as a %
25
Q

sedimentation

A

soil sample dispersed, dried, weighed then poured into column of water
Settling rate used as a standard method
Stokes Law 1851, settling rate ∝ diameter of particle
settling rate depends on particle diameter and density and density of the fluid.
Large grains settle out immediately, e.g. sand within 5 min,
silt after 8 hours and clay remains suspended for long time.
Very small particles (<1µm) never settle unless they are very dense.
Evaporate a 20cm3 sample withdrawn 10cm3 below surface. Weight of residue  solids still in suspension.

26
Q

hydrometer

A
  • Measures density of liquid as particles settle out density drops and hydrometer sinks.
  • used to grade fine-grained soils, silts and clays too small for sieve analysis
27
Q

see pp for

A

hydrometer diagram

28
Q

see pp for

A

soil texture key

29
Q

see pp for

A

triangular graph of soil texture

30
Q

types of soil aggregates - characterised in terms of what 3 things

A
  • shape (or type)
  • size (fine, medium, or coarse)
  • distinctness (or strength, e.g. strong, moderate, or weak).
31
Q

types of soil aggregates -soil structure is enhance by…

A
  • physical and chemical processes e.g.wetting/drying, or freeze/thaw
  • Biotic processes, e.g. soil compression by roots, burrowing activities of earthworms, enmeshment of mineral particles by network of roots and fungal hyphae
32
Q

surface area

A
  • The large interfacial area per unit volume in soils give rise to liquid-solid interaction and adsorption of water and chemicals.
  • The soil clay fraction dominates soil specific surface area
33
Q

moisture content

A 
•	An indicator of the amount of the water present in soil
•	Moisture concent, w(%)
see pp for equation
•	ASTM 2216 (conventional oven method)
•	ASTM D 4643 (Microwave oven method)
•	3 minutes at 50% power (mass=50g)
34
Q

soil porosity

A

• Total pore space of the soil
• Sand has less than clay
see pp for equation

35
Q

usual soil porosity %

A
  • Generally, between 30-60%.

* High porosity indicates lack of compaction and good soil condition

36
Q

see pp for

A

porosity diagrams

37
Q

see pp for

A

permeability diagram

38
Q

soil air

A

much higher in CO2 than normal air

39
Q

CO2 in soil is produced by what

A
  • Respiration of living organisms
  • Root respiration
  • Decay of organic matter
  • Humification where C  CO2 by soil microorganisms

Materials Identification (17 decks)

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