Soil 2125

Front 1

Five soil functions.

Back 1

Medium for plant growth

System for water supply and purification system Recycling system for nutrients and organic waste Habitat for soil organisms

Engineering medium

Front 2

Four components of soil and their percentages in an “average” soil (pie chart)

Back 2

25% air

5% organic

45% mineral

25% water

Front 3

Fine earth vs. coarse fragments

Back 3

Mineral and rock fragments: > 2mm = coarse fragments.

Mineral and rock fragments: < 2mm = fine earth.

Front 4

Sand and, silt and clay - Major properties of each size class, important management problemswith soils that are dominated by each size class.

Back 4

Sand-dominated - droughty,

Silt-dominated -highly erodible

Clay-dominated - tough to deal with physically/wet - sticky, dry - hard as a rock:Dinner bell soils.

Front 5

Primary vs. Secondary minerals.

Back 5

primary minerals (derived from parent rocks)secondary minerals (formed from the weathering products of primary minerals)

Front 6

Water and air in pore spaces - what does more water mean for oxygen content of soil? Why?

Back 6

Less oxygen, Air and water make up 50% total

Front 7

Typical shapes of each particle size class.

Back 7

Sand and silt - round blocky.

Clays - plate-like.

Front 8

Surface Area/particle size relationships - why? Don’t need to know any numbers here, justthe relationship between particle size and surface area.

Back 8

Fine particles: much larger surface area per unit mass than coarse particles.

Front 9

The soil color triad - three major agents

Back 9

Iron oxides, organic matter, silicate minerals

Front 10

Be aware that there are other minor colors - don’t need to know specifics

Back 10

White, blue and green, purple etc.

Front 11

Know components of Munsell soil color

Back 11

Hue, Value and Chroma. HUE is the PAGE andtells you how Red (R), Yellow (Y) or somewhere in between (YR) the color is. The reddest is10R, then 2.5 YR, 5YR, 7.5YR, 10YR, 2.5Y, and 5Y is the yellowest. VALUE is the VERTICALaxis of the page and tells you how light or dark the color is (black=low value, white=high value).CHROMA is the HORIZONTAL axis and tells you how bright or dull the color is (dull = lowchroma, bright = high chroma). The code goes HUE VALUE/CHROMA, so a 10YR 4/4 color hasa hue of 10YR, a value of 4/, and a chroma of /4.

Front 12

Soil structure - types and horizon associations -

Back 12

main are GR (A), PL(E), SBK(A&B), ABK(B), PR(Bt), SGR/MA(C)

Front 13

Cementing agents

Back 13

OM, clay, Fe oxides

Front 14

What is the major cause of soil structure in most A horizons?

Back 14

Granular, OM and biological activity (microbialand root exudates).

Front 15

Porosity - effects of particle size on total pore space and individual pore size.

Back 15

As particle size goes down (more clay), total porosity goes up, but the individual pore size (space betweenthe particles) gets smaller.

Front 16

3 major factors affecting bulk density

Back 16

OM, Clay, Compaction/Packing arrangement. How does each affect Db?

Front 17

Effects of human activities on bulk density

Back 17

ag, forestry, engineering

Front 18

20. Calculate Organic Matter given equations and data

21. Calculate gravimetric water content (Theta g) given equations and data

22. Calculate texture from hydrometer (40s and 2hr reading) given equations and data

23. Porosity - calculate given equation and data24. WFPS% - calculate WFPS given equation and data

Back 18

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Front 19

Pedon

Back 19

a three-dimensional sample of a soil just large enough to show the characteristics of all its horizons.

Front 20

Mineral

Back 20

A solid, inorganic substancethat has an ordered atomicstructure.Repeating crystal structures thatcan be described by a specificchemical formula.

Front 21

Rock

Back 21

naturally occurringaggregates of minerals.

Front 22

Coarse Fragment

Back 22

Mineral and rock fragments:> 2mm

Front 23

Fine earth

Back 23

Mineral and rock fragments:< 2mm

Front 24

Hydrometer

Back 24

measures the density of the soil/water solution (g/L)

Front 25

Soil Texture

Back 25

% of fine-earth (< 2mm) made up of each of the 3 main particle size classes(%sand, %silt, %clay) by dry mass.

Front 26

Particle Size Class

Back 26

Fine-earth mineral particles in the soil aregrouped into 3 major size classes:

Sand: > 2 – 0.05 mm (> 2000 – 50 um)

Silt: 0.05 – 0.002 mm (50 – 2 um)

Clay: < 0.002 mm (< 2 um)

Front 27

Peds

Back 27

Individual soil particles arebound or cementedtogether into aggregates

Front 28

Water content

Back 28

weight of water per weight of dry mass – highly dynamic.

Front 29

Porosity

Back 29

percent of total volume that is pore space (P%)

Front 30

Water filled pore space

Back 30

percent of pore volume that is filled with water (WFPS%).

Front 31

Bulk Density

Back 31

mass of soil solids per volume of bulk soil (includes pore space) (Db - g cm-3).

Front 32

Particle Density

Back 32

mass of soil solids per volume of solids (does not include pore space) (Dp - g cm-3).

Front 33

Hue

Back 33

Page in the book

Front 34

Value

Back 34

Lightness or darkness

Front 35

Chroma

Back 35

Brightness or purity

Front 36

*Size limits of particle size classes:

Back 36

Sand < 2000 um (2mm) - 50um;

Silt 50um - 2um;

Clay <2um.

Front 37

*Munsell code meanings. ie. which is the redder hue, 10YR or 2.5YR? which is darker, 10YR2/2 or 10YR 6/2? which is “brighter” (more orange), 10YR 4/2 or 10YR 4/6? See slide withsingle Munsell Book page in Lecture 3.

Back 37

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Front 38

*Oxygen diffuses through water...

Back 38

10,000 x slower than it diffuses through air.

Front 39

*Particle density

Back 39

2.65 g/cm3 in almost all cases for mineral soils

Front 40

*Typical range of bulk densities in cultivated topsoils

Back 40

0.8 - 1.7 g/cm3

Front 41

What are the 8 major elemental components of the earth’s crust and soilmineral fraction and their general abundance?

Back 41

O 46%, Si 28%, Al 8%, Fe 5%, Ca 4%, Na 2%, Mg 2%, K 2%

Front 42

Cations vs anions

Back 42

Positive, negative

Front 43

Oxygen is the only _____ of the Big 8.

Back 43

anion

Front 44

Fe3+, Al, Si have ionic potentials > 4 so form strong, stable, cation-oxygen bonds. Becauseof that, these elements in combination with oxygen predominate in soil mineral (inorganic)solids. Below that range, cation-oxygen bonds are much less stable.

Back 44

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Front 45

K, Na, Ca, Mg form less stable cation-oxygen bonds, so usually exist as individual ions insoils. They are only found as oxides or hydroxides in primary minerals (i.e. in rocks) or very dryenvironments (usually soluble solids - bonds are easily broken).

Back 45

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Front 46

The BIG 8 + 4. The biological 4.

Back 46

C highly enriched in soils relative to crust (plantproduction/photosynthesis - organic C compounds from atmospheric CO2),

N highly enrichedrelative to crust (biological nitrogen fixation from atmospheric nitrogen),

S moderately enrichedrelative to crust (almost all S in soils in organic matter),

P not enriched relative to crust, butusually > 50% soil P in organic fraction.

Front 47

6 Major groups of minerals in soils and their basic structures

Back 47

(Quartz and Feldspar are frameworks, Iron/Aluminum Oxides have various structures, and Kaolinite, Mica/Illite, Vermiculite/Smectite are phyllosilicates (layered silicates).

Kaolinite is a 1:1 (H+ bond interlayer),

Mica/Illites are 2:1 (K+ ion as interlayer glue that bridges negative charges on each clay layer above and below),

Vermiculites/Smectite are 2:1 (water and hydrated ions in interlayer, shrink/swell). You should know the simplified structures as we drew/represented them in discussion.

Front 48

Basic building blocks of the phyllosilicate minerals:

Back 48

Si-TETs form Si-TET sheets, Al-OCTsform Al-OCT sheets, and the sheets combine into layers (either 1:1 or 2:1).

Front 49

Common minerals in each particle size fraction

Back 49

Sand/Silt = Quartz & Feldspar,

Clay = Kaolinite, Mica/Illite, Vermiculite/Smectite, Fe&Al Oxides.

Front 50

What is isomorphous substitution?

Back 50

Substitution of a cation of a lesser charge into the Si-TET or Al-OCT sheets without changingthe structure.

Front 51

What property of 2:1 clay minerals does it cause?

Back 51

Permanent negative charge.

Front 52

Importance of Micas/Illites for soil K.

Back 52

The size of the K+ ion (radius) fits into the holes in the TET layer almost perfectly. Think of a lego piece. Na+ is too small and “rattles” around.In Micas/Ilites, the interlayer is occupied by K+ ions that hold the layers together tightly.K is released when Micas/Illites are chemically weathered. Water and acids enter the interlayer and release the K, which diffuses out into the soil solution and can be uptaken by plants!

Front 53

Which ions would tend to flocculate clays faster? Why?

Back 53

Secondary minerals?

Front 54

Which mineral group is the only one that has major shrink/swell properties?

Back 54

Smectite interlayer H2O cations shrink-swell clays

Front 55

Differentiate the three major organic matter “pools” in soil:

Back 55

Soil (microbial) biomass (living microbes),

Litter/Light Fraction (visually identifiable plant residues),

Humus (non-visually identifiable organic compound.

Front 56

Two major divisions of humus -

Back 56

humic substances (large, complex molecules - don’t look like stuff that comes from plants or microbes chemically);

non-humic substances (chemically identifiable compounds that are of plant or microbial origin). Humus is what gives the soil its dark color - this dark, complex mixture of well decomposed organic residues.

Front 57

C is in all organic compounds and makes up

Back 57

50% OM by weight

Front 58

N is mostly in...

Back 58

amino acids/proteins in organic matter.

Front 59

Relationship between total OM and microbial biomass.

Back 59

Soil (microbial) biomass increases as organic matter increases. Usually 1-12% (average of 5%) of the total soil organic matter mass

Front 60

3 factors that lead to organic matter stabilization and accumulation in soils:

Back 60

Low microbial activity (cold/wet),

Association with fine particles (clays),

Complex molecules (lignin/humic substances).

Front 61

Major properties and effects of OM in soils:

Back 61

color, water retention, structure, negative charge, fertility.

Front 62

On a global scale, where are organic soils located? Why?

Back 62

On a global scale, organic soils largely occur in peatlands. Climate is the most important factor for the accumulation of organic matter, so these are generally found in cold or wet (or both!) places

Front 63

What is the order of sapric, hemic, fibric organic materials in order of increasing degrees ofdecomposition?

Back 63

Fibric, Hemic, Sapric

Front 64

How a pH number relates to hydrogen ion (H+) concentration.

Back 64

LOW pH means there are MORE H+ ions in solution and HIGH pH means there are LESS H+ ions in solution

Front 65

Understand the major sources of H+ to soils:

Back 65

1. carbonic acid,

2. organic matter,

3. oxidationof nitrogen,

4. aluminum hydrolysis,

5. plant root exudation to balance charges.

Front 66

Acidic cations -

Back 66

Al (mostly) and Fe3+

Front 67

Non-acidic cations -

Back 67

Na, K, Ca, Mg, Fe2+, Si

Front 68

Two main problems in acid soils - below what pH, generally?

Back 68

Nutrient availability, Aluminum toxicity

Front 69

Understand the one source of OH- to soils:

Back 69

dissolution of soluble Ca and Na carbonate (-CO3) salts.

Front 70

Two main problems in alkaline soils.

Back 70

Micronutrient available, soil sealing/ crusting

Front 71

On a global or continental scale, what is the major factor affecting soil pH? Why?

Back 71

Rain fall. Water contains CO2 which soaks into the soils

Front 72

litter/light fraction

Back 72

Physically recognizable organismal residues. Litter = on surface, LF = in soil.

Front 73

phyllosilicate

Back 73

important group of minerals that includes the micas, chlorite, serpentine, talc, and the clay minerals

Front 74

Hydrolysis

Back 74

reaction involving the breaking of a bond in a molecule using water. The reaction mainly occurs between an ion and water molecules and often changes the pH of a solution

Front 75

*The BIG 8 +4 elements

Back 75

O,Si,Al,Fe,Ca,Na,Mg,K (+4: S,N,C,P)

Front 76

*Oxygen is the most abundant BIG 8 element, making up ____% of the earth’s crust.

Back 76

46%

Front 77

*Global average C:N:P:S ratio in OM is

Back 77

100:10:1:1

Front 78

*OM is ___% Carbon

Back 78

50%

Front 79

*Soil (microbial) biomass usually makes up

Back 79

5% of total measured organic matter.

Front 80

*Humic substances usually make up the majority of total measured organic matter.

Back 80

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Front 81

*Range of pH that optimizes nutrient availability for agronomic applications:

Back 81

5.5-7.0