Ren R 210 Module 2

kilo

10^3

centi

10^-2

mili

10^-3

micro

10^-6

porosity

The relative proportion of a volume of soil that is filled by air and water

particle density

density of solid mineral material (constant)

bulk density

weight of soil/volume of soil

Db and porosity of sand

1.55 Mg/m^3 and 42% (least aggregation)

Db and porosity of loam

1.20 Mg/m^3 and 55%

Db and porosity of clay

1.05 Mg/m^3 and 60% (most aggregation)

cohesion vs adhesion

cohesion - water molecules form weak bonds with each other
adhesion - water molecules form weak binds with other surfaces

hydrophillic

water loving (glass/sand)

hydrophobic

water repelling (OM)

water is affected by...

gravity force
matric force (adhesion/cohesion)
somatic force (salt content)

evapotranspiration

Work required to move water from point a (soil) to point b (atmosphere).

matric potential (Ψm)

adhesion/cohesion (adhesion of water to soil particles -> cohesion)

osmotic potential (Ψo)

salt content (water will move from low salt content to high salt content)

water availability to plants

grav pot (available to plants) 0.0 to -33 kPa
matric pot and osmotic pot (available to plants) -33 to -1500
matric pot and osmotic pot (unavailable to plants) -1500 to -3100
matric pot and osmotic pot (unavailable to everything) -3100 onwards

soil texture AW in descending order

loam > clay > sand

influence of texture on water infiltration rate (i)

coarse soil -> large particles, large pores, fast infiltration
fine soil -> small particles, small pores, slow infiltration

influence of structure on water infiltration rate (i)

Granular: fast (i), small round peds
Blocky: moderate (i), angular peds
Prism: moderate (i), salt crust, osmotic potiential high
Platy: slow (i), horizontal peds

Saturated flow is controlled by...

Darcy's law

saturated flow vs. infiltration rate

saturated flow - measure of how fast water moves through a soil
infiltration rate - rate at which water moves into a soil

ground water

saturated zone

water table

upper limit of ground water (can fluctuate seasonally)

vadose zone

zone of unsaturated material above the water table

capillary fringe

zone of capillary rise (can fluctuate seasonally)

what changes porosity of a soil

aggregation increases porosity. texture alone changes surface area, but not porosity. however, finer textures (i.e clay) have more aggregates).

rock types

igneous, metamorphic, sedimentary

primary vs secondary minerals

sand+silt -> primary minerals
clay -> secondary mineral
secondary minerals are primary minerals that have weathered

colloids

homogenous mixture of ultramicroscopic particles of one substance dispersed through a second substance. particles do not settle and can’t be separated (ex: gels, soils, and emulsions)

dominant colloid in AB soils

crystalline silicate clays = phyllosilicates = aluminosilicates

central cation replacement

isomorphic substitution
can take place during weathering

1:1 type mineral structure

1 tetrahedral to 1 octahedral

2:1 type mineral structure

1 octahedral between 2 tetrahdral
(generally have more isomorphic substitution, therefore more charge)

4 types of silicate clays

Kaolinite (dominant in australia)
Montmorillonite, illite and chlorite (dominate in AB)

Kaolinite structure

1:1

Montmorillonite, illite and chlorite structure

2:1

d spacing

distance from the top of one platelet to the top of the next platelet
0.72 nm in kaolinite
~ 1.0 - 2.0 nm in montmorillinite
1.0 nm in illite
1.4 nm in chlorite

Platelets are held together by hydrogen bonding in...

Kaolinite

Uses of Kaolinite

No shrink/swell so...
construction (bricks)
ceramics
glossy coating on magazines

no attraction between platelets in...

montmorillinite

Montmorillinite good for...

High shrink/swell so
good nutrient retention (higher isomorphic substitution and higher CEC compared to kaolinite)
construction (sealant)

K+ in interlayer causes cation bridging in...

illite

Mg^2+ in interlayer causes cation bridging in...

Chlorite

No shrink swell

Kaolinite

Min shrink/swell

Illite and chlorite

Max shrink/swell

Montmorillinite

CEC

property of a soil that describes it's capacity to supply nutrient cations to the soil solution for plant uptake.
increased CEC = increased fertility

Typical CEC values

CEC increases as texture becomes finer
CEC = mont > illite and chlorite > koal
Clay and OM have CEC

If ESP is >15%...

problem for soil function due to soil sodicity and clay deflocculation

General order of cation replacement

(looser) Li+< Na+ < K+ < Cs+ < Be+2 < Mg+2 < Ca+2 < Ba+2 < Al3+ < Fe3+ (tighter)
based on...
valence (higher valence cations can replace cations of lower valence)
ion size (cations with smaller hydrated radius have greater replacement power)

EC and ESP affect on plant growth and structure