Clays, CEC, Acidity, Allalinity Flashcards
Tetrahedral sheet
Two planes of exigen, mainly silicon between the spaces
Basic unit is a silicon atom connected to four oxygen atoms
Octahedral sheet
Six oxygen atoms with a central aluminum or magnesium atom.
Forms eight sided geometric solid, or octahedron
Trioctahedral sheet
Three Mg 2+ ions coordinated with six oxygens or hydroxls
Dioctrahedral sheet
6 oxygens or hydroxyls coordinated with two Ai3+ ions
Isomorphic substitution (add to)
Replacement by ions of similar radios or charge
Lower valence subs for higher
Usually results in net negative charge
Kaolinite
1:1
Octahedral layer, tetrahedral layer
No expansive
Simple, can’t absorb much
Acid environment, leaching
-mollisols 1, alfisols 1, spodosols 1, ultisols 3, oxisols 3
Smectite
2:1
Max swelling expansive clay
Inter later water, Inter later Mg2+, cations from cec
Alkaline environment or alteration of primary constituents
Semi arid to arid. Complicated structure, salts, deserts
Think Aridisols!!!! Also Vertisols, mollisols, and alfisols some
Micas
2:1
Tetrahedral, octahedral, tetrahedral
Inter k+ (potassium, can be carbón dated)
Non-expansive
Parent material from magma
Aridisols, also mollisols and alfisols
Illite, weathered form of mica, most abundant and almost everywhere
Vermiculite
2:1
Tetra, octa, terta
Inter later water and mg 2+
Expansive, can absorb stuff
Temperate to subtropical, depends on parent material
Mollisols, alfisols, ultisols
1:1 clays
Octahedral sheet (square) and tetrahedral shape (rhombus?) sharing Cygwin layer
Layers held together with hydrogen bonds
No real expansion, lower cec
Kaolinite
2:1 clays expansive
Weaker Inter layer bonding. Mg ions or O/OH ions
Expansive lattices
Smectite
Vermiculite
2:1 Clays, non expansive
Mica group, containing illite
Chlorite
Flocculation ??
Process where soil particles of soil adhere to one another, forming grains of a larger size
Negative clay particles attract positive ions such as ca2+, holds particles together
What ions are involved in acidity and why. Why is ph 7 neutral
Acidity is a measurement of H+ in soil, inversely to the amount of OH-
Following proton through reaction, in context of water.
Water dissociates into 2 different compounds…
An acid is a proton donor, increases the solution concentrations of H+ (hydronium) ions
Base is a proton acceptor, reduces the H+ and increases the OH- (hydroxide)
H+ vs H3O+ (hydronium)
pH 7 is neutral
Biggest Drivers of acidity
Climate
Rainfall and leaching
Biology
Ecosystems and OM
AI3+ and acidity
At vary low pH, aluminum gets into water and forms aluminum hydroxides, increases acidity
Aluminum reacts with water, creates 3 moles of acidity for each ion of aluminum in the system
pH
Concentration of hydronium ion
H20 goes to H+ OH -
More hydronium= more acid= lower pH
10^-14 (constant ion product)
pH= -Log [H+]
pOH=-log[OH-]
pOH+pH= 14
Sources of acidity
OM: Forms soluavle conplexes with non acid cations, keeps them from being lost
-carbonic acid
Nigrification= microbial oxidation of ammonia to nitrate=produces acidiy
-nitric acid
-problems w fertilizer
Sulfur Oxidation: produces soldering acid
Wetlands, coastal ecosystems, dredged sediments
Coal
Acid rains, fossil fuel: sulfur, N oxides, mix with atmospheric water and fall in rain
CEC, leaching or base cations…
Effects of acidity
Hard for plants to get nutrients, grow roots
Aluminum can be toxic, and I’d soluavle at low pH
“Acid soil headache”:
Tocxisity: Ai, H, Mn
Deficient: CA, Mg, Mo, P
Pools of acidity
Active: small, in ss
Echangible: salt replacible, AI3+ and H+ bond to chatgebsites in vary acid souks
Can be released in action exchange w un effected salt
Residual: H+ and AI3+ bound in non exchangibke form within crystal lattices, in om, slow release over time
Buffering Capacity
Ability of soul to resist changes in pH
Assessed via titration, important for ag.
Wbu might you use different measures of acidity [reaserch]
Salinity
Salts other than sodium salts CA2+, MG2+,
More flocculation, better for soil structure
EC above 4
SAR below 13
Saline-Spodic
Natural soluable salts and Na
-na bad got plants, but not dispersal issues
-EC > 4
SAR > 13
EC
Electrical conductivity
Pure water= Poot electrical conductor
EC increased with salts, thus EC I’d a measure of salts
EC >2 is bad for some
>4 is bad for all
Spodic
Na salts, sodium
Low natural salts and low EX,
Bad for structure, can disperse or become Indurated
EC < 4
SAR > 13
ESP
The exchangeable sodium percentage (ESP) measures the proportion of cation exchange sites occupied by sodium. Soils are considered sodic when the ESP is greater than 6, and highly sodic when the ESP is greater than 15
For measuring sodicity
ESP= exchangibke na (cmolc kg-1) *100
—————————————
CEC (cmolckg-1)
ESP > 15 associated with deteriorated soil physical properties
Sodium absorption ratio
Percent of salts that are na vs mg and ca
Measures what percent of salts are sodium vs magnesium and calcium
Bad to good flocculatirs, ration of Na+ to Ca2+ and Mg2+
Na+
————-
Square root of 1/2*(ca2+ + mg2+)
Star of 13 is eso of 15
Salt causes
Irrigation
Rain
Capillary water coming up from salty water table
Salt effects on soul prop
Induration
Issues with structure, inhibits clay flocculation
Can lead to dust that blows away
Salts issues
Flocculation and structure stuff
Also osmotic pressure for plants, so much Na that they don’t take up other nutrients..
CEC
Cation Exchange Capacity (CEC) refers to a soil’s ability to hold positively charged ions (cations) like calcium, magnesium, and potassium, which are essential nutrients for plant growth, through electrostatic attraction to negatively charged sites on soil particles.
