Term
|
Definition
• Extremely small size (clay-sized).
• Most smaller than 2 microns (µm) in
diameter.
• Large external and “internal” surface area.
• Hold a lot of water and cations (compared
to silt and sand-sized particles).
• Carry electronegative (-) charges and
some electropositive (+) charges.
• Can be either:
• mineral (clay crystals), or
• organic(humus). |
|
|
Term
| Crystalline Silicate Clays |
|
Definition
| Layer Silicates (tetrahedral and crystal sheets) |
|
|
Term
| Non-crystalline Silicate Clays (Andisols) |
|
Definition
| Dominantly amorphous clays (allophane and imogolite). |
|
|
Term
| Iron and Aluminum Oxides: |
|
Definition
| Dominately gibbsite (Al-oxide) and goethite (Fe-oxide). |
|
|
Term
| Organic Colloids (Humus): |
|
Definition
| Non-crystalline colloids dominated by long C-chain molecules. |
|
|
Term
| Most common elements in the earths crust? |
|
Definition
|
|
Term
|
Definition
|
|
Term
| Layered Silicon Clays, Dominant cations: |
|
Definition
| Si, Al, Mg, Fe coordinated to oxygen. |
|
|
Term
| What type of charge do Layered Silicon Clays have? |
|
Definition
|
|
Term
| Layer Silicate Clays basic building blocks |
|
Definition
• Silica or Al tetrahedron (Si+4/Al+3 coordinated to 4 O).
• Al or Mg octahedron (Mg +2 or Al+3 coordinated to 6 O). |
|
|
Term
| These basic building blocks of layered silicon clays can combine into what? |
|
Definition
tetrahedral and
octahedral sheets. |
|
|
Term
|
Definition
2 to 4 sheets can be stacked in sandwich-like arrangements
bound together by the sharing of oxygen atoms. |
|
|
Term
|
Definition
• Al+3 for Si+4 in the tetrahedral sheets,
• Mg+2 & Fe+2 (most commonly) for Al+3 in octahedral sheets |
|
|
Term
| Does Isomorphous Substitution change basic crystal structure |
|
Definition
|
|
Term
| Does Isomorphous Substitution change the electrical charge of the clay micelle |
|
Definition
|
|
Term
| Al+3 for Si+4 in a tetrahedron results in a net what what charge + or - |
|
Definition
|
|
Term
| Mg+2 for Al+3 in an octahedron results what type of charge? |
|
Definition
|
|
Term
|
Definition
|
|
Term
| Does Montmorillonite use Isomorphous substitution? and in what ways? |
|
Definition
• Mg+2 for Al+3 in octahedral sheet (mostly).
• Al+3 for Si+4 in tetrahedral sheet (some, but not much). |
|
|
Term
| Montmorillonite does is have a high or low cation absorption capacity. |
|
Definition
|
|
Term
| During Vermiculite Isomorphous substitution what is primarily substituted Si+4? |
|
Definition
| Al+3 for Si+4 in tetrahedral sheet. |
|
|
Term
| Vermiculite has Limited expansion due to presence of what? |
|
Definition
Mg+2 and some Al(OH)2+ ions
that act as “bridges” between the layers. |
|
|
Term
| what is an example of Nonexpanding 2:1 mineral. |
|
Definition
| Fine-grained micas (aka Illite) |
|
|
Term
| Fine-grained micas contain large amounts of what for Si+4 isomorphic substitution in tetrahedral layer. |
|
Definition
|
|
Term
| Fine-grained micas contain excess negative or postive charges satisfied by what cations in the interlayer. |
|
Definition
|
|
Term
| In fine-grained micas (aka Illite) K+ acts as a binding agent preventing what? |
|
Definition
| expansion of interlayers. |
|
|
Term
| Sources of charges on soil colloids a permenant charge is |
|
Definition
• Isomorphous substitution -
substitution of a cation of lower
valence for one of higher
valence
• Al+3 for Si+4 in tetrahedral layer
• Mg+2 for Al+3 in octahedral layer |
|
|
Term
| A pH-dependent charges are? |
|
Definition
Functional groups on colloid
surfaces that release or accept
a proton |
|
|
Term
| Constant negative charges on silicate clays are generated by? |
|
Definition
|
|
Term
| Minerals with trioctahedral sheets are most susceptible to development of what type of charge |
|
Definition
|
|
Term
| All layer silicates have some (+) charges but the net charge is |
|
Definition
|
|
Term
| Variable negative (-) charges are primarily associated with? |
|
Definition
| hydroxyl(OH) groups on edges and surfaces of inorganic colloids and humus. |
|
|
Term
| attachment of H+ ions to the surface OH groups of (1)oxides (Fe & Al) under acid conditions,(2) octahedral sheet of 1:1 Minerals & (3) broken edges of all layer silicates. |
|
Definition
|
|
Term
| have mostly pH dependent charge. |
|
Definition
| Humus, Kaolinite, Fe and Al Oxides, and Allophane |
|
|
Term
| Colloids are a mixture of ___ with a maze of (+) & (-) charges. |
|
Definition
silicate clays, oxides &
humus |
|
|
Term
| In temperate regions cations (+) or anions (-) dominate |
|
Definition
|
|
Term
| What serves to retain nutrients in the rooting zone of the soil for later plant uptake. |
|
Definition
|
|
Term
| The Cation Exchange Complex |
|
Definition
all soil colloids capable of
holding and exchanging cations |
|
|
Term
| Cations can be replaced by other cations through the process of |
|
Definition
|
|
Term
| Cation Exchange is or is not reversible? How fast does it occur |
|
Definition
| Is reversible, very quickly |
|
|
Term
| Which cation are held more tightly, large or small? |
|
Definition
|
|
Term
largest ionic radii and the
lowest hydration energy (fewer
water molecules surrounding
it) that is held most or least tightly on the permanent charge sites of
clay minerals. |
|
Definition
|
|
Term
|
Definition
any one cation can
replace any other if it’s
concentration is high enough |
|
|
Term
| Importance of Cation Exchange |
|
Definition
• The Exchange Complex retains cations necessary for plant growth
(Ca+2, Mg+2, K+, NH4
+, etc.).
• Thus, exchangeable ions are not leached away from roots of
growing plants yet are readily available to the plant.
• Further, many more cations reside on the exchange complex than in
soil solution. |
|
|
Term
|
Definition
the total amount of exchangeable cations (expressed in
moles of charge) that can be held by a given mass of soil. |
|
|
Term
CEC of a soil is function
of |
|
Definition
relative amounts and
types of colloids:
• humus,
• layer silicate clay
minerals
• oxides &
• amorphous
aluminosilicates
(allophane) |
|
|
Term
withincreasing pH and(decreasing H+
concentration) CEC increases or decreases? |
|
Definition
|
|
Term
| For a given cation, the proportion of the exchange sites occupied by that cation is called |
|
Definition
|
|
Term
If half of the total exchange sites are
occupied by Ca++ then we say the soil has ____% Calcium saturation. |
|
Definition
|
|
Term
| percentage base saturation |
|
Definition
| the % of the exchange sites occupied by basic cations. |
|
|
Term
| Mildly weathered soils have larger CEC values due to |
|
Definition
|
|
Term
| Intermediate weathered soils have less CEC and a gaining AEC due to |
|
Definition
|
|
Term
Strongly weathered soils aren’t very reactive at all, but show more of a
balance between |
|
Definition
|
|
Term
| What percentage of the worldwide soils are acidic |
|
Definition
|
|
Term
| a compound that releases H+ |
|
Definition
|
|
Term
| substance that combines with H+ |
|
Definition
|
|
Term
| an expression of the H+ activity in a solution |
|
Definition
|
|
Term
10 fold increase or decrease
in concentration of the
proton and hydroxyl |
|
Definition
| an increase in from a pH of 4 to 3 |
|
|
Term
|
Definition
|
|
Term
| Lemon is more acidic or basic? |
|
Definition
|
|
Term
| Acidic soil have a low or high pH? |
|
Definition
|
|
Term
| Alkaline soils have a low or high pH |
|
Definition
|
|
Term
The degree to which a soil is acid, neutral or alkaline (low pH, neutral
pH or high pH) is controlled by the amount of ___ and ___ ions in the
soil. |
|
Definition
|
|
Term
|
Definition
acidity due to H+ in the soil solution; this is what we
actually measure when we determine soil pH. |
|
|
Term
| Reserve or Exchangeable Acidity: |
|
Definition
exchangeable hydrogen and
aluminum that reside on the cation exchange sites within soil.
• Denoted “reserve acidity” because neutralization of H+ in the soil
solution brings a H+ ion from the exchange sites into solution (a
buffering process).
• Denoted “exchangeable” because added cations can displace these
acids and bring them into solution. |
|
|
Term
| commonly, a gazillion more ___ ions reside on the exchange sites than are in solution. |
|
Definition
|
|
Term
|
Definition
| the ability of a soil to resist change in pH. |
|
|
Term
|
Definition
Usually, the higher the CEC of a soil the greater its reserve
acidity and the higher its buffer capacity.
• This is important to 1) prevent drastic pH changes that could be
detrimental to soil organisms, and 2) determine the amount of
amendments needed to effect a desired change in soil pH. |
|
|
Term
When there are high levels of other (non acidic) cations on the
exchange sites the soil pH is seen to be.. neutral or alkaline. |
|
Definition
|
|
Term
| Common basic cations are: |
|
Definition
|
|
Term
| No-till increases or decreases acidity due to less soil organic matter oxidation |
|
Definition
|
|
Term
As a result, the optimum pH range
for nutrient availability is |
|
Definition
|
|
Term
| Toxicity of Soluble Aluminum is rarely a problem above a pH of |
|
Definition
|
|
Term
| Aluminum Toxicity in Ohio |
|
Definition
• Closely related to soil parent material.
• Acidic sandstones & shales in SE & acid glacial till in NE Ohio.
• Not found in limestone bedrock and high-lime glacial till in W Ohio |
|
|
Term
| Adding limestone to a soils does what to the pH |
|
Definition
|
|
Term
the amount of liming agent that is required
to bring about a desired pH change. Depends on: |
|
Definition
The change in pH desired
The buffer capacity of the soil
The type of liming agent |
|
|
Term
| A host of soil organisms feast on plant residues,left over residues,feces, corpses, and themselves. This results in the release of |
|
Definition
CO2, mineral nutrients,
and the formation of
more stable soil humus. |
|
|
Term
The ______ & ______ dominate
in the biological activity of most soils. |
|
Definition
|
|
Term
| _______, _______ and ______ account for 80% of the total metabolic activity in decomposition. |
|
Definition
Bacteria, fungi &
actinomycetes |
|
|
Term
|
Definition
Some existing humus is
also decomposed due to
the presence of fresh
residues |
|
|
Term
Factors Controlling the Rate of Decomposition and the
Transfer Between Soil Carbon Pools: |
|
Definition
1. The rate of plant residue decomposition depends on its
biochemical form.
2. The rate of plant residue decomposition depends on its
placement – either on the surface or within the soil.
3. The rate of plant residue decomposition depends on the
availability of other nutrients – mostly Nitrogen.
4. The rate of plant residue decomposition depends on a suitable
environment for food web members.
5. Organic matter can become physically sequestered or converted
to humus, slowing its decomposition. |
|
|
