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82 Cards in this Set
- Front
- Back
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What are the 6 main SOIL PROPERTIES ???
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Color
Texture Density Pore Space Structure Aggregate Stability |
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Explain the physical property - COLOR, and the three parts of it.
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The coating of the particle
HUE: the general color of the soil; related to MINERALOGY VALUE: how light/dark the soil is; related to ORGANIC MATTER (0=darkest) CHROMA: how vibrant/bright the soil is; related to the MOISTURE REGIME (0=grey) |
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Explain the physical property - TEXTURE, and what does it affect?
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The proportion of sand, silt, and clay in a soil.
It determines the water holding capacity, aggregate potential, stability, aeration, etc.... |
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What are the size ranges for Sand, Silt, and Clay???
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Sand = 2.0 - 0.05mm
Silt = 0.05 - 0.002mm Silt = < 0.002mm |
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What is the relationship between PORE SIZE and PARTICLE SIZE???
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They increase proportionally...the larger the particle the larger the pore.
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What is the relationship between PORE VOLUME and PARTICLE SIZE???
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They are INVERSELY related...the SMALLEST PARTICLES have the GREATEST VOLUME.
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Define and explain:
- Particle Density - Bulk Density - Porosity |
Particle Density (Dp): density of the solids (no pore space)
Typical Dp ~ 2.65 g/cm^3 = Mass [solid soil; compact]/Volume Bulk Density (Db): density of the entire soil (including pore space) Usually around HALF of 2.65 g/cm^3 = Mass [dry soil]/Volume Porosity (%PS): volume of pore space between soil solids. Typically ~ 50% = 100 x [1- (Db/Dp)] |
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What is the relation between POROSITY and BULK DENSITY???
*What if CLAY CONTENT was a factor, too? |
They are inversely related; as bulk density increases the %PS decreases.
*As clay content increases, %PS increases and Db decreases. |
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What are the 3 main goals of good SOIL MANAGEMENT???
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- Low bulk density
- Lots of macropores - Stable aggregates |
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We know what texture is...what is soil STRUCTURE???
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The spatial arrangement of those particles
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Why IS there structure in soil?
What factors contribute to its "aggregate stability"? |
Particles bind due to organic compounds and some minerals.
-Biological sources: roots, animals, organic complexes - Mineralogical sources: clay particles, carbonates, oxides **Primarily ORGANIC MATTER** |
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What are the three main effects that makes aggregation important?
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- Increased porosity/pore size distribution
- Increased infiltration, drainage; decreased runoff - Increased water holding capacity |
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What are the 3 main CHARACTERIZATIONS of STRUCTURE???
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TYPE: the SHAPE of the aggregates; Granular, platy, blocky, prismatic
SIZE: fine, medium, coarse GRADE: DISTINCTNESS (how visible) Strong, moderate, or weak |
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In general, CLAY abundance promotes which TYPE of aggregates (shape)?
What about OM abundance? |
Clay ~ STRONG structure, bigger blocks
OM ~ Granular structure |
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What is the size variance between MACRO and MICROPORES?
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Macropore > 0.08mm
Micropore < 0.08mm |
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What 5 conditions PROMOTE aggregate STABILITY???
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- Low disturbance
- Root abundance - Fungal biomass - Organic matter - Clay content |
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Define:
Basin/Catchment & Watershed (How are they different?) |
Basin: the area of land drained by a single system.
Watershed: the lines that divides basins. |
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What 6 things contribute to the amount of STORED WATER in soil?
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- Water inputs (frequency, type)
- Soil texture (clay holds more) - Soil structure (aggregates hold more) - Soil depth (deep soil holds more) - Presence of impeding layers - Organic matter content (more OM, more water) |
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what is the MASS-BASED calculation for measuring WATER CONTENT in a soil?
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Gravimetric Water Content (%)
= 100% (Wet mass - Dry mass) / Dry mass |
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What is the VOLUME-BASED calculation for measuring WATER CONTENT in a soil?
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Volumetric Water Content (%)
= (Gravimetric Content %) x (Db) |
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What are the 4 methods of measuring SOIL WATER?
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- Buried porous block
- Time domain reflectometry - Neutron probe - Tensiometer |
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Define:
Adhesion & Cohesion (How are they different?) |
Adhesion: the attraction of water to solid surfaces.
Cohesion: the attraction of water molecules to each other. |
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You can tell whether a surface is HYDROPHILIC/-PHOBIC by observing its contact angle.....
What should you see with each? |
Hydrophilic: ACUTE angle
Hydrophobic: OBTUSE angle |
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The rate of water movement through a soil is controlled by what?
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Tortuosity (influenced by soil texture, particle packing, water content, pore shape)
*Intrinsic permeability |
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What are the 3 categories of SOIL WATER?
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- Gravitational water (drains under gravity)
- Capillary water (retained by cohesion/adhesion; available to plants) - Hygroscopic water (bound to mineral surface; unavailable to plants) |
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Define:
Field capacity & Wilting point (What categories of soil water describe each?) |
Field capacity: the maximum amount of water retained after gravitational water has left (water in macropores); Capillary water.
Wilting point: water held too tightly against soil particles for plants to access; Hygroscopic water. |
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Water AVAILABLE to plants is in what PRESSURE RANGE?
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-10 to -1500 kPa
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Available water is found between what two stages?
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Field capacity and Wilting point
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A moisture release curve is related to the PORE SIZE DISTRIBUTION....what are the CURVES associated with an EVEN and UNEVEN distribution???
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Even: more LINEAR
Uneven: more EXPONENTIAL |
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What are the 3 GRADIENTS that move water in soil?
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Gravitational: a PRESSURE gradient associated with SATURATED soils
Osmotic: a CHEMICAL gradient seen in arid areas; how plants move water INTO ROOTS Matric: CAPILLARY forces (adhesion and cohesion) in UNSATURATED soils. |
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Pore size and capillary rise have a calculable relationship...what is it?
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When HEIGHT rise DOUBLES, the RADIUS of curvature (i.e. pore size) is HALVED.
Height (cm) = 0.15 / Radius (cm) |
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What are the 3 types of WATER MOVEMENT?
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Saturated flow: generally DOWNWARD; gravitational
Unsaturated flow: pores not filled to capacity, so water moves RADIALLY Vapor movement: HYGROSCOPIC water |
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When a soil is saturated, the pressure in the pores is.....?
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ZERO
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The rate of water movement is.....?
With more pores (pathways) for water, is [?] high or low? What two things affect it most? |
Hydraulic Conductivity (Ksat)
Ksat is HIGH with more pores Affected by: - total porosity - pore size distribution |
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What is Darcy's Law???
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Calculation for water flow rate....
Q = (Ksat) Area (head1 - head2) / Length |
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How does Ksat differ between SATURATED and NON-SATURATED conditions?
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Ksat is CONSTANT in saturated conditions
Ksat varies with WATER CONTENT when unsaturated |
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Define: soil colloid
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Organic and inorganic matter with very small particle size and a large surface area per unit mass.
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What are the 4 categories of SOIL COLLOIDS???
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1. Crystalline silicate clays (phyllosilicates)
2. Noncrystalline silicate clays (amorphous) 3. Iron and aluminum oxide clays 4. Organic matter (humus) |
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What are the 2 main SOIL PROCESSES??
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1. Weathering of MINERALS to CLAY
2. Decomposition of ORGANIC MATTER to HUMUS |
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What is CLAY (3 things)???
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- Particle SIZE class (<0.002mm)
- TEXTURAL class (soils with >45% clay) - MINERAL type with specific properties and characteristics (secondary mineral) |
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How are CLAYS different from SANDS/SILTS ???
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Sands/silts are CHEMICALLY identical, PRIMARY minerals, and differ only in SIZE.
Clays are chemically transformed SECONDARY minerals. |
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What are the 2 building blocks of clays?
What do they form? |
Silica tetrahedrons
& Aluminum octahedrons They come together to make SILICATE LAYER CLAYS |
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Define: Isomorphic Substitution...
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The replacement of ONE ION for another of similar size WITHIN the CRYSTALLINE STRUCTURE at the time of CRYSTAL FORMATION.
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What does an ISOMORPHIC substitution CHANGE???
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It changes the TOTAL CHARGE and the CHARGE LOCATION on the minerals.
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What are the 3 IONS that fit in a TETRAHEDRAL sheet (in the order of strongest to weakest) ???
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1. Silicon (4+)
2. Aluminum (3+) 3. Iron (3+) |
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What are the 5 IONS that fit in an OCTAHEDRAL sheet (in the order of strongest to weakest) ???
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1. Aluminum (3+)
2. Iron (3+) 3. Magnesium (2+) 4. Zinc (2+) 5. Iron (2+) |
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What are ALL the ions possibly found in the EXCHANGE SITES ???
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Aluminum (3+)
Iron (3+) Magnesium (2+) Zinc (2+) Iron (2+) Sodium (1+) Calcium (2+) Potassium (1+) |
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What are the 2 ANIONS that are found in BOTH tetra- and octa- sheets???
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Oxygen (2-)
Hydroxide (1-) |
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What are the UNIT CELLS in a SILICATE layer???
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Silica tetrahedrons and Aluminum octahedrons
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What are the 2 general CATEGORIES of CLAY MINERALS ???
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1:1 and 2:1 silicate clays
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What are the 1:1 clays?
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One tetrahedral sheet for every octahedral sheet.
*Kaolinite |
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What are the 2:1 clays?
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Two tetrahedral sheets for every octahedral sheet.
*Smectites, Micas, Vermiculites (and Chlorites) |
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What are the 4 FACTORS that define a CLAY MINERAL???
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- The number and layering of TETRA- and OCTA- sheets
- Number of CATIONS in octahedral sheet - SIZE and LOCATION of LAYER CHARGE - Absence/presence of INTERLAYER CATIONS |
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Explain: Kaolinite clays
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~COMPLETE DISSOLUTION~
1:1 clay (1 tetrahedral layer: 1 octahedral layer) Found in WARM, MOIST CLIMATES Stable at LOW pH Most WEATHERED of silicate clays No INTERNAL CHARGE ; nutrient POOR No SHRINK-SWELL **Oxisols and Ultisols** |
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Explain: Smectite clays
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~COMPLETE DISSOLUTION~
2:1 clay (2 tetrahedral layers: 1 octahedral layer) Bonded by Van der Waal's Forces Layer charge due to Mg2+ substituting for Al3+ Unstable under LOW pH and HIGH moisture ~MOST SWELLING~ Nutrient RICH |
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Explain: Vermiculite clays
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~MOST NUTRIENT RICH~
2:1 clay High layer charges; isomorphic substitution in BOTH tetra-/octa- sheets Little shrink-swell Stable under MOD-LOW pH **Mollisols** |
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Explain: Fine-grained Mica clays
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~K+ PACKING~
2:1 clay Nutrient POOR No shrink-swell Stable under MOD-LOW pH Potassium bonding in INTERLAYER ~CHARGE in TETRA- SHEETS~ |
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Explain: Chlorite clays
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~HYDROXYL SHEET in INTERLAYER SPACE~
No swelling, Nutrient POOR Isomorphic Sub. in BOTH tetra-/octa- sheets |
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Where does ISOMORPHIC SUBSTITUTION happen in each clay type???
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Kaolinite: EDGES (no permanent charge)
Smectite: OCTA- sheets Vermiculite: ALL SHEETS, interlayer space Mica: TETRA- sheets Chlorites: ALL LAYERS |
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What 2 processes form SILICATE clays???
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1. Dissolution and recrystalization
2. Chemical alteration of primary minerals |
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Clays differ in what 2 ways???
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1. Weathering conditions
2. Ions present and their concentration in the solution at time of crystallization. |
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What are 5 factors affecting MINERAL STABILITY???
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- Number of BASE CATIONS (soluble ions)
- Linked tetra- layers (more O2 sharing = more stable) - Al switched for Si (more Al = less stable) - Presence of Fe (more = less stable) - Bonds (ionic = heat tolerant; covalent = stronger, but not heat tolerant) |
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What are the 2 types of CHARGE in clay layers???
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PERMANENT charge: due to ISOMORPHIC substitution
pH-DEPENDENT charge: variable, due to EDGE charge |
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What type of charge is important in KAOLINITE and HUMUS where there is no INTERNAL charge???
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pH dependent / Edge charge
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What makes a charge pH dependent???
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Hydroxyl groups at the EDGES where the pH (potential Hydrogen) affects the amount of free charge locations
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What IS soil???
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a NEGATIVELY CHARGED...
4-dimensional, living, self-organizing HABITAT! |
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What are the 2 CONTROLS on ION EXCHANGE??
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- Relative CONCENTRATION**
- Strength of ABSORPTION |
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How is the strength of ABSORPTION calculated???
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Coulomb's Law:
F[attraction] = Charge / radius^2 |
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What is the LYOTROPIC SERIES???
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Hydrogen > Aluminum > Calcium > Magnesium > NH4+ = Potassium > Sodium
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Define: Cation Exchange Capacity (CEC)
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The NUMBER of NEGATIVE charges on a mineral surface
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If the CEC of a soil is 14 cmol/kg, how many Hydrogen ions can it absorb???
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14 cmol/kg !!!
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What 2 factors control CEC ???
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- AMOUNT of clay and OM
- TYPE of clays |
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What are the general CECs for Humus and Silicate clays???
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Humus = ~200 cmol/kg
Clays = ~50 cmol/kg |
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What are the 3 sources of ACIDITY in a soil???
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Hydrolysis
Biological decomposition Dissolution of minerals **ALL require WATER** |
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Based on what you know about ACIDIC soils (nutrient poor), WHERE can they typically be found?
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Very wet conditions; humid climates
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What are the relative CECs of the different soil components (in order from HIGHEST to LOWEST)
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~ Organic Matter ~
> 2:1 clays > Non-clayey soils > 1:1 clays ~ Highly weathered; oxides ~ |
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What is the RULE of THUMB for calculating CEC in a soil???
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CEC = (% OM x 200 cmol/kg) + (% clay1 x [cec1]) + (% clay2 x [cec2])....etc.
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Based on how "nutrient rich" each clay is, how would their CECs compare (in order of HIGH to LOW) ??
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Vermiculite > Smectite > Chlorite > Kaolinite
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In 1:1 clays and Humus, how does CEC change with pH ???
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1:1 clays and humus are pH-dependent due to EDGE CHARGE....
therefore: the LOWER the pH (more acidic; more H+) the LOWER the CEC (less free negative charge) |
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Is BIOCHAR pH dependent like 1:1 clays/humus or does it have a permanent charge like 2:1 clays???
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pH dependent!
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Define: Base saturation
*How do you calculate it??? |
A measure of the PROPORTION of basic CATIONS occupying the EXCHANGE sites
** [SUM (cations) / CEC] x 100% |
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What are the three benefits that define BIOCHAR?
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- Increased soil quality (CEC)
- Removal of CO2 from the atmosphere - Release of energy from biomass |
