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Soils > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Soil Colloids characteristics

A
  • small size
  • high specific surface area
  • net negative charge expressed at surface with adsorbed cations
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2
Q

Implications of adsorbed cations in colloids

A

-adsorbed cations exchange with cations in soil solution

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3
Q

Cation Exchange Capacity (CEC)

A
  • expressed as cmol(c)/kg
  • the sum of exchangeable cations soils can absorb
  • fn(amount and type of colloid)
  • organic matter and clay are the 2 types
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4
Q

what is a mole

A

-weight of element that contains 6.02 x 10^23 atoms (molecular weight

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5
Q

What is a centimole?

A

= to .01 mole

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6
Q

Equivalent weight

A
  • molecular weight/valance

- the amount needed to generate a charge

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7
Q

How to convert mass to charge

A
  • find the equivalent weight

- convert to cmol(c) by multiplying .01

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8
Q

Organic colloids

A
  • carbon based

- primarily C, H, O

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9
Q

What are the 2 major types of colloids

A
  • mineral

- organic

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10
Q

What is the source of the net negative charge in organic colloids

A
  • H+ dissociation from:
  • carboxyl group
  • phenol hydroxyl group
  • alcohol hydroxyl group
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11
Q

Dissociation is ________

A

pH dependent

-high pH, low acidity

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12
Q

Mineral colloids (3 types)

A
  • Crystalline silicate clays = phyllosilicates
  • Noncrystalline silicate clays (short range order and paracrystalline)
  • Fe and Al oxides and hydroxides (silicate missing, crystalline and amorphous)
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13
Q

What is the source of the net negative charge in for mineral (inorganic) colloids

A
  • Isomorphous substitution

- replacement of 1 atom by another of similar size

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14
Q

acid saturation

A

(H+Al)/CEC x 100

-percentage of CEC accounted for by H and Al ions

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15
Q

Cation saturation

A
  • Proportion of CEC satisfied by specific cation (expressed as %)
  • cation/CEC
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16
Q

Genesis of silicate clays

A
  • alteration of primary minerals
  • breakdown and recrystallization of primart minerals
  • weathering sequence
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17
Q

Strength of attraction of cations____

A

-depends on valance, hydrated radius

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18
Q

CEC determination

A
  • Buffer methods (extraction solution buffered)

- Unbuffered methods (extraction solution at pH of soil with neutral salt)

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19
Q

ECEC

A
  • effective cation exchange capacity

- the total amount of exchangeable cations, which are mostly sodium, potassium, calcium and magnesium

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20
Q

Soil acidity (pH) is correlated with _

A
  • nutrient availability

- organism activity

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21
Q

-one pH unit means ____ difference in H+

A

10^-4

22
Q

Source of H+ dissociation

A

-wear inorganic acids (high pKa, ex. carbonic acid), stronger organic acids (low pKa)

23
Q

Al and Al hydroxides generate acidity by ____

A

hydrolyzing water

hydrolysis of water

24
Q

Three conceptual pools of acidity

A

1) Active acidity (pool)
2) Salt replaceable acidity (pool)
3) Residual acidity (pool)

25
Q

Active pool

A

-the samllest pool,

H+ activity in soil solution

26
Q

Salt replacable pool

A
  • the mid-sized pool

- ions of H+ and Al+ are semi-readily available as exchangeable compounds

27
Q

residual pool

A
  • the largest pool
  • Bounded ions are help up in silicate clays and organic matter
  • the H+ ions are not readily available to exchange with
28
Q

why is soil pH relatively resistant to change

A

-the three pools are in dynamic equilibrium and act as a buffer

29
Q

What is a buffer

A
  • a system that resists change

- resists change in pH for soils

30
Q

Fact influencing soil pH or reaction

A

1) Acid Saturation
2) Type of colloid
3) adsorbed cations (Na results in higher pH)
4) parent material (limestone vs sandstone)
5) vegetation
6) precipitation
7) depth in the profile (going deeper increases alkaline)
8) season
9) fire
10) in the lab

31
Q

As acid saturation _____ pH ____

A

increases, decreases

32
Q

Which colloids can have a net positive charge?

A
  • Kaolinite
  • Fe and Al hydroxides and oxides
  • noncrystalline silicate clays
33
Q

Buffer curve

A

pH vs Base saturation

34
Q

how to intensify soil acidity

A
  • organic matter addition

- addition of FeSO4, S2, H2SO4

35
Q

How to reduce soil acidity

A
  • lime addition

- add manure

36
Q

6 requirements for plant growth

A

1) light
2) favorable temp
3) water
4) aeration
5) absence of toxic substances
6) nutrient elements (18 essential)

37
Q

Criteria for an element to be essential

A

1) required to complete life cycle
2) requirement is direct
3) cant be substituted by another element

38
Q

The average plant

A
  • 75% water and 25% solid
  • C is 42% of solid
  • H is 8% of solid
  • O is 42% of solid
39
Q

Macronutrients

A
  • required by plants in relatively large amounts

- S, P, Mg, K, Ca, N, O, C, H

40
Q

Micronutrients

A
  • required by plants in relatively small amounts

- Mo, Ni, Co, Cu, Zn, Mn, Fe, B, Cl

41
Q

Macronutrients C, H, O

A
  • structural role

- no shortage due to being in the air and water

42
Q

Macronutrients N, P, S

A
  • OM is the major source
  • S responsible for ATP and DNA
  • N plays a role in amino/nucleic acids
43
Q

Macronutrient K

A

-osmoregulator, protein synthesis

44
Q

Macronutrient Ca

A

-structural role, membrane regulation

45
Q

Macronutrient Mg

A

-chlorophyll, protein synthesis

46
Q

What is the general role of micronutrients

A

-to recycle enzyme cofactors

47
Q

Mineralizations

A

-conversion of organic to inorganic

48
Q

Immobilization

A

-conversion of inorganic to organic

49
Q

If the carbon to nitrogen ration is greater than 25:1 then _______ if less than 25:1 then ______

A
  • greater than the net effect is immobilization

- less than the net effect is mineralization

50
Q

Percentage of K in K2O (potash)

A

83%

51
Q

Percentage of P in P2O5 (soluble phosphate)

A

43.7%

Soils (3 decks)

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