Exam 3

Question 1

Soil Colloids characteristics

Answer 1

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

Question 2

Implications of adsorbed cations in colloids

Answer 2

-adsorbed cations exchange with cations in soil solution

Question 3

Cation Exchange Capacity (CEC)

Answer 3

• 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

Question 4

what is a mole

Answer 4

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

Question 5

What is a centimole?

Answer 5

= to .01 mole

Question 6

Equivalent weight

Answer 6

• molecular weight/valance

- the amount needed to generate a charge

Question 7

How to convert mass to charge

Answer 7

• find the equivalent weight

- convert to cmol(c) by multiplying .01

Question 8

Organic colloids

Answer 8

• carbon based

- primarily C, H, O

Question 9

What are the 2 major types of colloids

Answer 9

• mineral

- organic

Question 10

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

Answer 10

• H+ dissociation from:
• carboxyl group
• phenol hydroxyl group
• alcohol hydroxyl group

Question 11

Dissociation is ________

Answer 11

pH dependent

-high pH, low acidity

Question 12

Mineral colloids (3 types)

Answer 12

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

Question 13

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

Answer 13

• Isomorphous substitution

- replacement of 1 atom by another of similar size

Question 14

acid saturation

Answer 14

(H+Al)/CEC x 100

-percentage of CEC accounted for by H and Al ions

Question 15

Cation saturation

Answer 15

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

Question 16

Genesis of silicate clays

Answer 16

• alteration of primary minerals
• breakdown and recrystallization of primart minerals
• weathering sequence

Question 17

Strength of attraction of cations____

Answer 17

-depends on valance, hydrated radius

Question 18

CEC determination

Answer 18

• Buffer methods (extraction solution buffered)

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

Question 19

ECEC

Answer 19

• effective cation exchange capacity

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

Question 20

Soil acidity (pH) is correlated with _

Answer 20

• nutrient availability

- organism activity

Question 21

-one pH unit means ____ difference in H+

Answer 21

10^-4

Question 22

Source of H+ dissociation

Answer 22

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

Question 23

Al and Al hydroxides generate acidity by ____

Answer 23

hydrolyzing water

hydrolysis of water

Question 24

Three conceptual pools of acidity

Answer 24

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

Question 25

Active pool

Answer 25

-the samllest pool, | H+ activity in soil solution

Question 26

Salt replacable pool

Answer 26

- the mid-sized pool | - ions of H+ and Al+ are semi-readily available as exchangeable compounds

Question 27

residual pool

Answer 27

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

Question 28

why is soil pH relatively resistant to change

Answer 28

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

Question 29

What is a buffer

Answer 29

- a system that resists change | - resists change in pH for soils

Question 30

Fact influencing soil pH or reaction

Answer 30

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

Question 31

As acid saturation _____ pH ____

Answer 31

increases, decreases

Question 32

Which colloids can have a net positive charge?

Answer 32

- Kaolinite - Fe and Al hydroxides and oxides - noncrystalline silicate clays

Question 33

Buffer curve

Answer 33

pH vs Base saturation

Question 34

how to intensify soil acidity

Answer 34

- organic matter addition | - addition of FeSO4, S2, H2SO4

Question 35

How to reduce soil acidity

Answer 35

- lime addition | - add manure

Question 36

6 requirements for plant growth

Answer 36

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

Question 37

Criteria for an element to be essential

Answer 37

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

Question 38

The average plant

Answer 38

- 75% water and 25% solid - C is 42% of solid - H is 8% of solid - O is 42% of solid

Question 39

Macronutrients

Answer 39

- required by plants in relatively large amounts | - S, P, Mg, K, Ca, N, O, C, H

Question 40

Micronutrients

Answer 40

- required by plants in relatively small amounts | - Mo, Ni, Co, Cu, Zn, Mn, Fe, B, Cl

Question 41

Macronutrients C, H, O

Answer 41

- structural role | - no shortage due to being in the air and water

Question 42

Macronutrients N, P, S

Answer 42

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

Question 43

Macronutrient K

Answer 43

-osmoregulator, protein synthesis

Question 44

Macronutrient Ca

Answer 44

-structural role, membrane regulation

Question 45

Macronutrient Mg

Answer 45

-chlorophyll, protein synthesis

Question 46

What is the general role of micronutrients

Answer 46

-to recycle enzyme cofactors

Question 47

Mineralizations

Answer 47

-conversion of organic to inorganic

Question 48

Immobilization

Answer 48

-conversion of inorganic to organic

Question 49

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

Answer 49

- greater than the net effect is immobilization | - less than the net effect is mineralization

Question 50

Percentage of K in K2O (potash)

Answer 50

83%

Question 51

Percentage of P in P2O5 (soluble phosphate)

Answer 51

43.7%