Quiz 5 - Answers
1.)
a.)
List the five master horizons for describing soil profiles.
O, A, E, B, C
b.)
(2)
What is an elluvial horizon?
Horizon in which there has been movement OUT (exiting) of
clays, Fe, Al, O.M.; often designated master horizon=E
2.)
a.)
For the profiles at the bottom of the page:
which soil formed in more than one parent material?
B: (2C)
b.)
(2)
which soil has a transitional horizon?
A: (BC)
3.)
Name one diagnostic horizon and give a brief description of it.
(Table 3.1)
examples:
(2)
Argillic: subsurface accumulation of high activity clays
Natric: subsurface accumulation of high activity clays with >15% Na
Mollic: thick, dark colored, high B.S., strong structure
Umbric: same as mollic, but low B.S.
4.)
Which soil is the least weathered and which soil is the most weathered?
Oxisols, Alfisols, Mollisols, Entisols, and Inceptisols.
Least: Entisols
Most: Oxisols
5.)
(2)
What end products does Madison Metropolitan sewerage district produce?
+cleaned effluent (liquid)
+nutrient rich biosolids (solid)
(2)
Soil Colloids : Chapter 8
Primary Minerals
• Table 2.2 and Figure 2.4
• Remember definition of mineral
– general adjective to describe inorganic materials derived
from rocks
• ex: silicate clays
– specific noun to refer to distinct minerals found in nature
• ex: quartz, feldspar
Definitions
• colloids: organic and inorganic matter with very small particle
size and a correspondingly large surface area per unit of mass
• silicate clay: colloid with Si in framework
• nonsilicate clay: colloid withOUT Si in framework
• humus: more or less stable fraction of the soil O.M. remaining
after the major portions of added plant and animal residues
have decomposed
Definitions
• exchangeable ions:
– cations: Al3+, Ca2+, Mg2+, K+, H+, Na+
– anions: Cl-, NO3-, SO42-
• crystal structure: the orderly arrangement of atoms in a
crystalline material
• amorphous: noncrystalline
Important Properties of Soil Colloids
• Size
• Surface Area
• Surface Charge
• Cation/Anion Exchange
Four Major Types of Soil Colloids
• Inorganic
– 1) crystalline silicate clays
– 2) non-crystalline silicate clays
– 3) Fe/Al oxides (non silicate clays)
• Organic
– 4) humus
Structure of Soil Colloids
• Silicate clays
Fig 8.4
Building Blocks
– tetrahedral
• 4-sided
• 1 Si, 4 O
– octahedral
• 8-sided
• trioctahedral: 6O with 3 Mg2+
• dioctahedral: 6O with 2 Al3+
Fig. 8.4
Isomorphic Substitution
• Definition: the replacement of one atom by another of similar
size in a crystal lattice without disrupting or changing the crystal
structure of the mineral
• Table 8.2
• in tetrahedral sheets:
– expected ions: Si4+
– potential replacement ions: Al3+, Fe3+
• in octahedral sheets:
– expected ions: Al3+, Mg2+
– potential replacement ions: Al3+, Fe3+, Mg2+, Zn2+, Fe2+
Structure of Soil Colloids
• Nonsilicate clays = Fe/Al Oxides
– no Si
– octahedral only (no tetrahedral)
– little isomorphic substitution
– small negative, sometimes positive charge
• Humus
– noncrystalline
– large organic molecule (C, O, H, N)
– net negative charge
– Fig. 8.13
Genesis of Soil Colloids
• alteration
• decomposition and recrystallization
**parent material and weathering conditions**
Soils: An Introduction (Singer and Munns)