Quiz 5 - Answers1.) a.) List the five master horizons for describing soil profiles.

O, A, E, B, C (2)b.) 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.) For the profiles at the bottom of the page:a.) which soil formed in more than one parent material?

B: (2C) (2)b.) 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 claysNatric: subsurface accumulation of high activity clays with >15% NaMollic: thick, dark colored, high B.S., strong structureUmbric: 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 (2)Most: Oxisols

5.) What end products does Madison Metropolitan sewerage district produce?

+cleaned effluent (liquid) (2)+nutrient rich biosolids (solid)

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)