Quiz 5 - Answers 1.) a.) List the five master horizons for describing soil profiles.

1. Quiz 5 - Answers 1.) 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 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 (2) Most: Oxisols 5.) What end products does Madison Metropolitan sewerage district produce? +cleaned effluent (liquid) (2) +nutrient rich biosolids (solid)

2. Soil Colloids : Chapter 8

3. 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

6. 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

7. 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

8. Important Properties of Soil Colloids • Size • Surface Area • Surface Charge • Cation/Anion Exchange

9. 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

11. 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+

12. Fig. 8.4

15. 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+

16. 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

19. Genesis of Soil Colloids • alteration • decomposition and recrystallization **parent material and weathering conditions**

21. Soils: An Introduction (Singer and Munns)