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)

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: Al 3+, Ca 2+, Mg 2+, K +, H +, Na + –anions: Cl -, NO 3-, SO 4 2- 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 Mg 2+ dioctahedral: 6O with 2 Al 3+

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: Si 4+ –potential replacement ions: Al 3+, Fe 3+ in octahedral sheets: –expected ions: Al 3+, Mg 2+ –potential replacement ions: Al 3+, Fe 3+, Mg 2+, Zn 2+, Fe 2+

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)