1. Chapter 2 Inorganic Solids in Soil

2. Soil Chemistry includes:
Components of soil
Inorganic (soil minerals, salts, metals)
Organic (aggregates, humus, plant residues)
Solution
Gases
Processes important to plant growth and environmental applications
Ion exchange capacity
Sorption/Complexation

3. Composition Soils are: porous
open systems (to atmosphere, hydrosphere, biosphere)
multi-component
products of weathering
dynamic, constantly changing, not static

4. Soil Solids >90% solids are inorganic in most soils.
USDA major size fractions used by soil scientists in U.S.:
clay (<2 m)
silt (2 m – 50 m)
sand ( m = mm)
Engineering uses ASTM or other systems

5. Common elements in soil
Approximate % by weight
Oxygen
46.6
Silicon
27.7
Aluminum
8.1
Iron
5.0
Calcium
3.6
Sodium
2.8
Potassium
2.6
Magnesium
2.1
All others
1.5

6. O > Si >>> Al > Fe >> C, Ca, Mg, K, Na
Common elements
O and Si are two most common elements by weight and volume
O > Si >>> Al > Fe >> C, Ca, Mg, K, Na
‘aluminosilicates’ and ‘silicates’ – minerals that are made up of Si-O-Al and Si-O molecular framework

8. Essential and toxic ions
Macronutrients: H, C, N, O, Mg, P, S, K, Ca
Animals also need Na, Cl
Micronutrients: B, Cl, V, Mn, Fe, Cu, Zn, Mo
Animals also need F, Si, Cr, Ni, Co, As, Sn, Se, I
The list changes with progress in experimental techniques

10. Nutrients in plants and animals
Light atomic weight, concentrated at earth’s surface (heavier metals form the core of earth).
Evolution took advantage of elements abundant at the surface.
Plants can tolerate a much wider range of mineral concentrations than animals.
Chemical spatial variability of soils causes variations in mineral concentrations of plants
animals should eat a variety of plants and plants grown on different soils.

11. Minerals in Soil as Sources of Elements and Ions
Mineral: "natural, inorganic homogenous compound with definite chemical composition and ordered atomic arrangement”

12. Examples of ionic crystalline solids

13. Unit Cell Smallest repeating 3-D array of atoms in a crystal.
Minerals are often reported in half-cell formulas for simplification – be aware!
Ex: Kaolinite
Unit cell = Si4Al4O10(OH)8
Half-cell = Si2Al2O5(OH)4

14. http://www. gly. fsu. edu/~salters/GLY1000/6_Minerals/6_Minerals_index

15. science.kennesaw.edu/.../silicon/sil1cone.htm

16. Soil clay minerals Silica Tetrahedrons – one building block of soil minerals
Crystal pictures are from Bob Harter at Univ. of New Hampshire

17. Figure 1: Single silica tetrahedron (shaded) and the sheet structure of silica tetrahedrons arranged in a hexagonal network.

18. Aluminum Octahedrons – another building block or layer in minerals

19. Single octahedron (shaded) and the sheet structure of octahedral units.

20. Various linkages of the tetrahedra create classes of silicates:
week2/sillmin.jpg

21. socrates.berkeley.edu/~eps2/wisc/Lect4.html