horizons

Question 1

soil horizons are…

Answer 1

• distinct layers formed by pedogenic processes
• distinct differences in:
  
  • OM
  • color
  • sand/clay %
  • chemical composition

Question 2

O horizon

Answer 2

• OM: but can be different types
• fresh litter & well-decomp’d humus
• usually above mineral soil (forest)
• common and very deep in wetlands
• seldom found in grasslands

Question 3

A horizon

Answer 3

• surface mineral horizon, darkened by OM
• may have properties from cultivation
• usually more fertile

Question 4

E horizon

Answer 4

• Eluviated mineral hzn where dominant feature is a LOSS of clay, iron, aluminium, OM, etc
• loss is due to leaching (causing a gray/white color)

Question 5

B horizon

Answer 5

• mineral hzn w/ either or both:
  
  • illuvial increase in clay, Fe, Al, OM… from above (E)
  • substantial alteration of original parent material that eliminated rock structure, forms clay or oxides (giving color)
• orangish, yellowish, greyish

Question 6

C horizon

Answer 6

• mineral hzn that has little alteration of original PM
• lacks properties of AEB hzns
• lies outside of most biological activity

Question 7

R

Answer 7

• rock material
• _not_ a horizon

Question 8

L horizon

Answer 8

• limnic material, uncommon (but occ. in PacNW)
• lake deposits
• full of diatoms, clay, OM
• @ bottom of wetlands

Question 9

transition hzns

Answer 9

• transition btwn 2 masters
• dominant hzn listed first:
  
  • BC: smooth transition w/ B dominant
  • A/B: interfingered w/ A dominant

Question 10

subordinate O hzn designations

Answer 10

• Oi: little decomp, OM still recognizable
  
  • i = fibric
• Oe: intermediate
  
  • e = hemic
• Oa: highly decomp’d, OM not recognizable
  
  • a = sapric = saprophyte

Question 11

Ap

Answer 11

plowed; structural change

Question 12

subord: t

Answer 12

accumulation of silicate clays (Bt)

Question 13

subord: k

Answer 13

accum. of carbonate (Bk, Ck)

Question 14

subord: s

Answer 14

• illuvial accum. of sesquioxides (Fe/Al)
• orange-reddish color
• (Bs), illuvial

Question 15

subord: h

Answer 15

• accum. of humified OM (well decomp’d)
• Bh, Bhs, illuvial

Question 16

subord: g

Answer 16

• gleying, waterlogging, anaerobic, wet soil
• loss of O₂ makes Fe grey/mottled
• Bg, Cg

Question 17

subord: w

Answer 17

• some development of color/clumps, but not well developed
• Bw
• *** B always gets a subord, so Bw if nothing else is special about it

Question 18

subord: b

Answer 18

• buried
• Ab (an A under other O, A, & B)

Question 19

subord: o

Answer 19

• accumulation of Fe/Al oxides (Bo) (but not OM)
• formed in place (not illuvial)