The “Master” horizons organic horizon on the soil surface • O • A • E • B • C • R surface horizon high in organic matter, but composed of mineral soil – eluviation zone subsurf. horizon light in color due to leaching – eluviation zone subsurf horizon, from soil forming processes – illuviation zone least weathered (and deepest) of all the soil horizons – from Ror transported in bedrock
Subscripts: Processes occurring in these Horizons O horizon • Oi • Oe • Oa A horizon • Ap • Ab identifiable (recognizable) material Intermediate highly decomposed (almost all gone) plowed surface buried surface
More Subscripts clay B horizons • t • g • k • s • h • w • o “gleying” (very wet) carbonates (dry regions) sesquioxides (iron, aluminum, red/yellow) “histic” humus (high organic content) “cambic” – weakly altered by removal & chem rx, no illuviation “oxic” highly wx’d, tropical soils (Fe, Al oxides, red)
Last One (whew) and Rules • C horizon • r (weathered bedrock) • k (carbonates) • u (transported-in PM: unweathered) • ox (transported-in PM: weathered (“oxidized”) • Subscript Rules • rarely use more than three • t (almost) always first Examples: Btg, Cr, Bw, Ap, . . .
Types of Parent Material - Mode of transport Ice Low (all sizes) High (coarse dropped 1st) Stream/river Gravity Low Ice + wind High (silt only) Water (lakes) High None NA
A Bw 1m C Mixed alluvium Effect of Parent Material on Soil Formation – Transported PM A C 40cm Eolian sand
A A Bw AB 1.5m 40cm Bt1 C Bt2 C Residual shale Granite Effect of Parent Material on Soil Formation - Residuum
High (basic) Low (acidic) Why? Influence of climate on soil pH • Base cations soluble • Water = biomass (acids)
Influence of climate on Soil Organic Matter Hot= rapid losses Cold = low inputs
Influence of climate on Clay Formation So where find the soil with more clay, Alabama, or Nevada?
Influence of climate on Carbonate Layer Depth Depth i.e., near surface