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The “Master” horizons

The “Master” horizons

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The “Master” horizons

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  1. 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

  2. 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

  3. 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)

  4. 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, . . .

  5. 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

  6. A Bw 1m C Mixed alluvium Effect of Parent Material on Soil Formation – Transported PM A C 40cm Eolian sand

  7. A A Bw AB 1.5m 40cm Bt1 C Bt2 C Residual shale Granite Effect of Parent Material on Soil Formation - Residuum

  8. High (basic) Low (acidic) Why? Influence of climate on soil pH • Base cations soluble • Water = biomass (acids)

  9. Influence of climate on Soil Organic Matter Hot= rapid losses Cold = low inputs

  10. Influence of climate on Clay Formation So where find the soil with more clay, Alabama, or Nevada?

  11. Influence of climate on Carbonate Layer Depth Depth i.e., near surface