12-13 Soil characteristics and classification

Differentiated soil profile

Soil production vs soil erosion

• Soil production = creation of soil material from bedrock
  → driven by chemical weathering + bioturbation
  → produces regolith / saprolite (weathered rock)

• Soil formation = development of soil horizons
  → driven by translocation, transformation, OM accumulation, structure formation
  → can act on bedrock-derived material or sediments

• Key distinction

  • Soil ≠ just decomposed rock

  • Soil can form on pre-existing sediments (age & provenance matter)

• Rates matter

  • Typical production rates: ~10–100 mm/ka

  • Balance between:

    • Erosion > formation → soil loss

    • Erosion = formation → steady state

    • Erosion < formation → soil thickening

• Controls

  • Climate

  • Biota (bioturbation, roots)

  • Parent material

  • Time

  • Human activity (e.g. agriculture increases erosion)

Core idea:
Soil thickness and persistence depend on the balance between soil production and erosion, while soil properties depend on formation processes over time, not just rock weathering.

Typical CH soils

In Switzerland, soil types mainly reflect parent material + water regime (relief & groundwater), with strong human influence.

• Parent material dominates (mostly sediments: till, colluvium, fluvio-glacial, peat)

• Relief & groundwater control drainage → gleyic vs well-drained soils

• Human activity (drainage, filling, peat addition) strongly modifies soils

• Result: strong soil variability over short distances (Leptosol → Cambisol → Luvisol → Gleysol → Histosol)

Core idea: soil pattern follows landscape + sediments, not just bedrock

Luvisol Engelhalbinsel

1) Horizon vs. layer (core concept)

• Soil horizons = formed by pedogenesis (Ah, E, Bt/It, Ck)

• Geological layers = depositional history (fluvial/aeolian loam, gravels)
  → Soil properties ≠ original sediment only

2) Dominant process: clay translocation

• E horizon: clay eluviation (loss)

• Bt / It horizon: clay illuviation (accumulation)
  → Diagnostic feature of Luvisols

3) Carbonates control soil evolution

• Ck horizon: carbonate-rich gravels/sands

• Early stage: decalcification from top downward

• pH increases with depth due to carbonates

4) Vertical differentiation with depth

• Ah: humus accumulation, bioturbation

• E: bleaching, loss of clay and Fe

• Bt / It: clay enrichment, stronger structure

• Ck: parent material with secondary carbonate

5) Time dimension

• Soil developed over ~10–15 ka (post-glacial)

• Progressive sequence:

  • Humus formation

  • Decalcification

  • Clay translocation

  • Redox features locally

6) Why this example matters

• Shows how:

  • Pedogenesis overprints geology

  • Same parent material → different horizons

  • Luvisols record both transport (sediment) and in-situ soil processes

Major horizons (International WRB, German Ka5, Swiss KLABS)

International → has soil worldwide

KA5 (Deutschland) used in most textbooks

CH more used by practitioners, people who work in the field, agriculture

Major horizons to know

	WRB 2020 (int)	KA5 (D)	KLABS (CH)
H	peat	Peat
O	Organic cover	Organic cover	Organic cover
A	Topsoil	Topsoil/eluvial hor	Topsoil
E	Eluvial horizons	Plaggen	Eluvial horizons
B	Subsoil/illuvial	Subsoil/illuvial	Subsoil
I	Soil ice (>70%)		Illuvial
T		Clay rich (terra fusca)	Peat
C	Loose rock	Rock (loose and solid)	Loose rock
R	Bedrock	Deeply worked (rigolt)	Bedrock

Subordinate horizons to know

 

	WRB 2020	KA5	KLABS
f	permafrost	Moder zone	Moder zone
g	Stagnic conditions	Stagnic conditions	Moderately redoximorph
h	Humic (insitu/illuvial OM)	Humic (insitu/illuvial OM)	Humic (Oh, Ah, Ih)
l	Capillary redoximorphism	Eluviation clay	Litter
r	reduced	reduced	Reduced
s	Illuvial sesquioxides	Illuvial sesquioxides
t	Clay illuviation	Clay illuviation B /shrinked H	Clay enriched
w	weathered	Conducting stagnant water	weathered

 

Parents material in pedology (german approach)

Parent materials are grouped by physicochemical properties, not only by rock name

Silica-rich parent materials
(granite, gneiss, sandstone)

• Texture: light, sandy to sandy loam

• Drainage: well-drained

• Chemistry: acidic
  → Favors leaching, weaker buffering, podzolisation possible

Carbonatic parent materials
(limestone, dolomite, marble)

• Soil depth: often shallow

• Texture: fine-grained

• Chemistry: neutral to alkaline, strong buffering

• Organic matter: humus-rich
  → Slower acidification, carbonate control dominates pedogenesis

Claystones
(claystone, shale, schist)

• Texture: heavy (clay loam)

• Drainage: poor

• Chemistry: often acidic
  → Waterlogging, redox processes, strong structure effects

Marls (clay + carbonate mix)
(marlstone, lime mica schist)

• Drainage: moderate

• Texture: well-structured, balanced

• Chemistry: neutral → slightly acidic
  → Transitional behavior between clayey and calcareous systems
  → Includes calcareous sediments (moraine, loess, glaciofluvial)

Silica series

Granit/Gneiss rich in silica, soils form by humus accumulation, bases washed out

Soil acid, bleaching and organic matter goes down

Lime series

Limestone mainly calcium-carbonate

Karst, Limestone is dissolved, some dirt in there

Brown clay takes lot of time

Residual loam is what remains when limestone dissolves, mainly formed by clay

Clay series

Claystone

Surface goes up because of swelling of clay

Marl (mergel) series

Not on Mergel but on loose material → Moraine, Löss… → contains a bit of carbonate (20-40%), has carbonate, silica and clay

No redox, pure luvisol

Important to understand the three main parent material and the mix

Initial signs of pedogenesis

Interaction between lichen and granite in glacier forefield

Weathering rind of granite

Not a soil but some signs that a soil could start to form

Humification and bioturbation

• Main soils → Regosol and Chernozem

• Key processes:

  • Humification: accumulation and stabilization of organic matter

  • Bioturbation: mixing of soil by roots and soil fauna

• Main effects:

  • Dark, humus-rich topsoil

  • Strong aggregation, good structure

  • Weak horizon differentiation due to mixing

• Controls:

  • Vegetation → OM input

  • Climate → decomposition vs. accumulation

  • Parent material is secondary for morphology

Core idea:
The intensity and duration of humification and bioturbation control topsoil development: weak → simple soils; strong and long-lasting → thick, fertile, well-mixed soils

Brunification/Loamification → Cambisol/Braunerde

• Key pedogenetic processes:

  • Brunification: oxidation of Fe²⁺ to Fe³⁺ → formation of brown Fe-oxides/hydroxides (e.g. goethite), coating mineral grains

  • Loamification (Verlehmung): chemical weathering of silicates → production of fine earth (silt + clay), weak clay formation but little translocation

• Soil development:

  • Moderate chemical weathering, often after decalcification (if carbonates were present)

  • No strong eluviation/illuviation → processes mainly in situ

• Environmental setting:

  • Temperate climates, good drainage

  • Common on weakly weathered sediments or weathered rock

• Core idea:
  Cambisols represent an intermediate soil stage formed by brunification and loamification, showing clear weathering but little vertical material translocation.

Cambiso/Braunerde horizons

• Ah horizon

  • Topsoil with humus accumulation

  • Darker color, high biological activity

  • Rooting zone, mixing by bioturbation

• Bw horizon (diagnostic horizon)

  • Weathered B horizon

  • Brown color due to Fe-oxide formation (brunification)

  • Slight increase in clay and fine material, but no strong clay accumulation

  • Structure more developed than in C, but no clear eluviation/illuviation

• C horizon

  • Parent material (sediment or weathered rock)

  • Little pedogenic alteration

  • Source of minerals for soil formation

Cambisols/Braunerden are among the most widely used and reliable agricultural soils in Central Europe, especially when well managed.

Podzolisation

• Strong acidification (low pH, often < 4.5)

• Organic acids mobilise Fe, Al and humus

• Intense leaching (eluviation) from upper horizons

• Illuviation of organic–metal complexes deeper (Fe–Al–humus)

• Typical under humid climate + sandy, siliceous parent material

• Often associated with coniferous / heath vegetation

Main characteristics:

• Very bleached E horizon

• Strong chemical differentiation

• Low base saturation, low nutrient availability

• Often coarse-textured (sand), low buffering capacity

Plant growth & agriculture:

• Generally poor agricultural soil

• Limitations: Very acidic, Nutrient-poor, Sometimes impermeable spodic horizon (root restriction)

• Suitable mainly for:

  • Forest (conifers)

  • Natural vegetation

Podzol horizon

Typical horizon sequence:
O → EA / AE → E → Bhs / Bs → C

• O horizon
  Organic layer (litter, humus)
  → Source of organic acids

• EA / AE horizon
  Transition zone
  → Beginning of leaching and acidification

• E horizon (key diagnostic horizon)
  Strong eluviation
  → Loss of clay, Fe, Al, organic matter
  → Ash-grey / bleached appearance

• Bhs horizon (spodic horizon)
  Illuviation of humus + Fe/Al
  → Dark brown to black
  → Often dense, may limit roots and water

• Bs horizon
  More oxide-dominated (Fe, Al)
  → Reddish-brown

• C horizon
  Parent material (usually sandy, siliceous)

Humification (aerobic) and humus

Process (humification under aerobic conditions):

• Plant litter accumulates at surface

• Microbial + soil fauna decomposition in presence of O₂

• Degree of biological activity controls:

  • Speed of decomposition

  • Mixing of organic matter with mineral soil

• Controlled mainly by:

  • Vegetation type

  • pH

  • Climate (temperature, moisture)

Humus forms (aerobic):

1. Mull

• Fast decomposition, very high biological activity (earthworms)

• Organic matter well mixed into Ah horizon

• Thin or absent organic layer

• pH: weakly acidic to neutral

• Low C/N (≈ 9–18)

• Typical ecosystems: deciduous forest, meadow

• → Most fertile humus form

2. Moder

• Intermediate decomposition

• Partial mixing; organic layer still visible

• Moderate biological activity

• pH: acidic

• Intermediate C/N (≈ 17–25)

• Typical ecosystems: mixed forests

3. Mor (Rohhumus)

• Slow decomposition

• Thick organic layer (O horizon), little mixing

• Low biological activity

• Strongly acidic conditions

• High C/N (≈ 20–33)

• Typical ecosystems: coniferous forest, cold/wet sites

• → Low nutrient availability

Key gradient:

Mor → Moder → Mull
⬆ biological activity
⬇ organic layer thickness
⬇ C/N ratio
⬆ soil fertility

Redoximorphism

Core process

• Periodic or permanent oxygen shortage in soil → redox cycles of Fe and Mn

• Alternation of reduction (Fe³⁺ → Fe²⁺) when wet and oxidation when re-aerated

Key drivers

• Water saturation (stagnant water or groundwater)

• Slow drainage / impermeable layers

• Limited O₂ diffusion

Main mechanisms

• Wet phase:

  • O₂ depleted → Fe/Mn oxides reduced and mobilised

• Dry / aerated phase:

  • O₂ returns → Fe/Mn oxidise and precipitate

• Repeated cycles → spatial separation of redox conditions

Visible effects (redoximorphic features)

• Grey–bluish colours → reduced zones

• Orange–brown mottles, coatings, nodules → oxidised Fe/Mn

• Strong colour contrasts in horizons

Pedogenic significance

• Controls Fe/Mn distribution

• Affects nutrient availability, root aeration, and soil structure

Gley horizons

Key process

• Permanent or long-lasting water saturation

• → Low O₂ → reduction of Fe³⁺ to Fe²⁺

• → Grey/blue colors + rusty mottles (redoximorphism)

Typical horizons

• Ah

  • Dark, humus-rich topsoil

  • Often periodically waterlogged

• Bl / Bg

  • Mottled horizon

  • Oxidized Fe (rusty spots) on aggregate surfaces

  • Reduced (grey) interiors

• Cr / Gr

  • Permanently reduced zone

  • Grey–bluish colors, Fe²⁺ rich

  • Often influenced by groundwater

Is it good for plants?

Generally: problematic

• Poor aeration → root stress

• Low microbial activity (anaerobic)

• Risk of Fe/Mn toxicity

Can be usable if: Artificial drainage, Shallow-rooted, water-tolerant plants (grass, reeds), Meadow or pasture use > arable crops

Best suited for: Wet grasslands, Natural wetlands, Forestry with tolerant species (e.g. alder)

Short: Gley horizons form under waterlogging, show redox features, and limit plant growth unless drained or used with tolerant vegetation.

CH Groundwater classification

• Key idea: Soil type depends on depth & fluctuation of groundwater

• Shallow GW → strong gleying

• Deeper GW → weaker redox influence

Gradient (GW depth ↓):

• Moor / Halfmoor → permanent saturation (G6)

• Fahlgley / Buntgley → fluctuating GW, strong redox (G5)

• Braunerde–Gley → moderate gleying (G4)

• Braunerde → weak/no gleying (G3)

• Parabraunerde → no GW influence (G2)

We watch at current water system (could be influenced from man and not natural)

Anaerobic OM accumulation

• Process: Permanent waterlogging → O₂ deficit → very slow OM decomposition

• Result: Peat accumulation (organic matter dominates soil volume)

• Key conditions: High groundwater, low redox, cold or wet climate

• Horizons: Thick H horizons (H1–H3), mineral C often deep or absent

• Chemistry: Very high Corg, high C/N, low bulk density

Plant growth / agriculture:

• ❌ Poor naturally (anoxia, low nutrients)

• ✔ Productive only after drainage → but high CO₂ loss & subsidence risk

Human influences

Temperate humid transect (N Germany)

• Water regime: dry → periodically wet → permanently wet

• Redox conditions: oxic → alternating → reducing (gley features)

• Soil depth: shallow → deeper → often young/alluvial

• Pedogenesis: weak weathering → clay translocation → redoximorphism

• Fertility: often increases in loess positions, decreases in wet depressions

Temperate mountains transect

• Climate: warm/dry → cold/wet with altitude

• Vegetation: deciduous → conifer → tundra

• Processes: brunification → podzolization → cryoturbation / gleying

• Soils: deeper & developed → shallow, skeletal

• OM: low → accumulates in cold/wet zones

Core idea: altitude and climate drive rapid soil changes along the Alps.

Boreal to polar region transect

• Climate: cold → very cold; moisture often high, ET very low

• Permafrost: absent → discontinuous → continuous (controls everything)

• Hydrology: impeded drainage, waterlogging above frozen ground

• Processes: podzolization → gleying → cryoturbation / peat accumulation

• Soils: forest Podzols & Gleys → Histosols → Cryosols

• OM: strong accumulation, very slow decomposition

Core idea: permafrost + cold climate dominate soil development along the catena.

Temperate semi-humid to dry transect

• Main driver: climate gradient (parent material mostly uniform)

• N → S: forest-steppe → steppe → desert

• Water balance: precipitation ↓, evapotranspiration ↑

• Soil processes: decalcification → carbonate accumulation → salinization/sodification

• OM: highest in steppe, decreases toward desert

Key idea: increasing aridity controls soil properties and horizons along the catena.

Arid region transect

• Main driver: aridity + episodic rainfall

• Upslope → downslope: rock weathering → erosion → sedimentation (pediment → glacis → playa)

• Processes: weak chemical weathering, strong physical weathering

• Water movement: upward capillary rise dominates

• Soil trend: skeletal soils → calcic/gypsic soils → saline soils

Key idea: decreasing moisture and increasing evaporation control soil development and salt accumulation along the catena.

Mediterranean transect

• Climate control: mild, humid winters → leaching; hot, dry summers → oxidation

• Processes: decalcification + rubefaction (Fe oxidation → red colors)

• Upslope → downslope: shallow calcareous soils → deeper red soils → young sandy soils

• External inputs: Saharan dust contributes fine material and Fe

• Human impact: strong erosion, truncation, reworking of soils

Key idea: seasonal climate + carbonate parent material produce red Mediterranean soils along the catena.

Humid tropic transect

• Climate: hot, humid → extremely intense chemical weathering

• Processes: strong leaching, Fe/Al oxide accumulation, deep weathering profiles

• Soil trend: highly weathered upland soils (Ferralsols/Plinthosols) → hydromorphic soils in valleys

• Biology: closed forest → rapid nutrient cycling, low nutrient storage in soil

• Human signal: local enrichment by humans (terra preta)

Key idea: climate-driven extreme weathering dominates; nutrients are in biomass, not in the soil.

Arid regions properties and processes

• Climate: low precipitation, high evapotranspiration (P < ET)

• Main processes: upward water movement → capillary rise and salt accumulation

• Chemistry: alkaline pH, high salinity (Na, Ca, Mg salts), weak leaching

• Organic matter: very low (sparse vegetation, slow inputs)

• Typical features: salt/gypsum/carbonate horizons, surface crusts

• Key limitation: salinity + water stress strongly limit plant growth and agriculture

Humid tropical soils properties and processes

• Climate: hot, humid, high rainfall (P > ET)

• Main processes: intense chemical weathering (ferralisation), strong leaching

• Mineralogy: loss of bases & silica → kaolinite + Fe/Al oxides (hematite → red color)

• Chemistry: low pH, very low base saturation, low nutrient reserves

• Organic matter: rapid decomposition → thin, fast-cycling OM

• Agriculture: naturally low fertility, productive only with strong management (fertilization, OM inputs)

Soil classification strategies

• Factor-oriented

• Pedogenetic (Germany [+ geogenetic])

• Morphological (USA, WRB, France) linked to genesis and/or functioning

• Numerical (e.g. Hughes et al. 2014)

• User-oriented (non-pedological)

From different classification types there is no direct translation, most of the time you have to rewatch all the soil data and classify again

Soil mapping philosophy

Summary

Differences between classifications

Swiss (KLABS / CH):

• Process- and use-oriented

• Strong focus on water regime (groundwater, stagnation), soil functions and agricultural relevance

• Detailed horizon suffixes for redox, gleying, human influence

• Very site-specific, well adapted to Swiss landscapes

German (KA5):

• Morphogenetic approach

• Emphasis on soil-forming processes (e.g. lessivation, podzolisation, gleying)

• Very detailed horizon diagnostics and field morphology

• Less focused on land use, more on genesis

International (WRB):

• Globally comparable system

• Based on diagnostic horizons, properties and materials

• Strong climate signal indirectly (e.g. Podzols, Ferralsols, Cryosols)

• Less local detail, not designed for land-use planning

➡ In short:

• KLABS = practical & hydrology-focused

• KA5 = process & morphology-focused

• WRB = global & climate-sensitive comparability