Topic 2 WRBTopic 2 WRB

MINERAL SOILS CONDITIONED MINERAL SOILS CONDITIONED BY (SUBBY (SUB--) HUMID CLIMATE) HUMID CLIMATE

AlbeluvisolsAlbeluvisols, , LuvisolsLuvisols and and UmbrisolsUmbrisols

Soil Forming FactorsSoil Forming Factors

Significant period (season) when rainfall exceeds evapo-transpiration: Excess water for redistribution.

History of glaciation and periglacial conditions.

Natural vegetation is woodland (boreal and temperate).

Three major types of Landform:- Pleistocene sedimentary lowlands:

Glaciofluvial outwash; Glacial sands and Gravels: glacial till; glacio-lacustrine deposits; wind-blown silt (loess|) & sand.

- Uplifted & dissected Pre-Pleistocene sedimentary ‘Cuestas’:Limestones; Sandstones & Mudstones, often with thin loess cover.

- Uplifted and dissected Caledonian & Hercynian Massifs:Folded sedimentary, metamorphic and igneous rocks.

CLIMATECLIMATEThe The zonalzonal conceptconcept

Boreal Forset Long-grass Steppe Tropical Rainforest

Cool; P > Et Warm; P < Et Hot; P > Et

Strong leaching of mobile ions;Acidification;Low biological activity

& incorporation of OM

Weak upward flux of mobile ions (Ca & Na);Salinization;Strong biological activity;Deep rooting &

incorporation of OM

Leaching of mobile ions;Strong mineral weathering (Fe & Al oxides);Strong biological activity;

Rapid OM cycling (low OC)

Transport of weathered

products, Si, etc.

Recharge0-5050 – 250250 – 500500 10001000 – 20002000 - 3000

Climatic CharacteristicsClimatic Characteristics

Spring Temperature

Main soil forming processesMain soil forming processes

Eluviation / leaching.

Argilluviation (clay translocation).

Podzolization.

Temporary / seasonal saturation and (pseudo-) gleying, particularly of upper soil horizons.(‘Perched’ water tables). Associated with slowly permeable

and impermeable parent materials. ‘stagnic properties’

PARENT MATERIALPARENT MATERIALImpacts on soil formationImpacts on soil formation

A

B

C

A

B

C

A

B

C

Clay Loam Sand

A

B

C

A

B

C

Some leachingPerched waterGleying

LeachingClay translocation(maybe!)

Rapid leachingPodzolisation

AlbeluvisolsAlbeluvisols: Diagnostic Features: Diagnostic Features

An Argic horizon with an irregular upper boundarystarting within 1m of the soil surface.

Albeluvic tonguing.

Argichorizon

Albeluvic tongues

AlbeluvisolsAlbeluvisols: Characteristics: Characteristics

A

E

Bt

C

Under woodland, usually thin & dark with raw humus (but still Ochric). Where thicker can be Umbric or even Histic. When cultivated A & E horizons mixed to form a paler thick Ochric horizon.

Low in bases and naturally acid unless altered by management. Often gleyed with Stagnic features: a grey matrix with iron-rich segregations. Where sandy, the horizon is uniformly grey – all iron translocated laterally or vertically out of the layer.

Significantly more clay than overlying horizons. Can be acid (Alic or Alumic) or base-rich (Endoeutric or Haplic) and is often Fragic in some part.

Usually Glacial till or glacio-fluvial terrace material (often over lain by outwash sand) or loess.

In some cases, at the base of the E or top of the Bt, iron segregation can become so concentrated that a Ferric horizon is formed.

AlbeluvisolsAlbeluvisols: Genesis: Genesis

Elements of:argilluviation,periglacial freeze-thaw cycles,eluviation and seasonal saturation under acid and often cold conditions (low biological activity).

Albeluvic tongues:Usually the result of periglacial freeze-thaw: Ice-wedge casts.Some may be the result of tree roots exploiting natural cracks in the Argic horizon.

Most European Albeluvisols are ‘fossil’ soils.

AlbeluvisolsAlbeluvisols: Management & use: Management & use

Agricultural suitability limited by acidity and low nutrient status (in upper horizons), seasonal wetness and, most of all, short growing season.

In the northern taiga zone: virtually all forest

In the southern taiga zone: Mixed agriculture and forest but most agriculture is for pasture or hay.

Arable cropping increases to the south and west and in western Europe, where most Albeluvisols are fossil soils (the climate has changed!), cultivated Albeluvisols much more common. Liming, application of fertilizers and careful timing of cultivations on stagnic soils is required.

Cultivated Cultivated AlbeluvisolsAlbeluvisols

Ap

Ferric?Incipientspodic?

Ap

From Denmark And the UK

LuvisolsLuvisols: Diagnostic features: Diagnostic features

An argic horizon with a CEC* > 24cmol(+) kg-1 clay.Starts within 1m depth OR, if overlain by sandy material, within 2m

depth.

No Albeluvic tonguing.

No abrupt textural change if stagnic features occur.

No spodic horizon.

No Alic properties

Argic horizon

A

E

Bt

C

LuvisolsLuvisols: Characteristics: Characteristics

Brown to dark brown Ochric surface horizon (Under some woodland, thin & dark raw humus may be present (but still Ochric)..

Paler brown, usually weakly structured and decalcified (if parent material is calcareous). May have stagnic features if Bt is slowly permeable.

Significantly more clay than overlying horizons and in extreme cases there is an abrupt textural change (abruptic). Stable blocky structures. May have less than 50% base saturation in the upper parts (Dystric).

A wide variety of unconsolidated or weakly consolidated Pleistocene & soft pre-Pleistocene materials. Mainly clays, silts and loams.

LuvisolsLuvisols under woodland in the UKunder woodland in the UK

Ah

LuvisolsLuvisols: Genesis: Genesis

Argilluviation.

1. Mobilization of clay in the surface. Depends on:Charge characteristics of the clay;Ionic strength of soil solution;Composition of ions in the exchange complex.

2. Vertical transport in colloidal suspension via:Downward percolating water moving through coarse pores (> c. 20µm wide.)

3. Immobilization of transported clay in the horizon of accumulation:Flocculation caused by an increase in electrolyte or divalent cation concentration.Filtration by finer pores in drier soil layers.

May also be elements of:Seasonal saturation in slowly permeable materials (Stagnic).Seasonal saturation of lower horizons by rising groundwater in depressional areas (Gleyic).

Clay transport in a Clay transport in a LuvisolLuvisol

Calcaric Cambisol Haplic Luvisol

Same substrate

LuvisolsLuvisols: Management & use: Management & use

Normally fertile soils suitable for a wide range of uses.

Those with more extreme range of properties (Leptic, Vitric, Albic, Dystric) may be less fertile.

BUT, because of clay mobilization in their topsoils they are susceptible to:Structural degradation: slaking and compaction.

Erosion.Transfer of particulate clay and associated (agro-)chemicals to surface

waters.

Stagnic & Gleyic soils usually require artificial drainage and careful timing of cultivations.

UmbrisolsUmbrisols: Diagnostic features: Diagnostic features

An Umbric topsoil horizon.

No other diagnostic horizons except:An Anthropedogenic horizon less than 50cm thick.An Albic horizon.A Cambic horizon.

Umbric horizon

UmbrisolsUmbrisols: Characteristics: Characteristics

Thick, dark, acid organic-rich surface horizon rich in organic matter (Umbric horizon). ‘Acid or oligotrophic mull’, ‘moder’, ‘raw humus’, ‘mor’.May be modified by man to increase its fertility by liming and fertilisation (Anthric).

Usually weakly developed (Cambic) or incipient podzolic horizon not sufficiently developed to qualify as Spodic. Where stagnic properties are present may be more developed.

Mainly the (glacial and periglacial) weathering products of siliceous rocks in Caledonian and Hercynian massifs.

Ah

(B)

C

Types of Types of UmbrisolsUmbrisolsHaplicHaplic (Cambic?)Episkeletic / Leptic

Stagnic

UmbrisolsUmbrisols: Genesis: Genesis

Lack of significant period of soil moisture deficit, cool, wet mainly acid conditions: Typically upland massifs.

Accumulation of acid organic matter because of slow biological turnover under conditions of:acidity; low temperature; surface wetness; a combination of these.

Not sufficiently cold and/or wet for a Histic horizon to develop.

Accumulation of organic matter is more rapid than any associated formation of spodic or argichorizons.

UmbrisolsUmbrisols: Management & use: Management & use

Often still under natural or semi-natural vegetation.Montane or boreal forest; short grassland above the tree line.

Where cleared of forest cover (particularly in north & western Europe) short grass ‘moorland’.

Can support ‘improved’ grazing pasture if limed and fertilised but usually too wet and/or cold for arable crops.

Albeluvisols worldwideLuvisols worldwide

Umbrisols world-wide

Relationship between Relationship between AlbeluvisolsAlbeluvisols, , LuvisolsLuvisols & & UmbisolsUmbisols

Increasing cold winters but not wet

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LUVISOLS

UMBRISOLS

ALBELUVISOLS

UmbrisolsUmbrisols and rainfalland rainfall