Topic 2 WRB MINERAL SOILS CONDITIONED BY (SUB-) ) HUMID CLIMATE. Albeluvisols, Luvisols and Umbrisols

Transcription

1 Topic 2 WRB MINERAL SOILS CONDITIONED BY (SUB-) ) HUMID CLIMATE Albeluvisols, Luvisols and Umbrisols

2 Soil 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; glaciolacustrine 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.

3 CLIMATE The zonal concept 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.

4 Climatic Characteristics Spring Temperature Recharge

5 Main 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

6 PARENT MATERIAL Impacts on soil formation A A A B Some leaching Perched water Gleying B Leaching Clay translocation (maybe!) B Rapid leaching Podzolisation C C C Clay Loam Sand

7 Albeluvisols: : Diagnostic Features An Argic horizon with an irregular upper boundary starting within 1m of the soil surface. Albeluvic tonguing. Albeluvic tongues Argic horizon

8 Albeluvisols: : Characteristics A 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. E Bt 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 In some cases, laterally the or base vertically of the E out or of top the of layer. the Bt, iron segregation can become so concentrated Significantly that a Ferric horizon more clay is formed. than overlying horizons. Can be acid (Alic or Alumic) or base-rich (Endoeutric or Haplic) and is often Fragic in some part. C Usually Glacial till or glacio-fluvial terrace material (often over lain by outwash sand) or loess.

9 Albeluvisols: : 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.

10 Albeluvisols: : 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.

11 Cultivated Albeluvisols From Denmark And the UK Ap Ap Ferric? Incipient spodic?

12 Luvisols: : 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. Argic horizon No abrupt textural change if stagnic features occur. No spodic horizon. No Alic properties

13 Luvisols: : Characteristics A E 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. Bt 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). C A wide variety of unconsolidated or weakly consolidated Pleistocene & soft pre-pleistocene materials. Mainly clays, silts and loams.

14 Luvisols under woodland in the UK Ah

15 Luvisols: : 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).

16 Clay transport in a Luvisol Calcaric Cambisol Haplic Luvisol Same substrate

17 Luvisols: : 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.

18 Umbrisols: : Diagnostic features Umbric horizon An Umbric topsoil horizon. No other diagnostic horizons except: An Anthropedogenic horizon less than 50cm thick. An Albic horizon. A Cambic horizon.

19 Umbrisols: : Characteristics Ah (B) 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. C Mainly the (glacial and periglacial) weathering products of siliceous rocks in Caledonian and Hercynian massifs.

20 Types of Umbrisols HaplicHaplic (Cambic?) Episkeletic / Leptic Stagnic

21 Umbrisols: : 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 argic horizons.

22 Umbrisols: : 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.

23 Relationship between Albeluvisols, Luvisols & Umbisols Luvisols worldwide Albeluvisols worldwide Umbrisols world-wide Increasing wetness and lack of moisture deficit UMBRISOLS LUVISOLS ALBELUVISOLS Increasing cold winters but not wet

24 Umbrisols and rainfall