Orders

Ultisol

Formation of an argillic horizon with significant leaching of cations giving rise to low base saturation (BS)

Alfisol

Like Ultisol with accumulation of clay in the subsurface argillic horizons, kandic horizons, or natric horizons, but characterized (generally) by not as extensive removal of basic cations so higher BS than Ultisol.

Mollisol

development of mollic epipedon ie: the accumulation of humified OM with mineral material and high BS

Vertisol

dominance of process is the shrinking and swelling of smectitic clays.

Inceptisol

beginning, or begun, to show evidence of soil formation by development of a major diagnostic horizon but not fitting other class

Entisol

recent - very little soil development - can not have fully formed diagnostic horizon identifiable.

 

Table of Formative elements of soil Orders.  

 

Soil Order Derivation Formative element
Alfisols Nonsense symbol alf
Andisols Jap. ando, black soil and
Aridisols L. aridus, dry id
Entisols Nonsense symbol ent
Gelisols Gr. gelid, very cold el
Histosols Gr. histos, tissue ist
Inceptisols L. inceptum, beginning ept
Mollisols L. mollis, soft oll
Oxisols Fr. oxide, oxide ox
Spodosols Gr. Spodos, wood ash od
Ultisols L. ultimus, last ult
Vertisols L. verto, turn ert

 

Table 11.2.2. Brief description of Soil Orders.

 

Soil Order

General Features

Alfisols

Alfisols develop in humid and subhumid climates, have average annual precipitation of 500-1300 mm. They are frequently under forest vegetation.

Characteristic features: Clay accumulation in a Bt horizon, could have a thick E horizon, often have available water much of the growing season, and slightly to moderately acid.

Like Ultisols, Alfisols have an accumulation of clay in the subsurface argillic horizon, kandic horizon, or natric horizon but characterized -generally- by "not as extensive" of removal of 'basic cations,' soil higher base saturation than Ultisols.

Andisols

Andisols are soils with over 60 % volcanic ejecta (ash, cinder, pumice, basalt) with bulk densities below 900 kg/m3.

Characteristic features: Dark A horizon, early-stage secondary minerals (allophane, imogolite, ferrihydrite clays), high adsorption and immobilization of phosphorus, very high cation exchange capacity.

The dominant process is the accumulation of andic materials, SRO soil compounds, in the surface horizons usually associated with volcanic materials.

Aridisols

Aridisols exist in dry climates.

Characteristic features: horizons of lime or gypsum accumulation, salty layers, and/or A and Bt horizons.

Limited to leaching of weathering products because of the aridic Soil Moisture Regime (SMR).

Entisols

Entisols have no profile development except a shallow marginal A horizon. Many recent river floodplains, volcanic ash deposits, unconsolidated deposits with horizons eroded away, and sands are Entisols.

Recent -very little soil development- and cannot have fully formed diagnostic horizons identifiable.

Gelisols

 Soils with permafrost of gelic material within 100 cm

Histosols

Histosols are organic soils (peat and mucks) consisting of variable depths of accumulated plant remains in bogs, marshes, and swamps.

Have histic epipedon; dominantly organic material --greater than 30% to 40 cm.

Inceptisols

Inceptisols, especially in humid regions, have weak to moderate horizon development. Horizon development have been retarded because of cold climate, waterlogged soils, or lack of time for stronger development.

Characteristic feature: Texture has to be finer than loamy very fine sand.

Beginning or has begun to show evidence of soil formation by development of a major diagnostic horizon (umbric, mollic, or plaggen epipedon, or a cambic horizon), but not fitting another class.

Mollisols

Mollisols are frequently under grassland, but with some broadleaf forest-covered soils.

Characteristic features: Deep, dark A horizons, they may have B horizons and lime accumulation.

Development of mollic epipon i.e.:The accumulation of humified OM with mineral material and high BS --above 50% BS by NH4OAC in all depths above 180 cm.

Oxisols

Oxisols are excessively weathered, whereas few original minerals are left unweathered. They develop only in tropical and subtropical climates.

Characteristic features: Often Oxisols are over 3 m deep, have low fertility, have dominantly iron and aluminum clays, and are acid.

Oxic horizons or kandic horizons. The leaching of silica in Oxisols to form a residual accumulation of sesqui-oxides or kaolinite (low activity clay). To have a kandic horizon the upper 18 cm must have a clay content of more than 40% and the kandic horizon must not have more than 10% weatherable minerals.

Spodosols

Spodosols are typically the sandy, leached soils of cool coniferous forests.

Characteristic features: O horizons, strongly acid profiles, well-leached E horizons, Bh or Bs horizons of accumulated organic material plus iron and aluminum oxides.

Common thread for Spodosols is that they have spodic horizons. They don't have the properties of Histosols.

Ultisols

 

Ultisols are extensively weathered soils of tropical and subtropical climates.

Characteristic features: Thick A horizon, clay accumulation in a Bt, strongly acid.

Formation of an argillic horizon with significant leaching of cations giving rise to low BS.

Vertisols

 

Vertisols exist most in temperate to tropical climate with distinct wet and dry seasons. They have a high content of clays that swell when wetted and show cracks when dry.

Characteristic features: Deep self-mixed A horizon , top soil falls into cracks seasonally, gradually mixing the soil to the depth of the cracking.

Dominance of process is the shrinking and swelling of smectitic clays.