ACRISOLS, ALISOLS, LIXISOLS and NITISOLS

Otto Spaargaren

ISRIC – World Soil Information

WageningenThe Netherlands

Content of lecture

Acrisols and Lixisols

Alisols

Nitisols

Definition of Acrisols and Lixisols (1)

Common characteristics:

Acrisols and Lixisols have an argic horizon that, in some part, has a CEC < 24 cmol(+) kg-1 clay.

The argic horizon starts within 100cm from the soil surface, or within 200cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout.

Definition of Acrisols and Lixisols (2)

Differentiating characteristic:

Acrisols have a base saturation < 50 percent in the major part between 25 and 100cm depth

Lixisols have a base saturation 50 percent in the major part between 25 and 100cm depth

Argic horizon (1)

Results from illuvial accumulation of clay, predominant formation of clay in the subsoil or destruction of clay in the surface horizon, selective surface erosion, biological activity, or a combination of two or more of these processes

Argic horizon (2)

Diagnostic characteristics (1): Texture sandy loam or finer and at least 8

percent clay More total clay than overlying horizon:

– If overlying horizon has < 15 % clay, argic horizon must have 3 % (absolute) more clay;

– If overlying horizon has > 40 % clay, argic horizon must have 8 % (absolute) more clay;

– If overlying horizon has 15 - 40 % clay, argic horizon must have 1.2x (relative) more clay

Argic horizon (3)

Diagnostic characteristics (2):

Increase in clay content within 30cm if illuvial, or within 15cm in other cases

Less than 50 percent rock structure

Thickness 1/10th of all overlying horizons, but at least 7.5cm

Genesis of Acrisols and Lixisols

Main soil-forming factor is:

Climate

Main soil-forming processes are:

– Formation of a clay-rich subsoil horizon– Alteration to the extent that low-activity clay

(LAC) predominate– Acrisols: strong leaching of bases– Lixisols: slight to moderate leaching of bases

Classification of Acrisols (1)

Intergrade qualifiers: andic, arenic, gleyic, leptic, plinthic, umbric, and vitric

Secondary characteristics qualifiers, related to defined diagnostic horizons, properties or materials: abruptic, albic, ferric, geric, humic, hyperochric, lamellic, profondic, and stagnic

Classification of Acrisols (2)

Secondary characteristics qualifiers, not related to defined diagnostic horizons, properties or materials: alumic, chromic, hyperdystric, rhodic, skeletic, and vetic

Haplic qualifier, where non of the above applies: haplic

Classification of Lixisols (1)

Intergrade qualifiers: andic, arenic, calcic, gleyic, leptic, plinthic, and vitric

Secondary characteristics qualifiers, related to defined diagnostic horizons, properties or materials: abruptic, albic, ferric, geric, humic, hyperochric, lamellic, profondic, and stagnic

Classification of Lixisols (2)

Secondary characteristics qualifiers, not related to defined diagnostic horizons, properties or materials: chromic, rhodic, and vetic

Haplic qualifier, where non of the above applies: haplic

Example of an Acrisol

Alumi-Profondic Acrisol (Chromic), China

0 20 40 60 80

% clay and Al / CEC in cmol(+)

370-450 cm

220-270 cm

95-150 cm

22-45 cm

0-7 cm

Clay %Al-satCEC clay

Example of a Lixisol

Chromic Lixisol, Ghana

0 20 40 60 80 100

% clay and bases / ECEC in cmol(+)

85-136 cm

68-85 cm

32-68 cm

14-32 cm

5-14 cm

0-5 cm

% clayBase satECEC clay

Distribution of Acrisols (1)

Distribution of Acrisols (2)

Acrisols cover some billion ha or 8 % of the Earth’s land surface. They occur mainly in moist (sub)tropical and warm temperate regions, and as paleosols in other climatic zones.

Distribution of Lixisols (1)

Distribution of Lixisols (2)

Lixisols cover some 440M ha or 3.5 % of the Earth’s land surface. They occur mainly in dry (sub)tropical and warm temperate regions, usually bordering desert regions, and as paleosols other climatic zones.

Many Lixisols receive regularly air-borne dust from deserts, thus maintaining their high base status.

Associated soils

Acrisols occur associated with Ferralsols, Nitisols and Plinthosols on more level surfaces, and with Regosols and Cambisols on steeper land.

Lixisols occur associated with Luvisols, Nitisols, Vertisols and Planosols on more level surfaces, and with Calcisols and Cambisols towards the drier regions.

Alisols

Alisols are strongly to extremely acid soils with high-activity clays (HAC) accumulated in the subsoil.

Characteristically, they have a high amount of exchangeable aluminium, released from unstable secondary clay minerals such as smectites and vermiculites.

Definition of Alisols (1)

Alisols have An argic horizon with a CECclay 24

cmol(+) kg-1, either starting within 100cm from the soil surface, or within 200cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout

Alic properties in most of the layer between 25 and 100cm depth

Definition of Alisols (2)

Alisols have

No diagnostic horizons other than an ochric, umbric, albic, andic, ferric, nitic, plinthic or vertic horizon

Alic properties

CECclay 24 cmol(+) kg-1

Either TRBclay/TRBsoil 0.8, or silt/clay 0.60

pH (KCl) 4.0

KCl-extractable Al 12 cmol(+) kg-1 clay, and KCl-extractable Al/CECclay 0.35

60 percent aluminium saturation (exch. Al/ECEC x 100)

Genesis of Alisols (1)

Main soil-forming factor is:

Climate

Main soil-forming processes are:

Transformation and/or hydrolysis of primary weatherable minerals and production of smectite and vermiculite

Genesis of Alisols (2)

Redistribution of clay and formation of an argic horizon

Weathering of secondary high-activity clay, liberating large amounts of aluminium and – on basic parent materials – iron and magnesium

Classification of Alisols (1)

Intergrade qualifiers: andic, arenic, gleyic, nitic, plinthic, umbric, and vertic

Secondary characteristics qualifiers, related to defined diagnostic horizons, properties or materials: abruptic, albic, ferric, humic, lamellic, profondic, and stagnic

Classification of Alisols (2)

Secondary characteristics qualifiers, not related to defined diagnostic horizons, properties or materials: chromic, hyperdystric, rhodic, and skeletic

Haplic qualifier, where non of the above applies: haplic

Example of an Alisol

Hyperdystri-Profondic Alisol, Malaysia

Depth cm

CEC clay

pH KCl

Silt/ clay

Al/kg clay

Al/ CEC clay

Al/ ECEC x100

0-5 31 3.4 0.71 27 0.36 59

30-45 29 3.7 0.48 23 0.44 94

70-90 29 3.8 0.42 22 0.45 89

100-110

26 3.9 0.32 18 0.37 69

110-125

27 3.8 0.43 17 0.37 83

Distribution of Alisols (1)

Distribution of Alisols (2)

Alisols cover an estimated area of 100M ha or some 0.8 percent of the Earth’s land surface, mainly in Latin America, the West Indies, West Africa, the highlands of eastern Africa, Madagascar, southeast Asia and northern Australia.

Associated soils

In the humid tropics, Alisols are associated with Acrisols, Nitisols and Cambisols, possibly with Ferralsols

In the seasonally dry (sub)tropics, Alisols are associated with Vertisols, Cambisols and Gleysols

In Mediterranean areas, Alisols do occur on old river terraces, but are considered relict soils from wetter past climates

Nitisols

Nitisols comprise deep, well-drained, red, clayey soils with diffuse horizon boundaries and characteristic moderate to strong, nut-shaped angular blocky structures.

They are mainly associated with basic rocks and limestones.

Definition of Nitisols

Nitisols have:

A nitic horizon starting within 100cm from the soil surface

Gradual to diffuse horizon boundaries

No ferric, plinthic or vertic horizon within 100cm from the soil surface

The nitic horizon (1)

Diffuse or gradual horizon transition above and below

Have:– > 30 percent clay– Water-dispersible clay / total clay < 0.10– Silt / clay < 0.40

Have moderate to strong, nutty or polyhedral structure with many shiny ped faces

The nitic horizon (2)

No gleyic or stagnic properties Have:

4.0 percent citrate-dithionite extractable iron (“free iron”), and

– > 0.20 percent acid oxalate (pH 3) extractable iron (“active iron”), and

– Free iron / active iron 0.05 Thickness of 30cm or more

Genesis of Nitisols (1)

Main soil-forming factors are:

Climate and Parent material

Main soil-forming processes are:

“Ferralitization” – intense hydrolysis of primary weatherable minerals and relative accumulation of kaolinite, (meta)halloysite, and sesquioxides

Genesis of Nitisols (2)

“Nitidization” - formation of strongly angular, shiny peds, probably resulting from micro-swelling and –shrinking, and influenced by the relative high amount of “active iron”

“Homogenisation” – biological pedoturbation by termites, ants, worms and other soil fauna, resulting in the crumb and/or subangular blocky structures and gradual or diffuse horizon boundaries

Classification of Nitisols

Intergrade qualifiers: alic, andic, ferralic, mollic, and umbric

Secondary characteristics qualifiers, related to defined diagnostic horizons, properties or materials: humic

Secondary characteristics qualifiers, not related to defined diagnostic horizons, properties or materials: alumic, dystric, eutric, rhodic, and vetic

Example of a Nitisol

Eutri-Ferralic Nitisol, BrazilDepth

cmBoun-dary

% clay

Silt/ clay

Clay(d)/ Clay(t)

Fe(d) Fe(o) Fe(o)/ Fe(d)

0-15 Clear 55 0.67 0.45 8.1 0.6 0.07

15-30 Gradual 57 0.65 0.65 8.2 0.7 0.09

30-75 Diffuse 78 0.23 0.38 8.1 0.8 0.10

75-125

Diffuse 82 0.20 0.05 7.8 0.9 0.12

125-175

Diffuse 82 0.18 0.00 7.8 0.9 0.12

Distribution of Nitisols (1)

Distribution of Nitisols (2)

Nitisols cover some 200M ha worldwide, or 1.6 percent of the Earth’s land surface.

They are found mainly in tropical Africa (Ethiopia, Kenya, Congo, Cameroon), in tropical Asia, South and Central America, and Australia.

Associated soils

Nitisols occur over basic and ultra-basic rocks in association with Ferralsols (plateau position) and Vertisols (lowland position).

In volcanic regions, Nitisols occur in association with Andosols on the higher slopes.

In limestone areas, Nitisols occur in association with Luvisols and Cambisols.