1. ACRISOLS, ALISOLS, LIXISOLS and NITISOLS
Otto Spaargaren
ISRIC – World Soil Information
Wageningen
The Netherlands

2. Content of lecture
Acrisols and Lixisols
Alisols
Nitisols

3. 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.

4. 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

5. 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

6. 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 % clay, argic horizon must have 1.2x (relative) more clay

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Example of an Acrisol
Alumi-Profondic Acrisol (Chromic), China

14. Example of a Lixisol
Chromic Lixisol, Ghana

15. Distribution of Acrisols (1)

16. 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.

17. Distribution of Lixisols (1)

18. 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.

19. 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.

20. 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.

21. 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

22. Definition of Alisols (2)
Alisols have
No diagnostic horizons other than an ochric, umbric, albic, andic, ferric, nitic, plinthic or vertic horizon

23. 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)

24. 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

25. 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

26. 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

27. 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

28. 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
3.8
0.42 22
0.45 89 26
3.9
0.32 18
0.37 69
0.43 17 83

29. Distribution of Alisols (1)

30. 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.

31. 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

32. 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.

33. 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

34. 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

35. 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

36. Climate and Parent material
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

37. 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

38. 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

39. Example of a Nitisol Eutri-Ferralic Nitisol, Brazil Depth cm Boun-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
8.2
0.7
0.09
30-75
Diffuse 78
0.23
0.38
0.8
0.10
75-125 82
0.20
0.05
7.8
0.9
0.12
0.18
0.00

40. Distribution of Nitisols (1)

41. 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.

42. 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.