Download Parent material and world soil distribution

Symposium no. 21
Paper no. 2215
Presentation: poster
Parent material and world soil distribution
GRAY Jonathan and MURPHY Brian
NSW Department of Land and Water Conservation, 10 Valentine St, Parramatta, NSW
2150, Australia
Abstract
This paper examines the role of parent material in soil distribution. Parent material
is divided into ten categories based on chemical composition, chiefly silica and calciumferromagnesium content. The influence of parent material on various key soil properties
is discussed, including chemical fertility, texture, sodicity, salinity level, acidity,
structure, shrink/swell potential, erodibility and profile thickness.
The modelling of world soil types (using the World Reference Base scheme) under
various parent material, climate and drainage regimes is attempted. The model aids in
the prediction of likely soil types occurring in most world environments.
Keywords: parent material, soil properties, soil distribution, modelling
Introduction
It has long been recognised that parent material has a major influence on the
physical and chemical properties of soils. It is one of the five traditionally recognised
factors of soil formation, the others being climate, topography, organic material and
time. Broadly speaking, parent material is considered to provide the primary raw
material upon which the other influencing factors will serve to modify.
This paper examines how and why parent material influences soil properties and
soil distribution. It attempts to model soil distribution under different parent material
and environmental regimes. Parent material was taken as including primary bedrock and
also secondary material such as alluvial, aeolian and colluvial deposits.
Materials and Methods
The study extensively utilised existing published material. This included material
dealing specifically with the influence of parent material on soil properties, such as
Jenny (1941 , 1980), Whiteside (1953), Brewer (1954), Bear (1969), Chesworth (1973),
FitzPatrick (1980), and Paton et al. (1995). Also important were general publications on
soil distribution such as Stace et al. (1968), Isbell et al. (1997), ISSS Working Group
(1998, 1998b) and Charman and Murphy (2000) and published chemical analyses of
major rock types, particularly Joplin (1965), Krauskopf (1979) and Best (1982).
Another important source of data was the NSW Department of Land and Water
Conservation's Soil and Land Information System (SALIS) soils database, from which
data from over 8,000 soil profiles were analysed to derive statistical correlations
between soil types, parent material, climate and drainage. These correlations (based on
the Australian Soil Classification system) were presented in a series of over 50 charts in
Gray and Murphy (1999).
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17th WCSS, 14-21 August 2002, Thailand
In addition to these sources, the authors also considered whether the relationships
formulated were consistent with theoretical first principles of chemistry and soil
science.
Results and Discussion
Classification of parent material for pedologic purposes
For most pedologic purposes, including the modelling of soil properties and soil
distribution, the most important feature of the parent material is considered its chemical
composition. Physical properties such as grainsize or the presence of layering are
considered only of secondary importance. The most useful criteria are silica content
(SiO2) and calcium-ferromagnesium (Ca-Fe-Mg) oxide content. These criteria allow
parent material to be categorised in terms of their siliceous (ie, high in silica, low in
calcium-ferromagnesium) or mafic (low in silica, high in calcium-ferromagnesium)
character.
The more siliceous the parent material the greater the level of free quartz, the lower
the clay forming potential and the lower will be the calcium-ferromagnesium content
and cation exchange capacity (or "activity") of the clays. These properties have a major
influence on any derivative soils.
Ten categories of parent material are identified, as shown in Table 1. The first six
categories are defined by silica and calcium-ferromagnesium content while the last four
categories are defined by other properties. The average chemical composition of a range
of igneous, sedimentary and metamorphic rocks, corresponding to these different parent
material categories is given in Table 2. Average trace element contents for a range of
these materials is given in Table 3.
Influence of parent material on specific soil properties
From a consideration of the chemical and physical properties of different parent
materials, principles of soil science and the correlations derived from the SALIS
database, it is possible to draw conclusions on how parent material will influence
various specific soil properties.
Chemical fertility
Parent material is a major source of most nutrients necessary for plant growth, with
the notable exceptions of oxygen, hydrogen, nitrogen and carbon, which are primarily
derived from the atmosphere and organic material. From an examination of Tables 2
and 3 it is apparent that most of these nutrients increase as the parent material becomes
more mafic. For example, the table shows CaO concentrations increasing from 0.1% in
average granite, to 6.8% in average andesite, to 9.5% in average basalt, and then
dropping to 5.1% in average peridotite.
Also the ability of the soil to absorb and retain nutrients, as indicated by its cation
exchange capacity (CEC), increases with increasing mafic character of the parent
material. Clays produced from mafic parent materials, such as montmorillonite and
vermiculite, have higher CEC (or activity) than those produced from siliceous parent
materials such as illite and kaolin. Ultramafic parent materials frequently contain
concentrations of elements that are toxic to many plants particularly Ni, Cr, Co, Zn, Hg,
and Pb, as can be seen from Table 3.
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GRAY & MURPHY
Table 1 Broad classification of parent material for pedologic purposes.
1
CalciumFerromagnesium
Content (Ca, Mg &
Fe oxides)
Parent Material
Category
Silica
Content
(SiO2)
1. Extremely siliceous
>90%
extremely low
(generally <3%)
2. Highly siliceous
72-90%
Low
(generally 3-7%)
3.Transitional
siliceous/
intermediate
62-72%
moderately low
(generally 7-14%)
4. Intermediate
52-62%
Moderate
(generally 14-20%)
5. Mafic
45-52%
High
(generally 20-30%)
very high
(generally >30%)
6. Ultramafic
<45%
7. Calcareous
low1
8. Alluvial
9. Organic
variable1
low1
10. Sesquioxide
variable1
CaCO3 dominant,
other bases variable
variable
organic matter
dominant, bases
variable
variable, dominated by
sesquioxides such as
iron and aluminium
oxides
Examples
quartz sands (beach, alluvial or
aeolian), chert, quartzite, quartz
reefs and silicified rocks
granite, rhyolite, adamellite,
dellenite, quartz sandstone, quartz
siltstone and siliceous tuff
granodiorite, dacite, trachyte,
syenite, most greywacke, most
lithic sandstone,
siliceous/intermediate tuff and
most argillaceous rocks
(mudstone, claystone, shale, slate,
phyllite and schist)
monzonite, trachy-andesite,
diorite, andesite, intermediate tuff
and some greywacke, lithic
sandstone and argillaceous rocks.
gabbro, dolerite, basalt and mafic
tuff (uncommon)
serpentinite, dunite, peridotite,
amphibolite and tremolitechlorite-talc schists
limestone, dolomite, calcareous
shale and calcareous sands
alluvium
peat, coal and humified
vegetative matter
laterite, bauxite, ferruginous
sandstone and ironstone
category not defined by silica content
Texture
The parent material largely controls the potential quantity of clay, the potential
quantity of resistant minerals such as quartz and their grainsize, and the activity of the
clay produced. Most minerals apart from quartz eventually weather to form clay
minerals. Thus, the more mafic the parent material, the higher will be the clay content
and lower the quartz grain content. Argillaceous rocks such as shales are predominantly
composed of clay particles, thus they will give rise to soils with high amounts of clay.
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100.27
Total
99.88
78.33
0.25
4.77
1.07
0.3
1.16
5.5
0.45
1.31
1.63
5.03
0.08
Quartz
sandstone
(s)
100.07
71.30
0.31
14.32
1.21
1.64
0.05
0.71
1.84
3.68
4.07
0.77
0.05
0.12
Granite
(p)
99.96
72.82
0.28
13.27
1.48
1.11
0.06
0.39
1.14
3.55
4.30
1.41
0.08
0.07
Rhyolite
(v)
100.70
66.06
0.62
15.34
1.01
4.58
0.04
2.85
2.38
3.21
4.00
0.52
0.09
Greywacke2
(s)
99.90
66.09
0.54
15.73
1.38
2.73
0.08
1.74
3.83
3.75
2.73
1.04
0.08
0.18
Granodiorite
(p)
99.78
65.01
0.58
15.91
2.43
2.30
0.09
1.78
4.32
3.79
2.17
1.19
0.06
0.15
Dacite
(v)
Source: Average analysis: Best (1982); Australian sample analysis: Joplin (1965).
p: plutonic igneous (coarse grained); v: volcanic igneous (fine grained); s: sedimentary;
1
Cronulla, NSW, 2 Mt Nebo, Brisbane Qld, 3 Prospect, NSW.
97.62
1.32
0.4
0.13
0.28
0.52
-
SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
H2O
CO2
P 2O 5
Dune
sand 1
(s)
100.14
60.28
1.12
17.78
4.45
2.6
1.17
0.56
0.34
2.36
0.26
0.22
Shale3
(s)
99.98
57.48
0.95
16.67
2.50
4.92
0.12
3.71
6.58
3.54
1.76
1.36
0.10
0.29
Diorite
(p)
99.93
57.94
0.87
17.02
3.27
4.04
0.14
3.33
6.79
3.48
1.62
1.17
0.05
0.21
Andesite
(v)
99.95
49.2
1.84
15.74
3.79
7.13
0.2
6.73
9.47
2.91
1.1
1.38
0.11
0.35
Basalt
(v)
Table 2 Average chemical composition of some common igneous and sedimentary rocks. (expressed as % oxides).
GRAY & MURPHY
99.46
42.26
0.63
4.23
3.61
6.58
0.41
31.24
5.05
0.49
0.34
4.22
0.3
0.1
Peridotite
(p)
99.79
5.19
0.06
0.81
0.54
7.89
42.57
0.05
0.33
0.77
41.54
0.04
Limestone
(s)
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GRAY & MURPHY
Table 3 Average content of trace elements in main rock types and ionic radii of
common elements. (content in ppm).
Ultramafic
Igneous
P
Ga
Cr
Li
Ni
C
V
Ti
Zr
Mn
Sc
Cu
Sr
Pb
Ba
Rb
Zn
As
Mo
B
170
2
2000
<1
2000
200
40
300
30
1500
5
20
10
<1
1
2
Mafic
Igneous
1400
18
200
15
160
45
200
9000
100
2000
24
100
440
8
300
45
100
2
1
5
Intermediate
Igneous
1600
20
50
20
55
10
100
8000
260
1200
3
35
800
15
650
100
Shale
Highly
Siliceous
Igneous
750
25
100
60
80
20
130
4600
180
850
15
50
400
20
600
140
90
10
2
100
700
20
25
40
8
5
40
2300
200
600
3
20
300
20
830
200
50
1.5
1.5
15
Sandstones
170
12
35
15
2
0.3
20
1500
220
50
1
5
20
7
50
60
16
1
0.2
35
Carbonates
400
4
11
5
4
0.1
20
400
19
1100
1
4
610
9
10
3
20
1
0.4
20
Source: various tables in Krauskopf (1979).
The activity of the clay present will also influence the soil texture, with high
activity clays such as smectites and vermiculite giving heavier texture than low activity
clays such as kaolin and illite. Generally the more mafic the parent material, the higher
the activity of the clays produced. The coarser the grain size of the parent material, and
in particular that of the resistant quartz grains, the coarser will be the particle size of the
soil, especially of the surface soil.
Sodicity
Sodic problems develop where there is a high ratio of sodium relative to other
exchangeable bases. This ratio generally increases with increasing siliceous character of
the parent material. This is demonstrated by Table 2 which reveals a Na2O/CaO ratio of
0.3 for average basalt, 0.5 for average diorite, 1.0 for average granodiorite and 2.0 for
average granite. Highly siliceous parent materials such as quartz sandstones or granites
give rise to soils that are very susceptible to external sources of sodium (such as leached
solutions from upslope, windlblown dust or rising groundwaters) because of their
inherently low (non-sodium) base content (see Hallsworth and Waring, 1964).
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17th WCSS, 14-21 August 2002, Thailand
Salinity level
It is difficult to make generalisations about the potential salinity levels in soils
arising from different parent materials. Much of the salt present in soils may be derived
from external sources (see Isbell et al., 1983).
Salt content may be high in marine clay rich sediments (i.e. claystones, shales, etc)
as the salt and/or component ions may be bound up with the clays during the deposition
process. Note that not all marine sediments are high in salt content as the saline water is
generally not retained during the lithification process. Gunn and Richardson (1979),
studying the Cretaceous rocks of southern Queensland, reported significant quantities of
sodium, chloride and other salt forming ions in marine argillaceous sediments, but low
quantities in marine quartzose sediments. These authors show that most rocks, with the
probable exception of quartzose sandstones and siltstones, have sufficient sodium,
chloride and other ions to give rise to salty conditions without the need for atmospheric
accession of salt.
As is the case for sodicity effects noted above, soils derived from highly siliceous
parent materials are inherently more susceptible to the presence of salt than those
derived from mafic soils, due to their lower exchangeable base content, thus lower
buffering potential.
Soil acidity
Soil acidity tends to decrease with increasing mafic character of the parent material.
This is due to the greater abundance of exchangeable bases and higher CEC in soils
derived from mafic materials which have a buffering effect to increases in the H+ ion
ions (e.g. from plant growth, removal of basic cations in farm produce, or nitrate
leaching). Where carbonate is present in the soil, as is common over calcareous parent
materials (e.g., limestone or dolomite), they will usually be slightly or even strongly
alkaline in character. Thus soils derived from highly siliceous sandstones and granites
will generally be more acidic than those derived from andesites and basalts, other
factors being equal.
Soil structure
The most highly structured soils are generally formed where there are clays with
high calcium levels and low sodium levels; high levels of sesquioxides (as indicated by
the presence of free iron and aluminium oxides); and/or high organic matter and soil
fauna activity (particularly critical for lighter-textured soils). Generally speaking, these
attributes become more common in soils as the parent material becomes increasingly
mafic in character (but not ultramafic). Thus, soils with good structure, at least in
surface units, are commonly formed from parent materials of mafic to intermediate
composition, e.g. basalts and andesites.
Shrink/swell potential
This phenomena occurs where high levels of smectite clays such as
montmorillonite are present. Generally the more mafic the parent material the higher the
amount of smectite present. Illite, vermiculite and interstratified clays (i.e. material
composed of interlayers of various clay types) can be prone to a degree of
shrink/swelling activities. Kaolin and chlorite have low potential for these activities.
Thus, basalt-derived soils have a typically high potential for shrink/swell and related
phenomena, soils from more intermediate rocks such as andesites, shales and
GRAY & MURPHY
17th WCSS, 14-21 August 2002, Thailand
granodiorites have a moderate potential, while siliceous rocks such as granites and
sandstones give rise to soils with a typically low potential.
Erodibility
Soils with high levels of fine sand and silt and low clay levels are likely to be
highly erodible. The finer the sand/silt particles the more prone to erosion the soil is
likely to be. Thus, fine-grained siliceous parent materials such as siltstones and rhyolites
will be the most likely to give rise to erodible soils, at least in surface units. High clay
forming parent materials such as basalts and shales are generally the least likely, other
factors being equal.
Where the clays present are dispersible they are highly prone to erosion, where they
are flocculating they are less prone to erosion. Clays with dispersible behaviour are
frequently associated with the more siliceous parent materials, as they are more
susceptible to sodium problems. Note that "self mulching" clay soils derived from mafic
parent materials may be subject to high erosion because of their tendency to seal under
rainfall, thus leading to high runoff and water erosivity.
Soil thickness and rock outcrop
In the zone of soil depletion (i.e. middle and upper hillslopes), soil thickness is
determined by the rate of parent material weathering as opposed to the rate of soil
erosion from the site. Where the former is greater than the latter a relatively thick
profile will develop; where the reverse applies the profile will be relatively thin with
extensive rock outcrop. From a consideration of these weathering and erodibility
factors, it is possible to develop a sequence of parent materials giving rise to deeper
soils and decreasing rock outcrop. The following general sequence is suggested for
zones of depletion under equivalent environmental conditions:
carbonate parent material
fine-grained siliceous parent material
coarse-grained siliceous parent material
fine-grained intermediate parent material
coarse-grained intermediate parent material
fine-grained mafic parent material
coarse-grained mafic parent material.
shallowest soil
deepest soil
In the zone of soil accumulation (i.e., footslopes and valley floors) soils are
typically thick with rare outcrop. It is more difficult to determine trends as attempted
above for this zone.
Modelling of soil distribution based on parent material, climate and drainage
The modelling of potential soil types under various parent material, climate and
drainage regimes is attempted. This is based on an understanding of the influence that
these factors have on soil properties, an analysis of correlations derived from
approximately 8,000 soil profiles stored in the SALIS soil database, and an examination
of published soil relationships. The model aids in the prediction of likely soil types in
most world locations, using the World Reference Base for Soil Resources scheme (FAO
1998 and ISSS Working Group 1998a, 1998b).
The model is presented in the form of two x-y plots in Figures 1 and 2, showing the
typical distribution ranges of most World Reference Base soil types. Figure 1 deals with
Well Drained (Upland) Locations, characterised by good water drainage and a net
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17th WCSS, 14-21 August 2002, Thailand
removal of soil materials. Figure 2 deals with Imperfectly Drained (Lowland) Locations,
characterised by restricted drainage and a net accumulation of soil materials.
On the y axis of each of these plots is parent material category (based on silica
content) ranging from extremely siliceous at the top to ultramafic at the base. On the x
axis is annual rainfall, ranging from dry on the left to very humid on the right.
Although the maximum rainfall indicated is only 2,000 mm pa, the plot is in fact open
ended. Typical temperature conditions, be it cool, temperate or warm are indicated by
superscripts attached to each of the major soil groups in the body of the plot.
The plots comprise a series of "soil distribution stars". The centroid of the star
indicates the most common conditions under which the soil will occur while the arms of
the star indicate the ranges of conditions over which the soil may occur. For example,
Figure 1 reveals that in well drained (upland) locations, Calcisols range from highly
siliceous to mafic parent materials and from approximately 0 to 500 mm annual rainfall.
Note that several different soils are usually theoretically possible under any given set of
conditions. The figures do not cover the soil types that do not have clear parent material
- climate - drainage correlations, and thus cannot be easily presented on these plots, eg,
Anthrosols (human modified soils) and Cryosols (perenially frozen soils).
These plots represent the best fit model for World Reference Base soil distribution
that could be generated with the information available. They are, however, still only
approximations and need to be applied with caution. The precise positioning and ranges
of the soil distribution stars will very likely be modified as further data and user
feedback is gained.
Figure 1 Soil distribution in well drained (upland) locations.
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17th WCSS, 14-21 August 2002, Thailand
Figure 2 Soil distribution in imperfectly drained (lowland) locations.
A summary of the main diagnostic and land management features of the main
World Reference Base soils as identified in Figures 1 and 2 (together with their Soil
Taxonomy equivalents) are presented in Table 4.
Conclusion
Parent material has a major influence on the properties of soil. It provides the basic
starting material upon which other factors such as topography and climate serve to
modify. This paper has presented a model identifying the relationship of World
Reference Base soils to parent material, climate and topographic regimes. It is
recognised that considerable uncertainties exist in the model, and that it must be applied
with caution. Any resulting predictions should be treated as first approximations only.
The authors would welcome any feedback to help refine the model.
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Aqualts, Humults and Udults
Andisols
Human influence at sub-order
level
Psamments or Psammaquents
Pale- great groups of Alfisols &
Aridisols, & calcic subgoups
Inceptisols (Dystro- & Eutrochrepts)
Borrol ??
Gelisol order
Alfisols & Inceptisols, in Durorthid or Durargid great groups
Oxisols
ALBELUVISOLS
ALISOLS
ANDOSOLS
ANTHROSOLS
CALCISOLS
CHERNOZEMS
CRYOSOLS
DURISOLS
FERRALSOLS
CAMBISOLS
ARENOSOLS
Latosols, oxic Alfisols and
Ultisols
multiple
ACRISOLS
World Reference
Soil Taxonomy Equivalent
Base Soil
Deep and strongly weathered,
physically stable but chemically poor
subsoil
Accumulation of secondary silica
Subsoil with low activity clay and low
base saturation
Acidic, bleached horizon penetrating
into clay rich horizon
High activity clay subsoil, rich in
exchangeable aluminium
Young age, within recent volcanic
deposits
Formation conditioned by human
influences
Sandy, very weak or no pedologic
development
Accumulation of secondary calcium
carbonates
Only weak to moderate pedologic
development
Thick, blackish, organic rich topsoil,
calcareous subsoil
Permafrost within 1 m depth
Main Characteristics
Land Management Features
High agricultural potential - high available water capacity,
nutrients and organic matter; neutral pH
Very low agricultural potential - prone to high erosion and
melting and ponding of permafrost
Very low agricultural potential - duripan restricts plant
root and water penetration
Low to moderate agricultural potential - good physical
properties but low nutrients and pH
Low agricultural potential - low nutrients, CEC and
waterholding capacity
Moderate agricultural potential (but dry conditions are
limiting), prone to erosion and salinisation
Variable but generally moderate agricultural potential
Low agricultural potential - acid and nutrient poor, rapidly
degrade, prone to erosion
Low to moderate agricultural potential - acid, nutrient poor
and drainage and tillage problems
Low to moderate agricultural potential - low nutrients,
aluminium toxicity, high erodibility
Moderate agricultural potential - low water retention and
CEC, acid, aluminium toxicity
Variable agricultural potential
Table 4 Main characteristics and land management features of world reference base soils.
GRAY & MURPHY
Aquents, Aquepts and Aquolls
Aridisols (Gypsiorthid)
Histosols
Ustolls and Borolls
Entisols (lithic subgroups),
Rendolls
Latosols and Alfisols (oxic
subgroup)
Alfisols
Alfisols and Ultisols (kandic
group)
Aquolls
GLEYSOLS
GYPSISOLS
HISTOSOLS
KASTANOZEMS
LEPTOSOLS
NITISOLS
Albaqualfs, Albaqualts,
Argialbolls
Plinthaquox
PLANOSOLS
PLINTHOSOLS
PHAEOZEMS
LUVISOLS
LIXISOLS
Fluvents
FLUVISOLS
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Wet, hard layer of iron, clay and quartz
in subsoil
Deep and clay rich, shiny, nut shaped
structure
Thick, dark, organic rich topsoil,
carbonates removed
Bleached, temporarily water saturated
topsoil on a slowly permeable subsoil
Composed of organic materials
Thick, dark brown, organic rich
topsoil, calcareous or gypsum rich
subsoil
Very shallow depth over hard rock, or
very gravelly
Subsoil with low activity clay and high
base saturation
Subsoil with high activity clays
Permanent or temporary wetness near
the surface
Accumulation of secondary gypsum
Young soils in alluvial deposits
Main Characteristics
Land Management Features
Low agricultural potential - shallow depth, low water
holding capacity and typical steep slopes
Moderate agricultural potential - generally moderate
nutrient levels, low CEC, prone to erosion
High agricultural potential - good fertility, CEC and
waterholding capacity. Restricted drainage can be problem
High agricultural potential - good fertility (despite low
available phosphorous), structure and physical properties
High agricultural potential - high nutrient levels, organic
matter, and available water capacity and good structure
Low to moderate agricultural potential - dense subsoil
inhibits root growth, generally low in organic matter and
nutrients
Very low agricultural potential - plinthite layer means poor
plant rooting conditions but often useful as construction
material
Moderate to high agricultural potential - fertile and flat
land; acid sulfate problems in marine areas
Low to moderate agricultural potential - wet and poorly
drained, extensively cultivated for rice
Low to moderate agricultural potential - dissolution of
gypsum causes subsidence, gypsic pan may be restriction
Low agricultural potential - may be improved by drainage
Moderate to high agricultural potential - good physical
and chemical properties, but irrigation usually required
17th WCSS, 14-21 August 2002, Thailand
World Reference
Soil Taxonomy Equivalent
Base Soil
Table 4 (Cont.)
GRAY & MURPHY
Entisols
Salorthids
Natr-ustalfs, -ustolls, -xeralfs, argids and Nadurargids
Umbrepts and Humitropepts
Vertisols
REGOSOLS
SOLONCHAKS
SOLONETZ
UMBRISOLS
VERTISOLS
Subsurface clay accumulation, rich in
sodium
Acidic, medium textured, topsoil being
thick, dark and organic rich
Dark-coloured cracking and swelling
clays
Acidic, with illuvial iron-aluminiumorganic compounds
Very little soil development, in
unconsolidated material
Strongly saline
Information source: ISSS Working Group RB (1998a, 1998b)
Spodosols
PODZOLS
Main Characteristics
Land Management Features
Very low agricultural potential - sandy texture, low
nutrient levels, acidic and frequent aluminium toxicity
Low to moderate agricultural potential - variable
properties, generally low water holding capacity
Very low agricultural potential - salt limits growth to salt
tolerant plants. Salt also causes problems with
construction
Low agricultural potential - sodic conditions impede plant
growth and mean high erodibility
Low agricultural potential - acidic soil and wet, cold
climatic conditions, potential will improve with liming
High agricultural potential - very high fertility, but
physical problems eg, heavy, shrink-swell clays with low
infiltration
17th WCSS, 14-21 August 2002, Thailand
World Reference
Soil Taxonomy Equivalent
Base Soil
Table 4 (Cont.)
GRAY & MURPHY
GRAY & MURPHY
17th WCSS, 14-21 August 2002, Thailand
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