FAO Guidelines for Soil Description (2006)
I. Site Information
Site information refers to the data on the bio-physical characteristics of the site where the soil
to be examined is located including the name of the person doing the soil examination and the
date of examination.
a) Profile number
It is necessary to assign a profile number to each soil examined to allow easy and simple
retrieval of profile descriptions from computerised data storage systems.
b) Author(s)
The person who performs the description needs to be properly acknowledged in future uses of
the soil data and he or she holds responsibility for the quality of the data.
c) Date of description
The date of description is an important information and should be given as yymmdd (6 digits).
d) Location
This should include the distance (in meters or kilometers) and direction to the site from
permanent features which are recognizable in the field and on the topographic map.
e) Elevation
The elevation (in meters) of the site relative to sea level should be obtained from detailed
contour or topographic maps or by altimeter readings. At present determination of elevation
by a Global Positioning System (GPS) unit is inaccurate and unacceptable.
f) Map sheet number and Coordinates
The number of the topographic map sheet, preferably at 1 : 25 000 or 1 : 50 000 scale, on
which the soil observation occurs should be given. The latitude and longitude of the site (in
degrees, minutes, seconds and decimal seconds) can be derived directly from topographic
maps or a Global Positioning System (GPS) unit.
g) Atmospheric climate and weather conditions
Present weather conditions
Sunny/clear Partly cloudy Overcast
Rain Sleet Snow
Past weather conditions
No rain during the last month
No rain during the last week
No rain during the last 24 hours
Small rain during the last 24 hours
Stronger rain since some days or rainstorm during the last 24 hours
Extremely rainy time or snow melting
h) Soil climate
Soil temperature regime Soil moisture regime
Pergelic Aquic
Cryic Peraquic
Frigid Isofrigid Aridic
Mesic Isomesic Udic
Thermic Isothermic Perudic
Hyperthermic Isohyperthermic Ustic
Xeric and Torric
i) Landform and topography (relief)
Major landform
Landforms should be described by their morphology and not by their genetic origin, or
processes responsible for their shape.
1st Level 2
nd Level Gradient Relief Intensity
[%] (m km-1
)
Level land plain <10 <50
plateau <10 <50
depression <10 <50
valley floor <10 <50
Sloping land medium-gradient mountain 15-30 150-300
medium-gradient hill 10-30 100-150
medium-grad. escarpment zone 10-30 50-100
medium-gradient valley 10-30 100-150
dissected plain 10-30 50-100
Steep land high-gradient mountain >30 >300
high-gradient hill >30 150-130
high-gradient escarpment zone >30 150-130
high gradient valleys >30 >150
Slope position
Slope positions in undulating and mountainous terrain (redrawn from Schoeneberger et al.
1998)
CR = Crest (summit)
UP = Upper slope (shoulder)
MS = Middle slope (backslope)
LS = Lower slope (footslope)
TS = Toeslope
BO = Bottom (flat)
Slope form
Straight
Concave
Convex
Terraced
Complex (Irregular)
Slope gradient and orientation
Flat 0 - 0.2 % Sloping 5 - 10 %
Level 0.2 - 0.5 % Strongly sloping 10 - 15 %
Nearly level 0.5 - 1.0 % Moderately steep 15 - 30 %
Very gently sloping 1.0 - 2 % Steep 30 - 60 %
Gently sloping 2 - 5 % Very steep >60 %
The orientation which a slope is facing is coded with N for north, E for east, S for south and
W for west. SSW e.g. means south south-west.
j) Land use and vegetation
Land use
Settlement, industry Residential use Industrial use Transport Recreational use Excavations
Crop Agriculture
Annual field cropping Shifting cultivation Fallow system cultivation Ley system cultivation Rainfed arable cultivation Wet rice cultivation Irrigated cultivation
Perennial field cropping Non-irrigated cultivation Irrigated cultivation
Tree and shrub cropping Non-irrigated tree crop cultivation Irrigated tree crop cultivation Non-irrigated shrub crop cultivation Irrigated shrub crop cultivation
Animal Husbandry
Extensive grazing Nomadism Semi-nomadism Ranching
Intensive Grazing Animal production Dairying
Forestry
Natural forest and woodland Selective felling Clear felling
Plantation forestry
Mixed farming Agro-forestry Agro-pastoralism
Extraction and collection Exploitation of natural vegetation Hunting and fishing
Nature Protection Nature a. game preservation Reserves Parks Wildlife management
Degradation control Without interference With interference
Not used and not managed
Additional codes may be used to further specify the land utilization type. For example:
Rainfed arable cultivation Traditional Improved traditional Mechanized traditional Commercial Unspecified
For arable land use, the dominant crops which are grown should be mentioned, and as much
information as possible given on soil management, use of fertilizers, duration of fallow period,
rotation systems and yields.
Crops
Crops are plants that are cultivated for their economic value.
Barley
Beans
Cassava
Coconut
Coffee
Cashew
Cocoa
Cowpea
Cotton
Fruit trees
Groundnut
Maize
Millet
Oilpalm
Peas
Potato
Rice (flooded)
Rice
Rubber
Rice (upland)
Soyabean
Sugar cane
Sunflower
Sorghum
Sweet potato
Tobacco
Tea
Vegetables
Wheat
Yams
Human influence
This refers to the influence of humans on the site. Examples of human influences are:
No influence Bunding
Not known Burning
Vegetation slightly disturbed Terracing
Vegetation moderately disturbed Ploughing
Vegetation strongly disturbed Plaggen
Vegetation disturbed Raised beds
Sprinkler irrigation Sand additions
Furrow irrigation Mineral additions (unspecified)
Flood irrigation Pollution
Border irrigation Clearing
Irrigation (unspecified) Surface compaction
Artificial drainage Borrow pit
Application of fertilizers
Vegetation
Closed Forest 1)
Evergreen forest
Semi-deciduous forest
Deciduous forest
Xeromorphic forest
Woodland 2)
Evergreen woodland
Semi-deciduous woodland
Deciduous woodland
Xeromorphic woodland
1) Continuous tree layer, crowns overlapping,
large number of tree and shrub species in
distinct layers
2) Continuous tree layer, crowns usually not
touching, understorey may be present
Shrub
Evergreen shrub
Semi-deciduous shrub
Deciduous shrub
Xeromorphic shrub
Dwarf Shrub Evergreen dwarf shrub
Semi-deciduous dwarf shrub
Deciduous dwarf shrub
Xermomorphic dwarf shrub Tundra
Herbaceous Tall grassland
Medium grassland
Short grassland
Forb
In addition, other characteristics of the vegetation, such as height of trees or canopy cover,
may be recorded.
k) Parent material
Hierarchy of lithology
Major Class Group Type
Igneous rock acid igneous granite grano-diorite quartz-diorite rhyolite
intermediate andesite, trachyte, phonolite igneous diorite-syenite
basic igneous gabbro basalt dolerite
ultrabasic igneous peridotite pyroxenite ilmenite, magnetite, ironstone, serpentine
pyroclastic tuff, tuffite
volcanic scoria, breccia
volcanic ash
ignimbrite
Metamorphic acid metamorphic quartzite rock gneiss, migmatite slate, phyllite (pelitic rocks) schist
basic metamorphic slate, phyllite (pelitic rocks) green schist gneiss rich in Fe-Mg-minerals metamorphic limestone (marble)
Sedimentary clastic sediments conglomerate, breccia rock (consolidated) sandstone, greywacke, arkose silt-, mud-, claystone shale ironstone
carbonatic, organic limestone, other carbonate rock marl & other mixtures coals, bitumen & related rocks
evaporites anhydrite, gypsum halite
Sedimentary (unconsolidated)
fluvial sand and gravel clay, silt and loam
lacustrine sand silt and clay
marine, estuarine sand clay and silt
colluvial slope deposits
lahar
eolian loess sand
glacial moraine glacio-fluvial sand
glacio-fluvial gravel
kryogenic periglacial rock debris periglacial solifluction layer
organic rainwater-fed moor peat groundwater-fed bog peat
anthropogenic/ redeposited natural material technogenic industrial depsoit
unspecified clay deposits loam and silt sand gravelly sand grave, broken rock
l) Age of the land surface
Very young (1-10 years) anthropogeomorphic: with complete disturbance of natural surfaces
(and soils) like in urban, industrial and mining areas with very early soil development
from fresh natural or technogenic or mixed materials.
Very young (1-10 years) natural: with erosional loss or deposition of materials like on tidal
flats, of coastal dunes, in river valleys, landslides or desert areas
Young (10-100 years) natural: with erosional loss or deposition of materials like on tidal flats,
of coastal dunes, river valleys, landslides, or desert areas,
Young (10-100 years) anthropogeomorphic: with complete disturbance of any natural
surfaces (and soils) like in urban, industrial and mining areas with early soil
development from fresh natural or technogenic or mixed materials, or restriction of
flooding by dikes
Holocene (100-10,000 years) anthropogeomorphic: man- made relief modifications, like
terracing of forming hills or walls by early civilisations or during Middle Age or
earlier, or restriction of flooding by dikes
Holocene (100-10,000 years) natural: with erosional loss or deposition of materials like on
tidal flats, of coastal dunes, in river valleys, landslides or desert areas,
Late Pleistocene, ice covered, commonly the recent soil formation on fresh materials
Late Pleistocene, periglacial, commonly the recent soil formation on preweathered materials
Late Pleistocene; without periglacial influence
Older Pleistocene, ice covered, commonly the recent soil formation on younger over older
and preweathered materials
Older Pleistocene, with periglacial influence, commonly the recent soil formation on younger
over older and preweathered materials
Older Pleistocene without periglacial influence
Tertiary land surfaces, commonly high planes, terraces or peneplains, except incised valleys,
frequent occurrence of paleosoils
Older land surfaces, commonly high planes, terraces or peneplains, except incised valleys,
frequent occurrence of paleosoils
II. Soil profile description
1. Soil surface characteristics
a) Rock outcrops
Rock outcrops can limit the use of modern, mechanized, agricultural equipment. This can be
described using the table below:
Surface cover Distance between rock outcrops
None
Very few
Few
Common
Many
Abundant
Dominant
0 %
0 – 2 %
2 – 5 %
5 – 15 %
15 – 40 %
40 – 80 %
>80 %
>50 m
20 – 50 m
5 – 20 m
2 – 5 m
<2 m
b) Surface coarse fragments
Surface coarse fragments should be described using the table below:
Surface cover Size classes indicating the greatest dimension
None
Very few
Few
Common
Many
Abundant
Dominant
0 %
0 – 2 %
2 – 5 %
5 – 15 %
15 – 40 %
40 – 80 %
>80 %
Fine gravel 0.2– 0.6cm
Medium gravel 0.6– 2.0cm
Coarse gravel 2 – 6 cm
Stones 6 – 20 cm
Boulders 20 – 60 cm
Large boulders 60 –200 cm
c) Erosion
Main categories of erosion
No evidence of erosion
Water erosion or deposition Wind (eolian) erosion or deposition
Sheet erosion Wind deposition
Rill erosion Wind erosion and deposition
Gully erosion Shifting sands
Tunnel erosion Salt deposition
Deposition by water Water and wind erosion
Mass movement (landslides and similar phenomena)
Not known
Area affected
The total area affected by erosion and deposition is estimated following the classes below:
0 % 10 – 25 %
0 – 5 % 25 – 50 %
5 – 10 % > 50 %
Degree
Slight: Some evidence of damage to surface horizons. Original biotic functions
largely intact.
Moderate: Clear evidence of removal of surface horizons. Original biotic func-
tions partly destroyed.
Severe: Surface horizons completely removed and subsurface horizons exposed.
Original biotic functions largely destroyed.
Extreme: Substantial removal of deeper subsurface horizons (badlands). Original
biotic functions fully destroyed.
d) Surface sealing
Surface sealing refers to crusts which develop at the soil surface after the topsoil dries out.
Thickness Consistency
None Slightly hard
Thin <2 mm Hard
Medium 2 – 5 mm Very hard
Thick 5 – 20 mm Extremely hard
Very thick >20 mm
e) Surface cracks
Surface cracks develop in shrink-swell clayey soils after they dry out. They indicate the
dominance of expanding type of clay particularly montmorillonite.
Width Distance between cracks
Fine < 1 cm Very closely spaced <0.2 m
Medium 1 – 2 cm Closely spaced 0.2 – 0.5 m
Wide 2 – 5 cm Moderately widely spaced 0.5 – 2 m
Very wide 5 – 10 cm Widely spaced 2 – 5 m
Extremely wide > 10 cm Very widely spaced >5 m
2. Soil horizon characteristics
Subordinate characteristics within master horizons
a Highly decomposed organic material
b Buried genetic horizon
c Concentrations1 or nodules
d Dense layer (physically root restrictive)
e Moderately decomposed organic material
f Frozen soil
g Stagnic horizons2
h Accumulation of organic matter in mineral horizons
i Slightly decomposed organic material
j Jarosite accumulation
k Accumulation of pedogenic carbonates
l Capillary fringe mottling
m Strong cementation (pedogenic, massive)
n Pedogenetic accumulation of exchangeable sodium
o Residual accumulation of sesquioxides
p Plowing or other human disturbance
q Accumulation of pedogenetic silica
r Strong reduction3
t Illuvial accumulation of silicate clay
u Urban and other human-made materials
v Occurrence of plinthite
w Development of color or structure
x Fragipan characteristics
y Pedogenetic accumulation gypsum
z Pedogenetic accumulation of salts more soluble than gypsum
Note: In the USDA method, concentration1 is called concretions, g indicates strong gleying
2,
and r indicates weathered or soft bedrock3
a) Horizon boundary
Depth
Distinctness and topography
Abrupt 0 - 2 cm
Clear 2 - 5 cm
Gradual 5 - 15 cm
Diffuse > 15 cm
The topography of the boundary indicates the
smoothness of depth variation of the boundary
Smooth Nearly plane surface
Wavy Pockets less deep than wide
Irregular Pockets more deep than wide
Broken Discontinuous
b) Soil texture
Field estimation of textural classes
The soil textural class can be estimated in the field by easy field tests. For this, the soil sample
must be in a moist to weak wet state. Gravel and plant materials >2 mm must be removed.
Clay: makes fingers dirty, is cohesive (sticky), is formable, has a high plasticity and has a
shiny surface after squeezing between fingers.
Silt: makes fingers dirty, is nonsticky, only weak formable, has a rough and ripped surface
after squeezing between fingers and feels very floury (like talcum powder).
Sand: can not be formed, makes fingers not dirty and feels very grainy.
Key to the soil texture classes (adapted from Schlichting et al., 1995)
1. Not possible to roll a wire of about 7 mm Ø (about Ø of a pencil)~% clay
1.1 not dirty, not floury, no fine material in the finger rills sand <5
- if grain sizes are mixed unsorted sand <5
- if most grains are very coarse (>0.6 mm) coarse sand <5
- if most grains are of medium size (0.2-0.6 mm) medium sand <5
- if most grains are of fine size (<0.2 mm) but still grainy fine sand <5
- if most grains are of very fine size (<0.12 mm), tending
to be floury very fine sand <5
1.2 not floury, grainy, scarcely fine material in the finger rills,
weakly shapeable, adheres slightly to the fingers loamy sand <12
1.3 as 1.2 but moderately floury, sandy loam (clay poor) <10
2. Possible to roll a wire of about 7 to 3 mm Ø (about ½ Ø of a pencil) but breaks if trying
to form a ring, moderate cohesive, adheres to the fingers
2.1 very floury and not cohesive
- some grains to feel silt loam (clay poor) <10
- no grains to feel silt <12
2.2 moderately cohesive, adheres to the fingers, has a rough and ripped surface after
squeezing between fingers and
- very grainy and not sticky sandy loam (clay rich) 10-25
- has moderate sand grains loam 8-27
- not grainy but distinctly floury and somewhat sticky silt loam (clay rich) 10-27
2.3 has a rough and moderate shiny surface after squeezing between fingers and is sticky
and grainy to very grainy sandy clay loam 20-35
3. Possible to roll a wire smaller than 3 mm (less than ½ Ø of a pencil) and to form the
wire to a ring of about 2-3 cm Ø, cohesive, sticky, gnash between teeth, has a moderate
shiny surface after squeezing between fingers
3.1 very grainy sandy clay 35-55
3.2 grains can be seen and felt clay loam 25-40
3.3 no grains to see and to feel, low plasticity silty clay loam 25-40
3.4 no grains to see and to feel, high plasticity silty clay 40-60
4. Has a shiny surface after squeezing between fingers and a high plasticity
4.1 some grains to see or to feel, gnashes between teeth clay 40-60
4.2 no grains to see or to feel, does not gnash between teeth heavy clay >60
c) Rock fragments
Abundance (by volume), for estimation see Figure 5
None 0 %
Very few 0 - 2 %
Few 2 - 5 %
Common 5 - 15 %
Many 15 - 40 %
Abundant 40 - 80 %
Dominant >80 %
Charts for estimating proportions of coarse fragments and mottles
Size of rock fragments
Rock Particle Size
Fine gravel 0.2-0.6 cm
Medium gravel 0.6- 2 cm
Coarse gravel 2 - 6 cm
Stones 6 - 20 cm
Boulders 20 - 60 cm
Large boulders >60 cm
Shape of rock fragments
25 % 30 %
40 % 50 % 75 % 90 %
1 % 3 % 5 % 10 %
15 % 20 %
The general shape or roundness may be described using the following terms:
Flat Subrounded
Angular Rounded
State of weathering of rock fragments
The state of weathering of the coarse fragments is described as follows:
Fresh or slightly weathered: fragments show little or no signs of weathering
Weathered: partial weathering is indicated by discolouration and loss of crystal
form in the outer parts of the fragments while the centres remain relatively fresh
and the fragments have lost little of their original strength.
Strongly weathered: all but the most resistant minerals are weathered, strongly
discoloured and altered throughout the fragments, which tend to disintegrate
under only moderate pressure.
d) Soil color
Hue is the dominant spectral colour (red, yellow, green, blue, violet).
Value is the lightness or darkness of colour ranging from 1 (dark) to 8 (light).
Chroma is the purity or strength of colour ranging from 1 (pale) to 8 (bright).
If there is no dominant soil matrix color, the horizon is described as mottled and two or more
colors are given. In addition to the colour notations, the standard Munsell color names may be
given.
e) Mottling
Color of mottles
Abundance of mottles
None 0 % Common 5 - 15 % Very few 0 - 2 % Many 15 - 40 % Few 2 - 5 % Abundant >40 %
Size of mottles
Very fine <2 mm Medium 6 - 20 mm Fine 2 - 6 mm Coarse >20 mm
Contrast of mottles
The color contrast between mottles and soil matrix can be described as follows:
Faint: The mottles are evident only on close examination. Soil colors in both the matrix and mottles have closely related hues, chromas and values.
Distinct: Although not striking, the mottles are readily seen. The hue, chroma or value of the matrix are easily distinguished from those of the mottles. They may vary by as much as 2.5 units of hue or several units in chroma or value.
Prominent: The mottles are conspicuous and mottling is one of the outstanding features of the horizon. Hue chroma and value alone or in combination are at least several units apart.
f) Redoximorphic properties
Redoximorphic (or reductimorphic) properties of the soil matrix reflect permanently wet or at
least reduced conditions. They are expressed by neutral (white to black: Munsell N1 to N) or
bluish to greenish colours (Munsell 2.5Y, 5Y, 5G, 5B). The color pattern will often change by
aeration in minutes to days, due to oxidation processes.
Redoximorphic color pattern and occurrence of Fe compounds
Color Munsell Color Formula Mineral
Greyish green, light blue 5GY-5B2-3/1-3 FeII/Fe
III Fe-mix-compounds
(blue green rust)
White, after oxidation
brown N7-8 → 10YR4/5 FeCO3 siderite
White, after oxidation blue N7-8 → 5B Fe3(PO4) · 8 H2O vivianite
Bluish black
(w. 10% HCl H2S- smell) 5-10B1-2/1-3 FeS (or Fe3F4) Fe- sulphides
White, after oxidation white N8 → N8 - Complete loss of Fe-
compounds
g) Carbonates
CaCO3 Content Class Reaction
0 % Non-calcareous: No detectable visible or audible
effervescence.
0 - 2 % Slightly calcareous: Audible effervescence but not visible.
2 -10 % Moderately calcareous: Visible effervescence.
10 -25 % Strongly calcareous: Strong visible effervescence. Bubbles
form a low foam.
>25 % Extremely calcareous: Extremely strong reaction. Thick foam
forms quickly.
i) Readily soluble salts
Certain soils like coastal or desert soils can be enriched with water soluble salts or salts more
soluble than gypsum. The salt content of the soil can be estimated from an electrical
conductivity (EC in dS m-1
= mS cm-1
) measurement on a saturated soil paste or a more dilute
suspension of soil in water. Conventionally EC is measured in the laboratory in the saturation
extract (ECSE) and most classification values as well as data about salt sensitivity of crops
refer to ECSE.
ECSE
(dS m-1
at 25 ºC)
Not salty <0.75
Slightly salty 0.75 - 2
Moderately salty 2 - 4
Strongly salty 4 - 8
Very strongly salty 8 –15
Extremely salty >15
j) Field soil pH
In the field, pH is either estimated using indicator papers or measured with a portable pH
meter in a soil suspension (1 part soil and 2.5 part H20, 1 M KCl or 0.1M CaCl2 solution).
After shaking the solution and waiting for 15 minutes the pH value can be read. For the
measurement use a transparent 50 ml plastic cup with marks for 8 cm3 soil (~ 10 g) and 25 ml
water.
pH value
Very strongly alkaline >9.0
Strongly alkaline 8.5-9.0
Moderately alkaline 7.9-8.4
Mildly alkaline 7.4-7.8
Neutral 6.6-7.3
Slightly acid 6.1-6.5
Medium acid 5.6-6.0
Strongly acid 5.1-5.5
Very strongly acid 4.5-5.0
Extremely acid <4.5
k) Soil structure
Grade
Weak: Aggregates are barely observable in place and there is only a weak arrangement of
natural surfaces of weakness. When gently disturbed, the soil material breaks into a
mixture of few entire aggregates, many broken aggregates, and much material without
aggregate faces.
Moderate: Aggregates are observable in place and there is a distinct arrangement of natural
surfaces of weakness. When disturbed, the soil material breaks into a mixture of many
entire aggregates, some broken aggregates, and little material without aggregates faces.
Strong: Aggregates are clearly observable in place and there is a prominent arrangement of
natural surfaces of weakness. When disturbed, the soil material separates mainly into
entire aggregates.
The following classes may be used to describe soil structure:
Very weak Combined classes may be constructed as follows: Weak Weak to moderate Moderate Moderate to strong
Strong Very strong
Size
Class Platy Prismatic Blocky Granular mm mm mm mm
Very fine < 1 < 10 < 5 < 1 Fine 1 - 2 10 - 20 5 - 10 1 - 2 Medium 2 - 5 20 - 50 10 - 20 2 - 5 Coarse 5 - 10 50 - 100 20 - 50 5 – 10 Very coarse > 10 > 100 > 50 > 10
Combined classes may be constructed as follows:
Fine and very fine Coarse and very coarse Fine and medium Fine to coarse Medium to very coarse Medium and coarse
Type
Granular: Spheroids or polyhedrons, having curved or irregular surfaces which are not casts
of the faces of surrounding aggregates.
Blocky: Blocks or polyhedrons, nearly equidimensional, having flat or slightly rounded
surfaces which are casts of the faces of the surrounding aggregates. Subdivision is
recommended into angular blocky, with faces intersecting at relatively sharp angles, and
subangular blocky faces intersecting at rounded angles.
Prismatic: the dimensions are limited in the horizontal and extended along the vertical plane;
vertical faces well defined; having flat or slightly rounded surfaces which are casts of
the faces of the surrounding aggregates. Faces normally intersect at relatively sharp
angles. Prismatic structures with rounded caps are distinguished as Columnar.
Platy: Flat with vertical dimensions limited; generally oriented on a horizontal plane and
usually overlapping.
l) Consistence
Consistence when dry
This is determined by breaking an air-dried mass of soil between thumb and forefinger or in
the hand.
Loose: Non-coherent
Soft: Soil mass is very weakly coherent and fragile; breaks to powder or
individual grains under very slight pressure
Slightly hard: Weakly resistant to pressure; easily broken between thumb and
forefinger.
Hard: Moderately resistant to pressure; can be broken in the hands; not
breakable between thumb and forefinger.
Very hard: Very resistant to pressure; can be broken in the hands only with
difficulty.
Extremely hard: Extremely resistant to pressure; cannot be broken in the hands.
Additional description:
Soft to slightly hard
Slightly hard to hard
Hard to very hard
Consistence when moist
This is determined by attempting to crush a mass of moist or slightly moist soil material. This
is the usual condition in the field except in poorly drained soils or immediately after a heavy
rain.
Loose: Non-coherent
Very friable: Soil material crushes under very gentle pressure, but coheres when
pressed together.
Friable: Soil material crushes easily under gentle to moderate pressure between
thumb and forefinger, and coheres when pressed together.
Firm: Soil material crushes under moderate pressure between thumb and
forefinger, but resistance is distinctly noticeable.
Very firm: Soil material crushes under strong pressures; barely crushable
between thumb and forefinger.
Extremely firm: Soil material crushes only under very strong pressure; can not
be crushed between thumb and forefinger.
Additional description:
Very friable to friable
Friable to firm
Firm to very firm
Consistence when wet: maximum stickiness and maximum plasticity
Stickiness is the quality of adhesion of the soil material to other objects determined by noting
the adherence of soil material when it is pressed between thumb and finger.
Non sticky: after release of pressure, practically no soil material adheres to
thumb and finger.
Slightly sticky: after pressure, soil material adheres to both thumb and finger but
comes off one or the other rather cleanly. It is not appreciably
stretched when the digits are separated.
Sticky: after pressure, soil material adheres to both thumb and finger and tends
to stretch somewhat and pull apart rather than pulling free from either
digit.
Very sticky: after pressure, soil material adheres strongly to both thumb and
finger and is decidedly stretched when they are separated.
Additional description:
Slightly sticky to sticky
Sticky to very sticky
Plasticity is the ability of soil material to change shape continuously under the influence of an
applied stress and to retain the compressed shape after removal of stress. Determined by
rolling the soil in the hands until a wire about 3 mm in diameter has been formed.
Non plastic: No wire is formable
Slightly plastic: Wire formable but immediately breaks if bent into a ring; soil
mass deformed by very slight force.
Plastic: Wire formable but breaks if bent into a ring; slight to moderate force
required for deformation of the soil mass.
Very plastic: Wire formable and can be bent into a ring; moderately strong to
very strong force required for deformation of the soil mass.
m) Soil moisture
The soil moisture condition of the soil in the field can be estimated by the simple procedure of
Schlichting et al. (1995):
Crushing Forming (to a ball) Moistening Rubbing (in the hand) Moisture pF *)
dusty or
hard
not possible,
seems to be warm
getting very
dark not lighter very dry 5
makes no
dust
not possible,
seems to be warm
getting dark hardly lighter dry 4
makes no
dust possible (not sand)
getting
slightly dark obviously lighter
slightly
moist 3
is sticky finger moist and
cool, weakly shiny
no change of
colour obviously lighter moist 2
free water drops of water no change of
color
wet 1
free water drops of water
without crushing
no change of
color
very wet 0
*) pF (p = potential, F = free energy of water) is log hPa
m) Bulk density
Field estimation of bulk density for mineral soils (Schlichting et al., 1995)
Observation Structure Bulk Density
[g cm-3
]
Sandy, silty and loamy soils with low clay content
Many pores, moist materials drop easy out of the
auger; materials with vesicular pores, mineral soils
with andic properties.
granular <0.9
Sample disintegrates at the instant of sampling, many
pores visible on the pit wall. single grain, granular
0.9-1.2
Sample disintegrates into numerous fragments after
application of weak pressure.
single grain, suban-
gular, angular blocky
1.2-1.4
Knife can be pushed into the moist soil with weak
pressure, sample disintegrates into few fragments,
which may be further divided.
subangular and
angular blocky,
prismatic, platy
1.4-1.6
Knife penetrates only 1-2 cm into the moist soil, some
effort required, sample disintegrates into few
fragments, which cannot be subdivided further.
prismatic, platy,
(angular blocky)
1.6-1.8
Very large pressure necessary to force knife into the
soil, no further disintegration of sample. prismatic,
>1.8
Loamy soils with high clay content, clayey soils
When dropped, sample disintegrates into numerous
fragments, further disintegration of subfragments after
application of weak pressure.
angular blocky 1.0-1.2
When dropped, sample disintegrates into few
fragments, further disintegration of subfragments after
application of mild pressure.
angular blocky,
prismatic, platy,
columnar
1.2-1.4
Sample remains mostly intact when dropped, further
disintegration possible after application of large
pressure.
coherent, prismatic,
platy, (columnar, an-
gular blocky, platy)
1.4-1.6
Sample remains intact when dropped, no further
disintegration after application of very large pressure.
coherent (prismatic,
columnar)
>1.6
If organic matter content is >2%, bulk density has to be reduced by 0.03 g cm-3
for each %
increment of organic matter content.
n) Voids (Porosity)
Type
There is a large variety in the shape and origin of voids. The major types of voids may
be classified in a simplified way as follows:
Interstitial: Predominantly irregular and interconnected, generally the voids
between sand grains and rock fragments.
Vesicles: Discontinuous spherical or elliptical voids (chambers) of sedimentary
origin or formed by compressed air, for instance gas bubbles in
slaking crusts after heavy rainfall.
Vughs: Mostly irregular, equidimensional voids of faunal origin or resulting from
tillage or disturbance of other voids. Discontinuous or interconnected.
Channels: Elongate voids of faunal or floral origin. Mostly of tubular shape and
continuous, strongly varying in diameter.
Size
The diameter of the elongate or tubular voids is described using the following classes:
Very fine < 0.5 mm
Fine 0.5 - 2 mm
Medium 2 - 5 mm
Coarse 5 - 20 mm
Very coarse 20 - 50 mm
Abundance
The abundance of fine and very fine elongate pores as one group and of medium and coarse
pores as another is recorded as the number per unit area of a square decimeter.
< 2 mm > 2 mm
None 0 0
Very few 1 - 20 1- 2
Few 20 - 50 2- 5
Common 50 - 200 5- 20
q) Roots
The abundance of fine and very fine roots may be recorded similarly as for voids (see Figure
9), expressed in the number of roots per square decimetre.
Size (diameter)
Very fine < 0.5 mm
Fine 0.5 - 2 mm
Medium 2 - 5 mm
Coarse > 5 mm
Size
Abundance
very few few common
very fine(<0.5 mm)
fine(0.5-2 mm)
medium(2-5 mm)
1cm
Abundance
< 2 mm > 2 mm
None 0 0
Very few 1 - 20 1- 2
Few 20 - 50 2- 5
Common 50 - 200 5- 20
Many >200 >20
r) Other biological features
Biological features such as krotovinas, termite burrows, insect nests, worm casts or burrows
of larger animals are described in terms of abundance and kind. In addition, specific locations,
patterns, size, composition or any other characteristic may be recorded.
Abundance
Abundance of biological activity is recorded in the following general descriptive terms:
None Common
Few Many
Kind
Examples of biological features are the following:
Artefacts Earthworm channels
Burrows (unspecified) Pedotubules
Open large burrows Termite or ant channels and nests
Infilled large burrows Other insect activity
Charcoal
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Vbasio,SS212, Nov2013