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GUIDELINES FOR

SOIL DESCRIPTION
Universität Halle-Wittenberg,
Germany

GUIDELINES FOR SOIL DESCRIPTION
Universität Kiel,
Germany

Leyte State University,
The Philippines

ISRIC – World Soil Information,
The Netherlands

Technische Universität München,
Germany

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Guidelines for
soil description

Fourth edition

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 2006

The designations employed and the presentation of material in this information
product do not imply the expression of any opinion whatsoever on the part
of the Food and Agriculture Organization of the United Nations concerning the
legal or development status of any country, territory, city or area or of its authorities,
or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-105521-1

All rights reserved. Reproduction and dissemination of material in this information
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© FAO 2006

General site information. Introduction 1 2. Soil description 21 Surface characteristics 21 Rock outcrops 21 Coarse surface fragments 21 Erosion 22 Surface sealing 23 Surface cracks 23 . registration and location 5 Profile number 5 Soil profile description status 5 Date of description 5 Authors 5 Location 6 Elevation 6 Map sheet number and grid reference (coordinates) 7 3. iii Contents Acknowledgements ix List of acronyms x 1. Soil formation factors 9 Atmospheric climate and weather conditions 9 Soil climate 9 Landform and topography (relief) 10 Major landform 10 Position 10 Slope form 12 Slope gradient and orientation 12 Land use and vegetation 13 Land use 13 Crops 13 Human influence 13 Vegetation 16 Parent material 16 Age of the land surface 17 4.

iv Horizon boundary 24 Depth 24 Distinctness and topography 25 Primary constituents 25 Texture of the fine earth fraction 25 Rock fragments and artefacts 29 Degree of decomposition and humification of peat 32 Aeromorphic organic layers on forest floors 32 Soil colour (matrix) 33 Mottling 35 Colour of mottles 35 Abundance of mottles 35 Size of mottles 35 Contrast of mottles 36 Boundary of mottles 36 Soil redox potential and reducing conditions 36 Determination of redox potential by field method 36 Reducing conditions 37 Carbonates 38 Content 38 Forms 38 Gypsum 39 Content of gypsum 39 Forms of secondary gypsum 39 Readily soluble salts 40 Procedure 40 Field soil pH 41 Soil odour 42 Andic characteristics and volcanic glasses 42 Procedure 42 Organic matter content 43 Organization of soil constituents 44 Soil structure 44 Consistence 48 Soil-water status 50 Bulk density 50 Voids (porosity) 52 Porosity 52 Type 52 Size 53 Abundance 53 .

v Concentrations 53 Coatings 54 Cementation and compaction 56 Mineral concentrations 58 Biological activity 59 Roots 59 Other biological features 60 Human-made materials 60 Artefacts 60 Human-transported material (HTM) 61 Geomembranes and technic hard rock 62 Description of artefacts 63 Description and determination of human-transported material 64 Sampling 64 5. properties and materials 81 Appending texture and parent material information to the reference soil group 82 References 85 Annexes 1. Genetic and systematic interpretation – soil classification 67 Soil horizon designation 67 Master horizons and layers 67 Transitional horizons 71 Subordinate characteristics within master horizons and layers 71 Conventions for using letter suffixes 75 Vertical subdivisions 75 Discontinuities 76 Use of the prime 77 Principles of classification according to the WRB 77 Step 1 79 Step 2 79 Step 3 79 Step 4 79 Principles and use of the qualifiers in the WRB 80 Checklist of WRB diagnostic horizons. Explanation of soil temperature regimes 87 2. Equipment necessary for field work 97 . Explanation of soil moisture regimes 91 3.

Soil profile description status 6 2. Classification of boundary between mottle and matrix 36 . Classification of the abundance of mottles 35 33. Subdivisions for complex landforms 11 6. Classification of coarse surface fragments 22 16. Abundance of rock fragments and artefacts. Hierarchy of major landforms 11 5. by volume 29 27. by degree 22 19. Classification of erosion. Classification of surface cracks 24 22. Hierarchy of lithology 18 13. Slope gradient classes 12 8. by activity 23 20. Classification of total area affected by erosion and deposition 22 18. Classification of shape of rock fragments 31 29. Classification of attributes of surface sealing 23 21. Soil temperature and moisture regime codes 10 4. Classification of weathering of coarse fragments 31 30. Classification of slope forms 12 7. Crop codes 15 10.vi List of tables 1. Recommended codes for human influence 15 11. Land-use classification 14 9. Codes for weather conditions 9 3. Classification of horizon boundaries. Classification of the contrast of mottles 36 35. Classification of erosion. Field estimation and coding of the degree of decomposition and humification of peat 32 32. by distinctness and topography 25 25. Provisional coding for age of land surface 19 14. Classification of erosion. Classification of bleached sand characteristics 24 24. Vegetation classification 16 12. Codes for primary mineral fragments 31 31. Classification of salt characteristics 24 23. Key to the soil textural classes 28 26. by category 22 17. Recommended classification of rock outcrops 21 15. Classification of rock fragments and artefacts 30 28. Classification of the size of mottles 35 34.

Combinations of soil structures 47 53. Classification of the form of coatings 56 68. Classification of forms of secondary carbonates 38 40. Classification of abundance of pores 53 64. Classification of abundance of coatings 55 65. Classification of the nature of cementation/compaction 57 72. Reductimorphic colour pattern and occurrence of Fe compounds 37 38. Classification of moisture status of soil 50 58. Classification of voids 53 62. Estimation of organic matter content based on Munsell soil colour 43 47. Classification of types of soil structure 46 49. Consistence of soil mass when dry 48 54. Classification of porosity 52 61. Redoximorphic soil characteristics and their relation to rH values and soil processes 36 37. Classification of carbonate reaction in the soil matrix 38 39. Classification of soil odour 42 46. Field estimation of bulk density for mineral soils 51 59. Classification of diameter of voids 53 63. Classification of the fabric of the cemented/compacted layer 56 71. Classification of the degree of cementation/compaction 57 73. Classification of the continuity of cementation/compaction 56 70. Classification of the location of coatings and clay accumulation 56 69. Classification of gypsum content 39 41. Classification of soil plasticity 49 57. Classification of the abundance of mineral concentrations. Field estimation of volume of solids and bulk density of peat soils 52 60. Classification of pH value 41 45. Dependency of water content of saturation extract on texture and content of humus for mineral soils and on decomposition for peat soils 41 44. by volume 58 . Classification of soil stickiness 49 56. vii 36. Classification of forms of secondary gypsum 39 42. Classification of structure of pedal soil materials 45 48. Codes for types of soil structure 46 50. Consistence of soil mass when moist 49 55. Classification of the contrast of coatings 55 66. Classification of salt content of soil 40 43. Classification of the nature of coatings 55 67. Combined size classes for soil structure types 47 52. Size classes for soil structure types 47 51.

Slope positions in undulating and mountainous terrain 11 3. Classification of the abundance of roots 60 81. Examples of the nature of mineral concentrations 59 78. Classification of the size and shape of mineral concentrations 58 76. Relation of constituents of fine earth by size. Checklist of WRB diagnostic horizons. Classification of the hardness of mineral concentrations 58 77. Subordinate characteristics within master horizons 72 86. Soil structure types and their formation 45 7. Slope forms and surface pathways 12 4. Determination table and codes for human-made deposits 64 85. Colour names of mineral concentrations 59 79. Classification of kinds of artefacts 63 84. The process of soil description. defining textural classes and sand subclasses 27 5. Classification of the diameter of roots 60 80. Charts for estimating size and abundance of pores 54 .viii 74. Classification of the abundance of biological activity 60 82. properties and materials 81 List of figures 1. Charts for estimating proportions of coarse fragments and mottles 30 6. Classification of the kinds of mineral concentrations 58 75. classification. Examples of biological features 60 83. site quality and suitability evaluation 1 2. Qualification of bulk density 51 8.

ix

Acknowledgements

This revision was prepared by R. Jahn (University of Halle-Wittenberg), H.-P.
Blume (University of Kiel), V.B. Asio (Leyte State University), O. Spaargaren
(ISRIC) and P. Schad (Technische Universität München), with contributions
and suggestions from R. Langohr (University Gent), R. Brinkman (FAO), F.O.
Nachtergaele (FAO) and R. Pavel Krasilnikov (Universidad Nacional Autónoma
de México).

x

List of acronyms
EC Electrical conductivity
GPS Global Positioning System
HDPE High-density polyethylene
HTM Human-transported material
ISO International Organization for Standardization
PVC Polyvinyl chloride
RSG Reference Soil Group
USDA United States Department of Agriculture
UTM Universal Transverse Mercator
WRB World Reference Base for Soil Resources

1

Chapter 1
Introduction

The main objective of research in soil science is the understanding of the
nature, properties, dynamics and functions of the soil as part of landscapes and
ecosystems. A basic requirement for attaining that objective is the availability
of reliable information on soil morphology and other characteristics obtained
through examination and description of the soil in the field.
It is important that soil description be done thoroughly; it serves as the basis
for soil classification and site evaluation as well as interpretations on the genesis
and environmental functions of the soil. A good soil description and the derived
knowledge on the genesis of the soil are also powerful tools to guide, help explain
and regulate costly laboratory work. It can also prevent errors in soil sampling.
Figure 1 shows the role of soil description as an early step to classification, soil and
site assessment, and suitability evaluation.

FIGURE 1
The process of soil description, classification, site quality and suitability evaluation

1. Registration, Number, author, date,
location description status, locality

2. Soil formation Climate, landform, parent
factors material, land use, vegetation,
age and history of landscape

3.
Horizons and layers Identification of boundries
Observations
For each horizon/layer:
and measurements
Characteristics of rock fragments, texture, colour,
horizons/layers pH, carbonates, structure, bulk-
density, biological activity, ...

4. Interpretation of soil Qualities of 5.
formation processes horizons

Genetic and Interpretation
systematic Designation Qualities of soil of ecological
interpretation of horizons
site qualities
(classification)

Identification of Site qualities
soil unit

Suitability evaluation
comparison of land use
requirements with site qualities

1985). the use of a common language is of prime importance. the contents of the major sources were modified.2 Guidelines for soil description Soils are affected by human activities. 2003) and the second edition of the World Reference Base for Soil Resources (IUSS Working Group WRB. the Soil Map of the World (FAO– UNESCO. Field Book for Describing and Sampling Soils (Schoeneberger et al. 2003). 1990). the material of DVWK (1995). The guidelines provide a complete procedure for soil description and for collecting field data necessary for classification according to second edition of the . 2002). municipal and agriculture. 2006) are taken into consideration. In order to prevent soil degradation and to rehabilitate the potentials of degraded soils. Some new international developments in soil information systems and soil classification. 2002). ÿ Chapter 4 on soil description – Guidelines for Soil Description (FAO. 1990). 1990). Specifically. 2005). The increasing need for internationally accepted rules and systems of soil description and soil classification led to the development of various soil classification concepts. reliable soil data are the most important prerequisite for the design of appropriate land-use systems and soil management practices as well as for a better understanding of the environment.. e. as well as the personal experiences of the authors. 1974. ÿ Chapter 5 on horizon designation and soil classification – Guidelines for Soil Description (FAO. 2002). Field Book for Describing and Sampling Soils (Schoeneberger et al. ÿ Chapter 3 on the description of soil forming factors – Guidelines for Soil Description (FAO. To help beginners. and Keys to Soil Taxonomy (USDA Soil Survey Staff. 1990).. the FAO–UNESCO Legend for the Soil Map of the World (FAO–UNESCO. 2005) and the second edition of the World Reference Base for Soil Resources (IUSS Working Group WRB.g. and soil maps. 2005). such as industrial. and Soil Atlas of Europe (EC. the various chapters of this field guide were based on the following sources: ÿ Chapter 2 on general site description – Guidelines for Soil Description (FAO. Ad- hoc-AG-Boden. For practical reasons. 1999). 2002). some explanatory notes are included as well as keys based on simple tests and observations for the determination of soil characteristics.g. 1988) and Soil Taxonomy (USDA Soil Survey Staff 1975. also in soil science. 1970–1981. With the present internationalization. Soil Map of the European Communities (ECSC–EEC–EAEC. 2005). such as the Field Book for Describing and Sampling Soils (Schoeneberger et al. 1990) and partly the German Mapping Guide 5 (Kartieranleitung 5. shortened and rearranged. e. Field Book for Describing and Sampling Soils (Schoeneberger et al. 2003). These guidelines are based on the internationally accepted Guidelines for Soil Description (FAO. Keys to Soil Taxonomy (USDA Soil Survey Staff. 2002) and Keys to Soil Taxonomy (USDA Soil Survey Staff. updated SOTER (ISRIC. 2006). Updated Global and National Soils and Terrain Digital Databases (ISRIC... FAO. that often result in soil degradation and loss or reduction in soil functions.

Chapter 1 – Introduction 3 World Reference Base for Soil Resources (WRB) (IUSS Working Group WRB. it is not stated whether the described feature is a required one or is one of two or more options. 2006). In order to avoid being excessively lengthy. Notes for classification purposes are added to each chapter and explain the relevance of the described feature for classification according to the WRB. .

.

Example: DE/ST/HAL -0381 = Halle in Saxony- Anhalt in Germany. location. The date of description is given as: yymmdd (six digits). they hold responsibility for the quality of the data. AUTHORS The persons who perform the description need to be acknowledged properly in future uses of the soil data. elevation. map sheet number. such as profile number. . Table 1 lists the possible descriptions. SOIL PROFILE DESCRIPTION STATUS The status of the soil profile description refers to the quality of the soil description and the analytical data. author. The letter code should consist of a practical selection of codes referring to a country. This information is necessary for easy referencing and retrieval of the soil description from data storage systems. In addition. PROFILE NUMBER The profile number or profile identification code should be constructed in such a way that it meets local needs and also allows easy and simple retrieval of profile descriptions from computerized data storage systems. The profile identification code should be constructed from a combination of a location letter code and a profile number code. description status. registration and location Before any actual soil description should be done. The status is allocated after completion of the analyses and is indicative of the reliability of soil profile information entered into a database. 8 January 2006 would be coded 060108. a topographic map reference or any other defined area or town. it is necessary to take note of some relevant information related to the registration and identification of the soil to be described. preferably the internationally accepted International Organization for Standardization (ISO) code. DATE OF DESCRIPTION It is important to always indicate the date of description in order to inform future users of the soil data as to how old the data are. date of description. and grid reference. For example. The names or initials of the authors are given. 5 Chapter 2 General site information. profile 381.

6 Guidelines for soil description

TABLE 1
Soil profile description status
Status
1 Reference profile description No essential elements or details are missing from the description, sampling or
analysis. The accuracy and reliability of the description and analytical results
permit the full characterization of all soil horizons to a depth of 125 cm, or
more if required for classification, or down to a C or R horizon or layer, which
may be shallower.
1.1 If soil description is done without sampling.
2 Routine profile description No essential elements are missing from the description, sampling or analysis.
The number of samples collected is sufficient to characterize all major soil
horizons, but may not allow precise definition of all subhorizons, especially in
the deeper soil. The profile depth is 80 cm or more, or down to a C or R horizon
or layer, which may be shallower. Additional augering and sampling may be
required for lower level classification.
2.1 If soil description is done without sampling.
3 Incomplete description Certain relevant elements are missing from the description, an insufficient
number of samples was collected, or the reliability of the analytical data does
not permit a complete characterization of the soil. However, the description is
useful for specific purposes and provides a satisfactory indication of the nature
of the soil at high levels of soil taxonomic classification.
3.1 If soil description is done without sampling.
4 Soil augering description Soil augerings do no permit a comprehensive soil profile description. Augerings
are made for routine soil observation and identification in soil mapping,
and for that purpose normally provide a satisfactory indication of the soil
characteristics. Soil samples may be collected from augerings.
4.1 If soil description is done without sampling.
5 Other descriptions Essential elements are missing from the description, preventing a satisfactory
soil characterization and classification.
Note: Descriptions from soil augerings or from other observations made for routine soil mapping are either kept on
ordinary field data sheets or included in the database, with an appropriate indication of status.

LOCATION
A description of the soil location should be given. It should be as precise as possible
in terms of the distance (in metres or kilometres) and direction to the site from
permanent features that are recognizable in the field and on the topographic map.
Distances along roads or traverses relate to a marked reference point (0.0 km). The
description of the location should be such that readers who are unfamiliar with
the area are able to locate the approximate position of the site. The administrative
units, such as region, province, district, country or locality, are given in the profile
number section (above). Example: Agricultural research station Bad Lauchstädt,
Sachsen-Anhalt.

ELEVATION
The elevation of the site relative to sea level should be obtained as accurately
as possible, preferably from detailed contour or topographic maps. Where such
information is not available, the best possible estimate is made from general maps
or by altimeter readings. At present, determination of elevation by the Global
Positioning System (GPS) unit is inaccurate and unacceptable. Elevation is given
in metres (1 foot = 0.3048 m).

Chapter 2 – General site information, registration and location 7

MAP SHEET NUMBER AND GRID REFERENCE (COORDINATES)
The number of the topographic map sheet, preferably at 1:25 000 or 1:50 000 scale,
on which the soil observation occurs is given. Example: TK50 L4536 Halle (Saale)
= Topographic map 1:50 000 Number L4536 of Halle.
The grid reference number, Universal Transverse Mercator (UTM) or the
established local system, can be read directly from the topographic map. The
latitude and longitude of the site are given as accurately as possible (in degrees,
minutes, seconds and decimal seconds); they can be derived directly from
topographic maps or a GPS unit. Example: H: 56.95.250 or latitude: 51° 23´ 30.84´´
N; R: 44.91.600 or longitude: 11° 52´ 40.16´´ E.
Some countries use their own zero longitude, e.g. Italian topographic maps
show the Monte Mario meridian at Rome as zero. For international use, these
should be converted to the zero meridian of the Greenwich system.

no rain in the last week). 1978). SN snow The soil moisture and temperature Former weather conditions (Ad-hoc-AG-Boden. The information may be derived from a combination of field measurements. geological and geomorphological maps and documents. the present conditions are reported. topographical. Where such information is last 24 hours not available or cannot be derived WC 6 extremely rainy time or snow melting from representative climate data Note: For example: SU. the monthly mean temperature (in degrees Celsius) and the monthly mean precipitation (in millimetres) can be taken from the nearest meteorological station. with confidence. ATMOSPHERIC CLIMATE AND WEATHER CONDITIONS The climate conditions of a site are important site properties that influence plant growth and soil formation. Where available. it is preferable to . 25 °C. In addition. 2003) may be mentioned WC 4 rainy without heavy rain in the last 24 hours (Table 3. field observations and evaluation of climate. 9 Chapter 3 Soil formation factors This chapter provides the guidelines for the description of factors that define the kind and intensity of soil formation processes. the length of the growing period (in days) should be specified. explanations in Annexes 1 WC 5 heavier rain for some days or rainstorm in the and 2). climate records. The length of the growing period is defined as the period with humid conditions (excess of precipitation over potential evapotranspiration) during the time with temperature ≥ 5 °C (FAO. The present as well as the weather conditions days or weeks before the description influence soil moisture and structure.. hence these should be noted. SU sunny/clear PC partly cloudy OV overcast SOIL CLIMATE RA rain Where applicable. the soil climate SL sleet classification should be indicated. the prevailing general weather conditions and the air temperature TABLE 2 at the time of observation as well Codes for weather conditions as that of the near past should be Present weather conditions (Schoeneberger et al. 2002) documented (Table 2). temperature 25 °C. As minimum climate data. For land use and vegetation. WC 2 (= sunny. These factors are also part of the important site qualities. 2005) regimes according to Keys to Soil WC 1 no rain in the last month Taxonomy (USDA Soil Survey WC 2 no rain in the last week WC 3 no rain in the last 24 hours Staff.

Other agroclimate parameters worth mentioning would be a local climate class. Major landform Landforms are described foremost by their morphology and not by their genetic origin or processes responsible for their shape. . where the main terraces should have elevation differences of at least 10 m. the protruding landform should be at least 25 m high (if not it is to be considered mesorelief) except for terraced land. the older levels may become buried by down wash. in the case of mountains. The relief intensity is normally given in metres per kilometre. to intermontane plains. which refers to the morphology of the whole landscape. Finally. etc. These subdivisions are mainly applicable to level landforms. ÿ the slope form. With complex landforms. LANDFORM AND TOPOGRAPHY (RELIEF) Landform refers to any physical feature on the earth’s surface that has been formed by natural processes and has a distinct shape. Topography refers to the configuration of the land surface described in four categories: ÿ the major landform. subdivisions can be used (Table 5). e. length of growing period. For complex landforms. ÿ the slope angle. Note for classification purposes ¸ Soil temperature < 0 °C (pergelic soil temperature regime) → cryic horizon and Gelic qualifier. the major terraces may be very close to each other – particularly towards the lower part of the plain. Position The relative position of the site within the land should be indicated.g. The position affects the hydrological conditions of the site (external and internal drainage. The dominant slope is the most important differentiating criterion. In areas. followed by the relief intensity (Table 4). ÿ the position of the site within the landscape. the agroclimate zone.10 Guidelines for soil description TABLE 3 Soil temperature and moisture regime codes Soil temperature regime Soil moisture regime PG = Pergelic AQ = Aquic PQ = Peraquic CR = Cryic DU = Udic PU = Perudic FR = Frigid IF = Isofrigid US = Ustic ME = Mesic IM = Isomesic XE = Xeric TH = Thermic IT = Isothermic AR = Aridic and TO = Torric HT = Hyperthermic IH = Isohyperthermic leave the space blank. The relief intensity is the median difference between the highest and lowest point within the terrain per specified distance. to some extent to sloping landforms and. The specified distance can be variable.

. 2005. October 2004. . 2005. ISRIC. ISRIC. Source: Updated SOTER.Chapter 3 – Soil formation factors 11 TABLE 4 Hierarchy of major landforms 1st level 2nd level Gradient Relief intensity Potential (%) (m km-1) drainage density L level land LP plain < 10 < 50 0–25 LL plateau < 10 < 50 0–25 LD depression < 10 < 50 16–25 LV valley floor < 10 < 50 6–15 S sloping land SE medium-gradient escarpment zone 10–30 50–100 <6 SH medium-gradient hill 10–30 100–150 0–15 SM medium-gradient mountain 15–30 150–300 0–15 SP dissected plain 10–30 50–100 0–15 SV medium-gradient valley 10–30 100–150 6–15 T steep land TE high-gradient escarpment zone > 30 150–300 <6 TH high-gradient hill > 30 150–300 0–15 TM high-gradient mountain > 30 > 300 0–15 TV high-gradient valley > 30 > 150 6–15 Notes: Changes proposed at the SOTER meeting at Ispra. Potential drainage density is given in number of “receiving” pixels within a 10 × 10 pixels window. FIGURE 2 Slope positions in undulating and mountainous terrain CR CR UP UP MS MS Channel LS LS TS BO Alluvium Note: Position in undulating to mountainous terrain Position in flat or almost flat terrain CR = Crest (summit) HI = Higher part (rise) UP = Upper slope (shoulder) IN = Intermediate part (talf) MS = Middle slope (back slope) LO = Lower part (and dip) LS = Lower slope (foot slope) BO = Bottom (drainage line) TS = Toe slope BO = Bottom (flat) Source: Redrawn from Schoeneberger et al. TABLE 5 Subdivisions for complex landforms CU = Cuesta-shaped DO = Dome-shaped RI = Ridged TE = Terraced IN = Inselberg covered (occupying > 1% of level land) DU = Dune-shaped IM = With intermontane plains (occupying > 15%) KA = Strong karst WE = With wetlands (occupying > 15%) Source: Updated SOTER. 2002.

2 percent are usually clearly TABLE 7 visible. T terraced X complex (irregular) Slope form The slope form refers to the general shape of the slope in both the vertical and horizontal directions FIGURE 3 Slope forms and surface pathways (Figure 3). Source: Redrawn from Schoeneberger et al.5 irrigation and drainage. they may need 10 Very steep > 60 to be modified to fit the local topography (Table 7). the temperature regime. both the slope length (particularly above the site) and aspect (orientation) should be recorded. Slope gradient and orientation The slope gradient refers to the SS SV SC slope of the land immediately surrounding the site.. which may be Classification of slope forms interpreted as being predominantly S straight water receiving.2–0. the risk for wind impact and the character of humus formed in higher latitudes. for example.5–1. 01 Flat 0–0. The orientation influences. The proper recording of Slope gradient classes minor slope-gradient variations is Class Description % important. 03 Nearly level 0. slope gradients of 0. It is measured using a clinometer aimed in the direction of the steepest slope. measured value.12 Guidelines for soil description TABLE 6 subsurface runoff). 2002. water shedding or C concave V convex neither of these. field estimates of slope gradient should be matched CS CV CC against calculated gradients from contour maps.2 02 Level 0. In open plains. the precipitation input. VS VV VC Where clinometer readings are not possible.0 The slope gradient is recorded 04 Very gently sloping 1. and the 07 Strongly sloping 10–15 second by entering in one of the 08 Moderately steep 15–30 09 Steep 30–60 following classes. especially for erosion. In addition to the attributes of slope in Table 7.0–2. . Table 6 lists the slope form classes. The first and most 05 Gently sloping 2–5 important is by means of the 06 Sloping 5–10 actual.0 in two ways. Surface flow pathway Slope gradients in almost flat terrain are often overestimated.

its recording enhances the interpretative value of the soil data considerably (Table 8). the dominant crops grown should be mentioned (section on crops [below]). Erosion is dealt with separately in Chapter 4. For arable land use. Information on crops can be given in a general or detailed way as required. Crops Crops are plants that are cultivated for their economic value. Chernozems and Cambisols. ¸ Raised land surfaces → plaggic and terric horizons. SSW means south-southwest. S for south and W for west. duration of fallow period. Examples for the most common crops with their recommended codes are given in Table 9. use of fertilizers. rotation systems and yields. ¸ Special requirements if an eluvial horizon is part of a plough layer → argic and natric horizons. For various environments. Human influence This item refers to any evidence of human activity that is likely to have affected the landscape or the physical and chemical properties of the soil. ¸ Ploughing → anthraquic and anthric horizons and Aric qualifier. Note for classification purposes ¸ Constructed terraces → Escalic qualifier. E for east. ¸ Spade marks → plaggic horizon. whether agricultural or non- agricultural. it is useful to indicate the degree of disturbance of the natural vegetation. ¸ Does not form part of a plough layer → cambic horizon. Examples of human influences with their recommended codes are given in Table 10. . for example. The existing vegetation is described in the section on vegetation (below). Land use has a major influence on the direction and rate of soil formation. LAND USE AND VEGETATION Land use Land use applies to the current use of the land. Information on crops is important because it gives an idea of the nature of soil disturbance as a result of crop management practices as well as the nutrient and soil management requirements of the crop.Chapter 3 – Soil formation factors 13 The orientation that a slope is facing is coded N for north. in which the soil is located. ¸ Special depth limits if plough layers are present → Fluvisols. ¸ Mixing or soil layers or lumps of applied lime → anthric horizon. and as much information as possible given on soil management.

14 Guidelines for soil description TABLE 8 Land-use classification A = Crop agriculture (cropping) AA = Annual field cropping AA1 = Shifting cultivation AA2 = Fallow system cultivation AA3 = Ley system cultivation AA4 = Rainfed arable cultivation AA5 = Wet rice cultivation AA6 = Irrigated cultivation AP = Perennial field cropping AP1 = Non-irrigated cultivation AP2 = Irrigated cultivation AT = Tree and shrub cropping AT1 = Non-irrigated tree crop cultivation AT2 = Irrigated tree crop cultivation AT3 = Non-irrigated shrub crop cultivation AT4 = Irrigated shrub crop cultivation Additional codes may be used to further specify the land-use type. For example: AA4 = Rainfed arable cultivation AA4T = Traditional AA4I = Improved traditional AA4M = Mechanized traditional AA4C = Commercial AA4U = Unspecified M = Mixed farming MF = Agroforestry MP = Agropastoralism H = Animal husbandry HE = Extensive grazing HE1 = Nomadism HE2 = Semi-nomadism HE3 = Ranching HI = Intensive grazing HI1 = Animal production HI2 = Dairying F = Forestry FN = Natural forest and woodland FN1 = Selective felling FN2 = Clear felling FP = Plantation forestry P = Nature protection PN = Nature and game preservation PN1 = Reserves PN2 = Parks PN3 = Wildlife management PD = Degradation control PD1 = Without interference PD2 = With interference S = Settlement. industry SR = Residential use SI = Industrial use ST = Transport SC = Recreational use SX = Excavations SD = Disposal sites Y = Military area O = Other land uses U = Not used and not managed .

gravel and quarries) CR = Impact crater . midden) MI = Mine (surface. Wine. OiRa = Rape FrGr = Grapes. dry FoMa = Maize PuPe = Peas CeRy = Rye FoPu = Pumpkins Lu = Semi-luxury foods and tobacco CeSo = Sorghum Ro = Roots and tubers RoCa = Cassava LuCc = Cocoa CeWh = Wheat RoPo = Potatoes LuCo = Coffee Oi = Oilcrops OiCc = Coconuts RoSu = Sugar beets LuTe = Tea OiGr = Groundnuts RoYa = Yams LuTo = Tobacco OiLi = Linseed Fr = Fruits and melons Ot = Other crops FrAp = Apples OtSc = Sugar cane OiOl = Olives FrBa = Bananas OtRu = Rubber OiOp = Oil-palm FrCi = Citrus OtPa = Palm (fibres. kernels) OiSe = Sesame Raisins OiSo = Soybeans FrMa = Mangoes OiSu = Sunflower FrMe = Melons TABLE 10 Recommended codes for human influence N = No influence BU = Bunding NK = Not known BR = Burning VS = Vegetation slightly disturbed TE = Terracing VM = Vegetation moderately disturbed PL = Ploughing VE = Vegetation strongly disturbed MP = Plaggen VU = Vegetation disturbed (not specified) MR = Raised beds (agricultural purposes) IS = Sprinkler irrigation ME = Raised beds (engineering purposes) IF = Furrow irrigation MS = Sand additions ID = Drip irrigation MU = Mineral additions (not specified) IP = Flood irrigation MO = Organic additions (not specified) IB = Border irrigation PO = Pollution IU = Irrigation (not specified) CL = Clearing AD = Artificial drainage SC = Surface compaction FE = Application of fertilizers SA = Scalped area LF = Landfill (also sanitary) BP = Borrow pit LV = Levelling DU = Dump (not specified) AC = Archaeological (burial mound.Chapter 3 – Soil formation factors 15 TABLE 9 Crop codes Ce = Cereals Fo = Fodder plants Fi = Fibre crops CeBa = Barley FoAl = Alfalfa FiCo = Cotton CeMa = Maize FoCl = Clover FiJu = Jute CeMi = Millet FoGr = Grasses Ve = Vegetables CeOa = Oats FoHa = Hay Pu = Pulses PuBe = Beans CePa = Rice. paddy FoLe = Leguminous PuLe = Lentils CeRi = Rice. including openpit.

such as height of trees or canopy cover. In addition. and weathering materials overlying the hard rock from which they originate. understorey may be present. crowns usually not touching. indicating its origin and nature. A common example is the vegetation classification according to UNESCO (1973. There are transitional cases.16 Guidelines for soil description TABLE 11 Vegetation classification F = Closed forest 1 D = Dwarf shrub FE = Evergreen broad-leaved forest DE = Evergreen dwarf shrub FC = Coniferous forest DS = Semi-deciduous dwarf shrub FS = Semi-deciduous forest DD = Deciduous dwarf shrub FD = Deciduous forest DX = Xermomorphic dwarf shrub FX = Xeromorphic forest DT = Tundra W = Woodland 2 H = Herbaceous WE = Evergreen woodland HT = Tall grassland WS = Semi-deciduous woodland HM = Medium grassland WD = Deciduous woodland HS = Short grassland WX = Xeromorphic woodland HF = Forb S = Shrub M = Rainwater-fed moor peat SE = Evergreen shrub B = Groundwater-fed bog peat SS = Semi-deciduous shrub SD = Deciduous shrub SX = Xeromorphic shrub 1 Continuous tree layer. may be recorded. The parent material should be described as accurately as possible. other characteristics of the vegetation. The kind of vegetation can be described using a local. 2005). called alluvium (fluvial if transported by stream). called colluvium. crowns overlapping. 2 Continuous tree layer. either by water. There is no uniform acceptance of a system for the description of the natural or semi-natural vegetation. The reliability of the geological information and the knowledge of the local lithology will determine whether a general or a specific definition of the parent material can be given. There are basically two groups of parent material on which the soil has formed: unconsolidated materials (mostly sediments). Vegetation Vegetation is a dominant factor in soil formation as it is the primary source of organic matter and because of its major role in the nutrient cycling and hydrology of a site. or by gravity. such as partly consolidated materials and weathering materials that have been transported. regional or international system. large number of tree and shrub species in distinct layers. presented in Table 11 with codes added. see updated SOTER. PARENT MATERIAL The parent material is the material from which the soil has presumably been derived. . There are also restored natural soil materials or sediments as well as technogenic materials. ISRIC.

¸Bog peat saturated predominantly with groundwater or flowing surface water → Rheic qualifier. . a key to the most important rock types is provided below the extended hierarchical SOTER list. both are indicated. diatomaceous earth. The parent material is coded according to updated SOTER (ISRIC. Because many soils are formed from preweathered or moved materials. The code SA for saprolite is recommended where the in situ weathered material is thoroughly decomposed. ¸Organic material consisting of ≥ 75 percent of moss fibres → greater thickness of organic material required for Histosols. followed by the rock-type code. some additional natural and anthropogenic parent materials are included in Table 12. marl or gyttja → limnic material. It may also indicate possible climate changes during soil formation. As SOTER was developed to work with maps on a scale of 1:1 000 000. For identification in the field. ¸Remnants of birds or bird activity → ornithogenic material. ¸Recent sediments above the soil that is classified at the Reference Soil Group (RSG) level → Novic qualifier. it was a requirement to have not too many rock types. ¸Moor peat saturated predominantly with rainwater → Ombric qualifier. an estimate will help to interpret soil data and interaction between different soil forming processes. Alluvial deposits and colluvium derived from a single rock type may be further specified by that rock type. However. AGE OF THE LAND SURFACE The age of the landscape is important information from which the possible duration of the occurrence of soil formation processes can be derived. Note for classification purposes ¸ Remains intact when a specimen of 25–30 mm is submerged in water for 1 hour. ¸Differences in lithology → lithological discontinuity. no significant displacement has taken place → continuous rock. ¸Sedimentation through human-induced erosion → colluvic material. In order to be able to work in smaller scales. roots cannot penetrate except along vertical cracks that have an average horizontal spacing of ≥ 10 cm and that occupy < 20 percent (by volume). it is often difficult to obtain precise information. clay-rich but still showing rock structure. Where one parent material overlies another. ¸Coprogenous earth or sedimentary peat.Chapter 3 – Soil formation factors 17 For weathered rock. Table 13 provides a provisional coding. 2005) at the lowest level of hierarchy as possible. fluvial and eolian materials. the code WE is first entered. or may have been derived from an assemblage of autochthonous.

breccia (consolidated) SC2 sandstone. laterite (unconsolidated) UF fluvial UF1 sand and gravel UF2 clay. ironstone. bitumen and related rocks SE evaporites SE1 anhydrite. other carbonate rock SO2 marl and other mixtures SO3 coals. phyllite (pelitic rocks) MA4 schist MB basic metamorphic MB1 slate. arkose SC3 silt-. gypsum SE2 halite U sedimentary rock UR weathered residuum UR1 bauxite. silt and loam UL lacustrine UL1 sand UL2 silt and clay UM marine. claystone SC4 shale SC5 ironstone SO carbonatic. serpentine IP pyroclastic IP1 tuff. organic SO1 limestone. estuarine UM1 sand UM2 clay and silt UC colluvial UC1 slope deposits UC2 lahar UE eolian UE1 loess UE2 sand UG glacial UG1 moraine UG2 glacio-fluvial sand UG3 glacio-fluvial gravel UK * kryogenic UK1 periglacial rock debris UK2 periglacial solifluction layer . greenstone S sedimentary rock SC clastic sediments SC1 conglomerate. phyllite (pelitic rocks) MB2 (green)schist MB3 gneiss rich in Fe–Mg minerals MB4 metamorphic limestone (marble) MB5 amphibolite MB6 eclogite MU ultrabasic metamorphic MU1 serpentinite.18 Guidelines for soil description TABLE 12 Hierarchy of lithology Major class Group Type I igneous rock IA acid igneous IA1 diorite IA2 grano-diorite IA3 quartz-diorite IA4 rhyolite II intermediate igneous II1 andesite. greywacke. mud-. trachyte. tuffite IP2 volcanic scoria/breccia IP3 volcanic ash IP4 ignimbrite M metamorphic rock MA acid metamorphic MA1 quartzite MA2 gneiss. magnetite. migmatite MA3 slate. phonolite II2 diorite-syenite IB basic igneous IB1 gabbro IB2 basalt IB3 dolerite IU ultrabasic igneous IU1 peridotite IU2 pyroxenite IU3 ilmenite.

vYa Very young (1–10 years) anthropogeomorphic: with complete disturbance of natural surfaces (and soils) such as in urban. or surface raising.. of coastal dunes. technogenic or a mixture of materials. ice covered. T Tertiary land surfaces. commonly recent soil formation on preweathered materials. commonly recent soil formation on fresh materials. Chapter 4 provides more details on human-made materials. commonly high planes. terraces or peneplains. pre-Tertiary land surfaces. landslides or desert areas. frequent occurrence of palaeosoils. Ha Holocene (100–10 000 years) anthropogeomorphic: human-made relief modifications. lPp Late Pleistocene. industrial and mining areas with early soil development from fresh natural. commonly high planes. except incised valleys. lPf Late Pleistocene. industrial and mining areas with very early soil development from fresh natural or technogenic or mixed materials. terraces or peneplains. in river valleys. commonly the recent soil formation on younger over older. landslides or desert areas. preweathered materials. without periglacial influence. with periglacial influence. = dumped. Hn Holocene (100–10 000 years) natural: with loss by erosion or deposition of materials such as on tidal flats. = spoiled. 2005. oPp Older Pleistocene. Ya Young (10–100 years) anthropogeomorphic: with complete disturbance of any natural surfaces (and soils) such as in urban. except incised valleys. restriction of flooding by dykes. of coastal dunes. . frequent occurrence of palaeosoils. landslides or desert areas. of coastal dunes. river valleys.. oPf Older Pleistocene. in river valleys.. periglacial. ice covered. without periglacial influence. Source: Updated SOTER. such as terracing of forming hills or walls by early civilizations or during the Middle Ages or earlier. Yn Young (10–100 years) natural: with loss by erosion or deposition of materials such as on tidal flats. or restriction of flooding by dykes. Materials (natural and anthropogenic/technogenic) deposited by humans are coded: ÿ d. oPi Older Pleistocene. TABLE 13 Provisional coding for age of land surface vYn Very young (1–10 years) natural: with loss by erosion or deposition of materials such as on tidal flats. lPi Late Pleistocene. ÿ s. broken rock * Extended. preweathered materials. ISRIC.Chapter 3 – Soil formation factors 19 TABLE 12 Hierarchy of lithology (Continued) Major class Group Type UO organic UO1 rainwater-fed moor peat UO2 groundwater-fed bog peat UA anthropogenic/ UA1 redeposited natural material technogenic UA2 industrial/artisanal deposits UU * unspecified deposits UU1 clay UU2 loam and silt UU3 sand UU4 gravelly sand UU5 gravel. O Older.. commonly the recent soil formation on younger over older.

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A number of other surface characteristics. The rules of soil description and the coding of attributes are generally based on the guidelines for soil description according to FAO (1990). together with additional relevant information on the size. Coarse surface fragments TABLE 14 Coarse surface fragments. Additions have a citation. Table 14 lists the recommended classes of percentage of surface cover and of average distance between rock outcrops (single or clusters). worm casts. but only after scraping off sufficient material to expose the fresh soil. 21 Chapter 4 Soil description This chapter presents the procedure to describe the different morphological and other characteristics of the soil. cloddiness. and puddling. human-induced erosion. coarse rock fragments. D Dominant > 80 . spacing and hardness of the individual outcrops. First. This is best done using a recently dug pit large enough to allow sufficient examination and description of the different horizons. may be also be recorded. ant paths. should be recorded. Surface cover (%) outcrops should be described in terms of (m) percentage of surface coverage N None 0 V Very few 0–2 1 > 50 and of size of the fragments. starting with the uppermost one. such as the occurrence of salts. Rock outcrops Exposures of bedrock may limit the use of modern mechanized agricultural equipment. bleached sands. the soil description is done horizon by horizon. Old exposures such as road cuts and ditches may be used. as A Abundant 40–80 5 <2 per Table 15. surface characteristics. Recommended classification of rock outcrops Distance between rock including those partially exposed. Rock outcrops should be described in terms of percentage surface cover. the surface characteristics are recorded. such as rock outcrops. F Few 2–5 2 20–50 Classes of occurrence of coarse C Common 5–15 3 5–20 surface fragments are correlated M Many 15–40 4 2–5 with the ones for rock outcrop. surface sealing and surface cracks. litter. Then. SURFACE CHARACTERISTICS Where present.

TABLE 18 Classification of erosion. M Mass movement (landslides and similar phenomena) NK Not known Main categories Erosion can be classified as water or wind erosion (Table 16).6 includes wind-shaped gravel or V Very few 0–2 M Medium gravel 0. and TABLE 17 Classification of total area affected by erosion and include off-site effects such as deposition deposition. be equally appropriate for all soils V Severe Surface horizons completely removed and subsurface horizons exposed.22 Guidelines for soil description TABLE 15 Note for classification purposes Classification of coarse surface fragments ¸ Pavement (consisting of rock Size classes (indicating the Surface cover (%) greatest dimension) outcrops or surface coarse (cm) fragments) that is varnished or N None 0 F Fine gravel 0. also fit the various types of water E Extreme Substantial removal of deeper subsurface horizons (badlands). 1 0–5 2 5–10 Area affected 3 10–25 4 25–50 The total area affected by erosion 5 > 50 and deposition is estimated follow- ing the classes defined by SOTER (FAO. recommended (Table 18). overgrazing WD Deposition by water and removal or overexploitation of WA Water and wind erosion the natural vegetation. Original biotic functions and wind erosion. 1995) as per Table 17. a third major category % is mass movements (landslides and 0 0 related phenomena). by category always easy to distinguish between N No evidence of erosion natural and accelerated erosion W Water erosion or A Wind (aeolian) erosion or deposition deposition as they are often closely related. such as inappropriate WT Tunnel erosion AZ Salt deposition agricultural practices. which .2–0. the degree of erosion that would Original biotic functions partly destroyed.6–2. C Common 5–15 S Stones 6–20 M Many 15–40 B Boulders 20–60 A Abundant 40–80 L Large boulders 60–200 Erosion D Dominant > 80 In describing soil erosion. by degree Degree S Slight Some evidence of damage to surface horizons. Original biotic functions largely intact.0 stones or is associated with a F Few 2–5 C Coarse gravel 2–6 vesicular layer → yermic horizon. WS Sheet erosion AD Wind deposition Human-induced erosion is the WR Rill erosion AM Wind erosion and result of irrational use and poor deposition WG Gully erosion AS Shifting sands management. It is difficult to define classes of M Moderate Clear evidence of removal of surface horizons. It is not Classification of erosion. emphasis should be given to accelerated or TABLE 16 human-induced erosion. Original biotic and environments and that would functions largely destroyed. Four classes are fully destroyed.

These crusts may inhibit seed germination. Classification of attributes of surface sealing ¸ Cracks that open and close Thickness Consistence (mm) periodically. when dry. The average distance between cracks may also be indicated in centimetres. reduce water infiltration and increase runoff. ≥ 1 cm wide → N None S Slightly hard vertic properties. Note for classification purposes ¸ Evidence of aeolian activity: rounded or subangular sand particles showing a matt surface. and for deposition. F Thin <2 H Hard ¸ Polygonal cracks extending ≥ M Medium 2–5 V Very hard 2 cm deep when the soil is dry C Thick 5–20 E Extremely hard → takyric horizon. For example. wind erosion or sedimentation → aridic properties.Chapter 4 – Soil description 23 may have to be further defined TABLE 19 for each type or combination of Classification of erosion. or average width and maximum width) of the cracks at the surface is indicated in centimetres. wind-shaped rock fragments. the loss of topsoil. Note for classification purposes ¸ Surface crust that does not curl entirely upon drying → takyric horizon. the N Period of activity not known depth and spacing may need to be X Accelerated and natural erosion not distinguished recorded. Surface cracks Surface cracks develop in shrink–swell clay-rich soils after they dry out. the thickness of the layer. by activity A Active at present erosion and deposition and specific R Active in recent past (previous 50–100 years) environment. the height. V Very thick > 20 . The attributes of surface sealing are the consistence. in the H Active in historical times case of gully and rill erosion. ¸ Surface crust → Hyperochric qualifier. Table 21 lists the suggested classes. Note for classification purposes ¸ Cracks that open and close TABLE 20 periodically → Vertisols. Activity The period of activity of accelerated erosion or deposition is described using the recommended classes in Table 19. aeroturbation. Surface sealing Surface sealing is used to describe crusts that develop at the soil surface after the topsoil dries out. and thickness of the crust as per Table 20. for sheet erosion. The width (average. for dunes.

hence. litter. may be spaced V Very wide 5–10 W Widely spaced 2–5 recorded.2–0.2 occurrence of salts. the image obtained 1 Low 2–15 through remote sensing. ant paths. Cover Thickness (%) (mm) Note for classification purposes 0 None 0–2 N None ¸ Crust pushed up by salt crystals 1 Low 2–15 F Thin <2 → Puffic qualifier. W Wide 2–5 M Moderately widely 0. bleached M Medium 1–2 D Closely spaced 0. such as the (cm) (m) F Fine <1 C Very closely spaced < 0. Horizon boundaries are described in terms of depth. loose TABLE 23 sand grains on the surface is typical Classification of bleached sand characteristics for certain soils and influences the % reflection characteristics of the area 0 None 0–2 and. Table 22 lists the classes for TABLE 22 the percentage of surface cover and Classification of salt characteristics thickness. HORIZON BOUNDARY Horizon boundaries provide information on the dominant soil-forming processes that have formed the soil. In certain cases. Depth Most soil boundaries are zones of transition rather than sharp lines of division. they reflect past anthropogenic impacts on the landscape. . measured from the surface (including organic and mineral covers) of the soil downwards.5–2 cloddiness and puddling. E Extremely wide > 10 V Very widely spaced >5 Depth Salt S Surface <2 The occurrence of salt at the M Medium 2–10 surface may be described in terms D Deep 10–20 of cover. Table 23 2 Moderate 15–40 3 High 40–80 lists the classes based on the 4 Dominant > 80 percentage of surface covered. distinctness and topography. Precise notations in centimetres are used where boundaries are abrupt or clear. worm casts.5 sands. avoiding the suggestion of spurious levels of accuracy. 2 Moderate 15–40 M Medium 2–5 3 High 40–80 C Thick 5–20 Bleached sand 4 Dominant > 80 V Very thick > 20 The presence of bleached. appearance and type of V Very deep > 20 salt. The depth of the upper and lower boundaries of each horizon is given in centimetres.24 Guidelines for soil description TABLE 21 Other surface characteristics Classification of surface cracks A number of other surface Width Distance between cracks characteristics. Rounded-off figures (to the nearest 5 cm) are entered where the boundaries are gradual or diffuse.

5 cm). The topography of the boundary indicates the smoothness of depth variation of the boundary. Note for classification purposes ¸ Many diagnostic horizons and properties are found at a certain depth. ¸ Tonguing of a mollic or umbric horizon into an underlying layer → Glossic qualifier. and (ii) the coarse fragments fraction.Chapter 4 – Soil description 25 However. ranges in depth should be given in addition to the average depth. The names for the particle-size classes correspond closely with commonly used standard terminology. ¸ Diffuse horizon boundaries → Nitisols. ¸ Tonguing of an eluvial albic horizon into an argic horizon → albeluvic tonguing and Glossalbic qualifier. If required. Cryosols and Turbic qualifier. PRIMARY CONSTITUENTS This section presents the procedure on the description of soil texture and the nature of the primary rock and mineral fragments. Important boundary depths are 10. rounded. irregular and broken. Distinctness and topography The distinctness of the boundary refers to the thickness of the zone in which the horizon boundary can be located without being in one of the adjacent horizons (Table 24). 25. 50. In Distinctness Topography this case. 20. 100 and 120 cm. by distinctness and topography off figures should not be used. the depth is indicated as (cm) a medium value for the transitional A Abrupt 0–2 S Smooth Nearly plane surface zone (if it starts at 16 cm and C Clear 2–5 W Wavy Pockets less deep than terminates at 23 cm. or fractions) in a given soil volume and is described as soil textural class (Figure 4). if boundary depths are TABLE 24 near diagnostic limits.Classification of horizon boundaries. which are subdivided into: (i) the fine earth fraction. Note for classification purposes ¸ Cryoturbation → cryic horizon. the depth wide G Gradual 5–15 I Irregular Pockets more deep than should be 19. wavy. for example 28 (25–31) cm to 45 (39–51) cm. wide Most horizons do not have a D Diffuse > 15 B Broken Discontinuous constant depth. The variation or irregularity of the surface of the boundary is described by the topography in terms of smooth. including that of the system used by the . 40. Texture of the fine earth fraction Soil texture refers to the proportion of the various particle-size classes (or soil separates.

. The constituents have the following feel: ÿ Clay: soils fingers. taking the total of the sand fraction as being 100 percent (Figure 4). does not soil fingers and feels very grainy. However. silt loam. ÿ Sand: cannot be formed. This publication uses the 2000–63–2-µm system for particle-size fractions.26 Guidelines for soil description United States Department of Agriculture (USDA). only weakly formable. Field estimation of textural classes The textural class can be estimated in the field by simple field tests and feeling the constituents of the soil (Table 25). The proportions are calculated from the particle-size distribution. is formable. Soil textural classes The names of the textural classes (which describe combined particle-size classes) of the described soil material are coded as in Figure 4. Gravel and other constituents > 2 mm must be removed. ¸ ≥ 30 percent clay throughout a thickness of 15 cm → vertic properties. many national systems describing particle-size and textural classes use more or less the same names but different grain fractions of sand. silt and sand is indicated in a triangular form in Figure 4. medium. the soil sample must be in a moist to weak wet state. and textural classes. is non-sticky. ¸ A texture of silt. loamy sands and sandy loams are subdivided according to the proportions of very coarse to coarse. silt and clay. ÿ Silt: soils fingers. This estimate is useful for indicating increases or decreases in clay content within textural classes. fine and very fine sands in the sand fraction. has a high plasticity and has a shiny surface after squeezing between fingers. ¸ ≥ 30 percent clay throughout a thickness of 25 cm → vertic horizon. The relationship between the basic textural classes and the percentages of clay. is cohesive (sticky). and for comparing field estimates with analytical results. a field estimate of the percentage of clay is given. Note for classification purposes Important diagnostic characteristics derived from the textural class are: ¸ A texture that is loamy sand or coarser to a depth of ≥ 100 cm → Arenosol. ¸ A texture of loamy fine sand or coarser in a layer ≥ 30 cm thick within 100 cm of the soil surface → Arenic qualifier. For this. In addition to the textural class. ¸ A texture of clay in a layer ≥ 30 cm thick within 100 cm of the soil surface → Clayic qualifier. ¸ ≥ 30 percent clay between the soil surface and a vertic horizon → Vertisol. silty clay loam or silty clay in a layer ≥ 30 cm thick. has a rough and ripped surface after squeezing between fingers and feels very floury (like talcum powder). within 100 cm of the soil surface → Siltic qualifier. Subdivision of the sand fraction Sands.

Chapter 4 – Soil description 27 FIGURE 4 Relation of constituents of fine earth by size. unsorted and Coarse 50 san y coa 50 LVFS Loamy very fine sand sand LS LFS Loamy fine sand r Ve Sand LCS Loamy coarse sand unsorted FSL Fine sandy loam Medium SL CSL Coarse sandy loam Fine sand sand very fine sand 0 100 100 50 0 Very fine + fine sand 0.2 mm Source: According to FAO (1990) .6 y (Heavy clay) % Clay 50 % Silt <2 µm 50 Clay Silty 2 – 63 µm Sandy clay clay (Vertic horizon) Clay loam Silt clay Sandy clay loam loam Loam (Arenosols) Sandy Silt loam Loamy loam Silt 100 Sand Sand 0 100 50 0 % Sand 0.063 – 2 mm 100 0 Subdivisions of sandy textural classes VFS Very fine sand FS Fine sand mm e – 2 oars Me – 0. defining textural classes and sand subclasses Particle-size classes Textural classes 2 000 µm Very coarse sand S Sand (unspecified) 1 250 µm Coarse sand LS Loamy sand 630 µm Medium sand SL Sandy loam 200 µm Fine sand SCL Sandy clay loam 125 µm Very fine sand SiL Silt loam 63 µm Coarse silt SiCL Silty clay loam 20 µm Fine silt 0 CL Clay loam 2 µm Clay 100 L Loam Si Silt SC Sandy clay SiC Silty clay C Clay Silt Heavy clay 0.063 – 0.4 HC /cla 0.2 diu 3 m .6 S MS Medium sand 0.63 + c CS Coarse sand ms m d 0 rse US Sand.

3 no grains to see and to feel.2–0. moderately shiny surfaces: silty clay SiC 40–60 • high plasticity. < 20 percent change (relative) in clay content over 12 cm to layers immediately above and below. gnashes between teeth • moderate plasticity. chlorite and/or vermiculite composition.6 mm): medium sand MS <5 • if most grains are of fine size (< 0. ¸ Sandy loam or finer particle size → ferralic horizon.2 but moderately floury: sandy loam SL (clay-poor) < 10 2 Possible to roll a wire of about 3–7 mm in diameter (about half the diameter of a pencil) but breaks when trying to form the wire to a ring of about 2–3 cm in diameter. moderately shiny surfaces: clay loam CL 25–40 • high plasticity. loamy very fine sand. and kaolinitic clays are stickier. . adheres slightly to the fingers: 1.28 Guidelines for soil description TABLE 25 Key to the soil textural classes ~% clay 1 Not possible to roll a wire of about 7 mm in diameter (about the diameter of a pencil) 1. Source: Adapted from Schlichting. or finer → cambic horizon.2 moderately cohesive. The above key works mainly for soils having illite. sticky.4 → nitic horizon.2 mm) but still grainy: fine sand FS <5 • if most grains are of very fine size (< 0.1 very floury and not cohesive • some grains to feel: silt loam SiL (clay-poor) < 10 • no grains to feel: silt Si < 12 2. does not gnash between teeth • low plasticity: silty clay loam SiCL 25–40 • high plasticity. shiny surfaces: clay C 40–60 3. 1995. adheres to the fingers.6 mm): very coarse and coarse sand CS <5 • if most grains are of medium size (0. not floury. clay content can be overestimated for the former. scarcely fine material in the finger rills.3 rough and moderate shiny surface after squeezing sandy clay loam SCL 20–35 between fingers and is sticky and grainy to very grainy: 3 Possible to roll a wire of about 3 mm in diameter (less than half the diameter of a pencil) and to form the wire to a ring of about 2–3 cm in diameter. a silt/clay ratio of < 0. tending very fine sand VFS <5 to be floury: 1. gnashes between teeth. ¸ A texture of loamy sand or finer and ≥ 8 percent clay → argic and natric horizons. no fine material in the finger rills: sand S <5 • if grain sizes are mixed: unsorted sand US <5 • if most grains are very coarse (> 0. adheres to the fingers 2.3 similar to 1. grainy. Blume and Stahr. ¸ A texture in the fine earth fraction coarser than very fine sand or loamy very fine sand → Brunic qualifier. ¸ A texture in the fine earth fraction of very fine sand.1 very grainy: sandy clay SC 35–55 3. Smectite clays are more plastic. has a moderately shiny to shiny surface after squeezing between fingers 3. moderately cohesive. Thus.1 not dirty.2 some grains to see and to feel. loamy sand LS < 12 weakly shapeable. cohesive.12 mm).2 not floury. ¸ ≥ 30 percent clay. and underestimated for the latter. shiny surfaces: heavy clay HC > 60 Note: Field texture determination may depend on clay mineralogical composition. has a rough and ripped surface after squeezing between fingers and • very grainy and not sticky: sandy loam SL (clay-rich) 10–25 • moderate sand grains: loam L 8–27 • not grainy but distinctly floury and somewhat sticky: silt loam SiL (clay-rich) 10–27 2.

silty clay loam or finer → takyric horizon. human occupation. Artefacts (sections on artefacts and description of artefacts [below]) are useful for identifying colluviation. M Many 15–40 Where rock fragments are not A Abundant 40–80 distributed regularly within a D Dominant > 80 horizon but form a “stone line”. ¸ A higher clay content than the underlying soil and relative differences among medium. and nature of the fragments. ¸ The required amount of organic carbon depends on the clay content. and Alic.6 → Hyperalic qualifier. if the layer is saturated with water for ≥ 30 consecutive days in most years → organic and mineral materials. ¸ An absolute clay increase of ≥ 3 percent → Hypoluvic qualifier. use and management of the soil. ¸ The depth where an argic horizon starts depends on the texture → Alisols. sandy loam or silt loam or a combination of them → plaggic horizon. . ¸ ≥ 8 percent clay in the underlying layer and within 7. Large rock and mineral fragments (> 2 mm) and artefacts are described according to abundance. size. medium sand. clay loam. Rock fragments and artefacts The presence of rock fragments influences the nutrient status. and fine sand → lithological discontinuity. ¸ A texture of sandy clay loam. state of weathering. fine and very fine sand and clay < 20 percent → irragric horizon. by volume for surface coarse fragments and % mineral nodules.N None 0 percent boundary coincides with V Very few 0–2 the requirement for the skeletic F Few 2–5 C Common 5–15 phase (Table 26 and Figure 5). and the 40. Luvic and Lixic qualifiers. ¸ An abrupt change in particle-size distribution that is not solely associated with a change in clay content resulting from pedogenesis or a relative change of ≥ 20 percent in the ratios between coarse sand. ¸ A silt/clay ratio < 0. ¸ An argic horizon in which the clay content does not decrease by 20 percent of more (relative) from its maximum within 150 cm → Profondic qualifier. Luvisols and Lixisols. Acrisols. and industrial processes. ¸ The required amount of organic carbon depends on the texture → aridic properties. It also reflects the origin and stage of development of the soil. water movement.Chapter 4 – Soil description 29 ¸ A texture of sand.5 cm either doubling of the clay content if the overlying layer has less then 20 percent or 20 percent (absolute) more clay → abrupt textural change. Acric. but concentrated at a distinct depth of a horizon this should be indicated clearly. S Stone line any content. loamy sand. The abundance class TABLE 26 limits correspond with the ones Abundance of rock fragments and artefacts. shape.

Medium gravel gravel ¸ ≥ 20 (by volume. gravel ¸ < 40 percent (by volume) of gravels or other coarse fragments in all layers within 100 cm or to a petroplinthic.30 Guidelines for soil description Size of rock fragments and FIGURE 5 Charts for estimating proportions of coarse fragments artefacts and mottles Table 27 indicates the classification for rock fragments and artefacts. plinthic or salic horizon → Arenosols. ¸ ≥ 40 percent (by volume) gravel 40 % 50 % 75 % 90 % or other coarse fragments aver- aged over: ÿ a depth of 100 cm or to continuous rock → Skeletic qualifier. Note for classification purposes Important diagnostic characte- 1% 3% 5% 10 % ristics derived from the amount of rock fragments are: ¸ < 20 percent (by volume) fine earth averaged over a depth of 15 % 2% 25 % 30 % 75 cm or to continuous rock → Leptosols and Hyperskeletic qualifier. ÿ a depth of 20– 50 cm → Coarse Episkeletic qualifier. TABLE 27 Classification of rock fragments and artefacts Rock fragments (mm) Artefacts (mm) V Very fine artefacts <2 F Fine gravel 2–6 F Fine artefacts 2–6 M Medium gravel 6–20 M Medium artefacts 6–20 C Coarse gravel 20–60 S Stones 60–200 C Coarse artefacts > 20 B Boulders 200–600 L Large boulders > 600 Combination of classes FM Fine and medium gravel/artefacts MC Medium and coarse gravel/artefacts CS Coarse gravel and stones SB Stones and boulders BL Boulders and large boulders . ÿ a depth of 50–100 cm → Endoskeletic qualifier. by weighted Sand average) artefacts in the upper Fine 10 mm 100 cm → Technosols.

see section on artefacts (below). lithological discontinuity. Fragments of individual weatherable minerals (e.g. Nature of rock fragments The nature of rock fragments is described by using the same terminology as for the rock-type description (Table 12). where present in appreciable quantities. State of weathering of rock TABLE 30 fragments and artefacts Codes for primary mineral fragments The state of weathering of the QU Quartz coarse fragments is described as MI Mica FE Feldspar per Table 29. e. For artefacts. Note for classification purposes ¸ Rock fragments that do not have the same lithology as the underlying continuous rock → lithological discontinuity. such fragments should be mentioned separately in the description. strongly discoloured and altered throughout the fragments. S Subrounded R Rounded Shape of rock fragments The general shape or roundness of rock fragments may be described TABLE 29 using the terms in Table 28. other codes can be used.Chapter 4 – Soil description 31 ¸ Fragmental materials. For primary mineral fragments.g. fragments of rounded shape S Strongly weathered All but the most resistant minerals are or marked differences in size weathered. Nevertheless. as per Table 30. the TABLE 28 interstices of which are filled Classification of shape of rock fragments F Flat with organic material → A Angular Histosols. Classification of weathering of coarse fragments F Fresh or slightly Fragments show little or no signs of weathered weathering. . Note for classification purposes W Weathered Partial weathering is indicated by ¸ Layers with rock fragments discoloration and loss of crystal form in of angular shape overlying or the outer parts of the fragments while the centres remain relatively fresh and underlying layers with rock the fragments have lost little of their original strength. feldspars and micas) may be smaller than 2 mm in diameter. Note for classification purposes ¸ A layer with rock fragments without weathering rinds overlying a layer with rock fragments with weathering rinds → lithological discontinuity. and shape of resistant minerals which tend to disintegrate under only between superimposed layers → moderate pressure.

The three major forms. organic matter is commonly accumulated in more or less decomposed organic layers under terrestrial conditions. are described as follows: ÿ Raw humus (aeromorphic mor): usually thick (5–30 cm) organic matter accumulation that is largely unaltered owing to lack of decomposers. Colour and percentage of recognizable plant tissue of dry as well as of wet organic material can be used to estimate the degree of decomposition (Table 31). moder and mull. 2005 Degree of decomposition and humification of peat In most organic layers. Note for classification purposes ¸ Histosols have more than two-thirds (by volume) recognizable plant tissues → Fibric qualifier. the determination of the texture class is not possible. especially under temperate and cool climates.1 moderately 1/6 to 1/3 more or less all only heavy Hemic strong decompostable remnants D5. In acidic and nutrient poor mineral soils.2 very strong less than 1/6 no remnant Sapric mud Source: Adapted from Ad-hoc-AG-Boden. raw humus. easy to separate one layer from another and being very acid with a C/N ratio of > 29.32 Guidelines for soil description TABLE 31 Field estimation and coding of the degree of decomposition and humification of peat Attributes of dry peat Attributes of wet peat Degree of Code decomposition/ Colour Visible plant Goes between the Remnant humification tissues fingers by squeezing in the hand D1 very low white to light only ± clear not muddy water brown Fibric D2 low dark brown most brown to muddy D3 moderate dark brown to more than 2/3 muddy muddy D4 strong black 1/3 to 2/3 1/2 to 2/3 plant structure more visible than before D5. ¸ Histosols have less than one-sixth (by volume) recognizable plant tissues → Sapric qualifier. the nutrient stock of the organic layers is of vital interest for the vegetation cover. It is usually a sequence of Oi–Oe–Oa layers over a thin A horizon. More valuable is an estimate of the degree of decomposition and humification of the organic material. This kind of organic matter layer develops in extremely nutrient-poor and coarse- textured soils under vegetation that produces a litter layer that is difficult to decompose. ¸ Histosols have between two-thirds and one-sixth (by volume) recognizable plant tissues → Hemic qualifier. Aeromorphic organic layers on forest floors On forest floors. .

soil colour should be determined under uniform conditions. the determination of colour by the same or different individuals has often proved to be inconsistent. In addition to the colour notations. Because soil colour is significant with respect to various soil properties. 1975). Hue is the dominant spectral colour (red. brown. It is usually acidic with a C/N ratio of 18–29. Moreover. It is generally determined by coatings of very fine particles of humified organic matter (dark). In the sequence of Oi–Oe– Oa layers. blue or violet).Chapter 4 – Soil description 33 ÿ Moder (duff mull): more decomposed than raw humus but characterized by an organic matter layer on top of the mineral soil with a diffuse boundary between the organic matter layer and A horizon. the horizon is described as mottled and two or more colours are given. yellow. value and chroma as given in the Munsell Soil Color Charts (Munsell. the standard Munsell colour names may be given. such as Chromic . Where there is no dominant soil matrix colour. additional colours from crushed or rubbed material may be required. Note for classification purposes Intermediate colours should be recorded where desirable for the distinction between two soil horizons and for purposes of classification and interpretation of the soil profile. SOIL COLOUR (MATRIX) Soil colour reflects the composition as well as the past and present oxidation- reduction conditions of the soil. For special purposes. This develops in moderately nutrient-poor conditions. For routine descriptions. soil colours should be determined out of direct sunlight and by matching a broken ped with the colour chip of the Munsell Soil Color Charts. Early morning and late evening readings are not accurate. including organic matter contents. such as for soil classification. It is usually slightly acid to neutral with a C/N ratio of 10–18. and for soil classification. iron oxides (yellow. Intermediate hues (important for qualifiers. green. orange and red). may be noted. coatings and state of oxidation or reduction. The occurrence of contrasting colours related to the structural organization of the soil. The colour of the soil matrix l of each horizon should be recorded in the moist condition (or both dry and moist conditions where possible) using the notations for hue. value is the lightness or darkness of colour ranging from 1 (dark) to 8 (light). or it may be due to the colour of the parent rock. manganese oxides (black) and others. ÿ Mull: characterized by the periodic absence of organic matter accumulation on the surface owing to the rapid decomposition process and mixing of organic matter and the mineral soil material by bioturbation. cross-checks are recommended and should be established on a routine basis. such as ped surfaces. it is difficult to separate one layer from another. and chroma is the purity or strength of colour ranging from 1 (pale) to 8 (bright). Where possible. usually under a cool moist climate.

value < 3. ¸ Value 3. and for diagnostic horizons. when 3.5 (moist) → Rhodic qualifier. ¸ Value ≤ 3. and so on. ¸ Hue 7.34 Guidelines for soil description or Rhodic.5 (dry) and chroma ≥ 2 (moist) → aridic properties. such as cambic) that may be used are: 3. Hypoferralic and Rubic qualifier. rounded-off figures should not be used. value ≤ 4 (moist). ¸ Value ≥ 3 (moist) and ≥ 4. or by adding a + or a -. GY or G → gyttja (limnic material). ¸ Values 4 to 8 and chroma 4 or less (moist) and values 5–8 and chromas 2–3 (dry) → albic horizon. ¸ Value ≥ 5 (moist) → marl (limnic material). chroma ≤ 2 (moist) → puddled layer (anthraquic horizon). ¸ Value and chroma ≤ 3 (moist) → hortic horizon.5 (dry) → Hyperochric qualifier. B or BG. ¸ Redder hue. ¸ Value ≤ 2 (moist) and chroma ≤ 2 (moist) → melanic horizon.0 (dry) → voronic horizon. ¸ Value ≥ 5. ¸ Value ≤ 4 (moist) and ≤ 5 (dry) and chroma ≤ 2 (moist) → plaggic horizon.0 (moist) and < 3. 6.5 YR or both hue 7. or hue 7. ¸ Hue redder than 7.0 (moist) and value < 2. . 5 Y.5 YR and chroma > 4 (moist) → Chromic qualifier.5 (moist) → Pellic qualifier. 4. ¸ Lower value or chroma than the overlying horizon → sombric horizon. ¸ Value > 2 (moist) or chroma > 2 (moist) → fulvic horizon. or hue 7. ¸ Hue 5 Y. 4 or 5 (moist) → diatomaceous earth (limnic material).5 YR is noted. ¸ Hue N1 to N8 or 2. ¸ Value ≤ 4 (moist) → coprogenous earth or sedimentary peat (limnic material). For example. Important diagnostic hues.5 YR or yellower or GY. or 10 YR 3/1 (all moist) → spodic horizon. 5 G or 5 B → reductimorphic colours of the gleyic colour pattern.5 YR than 5 YR. ¸ Hue 5 YR or redder.5. If values and chromas are near diagnostic limits. ¸ Chroma ≤3 (moist) and value ≤ 3 (moist) and ≤ 5 (dry) → mollic and umbric horizon.5 (moist) and chroma ≤ 1. ¸ Chroma < 2.5 Y. or hue 10 YR or neutral and value and chroma ≤ 2.5 and 9 YR. it means that the intermediate hue is closer to 2. 8. higher value or higher chroma than the underlying or an overlying layer → cambic horizon. values and chromas are: ¸ Abrupt changes in colour not resulting from pedogenesis → lithological discontinuity. 6. ¸ Chroma ≤ 2 (moist) → Chernozem. 4 YR means closer to 5 YR. but accurate recordings should be made by using intermediate values.5 YR and value ≤ 5 and chroma 5 or 6. ¸ Hue redder than 5 YR. ¸ Hue redder than 10 YR or chroma ≥ 5 (moist) → ferralic properties. ¸ Hue 7.5 YR or yellower and value ≥ 4 (moist) and chroma ≥ 5 (moist) → Xanthic qualifier.5 YR and value ≤ 5 and chroma ≤ 5.5.

Colour of mottles It is usually sufficient to describe the colour of the mottles in general terms. size. boundary and colour. the predominant colours should be TABLE 33 determined and entered as soil Classification of the size of mottles matrix colours. ferric. When the abundance C Common 5–15 of mottles does not allow the M Many 15–40 distinction of a single predominant A Abundant > 40 matrix or groundmass colour. ¸ Mottles or coatings of jarosite or schwertmannite are diagnostic for the thionic horizon and the Aceric qualifier. hydragric. plinthic and petroplinthic horizons and for the gleyic colour pattern. ¸ Redox depleted zones in macropores with a value ≥ 4 and a chroma ≤ 2 are diagnostic for the hydragric horizon. plinthic. ¸ Mottles in the form of yellow concentrations are diagnostic for the thionic horizon. petroplinthic and. Note for classification purposes ¸ Mottles of oxides in the form of coatings or in platy. ¸ Mottles of oxides in the form of concretions or nodules are diagnostic for the hydragric. The class limits V Very few 0–2 correspond to those of mineral F Few 2–5 nodules. position or any other feature may be recorded. mm V Very fine <2 Size of mottles F Fine 2–6 Table 33 lists the classes used to M Medium 6–20 A Coarse > 20 indicate the approximate diameters . Mottling of the soil matrix or groundmass is described in terms of abundance. pisoplinthic horizons and for the stagnic colour pattern.Chapter 4 – Soil description 35 MOTTLING Mottles are spots or blotches of different colours or shades of colour interspersed with the dominant colour of the soil. corresponding to the Munsell Soil Color Charts. ferric. In addition. They indicate that the soil has been subject to alternate wetting (reducing) and dry (oxidizing) conditions. the shape. contrast. Abundance of mottles The abundance of mottles is described in terms of classes TABLE 32 indicating the percentage of the Classification of the abundance of mottles % exposed surface that the mottles N None 0 occupy (Table 32). polygonal or reticulate patterns are diagnostic for the anthraquic (plough pan).

have closely related hues.5 units of The colour contrast between hue or several units in chroma or value. Soil colours in both the matrix and mottles mineral nodules. Boundary of mottles The boundary between mottle and TABLE 35 Classification of boundary between mottle and matrix matrix is described as the thickness mm of the zone within which the S Sharp < 0. with a diameter that is 2 mm greater than the redox electrodes) to a depth about 1–2 cm less than the desired depth to be measured. D Distinct Although not striking.5–2 without being in either the mottle D Diffuse >2 or matrix (Table 35). chroma and value alone or in combination are at least several units apart. the mottles are readily seen. Immediately clean the platinum surface of the redox electrode with sandpaper and insert the electrode about 1 cm deeper than the prepared hole.5 colour transition can be located C Clear 0. drive a hole into the soil using a rigid rod (stainless steel. chroma and value of the matrix Contrast of mottles are easily distinguished from those of the mottles. see section on reducing conditions (below). DVWK. 20–100 cm long. At least two electrodes should be installed for each depth TABLE 36 Redoximorphic soil characteristics and their relation to rH values and soil processes Redoximorphic characteristics rH values and status Processes No redoximorphic characteristics at permanently > 35 strongly aerated permanently high potentials - < 33 NO3 reduction Black Mn concretions temporary < 29 MnII formation Fe mottles and/or brown Fe concretions. The hue. of the outstanding features of the horizon. Hue. They F Faint The mottles are evident only on close examina- correspond to the size classes of tion. 1995). in temporary < 20 FeII formation* wet conditions Blue-green to grey colour. mottles and soil matrix can be P Prominent The mottles are conspicuous and mottling is one described as per Table 34. permanently < 13 sulphide formation flammable methane present permanently < 10 methane formation * For field test. They may vary by as much as 2.36 Guidelines for soil description TABLE 34 Classification of the contrast of mottles of individual mottles. Fe2+ ions always permanently 13–19 formation of FeII/FeIII oxides (green rust)* present Black colour due to metal sulphides. SOIL REDOX POTENTIAL AND REDUCING CONDITIONS Determination of redox potential by field method Soil redox potential is an important physico-chemical parameter used to characterize soil aeration status and availability of some nutrients (Table 36). chromas and values. . The redox potential is also used in the WRB classification to classify redoximorphic soils. To measure redox potential (DIN/ISO Draft.

5 B). measure the redox potential with a millivoltmeter against a reference electrode (e. In this tube.α dipyridyl solution in 10-percent (V/V) acetic acid solution. etc. 1995 . Reducing conditions Reductimorphic properties of the soil matrix reflect permanently wet or at least reduced conditions (Table 37).Chapter 4 – Soil description 37 being measured. carbon dioxide.. after oxidation white N8 → N8 -. The test yields a striking reddish-orange colour in the presence of Fe2+ ions but may not give the strong red colour in soil materials with a neutral or alkaline soil reaction. +244 millivolt at 10 °C of Ag/AgCl in 1 M KCl.5 Y. light blue 5–GY–5–B2–3/1–3 FeII/FeIII Fe-mix compounds (blue-green rust) White. after oxidation blue N7–8 → 5–B FeII 3(PO4)2 · 8 H2O vivianite Bluish black FeS.g.smell) (or Fe3S4) White. and stagnic and gleyic lower level units of other RSGs. Gaseous emissions (methane. 5 Y. The measured voltage (Em) is related to the voltage of the standard hydrogen electrode by adding the potential of the reference electrode (e. Complete loss of Fe compounds Source: Schlichting et al. filled with 0. For dry topsoil. Ag/AgCl in KCl of the glass electrode of pH measurements. The colour pattern will often change by aeration in minutes to days owing to oxidation processes.) are diagnostic for the Reductic qualifier. the results should be transformed to rH values using the formula: rH = 2pH + 2Eh/59 (Eh in mV at 25 °C).5 percent (M/M) agar in KCl solution) should be installed in a hole beside and at the depth of the platinum electrodes.2-percent (M/V) α. a salt bridge (plastic tube 2 cm in diameter and with open ends. TABLE 37 Reductimorphic colour pattern and occurrence of Fe compounds Colour Munsell colour Formula Mineral Greyish green. Care is necessary as the chemical is slightly toxic. 5 G. They are expressed by neutral (white to black: Munsell N1 to N) or bluish to greenish colours (Munsell 2. FeS2 5–10–B1–2/1–3 Fe sulphides (with 10% HCl.g. H2S. Planosols and Stagnosols. the reference electrode should be installed. For interpretation. after oxidation brown N7–8→ 10 YR4/5 FeIICO3 siderite White. Note the rH value on the description sheet. +287 of Calomel electrode). The presence of FeII ions can be tested by spraying the freshly exposed soil surface with a 0. Note for classification purposes ¸ An rH value of < 20 is diagnostic for reducing conditions in Gleysols. After at least 30 minutes. installed in a small hole on the topsoil that has been filled with 1-M KCl solution).

. at least partly secondary → petrocalcic horizon. subsoil crusts. of soft powdery lime. Note for classification purposes Important carbonate contents for classification are: ¸ ≥ 2 percent calcium carbonate equivalent → calcaric material. Thick foam forms quickly. Secondary carbonates should be tested separately. The reaction to acid depends upon soil texture and is usually more vigorous in sandy material than in fine-textured material with the same carbonate content. resembling is difficult to distinguish in the field mycelia) between primary and secondary M marl layer HL hard cemented layer or layers of carbonates (less than carbonates. The forms of secondary carbonates should be indicated as per Table 39. concretions. and hard concretions are generally believed to be of hydrogenic nature. (secondary carbonates). ¸ Indurated layer with calcium carbonate.38 Guidelines for soil description TABLE 38 CARBONATES Classification of carbonate reaction in the soil matrix Content % N 0 Non-calcareous No detectable visible or Carbonates in soils are either audible effervescence. such as roots. Soft carbonate concentrations are considered to be illuvial. carbonates” if they migrate seasonally and have no permanent depth. residues of the parent material SL ≈ 0–2 Slightly calcareous Audible effervescence but not visible. they normally react much more intensely with HCl. it PM pseudomycelia* (carbonate infillings in pores. or the result of neo-formation MO ≈ 2–10 Moderately calcareous Visible effervescence. or hard banks. ¸ ≥ 15 percent calcium carbonate equivalent in the fine earth. The latter ST ≈ 10–25 Strongly calcareous Strong visible are concentrated mainly in the form effervescence. In many soils. Classes for the reaction 10 cm thick) of carbonates in the soil matrix are * Pseudomycelia carbonates are not regarded as “secondary defined as per Table 38. The degree of effervescence SC soft concretions of carbon dioxide gas is indicative HC hard concretions HHC hard hollow concretions for the amount of calcium D disperse powdery lime carbonate present. surface or reaction. Other materials. The presence of calcium carbonate (CaCO3) is established by adding TABLE 39 some drops of 10-percent HCl to Classification of forms of secondary carbonates the soil. may also give an audible reaction. coatings EX ≈ > 25 Extremely calcareous Extremely strong on peds. Dolomite commonly reacts more slowly and less vigorously than calcite. Bubbles form a low foam. at least partly secondary → calcic horizon. Forms The forms of secondary carbonates in soils are diverse and are considered to be informative for diagnostics of soil genesis.

8 dS m-1 in 10 g soil/250 ml H2O MO ≈ 5–15 Moderately gypsiric EC = > 1. at least partly secondary → Hypocalcic qualifier. as nests. The latter form gives the gypsic horizon a massive structure and a sandy texture. gypsum can be estimated in the field by measurements of electrical conductivity (EC in dS m-1) in soil suspensions of different soil–water relations (Table 40) after 30 minutes (in the case of fine- grained gypsum). ¸ ≥ 50 percent calcium carbonate equivalent in the fine earth. it is only a Calcisol if the soil matrix between 50 cm from the soil surface and the calcic horizon is calcareous throughout. EC = < 0.8 dS m-1 in 10 g soil/250 ml H2O ST ≈ 15–60 Strongly gypsiric higher amounts may be differentiated by abundance of H2O-soluble pseudomycelia/crystals and soil colour EX ≈ > 60 Extremely gypsiric ¸ 15–25 percent calcium carbonate equivalent in the fine earth.Chapter 4 – Soil description 39 TABLE 40 Classification of gypsum content % N 0 Non-gypsiric EC = < 1. GYPSUM Content of gypsum Gypsum (CaSO4·2H2O) may be found in the form of residues of gypsiric parent material or new formed features. at least partly secondary → Hypercalcic qualifier. The forms of secondary carbonates should be indicated as per Table 41. coarse-sized crystals (individualized. Forms of secondary gypsum The forms of secondary gypsum in soils are diverse and are considered to be informative for diagnostics of soil genesis. The latter are pseudomycelia. ¸ Where a soil has a calcic horizon starting 50–10 cm from the soil surface. TABLE 41 Classification of forms of secondary gypsum Note for classification purposes SC soft concretions Important contents of gypsum for D disperse powdery gypsum G “gazha” (clayey water-saturated layer with high gypsum classification are: content) ¸ ≥ 5 percent (by volume) gypsum HL hard cemented layer or layers of gypsum (less than 10 cm → gypsiric material. thick) .18 dS m-1 in 10 g soil/250 ml H2O SL ≈ 0–5 Slightly gypsiric EC = < 1. Where more readily soluble salts are absent. beards or coatings. ¸ Calcisols and Gypsisols can only have an argic horizon where the argic horizon is permeated with calcium carbonate (Calcisols) or calcium carbonate or gypsum (Gypsisols).8 dS m-1 in 10 g soil/25 ml H2O. or as elongated groupings of fibrous crystals) or loose to compact powdery accumulations.

Most classification values and data about salt sensitivity of crops refer to ECSE. Use water with an EC < 0. log Ks = -4. ¸ ≥ 50 percent (by mass) gypsum and ≥ 1 percent (by volume) secondary gypsum → Hypergypsic qualifier.5) and to calculate ECSE depending on the texture and content of organic matter (Table 43). The EC is measured with a field conductometer after 30 minutes in the clear solution. ¸ Gypsisols can only have an argic horizon if the argic horizon is permeated with calcium carbonate or gypsum. Source: DVWK. Procedure Use a transparent plastic cup with marks for 8 cm3 soil (~ 10 g) and 25 ml water and mix carefully with a plastic stick. Conventionally. READILY SOLUBLE SALTS Coastal or desert soils can be especially enriched with water-soluble salts or salts more soluble than gypsum (CaSO4·2H2O. The EC2.40 Guidelines for soil description ¸ ≥ 5 percent (by mass) gypsum TABLE 42 and ≥ 1 percent (by volume) Classification of salt content of soil secondary gypsum → gypsic ECSE = dS m-1 (25 ºC) horizon. 1995.5 [mS cm-1] · 0. ¸ 15–25 percent (by mass) gypsum and ≥ 1 percent (by volume) secondary gypsum → Hypogypsic qualifier. .85 at 25 °C). The salt content (NaCl equivalent) can be estimated from EC2.067 · 2. 25 °C) → salic horizon. N (nearly)Not salty < 0. An easier and more comfortable method of determining EC in the field is to use a 20 g soil/50 ml H2O (aqua dest) suspension (EC2. 25°C) in at least some layer within 100 cm → Hyposalic qualifier. The salt content of the soil can be estimated roughly from an EC (in dS m-1 = mS cm-1) measured in a saturated soil paste or a more diluted suspension of soil in water (Richards.75–2 5 percent (by mass) gypsum MO Moderately salty 2–4 ST Strongly salty 4–8 and ≥ 1 percent (by volume) VST Very strongly salty 8–15 secondary gypsum → EX Extremely salty > 15 petrogypsic horizon.01 dS m-1.5 by: salt [%] = EC2. 1954).5.75 ¸ Indurated layer with ≥ SL Slightly salty 0.5 can be converted to ECSE depending on the texture and content of humus according to the formula below and Table 43. Note for classification purposes ¸ Threshold values of ≥ 8 and ≥ 15 dS m-1 (ECSE. EC is measured in the laboratory in the saturation extract (ECSE). ¸ ≥ 4 dS m-1 (ECSE.

. if < 4% OM qualifier it may be used in the field for < 3.5% 0. or measured with a portable pH meter in a soil suspension (1 part soil and 2. 1995.3. TABLE 44 Classification of pH value Note for classification purposes pHCaCl of < 5. The field soil pH should not be a substitute for a laboratory determination. otherwise → Eutric correlates with the base saturation. if > 15% OM is an indication for a base saturation of less than 10% preliminary classification purposes < 3. if > 15% OM is an indication for a Dystric 2 qualifier (= base saturation As the pH value in many soils < 4. if < 4% OM Hyperalic qualifier laboratory is necessary.g. recalculated to FAO textural classes.3) D1 fibric D2 low D3 moderate D4 strong D5 sapric 80 120 170 240 300 Source: Adapted from DVWK (1995). ¸ ≥ 30 dS m-1 (ECSE. Hellige). Blume and Stahr.Chapter 4 – Soil description 41 TABLE 43 Dependency of water content of saturation extract on texture and content of humus for mineral soils and on decomposition for peat soils Textural class Water content of saturation extract WCSE in g/100 g Mineral soils Content of humus < 0.5–1% 1–2% 2–4% 4–8% 8–15% Gravel. < 4. C 40–60% clay 63 65 68 73 83 102 HC > 60% clay 105 107 110 116 126 147 Peat soils Decomposition stage (see section 3.6. CS 5 6 8 13 21 35 MS 8 9 11 16 24 38 FS 10 11 13 18 26 40 LS.2. Field soil pH measurements should be correlated with laboratory determinations where possible. Source: Adapted from Schlichting. In the field.5 parts 1 M KCl or 0. if 4–15% OM and for a high Al saturation → (Table 44). if 4–15% OM <50%). use a transparent 50- ml plastic cup with marks for 8 cm3 soil (~ 10 g) and 25 ml solution. For the measurement. It affects the availability of mineral nutrients to plants as well as many soil processes. However. 25°C) in at least some layer within 100 cm → Hypersalic qualifier. the pH value can be read. FIELD SOIL PH Soil pH expresses the activity of the hydrogen ions in the soil solution. SiCL 44 46 48 53 63 80 SC 51 53 55 60 70 88 SiC.2.1. the method used should be indicated on the field data sheet. When the pH is measured in the field. SL < 10% clay 14 15 17 22 30 45 SiL < 10% clay 17 18 20 25 34 49 Si 19 20 22 27 36 51 SL 10–20% clay 22 23 26 31 39 55 L 25 26 29 34 42 58 SiL 10–27% clay 28 29 32 37 46 62 SCL 32 33 36 41 50 67 CL. proof in the < 3.6.4.1 M CaCl2 solution). pH is either estimated using indicator papers. After shaking the solution and waiting for 15 minutes. indicator liquids (e.

measure the pH of a suspension of 1 g soil in 50 ml 1 M NaF (adjusted to pH 7.42 Guidelines for soil description SOIL ODOUR TABLE 45 Classification of soil odour Record the presence of any strong Odour – kind Criteria smell (Table 45). volcanic glasses. Note in the description sheet the sign of a + or a -.5 indicates the presence of abundant allophanic products and/or organo-aluminium complexes. commonly associated with stronglyVOLCANIC GLASSES reduced soil containing sulphur compounds. Procedure Place a small amount of soil material on a filter paper previously soaked in phenolphthalein and add some drops of 1 M NaF (adjusted to pH 7. and a smeary consistence (owing to higher contents of allophane and/or ferrihydrite). If the pH is more than 9. In many young volcanic materials.5.5) after 2 minutes. In addition. Alternatively. No N None No odour detected entry implies no odour.9 kg dm-3 or less. “rotten eggs”). Surface horizons with andic characteristics are normally black because of high humus contents. However. P Petrochemical Presence of gaseous or liquid gasoline. finer fractions may be checked by microscope. soils with free carbonates also react. the same reaction occurs in spodic horizons and in certain acid clayey soils that are rich in aluminium-interlayered clay minerals. S Sulphurous ANDIC CHARACTERISTICS AND Presence of H2S (hydrogen sulphide. Soils formed from young volcanic materials often have andic properties: a bulk density of 0.5). by horizon. it is important to check soil pH (the test is not suitable for alkaline soils) and the presence of free carbonates (using HCl field test). Andic characteristics may be identified in the field using the pHNaF field test developed by Fieldes and Perrott (1966). Coarser fractions may be checked by a ×10 hand-lens. glassy aggregates and other glass-coated primary minerals occur. A pHNaF of more than 9. . etc. Note for classification purposes ¸ Positive field test for allophanic products and/or organo-aluminium complexes → andic properties. it is a positive indication. ¸ Thixotropy → Thixotropic qualifier. the soil material changes under pressure or by rubbing from a plastic solid into a liquefied stage and back into the solid condition. The method depends on active aluminium sorbing fluoride ions with subsequent release of OH+ ions. oil. The test is indicative for most layers with andic properties. except for those very rich in organic matter. A positive reaction is indicated by a fast change to an intense red colour. creosote. Before applying a field NaF test. soil material with andic characteristics may exhibit thixotropy.

6 0.5–3 5–8 9–15 9–15 Black grey 3 1. C SCL. The content of organic matter of mineral horizons can be estimated from the Munsell colour of a dry and/or moist soil.3 < 0.3 < 0. ORGANIC MATTER CONTENT Organic matter refers to all decomposed.4 0. in the fraction 0. Therefore. Blume and Stahr. SL. glassy materials.5 3–5 6–9 6–9 Black grey 3.2 1.3–0.6–1 0.4–0.5 0.2 Grey 6 0. SiC.9–1.5 0.5 3–6 >4 >5 > 12 Black 2 >6 Note: If chroma is 3. CL. SCL. glass-coated primary minerals.0 to value. SiCL.6 0. SC. .5 < 0. Si.3–0.3–0.6 Light grey 6. It is generally synonymous with humus although the latter is more commonly used when referring to the well- decomposed organic matter called humic substances.5–6.6 0.02– 0. L SiL.02–2 mm particle-size fraction → tephric material. TABLE 46 Estimation of organic matter content based on Munsell soil colour Colour Munsell Moist soil Dry soil value S LS.8 0. add 0. C (%) Light grey 7 < 0.Chapter 4 – Soil description 43 Note for classification purposes ¸ ≥ 5 percent (by grain count) volcanic glass. Source: Adapted from Schlichting.9 0. S LS. L SiL. the organic matter values should always be locally checked as they only provide a rough estimate.9 2–3 4–6 4–6 Dark grey 4 0. It tends to overestimate organic matter content in soils of dry regions.3 1–1. 1995.25 mm → vitric properties.05–2 mm. CL.5 1–2 1. and glassy aggregates in the 0. Si.5–2 2–4 3–4 Dark grey 4. taking the textural class into account (Table 46).6–1 0. SC.6 1.5–3 2–4 3–5 8–12 > 15 > 15 Black 2.6–0. and to underestimate the organic matter content in some tropical soils.9–1.6–0. if chroma is > 6. SL.8–1. SiCL.5–0. partly decomposed and undecomposed organic materials of plant and animal origin. SiC. This estimation is based on the assumption that the soil colour (value) is due to a mixture of dark coloured organic substances and light coloured minerals. This estimate does not work very well in strongly coloured subsoils.2–2 Grey 5. glassy aggregates and other glass- coated primary minerals.2–2 2–3 Grey 5 < 0.5 1. ¸ ≥ 30 percent (by grain count) volcanic glass. or in the fraction 0.6–1. add 1.5 to value.5 0.5 < 0.

1)]% organic carbon or ≥ 18 percent organic carbon. no aggregates are observable in place and there is no definite arrangement of natural surfaces of weakness. (Note: the ratio of organic carbon to organic matter is about 1:1. ¸ Organic material saturated with water for < 30 consecutive days in most years → folic horizon. the first division is into apedal soils (lacking soil structure) and pedal soils (showing soil structure). size and type of aggregates. It will not always be possible to make clear distinctions between primary and secondary elements of the organization.) Write the range or average value in the description sheet. Voids (pores). It is preferred to describe the structure when the soil is dry or slightly moist. Primary organization is considered as being the overall arrangement of the soil mass without concentrations. ¸ Weighted average of ≥ 6 percent organic carbon. Soil structure Soil structure refers to the natural organization of soil particles into discrete soil units (aggregates or peds) that result from pedogenic processes.44 Guidelines for soil description Note for classification purposes ¸ If saturated with water for ≥ 30 consecutive days in most years (unless drained): ≥ [12 + (clay percentage of the mineral fraction × 0. Structureless soils are subdivided into single grain and massive (see below). else ≥ 20 percent organic carbon → organic material. from various parts of the horizon if necessary. which relate to the structural organization of soil. are described in a later section. Single-grain soil material .7–2.5 percent → voronic horizon. together with the consistence of the constituents. The aggregates are separated from each other by pores or voids.6 percent → mollic and umbric horizon. ¸ Organic carbon content of ≥ 1. a large lump of the soil should be taken from the profile. In apedal or structureless soil. For the description of soil structure. ¸ Organic material saturated with water for ≥ 30 consecutive days in most years (unless drained) → histic horizon. Grade In describing the grade or development of the structure. rather than observing the soil structure in situ. Where a soil horizon contains aggregates of more than one grade. it is advisable to leave the description of structure to a later time when the soil has dried out. reorientations and biological additions. the different kinds of aggregates should be described separately and their relationship indicated. ¸ Organic carbon content of ≥ 0. ORGANIZATION OF SOIL CONSTITUENTS This section describes the primary physical organization of arrangement of the soil constituents. Soil structure is described in terms of grade. In moist or wet conditions. size or type. and ≥ 4 percent organic carbon in all parts → fulvic and melanic horizon.

Massive soil material normally has a stronger consistence and is more coherent on rupture. When disturbed. the soil material breaks into a mixture of few entire aggregates. Grades of structure of pedal soil materials are defined as per Table 47. When disturbed. Aggregate surfaces differ in some way from the aggregate interior. and much material without aggregate faces. Massive soil material may be further defined by consistence (below) and porosity (below). soft or very friable consistence and consists on rupture of more than 50 percent discrete mineral particles. Combined classes may be constructed as follows: WM Weak to moderate MS Moderate to strong FIGURE 6 Soil structure types and their formation Pedogenic ped formation? No Caronates Yes Single Massive Layered Gypsum grain (coherent) (coherent) Formed by cementation from precipitates of Humus Iron Silica Formed by assemble Formed by separation Formed by fragmentation (biotic) (abiotic) or compaction Granular Worm. TABLE 47 Classification of structure of pedal soil materials WE Weak Aggregates are barely observable in place and there is only a weak arrangement of natural surfaces of weakness. Aggregates surfaces generally differ markedly from aggregate interiors. the soil material separates mainly into entire aggregates. some broken aggregates. the soil material breaks into a mixture of many entire aggregates. ST Strong Aggregates are clearly observable in place and there is a prominent arrangement of natural surfaces of weakness. When gently disturbed. Aggregates surfaces generally show distinct differences with the aggregates interiors. MO Moderate Aggregates are observable in place and there is a distinct arrangement of natural surfaces of weakness.Chapter 4 – Soil description 45 has a loose.Blocky Blocky Prismatic Columnar Platy Crumbly Lumpy Clody casts subangular angular . many broken aggregates. and little material without aggregates faces.

having flat or slightly rounded surfaces that are casts of the faces of the surrounding aggregates. tillage. its relation to the first structure is described. Crumbs. For prismatic. MA Massive Where required. . and subangular blocky faces intersecting at rounded angles. e.g.g. These can be indicated as per Table 52. interlocking lenses that terminate in sharp angles. special cases PM Porous massive or combinations of structures BL Blocky AB Angular blocky may be distinguished. nearly equidimensional. Where a second structure is present.g. Platy Flat with vertical dimensions limited. lumps and clods Mainly created by artificial disturbance. SB Subangular blocky SN Nutty subangular blocky Size PR Prismatic PS Subangular prismatic Size classes vary with the structure WE Wedge-shaped type. vertical faces well defined.g. the size classes GR Granular WC Worm casts refer to the measurements of the PL Platy smallest dimension of the aggregate CL Cloddy (Table 50). platy merging into prismatic). having curved or irregular surfaces that are not casts of the faces of surrounding aggregates. which are AP Angular blocky (parallelepiped) subdivisions of the basic structures. Prismatic structures with rounded caps are distinguished as Columnar. Granular Spheroids or polyhedrons. Faces normally intersect at relatively sharp angles. Rock structure Rock structure includes fine stratification in unconsolidated sediment. Prismatic the dimensions are limited in the horizontal and extended along the vertical plane. The primary structure may break down into a secondary structure (e. CR Crumbly LU Lumpy Combined classes may be constructed as per Table 51. Subdivision is recommended into angular. AS Angular and subangular blocky The recommended codes are given AW Angular blocky (wedge-shaped) SA Subangular and angular blocky in Table 49. The first structure may merge into the second structure (e. with faces intersecting at relatively sharp angles. columnar and prismatic structures). having flat or slightly rounded surfaces that are casts of the faces of the surrounding aggregates. not limited to vertic materials. prismatic breaking into angular blocky). Wedge-shaped Elliptical. columnar and CO Columnar platy structures.46 Guidelines for soil description TABLE 48 Classification of types of soil structure Blocky Blocks or polyhedrons. The first and second structures may both be present (e. and pseudomorphs of weathered minerals retaining their positions relative to each other and to unweathered minerals in saprolite from consolidated rocks. TABLE 49 Type Codes for types of soil structure The basic natural types of structure RS Rock structure (Figure 6) are defined as per SS Stratified structure SG Single grain Table 48. bounded by slickensides. generally oriented on a horizontal plane and usually overlapping.

Chapter 4 – Soil description 47 TABLE 50 Size classes for soil structure types Granular/platy Prismatic/columnar/wedge. umbric and anthric horizons. ¸ Separations between structural soil units that allow roots to enter have an average horizontal spacing of ≥ 10 cm → fragic horizon. ¸ Platy layer → yermic horizon. . ¸ Platy or massive structure → takyric horizon. ¸ Wedge-shaped aggregates → vertic properties. ¸ Uniformly structured → irragric horizon. ¸ Soil structure sufficiently strong TABLE 52 that the horizon is not both Combinations of soil structures massive and hard or very hard CO + PR Both structures present when dry (prisms larger than PR → AB Primary breaking to secondary structure 30 cm in diameter are included PL / PR One structure merging into the other in the meaning of massive if there is no secondary structure within the prisms) → mollic. angular blocky structure breaking to flat-edged or nut- shaped elements with shiny ped faces → nitic horizon. ¸ Moderate to strong. Blocky/crumbly/lumpy/ shaped cloddy (mm) (mm) (mm) VF Very fine/thin <1 < 10 <5 FI Fine/thin 1–2 10–20 5–10 ME Medium 2–5 20–50 10–20 CO Coarse/thick 5–10 50–100 20–50 VC Very coarse/thick > 10 100–500 > 50 EC Extremely coarse – > 500 – Note for classification purposes TABLE 51 ¸ Soil structure. ¸ Granular or fine subangular blocky soil structure (and worm casts) → voronic horizon. ¸ Columnar or prismatic structure in some part of the horizon or a blocky structure with tongues of an eluvial horizon → natric horizon. ¸ Wedge-shaped structural aggregates with a longitudinal axis tilted 10–60 ° from the horizontal → vertic horizon. ¸ Platy structure → puddled layer (anthraquic horizon). or absence Combined size classes for soil structure types of rock structure (the term FF Very fine and fine VM Very fine to medium “rock structure” also applies FM Fine and medium to unconsolidated sediments FC Fine to coarse in which stratification is still MC Medium and coarse visible) in half of the volume or MV Medium to very coarse more of the fine earth → cambic CV Coarse and very coarse horizon.

¸ A platy structure and a surface crust → Hyperochric qualifier. cannot be broken in the hands. Consistence when dry The consistence when dry (Table 53) is determined by breaking an air-dried mass of soil between thumb and forefinger or in the hand. Consistence when wet: maximum stickiness and maximum plasticity Soil stickiness depends on the extent to which soil structure is destroyed and on the amount of water present. It depends greatly on the amount and type of clay. easily broken between thumb and forefinger. and HVH. stickiness and resistance to compression. plasticity. In this way. breaks to powder or individual grains under very slight pressure. . ¸ Stratification in ≥ 25 percent of the soil volume → fluvic material. hard to very hard. For routine descriptions.48 Guidelines for soil description ¸ Strong structure finer than very coarse granular → Grumic qualifier. the smeariness (thixotropy) and fluidity may also be recorded. not breakable between thumb and forefinger. needed occasionally to distinguish between two horizons or layers. moist and wet (stickiness and plasticity) states. EHA Extremely hard Extremely resistant to pressure. Chapter 2). The same principle applies to soil plasticity. ¸ Massive and hard to very hard in the upper 20 cm of the soil → Mazic qualifier. VHA Very hard Very resistant to pressure. TABLE 53 Consistence of soil mass when dry LO Loose Non-coherent. the maximum stickiness will be determined and comparison between degrees of stickiness of various soils will be feasible. SO Soft Soil mass is very weakly coherent and fragile. It includes soil properties such as friability. a recording of consistence is required for the dry. Wet consistence can always be described. Consistence when moist Consistence when moist (Table 54) is determined by attempting to crush a mass of moist or slightly moist soil material. organic matter and moisture content of the soil. SHA Slightly hard Weakly resistant to pressure. soft to slightly hard. can be broken in the hands only with difficulty. Consistence Consistence refers to the degree of cohesion or adhesion of the soil mass. For reference descriptions (Status 1. the soil consistence in the natural moisture condition of the profile may be described. slightly hard to hard. and moist conditions where the soil is dry. Where applicable. are: SSH. Note: Additional codes. HA Hard Moderately resistant to pressure. The determination of stickiness should be performed under standard conditions on a soil sample in which structure is completely destroyed and which contains enough water to express its maximum stickiness. SHH. by adding water to the soil sample. can be broken in the hands.

Plasticity is the ability of ST Sticky After pressure. of an applied stress and to retain VST Very sticky After pressure. slightly plastic to plastic. and PVP.Chapter 4 – Soil description 49 TABLE 54 Consistence of soil mass when moist LO Loose Non-coherent. the adherence of soil material when SST Slightly sticky After pressure. soil material adheres to both thumb and finger but comes off it is pressed between thumb and one or the other rather cleanly. firm to very firm. 5–10 cm in force required for deformation of the diameter. Determined by rolling separated. TABLE 56 Note for classification purposes Classification of soil plasticity ¸ Extremely hard consistence when NPL Non-plastic No wire is formable. but resistance is distinctly noticeable. but coheres when pressed together. when wet → takyric horizon. appreciably stretched when the digits are separated. VFR Very friable Soil material crushes under very gentle pressure. sticky the soil in the hands until a wire to very sticky. SPL Slightly plastic Wire formable but breaks immediately if bent into a ring. Note: Additional codes are: SSS. FI Firm Soil material crushes under moderate pressure between thumb and forefinger. cannot be crushed between thumb and forefinger. EFI Extremely firm Soil material crushes only under very strong pressure. soil mass deformed by ¸ Surface crust with very hard very slight force. practically no soil other objects determined by noting material adheres to thumb and finger. slight to moderate force required plastic and sticky consistence for deformation of the soil mass. Note: Additional codes are: VFF. water within 10 minutes → Note: Additional codes are: SPP. very friable to friable. VFI Very firm Soil material crushes under strong pressures. It is not finger (Table 55). and very PL Plastic Wire formable but breaks if bent into a ring. friable to firm. . soil material adheres to soil material to change shape both thumb and finger and tends to stretch somewhat and pull apart rather continuously under the influence than pulling free from either digit. plastic to very plastic. Stickiness is the quality of TABLE 55 adhesion of the soil material to Classification of soil stickiness NST Non-sticky After release of pressure. and SVS. slightly sticky to sticky. VPL Very plastic Wire formable and can be bent into a ring. and FVF. FR Friable Soil material crushes easily under gentle to moderate pressure between thumb and forefinger. about 3 mm in diameter has been formed (Table 56). slake or fracture in soil mass. ¸ Penetration resistance of ≥ 450 N cm-2 → petroplinthic horizon. fragic horizon. moderately strong to very strong ¸ Air-dry clods. and coheres when pressed together. barely crushable between thumb and forefinger. consistence when dry. soil material adheres strongly to both thumb and finger and the compressed shape on removal is decidedly stretched when they are of stress. ¸ Penetration resistance at field capacity of ≥ 50 kN m-1 → fragic horizon. FRF. dry → petrocalcic horizon.

thus. High bulk density values indicate a poorer environment for root growth. ¸ Organic material floating on water → Floatic qualifier. There are several methods of determining soil bulk density. Field determinations of bulk density may be obtained by estimating the force required to push a knife into a soil horizon exposed at a field moist pit wall (Table 58). ¸ Permanently submerged under water < 2 m → Subaquatic qualifier. One method is to obtain a known volume of soil. Oxyaquic and Reductaquic qualifiers. seems to be warm going dark hardly lighter dry 4 makes no dust possible (not sand) going slightly dark obviously lighter slightly moist 3 finger moist and cool. For surface horizons. ¸ Temporarily water-saturated → Gelistagnic. Bulk density is an important parameter for the description of soil quality and ecosystem function. . reduced aeration. bulk density reflects the total soil porosity. and then to determine the dry mass. and weigh the dry mass.50 Guidelines for soil description TABLE 57 Classification of moisture status of soil Rubbing Crushing Forming (to a ball) Moistening Moisture pF* (in the hand) dusty or hard not possible. and undesirable changes in hydrologic function. F = free energy of water) is log hPa. seems to be warm going very dark not lighter very dry 5 makes no dust not possible. Low bulk density values (generally below 1. BULK DENSITY Bulk density is defined as the mass of a unit volume of dry soil (105 °C). weakly is sticky no change of colour obviously lighter moist 2 shiny free water drops of water no change of colour wet 1 free water drops of water without crushing no change of colour very wet 0 * pF (p = potential. Another uses a special coring instrument (cylindrical metal device) to obtain a sample of known volume without disturbing the natural soil structure. such as reduced water infiltration. folic and cryic horizons depend on the soil-water status. This volume includes both solids and pores and. The moisture status can be estimated in the field as per Table 57. a simple method is to dig a small hole and fill it completely with a measured volume of sand. but not covered at mean low tide → Tidalic qualifier. ¸ Artificially drained histic horizon → Drainic qualifier. dry it to remove the water. ¸ Flooded by tidewater. Note for classification purposes ¸ The definitions of mineral and organic materials and of the histic. Soil-water status Soil-water status is the term used for the moisture condition of a horizon at the time the profile is described.3 kg dm-3) generally indicate a porous soil condition.

6–1. wedge– shaped) Sample remains intact when dropped. silty and loamy soils with low clay content Many pores. columnar. the ) evaluation of bulk density has to 0 50 100 % Clay content take soil texture into account. 2005. 1. subangular.2–1. further angular blocky. which cannot be subdivided blocky) BD4 further. For evaluation purposes the “packing Source: according to Ad-hoc-AG-Boden. platy. platy. materials with granular < 0. ¸ In the plough pan. which may be further divided.0–1.2–1. further disintegration coherent. clayey soils When dropped. blocky. further angular blocky 1.4–1. density” (PD = BD + 0.6 disintegrates into few fragments. some effort required. Fine-textured soils contain BD4 D5) Firm BD3 1. BD1 Sample disintegrates at the instant of sampling.4 pressure. angular blocky BD2 Knife can be pushed into the moist soil with weak pressure. moist materials drop easily out of the auger. 1.90 kg dm-3 or less → andic properties. platy. 1. Therefore. sample subangular and angular 1. platy.03 kg dm-3 for each 1% increment in organic matter content. many pores visible on single grain. a bulk FIGURE 7 Qualification of bulk density density ≥20 percent (relative) higher than that of the puddled Si SiL SiCL SiC layer → anthraquic horizon. L CL C HC SL SCL SC Root penetration is not only LS Texture classes S limited by bulk density. prismatic.0 BD5 g cm-3 Bulk densty Very firm (P texture.0 Very loose 2) (PD1 root growth.2 the pit wall.5 Interm (PD4) fewer pores in size and abundance BD2 Loos ediate (PD3 e (PD ) BD1 than needed for unrestricted 1. sample disintegrates into numerous fragments.2 disintegration of subfragments after application of weak pressure. sample disintegrates into few fragments. prismatic. Note for classification purposes ¸ Bulk density of 0. granular 0.Chapter 4 – Soil description 51 TABLE 58 Field estimation of bulk density for mineral soils Observation Frequent ped shape Bulk density (kg dm-3) Code Sandy. bulk density has to be reduced by 0.8 sample disintegrates into few fragments. Very large pressure necessary to force knife into the soil.009 ·% clay) can also be used (Figure 7). no further prismatic > 1. BD1 Sample disintegrates into numerous fragments after application of weak single grain. (columnar. platy BD3 Knife penetrates only 1–2 cm into the moist soil.4–1.9 vesicular pores.4 disintegration of subfragments after application of mild pressure. prismatic. no further disintegration after coherent (prismatic.6 application of very large pressure.6 possible after application of large pressure. wedge– BD4. . prismatic. BD1 When dropped. angular BD3 blocky. (angular 1. columnar BD2 Sample remains mostly intact when dropped. >1.9–1. but also by 2.8 disintegration of sample. 5 shaped) Note: If organic matter content is > 2%. BD5 Loamy soils with high clay content. mineral soils with andic properties.

They are related to the arrangement of the primary soil constituents. In addition. continuity.07–0. VOIDS (POROSITY) Voids include all empty spaces in the soil. . The term void is almost equivalent to the term pore.04 SV1 Weakly drained Weakly Loose D2 Low (fibric) 3– < 5 0. but the latter is often used in a more restrictive way and does not. Voids are described in terms of type. 2005. Weakly drained and weakly decomposed peat materials are characterized by a lower bulk density and a lower solid volume than well-drained and strongly decomposed peat materials (Table 59). Organic surface horizons of mineral soils may be treated like strongly decomposed peat layers. translocation and leaching.11 drained SV3 Well drained Moderately Rather dense D4 Strong (hemic) 8– < 12 0.52 Guidelines for soil description TABLE 59 Field estimation of volume of solids and bulk density of peat soils Drainage conditions Solid volume Bulk density Bog Fen Peat characteristics Classes of decomposition Vol. include fissures or planes. Porosity The porosity is an indication of the total volume of voids discernible with a ×10 hand-lens measured by area and recorded as the percentage of the surface occupied by pores (Table 60). for example. burrowing of animals or any other soil-forming processes.04–0. rooting patterns.11–0. (%) g cm-3 Code Undrained Undrained Almost swimming D1 Very low (fibric) <3 < 0. orientation or any other feature may also be recorded. size and abundance. such as cracking. Type TABLE 60 Classification of porosity There is a large variety in the shape % and origin of voids. It is impractical 1 Very low <2 and usually not necessary to 2 Low 2–5 describe all different kinds of 3 Medium 5–15 voids comprehensively. Bulk density and volume of solids of organic soils may be estimated after the decomposition stage or the extent of peat drainage.17 SV5 Source: Adapted from Ad-hoc-AG-Boden.17 drained SV4 Well drained Well drained Dense D5 Very strong (sapric) ≥ 12 > 0.07 drained SV2 Moderately drained Weakly Rather loose D3 Moderate (fibric) 5– < 8 0. Emphasis 4 High 15–40 should be given to estimating the 5 Very high > 40 continuous and elongated voids.

g. ¸ Sorted soil aggregates and vesicular pores → anthraquic TABLE 63 Classification of abundance of pores horizon. FF fine and very fine. of the soil particles.Chapter 4 – Soil description 53 TABLE 61 Classification of voids I Interstitial Controlled by the fabric. In most cases. May be quantified in specific cases. varying strongly in diameter. Size The diameter of the elongated or tubular voids is described as per Table 62. V Vughs Mostly irregular. < 2 mm (number) > 2 mm N None 0 0 CONCENTRATIONS V Very few 1–20 1–2 This section deals with the most F Few 20–50 2–5 common concentrations of soil C Common 50–200 5–20 materials. which are mostly continuous tubular pores. Subdivision possible into simple packing voids. For the other types of voids. equidimensional voids of faunal origin or resulting from tillage or disturbance of other voids. be described (Figure 8). When wider than a few centimetres (burrow holes).5 F Fine 0. Abundance The abundance of very fine and fine elongated pores as one group. also known as textural voids. including secondary M Many > 200 > 20 enrichments. mostly tubular in shape and continuous. they are more adequately described under biological activity. describing width and frequency. which relate to the packing of sand particles. or arrangement. fine and medium. C Channels Elongated voids of faunal or floral origin. Relatively unimportant in connection with plant growth. . Predominantly irregular in shape and interconnected. layer or pavement with a vesicular layer → yermic horizon. They are often not persistent and vary in size. and compound packing voids. Planar voids may be recorded.5–2 decimetre (Table 63). it is recommended that only the size and abundance of the channels. and MC. e. related to accommodating ped surfaces or cracking patterns. the following size and abundance classes should serve as a guide for the construction of suitable classes for each category. P Planes Most planes are extra-pedal voids. cementations and reorientations. B Vesicular Discontinuous spherical or elliptical voids (chambers) of sedimentary origin or formed by compressed air. gas bubbles in slaking crusts after heavy rainfall. medium and coarse. and hard to quantify in the field. Discontinuous or interconnected. which result from the packing of non-accommodating peds. shape and quantity depending on the moisture condition of the soil. TABLE 62 and of medium and coarse pores as Classification of diameter of voids another group is recorded as the mm number per unit area in a square V Very fine < 0. M Medium 2–5 C Coarse 5–20 Note for classification purposes VC Very coarse 20–50 ¸ Vesicular layer below a platy Note: Additional codes are: FM. The major types of voids may be classified in a simplified way as per Table 61.

nature.54 Guidelines for soil description FIGURE 8 Charts for estimating size and abundance of pores Abundance Very few Few Common Size Very fine (<0. . contrast. Contrast Table 65 shows the classification of the contrast of coatings.5 mm) Fine (0. organic or silt). Abundance For coatings. and concentrations associated with surfaces but occurring as stains in the matrix (“hypodermic coatings”). coatings of other composition (such as calcium carbonate.5–2 mm) Medium (2–5 mm) 1 cm Coatings This section describes clay or mixed-clay illuviation features. Corresponding criteria should be applied when the cutanic feature is related to other surfaces (voids. All these features are described according to their abundance. form and location. an estimate is made of how much of the ped or aggregate faces is covered (Table 64). manganese. and coarse fragments) or occurs as lamellae. reorientations (such as slickensides and pressure faces).

slickensides. smoothness or any other property to the adjacent surface. Location D Distinct Surface of coating is distinctly smoother or The location of the coatings or different in colour from the adjacent surface. partly intersecting SN Slickensides. Lamellae are more than 5 mm thick.) JA Jarosite MN Manganese SL Silica (opal) SA Sand coatings ST Silt coatings SF Shiny faces (as in nitic horizon) PF Pressure faces SI Slickensides. Lamellae are less than 2 mm thick. the form C Common 5–15 may be informative for their M Many 15–40 genesis (Table 67). located on pedfaces. For example.. Micromorphological hypodermic coatings include non-redox features [Bullock et al. Lamellae are (Table 68). Fine sand grains are readily apparent in the cutan. colour. as used here. For pressure faces and 2–5 mm thick. 2002. 1985]. predominantly intersecting (Slickensides are polished and grooved ped surfaces that are produced by aggregates sliding one past another. Fine sand grains are enveloped in the coating clay accumulation is indicated but their outlines are still visible. are field-scale features.Chapter 4 – Soil description 55 Nature TABLE 64 The nature of coatings may be Classification of abundance of coatings described as per Table 66. no location is given P Prominent Surface of coatings contrasts strongly in smoothness or colour with the adjacent surfaces. TABLE 66 Classification of the nature of coatings C Clay S Sesquioxides H Humus CS Clay and sesquioxides CH Clay and humus (organic matter) CC Calcium carbonate GB Gibbsite HC Hypodermic coatings (Hypodermic coatings.) SP Slickensides. . because they are by definition Outlines of fine sand grains are not visible. commonly only expressed as hydromorphic features. non intersecting Source: Adapted from Schoeneberger et al. A Abundant 40–80 D Dominant > 80 manganese and iron–manganese coatings of dendroidal form indicate their formation owing to TABLE 65 poor infiltration and periodically Classification of the contrast of coatings reductive conditions because of F Faint Surface of coating shows only little contrast in percolating water. % N None 0 V Very few 0–2 Form F Few 2–5 For some coatings.

compacted. C Continuous e. and is only interrupted in places by cracks or fissures.56 Guidelines for soil description Note for classification purposes TABLE 67 Classification of the form of coatings ¸ Evidence of silica accumulation. heterogeneous) horizon. cemented or compacted. NS No specific location ¸ Coatings that have a different colour from the matrix (section on mottling [above]). and shows a rather irregular appearance. DI Discontinuous irregular ¸ Slickensides → vertic horizon DE Dendroidal and vertic properties. of the continuity of cementation/ P Pisolithic The layer is largely constructed from compaction. natric and VO Voids spodic horizon → Lamellic BR Bridges between sand grains qualifier. as coatings → petroduric CI Continuous irregular (non-uniform. structure. agent and C Continuous The layer is more than 90 percent degree. PH Horizontal pedfaces CF Coarse fragments ¸ Illuviation in the form of LA Lamellae (clay bands) lamellae in the argic. DC Discontinuous circular O Other ¸ Evidence of clay illuviation → argic and natric horizons. D Nodular The layer is largely constructed from cemented nodules or concretions of irregular Structure shape. The fabric or structure of the cemented or compacted layer may be described as per Table 70. Compacted material has a firm or stronger consistence when moist and a close packing of particles. TABLE 69 Classification of the continuity of cementation/compaction Cementation and compaction B Broken The layer is less than 50 percent cemented The occurrence of cementation or or compacted. Cemented material does TABLE 70 not slake after 1 hour of immersion Classification of the fabric of the cemented/compacted in water.g. ¸ Cracked coatings on sand grains TABLE 68 → spodic horizon. Table 69 indicates the classification V Vesicular The layer has large. equidimensional voids that may be filled with uncemented material. compaction in pans or otherwise is D Discontinuous The layer is 50–90 percent cemented or described according to its nature. cemented spherical nodules. continuity. P Pedfaces ¸ Clay coatings in the argic PV Vertical pedfaces horizon → Cutanic qualifier. Classification of the location of coatings and clay ¸ Uncoated sand and silt grains → accumulation Greyic qualifier. . layer P Platy The compacted or cemented parts are plate- like and have a horizontal or subhorizontal Continuity orientation. and in general shows a regular appearance.

as indicated in KQ Carbonates–silica F Iron Table 71. ¸ Cementation on repeated wetting and drying → plinthic horizon. Y Compacted but non-cemented Compacted mass is appreciably harder or more brittle than other comparable soil mass (slakes in water). ¸ Strongly cemented or indurated horizon consisting of clods with an average horizontal length of < 10 cm → Fractipetric and Fractiplinthic qualifiers. ¸ Iron pan that is 1–25 mm thick and is continuously cemented by a combination of organic matter.Chapter 4 – Soil description 57 Nature TABLE 71 The nature of cementation or Classification of the nature of cementation/compaction compaction is described according K Carbonates to the cementing agent or Q Silica compacting activity. Petrogleyic and Petrosalic qualifiers. but can be broken in the hands. petroduric and petrogypsic horizons. ¸ Strongly cemented or indurated → petrocalcic. ¸ Cementation by organic matter and aluminium → spodic horizon. Petric. W Weakly cemented Cemented mass is brittle and hard. . M Moderately cemented Cemented mass cannot be broken in the hands but is discontinuous (less than 90 percent of soil mass). TABLE 72 Classification of the degree of cementation/compaction N Non-cemented and non-compacted Neither cementation nor compaction observed (slakes in water). ¸ Natural or artificial compaction → Densic qualifier. duric. FM Iron–manganese (sesquioxides) FO Iron–organic matter Degree I Ice Table 72 indicates the classification GY Gypsum of the degree of cementation/ C Clay compaction. CS Clay–sesquioxides M Mechanical Note for classification purposes P Ploughing ¸ Ice overlain by organic material NK Not known → Histosols. gypsic and plinthic horizons. I Indurated Cemented mass cannot be broken by body weight (75-kg standard soil scientist) (more than 90 percent of soil mass). ¸ Cementation by ice or readily visible ice crystals → cryic horizon. ¸ Roots cannot penetrate except along vertical fractures that have an average horizontal spacing of ≥ 10 cm and occupy < 20 percent (by volume) of the layer → petrocalcic. ¸ ≥ 75 percent ice (by volume) → Glacic qualifier. iron and/or aluminium → Placic qualifier. C Cemented Cemented mass cannot be broken in the hands and is continuous (more than 90 percent of soil mass). ¸ Cemented spodic horizon → Ortsteinic qualifier.

size. kind. T Crystal The mineral concentrations are C Concretion A discrete body with a concentric described according to their internal structure. Table 77 provides some examples. M Medium 6–20 F Flat C Coarse > 20 I Irregular A Angular Hardness Table 76 describes the classification of the hardness of mineral concen- TABLE 76 trations. irregular M Many 15–40 concentrations (mottles). (or soft in colour and composition but is not accumulation) easily separated as a discrete body. Abundance (by volume) N Nodule Discrete body without an internal organization. Gradual transitions exist with mottles (above). according to the composition or impregnating substance. microcrystalline and V Very few 0–2 amorphous concentrations of non- F Few 2–5 organic substances as infillings. abundance. TABLE 75 Classification of the size and shape of mineral concentrations Size and shape Size (mm) Shape Table 75 describes the classification V Very fine <2 R Rounded (spherical) of the size and shape of mineral F Fine 2–6 E Elongated concentrations. IC Crack infillings R Residual rock Discrete impregnated body still fragment showing rock structure. .58 Guidelines for soil description TABLE 73 Mineral concentrations Classification of the abundance of mineral concentrations. generally cemented. some TABLE 74 of which may be considered as Classification of the kinds of mineral concentrations weak expressions of nodules. Mineral concentrations cover by volume a large variety of secondary % N None 0 crystalline. Kind O Other Table 74 describes the classification of the kinds of mineral concen- trations. Table 73 describes the classification IP Pore infillings Including pseudomycelium of of the abundance of mineral carbonates or opal. Nature S Soft Can be broken between forefinger and thumb nail Mineral concentrations are described B Both hard and soft. SC Soft concretion S Soft segregation Differs from the surrounding soil mass hardness. nodules A Abundant 40–80 D Dominant > 80 of mainly pedogenetically formed materials. shape. C Common 2–15 soft concretions. concentrations. Classification of the hardness of mineral concentrations H Hard Cannot be broken in the fingers. nature and colour.

additional information can be noted. Q Silica (siliceous) silica-enriched nodules F Iron (ferruginous) (durinodes) → duric horizon. expressed in the number of roots per decimetre square.Chapter 4 – Soil description 59 Colour TABLE 77 The general colour names given in Examples of the nature of mineral concentrations K Carbonates (calcareous) Table 78 are usually sufficient to KQ Carbonates–silica describe the colour of the nodules C Clay (argillaceous) (similar to mottles) or of artefacts. The abundance of roots can only be compared within the same size class. TABLE 78 ¸ Firm to weakly cemented Colour names of mineral concentrations nodules or mottles with a WH White stronger chroma or redder hue RE Red RS Reddish than the surrounding material YR Yellowish red → plinthic horizon. BR Brown ¸ Strongly cemented or indurated BS Brownish RB Reddish brown reddish to blackish nodules → YB Yellowish brown pisoplinthic horizon. Abundance Table 80 indicates the classification of the abundance of roots. In specific cases. is recorded. YE Yellow RY Reddish yellow GE Greenish BIOLOGICAL ACTIVITY GR Grey In this section. . including BU Blue BB Bluish-black human activity. FM Iron–manganese (sesquioxides) ¸ Reddish to blackish nodules of M Manganese (manganiferous) NK Not known which at least the exteriors are at least weakly cemented or indurated → ferric horizon. Size (diameter) Table 79 indicates the classification of the size of roots. The abundance of fine and very fine roots may be recorded similarly as for voids (Figure 8). BL Black MC Multicoloured Roots The recording of both the size and the abundance of the roots is in general sufficient to characterize the distribution of roots in the profile. such as a sudden change in root orientation. evidence of past or GS Greyish present biological activity. CS Clay–sesquioxides GY Gypsum (gypsiferous) SA Salt (saline) Note for classification purposes GB Gibbsite ¸ ≥ 10 percent (by volume) of JA Jarosite S Sulphur (sulphurous) weakly cemented to indurated.

and MC. or (ii) brought to the surface by human activity . Classification of the abundance of roots < 2 mm > 2 mm N None 0 0 Abundance V Very few 1–20 1–2 Abundance of biological activity is F Few 20–50 2–5 recorded in the general descriptive C Common 50–200 5–20 terms indicated in Table 81. BI Infilled large burrows C Charcoal E Earthworm channels HUMAN-MADE MATERIALS P Pedotubules With the growing human influence T Termite or ant channels and nests in the world. specific locations. patterns. amount. worm casts and burrows of F Fine 0. insect VF Very fine < 0.60 Guidelines for soil description TABLE 79 Other biological features Classification of the diameter of roots Biological features. TABLE 82 Examples of biological features ¸ ≥ 25 percent (by volume) of A Artefacts animal pores. N None F Few Note for classification purposes C Common ¸ ≥ 50 percent (by volume) of M Many wormholes. composition or any other characteristic may be TABLE 80 recorded. Their age. medium and coarse. 2006) are solid or liquid substances that are: (i) created or modified substantially by humans as part of an industrial or artisanal manufacturing process. casts or filled animal burrows → voronic horizon and Vermic qualifier. very fine and fine. medium. size. Note: Additional codes are: FF. M Many > 200 > 20 Kind TABLE 81 Examples of biological features are Classification of the abundance of biological activity given in Table 82. are described in C Coarse >5 terms of abundance and kind. coprolites or B Burrows (unspecified) other traces of animal activity BO Open large burrows → hortic and irragric horizons. Artefacts Artefacts (IUSS Working Group WRB. such as mm krotovinas.5–2 M Medium 2–5 larger animals. termite burrows. it becomes increasingly important to document the type and degree of influence. fine and In addition. especially in urban I Other insect activity and mining areas. Of particular importance are the human-made materials found in soils.5 nests. FM. state and composition determine to a large extent the duration of human influence and the environmental impact.

ÿ pavements and paving stones. ÿ If it has been transformed so that its origin is no longer identifiable. it is no longer an artefact. without substantial reworking or displacement by natural forces” (Rossiter. asphalt and lead shot. concrete. It has been defined as: “Human-transported material (abbreviation ‘HTM’): Any solid or liquid material moved into the soil from a source area outside of its immediate vicinity by intentional human activity. ÿ natural materials recognizably reworked by humans: flint knives and arrowheads. Some examples of artefacts are: ÿ synthetic solids (compounds not found in nature): slag and plastic. . such as coal. They have properties substantially different from the environment where they are placed. dredgings). and they have substantially the same properties as when first manufactured. ÿ mine spoil or crude oil Note for classification purposes ¸ ≥ 20 percent (by volume. 2004). by analogy to fluvial sediments and colluvium. for human settlement. ÿ It does not include mining overburden that has been influenced by surface processes or transported soil. by weighted average) artefacts → Technosols. spilled crude oil and bitumen. ÿ It includes excavated natural solids and liquids. ÿ The human origin must be evident in the material itself. ÿ waste liquids: sludges (e. bricks.g. usually with the aid of machinery. ÿ synthetic liquids: creosote and refined hydrocarbons.g. ÿ natural materials minimally processed but mixed in a way not found in nature: organic garbage. or simply to dispose of material that is unwanted in its original location (e. This can be for agricultural purposes (e. ÿ mixed materials: building rubble. not from written records or inference. This definition has several implications: ÿ “Liquid” includes chemicals of industrial origin.g. ÿ natural materials processed by humans into a form or composition not found in nature: pottery. large-scale terracing.Chapter 4 – Soil description 61 from a depth where they were not influenced by surface processes. modified or excavated. Human-transported material (HTM) Human-transported material (HTM) is any material in the soil to be classified brought from “outside”. often by machinery. brewery and municipal). ÿ industrial dusts (both natural and synthetic). It is a parent material for pedogenesis. mine spoil re-vegetation).

may be used as an indication of where to find HTM but it is not diagnostic. a soil layer may consist of part HTM and part non-transported (but reworked in situ) material. site plans. this is the same as for fluvic sediments. Thus.g.g.g. and it is no longer HTM.g. compaction. by frost). ÿ “Liquids” can be of any viscosity and include slurries. ÿ Similarly.g. which must be identified only from morphology. not from records of flooding. not from historical records. Note for classification purposes ¸ HTM → Transportic qualifier. voids. if the material is substantially reworked in situ (e. “colluvium from HTM”. ÿ by absence of pedogenesis that masks evidence of deposition. HTM may have substantial pedogenesis and still be identified as such. Geomembranes and technic hard rock A geomembrane (IUSS Working Group WRB. It could be referred to as “cyroturbated soil material originally human-transported”. layering from flooding) or reworking in situ (e. the human influence is reduced. cryoturbation). and disorganized fragments of diagnostic horizons). the human influence is reduced. ÿ The requirement that materials be moved farther than from the “immediate vicinity” excludes materials from ditching. e. ÿ by absence of evidence of transportation by natural forces (e. etc. liquid manures. Historical evidence. spoil that is partially ploughed into underlying natural soil. the “transportation” is too local. where the transported material is placed as close as possible to the source. It is a different substrate and could be referred to as e. ÿ by artefacts (not always present). The intention must be inferred from the type of material and manner of deposition.g. slumps) caused by human activity. and so it is no longer HTM. In each case. HTMs may be identified in several ways: ÿ by evidence of deposition processes after transportation (e. the classifier must state the specific evidence for HTM. ÿ If material originally transported by humans has been further moved by natural forces. such as erosion (water or wind) or flooding.g.62 Guidelines for soil description The definition has several implications: ÿ The restriction to “intentional” excludes dusts from wind erosion or mass movement (e. 2006) is consolidated material resulting . terracing.g. e. although isolated artefacts may be mixed into non-transported soil by ploughing or bioturbation. 2006) is a synthetic membrane laid on the surface or into the soil or any other substrate. Technic hard rock (IUSS Working Group WRB. hydrocarbons and other industrial chemicals transported by humans. HTM may be mixed with non-transported material. Many geomembranes are made of polyvinyl chloride (PVC) or high-density polyethylene (HDPE).

Hardness Hardness is described with the same rules as for mineral nodules (above). with properties substantially different from those of natural materials. Note for classification purposes TABLE 83 Classification of kinds of artefacts ¸ ≥ 35 percent of the artefacts AN Artesanal natural material consisting of organic waste ID Industrial dust materials → Garbic qualifier. rubble. Size Size is described with the same rules as for rock fragments (above) or mineral nodules (above). SL Synthetic liquid SS Synthetic solid dredgings. if applicable. weathering stage. Abundance Abundance is described with the same rules as for rock fragments (above). ¸ Technic hard rock starting within 5 cm of the soil surface and covering ≥ 95 percent of the horizontal extent of the soil → Technosols with the Ekranic qualifier. MM Mixed material ¸ ≥ 35 percent of the artefacts OG Organic garbage consisting of industrial PS Pavements and paving stones waste materials (mine spoil. Note for classification purposes ¸ A continuous. size. very slowly permeable to impermeable. Colour Colour is described with the same rules as for mineral nodules (above). hardness. . constructed geomembrane starting within 100 cm of the soil surface → Technosols with the Linic qualifier. Description of artefacts Artefacts are described according to their abundance.) → WL Waste liquid Spolic qualifier. etc. and colour. kind. Weathering State of weathering of the material is described with the same rules as for rock fragments (above).Chapter 4 – Soil description 63 from an industrial process. Kind Table 83 lists the kinds of artefacts classified.

. H2S smell dredge mud of lakes .UA1 e) dark grey to black. regardless of the horizon they are taken from (some may not be sampled while others may be sampled twice).UU5 h) > 30 percent pieces of grey to reddish-brown slag slag .e.. (dumped substrate) 2 Test for colour and texture a) light to dark grey. fine sand to silt. fine sand to silt.UA1 d) dark grey to black. NH3 smell..UA1 b) loamy.... D. C..) and depth range at which each sample has been collected from top to bottom.UU2 f) mainly gravel gravel .UU3 d) clayey clay .. SAMPLING The sample code and sampling depth are given.. It is recommended that the number given to the sample be the profile number followed by an additional capital letter (A.. it occupies more than 50 percent (by volume) of the soil. small Fe/Mn concretions dredge mud of rivers . H2S smell... The weight of material taken for each sample is usually 1 kg. artefacts faecal sludge . ¸ ≥ 35 percent of the artefacts consisting of rubble and garbage of human settlements → Urbic qualifier.UU1 e) mixture of sand. artefacts sewage sludge . visible particles of coal coke mud .UA2 3 Test for texture.. silt and clay loam . coarser grains have vesicular pores fly and bottom ash . B. humic (grey to blackish grey) topsoil material . plastic..UA2 i) > 30 percent pieces of bricks and mortar and concrete construction rubble .. leather. faecal smell. texture and/or artefacts go to step 3 d.UA2 wood...64 Guidelines for soil description TABLE 84 Determination table and codes for human-made deposits 1 Observation at the profile a) stratified (spoiled materials) go to step 2 s. shortened. i......UA2 b) dark grey to black. waste ....UA2 j) grey to black. Use the determination table (Table 84) and record the code.UA2 c) light to dark brown.. consistence and colour a) earthy. it is sufficient to identify the type of HTM. ..UU5 g) mainly broken rock broken rock ... Description and determination of human-transported material Where HTM is dominant. Horizon symbols should not be used as sample codes because the horizon classifications may be changed later... metals) Source: According to Meuser (1996)..UU3 c) mainly sandy sand . b) not stratified but clods of different colour. etc.. > 30 percent artefacts (glass.. ceramic.UA2 f) dark grey to black. Samples are never taken across horizon boundaries. with carbonates calcareous loam ...

A 0–20 cm.Chapter 4 – Soil description 65 There are basically two methods of collecting samples: ÿ To collect the sample in equal proportions over the whole horizon. In both methods. To indicate the occurrence of an argic horizon that is defined as having a specified clay increase over a vertical distance of 15 or 30 cm. Depth criteria of diagnostic horizons and properties should be taken into account in determining the depth of sampling.g. the samples are preferably taken at that depth interval (e. In detailed descriptions of soils with horizons no more than 30–40 cm thick. if more than one sample is to be taken from the same horizon. . This is the recommended method and should be used for reference (Status 1) descriptions where a dense sampling is required. ÿ To take the sample in equal proportions within a depth of 20 cm. Another example is for the classification of Nitisols: a sample should be taken at a depth of 140–160 cm. This will facilitate comparison of topsoil characteristics in soil inventories and land evaluation. or shallower where the horizon depth is less. at balanced intervals. either from the centre (area of maximum expression) of the horizon. there will be little difference between the two methods in practice. the sampling depth for a soil with a solum more than 60 cm thick may be more than 20 cm but not exceeding 30 cm. If the presence of a mollic horizon is assumed. It is recommended that the topsoil be sampled within the first 20 cm of the surface. or. in addition to the one taken from that part of the B horizon where the clay content is assumed to be highest. B 20–30 cm or 30–50 cm). the boundary area itself should not be sampled.

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L and W represent the master horizons or layers in soils or associated with soils. it is essential that correct horizon symbols be given. Master horizons and layers The capital letters H. ten master horizons and layers and seven transitional horizons are recognized. the soil morphological and other characteristics are presented as they are described by horizon. B. E. C. An H horizon may be on top of mineral soils or at any depth beneath the surface if it is buried. Genetic horizons are not equivalent to diagnostic horizons. In this chapter. For the presentation and understanding of the soil profile description. All H horizons are saturated with water for prolonged periods. O. I. and W for water layers. although they may be identical in soil profiles. I for ice. 67 Chapter 5 Genetic and systematic interpretation – soil classification SOIL HORIZON DESIGNATION The soil horizon designation summarizes many observations of the soil description and gives an impression about the genetic processes that have formed the soil under observation. Horizon symbols consist of one or two capital letters for the master horizon and lower case letter suffixes for subordinate distinctions. Three additional layers associated with some soils are identified. Currently. viz. Most horizons and layers are given a single capital letter symbol. R. Diagnostic horizons are quantitatively defined features used in classification. Most are genetic soil horizons. but some require two. L for limnic materials. H horizons or layers These are layers dominated by organic material formed from accumulations of undecomposed or partially decomposed organic material at the soil surface. A. with or without a figure suffix. The capital letters are the base symbols to which other characters are added in order to complete the designation. The master horizons and their subdivisions represent layers that show evidence of change and some layers that have not been changed. or were once saturated but are now drained artificially. which may be underwater. . reflecting a qualitative judgement about the kind of changes that have taken place.

recent alluvial or aeolian deposits that retain fine stratification are not considered to be an A horizon unless cultivated. or similar kinds of disturbance. twigs. However. A horizons These are mineral horizons that formed at the surface or below an O horizon. the undisturbed surface horizon is less dark than the underlying horizon and contains only small amounts of organic matter. O horizons are not saturated with water for prolonged periods. ÿ a morphology that is different from the underlying B or C horizon. that has accumulated on the surface. needles. An O layer may be at the surface of a mineral soil or at any depth beneath the surface where it is buried. in which all or much of the original rock structure has been obliterated and which are characterized by one or more of the following: ÿ an accumulation of humified organic matter intimately mixed with the mineral fraction and not displaying properties characteristic of E or B horizons (see below). leaving a concentration of sand and silt particles. In some places. aluminium. Examples of epipedons that may have a different structure or morphology owing to surface processes are Vertisols. and soils in deserts. iron. It has a morphology distinct from the C layer. resulting from processes related to the surface. Such a horizon is designated A because it is at the surface. they may be on top of either mineral or organic soils. The mineral fraction of such material is only a small percentage of the volume of the material and is generally much less than half of the weight. and in which all or much of the original rock structure has been obliterated. ÿ properties resulting from cultivation. If a surface horizon (or epipedon) has properties of both A and E horizons but the dominant feature is an accumulation of humified organic matter. moss and lichens. soils in pans or playas with little vegetation. lighter in colour than an underlying B horizon. such as leaves. A horizon formed by illuviation of organic material into mineral subsoil is not an O horizon. but in many soils coatings of iron oxides or other compounds mask the colour of . although some horizons formed in this manner contain much organic matter. where warm and arid climates prevail. In some soils. but not necessarily. pasturing. although the mineral fraction may be unaltered or only slightly altered by weathering. it is designated an A horizon. E horizons These are mineral horizons in which the main feature is loss of silicate clay. An E horizon is usually. or some combination of these.68 Guidelines for soil description O horizons or layers These are layers dominated by organic material consisting of undecomposed or partially decomposed litter. the colour is that of the sand and silt particles.

and layers with gleying but no other pedogenetic changes. such as shells. Examples of layers that are not B horizons are: layers in which clay films either coat rock fragments or are on finely stratified unconsolidated sediments. or both. together with one or a combination of the following: ÿ illuvial concentration. Plant roots can penetrate C horizons. An E horizon is most commonly differentiated from an underlying B horizon in the same soil profile: by colour of higher value or lower chroma. blocky or prismatic structure if volume changes accompany changes in moisture content. gypsum or silica. C horizons or layers These are horizons or layers. excluding hard bedrock. or redder in hue than overlying and underlying horizons without apparent illuviation of iron. An E horizon is commonly near the surface. ÿ alteration that forms silicate clay or liberates oxides or both and that forms a granular. coral and diatomaceous earth. ÿ brittleness. subsurface horizons. of silicate clay. alone or in combination. E or B horizons. such as prismatic structure or illuvial accumulation of clay. The material of C layers may be either like or unlike that from which the solum presumably formed. H or O horizon. and unconsolidated bedrock and other geological materials that commonly slake within 24 hours when air dry or . whether the films were formed in place or by illuviation. gypsum or silica that are the result of pedogenetic processes (these layers may or may not be cemented) and brittle layers that have other evidence of alteration. or were originally. All kinds of B horizons are. O. However. that are little affected by pedogenetic processes and lack properties of H. by coarser texture. the symbol E may be used without regard to position in the profile for any horizon that meets the requirements and that has resulted from soil genesis. iron. B horizons These are horizons that formed below an A. which provide an important growing medium. Included as C layers are sediments. E. ÿ residual concentration of sesquioxides. ÿ coatings of sesquioxides that make the horizon conspicuously lower in value. aluminium. or by a combination of these properties. humus. higher in chroma. A C horizon may have been modified even where there is no evidence of pedogenesis. are included. below an O or A horizon and above a B horizon. ÿ evidence of removal of carbonates.Chapter 5 – Genetic and systematic interpretation – soil classification 69 the primary particles. and in which the dominant features are the obliteration of all or much of the original rock structure. layers into which carbonates have been illuviated but that are not contiguous to an overlying genetic horizon. but some siliceous and calcareous layers. A. saprolite. Included as B horizons are layers of illuvial concentration of carbonates. Most are mineral layers. carbonates.

also known as limnic material. as in tidal flats. diatomaceous earth (mostly siliceous). although it may be chipped or scraped. as in the case of shallow lakes. but these are so few and so small that few roots can penetrate. Granite. Ice bodies in soils can grow to such an extent that they form lenses of wedges that separate entire soil layers. carbonates or gypsum. 2003). The R layer is sufficiently coherent when moist to make hand digging with a spade impractical. In such cases. Layers having accumulations of silica. and such material that does not meet the requirements of A. Limnic material is either: (i) deposited by precipitation or through action of aquatic organisms. such as algae or diatoms.e. or cyclic. even if indurated. or (ii) derived from underwater and floating aquatic plants and subsequently modified by aquatic animals (USDA Soil Survey Staff. L layers include coprogenous earth or sedimentary peat (mostly organic).70 Guidelines for soil description drier chunks are placed in water and when moist can be dug with a spade. Some soils form in material that is already highly weathered. shallow water (i. Air-dry or drier chunks of an R layer when placed in water will not slake within 24 hours. quartzite and indurated limestone or sandstone are examples of bedrock that are designated R. I layers These are ice lenses and wedges that contain at least 75 percent ice (by volume) and that distinctly separate organic or mineral layers in the soil. they can be designated as an I layer. Changes not considered pedogenetic are those not related to overlying horizons. In other cases. The cracks may be coated or filled with clay or other material. R layers These consist of hard bedrock underlying the soil. W layers These are water layers in soils or water submerging soils. The I symbol is not used in transitional horizon designations. water not deeper than 1 m) may cover the soil permanently. then it is a B horizon. either permanently or cyclic within the time frame of 24 hours. may be included in C horizons unless the layer is obviously affected by pedogenetic processes. basalt. E or B horizons is designated C. Ice comes and goes in soils in areas affected by permafrost. The bedrock may contain cracks. the W symbol may be used at the end of the soil description to indicate the floating character. where ice concentrations occur within the depth of soil description. Some R layers can be ripped with heavy power equipment. L layers These are sediments deposited in a body of water (subaqueous) composed of both organic and inorganic materials. The symbol W is then used . Some organic soils float on water. The L symbol is not used in transitional horizon designations. and marl (mostly calcareous). In case such.

For example. Subordinate characteristics within master horizons and layers Designations of subordinate distinctions and features within the master horizons and layers are based on profile characteristics observable in the field and are applied during the description of the soil at the site. Lower case letters are used as suffixes to designate specific kinds of master horizons and layers. it is transitional to assumed parent material. a horizon can be designated as transitional even if one of the master horizons to which it is apparently transitional is not present. A BE horizon may be recognized in a truncated soil if its properties are similar to those of a BE horizon in a soil in which the overlying E horizon has not been removed by erosion. Highly decomposed organic material has less than one-sixth (by volume) visible plant remains. EB. Commonly. Highly decomposed organic material: Used with H and O horizons only. b. but the two capital letters are separated by a virgule (/). A BC horizon may be recognized even if no underlying C horizon is present. two capital letter symbols are used. The symbol is not used in organic soils or to separate an organic layer from a mineral layer. The master horizon symbol that is given first designates the kind of horizon whose properties dominate the transitional horizon. in cryoturbated soils. An AB or a BA horizon may be recognized where bedrock underlies the transitional horizon. Horizons in which distinct parts have recognizable properties of two kinds of master horizons are indicated as above. B/C and C/R. Genetic horizons may or may not have formed in the overlying materials. The list of symbols and terms is shown in Table 85 and explanations of them are given below: a. such as AB. A CR horizon can be used for weathered bedrock that can be dug with a spade although roots cannot penetrate except along fracture planes. but it is more like the A than like the B. For horizons dominated by properties of one master horizon but having subordinate properties of another. which may be either like or unlike the assumed parent materials of the buried soil. or with C horizons. The I.Chapter 5 – Genetic and systematic interpretation – soil classification 71 to indicate the depth of submergence at the start of the horizon or layer sequence. such as E/B. In some cases. and those with the two properties separate. Transitional horizons There are two kinds of transitional horizons: those with properties of two horizons superimposed. B/E. L and W symbols are not used in transitional horizon designations. . BE and BC. to indicate the state of decomposition of the organic material. most of the individual parts of one of the components are surrounded by the other. an AB horizon has characteristics of both an overlying A horizon and an underlying B horizon. Buried genetic horizon: Used in mineral soils to indicate identifiable buried horizons with major genetic features that were formed before burial. The occurrence of tidal water can be indicated by (W). and other features.

Coprogenous earth: With limnic material L it denotes coprogenous earth.72 Guidelines for soil description TABLE 85 Subordinate characteristics within master horizons Suffix Short description Used for a Highly decomposed organic material H and O horizons b Buried genetic horizon mineral horizons. mostly earthy material that is non-cemented. organic materials deposited under water and dominated by faecal material from aquatic animals. it is used . E. O. Dense layer: Used in mineral soils to indicate a layer of relatively unaltered. E. not with m d Diatomaceous earth L horizon e Moderately decomposed organic material H and O horizons f Frozen soil not in I and R horizons g Stagnic conditions no restriction h Accumulation of organic matter mineral horizons i Slickensides mineral horizons i Slightly decomposed organic material H and O horizons j Jarosite accumulation no restriction k Accumulation of pedogenetic carbonates no restriction l Capillary fringe mottling (gleying) no restriction m Strong cementation or induration (pedogenetic. the symbol is not used in combination with the symbols m (cementation) and x (fragipan). A.e. d. Concretions or nodules: In mineral soil. massive) mineral horizons m Marl L horizon n Pedogenetic accumulation of exchangeable sodium no restriction o Residual accumulation of sesquioxides (pedogenetic) no restriction p Ploughing or other human disturbance no restriction. it indicates a significant accumulation of concretions or nodules. The nature and consistence of the nodules is specified by other suffixes and in the horizon description. but that has such bulk density or internal organization that roots cannot enter except in cracks. i. not cryoturbated c Concretions or nodules mineral horizons c Coprogenous earth L horizon d Dense layer (physically root restrictive) mineral horizons. Diatomaceous earth: In combination with limnic material L. B or C as Ap q Accumulation of pedogenetic silica no restriction r Strong reduction no restriction s Illuvial accumulation of sesquioxides B horizons t Illuvial accumulation of silicate clay B and C horizons u Urban and other human-made materials H. B and C horizons v Occurrence of plinthite no restriction w Development of colour or structure B horizons x Fragipan characteristics no restriction y Pedogenetic accumulation of gypsum no restriction z Pedogenetic accumulation of salts more soluble than gypsum no restriction @ Evidence of cryoturbation no restriction c.

The layer is root restrictive and roots do not enter except along fracture planes. by both lime and silica. l. qm. wedge-shaped peds and seasonal surface cracks are commonly present. and by salts more soluble than gypsum.e. it indicates the state of decomposition of the organic material. the interiors of the aggregates show oxidizing colours and the surface parts reducing colours. oblique shear faces 20–60 º of horizontal owing to the shrink–swell action of clay.e. g. If the horizon is cemented by carbonates km is used. i. Frozen soil: Designates horizons or layers that contain permanent ice or are perennially colder than 0 °C. although they may be fractured. Slickensides: Denotes in mineral soils the occurrence of slickensides. “dry frozen soil” layers may be labelled (f). the interiors of the aggregates show reducing colours and the surface parts oxidizing colours.e. i. The accumulation may occur in surface horizons. e. n. Marl: In combination with limnic material it is used to indicate marl. commonly calcium carbonate. If aggregates are present. materials deposited under water and dominated by the siliceous remains of diatoms. i. i. If needed. zm. Moderately decomposed organic material has between one-sixth and two- thirds (by volume) visible plant remains. by iron. ym. by silica. and is used only for horizons that are more than 90 percent cemented.Chapter 5 – Genetic and systematic interpretation – soil classification 73 to indicate diatomaceous earth. Strong cementation or induration: Indicates in mineral soils continuous or nearly continuous cementation. Slightly decomposed organic material: In organic soils and used in combination with H or O horizons. Moderately decomposed organic materials: Used with H and O horizons only. j. Capillary fringe mottling: Indicates mottling caused by ascending groundwater. kqm. typically grey in colour. It is not used for seasonally frozen layers or for bedrock layers (R). sm. slightly decomposed organic material has in more than two-thirds (by volume) visible plant remains. Accumulation of organic matter: Designates the accumulation of organic matter in mineral horizons. coatings or hypodermic coatings. . Stagnic conditions: Designates horizons in which a distinct pattern of mottling occurs that reflects alternating conditions of oxidation and reduction of sesquioxides. k. Jarosite: Indicates the presence of jarosite mottles. to indicate the state of decomposition of the organic material. materials deposited under water and dominated by a mixture of clay and calcium carbonate. caused by seasonal surface waterlogging. Pedogenetic accumulation of exchangeable sodium: Indicates an accumulation of exchangeable sodium. or in subsurface horizons through illuviation. If aggregates are present. Accumulation of pedogenetic carbonates: Indicates an accumulation of alkaline earth carbonates. The single predominant or codominant cementing agent may be indicated using defined letter suffices single or in pairs. h. by gypsum. f.

E. O. The symbol is also used in combination with h as Bhs if both the organic matter and sesquioxides components are significant and both value and chroma are about 3 or less.Development of colour or structure in B: Used with B only to indicate development of colour or structure. A. even though clearly once an E. Residual accumulation of sesquioxides: Indicates residual accumulation of sesquioxides. it is no longer called plinthite but a hardpan. B and C. dispersible organic matter–sesquioxide complexes if the value and chroma of the horizon are more than 3. If r is used with B. It differs from the use of symbol s. v is used in combination with m. but some horizons designated x do not have all the properties of a fragipan. s. amorphous. pedogenetic change in addition to reduction is implied. humus-poor material that is firm or very firm when moist and that hardens irreversibly when exposed to the atmosphere. as lamellae. u. or as bridges between mineral grains. brittleness or high bulk density. the horizon is designated Cr. a petroferric or a skeletic phase. q. which indicates illuvial accumulation of organic matter and sesquioxide complexes. sorted rock fragments (patterned ground). B or C. p. ironstone. v. t. If silica cements the layer and cementation is continuous or nearly continuous. w. The symbol can be used in combination with H. Urban and other human-made materials: Used to indicate the dominant presence of human-made materials. z. including technogenic ones. r. It is not used to indicate a transitional horizon. or both. A disturbed organic horizon is designated Op or Hp. or both. is designated Ap. These features are characteristic of fragipans. Accumulation of silicate clay: Used with B or C to indicate an accumulation of silicate clay that either has formed in the horizon or has been moved into it by illuviation. qm is used.74 Guidelines for soil description o. In that case. When hardened. if no other change has taken place. Fragipan characteristics: Used to indicate genetically developed firmness. Ploughing or other human disturbance: Indicates disturbance of the surface layer by ploughing or other tillage practices. Illuvial accumulation of sesquioxides: Used with B to indicate the accumulation of illuvial. y. Pedogenetic accumulation of gypsum: Indicates an accumulation of gypsum. or organic matter in the lower boundary . Pedogenetic accumulation of salts more soluble than gypsum: Indicates an accumulation of salts more soluble than gypsum. At least some part should show evidence of clay accumulation in the form of coatings on ped surfaces or in pores. @ Evidence of cryoturbation: irregular or broken boundaries. x. Occurrence of plinthite: Indicates the presence of iron-rich. Strong reduction: Indicates presence of iron in reduced state. A disturbed mineral horizon. Accumulation of pedogenetic silica: Indicates an accumulation of secondary silica.

is designated Bt (t has precedence over w. If illuvial clay is also present. z or o unless needed for explanatory purposes.g. y. n.g. Some examples: Btc. The suffix is always used last. silica. Conventions for using letter suffixes Many master horizons and layers that are symbolized by a single capital letter will have one or more lowercase letter suffixes. m.g. Bd indicates a dense B horizon. C2. In all other combinations. e. q. Similarly. e. g. or both.g. y. ÿ A B horizon that has significant accumulation of clay and also shows evidence of development of colour or structure. s and w are normally not used with g. ÿ If more than one suffix is needed and the horizon is not buried. which follow all the letters. ÿ If a horizon is buried. For example. The following rules apply: ÿ Letter suffixes should follow the capital letter immediately. if used.. z or o. ÿ Suffix @ is always used last. the following letters. ÿ Suffixes a and e are used only in combination with H or O. gypsum. suffixes are listed alphabetically. t. i and m have two different meanings. e. ÿ Suffixes c. these symbols. or residual accumulation or sesquioxides carries the appropriate symbol g. ÿ Suffixes h. colour or texture. and Bsv. are written first: r. A B horizon that is gleyed or that has accumulations of carbonates. Btu. depending on the master horizon designation they are coupled to. k. the suffix b is written last. within a C. The symbol t has precedence over all other symbols. Hi@. Btr. n. ÿ When more than one suffix is needed. e. The different combinations are mutually exclusive. are written last: c. or if the lower part is gleyed and the upper part is not. etc. These conventions apply whatever the purpose of subdivision. successive layers could be C1. v and x. q. sodium.g. such as structure. s. More than three suffixes are rarely used. the designations could be C1-C2-Cg1-Cg2 or C-Cg1-Cg2-R. d. and cannot be combined with b. whereas Hi indicates a slightly decomposed H horizon. Bto. ÿ Unless otherwise indicated. u and w. e. t precedes the other symbols. A horizon identified by a single set of letter symbol may be subdivided on the basis of evident morphological features. These subdivisions are numbered consecutively. and Ld diatomaceous earth in a limnic layer. f. if used.Chapter 5 – Genetic and systematic interpretation – soil classification 75 between the active layer and permafrost layer. the symbols are listed alphabetically. salts more soluble than gypsum. C3. Bi indicates presence of slickensides in the B horizon. s and h). Cru. Bkm. The numbering starts with 1 at whatever level in the . Vertical subdivisions Horizons or layer designated by a single combination of letter symbols can be subdivided using Arabic numerals. k.

the Arabic number prefix is not used. The numbers indicate a change in the material. Where two or more consecutive horizons formed in one kind of material. the same prefix number applies to all of the horizon designations in that material: Ap-E-Bt1-2Bt2-2Bt3-2BC. Eg1. the number prefix is used. Ap1. not Bs1-Bs2-2Bs1-2Bs2. Ap2. the uppermost material in a profile having two or more contrasting materials is understood to be material 1. not Bt1-Bt2-Btk3-Btk4. Thus.76 Guidelines for soil description profile. A2. Symbols to identify discontinuities are used only when they will contribute substantially to the reader’s understanding of relationships among horizons. However.g. A prefix is not used to distinguish material of such buried horizons. Even where a layer below material 2 is similar to material 1. Arabic numerals are used as prefixes to indicate discontinuities. A3. If part of the solum formed in residuum. Discontinuities In mineral soils. Ap. The number suffixes designating subdivisions of the Bt horizon continue in consecutive order across the discontinuity. The numbering of vertical subdivisions within a horizon is not interrupted at a discontinuity (indicated by a numerical prefix) if the same letter combination is used in both materials: Bs1-Bs2-2Bs3-2Bs4 is used. E. If the R layer would not produce material like that in the solum. a prefix is omitted from the symbol. B. not the type of material. e. but the number is omitted. A discontinuity is a significant change in particle-size distribution or mineralogy that indicates a difference in the material from which the horizons formed or a significant difference in age or both. C and R. R is given the appropriate prefix: Ap-Bt1-2Bt2- 2Bt3-2C1-2C2-2R. Similarly. They are not used with I and W. Numbering starts with the second layer of contrasting material. unless that difference in age is indicated by the suffix b. some buried horizons formed in material lithological like that of the overlying deposit. they are used preceding A. E2. If the material in which a horizon of a buried soil formed is lithological unlike that of the . A1. Where a soil has formed entirely in one kind of material. although these symbols clearly indicate a discontinuity. These prefixes are distinct from Arabic numerals used as suffixes to denote vertical subdivisions. A and E horizons can be subdivided similarly. A buried horizon is not the same deposit as horizons in the overlying deposit. as in A-Bt-C-2R or A-Bt-2R. Wherever needed. which is designated 2. Eg2. Buried horizons (designated b) are special problems. The stratification common in soils formed in alluvium is not designated as discontinuities unless particle-size distribution differs markedly from layer to layer even though genetic horizons have formed in the contrasting layers. A2. A1. it is designated 3 in the sequence. Underlying contrasting layers are numbered consecutively. and E1. Bt1-Bt2-Btk1-Btk2 is used. If an R layer is below a soil that formed in residuum and the material of the R layer is judged to be like that from which the material of the soil weathered. the whole profile is material 1.

the differences are shown by the letter suffix designations. . To make communication easier. Rarely. if the different layers are organic. It is recommended that the occurrence and depth of diagnostic horizons. The prime is used only to distinguish two or more horizons that have identical symbols: O-C-C’-C’’. properties and materials. be used as differentiating criteria. It is recognized that an understanding of soil- forming processes contributes to a better characterization of soils but that they should not. or by the master symbol if the different layers are mineral. The final classification is made after the analytical data have become available. The prime is applied to the capital letter designation. in dynamic combination with soil properties. which to the greatest extent possible should be measurable and observable in the field. ÿ Climate parameters are not applied in the classification of soils. The prime is not used unless all letters of the designations of two different layers are identical. The same principle applies in designating layers of organic soils. Use of the prime Identical designations may be appropriate for two or more horizons or layers separated by at least one horizon or layer of a more different kind in the same pedon. The prime is added to the lower C layer to differentiate it from the upper. ÿ To the extent possible at a high level of generalization. The general principles on which the classification according to the WRB is based (IUSS Working Group WRB 2006)can be summarized as follows: ÿ The classification of soils is based on soil properties defined in terms of diagnostic horizons. In organic soils. It is fully realized that they should be used for interpretation purposes. the discontinuity is designated by number prefixes and the symbol for a buried horizon is used as well: Ap-Bt1-Bt2-BC-C-2ABb-2Btb1- 2Btb2-2C. properties and materials identified be listed (below). diagnostic features are selected that are of significance for soil management. PRINCIPLES OF CLASSIFICATION ACCORDING TO THE WRB The surveyor should attempt to classify the soil in the field as precisely as possible on the basis of the soil morphological features that have been observed and described. In most cases. discontinuities between different kinds of layers are not identified. a prime is used with the master horizon symbol of the lower of two horizons having identical letter designations: A-E-Bt-E’-Btx-C. as such. The sequence A-E-Bt-E-Btx-C is an example – the soil has two E horizons. ÿ The selection of diagnostic characteristics takes into account their relationship with soil forming processes. three layers have identical letter symbols.Chapter 5 – Genetic and systematic interpretation – soil classification 77 overlying material. a double prime can be used: E’’. and any lower case symbol follows it: B’t. but they should not form part of soil definitions.

Although the basic framework of the FAO Legend (with its two categorical levels and guidelines for developing classes at a third level) was adopted. ÿ In addition to serving as a link between existing classification systems. published in 1998. could accommodate local diversity at country level. ÿ The Reference Base is not meant to substitute for national soil classification systems but rather to serve as a common denominator for communication at an international level. ÿ Definitions and descriptions of soil units reflect variations in soil characteristics both vertically and laterally in order to account for spatial linkages within the landscape. comprised 30 RSGs. the WRB also serves as a consistent communication tool for compiling global soil databases and for the inventory and monitoring of the world’s soil resources. They are defined precisely in order to avoid the confusion that occurs where names are used with different connotations. possibly a third category of the WRB. Its units have sufficient width to stimulate harmonization and correlation of existing national systems. ÿ The first edition of the WRB. This implies that lower-level categories. Concurrently. classes are differentiated mainly according to the primary pedogenetic process that has produced the characteristic soil features. allowing very precise characterization and classification of individual soil profiles. it has been decided to merge the lower levels.78 Guidelines for soil description ÿ The WRB is a comprehensive classification system that enables people to accommodate their national classification system. ÿ Many RSGs in the WRB are representative of major soil regions so as to provide a comprehensive overview of the world’s soil cover. published in 2006. the second edition. The broad principles that govern the WRB class differentiation are: ÿ At the higher categorical level. has 32 RSGs. It comprises two tiers of categorical detail: • the Reference Base. except where special soil parent materials are of overriding importance. ÿ The Revised Legend of the FAO/UNESCO Soil Map of the World (FAO. 1988) has been used as a basis for the development of the WRB in order to take advantage of international soil correlation that has already been conducted through this project and elsewhere. ÿ The term Reference Base is connotative of the common denominator function that the WRB assumes. ÿ The nomenclature used to distinguish soil groups retains terms that have been used traditionally or that can be introduced easily in current language. limited to the first level only and having 32 RSGs. consisting of combinations of a set of prefix and suffix qualifiers that are uniquely defined and added to the name of the RSG. from which the user can construct the second-level units. the lower levels emphasize soil features that are important for land use and management. Each RSG of the WRB is provided with a listing of possible prefix and suffix qualifiers in a priority sequence. • the WRB Classification System. .

classification is done in four steps. all applying qualifiers have to be added to the name of the RSG. Redundant qualifiers (the characteristics of which are included in a previously set qualifier) are not added. properties and materials is compared with the WRB Key (IUSS Working Group WRB. All other qualifiers are listed as suffix qualifiers. attributes are described as much as possible to support field identification. Including the soil description. soil units are differentiated according to any secondary soil-forming process that has affected the primary soil features significantly. In line with the WRB objectives. Step 1 The profile description is checked to find references to soil-forming processes (qualitatively) and express them in the horizon designation. ÿ Browning and finer texture in the middle part of a soil profile in comparison to the parent material → enrichment of Fe-oxides and clay → weathering → Bw-horizon. Step 2 The profile description and the horizon designation are to be checked whether the expression. thickness and depth of certain soil characteristics correspond with the requirements of WRB diagnostic horizons. The qualifiers are listed in the Key with each RSG as prefix and suffix qualifiers. Step 4 For the second level of WRB classification. qualifiers are used. However. The user should go through the Key systematically. which is the first level of WRB classification. . It is recognized that a number of RSGs may occur under different climate conditions. it was decided not to introduce separations on account of climate characteristics so that the classification of soils is not subordinated to the availability of climate data. starting at the beginning and excluding one by one all RSGs for which the specified requirements are not met. 2006) in order to find the RSG.Chapter 5 – Genetic and systematic interpretation – soil classification 79 ÿ At the second level. Prefix qualifiers comprise those that are typically associated to the RSG and the intergrades to other RSGs. soil characteristics that have a significant effect on use may be taken into account. Step 3 The described combination of diagnostic horizons. In certain cases. The soil belongs to the first RSG for which it meets all specified requirements. Examples may be: ÿ Darkening of topsoil in comparison to subsoil → enrichment with organic material → Ah-horizon. properties and materials. For classification at the second level. These are defined in terms of morphological characteristics and/or analytical criteria (IUSS Working Group WRB. 2006).

For mapping purposes.specifier. Prefix qualifier names are always put before the RSG. The qualifier listing for each RSG accommodates most cases. the scale will determine the number of qualifiers used.specifier and -ic added to the RSG name of the buried soil. In all other cases. (2) qualifiers related to chemical characteristics. listed in IUSS Working Group WRB (2006). Gleysol. if it stood alone. comprising: ÿ Prefix qualifiers: typically associated qualifiers and intergrade qualifiers. (4) qualifiers related to mineralogical characteristics.are used to indicate a certain expression of the qualifier. Vertisol. Principles and use of the qualifiers in the WRB A two-tier system is used for the qualifier level. the overlying material is indicated with the Novic qualifier. (3) qualifiers related to physical characteristics. The overlying new material and the buried soil are classified as one soil if both together qualify as Histosol. Technosol. Fluvisol. ÿ Suffix qualifiers: other qualifiers. (5) qualifiers related to surface characteristics. Combinations of qualifiers that indicate a similar status or duplicate each other are not permitted. In that case.and Ortho. Otherwise. If the buried soil is classified at the first level. (6) qualifiers related to textural characteristics. Where a soil is buried under new material. The whole is placed in brackets after the name of the overlying soil. Para-. which can be used with any qualifier. Where not listed qualifiers are needed. Proto-. Stagnosol or Arenosol. Hypo-. 4. Endo-. prefix qualifiers have priority over the suffix qualifiers. properties or materials. Hyper-.80 Guidelines for soil description Specifiers can be used to indicate the degree of expression of qualifiers. including coarse fragments. such as combinations of Thionic and Dystric. with the exception of Arenosols. and (8) remaining qualifiers. e. suffix qualifier names are always placed between brackets following the RSG name. Cryosol. Buried layers can be indicated by the Thapto. Thapto-. Technic Umbrisol (Greyic) (Thapto-Podzolic). If the overlying soil is classified at the first level. Planosol. the new material is classified at the first level if the new material is 50 cm or more thick or if the new material. 2. or Rhodic and Chromic. the following rules apply: 1. this intergrade is ranked with the textural suffix qualifiers (see below). Cumuli. all applying qualifiers of the listing must be recorded. Haplic closes the prefix qualifier list indicating that neither typically associated nor intergrade qualifiers apply. Specifiers such as Epi-. Calcaric and Eutric. . 3. Leptosol. the cases should be documented and reported to the WRB Working Group. fits the requirements of a RSG other than a Regosol. Andosol. sequenced as follows: (1) qualifiers related to diagnostic horizons. the buried soil is classified at the first level. the sequence of the intergrade qualifiers follows that of the RSGs in the WRB Key. (7) qualifiers related to colour. When classifying a soil profile. the buried soil is recognized with the Thapto. Bathy-.g.

The field classification of this soil is: Lixic Ferralsol (Ferric. TABLE 86 Checklist of WRB diagnostic horizons. Rhodic). PROPERTIES AND MATERIALS While still in the field. If subsequent laboratory analysis reveals that the cation exchange capacity of the ferralic horizon is less than 4 cmolc kg-1 clay. Rhodic). The pH is between 5. Table 86 provides a checklist of diagnostic horizons. 2006). properties and materials in the order as they appear in the WRB (IUSS Working Group WRB. It is recommended that Procedures for Soil Analysis (Van Reeuwijk. The B horizon is dark red. Reducing conditions Sulphidic material Folic horizon Sombric horizon Secondary carbonates Technic hard rock Fragic horizon Spodic horizon Stagnic colour pattern Tephric material Fulvic horizon Takyric horizon Vertic properties Gypsic horizon Terric horizon Vitric properties Histic horizon Thionic horizon Hortic horizon Umbric horizon Hydragric horizon Vertic horizon Irragric horizon Voronic horizon Melanic horizon Yermic horizon Mollic horizon . mottling occurs. Example of WRB soil classification A soil has a ferralic horizon. properties and materials Diagnostic horizons Diagnostic properties Diagnostic materials Albic horizon Natric horizon Abrupt textural change Artefacts Anthraquic horizon Nitic horizon Albeluvic tonguing Calcaric material Anthric horizon Petrocalcic horizon Andic properties Colluvic material Argic horizon Petroduric horizon Aridic properties Fluvic material Calcic horizon Petrogypsic horizon Continuous rock Gypsiric material Cambic horizon Petroplinthic horizon Ferralic properties Limnic material Cryic horizon Pisoplinthic horizon Geric properties Mineral material Duric horizon Plaggic horizon Gleyic colour pattern Organic material Ferralic horizon Plinthic horizon Lithological discontinuity Ornithogenic material Ferric horizon Salic horizon. the soil finally classifies as: Lixic Vetic Ferralsol (Ferric. below 50 cm. indicating moderate to high base saturation. for each horizon. the diagnostic characteristics that apply to the classification system used. The final classification is made when analytical data are available. 2006) be followed in determining chemical and physical characteristics.5 and 6. CHECKLIST OF WRB DIAGNOSTIC HORIZONS.Chapter 5 – Genetic and systematic interpretation – soil classification 81 The field classification provides a preliminary assessment using all observable or easily measurable properties and features of the soil and associated terrain. texture in the upper part of the ferralic horizon changes from sandy loam to sandy clay within 15 cm. it is advisable to determine or estimate.

. 2004)./... UG2)/SSK(UG3) 1 2 3 4 5 1 = Coding of soil unit according to the WRB (IUSS Working Group WRB. texture (e. 2006). siltic.g.. Arenosol. gleysation – Gleysol). the following framework for a reference soil series is recommended (Jahn. 2 = Coding of texture class for the upper part of the soil body. as “shallow … over …” where occurring at a depth of 0–3 dm. SK = skeleton with coarse fragments of 80 percent or more (by volume). skeletic.. 3 = The parent material is given in descending order of importance from left to right within brackets. and gypsiric subunits) and others.g. silSK = silt loamy skeleton with coarse fragments of from 40 to <80 percent (by volume). SiL(UE2. and clayic subunits). 5 = The lower part of the soil body is described according to 2 and 3.. In order to overcome this problem and to provide users with more systematic and precise information about texture. ..//. the WRB (IUSS Working Group WRB.. skSiL= skeletal silt loam with coarse fragments of from 10 to < 40 percent (by volume). Example A Cambisol to which only the Dystric qualifier applies and which has variations in texture and in which the upper part has developed from loess with some fluvial gravelly sand and the lower part has developed from glacio-fluvial gravelly sand.. as “… over …” where occurring at a depth of 3–7 dm.g. The texture class for the fine earth is used according to Chapter 4 and combined with four classes of coarse fragments. as “… over deep …” where occurring at a depth of 7–12 dm.\. by history and practical purposes..g.. mixing information about soil genesis (e. e.82 Guidelines for soil description APPENDING TEXTURE AND PARENT MATERIAL INFORMATION TO THE REFERENCE SOIL GROUP In its present state. silt loam from loess with glacio-fluvial gravelly sand over sandy skeleton from glacio-fluvial gravel It is coded: CMdy.. Fluvisols. The system distinguishes second-level units only in a generalized manner by texture and only in the parent material of some RSGs. Anthrosols. calcaric. . podzolization – Podzol. (the intermediate of 5 dm is corresponding with the WRB-epi and -endo). 4 = A change of material with depth (either by texture or by parent material or by both is coded with: . an extended hierarchical lithology list.: SiL = silt loam with coarse fragments < 10 percent (by volume). parent materials (e. For coding. 2005) is used.. parent material and layering. 2006) is. The full description is: Haplic Cambisol (Dystric). arenic. based on updated SOTER (ISRIC.

Thin (extension < 2 cm ) horizons are neglected.: SiL/skSiL(UE2. ÿ e. .g.: .Chapter 5 – Genetic and systematic interpretation – soil classification 83 Further rules in describing texture and parent material are: ÿ e. UG2/UG3) where no change in texture but in parent material.: skSiL(UE2.g. UG3) where no change in parent material but in texture../R(and lithology) means: over massive rock.. and (3) lithology differs for one class.g. ÿ e. (2) coarse fragments. ÿ Horizons are combined to one complex and described with the average where not more than one of the three parameters: (1) texture (fine earth).

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1. Rome. DVWK Regeln 129. Jongerius. 2005. Handbook for soil thin section description. Soil map of the European Communities 1:1 000 000. P. International Soil Reference and Information Centre (ISRIC). Waine publications. 207–222. D. Z. European Commission Joint Research Centre. Vol.. World Soil Resources Report No. 1975. Freiburg im Breisgau. 60. G. 124 pp. Updated global and national soils and terrain digital databases (SOTER). 2004. Gas und Wasser. Teil I: Ansprache von Böden.. FAO. Rome. 3rd Edition. 48/1. Paris. Paris. Meuser. 2005. Revised legend. Auflage. Wirtschafts. T. Tursina. The nature of allophane soils: 3. 1988. Z. L. Hannover. Thailand. Land and Water Digital Media Series #1 rev 1. In: Abstracts Eurosoil 2004. Fieldes. Guidelines for profile description. Cha-Am. 1974. FAO–UNESCO.und Verlagsges. Vol. Jahn. Luxembourg. 2–9. & Perrott. Federoff. Proceedings of International Conference on Innovative Techniques in Soil Survey. 1985.. I – legend. 1985. 2004. 1978. Munsell. 60. Proposal: classification of urban and industrial soils in the World Reference Base for Soil Resources (WRB). Bodenkundliche Untersuchungen im Felde zur Ermittlung von Kennwerten zur Standortscharakterisierung. FAO–ISRIC. 59 pp. 1966. Rapid field and laboratory test for allophane.G. Pflanzenernähr. Soil map of the world 1:5 000 000. 2006. Germany. 1990. 438 pp. FAO–UNESCO. Bodenk. ECSC–EEC–EAEC. Agriculture Handbook No. Germany. Report on the agro-ecological zones project. K. 9: 623–629. 85 References Ad-hoc-AG-Boden. Vol. 103. 2002. World reference base for soil resources 2006.. N. 1996. USDA Rossiter. IUSS Working Group WRB. 2005. H. 152 pp. Bullock. N. Rome. Richards. U. . & Babel. 1970–1981. M. Research needs and new developments in soil classification and mapping: meeting the changing demands for soil information. Sci. FAO. Diagnosis and improvement of saline and alkali soils. Stoops. 159: 305–312. Soil map of the world. FAO. Standard soil color charts. Ein Bestimmungsschlüssel für natürliche und technogene Substrate in Böden städtisch-industrieller Verdichtungsräume. FAO–UNESCO. pp.A. Rome.. A. World Soil Resources Reports No. 1954. DVWK. Germany. 1995.. World Soil Resources Report No. J. Bodenkundliche Kartieranleitung – 5. Soil map of the world. Soil atlas of Europe. and paper maps.W. FAO. R. Rome. Methodology and results for Africa. FAO/UNESCO Digital Soil Map of the World and derived soil properties. Bonn.

754 pp. K. USA. E. Blume. Soil taxonomy.J. Wageningen. Natural Resources Conservation Service. a basic system of soil classification for making and interpreting soil surveys.0.-P. Technical Report 9. Van Reeuwijk. H. USDA. 2002. 295 pp. 9th edition.A. Blackwell. 332 pp.C. USDA. 2003. United States Department of Agriculture (USDA) Soil Survey Staff. W. Field book for describing and sampling soils. Agricultural Handbook No. 436. 1999. Benham. & Broderson. & Stahr. Keys to soil taxonomy. Version 2. Agricultural Handbook No. Netherlands. UNEP–ISSS–ISRIC–FAO. Lincoln. Procedures for soil analysis. Natural Resources Conservation Service. P. United States Department of Agriculture (USDA) Soil Survey Staff. L. Global and national soils and terrain digital database (SOTER). Berlin. 1. Soil taxonomy. . 1995. 1995. 7th edition. ISRIC – World Soil Information. World Soil Resources Report No. Rome. Washington. Washington. 2nd edition.. 1975. Bodenkundliches Praktikum. DC. DC. E. Schoeneberger. Vienna. 74 Rev. 869 pp. DC. National Soil Survey Center.D. Washington. United States Department of Agriculture (USDA) Soil Survey Staff. Wysocki. D. 2nd edition.86 Guidelines for soil description Schlichting. 436.P. 2006.

The mean annual soil temperature is related most closely to the mean annual air temperature. and content of organic matter. the amount of snow. root growth of most plant species and germination of most seeds are impossible. Within limits. and irrigation. and. and the mean warm or cold seasonal temperature gradient within the main rootzone. . the differences are so small that it seems valid and useful to take a single value as the mean annual temperature of a soil. the readings may fluctuate from the mean fully as much as those of the air temperature. However. which weather events make somewhat irregular in most places. but this relationship is affected to some extent by: the amount and distribution of rain. 87 Annex 1 Explanation of soil temperature regimes1 The temperature of a soil is one of its important properties. the temperature regime can be described by: the mean annual soil temperature. For most practical purposes. time stands still for the soil. such as soil colour. Each pedon has a characteristic temperature regime that can be measured and described. the slope aspect and gradient. have negligible effects. Other factors. The measured mean annual soil temperature is seldom the same in successive depths at a given location. FLUCTUATIONS IN SOIL TEMPERATURE The mean annual temperature of a soil is not a single reading but the average of a series of readings. Near the surface. The fluctuations decrease with increasing depth and are ultimately damped out in the substrata 1 Adapted from USDA. water no longer moves as a liquid. which is the zone from a depth of 5 to 100 cm. especially where there is no insulating cover. 1999. Below freezing point. Between 0 and 5 °C. A horizon as cold as 5 °C is a thermal pan to the roots of most plants. The fluctuations occur as daily and annual cycles. the protection provided by shade and by O horizons in forests. unless there is frost heaving. temperature controls the possibilities for plant growth and for soil formation. texture. MEAN ANNUAL SOIL TEMPERATURE Each pedon has a mean annual temperature that is essentially the same in all horizons at all depths in the soil and at depths considerably below the soil. the average seasonal fluctuations from that mean. there is no biotic activity.

6 °C for each 10 cm above or below a depth of 50 cm. if the soil is saturated with water during some part of the summer and: (1) If there is no O horizon: lower than 13 °C. The mean winter temperature of many mid-latitude soils can be estimated from the difference between the mean annual temperatures and the mean summer temperatures because the differences are of the same magnitude but have opposite signs. CR – Cryic (Greek kryos. In organic soils. Soils in this temperature regime have a mean annual temperature lower than 8 °C but do not have permafrost. 2. . and December. meaning very cold soils). or b. throughout in time and space. In mineral soils. the measurement of soil temperature need not be a difficult or a time-consuming task. it is possible to take the average summer temperatures of the upper 100 cm and correct for the temperature-depth gradient by adding or subtracting 0. or (2) If there is an O horizon: lower than 8 °C. if the soil is not saturated with water during some part of the summer and: (1) If there is no O horizon: lower than 15 °C. Cryic soils that have an aquic moisture regime are commonly churned by frost. lithic or paralithic contact. whichever is shallower. or dry frost if there is no excess water. These are soils that have permafrost if they are moist. To make this estimate. Soils with a pergelic temperature regime have a mean annual temperature lower than 0 °C. to freeze. CLASSES OF SOIL TEMPERATURE REGIMES The following is a description of the soil temperature regimes used in defining classes at various categoric levels in the soil taxonomy of the United States of America. Frequently. the mean annual soil temperature for much of the United States of America is estimated by adding 1 °C to the mean annual air temperature. meaning permanent frost). January. coldness. the mean summer soil temperature (June. the mean annual soil temperature is lower than 6 °C. and February in the Southern Hemisphere) either at a depth of 50 cm from the soil surface or at a densic. or (2) If there is an O horizon or a histic epipedon: lower than 6 °C. Where it is not possible to make reasonably precise estimates. 1.88 Guidelines for soil description in a zone where the temperature is constant and is the same as the mean annual soil temperature. ESTIMATION OF SOIL TEMPERATURE Soil temperature can often be estimated from climatological data with a precision that is adequate for the present needs of soil surveys. and gelare. The mean summer soil temperature at a specific depth can also be estimated. PG – Pergelic (Latin per. is as follows: a. July and August in the Northern Hemisphere.

IT – Isothermic The mean annual soil temperature is 15 °C or higher but lower than 22 °C and the mean summer and mean winter soil temperatures differ by less than 6 °C at a depth of 50 cm or at a densic. whichever is shallower. IM – Isomesic The mean annual soil temperature is 8 °C or higher but lower than 15 °C and the mean summer and mean winter soil temperatures differ by less than 6 °C at a depth of 50 cm or at a densic. whichever is shallower. July and August) and mean winter (December. lithic or paralithic contact. and the difference between mean summer and mean winter soil temperatures is more than 6 °C either at a depth of 50 cm from the soil surface or at a densic. whichever is shallower. IF – Isofrigid The mean annual soil temperature is lower than 8 °C and the mean summer and mean winter soil temperatures differ by less than 6 °C at a depth of 50 cm or at a densic. A few with organic materials in the upper part are exceptions. However. whichever is shallower. lithic or paralithic contact. and the difference between mean summer and mean winter soil temperatures is more than 6 °C at a depth of . FR – Frigid A soil with a frigid temperature regime is warmer in summer than a soil with a cryic regime. TH – Thermic The mean annual soil temperature is 15 °C or higher but lower than 22 °C. and the difference between mean summer and mean winter soil temperatures is more than 6 °C either at a depth of 50 cm from the soil surface or at a densic. The concepts of the soil temperature regimes described below are used in defining classes of soils in the low categories. lithic or paralithic contact. lithic or paralithic contact.Annex 1 – Explanation of soil temperature regimes 89 Isofrigid soils could also have a cryic temperature regime. ME – Mesic The mean annual soil temperature is 8 °C or higher but lower than 15 °C. whichever is shallower. whichever is shallower. lithic or paralithic contact. January and February) soil temperatures is more than 6 °C either at a depth of 50 cm from the soil surface or at a densic. its mean annual temperature is lower than 8 °C and the difference between mean summer (June. HT – Hyperthermic The mean annual soil temperature is 22 °C or higher. lithic or paralithic contact.

whichever is shallower. whichever is shallower. lithic or paralithic contact. IH – Isohyperthermic The mean annual soil temperature is 22 °C or higher and the mean summer and mean winter soil temperatures differ by less than 6 °C at a depth of 50 cm or at a densic. . lithic or paralithic contact.90 Guidelines for soil description 50 cm from the soil surface or at a densic.

a horizon is considered dry when the moisture tension is 1 500 kPa or more. 1 Adapted from USDA. there have been significant changes in climate. During geological time. and winter refers to December. It may be either moist in winter and dry in summer or the reverse. most of the accessory characteristics and those most important for interpretations are associated with the present moisture regime. SIGNIFICANCE TO SOIL CLASSIFICATION The moisture regime of a soil is an important property of the soil as well as a determinant of processes that can occur in the soil. July and August. and it is considered moist when water is held at a tension of less than 1 500 kPa but more than zero. it is considered salty rather than dry.2) in the soil or in specific horizons during periods of the year. It is a property of the soil. and small-scale maps can be interpreted in terms of the many accessory characteristics that are common to most of the soils that have a common climate. Such soils have relict features that reflect the former moisture regime and other features that reflect the present moisture regime. the base status of the soil. 1999. even if the present regime differs widely from some of the earlier. Soils that could have formed only in a humid climate are now preserved in an arid climate in some areas. The availability of water is also affected by dissolved salts. In the Northern Hemisphere. and the presence or absence of salts. . January and February. Consequently. 91 Annex 2 Explanation of soil moisture regimes1 The term “soil moisture regime” refers to the presence or absence either of groundwater or of water held at a tension of less than 1 500 kPa (pF 4. the present climate determines use and management of the soil. Water held at a tension of 1 500 kPa or more is not available to keep most mesophytic plants alive. nature and distribution of organic matter. the moisture regimes of most soils are inferred from the present climate. Each of the moisture regimes in the history of a soil is a factor in the genesis of that soil and is the cause of many accessory characteristics. Furthermore. A soil may be continuously moist in some or all horizons either throughout the year or for some part of the year. summer refers to June. However. These characteristics include: the amount. More importantly. Where a soil is saturated with water that is too salty to be available to most plants.

These depths do not include the depth of moistening along any cracks or animal burrows that are open to the surface. when catastrophic events occur during a year. but not air-dry) soil will be moistened by 2. However.5 cm of water moistens the soil to a densic. The upper boundary of this control section is the depth to which a dry (tension of more than 1 500 kPa. the weighted average depth of moistening in a pedon is used for the limits of the moisture control section. A number of methods have been devised to relate soil moisture to meteorological records. SOIL MOISTURE CONTROL SECTION The intention in defining the soil moisture control section is to facilitate estimation of soil moisture regimes from climate data. In addition. lithic. the moisture status of the soil must be characterized by probability. the mean monthly precipitation in a normal year must be plus or minus one standard deviation of the long-term monthly precipitation for 8 of the 12 months. A normal year is defined as a year that has plus or minus one standard deviation of the long-term mean annual precipitation (long term refers to 30 years or more). there are natural plant communities that have their roots either above or below the control section. Attempts are currently being made to improve the parameters of the soil moisture control section. Weather probabilities can be determined from long-term weather records and observations of how each soil responds to weather conditions as modified by its landscape position. but quantitative data are rare. Dew and fog can add appreciable amounts of moisture to some soils. The concept of the soil moisture control section does not apply well to the cracking clays. However. Normal years can usually be calculated from the mean annual precipitation. paralithic or petroferric contact or to a petrocalcic or petrogypsic horizon or a duripan. all these methods have some shortcomings. because these clays remoisten from both the surface and the bases of the cracks.5 cm of water within 48 hours. The lower boundary is the depth to which a dry soil will be moistened by 7. The soil moisture patterns of these soils are defined in terms of the pattern of cracking over time. even for gently sloping soils that depend primarily on precipitation for their moisture. the contact or the upper boundary of the cemented horizon constitutes the lower boundary of the soil moisture control section.92 Guidelines for soil description NORMAL YEARS In the discussions that follow and throughout the keys. If moistening occurs unevenly. If 7.5 cm of water within 24 hours. The boundaries for the soil moisture control section correspond to the rooting depths for many crops. the standard deviations of the monthly means should also be calculated. . While no two years have exactly the same weather conditions. the term “normal years” is used. ESTIMATION The landscape position of every soil is subject to extremes in climate. To date.

However. i. and that the amount of stored moisture is not being increased by irrigation or fallowing. there are soils in which the groundwater is always at or very close to the surface.1–75 mm and < 18 percent clay in fine earth).Annex 2 – Explanation of soil moisture regimes 93 The moisture control section of a soil extends approximately: ÿ from 10 to 30 cm below the soil surface if the particle-size class of the soil is fine-loamy (> 15 percent particles 0. water) moisture regime is a reducing regime in a soil that is virtually free of dissolved oxygen because it is saturated by water. The limits of the soil moisture control section are affected not only by the particle-size class but also by differences in soil structure or pore-size distribution or by other factors that influence the movement and retention of water in the soil.1–75 mm and 18–35 percent clay). grass or native vegetation. crops.. such a regime is not considered aquic. the duration must be at least a few days.1–75 mm and 18–35 percent clay in fine earth). the level of groundwater fluctuates with the seasons. fine-silty (< 15 percent particles 0. Examples are soils in tidal marshes or in closed. the limits of the moisture control section are deeper. It is not known how long a soil must be saturated before it is said to have an aquic moisture regime. These cultural practices affect the soil moisture conditions as long as they continued.1–75 mm and < 18 percent clay in fine earth). Such soils are considered to have a peraquic moisture regime. ÿ from 20 to 60 cm if the particle-size class is coarse-loamy silty (>15 percent particles 0.e. or clayey (> 35 percent clay). AQ – Aquic moisture regime The aquic (Latin aqua. where the temperature is less than 1 °C). CLASSES OF SOIL MOISTURE REGIMES The soil moisture regimes are defined in terms of the level of groundwater and in terms of the seasonal presence or absence of water held at a tension of less than 1 500 kPa in the moisture control section.g. landlocked depressions fed by perennial streams. . However. If the soil contains rock and pararock fragments that do not absorb and release water. coarse-silty (< 15 percent particles 0. either because the water is moving or because the environment is unfavourable for micro-organisms (e. PQ – Peraquic moisture regime Very commonly. Some soils are saturated with water at times while dissolved oxygen is present. ÿ from 30 to 90 cm if the particle-size class is sandy (texture of sand or loamy sand). It is assumed in the definitions that the soil supports whatever vegetation it is capable of supporting. because it is implicit in the concept that dissolved oxygen is virtually absent.

such as a crusty surface that virtually precludes the infiltration of water. implying dryness) moisture regime is intermediate between the aridic regime and the udic regime. The water moves through the soil in all months when it is not frozen. as in coastal areas. the udic moisture regime requires. Water moves downwards though the soils at some time in normal years. or have adequate winter rains to recharge the soils and cool. Its concept is one of moisture . humid) In climates where precipitation exceeds evapotranspiration in all months of normal years. Such an extremely wet moisture regime is called perudic. although there are occasional brief periods when some stored moisture is used. a three-phase system. the amount of evapotranspiration. Where the mean annual soil temperature is lower than 22 °C and where the mean winter and mean summer soil temperatures at depth of 50 cm from the soil surface differ by 6 °C or more. in part or all of the soil moisture control section when the soil temperature is above 5 °C. the moisture tension rarely reaches 100 kPa (pF 3) in the soil moisture control section. have enough rain in summer so that the amount of stored moisture plus rainfall is approximately equal to.94 Guidelines for soil description AR – Aridic and TO – torric (Latin aridus. or exceeds. Soils that have an aridic (torric) moisture regime normally occur in areas of arid climates. and soluble salts accumulate in the soils if there is a source. or are on steep slopes where runoff is high. In addition. and udus. humid) moisture regime is one in which the soil moisture control section is not dry in any part for as long as 90 cumulative days in normal years. In the aridic (torric) moisture regime. throughout in time. ÿ moist in some or all parts for less than 90 consecutive days when the soil temperature at a depth of 50 cm is above 8 °C. the soil moisture control section in normal years is dry in all parts for less than 45 consecutive in the 4 months following the summer solstice. hot and dry) moisture regimes These terms are used for the same moisture regime but in different categories of the taxonomy. solid–liquid–gas. There is little or no leaching in this moisture regime. and torridus. PU – Perudic moisture regime (Latin per. A few are in areas of semi-arid climates and either have physical properties that keep them dry. UD – Udic moisture regime The udic (Latin udus. dry. burnt. foggy summers. the moisture control section in normal years is both: ÿ dry in all parts for more than half on the cumulative days per year when the soil temperature at a depth of 50 cm from the soil surface is above 5 °C. The udic moisture regime is common to the soils of humid climates that: have well-distributed rainfall. US – Ustic moisture regime The ustic (Latin ustus. except for short periods.

The moisture. In tropical and subtropical regions that have a monsoon climate with either one or two dry seasons. In temperate regions of subhumid or semi-arid climates. the moisture control section is moist in some part for more than half of the cumulative days per year when the soil temperature at a depth of 50 cm from the soil surface is higher than 6 °C or for 90 or more consecutive days when the soil temperature at a depth of 50 cm is higher than 8 °C. but it is not dry in all parts for more than half of the cumulative days when the soil temperature at a depth of 50 cm is higher than 5 °C. Native plants are mainly annuals or plants that have a dormant period while the soil is dry. In such regions. in normal years. the moisture control section is dry in all parts for less than 45 consecutive days in the 4 months following the summer solstice. the rainy seasons are usually spring and summer or spring and autumn. in normal years. If in normal years the moisture control section is moist in all parts for 45 or more consecutive days in the 4 months following the winter solstice.Annex 2 – Explanation of soil moisture regimes 95 that is limited but is present at a time when conditions are suitable for plant growth. In areas of a xeric moisture regime. The mean annual soil temperature is lower than 22 °C. but never winter. lithic or paralithic contact if shallower. . it is moist in some part either for more than 180 cumulative days per year or for 90 or more consecutive days. XE – Xeric moisture regime The xeric (Greek xeros. the soil moisture control section in areas of the ustic moisture regime is dry in some or all parts for 90 or more cumulative days in normal years. the soil moisture control section. If the mean annual soil temperature is lower than 22 °C and if the mean summer and winter soil temperatures differ by 6 °C or more at a depth of 50 cm from the soil surface. which falls during the winter. is particularly effective for leaching. the soil moisture control section in areas of the ustic moisture regime is dry in some or all parts for 90 or more cumulative days in normal years. summer and winter seasons have little meaning. when potential evapotranspiration is at a minimum. If the mean annual soil temperature is 22 °C or higher or if the mean summer and winter soil temperatures differ by less than 6 °C at a depth of 50 cm below the soil surface. the moisture regime is ustic if there is at least one rainy season of three months or more. The concept of the ustic moisture regime is not applied to soils that have permafrost or a cryic soil temperature regime (defined above). Moreover. and the mean summer and mean winter soil temperatures differ by 6 °C or more either at a depth of 50 cm from the soil surface or at a densic. is dry in all parts for 45 or more consecutive days in the 4 months following the summer solstice and moist in all parts for 45 or more consecutive days in the 4 months following the winter solstice. dry) moisture regime is the typical moisture regime in areas of Mediterranean climates. where winters are moist and cool and summers are warm and dry. However.

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9. spade. per pH or EC measurement 10 ÿ drop flask with 10 percent HCl (~ 50 ml) ÿ drop flask with phenolphthalein pH indicator (8. palette-knife 7 ÿ hand lens (×10) ÿ platinum electrodes (redox measurement) 8 ÿ bottle with tap water ÿ bottle with aqua dest ÿ bottle with 1 M KCl or 0. pick-axe.5 (~ 30 ml) ÿ drop flask with 0. standard solutions Box with: 6 ÿ pocket rule ÿ knife.α-dipyridyl solution in 10 percent 12 (V/V) acetic acid solution (~ 50 ml). 1 vegetation where available) Global positioning system unit.8) solution (~ 30 ml) 11 ÿ drop flask with 1 M NaF adjusted to pH 7.2. reading form 4 Munsell soil color charts 5 Shovel. 97 Annex 3 Equipment necessary for field work 0 cm Map of topography (at least 1:25 000). land use.2 percent (M/V) α... auger and hammer Field pH-/conductometer. compass 2 Guideline for soil description Guideline for soil classification 3 Field book. geology (geomorphology.01 M CaCl2 solution (25 ml per pH measurement) 9 3 ÿ five transparent plastic cups with marks for 8 cm soil (~ 10 g) and 25 ml water. 13 14 15 .

Germany GUIDELINES FOR SOIL DESCRIPTION Universität Kiel. Germany ������������������ FAO � ������ ������ ������������������������ . The Netherlands Technische Universität München. GUIDELINES FOR SOIL DESCRIPTION Universität Halle-Wittenberg. The Philippines ISRIC – World Soil Information. Germany Leyte State University.