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Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam

Field Manual for Soil Type Identification

CSIRO Land and Water Department of Agriculture

2008 Brunei Darussalam

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Publication information

Grealish GJ, Fitzpatrick RW, Ringrose-Voase AJ (2008) ‘Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam – Field Manual for Soil Type Identification’. CSIRO Land and Water, Australia.

Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam

Field Manual for Soil Type Identification

CSIRO Land and Water Department of Agriculture

2008 Brunei Darussalam

Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page ii

Contacts: Project Director Dr Chris Smith, CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601

Tel: +61-2-6246 5960; e-mail: [email protected] Project Coordinator Dr Anthony Ringrose-Voase, CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601

Tel: +61-2-6246 5956; e-mail: [email protected]

Other project staff: Project Management Mr Edward A’Bear

URS Australia Pty Limited, Adelaide, SA Soil Surveyor Mr Gerard Grealish

URS Australia Pty Limited, Perth, WA Soil Taxonomy Dr Rob Fitzpatrick

CSIRO Land and Water, Adelaide, SA Soil Fertility Dr Mike Wong

CSIRO Land and Water, Perth, WA Tropical Crops Mr Ted Winston

URS Australia Pty Limited, Mission Beach, Qld

Acid Sulfate Soils Mr Warren Hicks

CSIRO Land and Water, Canberra, ACT GIS/Database Mr Rob Kingham, Ms Tania Laity

Bureau of Rural Sciences, Canberra, ACT Remote Sensing Mr Alan Marks

CSIRO Land and Water, Canberra, ACT Laboratory analysis Mr Adrian Beech

CSIRO Land and Water, Adelaide, SA Quality Control/Assurance Mr Bernie Powell & Dr Phil Moody

Queensland Department of Natural Resources and Water, Brisbane, Queensland

mailto:[email protected]

mailto:[email protected]

Field Manual for Soil Type Identification Page iii

Table of Contents 1. Introduction ............................................................................................................................................1

1.1. Soil Classifications 1 2. Describing Soil Properties ....................................................................................................................3

2.1. Instructions 3 2.2. Site Characteristics 4

Location 4 Slope 4 Landscape position 4 Watertable depth 4 Earthcover 4

2.3. Observable Soil Characteristics 5 Soil Depth 5 Soil Layer Thickness 5 Soil Moisture 5 Soil Texture 6 Soil Consistence 7 Soil Colour 8 Soil pH 10 Soil Cracks 10

3. Soil Type Identification Key ................................................................................................................11 3.1. Organic Soils (Saprists) 14 3.2. White Soils (Aquods) 16 3.3. Cracking Clay Soils (Aquerts) 18 3.4. Texture Contrast Yellow Soils (Udults) 20 3.5. Very Deep Yellow Soils (Humults) 22

Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page iv

3.6. Yellow Soils (Haplohumults) 26 3.7. Brown Over Grey Soils (Aqualfs) 28 3.8. Sulfuric Soils (Aquepts) 30 3.9. Sulfidic Soils (Aquents) 32 3.10. Grey Soils (Aquents) 36

References........................................................................................................................................................... 38

Field Manual for Soil Type Identification Page 1

1. Introduction This Field Manual is an output for the project Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam. The manual summarises the major soil types within the 27 Agricultural Development Areas surveyed during the project. The aim of the manual is to allow recognition of Soil Types and Subtypes using site and soil properties that can be observed in the field. It first describes some simple soil properties that must be described or measured for a soil profile. It then provides a key that uses these properties to identify the soil profile. A more complete description of the Soil Types can be found in Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Report P1-2 – Soil Properties and Soil Identification Key for Major Soil Types. (Grealish et al. 2007). Once a Soil Type or Subtype is identified, users can check the tables in Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Report P2-1 – Suitability of Major Soil Types for Cropping (Ringrose-Voase et al. 2008) to identify the possible limitations to cropping and determine suitability of the soil for various crops.

1.1. Soil Classifications Soil Taxonomy Soils are classified to make it easier to remember and communicate their significant characteristics. Classification assembles knowledge about soils, reveals their relationship to one another and the whole environment, and develops principles that help understanding of their behaviour and their response to land use. If an internationally recognized soil classification is used, international technology transfer is possible, as similar soils anywhere in the world can be identified and successful management practices can be copied without the need for extensive local trials.

The soil classification system used in this soil survey is the United States Department of Agriculture Soil Taxonomy, 2003 revision (Soil Survey Staff 2003). The soil classification system defined in Soil Taxonomy is a hierarchical system with mutually exclusive classes and rigidly defined boundaries. There are six categories with each category progressively having more classes and including more descriptive features than the one above.

Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 2

The highest category is the order, then the suborder, great group, subgroup, family, and series. In this survey, soils are classified to the subgroup level.

Simplified Soil Identification Key Using Soil Taxonomy to classify soils requires experience in describing soil features, often involves laboratory analysis and calls for an understanding of soil classification. Most users do not have this level of experience, access to analytical data or understanding of the complexity of using Soil Taxonomy as a soil classification system to identify soils. Therefore a very simplified Soil Identification Key, specific to the soils that occur within this soil study of Brunei Darussalam, was developed.

The Soil Identification Key is based on easily observable soil characteristics. These are not a direct replacement of the specific diagnostic horizons and diagnostic soil characteristics outlined above that are used for Soil Taxonomy classification. The Soil Identification Key has been constructed to separate out the same soil classes as would occur if Soil Taxonomy was to be used. However, because the Soil Identification Key is a simplification and does not use the detailed, technically-defined diagnostic characteristics, it may occasionally lead to errors in identification of soils in the field. Also it should only be used in the areas for which it was developed, namely the ADAs surveyed as part of Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam (see Grealish et al. 2007).

This Soil Identification Key works on the basis that the soil is allocated to the first available decision (even though it may also fit later decisions), and the questions are related to observable soil characteristics. A collection of plain language soil type and subtype names was developed to correspond to the major Soil Taxonomy Suborder and Subgroup classes found in the survey. These names are intended to provide some assistance in understanding the intent and general nature of the soil groups as defined using the Soil Taxonomy classification.

The Soil Identification Key recognises 10 Soil Types and 24 Subtypes. These are summarized in Section 3.


2. Describing Soil Properties There are many text books and manuals available (e.g. Schoeneberger et al. 2002) that provide detailed information on how to describe soils. These should be referred to if a better understanding is required. However, the soil characteristics explained below are simple to describe and provide sufficient information to allow the Soil Identification Key to be used.

2.1. Instructions 1. Dig a small pit in the soil using a spade. The hole should be sufficiently large to allow a vertical face (side of

the pit) to be observed to a depth of about 50 cm from the soil surface or to the depth at which free water flows into the pit. Then use a soil auger to obtain soil samples below the pit noting the depths that the soil is retrieved from. Auger to a depth of at least 100 cm on flat areas or 150 cm on sloping areas, or until the auger refuses to go deeper because of the underlying bedrock.

2. Determine layers in the soil by observing the depths where the appearance or ‘feel’ of the soil changes, such as colour or texture or consistence. Generally there is a topsoil layer that is about 10 to 25 cm thick and usually a darker colour than the soil below, and at least two distinct subsoil layers below the topsoil.

3. Record the site characteristics (see Section 2.2) as well as the major observable soil characteristics (Section 2.3) that will be used in the soil identification key on a field sheet. Site characteristics include landscape position, land use, slope, slope position and drainage. Soil layer characteristics include the depth and thickness of the layer and its colour, texture, consistence and soil reaction (pH).

4. Using this soil information work through the Soil Identification Key to determine the Soil Type or Subtype (Section 3).


2.2. Site Characteristics The following site characteristics should be recorded when observing a soil profile. Whilst not essential for the Soil Identification Key, they are useful information that help put the soil observations and classification in context and are important attributes for determining land suitability.

Location The location of the site should be recorded with sufficient accuracy that it can be relocated. Use of a geographic positioning system (GPS) is recommended. The accuracy of a location recorded by GPS can be improved by averaging the reading over several minutes.

Slope Slope should be estimated or preferably measured using a clinometer.

Landscape position Landscape position is the location of the observation site relative to the landscape. Examples are flats, footslope, mid-slope, upper slope and crest.

Watertable depth After digging a small pit and/or auger hole to observe the soil profile, record whether a water table is present and, if so, its depth.

Earthcover Record the cover at the site. This is usually the vegetation growing, but could be bare ground. If the soil is fallow between crops, the normal cropping system should be recorded, if known.


2.3. Observable Soil Characteristics Soil Depth Using a tape measure, determine the soil depth by measuring from the soil surface to the maximum depth that soil was obtained from. This measurement may have to be done by measuring the soil auger and how far it penetrated down into the soil. Record the depth in centimetres.

Soil depth provides information on the potential depth for plant roots to explore.

Soil Layer Thickness By observing the soil, identify the soil layers by determining where changes occur in soil colour, texture or consistence. Using a tape measure determine the upper and lower depths of each layer by measuring from the soil surface. Record the depths in centimetres. The soil layer thickness can be determined as the difference between the lower and upper depth for each layer.

Soil layer thickness provides information on the available volume of different soil materials.

Soil Moisture Soil moisture content can be determined by the ‘feel’ of the soil in the hand. It will vary over time depending on rainfall or irrigation frequency and proximity to the water table.

Soil Moisture Description

Dry Hands remain dry when holding sample, soil readily absorbs moisture when applied.

Moist Hand will feel damp when holding the sample but no free water visible

Wet Free water easily visible

Soil moisture provides information on the soil drainage and the potential water table depth (wet soil).


Soil Texture Soil texture is determined by the proportions of organic material, sand, silt, and clay in a soil. If a soil is dominated by decomposed plant fibres then it is called an organic soil (commonly known as peat). Mineral soils generally have a small amount or no organic material, and are composed of sand, silt and clay.

Texture can be determined in the field by taking a half hand-full of soil, adding some water so that the soil binds and can be moulded. The soil is then rolled into a ball and texture determined.

Texture Description

Organic material Dominated by decomposed plant fibres. Often soft and easily squeezed when moulded in the hand.

Sandy The soil stays loose and separated. It cannot be moulded into a ball or rolled into a ribbon.

Loamy The soil becomes slightly sticky, and can be moulded into a ball that does not break apart. It can be rolled into a ribbon between 15 and 50 mm long that will break when bent.

Clayey The soil is sticky, and is initially firm and resistant to moulding into a ball. It can be rolled into a ribbon that is greater than 50 mm long and bends without breaking.

Soil texture provides information on water holding capacity, aeration, resistance to root penetration, and nutrient holding capacity.


Soil Consistence Soil consistence describes the strength and coherence of a soil.

Soil consistence can be determined in the field by taking a spade sized block of soil at field water content and gently breaking the soil apart by hand. If the soil is structured it will separate into aggregates. If the soil has no structure then the break will be jagged and there will be no identifiable aggregates. Soil consistence describes the force required to break, crumble or squeeze the soil.

Soil Consistence Description Implied Soil Texture

Soft Soil is easily squeezed by hand and there is no resistance when pressure is applied to the soil block between the thumb and forefinger

Usually organic material and occasionally sandy soils that are saturated.

Loose, weak Soil block crumbles under slight force applied between thumb and forefinger.

Usually sandy soils

Friable, firm Soil block crumbles under moderate to strong applied force applied by the hand.

Usually loamy soils

Strong to rigid Soil block cannot be crumbled by hand force. Usually clayey soils

Soil consistence provides information on the ease of root penetration, weight bearing capacity of the soil, and indicates the soil texture.


Soil Colour Soil colour is an easily observed characteristic for determining different types of soil materials. Usually Munsell colour charts are used to place a soil into a colour grouping. For the purposes of this Soil Identification Key a few broad groups are used. To determine the soil colour find a clean sample, moisten the surface and match to Munsell colour chips or examples provided here.

Soil Colour Typical Munsell hue/ value/chroma

Description Example soil colour

Black 5YR/ <3/ 1-2 7.5YR/ <3/ 1-2 10YR/ <3/ 1-2

Peat / organic soils – high in organic matter

White -/ 8/ <4 Sandy / quartz

Red 10R/ -/ 6-8

2.5YR/ -/ 6-8 Presence of iron oxides

Yellow 7.5YR/ >6/ >6

10YR/ >6/ >6 2.5Y/ >6/ >3 5Y/ >6/ >2

Some iron oxides


Soil Colour Typical Munsell hue/ value/chroma

Description Example soil colour

Brown 2.5YR/ <7/ 3-4 5YR/ <6/ 3-4 7.5YR/ <6/ 3-4 10YR/ <6/ 3-8 2.5Y/ <5/ 2-6

Moderate soil organic matter content, and some iron oxides

Grey Gley charts/ -/ 3-7/ 1

Near permanent waterlogging; anaerobic conditions

Mottles Orange, yellow, red spots throughout the dominant soil colour

Intermittent water logging; intermittent anaerobic conditions

Soil colour provides information on the soil drainage, organic matter content, and sometimes can be used to infer soil fertility when used with soil texture.


Soil pH Soil pH measures the concentration of hydrogen ions in the soil. A pH of 7 is neutral, pH less than 7 is acidic, and pH greater than 7 is alkaline. Soil pH can be measured by a number of different methods and instruments. In the field pH paper sticks provide a good indication. Place the pH stick on a moistened soil sample: the colour will change to indicate the pH level.

For the Soil Identification Key, pH is used to determine if a soil has a sulfuric layer (when the pH <3.5) or sulfidic material (pH >3.5 which changes on ageing to pH 3.5).

Sulfidic Material: contains oxidisable sulfur compounds. They are mineral or organic soil materials that have a pH value of more than 3.5 that will, under moist aerobic conditions, show a drop in pH of 0.5 or more units to a pH value of 4.0 or less. This drop in pH is referred to as aging, and occurs over an 8 week period or can be accelerated by mixing the soil sample with hydrogen peroxide. Sulfidic materials accumulate in a soil or sediment that is permanently saturated, and if drained or exposed to aerobic conditions, the sulfides oxidize and form sulfuric acid.

Sulfuric Horizon: is 15 cm or more thick and is composed of either mineral or organic soil material that has a pH value of 3.5 or less or shows evidence that the low pH value is caused by sulfuric acid.

Soil pH provides information on the level of acidity which will impact on the use of the soil; plant growth will vary depending on the crop’s tolerance to acidity.

Soil Cracks Soil cracks occur only in clayey soils when they are dry. They are difficult to observe as they occur only when the soil is dry and often in the soil layers below the surface. Knowledge about the soil behaviour during the year will be required to determine if these features exists. If the cracks cannot be observed then it may be possible to observe other indicators of cracking in the subsoil such as slickensides, which are polished and grooved surfaces between aggregates.

Soil cracks provide information that the soil material contains shrink/swelling clays. These clayey soils are very slowly draining and sticky when wet and often set hard when dry making them very difficult to cultivate.


3. Soil Type Identification Key This key allows identification of the major soil types found within the Agricultural Development Areas surveyed for the project Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam.

Instructions After examining the soil profile as described above, and taking careful note of all the layers and features, use the key below to identify the Soil Type and its corresponding classification in Soil Taxonomy.

• Use the information gathered during your examination to answer the first question in the key. • If the answer is “Yes”:

- The Soil Type of the profile is shown in the right hand column. The corresponding Soil Taxonomy classification is also shown.

- Stop answering the questions in the Soil Type key. - Turn to the page shown for a description of the Soil Type. - If required, use the Soil Subtype identification key to identify the Soil Subtype. This can be found in the

section on each Soil Type. • If the answer is “No”, proceed to the next question. • Continue answering the questions until the answer is “Yes”. It is important the questions are answered in

sequence. The correct Soil Type is that obtained by the first “Yes” answer (even though the answer to later questions may also be “Yes”).

• If you reach an answer shown as “No*” you should restart the key in case you have made a mistake. If you still reach “No*” it is possible you have identified a new soil type not included in this classification.


Soil Type identification key

Diagnostic features for Soil Type Soil Type Soil Taxonomy classification

Does the upper 80 cm of soil consist of more than 40 cm of organic material (peat)? No Yes

Organic soil Saprist page 14

Does the subsoil have a whitish to light grey coloured soil layer overlying a dark brown coloured (organic) layer that is within 2 m of the soil surface?

No Yes White soil Aquod page 16

Does the soil develop cracks at the surface OR in a clay layer within 100 cm of the soil surface OR have slickensides (polished and grooved surfaces between aggregates),

AND is the subsoil uniformly grey coloured (poorly drained or very poorly drained)? No Yes

Cracking clay soil Aquert page 18

Does the subsoil have a dominantly yellowish colour AND a texture contrast (sandy surface layer above loamy or clayey subsoil)? No Yes

Texture contrast yellow soil Udult page 20

Does the upper subsoil have a dominantly yellowish or brownish colour, AND is the soil depth greater than 150 cm? No Yes

Very deep yellow soil Humult page 22


Diagnostic features for Soil Type Soil Type Soil Taxonomy classification

Does the subsoil have a dominantly yellowish or brownish colour, AND is the soil depth less than 150 cm? No Yes

Yellow soil Haplohumult page 26

Does the subsoil have a yellowish brown coloured layer with red/orange mottles (spots) overlying a grey layer that has its upper boundary within 50 cm of the soil surface?

No Yes Brown over grey soil Aqualf page 28

Does a sulfuric layer (pH<3.5) occur within 150 cm of the soil surface, AND is the subsoil uniformly grey coloured (poorly drained)? No Yes

Sulfuric soil Aquept page 30

Does sulfidic material (pH>3.5 which changes on ageing to pH<3.5) occur within 100 cm of the soil surface,

AND is the subsoil uniformly grey coloured (poorly drained)? No Yes

Sulfidic soil Aquent page 32

Does the subsoil have a greyish colour and no other diagnostic features within 150 cm of the soil surface?

No * Yes Grey soil Aquent page 36

* If you reach an answer shown as “No*” you should restart the key in case you have made a mistake. If you still reach “No*” it is possible you have identified a new Soil Type not included in this classification.


Depth, cm

0 - 5

5 - 10

10 - 30

30 - 50

50 - 80

80 - 100

100 - 150

150 - 175

3.1. Organic Soils (Saprists) Occurrence Occur on flats Formed in organic material and alluvial

sediments

Features Soil is highly decomposed organic material

(peat) − More than 40 cm in upper 80 cm

Dark grey to black colour Very poorly drained − Watertable near to the

surface

Soil Subtypes 4 Soil Subtypes identified based on:

Presence of sulfuric layer or sulfidic material

Presence of mineral soil layer


Soil Subtype identification key for Organic Soils

Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup

Does a sulfuric layer (pH<3.5) occur within 50 cm of the soil surface? No Yes

Sulfuric organic soil (Sulfosaprist) Does a mineral soil layer >30 cm thick occur within 100 cm of the soil surface? No Yes

Mineral sulfuric organic soil Terric Sulfosaprist

Sulfuric organic soil Typic Sulfosaprist

Does sulfidic material (pH>3.5 which changes on ageing to pH<3.5) occur within 100 cm of the soil surface? No * Yes

Sulfidic organic soil (Sulfisaprist) Does a mineral soil layer >30 cm thick occur within 100 cm of the soil surface? No Yes

Mineral sulfidic organic soil Terric Sulfisaprist

Sulfidic organic soil Typic Sulfisaprist

Organic Soils – soil attributes affecting cropping Organic (peaty) topsoil Prolonged waterlogging Shallow sulfidic/sulfuric material (often within 30 cm of surface) Acid, with aluminium toxicity High potential for P fixation and iron toxicity


Depth, cm

-5 - 0

0 - 5

5 - 10

10 - 30

30 - 35

35 - 40

40 - 60

60 - 100

3.2. White Soils (Aquods) Occurrence Occur on old dunes Formed from sand dune material

Features Whitish or pale grey layer (eluvial horizon)

overlying dark brown organic layer (illuvial horizon) that may be quite thin (<10 cm)

Sandy texture or loamy in some areas − Sand is well sorted and leached of organic

and iron material

Usually very deep (>150 cm)

Poorly drained


Soil texture Dark organic topsoil layer


Soil Subtype identification key for White Soils


Does an unsaturated soil (dry to moist) layer occur over saturated (wet) layers? No * Yes

Poorly drained white soil (Epiaquod) Is the subsoil texture loamy AND is its consistency firm? No Yes

Loamy poorly drained white soil Ultic Epiaquod

Is the subsoil texture sandy AND with an overlying darker coloured topsoil? No * Yes

Sandy poorly drained white soil Umbric Epiaquod

White Soils – soil attributes affecting cropping Loamy poorly drained white soils Waterlogging Acid, with aluminium toxicity Low nutrient reserves

Sandy poorly drained white soils Sandy texture Prolonged waterlogging Low nutrient reserves Nutrients easily leached


Depth, cm

-10 - 0

0 - 5

5 - 40

40 - 90

90 - 160

3.3. Cracking Clay Soils (Aquerts) Occurrence Occur on flats Formed in alluvial clay sediments

Features Grey coloured subsoil, with orange yellow spots

in upper subsoil layer Heavy clay texture, usually sticky Crack to depth when dry and have slickensides

(polished and grooved surfaces between soil aggregates)

Usually very deep (>150 cm) Acidic pH <4.5 Poorly drained


Presence of sulfidic material or sulfuric layer


Soil Subtype identification key for Cracking Clay Soils


Does a sulfuric horizon (pH<3.5) OR do sulfidic materials (pH>3.5 which

changes on ageing to pH<3.5) occur within 100 cm of the soil surface? No Yes

Poorly drained cracking clay soil (Aquert) Does sulfidic material occur within 100 cm of the soil surface? No * Yes

Sulfidic poorly drained cracking clay soil Sulfic Sulfaquert

Poorly drained cracking clay soil (Aquert) Does a soil layer with pH<4.5 occur within 50 cm of the soil surface? No * Yes

Acid poorly drained cracking clay soil Typic Dystraquert

Cracking Clay Soils – soil attributes affecting cropping Heavy clay texture Prolonged waterlogging Acid, with aluminium toxicity for sensitive crops High potential for P fixation and iron toxicity

Sulfidic poorly drained cracking clay soils only Shallow sulfidic material (often within 40 cm of surface)


Depth, cm

0 - 25

25 - 70

70 - 100

3.4. Texture Contrast Yellow Soils (Udults)

Occurrence Occur on slopes of hills Formed in old sand dune material

Features Sandy layer overlying a loamy or clayey layer

with a sharp boundary between the layers Yellowish brown colour Very deep (>150 cm) Well drained

Soil Subtypes 1 Soil Subtype identified


Soil Subtype identification key for Texture Contrast Yellow Soils


Texture contrast yellow soil Arenic Paleudult

Texture Contrast Yellow Soils – soil attributes affecting cropping Sandy textured topsoil Steep slopes (approximately 25%) Erosion hazard Acid, with aluminium toxicity Low nutrient reserves Nutrients easily leached


Depth, cm

0 - 5

5 - 25

25 - 70

70 - 100

3.5. Very Deep Yellow Soils (Humults) Occurrence Occur on slopes of hills or on river terraces Formed in weathered sandstone and shale

Features Yellowish brown colour Very deep (>150 cm) Generally loamy or clayey subsoil texture Well drained to somewhat poorly drained


Soil texture Drainage


Soil Subtype identification key for Very Deep Yellow Soils


Does the subsoil have a sandy texture? No Yes

Sandy very deep yellow soil (Kandihumult) Is the lower part of the subsoil a greyish colour (somewhat poorly drained)? No Yes

Somewhat poorly drained sandy very deep yellow soil Aquic Kandihumult

Is the subsoil a uniform bright yellowish colour throughout (well drained)? No * Yes

Well drained sandy very deep yellow soil Typic Kandihumult

Does the subsoil have a loamy or clayey texture? No * Yes

Clayey very deep yellow soil (Palehumult) Is the lower part of the subsoil a greyish colour (somewhat poorly drained)? No Yes

Somewhat poorly drained clayey very deep yellow soil Aquic Palehumult

Is the subsoil yellowish brown with red/ orange mottles (spots) (moderately well drained) No Yes

Moderately well drained clayey very deep yellow soil Oxyaquic Palehumult

Is the subsoil a uniform yellowish or brownish colour (well drained)? No * Yes

Well drained clayey very deep yellow soil Typic Palehumult


Very Deep Yellow Soils – soil attributes affecting cropping Acid, with aluminium toxicity Low nutrient reserves

Sandy very deep yellow soils only Nutrients easily leached

Somewhat poorly drained sandy very deep yellow soils only Waterlogging

Well drained sandy very deep yellow soils only Steep slopes (commonly 25-70%) Erosion hazard

Clayey very deep yellow soils only Clayey textured subsoil High potential for P fixation

Somewhat poorly drained clayey very deep yellow soils only Waterlogging

Moderately well drained clayey very deep yellow soils only Often on steep slopes (up to 30%)

Well drained clayey very deep yellow soils only Steep slopes (commonly 15-30%) Erosion hazard


Depth, cm

0 - 5

5 - 15

15 - 35

35 - 70

70 - 100

3.6. Yellow Soils (Haplohumults) Occurrence Occur on slopes of hills Formed in weathered sandstone and shale

Features Yellowish brown colour Deep (between 100 and 150 cm) Loamy or clayey subsoil texture Well drained to somewhat poorly drained


Drainage


Soil Subtype identification key for Yellow Soils


Is the subsoil yellowish brown with red/orange mottles (spots) (moderately well drained or somewhat poorly drained)? No Yes

Moderately well drained yellow soil Oxyaquic Haplohumult

Is the subsoil a uniform yellowish or brownish colour (well drained)? No * Yes

Well drained yellow soil Typic Haplohumult

Yellow Soils – soil attributes affecting cropping Clayey textured subsoil Steep slopes (commonly 20-70%) Erosion hazard Acid, with aluminium toxicity Low nutrient reserves High potential for P fixation


Depth, cm

0 - 3

3 - 20

20 - 35

35 - 90

90 - 100

3.7. Brown Over Grey Soils (Aqualfs)

Occurrence Occur on flats Formed in alluvial clay sediments

Features Yellowish brown coloured layer

with red/orange mottles overlying grey clay layer within 50 cm of surface

Deep or very deep (>100 cm) Clayey subsoil texture Poorly drained − Watertable near the surface


Water table depth


Soil Subtype identification key for Brown Over Grey Soils


Does the soil have greater than 50 percent brown colour between 25 and 75 cm of the soil surface? No Yes

Somewhat poorly drained brown over grey soil Aeric Epiaqualf

Poorly drained brown over grey soil Typic Epiaqualf

Brown Over Grey Soils – soil attributes affecting cropping Clayey texture Low nutrient reserves

Somewhat poorly drained brown over grey soils only Waterlogging Acid, with aluminium toxicity

Poorly drained brown over grey soils only Prolonged waterlogging Acid, with aluminium toxicity for sensitive crops High potential for P fixation and iron toxicity


Depth, cm

0 - 5

5 - 10

10 - 20

20 - 30

30 - 60

60 - 100

100 - 200

3.8. Sulfuric Soils (Aquepts) Occurrence Occur on flats Formed in alluvial clay sediments

Features Sulfuric layer (pH <3.5)within 150 cm depth Grey colour Clayey or loamy subsoil texture Very deep (>150 cm) Poorly drained − Watertable near the

surface


Depth to sulfuric layer Presence of a soft

mineral layer


Soil Subtype identification key for Sulfuric Soils


Does the sulfuric layer occur within 50 cm of the soil surface? No * Yes

Poorly drained sulfuric soil (Sulfaquept) Does a soft layer occur within 100 cm of the soil surface? No Yes

Soft poorly drained sulfuric soil Hydraquentic Sulfaquept

Poorly drained sulfuric soil Typic Sulfaquept

Sulfuric Soils – soil attributes affecting cropping Waterlogging Shallow sulfidic/sulfuric material (often within 30 cm of surface) Acid, with aluminium toxicity

Soft poorly drained sulfuric soils only Sandy texture Low nutrient reserves Nutrients easily leached

Poorly drained sulfuric soils only Clayey subsoil texture High potential for P fixation


Depth, cm

0 - 10

10 - 30

30 - 110

110 - 180

180 - 200

3.9. Sulfidic Soils (Aquents) Occurrence Occur on flats Formed in alluvial clay sediments

Features Sulfidic material (pH >3.5, but decreases on

ageing to <3.5) within 100 cm depth Grey colour Very deep (>150 cm) Clay or loamy texture Poorly drained − Watertable near the surface


Depth to sulfidic material Presence of a soft mineral layer Presence of a buried organic layer


Soil Subtype identification key for Sulfidic Soils


Does the sulfidic material occur within 50 cm of the soil surface? No Yes

Poorly drained sulfidic soil (Sulfaquent) Does a soft layer occur between 20 and 50 cm of the soil surface? No Yes

Soft poorly drained sulfidic soil Haplic Sulfaquent

Does a buried organic layer (organic material covered by mineral soil) occur within 100 cm of the soil surface? No * Yes

Organic poorly drained sulfidic soil Thapto-Histic Sulfaquent

Poorly drained moderately deep sulfidic soil (Aquent) Does a buried organic layer (organic material covered by mineral soil) occur within 125 cm of the soil surface? No * Yes

Organic poorly drained moderately deep sulfidic soil Sulfic Fluvaquent


Sulfidic Soils – soil attributes affecting cropping

Poorly drained sulfidic soils Shallow sulfidic material (often within 30 cm of

surface)

Soft poorly drained sulfidic soils only Clayey textured topsoil Prolonged waterlogging Acid, with aluminium toxicity Low nutrient reserves High potential for P fixation and iron toxicity

Organic poorly drained sulfidic soils only Organic (peaty) topsoil Waterlogging Acid, with aluminium toxicity for sensitive

crops High potential for P fixation

Organic poorly drained moderately deep sulfidic soils Sandy texture Waterlogging Sulfidic material (below 50 cm depth) Acid, with aluminium toxicity Low nutrient reserves Nutrients easily leached


Depth, cm

0 - 5

5 - 20

20 - 50

50 - 90

90 - 180

3.10. Grey Soils (Aquents) Occurrence Occur on flats Formed in alluvial sand sediments

Features Sandy to clayey texture Grey colour Very deep (>150 cm) Poorly drained − Water table near the surface

Soil Subtypes 1 Soil Subtype identified


Soil Subtype identification key for Grey Soils


Is the topsoil a dark colour? No * Yes

Poorly drained grey soil Humaqueptic Endoaquent

Grey Soils – soil attributes affecting cropping Clayey texture Waterlogging Acid, with aluminium toxicity Low nutrient reserves High potential for P fixation


References Grealish GJ, Fitzpatrick RW, Ringrose-Voase AJ (2007). ‘Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Report P1-2 – Soil Properties and Soil Identification Key for Major Soil Types.’ Science Report 76/07, CSIRO Land and Water, Australia.

Ringrose-Voase AJ, Grealish GJ, Wong MTF, Winston EC (2008). ‘Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Report P2-1 – Suitability of Major Soil Types for Cropping.’ Science Report 04/08, CSIRO Land and Water, Australia.

Soil Survey Staff (2003) ‘Keys to Soil Taxonomy’. 9th Edition. United States Department of Agriculture – Natural Resources Conservation Service

Schoeneberger PJ, Wysocki DA, Benham EC Broderson WD (editors) (2002) ‘ Field Book for Describing and Sampling Soils’. Version 2.0. Natural Resources Conservation Service, National Soil Survey Center, Lincoln, NE.

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