Field Manual for Soil Type Identification

Transcription

1 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

2 Copyright and Disclaimer 2008 Department of Agriculture, Negara Brunei Darussalam. All rights reserved. No parts of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission of the Department of Agriculture. Important Disclaimer: CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. 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.

3 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

4 Contacts: Project Director Dr Chris Smith, CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601 Tel: ; Project Coordinator Dr Anthony Ringrose-Voase, CSIRO Land and Water, GPO Box 1666, Canberra ACT 2601 Tel: ; 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 Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page ii

5 Table of Contents 1. Introduction Soil Classifications 1 2. Describing Soil Properties Instructions Site Characteristics 4 Location 4 Slope 4 Landscape position 4 Watertable depth Earthcover Observable Soil Characteristics 4 5 Soil Depth 5 Soil Layer Thickness 5 Soil Moisture 5 Soil Texture Soil Consistence 6 7 Soil Colour 8 Soil ph 10 Soil Cracks Soil Type Identification Key Organic Soils (Saprists) White Soils (Aquods) Cracking Clay Soils (Aquerts) Texture Contrast Yellow Soils (Udults) Very Deep Yellow Soils (Humults) 22 Field Manual for Soil Type Identification Page iii

6 3.6. Yellow Soils (Haplohumults) Brown Over Grey Soils (Aqualfs) Sulfuric Soils (Aquepts) Sulfidic Soils (Aquents) Grey Soils (Aquents) 36 References Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page iv

7 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 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. Field Manual for Soil Type Identification Page 1

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

9 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 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). Field Manual for Soil Type Identification Page 3

10 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. Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 4

11 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 Dry Moist Wet Description Hands remain dry when holding sample, soil readily absorbs moisture when applied. Hand will feel damp when holding the sample but no free water visible Free water easily visible Soil moisture provides information on the soil drainage and the potential water table depth (wet soil). Field Manual for Soil Type Identification Page 5

12 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 Organic material Sandy Loamy Clayey Description Dominated by decomposed plant fibres. Often soft and easily squeezed when moulded in the hand. The soil stays loose and separated. It cannot be moulded into a ball or rolled into a ribbon. 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. 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 Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 6

13 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 Loose, weak Friable, firm Soil is easily squeezed by hand and there is no resistance when pressure is applied to the soil block between the thumb and forefinger Soil block crumbles under slight force applied between thumb and forefinger. Soil block crumbles under moderate to strong applied force applied by the hand. Usually organic material and occasionally sandy soils that are saturated. Usually sandy soils 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. Field Manual for Soil Type Identification Page 7

14 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 Black 5YR/ <3/ YR/ <3/ YR/ <3/ 1-2 Description Peat / organic soils high in organic matter Example soil colour White -/ 8/ <4 Sandy / quartz Red 10R/ -/ YR/ -/ 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 Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 8

15 Soil Colour Typical Munsell hue/ value/chroma Brown 2.5YR/ <7/ 3-4 5YR/ <6/ YR/ <6/ YR/ <6/ Y/ <5/ 2-6 Grey Gley charts/ -/ 3-7/ 1 Description Moderate soil organic matter content, and some iron oxides Near permanent waterlogging; anaerobic conditions Example soil colour 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. Field Manual for Soil Type Identification Page 9

16 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. Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 10

17 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. Field Manual for Soil Type Identification Page 11

18 Soil Type identification key Diagnostic features for Soil Type Does the upper 80 cm of soil consist of more than 40 cm of organic material (peat)? 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? 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)? Does the subsoil have a dominantly yellowish colour AND a texture contrast (sandy surface layer above loamy or clayey subsoil)? Does the upper subsoil have a dominantly yellowish or brownish colour, AND is the soil depth greater than 150 cm? Soil Type Soil Taxonomy classification Organic soil Saprist page 14 White soil Aquod page 16 Cracking clay soil Aquert page 18 Texture contrast yellow soil Udult page 20 Very deep yellow soil Humult page 22 Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 12

19 Diagnostic features for Soil Type Does the subsoil have a dominantly yellowish or brownish colour, AND is the soil depth less than 150 cm? 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? Does a sulfuric layer (ph<3.5) occur within 150 cm of the soil surface, AND is the subsoil uniformly grey coloured (poorly drained)? 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)? Does the subsoil have a greyish colour and no other diagnostic features within 150 cm of the soil surface? No * Yes Soil Type Soil Taxonomy classification Yellow soil Haplohumult page 26 Brown over grey soil Aqualf page 28 Sulfuric soil Aquept page 30 Sulfidic soil Aquent page 32 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. Field Manual for Soil Type Identification Page 13

20 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 Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 14

21 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? Does sulfidic material (ph>3.5 which changes on ageing to ph<3.5) occur within 100 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? Sulfidic organic soil (Sulfisaprist) Does a mineral soil layer >30 cm thick occur within 100 cm of the soil surface? Mineral sulfuric organic soil Terric Sulfosaprist Sulfuric organic soil Typic Sulfosaprist 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 Field Manual for Soil Type Identification Page 15

22 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 Subtypes 2 Soil Subtypes identified based on: Soil texture Dark organic topsoil layer Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 16

23 Soil Subtype identification key for White Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup 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? 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 Field Manual for Soil Type Identification Page 17

24 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 Soil Subtypes 2 Soil Subtypes identified based on: Presence of sulfidic material or sulfuric layer Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 18

25 Soil Subtype identification key for Cracking Clay Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup 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? Poorly drained cracking clay soil (Aquert) Does sulfidic material occur within 100 cm of the soil surface? No * Yes Poorly drained cracking clay soil (Aquert) Does a soil layer with ph<4.5 occur within 50 cm of the soil surface? No * Yes Sulfidic poorly drained cracking clay soil Sulfic Sulfaquert 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) Field Manual for Soil Type Identification Page 19

26 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 Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 20

27 Soil Subtype identification key for Texture Contrast Yellow Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup 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 Field Manual for Soil Type Identification Page 21

28 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 Subtypes 5 Soil Subtypes identified based on: Soil texture Drainage Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 22

29 Soil Subtype identification key for Very Deep Yellow Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup Does the subsoil have a sandy texture? Does the subsoil have a loamy or clayey texture? No * Yes Sandy very deep yellow soil (Kandihumult) Is the lower part of the subsoil a greyish colour (somewhat poorly drained)? Is the subsoil a uniform bright yellowish colour throughout (well drained)? No * Yes Clayey very deep yellow soil (Palehumult) Is the lower part of the subsoil a greyish colour (somewhat poorly drained)? Is the subsoil yellowish brown with red/ orange mottles (spots) (moderately well drained) Is the subsoil a uniform yellowish or brownish colour (well drained)? No * Yes Somewhat poorly drained sandy very deep yellow soil Aquic Kandihumult Well drained sandy very deep yellow soil Typic Kandihumult Somewhat poorly drained clayey very deep yellow soil Aquic Palehumult Moderately well drained clayey very deep yellow soil Oxyaquic Palehumult Well drained clayey very deep yellow soil Typic Palehumult Field Manual for Soil Type Identification Page 23

30 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 Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 24

31 Field Manual for Soil Type Identification Page 25

32 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 Soil Subtypes 2 Soil Subtypes identified based on: Drainage Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 26

33 Soil Subtype identification key for Yellow Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup Is the subsoil yellowish brown with red/orange mottles (spots) (moderately well drained or somewhat poorly drained)? Is the subsoil a uniform yellowish or brownish colour (well drained)? No * Yes Moderately well drained yellow soil Oxyaquic Haplohumult 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 Field Manual for Soil Type Identification Page 27

34 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 Soil Subtypes 2 Soil Subtypes identified based on: Water table depth Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 28

35 Soil Subtype identification key for Brown Over Grey Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup Does the soil have greater than 50 percent brown colour between 25 and 75 cm of the soil surface? 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 Field Manual for Soil Type Identification Page 29

36 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 Soil Subtypes 2 Soil Subtypes identified based on: Depth to sulfuric layer Presence of a soft mineral layer Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 30

37 Soil Subtype identification key for Sulfuric Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup 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? 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 Field Manual for Soil Type Identification Page 31

38 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 Soil Subtypes 3 Soil Subtypes identified based on: Depth to sulfidic material Presence of a soft mineral layer Presence of a buried organic layer Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 32

39 Soil Subtype identification key for Sulfidic Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup Does the sulfidic material occur within 50 cm of the soil surface? Poorly drained sulfidic soil (Sulfaquent) Does a soft layer occur between 20 and 50 cm of the soil surface? Does a buried organic layer (organic material covered by mineral soil) occur within 100 cm of the soil surface? No * Yes 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 Soft poorly drained sulfidic soil Haplic Sulfaquent Organic poorly drained sulfidic soil Thapto-Histic Sulfaquent Organic poorly drained moderately deep sulfidic soil Sulfic Fluvaquent Field Manual for Soil Type Identification Page 33

40 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 Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 34

41 Field Manual for Soil Type Identification Page 35

42 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 Depth, cm Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 36

43 Soil Subtype identification key for Grey Soils Diagnostic features for Soil Subtype Soil Subtype Soil Taxonomy Subgroup 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 Field Manual for Soil Type Identification Page 37

44 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. Soil Fertility Evaluation/Advisory Service in Negara Brunei Darussalam Page 38