Department of Geography and Environmental Studies Wilfrid Laurier University GG282 Lab Exercise Six Applied Geomorphology: Soil Horizons, Profiles and Classification Introduction In this exercise, students will review: (i) the basics of soil horizons, (ii) the textural terms that are used to describe soil horizons, (iii) the physical properties that can help us to differentiate between horizons, (iv) sample data on soil horizons and profiles, and (v) classifying soil profiles into Soil Orders. Some of the materials in this lab have been covered in earlier exercises and in lecture. These materials that are reviewed here are to support the topics that are included in this lab. Canadian System of Soil Classification Reference The Canadian System of Soil Classification, Third Edition (1998). Agriculture and Agri-Food Canada Publication 1646, 187 pp. Available online at: Soil Horizons A soil horizon is a laterally continuous layer in a soil profile that is approximately parallel to the surface. Within a given horizon the physical properties of texture, colour, consistency, organic content, and structure are relatively uniform. Horizons are classified based on their position in the soil profile, their composition and on their physical characteristics. Soil types or soil orders are determined based on the sequence and characteristics of horizons that are present in a profile (or pedon) at a location. There are two tables that follow which present the codes that are used to designate soil horizons in Canada. Table 1 presents the major mineral and organic horizons of the Canadian System of Soil Classification. The major mineral horizons are designated as either A, B, or C depending upon their position and characteristics. There are also organic horizons that are designated as either O, L, F or H. The properties of the major mineral and organic horizons are described in Table 1. These major horizons can, in turn, be divided into subhorizons. The common subhorizons designations employed in the Canadian System of Soil Classification are presented in Table 2. The suffixes that are presented in Table 2 are used to modify the terms in Table 1. Note that Table 2 presents only the commonly used subhorizon designations or modifiers. Horizon Properties: Texture One of the most important properties of a soil horizon is its texture. When we determine the texture of a soil horizon we exclude particles that are larger than sand sized. The gravel sized particles are referred to as stones, and we reviewed in Lab 5 a series of terms that are used to denote stoniness. There are a series of common terms that are used to characterize soil texture, these are terms such as loam, silty loam. In a field setting it is relatively simple to approximate the texture of a sample by a hand test (recall Lab 1) and laboratory techniques can be used to determine the percentages of sand, silt and clay (recall Lab 2) that are then used to classify the texture of a soil sample. The terms that follow are just some of the commonly used terms for you to review, this is not an exhaustive list: 1) Sand – individual grains can be seen, when moist it will form a cast that crumbles when touched 2) Sandy Loams – sand dominated but with enough silt and clay to give some coherence, when moist it will form a cast that can be handled 3) Loam – a even mixture of sand, silt and clay, has a gritty feel but is somewhat plastic, will form a cast when dry, a moist cast can be handled without breaking 4) Silt Loam – more than 50% silt, with a moderate amount of (fine) sand and a small amount of clay, may form clods when dry, but when crushed feels floury, when moist can form into a rough, broken ribbon 5) Clay Loam – fine soil that has moderate amount of clay mixed with silt and ( fine) sand, forms hard clumps when dry, when moist it will form a ribbon, but will break with much handling 6) Clay – dominated by clay, forms hard clumps when dry, plastic and often sticky when wet, will form a thin flexible ribbon when wet (normally) From a full particle size analyses it is possible to determine the %’s of sand, silt and clay in a soil sample. The textural classification used by the Canadian System of Soil Classification is shown here. These textural classifications are often shown as ternary diagrams (triangular graphs). The graph here allows the texture of the soil sample to be determined if the %’s of clay and sand are known. The % clay and % sand data are plotted as a point on the graph and the soil texture is read off. For example, a sample that is 30% clay, 30% silt and 40% sand would plot in the Clay Loam portion of the classification. Soil texture plays an important role as an influence on water movement and moisture storage, soil structure as well as a control on the distribution of nutrients. For the four samples below, plot the data on the textural triangle and confirm the appropriate textural term to describe those samples. Soil Sample % Sand % Silt % Clay Textural Term 1 40 40 20 Loam 2 30 55 15 Silt Loam 3 10 35 55 Clay 4 80 15 5 Loamy Sand Horizon Properties Soil Colour The colour of each horizon, or a sampling point in a profile, should be determined by using a Munsell Soil Colour Chart. To use the Munsell System for soil colour, a soil sample is held up against a series of coloured standards (chips) and the soil colour is determined by comparing the sample to the standards until a match is found. The Munsell System describes colour using three components: Hue (a specific colour in the visible spectrum), Value (refers to lightness or darkness), and Chroma (refers to the colour intensity or saturation). The standard colour chips are arranged by Hue in pages of colour chips. The soil Hue is first determined and then the Value and Chroma are determined. The Hue is denoted using a number and uppercase letter(s) such as 7.5YR (for Yellow Red). The Value is denoted by a number that runs vertically on the page, with lower values indicating darker colours and higher values lighter colours. The Chroma is arranged horizontally on the page with the lower Chroma indicating less colour intensity (more grey) and higher Chroma more intense colours. The Munsell colour is given in the sequence: Hue Value/Chroma. In the example circled in Yellow to the right, the colours is 7.5YR 5/4. For a complete description of colour it should be recorded under the following conditions: (i) moist soil colour, (ii) ped face colour, (iii) air dry colour (in lab), (iv) rubbed colour (rub soil onto a clean white surface). The Munsell System is described at: Example Munsell charts can be seen at: and There is an interesting blog post from European Geosciences Union on soil colour at: Unfortunately there are several photographs from that post that have been moved off that page, the captions for the first 10 photographs are visible but the photos are missing, they are on the photo site imaggeo and the links are below. Note that these are examples from outside of Canada and the classification terminology reflects the systems used in those areas. Stoniness As was reviewed in Lab 5, the textural terms used for soil horizons or samples can be modified if a soil horizon has a very coarse texture. The gravel components of a sample are referred to as stones. The term stoniness is used to denote the relative proportions of gravel sized particles (stones) in a soil sample. An assessment of stone prevalence can be made in each soil horizon in a profile (or sample) by determining the percentage of the mass of a horizon (or sample) that is comprised of gravel sized clasts. The intent is to describe what fraction of the soil horizon or sample is comprised of gravel materials (anything coarser than sand). One of the commonly used classifications of stoniness is: Few stones (1-5%), Common Stones (6-15%), Many Stones (16-35%), Abundant Stones (36-70%), and Extremely Abundant Stones (>70%). The term stony or gravelly can be used to modify the textural description of a sample (e.g. gravelly loam) Mottling Mottles are localized nodular (spot) or streaked shaped discolourations that have a substantially different colour than the surrounding dominant soil colour (colour of the soil matrix). Mottles can occur under a range of conditions but in Canadian soils they are most common in poorly drained soils such as Gleysols. The typical colour of a Gleysol is a blue grey. As Gleysols periodically dry out there maybe some localized oxidation which can produce pale yellow or reddish discolourations (mottles). Alternatively the mottle colours could be different, such as a grey or blue colour and be found in a soil with a different dominant colour. The presence, abundance, size and boundary conditions of mottles should be noted if they are present. Mottles can be an indicator of gleying in a soil. Organic Matter The distribution of organic matter should be noted in a soil horizon, include information on the state of decomposition, presence of organic coatings on stones, degree of mixing, and the presence of roots or other organics. Samples can be taken in the field and the organic matter content can be measured in the lab through combustion or a wet chemical technique. In Lab 2 we used a combustion technique (Loss on Ignition) to determine the organic matter content of a series of samples, including some soil horizons. Organic matter in the soil plays a key role in water retention and transmission, in nutrient storage and exchange, influences soil cohesion, and can impact soil pH and soil forming processes. It strongly influences soil colour and the colour can be used to make a relative determination of the organic content. Soil Structure Soil structure should be described based on the size, shape and development of aggregates of soil particles (peds). Common soil structures are: Platy (sheet like peds), Columnar (or prismatic, long vertically developed peds), and Granular (small equant peds). When a large granular structure is seen the term Blocky is used. If no soil structure can be discerned, use the term Apedal. Soil structure influences the exchange and transfer of water and air in the soil, it can reflect and influence specific soil forming processes and or the physical properties of the soil parent material. Soil Consistence Consistence can be described by measuring the: (i) strength, (ii) stickiness, (iii) cementation, and (iv) plasticity. Elements of soil consistency were covered in Lab 2. The quantity and type of fine textured materials in a soil horizon or sample has a significant impact on the soil consistency. Soil Orders and Horizons We determine the soil order by examining the sequence of horizons that are present and for looking for diagnostic horizons and their characteristics. The characteristics of the major horizons and properties of soil samples and horizons were first reviewed in lecture in the early part of the course. Lecture 12 has information on soil classification. Table 1 presents information on the major horizons focusing on the mineral and organic horizons. Information on subhorizons is presented in Table 2. The suffixes that are presented in Table 2 are used to modify the terms in Table 1. Table 1: The major Mineral and Organic Horizons of the Canadian System of S oil Classification. Mineral Horizons (contain 17% or less organic Carbon (about 30% organic matter) by A This mineral horizon forms at or near the surface. It is characterized by: leaching, eluviation, accumulation of organic matter or some combination of these. An accumulation of organic matter is usually seen by a darkening of the soil (Ah). Conversely, the removal of organic matter is usually expressed by a lightening of the soil colour (Ae). An Ae horizon may have a light ash grey appearance. The removal of clay (Ae) is expressed by a coarser soil texture relative to the underlying layers. The removal of iron is indicated by a paler or less red soil colour (Ae) relative to the lower part of the subsoil. B This mineral horizon is characterized by enrichment in organic matter, sesquioxides (iron and aluminum oxides), or clay; or by the development of soil structure; or by a change of colour denoting hydrolysis, reduction, or oxidation. B horizons enriched in iron compounds often have a red or reddish orange colour (Bf). In B horizons, accumulated organic matter (Bh) is evidenced usually by dark colours relative to the C horizon. Clay accumulation is indicated by finer soil textures and by clay coatings on particles and lining pores (Bt). Soil structure developed in B horizons includes prismatic or columnar units with coatings or stainings and significant amounts of exchangeable sodium (Bn) and other changes of structure (Bm) from that of the parent material. Colour changes include relatively uniform browning due to oxidation of iron (Bm), and mottling and gleying of structurally altered material associated with periodic reduction (Bg). C R This mineral horizon is comparatively unaffected by the soil forming processes operating in the A and B horizons, except the process of gleying (Cg), and the accumulation of calcium and magnesium carbonates (Cca) and more soluble salts (Cs, Csa). Bedrock layer that is too hard to break with the hands or to dig with a spade when moist. It does not meet the requirements of a C horizon. Organic Horizons (contain >17% organic Carbon (about 30 % or more organic matter) O This peat rich organic horizon is developed from mosses, rushes, and woody materials L, F, H: These organic horizons are developed primarily from the accumulation of leaves, twigs, and woody materials with or without a minor component of mosses. They are subdivided into three types. L Original structures are easily discernible. F Partly decomposed organic matter. Some of the original structures difficult to recognize. H Characterized by an accumulation of decomposed organic matter in which the original structures are indiscernible. This horizon differs from F by having greater humification due chiefly to the action of organisms. Table 2: Subhorizons of the Canadian System of Soil Classification (abbreviated and simplified, see CSCS for full table) Subhorizons : Lowercase suffixes b Buried soil horizon. c Cemented (irreversible) soil horizon (e.g. a layer cemented by calcium carbonate (CaCO3)). ca Horizon of secondary carbonate enrichment in which the concentration of lime exceeds that in the unenriched parent material. e Horizon characterized by the eluviation of clay, Fe, Al, or organic matter alone or in combination. It is used in combination with A. f Horizon enriched with amorphous material, principally Al and Fe combined with organic matter; reddish in colour near upper boundary becoming yellower with depth. g Horizon characterized by grey colours, or prominent mottling, or both, indicating permanent or periodic intense reduction (gleying). h Horizon enriched with organic matter. j A modifier of suffixes e, f, g, n, t, and v to denote an expression of, but failure to meet, the specified limits of the suffix it modifies. k Denotes the presence of carbonate as indicated by visible effervescence when dilute HCI is added m Horizon slightly altered by hydrolysis, oxidation, or solution, or all three to give a change in colour or structure, or both. n Horizon in which the ratio of exchangeable Ca to exchangeable Na is 10 or less. It must also have a prismatic or columnar structure, have dark coatings on ped surfaces, and have a hard to very hard consistence when dry. p Horizon disturbed by anthropogenic activities such as cultivation, logging, and habitation. s Horizon with salts, including gypsum, which may be detected as crystals, veins or surface crusts of salts. sa Horizon with secondary enrichment of salts more soluble than Ca and Mg carbonates; the concentration of salts exceeds that in the unenriched parent material. t An illuvial horizon enriched with silicate clay. It is used with B alone (Bt), with B and g (Btg), with B and n (Bnt), etc. u Horizon that is markedly disrupted by physical or faunal processes other than cryoturbation or argillipedoturbation. v Horizon affected by argillipedoturbation (disruption and mixing caused by shrinking and swelling of the soil). y Horizon affected by cryoturbation; produces disrupted and broken horizons, and the incorporation of materials from other horizons, and mechanical sorting. z A frozen layer. Soil Classification and Taxonomy At the local scale, the three dimensional space that we use to examine a soil is called the Pedon. When we examine a group of pedons we may see similarities in soil properties over small distances. However, we may also note that pedons (soils) that are widely separated have much different physical properties and characteristics. We look for patterns in nature by classifying features. Taxonomy is the practice and science of classification. Through soil classification, we may increase our understanding of the factors and processes that influence soil development. We may also be able to recognize associations that exist between the characteristics of soils and the abiotic and biotic environmental variables such as climate, sediments (parent amterials), drainage and vegetation. Soils may be classified using a variety of criteria. We will use the Canadian System of Soil Classification. This system is based on the processes that influence soil development (genetic processes). The system is hierarchical and soils are grouped into similar units (taxa) based on a series of relatively objective measurable soil properties. At the highest level in the system, soils are grouped into broad categories that reflect generalized differences in the soil environment and the soil forming processes that influence soil development. Soil Orders Groups of soils (taxa) are organized at the at highest level into Soil Orders. At this level, soils with similar properties reflect the nature the dominant, soil-forming processes. Soil Orders are in turn divided into Great Groups, Subgroups, Families, and Series. With each successive level, more details on soil properties are included and finer spatial divisions on the landscape are the result. The important soil forming processes that influence the soil orders include: (i) leaching, (ii) calcification, (iii) podzolization, (iv) lessivage (clay translocation), (v) gleying, (vi) upward translocation, (vii) cryoturbation (physical mixing), (viii) decomposition of organic material (humification) and melanization, (ix) salinization, and a variety of other biological, chemical and physical weathering processes. Map of Soil Orders The map on the following page shows the general distribution of the soil orders that are used in the Canadian System of Soil Classification. This map is the same as the one that is used in the lecture. Students should review the materials in Lecture 12 and review the supporting information. A brief description of each of the soil orders is in Table 3 of this handout. An online map that shows the distribution of Soil Orders and the Great Groups is available from a webpage of interactive maps from the Canadian Soil Information System of the federal government at: At this page, click on the image that is below the heading Soils of Canada. An example of that map is shown in the lecture 12 notes. Figure 1: Distribution of the Soil Orders in Canada (produced from data from Agriculture Canada). Soil Order Characteristics Table 3: General Characteristics of the Soil Orders Brunisolic Chernozemic Cryosolic Gleysolic Luvisolic Soils with horizons that are sufficiently developed to exclude them from the Regosolic order, but they lack the development required for soils of other orders. These soils, which occur under a wide variety of climatic and vegetative conditions, all have brownish Bm or Btj horizons. Soils that have developed under grasses and herbs, or under a mixed grassland forest vegetation, in cool to cold, subarid to subhumid climates. These soils have a dark coloured A horizon (Ah, Ahe, Ap) and often a B or C horizon (or both) in which there are high levels of base cations (Ca2+ , Mg2+, K+). Soils that are developed in either mineral or organic materials that have permafrost within 1 m of the surface or within 2 m if the soil has been strongly cryoturbated as indicated by disrupted, mixed, or broken horizons. Soils that have developed under wet conditions. Some horizons are grey or blue grey in colour and usually exhibit prominent mottles. This character results from reduction of iron and other compounds in the process of gleying. Soils that have light coloured, eluvial horizons (Ae) and have illuvial B horizons in which silicate clays have accumulated (Bt). These soils develop under deciduous or mixed forest or mixed forest grasslands in subhumid to humid, mild to very cold climates. Organic Soils that have developed in organic deposits. Includes soils commonly known as peat, muck, or bog and fen soils. Most Organic soils are saturated with water for prolonged periods. Common in poorly and very poorly drained depressions and level areas in regions of subhumid to humid climate. Podzolic Soils that have B horizons in which the dominant accumulation product is amorphous material composed mainly of humified organic matter combined in varying degrees with Al and Fe (Bh, Bhf, or Bf). Typically Podzolic soils occur in coarse to medium textured, acid parent materials, under forest or heath vegetation in cool to very cold and humid climates. Regosolic Soils having insufficient A or B horizon development to meet the requirements of other orders, perhaps on young parent materials Solonetzic Soils that have B horizons that are very hard when dry and swell to a sticky very low permeability mass when wet. The B horizon has prismatic or columnar structure. They occur on saline parent materials in some areas of the semi-arid to subhumid Interior Plains. Vertisolic Soils with a relatively high clay content (including the mineral smectite) that are subject to periodic swelling and shrinking (due to absorption and loss of water in wetting and drying cycles) which produces prominent cracks, mixing (called argillipedoturbation) and smooth to striated planar surfaces (called slickensides). Most common in the cool, subarid to subhumid, grassland portion of the Interior Plains of western Canada. Identifying and Classifying Soils To understand the distribution of soil orders we must review how we describe and classify soils and what variables influence this distribution. Soils are classified based on their sequence of horizons, the characteristics of the horizons, and several other physical and chemical parameters. The general attributes of the main horizons (O, L, F, H, A, B, C, R) and subhorizons (Ah, Ae, Bt, Bg etc) were reviewed in the handout in Lab 5. Details on the classification of soils and on the characteristics of horizons, subhorizons and sequences of horizons that comprise each order are presented in The Canadian System of Soil Classification. The diagram below illustrates one typical horizon sequence that is associated with each of the soil orders (Organic and Vertisolic orders are not shown). Figure 2: Typical horizon sequences associated with the soil orders. These sequences are not the only combination of horizons that are possible for each order but rather are typical assemblages. In a real soil profile (or pedon) in the field, the boundaries between horizons are normally horizontal. The boundaries in this diagram are shown as inclined planes to represent the variations in horizon thicknesses that are commonly observed. For example, in the Brunisolic order (Brunisols), there is a horizon sequence of a thin organic layer at the surface (LF), an Ah horizon that varies between approximately 10 and 20 cm in thickness, a Bm horizon that varies between 5 and 30 cm in thickness which overlies the C horizon. In the table on the following page, there are three sequences of horizons presented, what soil order do each represent? Soil 1 Soil 2 Soil 3 Horizon Thickness (cm) Horizon Thickness (cm) Horizon Thickness (cm) L 5 Ah 30 Ah 30 Ah 5 Bg 10 Btj 15 Ck 95 Cg 60 Cca 55 (Answers: Soil 1: Regosol; Soil 2: Gleysol; Soil 3: Chernozem) We may also use a key to assist us in classifying soils, a detailed key is presented in the Canadian System of Soil Classification, a simplified key is presented below in Table 4 (use caution: this simplified key will not work in all cases). Table 4: Simplified Key to Soil Orders Criteria Order 1 Soil has permafrost within 1 m of the surface (within 2 m if cryoturbated) Cryosolic 2 Soil has a vertic horizon and a slickenside horizon (within 1 m of surface) Vertisolic 3 Soil has a Bf, Bhf, or Bh horizon that is at least 10 cm thick, if a Bt horizon is present it is at least 50 cm below the surface Podzolic 4 Soil has a Bg or Cg horizon that is within 50 cm of surface Gleysolic 5 Soil has a Bn or Bnt horizon Solonetzic 6 Soil has a Ah, Ahe or Ap horizon that at least 10 cm thick, brown to black in colour, has an organic carbon content between 1-17%, is calcareous, and the soil is an area with a mean annual soil temperature of at least 0°C and an arid to subhumid climate 7 Soil has a Bt horizon in the upper 50 cm of the soil (not Btj) Luvisolic 8 Soil has a Bm horizon that is at least 5 cm thick Brunisolic 9 Soil lacks a B horizon or the B horizon is less than 5 cm thick Regosolic 10 Soil is greater than 30% organic matter by weight Chernozemic Organic To use this key, start at the top of the table at criteria number 1. Evaluate the unknown soil using the condition outlined in that criteria. If the unknown soil satisfies the condition specified then it is very likely from the soil order listed in the far right column. If the soil does not satisfy the condition listed then move down to the next criteria and evaluate for that condition. Continue down the table until you have placed the soil in the appropriate order. Recall the Canadian system has a hierarchical structure, soil orders are subdived into smaller units called great groups which in turn are divided into subgroups. Similar keys are also available to help place soils in the more detailed levels in classification system (Soil Great Groups and Soil Subgroups). GG282: Lab 6 Questions In the tables below there are a series of tables. Each table represents a soil profile. Each profile has a series of horizons. Each line in the table represents a separate horizon. There are dimensions given above and below a zero datum. The zero datum is the contact between the surface organic materials (if present) and the top of the A horizon. The data that are included are descriptions of the field appearance of the soil horizons as well as properties that were determined in the lab. You will identify the types of horizons that are present, based on the data that are available below. Horizon Descriptions The tables below provide profile data on four unknown soils, your task is to determine the sequence of horizons that are present in each soil. Using the data provided determine the type of horizons that are present. Use the Lab 6 background document, the lecture materials as well as the Canadian System of Soil Classification to make the determinations. The first table shows an example soil,. This table has been completed. Your task is to do the same for the other four unknown soils. When you complete your determination, fill in the sentences that appear below the tables. Example Soil Surface cover is mainly coniferous forest with a mixture of spruce, pine, fir and trembling aspen, the area has much precipitation, the underlying bedrock is igneous and metamorphic and the parent material is coarse textured glacial till. Position in Profile (cm) Texture 0 to +4 NA Colour Organic Carbon (% by weight) Other Features Horizon dark brown 50 partially decomposed needles and twigs L or F brown black 5YR4/3 10 horizon has a low pH, surface is covered in 4 cm of organics light ash grey 7.5YR7/1 2 reddish dark brown 7.5YR3/4 7 Clear Smooth Boundary 0 to -15 -15 to -22 -22 to -35 loam sandy loam sandy clay loam Ah granular structure, ash grey colour, low pH, boundaries above and below are wavy and diffuse, few stones blocky structure, humic (organic coatings on some peds and clasts), low pH, few stones Ae Bh -35 to -50 -50 to -75 sandy clay loam clay loam red and yellowish brown2.5Y 4/4 1 light brown 0 blocky structure, horizon has presence of iron and aluminum oxides Bf no soil structure, low pH C This soil has a horizon sequence from top to bottom of: L/F, Ah, Ae, Bh, Bf, C Soil 1: Surface cover is an open deciduous woodland mixed with grasses, the parent materials are fine textured glaciolacustrine deposits, the site is seasonally wet and much organic material has accumulated on the surface. Position in Profile (cm) Texture Colour Organic C Carbon (% by weight) Other Features 0 to +9 silty loam dark brown 45 partially decomposed leaves (deciduous), twigs, and grasses Horizon Abrupt boundary to the mineral horizon 0 to -5 loam brown 10YR6/2 6 granular and blocky structure, humic, soil surface covered in layer of organic rich material -5 to -20 silt loam light grey brown 7.5YR7/2 2 granular structure, ash grey brown colour, very gradual colour changes to underlying horizon, much less organic material than overlying horizon -20 to -70 silty clay light brown 10YR6/2 1 platy and granular structure in upper part of horizon, low permeability, clay coatings are found on peds and on coarse clasts and in pores and openings -70 to -80 clay loam light brown 10YR6/2 0 high bulk density, no soil structure, very weakly calcareous, does show effervescence when dilute HCl is added Soil 2: Surface cover is an coniferous forest dominated by white spruce, red pine, tamarack, and trembling aspen. Canopy is partially open and the site is relatively dry. Parent Material for the soil is a gravel and sand textured ice contact stratified deposit. Position in Profile (cm) Texture Colour Organic Other Features Carbon (% by weight) Horizon 0 to +5 sandy loam dark brown 40 moderately decomposed needles, leaves and twigs Gradual Wavy Boundary 0 to -17 loam brown 5YR5/2 in upper portion 6 in upper portion, less in lower portion granular and blocky structure, humic, soil surface covered in 5 cm of decomposed organic materials, few stones, lower boundary is smooth and clear, pH ~6.0. -17 to -65 loamy sand light brown, 7.5YR7/2 2 granular structure, few stones increasing to base of horizon, evidence of some weathering but poor horizon development, carbonates have been removed, horizon is redder than horizon below, pH>5.5. -65 to -103 gravel and sand light brown, 10YR6/2 5.5. Soil 3: Surface cover is grasses, sedges and brush on a floodplain. The floodplain has a low gradient and is poorly drained, there is frequent innundation (flooding), the site is wet for much of the year. Position in Profile (cm) Texture Colour Organic Carbon (% by weight) Surface NA dark brown 40 Other Features in some locations there are moderately decomposed grasses, sedges, leaves and twigs on the surface of the soil Abrupt Boundary 0 to -14 silty clay loam brown 10YR4/1 8 coarse blocky structure, humic, soil surface covered in 2 cm of decomposed organic materials, few stones, lower boundary is clear -14 to -32 silty clay very light grey brown 2.5Y8/1 1 granular and platy structure, poorly drained, few stones -32 to -52 silty clay light grey 1 poorly developed platy and granular structure, low permeability, mottles are present, poorly drained, few stones Horizon -52 to base clay light grey brown 6.0, there is poor horizon development -40 to -66 silt loam light brown

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