Ngogo Mn. Ge:140 @2019

SOIL CLASSIFICATION

An Introduction

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 Introduction • Classification of is the separation of soil into classes or groups each having similar characteristics and potentially similar behaviour. • The criteria for grouping depend on the purposes of classification. • Soil is not uniformly distributed. Properties of soil vary due to several soil forming factors. properties vary very widely. Soil types are many. To identify, understand, and manage soils, soil scientists have developed a set of or taxonomy systems.

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Methods of Soil Classification Systems

• Systems which use the properties of the soils are called TAXONOMIC SYSTEMS OF CLASSIFICATION. • Systems that employ soil usage are called CAPABILITY CLASSIFICATION. • Though these systems are considered to be subjective or utilitarian system of classification. • International soil classification are primarily for use by soil specialists.

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Soil Classification Used in the Tropics

I. The FAO/UNESCO of the world (FAO/UNESCO, 1977) II. The New Comprehensive Classification System or US Soil Taxonomy Classification (Soil-Survey Staff, 1975) III. The French Classification System (Aubert (1964)

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FAO Soil Classification System

• In 1977 FAO/UNESCO published the first soil map with a uniform classification throughout. • The World Soil Map is not based on any one system, but rather, a collection of national soil maps influenced by US System. • In the FAO system, the soils that occur in a particular region and exhibit a certain relationship to one another are grouped in association or “ major soil Units”

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Terms used in the FAO nomenclature

Term Connotation Acric Extremely poor in nutrients Argillic Horizon with accumulation Chromic Soils with deep brown or red-brown B- horizon Dystric Base saturation less than 50% (relatively poor in nutrients)

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Term Connotation Eutric Base saturation greatter than 50% (relatively rich in nutrients) Ferralic Soil with Ferralsol properties; low CEC, high in Fe, and Al-oxide Ferric Soil with iron concretions Gleyic Soils with hydromorphic properties at 0-50 cm depth Hapiic Soils with less strongly developed typical characteristics

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Term Connotation Humic Soil with “umbric” horizon, i.e. relatively humus Mollic A horizon with high base saturation Ochric Relatively weak defined A horizon without “mollic and ‘umbric x-tics Orthic Normal soil formation no special featurs Oxic Oxide, complete mineral weathering; porous, permeable

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Term Connotation Plinthic With from 0-125 cm( develops from plinthite) Rhodic Bright red Vertic characteristics (swlling, Shrinking) Xanthic Bright yellow Source: FAO/UNESCO (1977)

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 1. (H)

• Organic or soils with an organic surface layer of greater or equal to 40 cm. • They contain at least 20 -30% organic matter depending on clay content. • Have limitations for agricultural use because they are usually wet.

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2. (V)

• Very heavy clay soils which develop wide deep cracks in the dry season. • Their topsoil has a x-tics micro-relief (gilgai). • They are found in basins with poor drainage or broad plains with variably moist climates. • Have poor physical properties. • Due to poor drainage and their tendency to swell make them prone to water logging

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3.

• Are young deposits in river valleys, estuaries and coastal regions. • They do not form any distinct horizons other than ochric, histic and sulfic horizons • They are cultivated for dryland crops or rice and are used for grazing in the dry season. They occupy about 2.8 percent of the continental land area on Earth, mainly in the great river basins and deltas of the world (e.g., the Amazon basin and the Nile delta). •

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4. Solonchanks (Z)

• Are structure-less saline soils with free salts often with crystallisation of salts on the surface. • Thy occur in arid and semi-arid and semi-arid regions and generally have a high ground water level with a high salt content (Chlorides and sulphates).

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5. (T)

• Are soils developed from volcanic ash. • They frequently form heavy topsoil with dark humus. Most andosols are well supplied with water and have a high water holding capacity. • Andosols occur mostly in volcanic mountainous of the humid tropics

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6. (G)

• Are hydromorphic soil (soil developed in the presence of water) • Are water logged throughout the year. • They exhibit a friable, light coloured layer of clay that graduates into a water-impermeable stratum where typical manganese concretions are found. • Occur in depressions and plains of the humid and sub-humid tropics and vary widely in character (mollic, plinthic etc.)

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7. Lithosols (I)

• Are very shallow soils, less than 10 cm deep on bedrock. • Have little available volume of soil for root extension and offer crop plants scant growth potential due to lack of water and nutrients. • They dry out quickly

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8. Arenosols (V)

• Are sandy soils with various B-Horizon which fall below the treshold of the definition “moderately pronounced” • Include soils of several groups. • Lower clay content and a higher proportion of (more than 50%). • They possess good roots and water permeability but have low water holding capacity

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9. Ferralsos (F)

• Are deeply weathered, uniformly red, yellow- red or yellow soils composed mainly of kaolinite clay (cemented through iron oxide). • Are typical soils of constantly humid tropics. • They are poor in nutrients due to heavy and deep weathering.

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10. Aerisols (A)

• Are old, acidic clay soils with low base saturtion (<5%) and a pronounced clay enriched horizon (Bt) derived from clay deposits and clay accumulation. • The name is derived from the latin acris (sour), developed from base-poor, quartz-rich parent rock (granite, sand stone). • They are typical of the subhumid tropics • They are deficient in nitrogen and trace elements.

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11. Luvisols (L)

• Have a typical clay-enriched horizon, but also higher base saturation (over 50%) • Better siuted for crop growing than . • Posses vertisol-like x-tics or “ferric” properties with iron oxide concretions. • The soils are suitable for crop production hoever, it have some limitations similar to those encountered in acrisol.

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12. (B)

• Are broen soils, which have undergone little or no ferrallisation or podzolisation. • There is almost no accumulation of the products of weathering. • Are often found in mountain areas in the tropics • Usally possess good cropping X-tics with good root permeability and little tendency to compaction

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• In Tanzania the National Soil Service has adopted the FAO/UNESCO classification as one of the framework for a national soil classification. • In order to provide information useful at a national level, soils have been correlated with the FAO/UNESCO systemes and another major international system such as US SOI Taxonomy.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019

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SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 THE NEW COMPREHENSIVE CLASSIFICATION SYSTEM (US Soil Taxonomy) • NCCS is the mos comprehensive and logical system presently existing for the worldwide classification of soil. • The basic feature of the system is that it maintains the natural body concept and has two other major features. – Based on soil properties that are easily verified by others – It employs a unique nomenclature, which gives a definite connotation of the major characteristics of the soils in question

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Soil Taxonomy categories: • Soil Taxonomy has six categories (From top to bottom) –order, –suborder, –great group, – subgroup, – family and –series

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• Ten classes are in the order level. • Criteria used to differentiate orders are highly generalized and based more or less on the kinds and degrees of soil-forming processes. • Mostly these criteria include properties that reflect major differences in the genesis of soils.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 A suborder

• is a subdivision of an order within which genetic homogeneity is emphasized. • Soil characteristics used to distinguish suborders within an order vary from order to order. • The great group category is a subdivision of a suborder. • They are distinguished one from another by kind and sequence of soil horizons. • All soils belonging to one of the suborders will have more horizons.

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Great group & sub goups • Are divided into three kinds of subgroups – typic, intergrade and extragrade. • A typic subgroup represents the basic concept of the great group from which it derives. • An intergrade subgroup contains soils of one great group, but have some properties characteristic of soils in another great group or class. These properties are not developed or expressed well enough to include the soils within the great group toward which they grade.

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• Extragrade subgroup soils have aberrant properties that do not intergrade to any known soil.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 A soil family category • Is a group of soils within a subgroup that has similar physical and chemical properties that affect response to management and manipulation. • The principal characteristics used to differentiate soil families are texture, mineralogy and temperature. • Family textural classes, in general, distinguish between clayey, loamy and sandy soils. • For some soils the criteria also specify the amount of , sand and coarse fragments such as gravel, cobbles and rocks.

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The

• is the narrowest category in soil taxonomy • It is based on their horizontal arrangement and properties; i.e. colour, texture, structure, consistence, chemical and mineral compositions. • Soil surveyors who use the name of the town, village or river where the represantative pedon (sample) was first describe usually assign series of names.

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Soil Orders:

• To identify, understand, and manage soils, soil scientists have developed a soil classification or taxonomy system. • Like the classification systems for plants and animals, the soil classification system contains several levels of detail, from the most general to the most specific. • The most general level of classification in the United States system is the soil order

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12 orders of soils (USDA)

• Each order is based on one or two dominant physical, chemical, or biological properties that differentiate it clearly from the other orders. • Each order is based on one or two dominant physical, chemical, or biological properties that differentiate it clearly from the other orders. • The 12 soil orders all end in "sol" which is derived from the Latin word "solum" meaning soil or ground. Most of the orders also have roots that tell you something about that particular soil. • For example, "molisol" is from the Latin "mollis" meaning soft.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 1. : • Gelisols (from the Latin gelare – to freeze) are soils that are permanently frozen (contain “permafrost”) or contain evidence of permafrost near the soil surface. • Are found in the Arctic and Antarctic, as well as at extremely high elevations. • Permafrost influences land use through its effect on the downward movement of water and freeze-thaw activity (cryoturbation) such as frost heaves. Gelisols make up about 9% of the world’s glacier-free land surface.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 2. Histosols: • Histosols (from the Greek histos – tissue) are dominantly composed of organic material in their upper portion. • Mainly contains soils commonly called bogs, moors, peat lands, muskegs, fens, or and mucks. • Form when organic matter, such as leaves, mosses, or grasses, decomposes more slowly than it accumulates due to a decrease in microbial decay rates. • This most often occurs in extremely wet areas or underwater; thus, most of these soils are saturated year- round. • Histosols can be highly productive farmland when drained; however, drained Histosols can decompose rapidly and subside dramatically

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 3. Spodosols: • (from the Greek spodos – wood ash) are among the most attractive soils. • They often have a dark surface underlain by an ashy gray layer, which is subsequently underlain by a reddish, rusty, coffee-colored, or black horizon. • These soils form as rainfall interacts with acidic vegetative litter, such as the needles of conifers, to form organic acids. • Spodosols most often develop in coarsely textured soils ( and loamy sands) under coniferous vegetation in humid regions of the world. • They tend to be acidic, and have low fertility and low clay content

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 4.: • Andisols (from the Japanese ando – black soil) typically form from the weathering of volcanic materials such as ash, resulting in minerals in the soil with poor crystal structure. • These minerals have an unusually high capacity to hold both nutrients and water, making these soils very productive and fertile. • Andisols include weakly weathered soils with much volcanic glass, as well as more strongly weathered soils. They typically occur in areas with moderate to high rainfall and cool temperatures.

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5. : • Oxisols (from the French oxide – oxide) are soils of tropical and subtropical regions, which are dominated by iron oxides, quartz, and highly weathered clay minerals such as kaolinite. • These soils are typically found on gently sloping land surfaces of great age that have been stable for a long time. • For the most part, they are nearly featureless soils without clearly marked layers, or horizons. Because they are highly weathered, they have low natural fertility, but can be made productive through wise use of fertilizers and lime

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 6. Vertisols • Vertisols (from the Latin verto – turn) are clay- rich soils that contain a type of “expansive” clay that shrinks and swells dramatically. These soils therefore shrink as they dry and swell when they become wet. • Vertisols are highly fertile due to their high clay content; however, water tends to pool on their surfaces when they become wet. • Vertisols are located in areas where the underlying parent materials allow for the formation of expansive clay minerals.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 7. : • Aridisols (from the Latin aridus – dry) are soils that occur in climates that are too dry for “mesophytic” plants (plants adapted to neither too wet nor too dry environments)to survive. • The climate in which Aridisols occur also restricts soil weathering processes. • Aridisols often contain accumulations of salt, gypsum, or carbonates, and are found in hot and cold deserts worldwide.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 8. :

• Ultisols (from the Latin ultimus – last) are soils that have formed in humid areas and are intensely weathered. • They typically contain a subsoil horizon that has an appreciable amount of translocated clay, and are relatively acidic. • Most nutrients are held in the upper centimeters of soils, and these soils are generally of low fertility although they can become productive with additions of fertilizer and lime.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 9. : • Mollisols (from the Latin mollis – soft) are prairie or grassland soils that have a dark colored surface horizon, are highly fertile, and are rich in chemical “bases” such as calcium and magnesium. • The dark surface horizon comes from the yearly addition of organic matter to the soil from the roots of prairie plants. • Mollisols are often found in climates with pronounced dry seasons

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 10. : • Alfisols (from the term – aluminum and iron) are similar to Ultisols but are less intensively weathered and less acidic. • They tend to be more inherently fertile than Ultisols and are located in similar climatic regions, typically under forest vegetation. • They are also more common than Ultisols, occupying about 10% of the glacier-free land surface.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 11. : • Inceptisols (from the Latin inceptum – beginning) exhibit a moderate degree of soil development, lacking significant clay accumulation in the subsoil. • They occur over a wide range of parent materials and climatic conditions, and thus have a wide range of characteristics.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 12. : • Entisols (from recent – new) are the last order in soil taxonomy and exhibit little to no soil development other than the presence of an identifiable topsoil horizon. • These soils occur in areas of recently deposited sediments, often in places where deposition is faster than the rate of soil development. • Some typical landforms where Entisols are located include: active flood plains, dunes, landslide areas, and behind retreating glaciers. They are common in all environments.

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 Textural Classification ( Triangular classification ) • In a general sense, texture of soil refers to its surface appearance. • is influenced by the size of the individual particles present in it, this classification divided soils into gravel, sand, silt, and clay categories on the basis of particle size.

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• The textural classification systems developed by the U.S. Department of Agriculture is used to classify soils. • This chart is based on only the fraction of soil that passes through the No. 10 sieve ( 2 mm diameter ), Hence, if the particle-size distribution of a soil is such that a certain percentage of the soil particles is larger than 2 mm in diameter, a correction will be necessary

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 U.S. Department of Agriculture textural classification (USDA)

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 Working examples on how to use the triangle • Illustrative example-1: • If the particle-size distribution of soil A shows 30% sand, 40% silt, and 30% clay-size particles, to classify this soil using the triangular classification, can be determined by proceeding in the manner indicated by the arrows in Figure above. • This soil falls into the zone of clay .

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 • Illustrative example-2: If soil B has a particle- size distribution of 20% gravel,10% sand, 30% silt, and 40% clay, the modified textural compositions are:

On the basis of the preceding modified percentages , textural classification is clay. However, because of the large percentage of gravel, it may be called gravelly clay

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 • Illustrative example-3: • Classify the following soils according to the USDA textural classification system.

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• Solution • Step 1. Calculate the modified percentages of sand, gravel, and silt as follows:

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Step 2. With the modified composition calculated, refer to the triangle to determine the zone into which each soil falls.

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The results are as follows:

Note: The word gravelly was added to the classification of soils A, B, and D because of the large percentage of gravel present in each.

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THE FRENCH CLASSIFICATION SYSTEM

• The French classification or Systeme ORSTOM as described in AUBERT (1964) and Young (1976) is used in all former french African countries. • It is a nutural classification system, based on climate and soil genetics (degree of development) and group soils primarily according to morphological, physical and chemical properties. • In this system soil is divided into ten classes, subclasses, groups and subgroups.

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Conclusion

• Classification of soils is necessary for all program and mapping the soils of any region. • Soil surveys employ the principles, functions of soil science to agriculture, forestry and engineering to predict soil behavior for different use , management or manipulation.

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Soil Conservation

• Soil is crucial aspect of land management, which make land possible to support the survival of man and other forms of life. • Most of the land in Tanzania is affected to some extent by

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 Introduction to Soil Erosion • Definition : – soil erosion is the detachment, transport & deposition soil erosion is the detachment, transport & deposition of soil particle on land surface - termed as loss of soil. – measured as mass /unit area measured as mass /unit area - tonne/ha or Kg/sq.m tonne/ha or Kg/sq.m • Soil loss is of interest primarily on -site effect of erosion such as loss of crop productivity • Off site effect of erosion are siltation in ditches, streams , reservoirs • Sediment generated by erosion processes are prime carrier of agricultural chemicals that pollutes stream or lakes

SAUT; Geography Dept Ngogo Mn. Ge:140 @2019 • Soil erosion deteriorates & reduces productivity of natural, a gricultural & forest ecos ecosystem report 2009 MoEF p y ,g y  Soil erosion deteriorates quality of water  Increased sedimentation causes reduction of carrying capacity of water bodies 5 .

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