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Home , Aridisol, Histosol, Inceptisol, Leaching (agriculture), Mollisol, Oxisol

Programme: M.Sc.(Environmental Science) Course: Science Semester: IV Code: MSESC4007E04

Topic:

Prof. Umesh Kumar Singh Department of Environmental Science School of Earth, Environmental and Biological Sciences Central University of South Bihar, Gaya

Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data/figures/materials are taken from several research articles/e-books/text books including Wikipedia and other online .

1 • : The origin of the soil , its classification, and its description are examined in pedology (pedon-soil or earth in greek). Pedology is the study of the soil as a natural body and does not focus primarily on the soil’s immediate practical use. A pedologist studies, examines, and classifies as they occur in their .

• (concerned with the influence of soils on living things, particularly ) is the study of soil from the stand point of higher plants. Edaphologist considers the various properties of soil in relation to production. • Soil Profile: specific series of layers of soil called soil horizons from soil surface down to the unaltered .

2 • By area Soil – can be small or few hectares. • Smallest representative unit – k.a. Pedon • Polypedon • Bordered by its side by the vertical section of soil …the soil profile. • Soil profile – characterize the pedon. So it defines the soil. • Horizon tell- soil properties- colour, texture, structure, permeability, , bio-activity etc. • 6 groups of horizons k.a. master horizons. O,A,E,B,C &R.

3 Soil Sampling and Mapping Units

4 Typical soil profile

5 O

• OM deposits (decomposed, partially decomposed) • Lie above horizon • Histic epipedon (Histos Gr. – tissue)

• Oi (non to slightly decomposed)

• Oe (intermediately decomposed)

6 A

• Top most mineral horizons • Inorganic – OM • Usually dark in colour

• If O horizon not there – k.a. – Ap (p= plow) • A horizon- used to classify soil (a.k.a diagonsistic epipedons) (Gr. Epi= over; pedon = soil) • Seven major epipedons are there.

7 Diagnostic Surface Horizons

8 E horizons

• Located under A • Zone of eluviation (, , Fe, Al) • Deposit (eluvial deposit) is the remaining material. • Usually white and pale (k.a. albic horizon) • AE • EB

9 B horizons • Illuviation • The B horizon is a zone of illuviation where downward moving, especially fine material, is accumulated. The accumulation of fine material leads to the creation of a dense layer in the soil. • Accumulation from A, E (Clay, Fe, Al, Humus) • Transition zone BC • Diagnostic subsurface horizons.

10 DIAGNOSTIC SUBSURFACE HORIZONS

• Cambic Horizon (Bw horizon)- recently young • Argillic (Bt horizons) – enriched with clay • Natric Horizons - sodium • Albic Horizon- white in colour • Oxic Horizon – highly weathered horizon • Calcic Horizons, • Gypsic Horizons, and • Salic Horizons

11 DIAGNOSTIC SUBSURFACE HORIZONS: • Cambic Horizon (Bw horizon) • A young B Horizon • The cambic horizon can form quickly, relatively speaking, because changes in the color and structure, and some will convert the parent material into a cambic horizon. • Cambic horizons are not illuvial horizons and, generally, they are not extremely weathered. A cambic horizon is a Bw horizon.

12 DIAGNOSTIC SUBSURFACE HORIZONS

• Argillic (Bt horizons) and Natric Horizons (Btn horizons) • The gradual illuvial accumulation of clay in a cambic horizon converts a cambic horizon (Bw horizon) into a Bt horizon. Typically, clay skins occur on the ped surfaces of Bt horizons

• A natric horizon is a special kind of argillic horizon. These horizons have typically been affected by soluble salts. The natric horizon is a Btn horizon; the n indicates the accumulation of exchangeable sodium.

13 DIAGNOSTIC SUBSURFACE HORIZONS

• Albic Horizon • The loss by eluviation of sesquioxides • (A sesquioxide is an containing three atoms of with two atoms (or radicals) of another element. For example, oxide (Al2O3) is a sesquioxide),and clay, during the formation of spodic and argillic horizons, tends to leave behind a light-colored overlying eluvial horizon called the albic horizon. • Albic is derived from the word white. The horizon is eluviated and is labeled an E horizon. The color of the albic horizon is due to the color of the primary and particles rather than to the particle coatings. Albic horizons are commonly underlain by spodic, argillic, or kandic horizons.

14 DIAGNOSTIC SUBSURFACE HORIZONS

• Oxic Horizon • The oxic horizon (Bo horizon) is a subsurface horizon at least 30 centimeters thick, that is in an advanced stage of . It is not dependent on a difference in the clay content of subsoil versus the horizons. • Oxic is derived from the word oxide. • Oxic horizons consist of a mixture of and/or aluminum with variable amounts of and highly insoluble accessory such as sand. • Soils with oxic horizons have essentially reached the end point of weathering.

15 DIAGNOSTIC SUBSURFACE HORIZONS • Calcic, Gypsic, and Salic Horizons • The calcic horizon is a horizon of carbonate or calcium and magnesium carbonate accumulation. • Calcic horizons develop in soils in which there is limited leaching and the carbonates are translocated downward. However, the carbonates are deposited within the soil profile because there is insufficient to leach the carbonates to the water table. The symbol k indicates an accumulation of carbonates, as in Bwk or Ck. • Gypsic horizons have an accumulation of secondary sulfates, and that is indicated with the symbol y. Cemented calcic and gypsic horizons are petrocalcic and petrogypsic horizons, respectively. • Salic horizons contain a secondary enrichment of salts more soluble than gypsic and are indicated with the symbol z. 16 Soil Profile = layers in soil observed with depth; Individual layers are horizons

O horizon – contains litter on surface, humus + OM beneath

A horizon – various stages of breakdown of

B horizon – mineral soil in which organic compounds have been converted into inorganic

C horizon – unmodified parent material Bedrock 17 Zonation in Soil Profile

Rain, Leaching

A horizon – may show color gradient as OM decreases – eluvial horizons = leaching

B horizon – inorganic compounds leached from A horizon accumulate here – illuvial horizons = accumulation

Bedrock 18 Eluviation: It is the mobilization and translocation of certain constituent’s viz. Clay, Fe2O3, Al2O3, SiO2, humus, CaCO3, other salts etc. from one point of soil body to another. Eluviation means washing out. It is the process of removal of constituents in suspension or solution by the percolating water from the upper to lower layers. The eluviation encompasses mobilization and translocation of mobile constituents resulting in textural differences. The horizon formed by the process of eluviation is termed as eluvial horizon (A2 or E horizon).

Illuviation: The process of deposition of soil materials (removed from the eluvial horizon) in the lower layer (or horizon of gains having the property of stabilizing translocated clay materials) is termed as Illuviation. The horizons formed by this process are termed as illuvial horizons (B-horizons, especially Bt) The process leads to textural contrast between E and Bt horizons, and higher fine: total clay ratio in the Bt horizon.

19 Soil Profile is determined by

• • ---- rainfall and leaching • Weathering ---- geological history, age • Topography • Parent Material • Etc.

20 Soil Classification

• Profile • Texture • Origin • Vegetation • Minerals • Climate • Age • Etc.

21 Soil Taxonomy Hierarchy

Kingdom Phylum Order Class 12 Order Family Suborder 63 Genus Species Great group 250

Sub group 1400

Family 8000

Series 19,000

22 Soil Orders 12 recognized, 10 used in 1. 2. 3. 4. 5. 6. 7. 8. Spodosols 9. 10. 11. 12.

23 Soil Orders Use in Agriculture • • Best • • Many types respond to • management (, ) • • • Spodosol • Poor •

24 Formative Syllables, Derivations, and Meanings of Soil Orders

Gelisols el Gk. Gelid very cold, pergelic soil temp. regime 25 Diagnostic Subsurface Horizons

Formation Translocation Transformation

Clays Organic Matter Oxides

26 Mollic Horizon • The word mollic is derived from mollify, which means to soften . The mollic horizon is a surface horizon that is soft rather than hard and massive when dry. • Mollic epipedon formation is favored where numerous grass roots permeate the soil and a moderate to strong grade of structure is created. • Except for special cases, mollic horizons are dark-colored, contain at least 1 percent organic matter, and are at least 18 centimeters thick. • They are only minimally or moderately weathered and leached. • The cation exchange capacity is 50 percent or more saturated with calcium, magnesium, , and sodium when the cation exchange capacity is determined at pH 7. • The major soils of the world have mollic epipedons.

27 Umbric and Ochric Horizons

• The umbric epipedon is similar to the mollic in overall appearance of thickness and color; however, it is more leached and has a saturation with basic cations calcium, magnesium, potassium, and sodium that is less than 50 percent when the cation exchange capacity is determined at pH 7.

• The epipedon is thinner than that of the umbric, is lower in organic matter, and is lighter in color. This epipedon is called ochric.

28 Histic Horizon • Where soil development occurs under conditions of extreme wetness, as in swamps or lakes, the epipedon is organic in nature and is, typically, a histic epipedon. Histic epipedons are o horizons. • A histic epipedon must be water saturated for at least 30 consecutive days during the year, unless the soil has been drained. • The degree of of the organic matter in histic horizons is indicated with the following symbols: • i - for fibric, • e - for hemic, and • a - for . • Fibric (i) is the least decomposed and contains a large amount of recognizable plant fibers; • sapric (a) is the most decomposed; and • hemic (e) is of intermediate decomposition.

29 Melanic Horizon • Melanic epipedons are thick, black colored, and contain high concentrations of organic matter, similar to some histic horizons. • The organic content is 6% or more but less than 25%. • The organic matter is thought to result from the supply of large amount of root residues from a graminaceous vegetation in contrast to organic matter that results from a vegetation.

• Even though the organic matter content is high, the organic matter in melanic horizons is mostly associated or complexed with minerals, which results in properties dominated by the mineral fraction rather than the organic fraction. • The horizon is also characterized by low and high anion exchange capacity.

30 Anthropic and Plaggen Horizons

• The anthropic and plaggen horizons are formed by human activity. The anthropic epipedon resembles the mollic horizon in color, structure, and organic matter content; however, the

content is 250 or more ppm of P2O5 equivalent soluble in 1 percent citric acid solution. The anthropic horizon occurs where human activity resulted in the disposal of bones and other refuse near places of residence, or in agriculture at sites of long-continued use of soil for irrigated.

• The plaggen epipedon is found in where long-continued manuring has produced a surface layer 50 centimeters or more thick. During the Middle Ages, farmers in northwestern Europe collected sods from where soils were very sandy. The manure from the barn was applied to the , which resulted in the slow accumulation of a thick, sandy epipedon enriched with organic matter. 31 Entisols: •Young and shallow soil •A/C or A/R profiles •Immature soils and no B Horizons •Time of formation is too short •Occurrence of steep slope •Actively eroding slope •Receiving frequent deposits from •Alluvial soils in India along the banks of river Ganges and Indus •Causes of delayed or absent development 32 Gelisols:

• They are soils of very cold which are defined as containing within two meters of the soil surface.

• The word "" comes from the Latin gelare meaning "to freeze", a reference to the process of that occurs from the alternating thawing and freezing characteristic of Gelisols.

• Structurally, Gelisols have no B horizon and have an A horizon resting on the permafrost. 33 • Because accumulates in the upper layer, most Gelisols are black or dark in , followed by a shallow mineral layer. – underlaid by Permafrost.

• Despite the influence of glaciation in most areas where Gelisols occur, chemically they are not highly fertile because , especially calcium and potassium, are very easily leached above the permafrost.

• The permafrost greatly restricts the engineering use of Gelisols, as large structures (e.g. buildings) subside as the frozen earth thaws when they are put in place.

34 Inceptisols:

• Inceptisols mark the beginning of mature soils and have A/Bw/C profile. • B horizons are in the stage of formation and are called as Cambic Horizons (Bw). Paddy soil

35 Mollisols: Mature soils A/Bk/C profiles Mollisoils are formed by calcification A horizon is a mollic epipedon B- calcic horizon (Bk) Mollisols are formed by calcification in semihumid climates with tall Imp. Grassland soils Very fertile soils in world of Canada, of Mongolia, of , Ukraine k.a.- (Black earth) High OM and N content, More base saturation Soil Physically and chemically excellent.

36 Spodosols A/E/Bh or Bhs/C profiles • Formation process is Podolization • Occurs in cool humid regions under the influence of coniferous forest or mixed conifer-hardwood vegetation • Under the influence of acid leaching- Al, Fe compounds or humus are translocated to the B Horizons creating spodic B Horizon. • When B horizon enriched with Humus called as Bh Horizon = Humod (Hum= Humus and od = formative element from spodozols). • When mixture of Fe and Al compounds and humus is accumulated Bhs horizon is formed. • Under certain condition if only Fe is accumulated it is Bs horizon and called as Ferrod . • FAO called this order as Podozols (Russian Pod = under and Zola = white layer of ash) [Taiga forest] • Soils are very acidic, need adequate and lime for crop production 37 Podzolization

• Cool climates • Forested areas generally • Strongly leached • Acidic soils • Low CEC and low fertility • Generally an E or spodic horizon of leached/bleached gray/white • Large surface humus layer • Iron and Aluminum in B horizon • Poor farming areas • NE US

38 Alfisols A/E/Bt/C - mature soils • Formed by the combination of Podolozation and laterization in cool to warm temperature humid regimes usually under hardwood forests.

•Soils are affected by more drastic leaching than mollisols and are therefore in a more advanced stage of profile development.

•Surface soil colour- gray-brown to reddish brown- a.k.a. Gray-brown podozolic soil. •Because of eluviations process B horizon is enriched with illuvial clay called as agrillic horizon (Bt horizon) [a.k.a. luvisols L. Lou= to wash, illuvial clay]

•Alfisols are highly productive soils as base saturation is >35% , illuvial clay – unfavorable conditions.

• need to neutralize moderate acidic conditions. 39 Ultisols

• Mature soils – A/E/Bt/C profiles •Formed by a combination of laterization and podolization with more emphasis on laterization in warm humid temperature regions to humid tropics where leaching process is very much pronounced. •Soils are highly weathered and A horizon accumulate varying amounts of Fe oxides which gives yellow colour to red colours. •Enrichment of B horizons with illuvial clay cause agrillic horizons (Bt horizons). •Due to drastic leaching process soil has low base status <35% . •Adequate liming, OM, Fertilizers, proper management- soils can be quite productive. 40 OXISOLS (A/B/C profiles) Oxisols are the most intensively weathered soils, consisting largely of mixtures of quartz, kaolinite, oxides of iron and aluminum, and some organic matter. [hydrous oxides of clay and sesquioxides]

Generally, Oxisols represent the most naturally infertile soils for agriculture

41

42 Laterization

Formed by laterization process in warm humid and tropical regions. More weathered soils more than ultisols. Soils are highly leached and are acidic in reaction and low in bases. Depending on the iron content some oxisols may convert it into laterites .

43 Soil types: oxisols

Laterite = highly developed oxisol.

Forms in a hot, humid climate. Soil is deep red, hard and infertile.

Plants recycle nutrients in a thin A and O horizon.

Laterite formation on gneiss, Kerala, India 44 Oxisols being used for building materials in India 45 Aridisols

•PET >> Precipitation •Desert soils •Pale, light color near surface •Long periods of deficit •Little if any organic matter •High CEC •Very fertile if add water •Salinization is common •Here the white color is from salts that have precipitated in the soil

46 Aridisols

47 Vertisols Conditions that give rise to the formation of Vertisols are: (1) parent materials high in, or that weather to form, a large amount of expanding clay, usually smectites; and (2) a climate with alternating wet and dry seasons.

Expansion or swelling of soil in the vicinity of cracks results in great lateral and upward pressures, which cause a slow gradual movement of soil upward between areas that crack. This soil movement produces a microrelief called gilgai.

48 Genesis of Vertisols

49 50 Summary:

• 3 orders with unique parent materials (Andisols, Histisols, Vertisols). • 3 orders with unique environments (Aridisols, Gelisols, Oxisols). • 3 orders by age of development (Entisols, Inceptisols, Ultisols). • 3 orders by unique vegetative influence (Alfisols, Mollisols, Spodosols).

51 References: 1. N.C Brady -The Nature and Properties of Soil 2. McBride - Environmental Chemistry of Soils 3.Dutta -Principles and Practice of

Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data/figures/materials are taken from several research articles/e-books/text books including Wikipedia and other online resources.

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