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ASAC 1101 : FUNDAMENTALS OF SOIL SCIENCE (2+1), Level : B.Sc (Ag), I semester, , Dr. PEDDA GHOUSE PEERA S.K., SOIL SCIENCE AND AGRICULTURAL CHEMISTRY, M.S.SWAMINATHAN SCHOOL OF AGRICULTURE,CUTM,, PARLAKHEMUNDI, , Topic, Soil profile

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The Master horizons and layers:, • Six master soil horizons, are commonly, recognized and are, designated using the, capital letters, • O, A, E, B, C, and R., • Subhorizon horizons may, occur within a master, horizon these are, designated by lowercase, letters following the, capital master horizon, letter, • e.g., Bt, Ap, or Oi

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O Horizon:, • Organic horizon., • Found above the mineral soil., • Occur in an organic soil profile., • Commonly referred to as the, forest floor.

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Often has three subhorizons:, , 1. Oi horizon - fibric, materials— recognizable, plant and animal parts., 2. Oe horizon - hemic, materials—finely, fragmented, residues, intermediately, decomposed., 3. Oa horizon - sapric, materials—highly, decomposed, smooth,, amorphous residues.

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A Horizon:, • The topmost mineral, horizons., , • Generally contain enough, partially decomposed, organic matter, • Soil color is darker than that, of the lower horizons.

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R horizon:, • Consolidated rock., • Little evidence of, weathering

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Subdivisions Within Master, Horizons, • Often distinctive layers exist, within a given master horizon., • These are indicated by a, numeral following, the letter designation., • Three different combinations, of structure and colors can, be seen in the B horizon,, then the profile may include, a sequence such as B1–B2–, B3

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Transition Horizons:, • Transitional layers between the master horizons (O,, A, E, B, and C) may be dominated by properties of, one horizon but also have characteristics of another., • Written as AE, EB, BE., • E/B when distinct parts of the horizon have properties, of E while other parts have properties of B.

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Subhorizon Distinctions:, • Since the capital letter designates the nature of a master, horizon in only a very general way, specific horizon, characteristics may be indicated by a lowercase letter, following the master horizon designation., • E.g., Oi – O horizon with slightly decomposed organic, matter.

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End of Module I