CDS (II) 2021 General Knowledge · Question 66 of 120

Correct — B, Soil. Inceptisols, Entisols, Vertisols and Mollisols are four of the twelve orders of the United States Department of Agriculture's soil taxonomy, the classification used for soil mapping across much of the world including India's national soil survey. The suffix is the tell — every order in that scheme ends in -sol, from the Latin solum for soil, and the stem before it names what makes the order distinctive. Entisols are so young or so freshly deposited that no horizons have developed; Inceptisols have only the beginnings of a horizon; Vertisols are the cracking clay soils that swell when wet and shrink when dry, turning the profile over on itself; Mollisols are the deep, soft, base-rich soils of grasslands. Nothing about sugarcane, coal or copper is classified in orders of this kind.

• (a)Sugarcane — Sugarcane varieties are named by breeding-station codes such as the Co series, not by orders; a crop is classified by genus, species and variety, and none of those end in -sol.
• (c)Coal — Coal is graded by rank — peat, lignite, bituminous, anthracite — according to how far carbonisation has gone, and by grade for ash and moisture content.
• (d)Copper — Copper is a chemical element; its ores are named as minerals, chalcopyrite and malachite among them, and there is no system of copper orders.

Soil taxonomy classifies soils by what the profile actually shows — the diagnostic horizons present, the moisture and temperature regimes, the degree of weathering — rather than by the parent rock or by the crop grown on it. The highest rank is the order, and there are twelve of them: Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols and Vertisols. Below the order come suborders, great groups, subgroups, families and finally soil series.

This is a vocabulary question, and the -sol ending gives it away even to a candidate who has never met a single one of the four names. It is worth knowing which of them matter in India: Inceptisols cover the largest share of the country's area, spread across the Indo-Gangetic alluvium; Entisols occupy young alluvium and the desert margin; Vertisols are the black cotton soils of the Deccan trap country; and Mollisols are the more limited grassland and tarai soils. Note that India's older descriptive classification — alluvial, black, red and yellow, laterite, arid, saline, peaty and forest soils — is a different scheme, and the two should not be mixed in one answer.

• The United States Department of Agriculture soil taxonomy recognises twelve soil orders, every one of which ends in -sol.
• Entisols show the least profile development and have no diagnostic subsurface horizons.
• Inceptisols show the beginnings of a horizon and cover the largest area of any order in India.
• Vertisols are cracking clay soils that swell and shrink with moisture; in India they are the black cotton soils of the Deccan.
• Mollisols are dark, base-rich soils with a thick surface horizon, typical of grasslands.

• Mixing the -sol orders with India's descriptive soil groups in the same answer.
• Assuming Vertisols are named for a place; the name comes from the vertical churning of the profile as clays swell and shrink.
• Treating laterite as an order of the taxonomy — laterite is a descriptive Indian category, and the corresponding order is Oxisols.

Most often as a match-the-order-to-its-characteristic item, sometimes as a single question on which order covers the largest area of India.

• practice — not a real PYQ

  The cracking clay soils that swell when wet and shrink when dry belong to which one of the following soil orders?

  • (a)Entisols
  • (b)Vertisols
  • (c)Spodosols
  • (d)Histosols

  Answer(b) Vertisols — the name records the vertical churning of the profile as the clays alternately swell and shrink.

• practice — not a real PYQ

  Soils with a very high content of organic matter in the upper layers belong to which one of the following orders?

  • (a)Aridisols
  • (b)Oxisols
  • (c)Histosols
  • (d)Alfisols

  Answer(c) Histosols — the peaty and organic soils, formed where waterlogging slows decomposition.