CDS (II) 2024 General Knowledge · Question 6 of 120

Correct — B, Saline soil. The name gives the answer away to anyone who knows one Greek root: halo means salt, and a halophyte is a plant that tolerates and grows in soil or water of high salinity. Mangroves are the familiar Indian example, growing in tidal creeks where the ground is flooded with seawater twice a day, and so are the fleshy glassworts and saltbushes of salt flats and salt marshes. Such plants face the same difficulty a desert plant faces — a shortage of usable water — but for a different reason. Salt in the soil water lowers its potential, so the roots must work against it to draw water in at all, and any salt taken up has then to be excreted through salt glands, shed with old leaves or diluted in swollen, water-filled tissue. Salt-tolerant plants are a small minority: roughly two per cent of plant species are halophytes, the rest being glycophytes that suffer in salty ground.

• (a)Acidic soil — Plants of strongly acidic ground are oxylophytes; tea is the familiar Indian crop of acid soils. Acidity is a hydrogen-ion problem, not a salt problem, and the two call for different adaptations.
• (c)Black soil — Black or regur soil is the clayey, moisture-retentive cotton soil of the Deccan lava country. It is defined by its parent rock and its clay content, not by salinity, and it is among India's more fertile soils.
• (d)Sandy soil — Plants of dry sandy ground are xerophytes, sometimes called psammophytes when the substrate is specifically sand. Sandy soil drains fast and holds little water, but that is a scarcity problem rather than a salinity one.

Plants are classified by the habitat they are built for. Halophytes grow where the ground or water is salty; xerophytes where water is scarce; hydrophytes in water; mesophytes in ordinary moist ground. In India, saline and alkaline soils occur in western Gujarat and the Rann, in the deltas of the eastern coast, and in the Sundarban tract of West Bengal, and they are also created inland wherever over-irrigation without drainage draws salts to the surface.

The single most useful habit here is to break the word open: halo for salt, phyte for plant, so a halophyte is a salt plant. The same trick decodes xerophyte as a dry-ground plant and hydrophyte as a water plant. The trap the item sets is the fourth option, because deserts, sand and salt often occur together in the same landscape — the Rann of Kutch is sandy, dry and salty all at once — and a candidate who reasons from the landscape instead of the word can settle on sandy soil. What defines a halophyte is not the texture of the ground but the salt dissolved in its water.

• A halophyte is a salt-tolerant plant that grows in soil or water of high salinity.
• Only about two per cent of plant species are halophytes; the rest are glycophytes, which salt injures.
• Mangroves are the best-known halophytes, and India's largest mangrove tract is the Sundarban.
• Saline soils in India are widespread in western Gujarat, the deltas of the eastern coast and the Sundarban area.
• Salinity in irrigated land is largely man-made, caused by watering without adequate drainage so that salts rise and accumulate near the surface.

• Reading the option 'sandy soil' as the answer because salt flats are often sandy; the defining condition is salt, not texture.
• Assuming saline soil is always coastal; over-irrigated inland tracts turn saline too.
• Confusing saline with alkaline soil — the two often occur together but are separate problems, one of salts and one of exchangeable sodium and pH.

Usually as a plain definition, or through the characteristics of India's saline soils in the geography section; mangroves are the recurring worked example.

• practice — not a real PYQ

  Plants adapted to grow in water or in ground that is permanently waterlogged are known as

  • (a)xerophytes
  • (b)hydrophytes
  • (c)halophytes
  • (d)mesophytes

  Answer(b) hydrophytes — hydro is the root for water, just as halo is the root for salt in halophyte.

• practice — not a real PYQ

  Which one among the following is the chief cause of soil salinity in India's canal-irrigated tracts?

  • (a)Excessive use of nitrogenous fertiliser
  • (b)Irrigation without adequate drainage
  • (c)Deep ploughing before the monsoon
  • (d)Growing leguminous crops year after year

  Answer(b) Irrigation without adequate drainage — water applied without a way out raises the water table and draws salts up to the surface, where they are left behind as the water evaporates.