Consider the following characteristics of a soil type: 1. These soils consist of various proportions of sand, silt and clay. 2. These soils contain adequate proportions of potash, phosphoric acid and lime. 3. These soils can be further classified on the basis of their age. Identify the type of soil on the basis of the given characteristics.
- (a)Alluvial
- (b)Laterite
- (c)Arid
- (d)Black
Correct — A, Alluvial. All three characteristics come almost word for word from the standard school description of alluvial soil. The NCERT account says the alluvial soil 'consists of various proportions of sand, silt and clay', which is statement 1; that 'mostly these soils contain adequate proportion of potash, phosphoric acid and lime which are ideal for the growth of sugarcane, paddy, wheat and other cereal and pulse crops', which is statement 2; and that 'according to their age alluvial soils can be classified as old alluvial (Bangar) and new alluvial (Khadar)', which is statement 3. Alluvium is the only Indian soil type routinely classified by age, because it is river-laid and each flood adds a fresh layer — the khadar of the active floodplain against the older, kanker-bearing bangar of the terraces above it.
- (b)Laterite — Laterite soil is formed by intense leaching in a hot, wet climate, which strips out the bases and leaves iron and aluminium oxides behind. It is therefore poor in lime, potash and nitrogen — the opposite of statement 2 — and it is not classified by age.
- (c)Arid — Arid soil is sandy and saline, low in humus and moisture, with calcium carbonate often forming a kankar layer that impedes water. Neither the balanced texture of statement 1 nor the age classification of statement 3 fits it.
- (d)Black — Black or regur soil is made of extremely fine clayey material weathered from the Deccan lava, so the sand-silt-clay mix of statement 1 does not describe it. It is rich in lime, potash, calcium carbonate and magnesium but poor in phosphoric acid and nitrogen, and it is classified by depth and location rather than by age.
Alluvial soil is the most widespread and the most important soil in India. It has been laid down by the Indus, the Ganga and the Brahmaputra, it makes up the whole of the northern plains, it reaches Rajasthan and Gujarat through a narrow corridor, and it recurs in the deltas of the Mahanadi, the Godavari, the Krishna and the Kaveri. Its texture coarsens upstream, so piedmont tracts such as the Duars, the Chos and the Terai carry coarser material, while the lower plains are finer. Its fertility supports the densest cultivation and the densest population in the country.
Whenever a soil item lists characteristics, look for the one that only a single soil type can satisfy. Here that is statement 3. Indian soils are usually classified by parent rock, texture or climate; alluvium is the one classified by age, into bangar and khadar, precisely because it is deposited afresh by rivers. The nutrient list in statement 2 is the second discriminator, and it is worth holding as a pair with the black-soil list, because CDS has asked both. Alluvial soils are adequate in potash, phosphoric acid and lime, and generally short of nitrogen and humus; black soils are rich in lime, potash, calcium carbonate and magnesium, and short of phosphoric acid and nitrogen. One caution about the nutrient statement: an earlier CDS paper keyed alluvial soils as rich in potash and poor in phosphorus, which is the standard textbook line for the drier alluvium of the plains, while this paper reproduces the NCERT sentence that groups potash, phosphoric acid and lime together as adequate. Both are quoting textbooks; answer whichever text the stem is quoting.
- Alluvial soil consists of various proportions of sand, silt and clay, and its particles coarsen towards the upper reaches of river valleys.
- By age it is classified into bangar, the older alluvium with more kankar nodules, and khadar, the newer alluvium of the active floodplain.
- It generally contains adequate potash, phosphoric acid and lime, and is deficient in nitrogen and humus.
- It covers the entire northern plains and extends into Rajasthan and Gujarat through a narrow corridor, and into the east-coast deltas.
- Black or regur soil, by contrast, is clayey lava-derived soil of the Deccan trap country, rich in lime and potash but poor in phosphoric acid.
- Reading the nutrient list without checking whether the soil is also classified by age; that third clue is what fixes alluvium.
- Swapping the nutrient profiles of alluvial and black soil, which overlap on potash and lime but differ on phosphoric acid.
- Assuming khadar is the older alluvium; khadar is the new, bangar the old.
As an identify-the-soil item from three or four listed characteristics — a format CDS has used in at least three separate papers.
Which of the following statements regarding laterite soils of India are correct? 1. They are generally red in colour. 2. They are rich in nitrogen and potash. 3. They are well-developed in Rajasthan and UP. 4. Tapioca and cashew nuts grow well on these soils. Select the correct answer using the codes given below.
- (a) 1, 2 and 3
- (b) 2, 3 and 4
- (c) 1 and 4
- (d) 2 and 3 only
Answer(c) 1 and 4
The soil that option (b) offers here, examined on the very property that rules it out. Laterite is poor in nitrogen and potash, which is why a soil described as adequate in potash, phosphoric acid and lime cannot be laterite.
CDS_GK_2021_I_Q572021Alluvial soils vary in nature from sandy loam to clay. They are generally
- (a) poor in potash and rich in phosphorus.
- (b) poor in both potash and phosphorus.
- (c) rich in both potash and phosphorus.
- (d) rich in potash and poor in phosphorus.
Answer(d) rich in potash and poor in phosphorus.
The same soil, examined on its nutrient balance. Note that the textbook line quoted there and the one quoted in this stem are not identical on phosphorus, so read carefully which description a paper is working from before answering.
CDS_GK_2021_I_Q212021Identify the type of soil on the basis of the given characteristics : 1. They are rich in lime, iron, magnesia and alumina. 2. They are generally clayey, deep and impermeable. 3. They are mainly found in Maharashtra, Madhya Pradesh and Gujarat. Select the correct answer from the given alternatives :
- (a) Laterite soil
- (b) Red and yellow soil
- (c) Saline soil
- (d) Black soil
Answer(d) Black soil
The identical format two years earlier, pointing at black soil instead. Practising the two side by side is the fastest way to fix which nutrient list and which texture belong to which soil.
- practice — not a real PYQ
In the northern plains of India, the older alluvium that lies above the flood level and contains kankar nodules is known as
- (a)khadar
- (b)bangar
- (c)regur
- (d)terai
Answer(b) bangar — the newer alluvium of the active floodplain is khadar.
- practice — not a real PYQ
Which one of the following soils of India is formed by the weathering of lava flows and is best suited to cotton?
- (a)Alluvial soil
- (b)Laterite soil
- (c)Black soil
- (d)Arid soil
Answer(c) Black soil — the regur of the Deccan trap country, made of very fine clayey material with a high moisture-holding capacity.