Soils - Solutions

 CBSE Class 11 Geography

NCERT Solutions
Chapter 22

1. Choose the right answer from the four alternatives given below:
(i) Which one of the following is the most widespread and most productive category of soil?

(a) Alluvial Soil
(b) Laterite Soil
(c) Black Soil
(d) Forest Soil.

Ans. (a) Alluvial Soil. A fine-grained fertile soil deposited by water flowing over flood plains or in river beds.

(ii) 'Regur Soil' is another name for the.

(a) Saline Soil
(b) Arid Soil
(c) Black Soil
(d) Laterite Soil.

Ans. (c) Black Soil. The black soils are also called regur (from the Telugu word Reguda) and black cotton soils because cotton is the most important crop grown on these soils.

(iii) Which one of the following is the main reason for the loss of the top soil in India?

(a) Wind erosion
(b) Water erosion
(c) Excessive leaching

(d) None of these.

Ans. (a) Wind erosion. The wind erosion process detaches soil particles from the land surface and transports them by wind.

(iv) Arable land in the irrigated zones of India is turning saline due to which of the following reasons?

(a) Addition of gypsum
(b) Over grazing
(c) Over irrigation
(d) Use of fertilisers.

Ans. (c) Over Irrigation. Excess water affects soil aeration and hence plants roots do not grow.

2. Answer the following questions in about 30 words.
(i) What is soil?

Ans. Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is a natural body called the pedosphere which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil. Soil is also the mixture of rock debris and organic materials which develop on the earth's surface. The various agents of weathering and gradation have acted upon the parent rock material to produce a thin layer of soil. Important components of the soil are mineral particles, humus, water and air. The actual amount of each of these depend upon the type of soil. Soil has also been called the Skin of the Earth as it interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere.

(ii) What are the main factors responsible for the formation of soil?

Ans. Relief, parent material, climate, vegetation and other life-forms and time are the important factors that affect formation of soil. Besides these, human activities also influence it to a large extent. For example, the laterite soils develop in areas with high temperature and high rainfall. Black soils are made from volcanoes. Forest soils are formed in the forest areas where sufficient rainfall is available. Peaty soils are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. Various forces of nature such as change in temperature, actions of running water, wind and glaciers, activities of the decomposers etc. contribute to the formation of soil chemical and organic. Changes which take place in the soil are also equally important. Soil also consists of organic matter (humus) and inorganic materials.

(iii) Mention the three horizons of a soil profile.

Ans. Like a biography, each profile tells a story about the life of a soil. Most soils have three major horizons (A, B, C) and some have an organic horizon (O).(humus or organic) Mostly organic matter such as decomposing leaves. Three horizons of soil profile are:

  1. Horizon A: It is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants. This layer generally contains enough partially decomposed (humified) organic matter to give the soil a color darker than the lower horizons.
  2. Horizon B: It is a transition zone between the 'horizon A' and 'horizon C', and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered. B horizons are commonly referred to as the subsoil. They are a zone of accumulation where rain water percolating through the soil has leached material from above and it has precipitated within the B horizons or the material may have weathered in place.
  3. Horizon C: It is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers.The C horizon (parent material) is below the B Horizon. This layer is barely affected by soil-forming processes and they thus have a lack of pedological development. In other words, the C horizon is the unconsolidated material underlying the solum (A and B horizons).

(iv) What is soil degradation?

Ans. Soil degradation is the decline in soil quality caused by its improper use, usually for agricultural, pastural, industrial or urban purposes. Soil degradation is a serious global environmental problem and may be exacerbated by climate change. It encompasses physical, chemical and biological deterioration.Soil degradation can also be defined as the decline in soil fertility, when the nutritional status declines and depth of the soil goes down due to erosion and misuse. Soil degradation is the main factor leading to the depleting soil resource base in India.
The degree of soil degradation varies from place to place according to the topography, wind velocity and amount of the rainfall.

(v) What is the difference between Khadar and Bhangar?


CompositionIt is a highland composed of old allubium.It’s a lowland composed of new alluvium.
FloodIt is always above the level of flood plains.It is flooded almost every year.
FertilityIt comprises of canvanious nodules.It comprises of clay soil which is normally fertile.
SuitabilityIt is not much suited for agriculture.It is suited for agriculture. Intensive agriculture is practiced here.
Other nameIt is known as dhaya in Punjab.It is known as bate in Punjab.

3. Answer the following questions in about 125 words.
(i) What are black soils? Describe their formation and characteristics.

Ans. The black soils are popularly known as Black Cotton Soil. They are also known as regur soil. They are derived from two groups of rocks—the Deccan trap and the ferruginous, gneiss and schist rocks. Black soils are formed by volcanoes.
Features: The black soils are generally clayey, deep and impermeable.
They swell and become sticky when wet and shrink when dried. So, during the dry season, these soil develop wide cracks.
Thus, there occurs a kind of 'self ploughing'. Because of this character of slow absorption and loss of moisture, the black soil retains the moisture for a very long time, which helps the crops, especially; the rain fed ones, to sustain even during the dry season.
Chemical Composition: Chemically, the black soils are rich in lime, iron, magnesia and alumina. They also contain potash. But they lack in phosphorous, nitrogen and organic matter. The colour of the soil ranges from deep black to grey.
Areas: Black soil covers most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu. In the upper reaches of the Godavari and the Krishna, and the north western part of the Deccan Plateau, the black soil is very deep.

(ii) What is soil conservation? Suggest some measures to conserve soil.

Ans. Soil conservation is the prevention of soil loss from erosion or reduced fertility caused by over usage, acidification, salinization or other chemical soil contamination. Soil conservation is also a methodology to maintain soil fertility, prevent soil erosion and exhaustion, and improve the degraded condition of the soil.
We can use following measures to conserve soil:
(a) Check open cultivable lands on slopes from farming.
(b) Lands with a slope gradient of 15 - 25 per cent should not be used.
(c) If at all the land is to be used for agriculture, terraces should carefully be made.
(d) Contour bunding, Contour terracing, regulated forestry, controlled grazing, cover cropping, mixed farming and crop rotation to conserve soil.
(e) Integrated land use planning, therefore, seems to be the best technique for proper soil conservation.
(f) Lands should be classified according to their capability; land use maps should be prepared and lands should be put to right uses.

(iii) How do you know that a particular type of soil is fertile or not? Differentiate between naturally determined fertility and culturally induced fertility.

Ans. To know about the fertility of a particular type of soil we have to know the inherit characteristics and external features of soil such as texture, colour, slope of land and moisture in the soil.The fine-grained red and yellow soils are normally fertile, whereas coarse-grained soils found in dry upland areas are poor in fertility. They are generally poor in nitrogen, phosphorous and humus. Some soils have phosphorus, potassium, humus, nitrogen and calcium naturally. It increases the fertility of these soils. Such fertility is called naturally determined fertility. It includes the texture, colour and moisture in the soil. The other element of the soil is the amount of humous which is the important factor for the fertility.

On the other hand, if soil is deficient in these substances, such substances are added in the form of fertilizers and manures. If fertility of soil is increased through human efforts, such fertility is called culturally induced fertility. Naturally determined fertility makes human dependent on nature. Culturally induced fertility indicates that man has become master of the nature. It is an indicator of development of human race. Soils are living systems. Like any other organism, they too develop and decay, get degraded, respond to proper treatment if administered in time. A human being may be intelligent by birth or may be made intelligent by efforts. Similarly, soil may be fertile naturally and may be made fertile by human efforts. Former is called naturally determined fertility and the latter is called culturally induced fertility.