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Question 3

Match the items in Column I with those in Column II:
Column I                                              Column II
(i) A home for living organisms         (a) Large particles
(ii) Upper layer of the soil                 (b) All kinds of soil
(iii) Sandy soil                                   (c) Dark in colour
(iv) Middle layer of the soil                (d) Small particles and packed tight                                                                                                                                               (v) Clayey soil                                  (e) Lesser amount of humus

Answer

     Column I                                              Column II

(i) A home for living organisms               (b) All kinds of soil
(ii) Upper layer of the soil                       (c) Dark in colour
(iii) Sandy soil                                         (a) Large particles
(iv) Middle layer of the soil                     (e) Lesser amount of humus
(v) Clayey soil                                        (d) Small particles and packed tight

1. Soil is the topmost layer of the earth’s surface. It consists of rocks and mineral particles, water and air mixed with the soil organic matter. Soil formation begins with the breakdown of rocks called weathering and other materials into smaller pieces on the surface of the earth; and ends with humification and mineralization process.

2. The layers of the soil are called horizons. The uppermost horizon is known as topsoil layer. The topsoil layer is a mixture of sand, slit, clay and broken down organic matter, is called humus. Humus is rich, highly decomposed organic matter mostly made from dead plants, dead insects and twigs; incomplete decomposed black coloured organic matter.



3. Sandy soils contains mainly sand about 70 - 80% of sand, large particles with large spaces. It contains very few amount of humus. It is found in desert  or dried areas. Sandy soil has large particles with large spaces between them which dries out quickly that is not good for plants. Its water holding capacity is very low. 

4. The middle layer is called subsoil. Subsoil is the layer of soil under the topsoil on the surface of the ground. It contains lower amount of humus.

5. Clayey soil contains mainly clay about > 50% clay having very small particles with very small spaces. Clayey soil also contains very few amount of humus. Clayey soil is heavy because it has ability to hold more water than the sandy soil.

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