1. (A)Climate: The climate in which Soil develops is the most important factor. It is responsible for the following:
(a) Weathering: Extremes of temperature, freezing and thawing of ice break down rocks and favour soil formation.
(b) Vegetation: The growth and decay of vegetation determines the humus content of the Soil. Roots of plants penetrate the Soil and make it porous.
(c) Bio-chemical processes taking place in Soil: Bacteria and fungi cause the decay of plants and animal remains. Some transform the atmospheric nitrogen into Soil nitrogen.
(B). The Parent rock: The physical and chemical composition of the parent rock determines the relative proportion of different minerals in the Soil layers.
(C). The Topography: The slope of the land surface is an important factor in the formation of Soil layer.
(a) Hills and slopes: Steep slopes usually have a thin Soil layer because weathered particles are easily carried down-slope by running water and wind.
(b) Plains and Valleys: On flat plains and in valleys, thick fertile Soils are developed.
3. (i) Silica: The main constituent of sand, it is present as small crystalline grains. It is mainly derived from the weathering of rocks.
(ii) Clay: It is a mixture of silicates and contains many minerals like iron, potassium, calcium, sodium and aluminium. Particles of clay absorb water and swell.
(iii) Chalk: It consists of calcium carbonate which provides the important element calcium.
(iv) Humus: It is the organic matter present in the Soil formed by the decomposition of plants and animal remains and animal manure. It is the most important element that determines the fertility of the Soil.
4. Alluvial Soils are of two varieties: Bhangar and Khadar. 'Bhangar' is older alluvium. It is found usually higher up in the plains, and occurs at river terraces away from the river. It is found in massive beds, and is characterized by calcareous clays. It is light grey and less fertile. 'Khadar' is newer alluvium. It occurs in the lower levels near the river, and is mainly clay loamy. Its new layers are deposited year after year during the season of monsoon floods.
5. Regur or Black Soil is formed by weathering of volcanic (basalt) rock formed by the Deccan Lava. Four important features of Regur Soil are:
(i) Fine grained
(ii) Moisture retentive
(iii) Sticky when wet
(iv) Cracks when dry.
6. (i) Red Soils are formed and metamorphic rocks. properties of Red Soil. in situ by weathering of the ancient crystalline.
(ii) They are rich in iron content, hence, they are red in colour.
(iii) The productivity of the Red Soil increases with regular use of fertilizers.
(iv) Red Soils are porous in nature but not retentive to moisture.
(v) They are suited for dry farming as it does not require much moisture.
7. (i) Laterite Soils are leached Soils because alternating dry and wet spells cause the soluble silica to be removed.
(ii) These Soils are acidic in nature and coarse and crumbly in texture.
(iii) The proportion of lime and silica is reduced when leaching takes place.
(iv) In the upper layers, the compounds of iron and aluminium become higher giving a reddish colour to the Soil.
(v) Lack of nitrogen, potassium and organic elements make these Soils unsuitable for cultivation. These Soils support pastures and scrub forests.
(vi) With the use of manures, coffee, rubber, cashew, etc., can be grown on these Soils.
8. Methods of Controlling Erosion:
(i) Erosion by water: During heavy downpours deep 'gullies' are made on account of water run off. Gully erosion can be stopped by plugging it with stones and pebbles or quick growing grasses can be grown in gullies to stop its expansion.
(ii) Erosion by wind: Wind erosion reduces the productive capacity of the soil by removing the loose particles of soil with the high velocity wind. The nutrients required by the plants are taken away by the wind. Therefore more and more trees should be planted along the edges of the field, the waste land and also on the steep slopes. If it is difficult to grow trees, grass should be grown but no land
should be left devoid of plants.
9. The protection of the top Soil, which is constantly being shifted by wind and water from one area to another is called Soil conservation. In other words, Soil conservation refers to the steps taken to protect the Soil from erosion.
10. Soil is our most precious resource. It is important to our national economy as productive Soil ensures prosperity in agriculture, industrial development and general economic development.