Resources and Development Test - 15

• Water contains lots of impurities inside it. it includes fine sand, clay and many other materials present in it. These are carried away by the flow of running water. They are then deposited or sedimented at the bottom of the water reservoirs.
• This sedimentation forms silt. As it is present at the bottom, it is usually accumulated at the bed of the river. 
• So, option C "Silt" is the correct answer.

Soil is a complex mixture, having five components: (i) mineral matter - 45%, organic matter - 5%, water - 25%, air - 25% and living organisms. All these components are essential for plant growth.

The given figure shows intercropping patten of growing crops in a field. In it, different types of crops are grown in distinct rows placed at regular intervals. As the crops grown together are selected carefully, they do not compete for resources instead they subsidise growth of one another. Thus, this method helps in obtaining better productivity and maintaining soil fertility.

Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern parts of the Deccan plateau. Yellow and red soils are also found in parts of Odisha, Chhattisgarh, southern parts of the middle Ganga plain and along the piedmont zone of the Western Ghats. These soils develop a reddish colour due to diffusion of iron in crystalline and metamorphic rocks. It looks yellow when it occurs in a hydrated form.

Ploughing along the contour lines can decelerate the flow of water down the slopes. This is called contour ploughing. Contours act like bunds. Terraces are levelled into step-like small fields with even slope.

Dustbowl catastrophe is nothing but the dust storm that greatly damaged the ecology of US and Canadian prairies. The main reason for this storm was the wind erosion. Hence to prevent such catastrophes people should be taught well to prevent soil erosion. 

Value means worth. Some resources have economic value, some do not. For example, metals may have an economic value, a beautiful landscape may not. But both are important and satisfy human needs. 

Soil conservation is a method of protecting soil from getting eroded either by wind or by water.

• Few soil conservation methods include:
  
• Graduated terrace steps which are commonly used to farm on hilly or mountainous terrain. Terraced fields decrease both erosion and surface runoff.
  
• Wind breaks: Row of trees or a fence, wall, or screen that provides shelter or protection of soil from the wind.
  
• Conservation tillage is a method of preparing soil from getting eroded. This technique involves leaving the previous year crop residues until the next crop is planted.

This is the most widely spread and important soil. Alluvial soils as a whole are very fertile. Mostly these soils contain adequate proportion of potash, phosphoric acid and lime. Due to its high fertility, regions of alluvial soils are intensively cultivated and densely populated.