Soil Science

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz making it most friable.

High percolation is characteristic of soils with large, interconnected pores, such as sandy soils, which allow water to pass through quickly.

Clayey soil has very small, tightly packed particles, which significantly restricts the movement of water, resulting in the lowest percolation rate.

Loamy soil is generally considered to have the best balance of water retention (absorption) and drainage, making it ideal for agriculture.

Sandy soil has larger particles and larger spaces between them, which allows water to pass through much faster than in clayey soil. Clayey soil has very fine particles that hold water tightly, resulting in a much lower percolation rate.

The top layer of soil, often called topsoil, contains the highest concentration of organic matter and nutrients, making it the most fertile layer for plant growth.

A duricrust is a hard, mineralized crust formed at or near the surface of the soil, often through the accumulation of minerals like iron or silica.

While streams cause erosion, water (in general) or wind are often cited as primary agents, but the statement 'Stream is the most important agent of soil erosion' is generally considered incorrect in a broad context compared to the overall impact of water runoff or wind.

Water erosion is the primary cause of topsoil loss in India, particularly due to the intensity of monsoon rains. While wind erosion occurs in arid regions, water erosion is more widespread across the country.

Roots of trees hold the soil particles and prevent their loss. When trees are cut on a large scale land becomes barren. This results in the loss of upper soil layer due to heavy wind or flowing water leading to soil erosion. Hence afforestation prevents soil erosion. Thus the correct answer is option A.  

Eolian (or Aeolian) processes pertain to the activity of the wind, specifically the erosion, transport, and deposition of soil and sediment by wind.

Colluvial soil refers to material that has been transported and deposited by gravity, typically at the base of slopes.

(i) Mineral is a naturally occurring substance that is solid and inorganic represented by chemical formula and has ordered structure. Minerals are differentiated based on their physical and chemical properties.
(ii) Ore is a type of rock that contains sufficient minerals with metals which are economically extracted by mining. Metal ores are generally oxides,sulphides,silicates. The ores are processed to extract metals.
(iii) Gangue are the impurities which are mixed closely with the ores. It is unwanted material which is of no market value and it is waste rock or mineral or sand etc.

• The black soils are also called regur soils. Cotton is the most important crop grown on these soils.
  

Rice requires abundant water and nutrient-rich soil, and alluvial soil, which is found in river deltas and plains, is ideal for its cultivation.