Soil Science

• Arid soils range from red to brown in colour. 
  
• They are generally sandy in texture and saline in nature. In some areas the salt content is very high and common salt is obtained by evaporating the water. 
  
• Due to the dry climate, high temperature, evaporation is faster and the soil lacks humus and moisture. 
  
• After proper irrigation these soils become cultivable as has been in the case of western Rajasthan.
  

Strip cropping is a method or farming in which more than one variety of crops are grown in different strips.

One of the important crop that is usually grown along with other crops is gram. This is because it has good soil holding capacity and prevents soil erosion.

Alluvial soil is considered the most fertile and useful soil for agriculture in India due to its high nutrient content and ability to support a wide range of crops.

Chernozems are known as the richest soils (3), Black soil is rich in calcium carbonate (1), Laterite contains aluminium compounds (2), Terra Rosa is formed in limestone (4), and Alluvial soil is a mixture of clay, sand, and silt (5).

Khadar, Bangar, and Bhabar are all types of alluvial soils classified by their age and location in river plains. Regur (Black soil) is formed from volcanic rock, making its formation process distinct.

Black soils are rich in soil nutrients, such as calcium carbonate, magnesium, potash and lime. These soils are generally poor in phosphoric contents.

Deserts soils are usually light coloured with minimal humus content due to which the plant productivity is low. Also the water retaining capacity is very less. However they are rich in minerals-calcium carbonate (caliche), gypsum, and/or salts.

The difference in a rock formation is responsible for the variation in the color of the soil in different parts of India. Rocks are made up of different minerals. Soils are dynamic, forming continuously over a long period of time. Soil types differ, depending on the parent materials from which they came and from the surrounding environment. Soil is a complex mixture of minerals (approximately 45%), organic matter (approximately 5%), and empty space (approximately 50%, filled to varying degrees with air and water). The mineral content of soils is variable but is dominated by clay minerals and quartz, along with minor amounts of feldspar and small fragments of rock.

• Lime is a valuable soil amendment that helps plants and lawns flourish by raising soil pH.
• Most vegetables grow best in a slightly acidic to neutral soil, with a pH between 6.0 and 7.0 hence acidic soils having low pH is added with lime for raising its pH.
  
• Hence Lime is added to soil which is acidic.
• So, the correct answer is 'Lime'.

Soil salinity in arid regions is primarily caused by the accumulation of soluble salts near the surface due to high evaporation rates exceeding precipitation. This prevents salts from being leached away.

Edaphic factor is an abiotic factor relating to the physical or chemical composition of the soil found in a particular area. For example, very alkaline soil may be an edaphic factor limiting the variety of plants growing in a region.

Oxalophytes are the plants that grow in acidic soil that maintained at pH 5.5 as this enables the plant to absorb nutrients required for the growth.

Plants and animals aid in the development of a soil through the addition of organic matter. Fungi and bacteria decompose this organic matter into a semi-soluble chemical substance, known as humus. Larger soil organisms, like earthworms, beetles, and termites, vertically redistribute this humus within the mineral matter found beneath the surface of a soil. Humus is the biochemical substance, that makes the upper layers of the soil become dark. It is coloured as dark brown to black. 

Loam is considered ideal for gardening and agricultural uses, because it retains nutrients well and retains water, while still allowing excess water to drain away.