Theory:

Texture of the soil:
 
Texture of the soil depends upon the proportion of soil particles and the fineness or roughness of a soil. Different kinds of soil has various textures. Clay has the smallest sized particles, and because of its tiny size, clay is felt smooth. Silt particles are larger than the clay and smaller than Sand. So, silt does not feel slippery. Sand particles are the largest sized particles of soil. These are rough to touch because of their larger size.
 
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Colour of the soil:
Soil colour does not affect the behaviour and use of soil; however, it indicates the soil's composition. In the below picture we can see the soil in different colours. They are red, white, brown and black. Due to the accumulation of iron and aluminium oxides, the soil looks red colour. White indicates the abundance of silica or salts; brown and black indicate the level and type of organic matter (humus). Black soil is suitable for growing crops such as cotton, groundnut, tobacco, wheat, millets, and oilseeds.
 
Important!
Black soil is also called black cotton soil because it is most suitable for the cotton crop.
 
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pH of the soil:
Soils can have different pH. According to their nature, it can be acidic, basic and neutral. Some crops like potato and blueberry grow in acidic soil (pH below 7). Vegetables like Carrot and cucumber grow well in neutral soil  (pH equals 7). Beans and garlic grow well in alkaline soil (pH above 7).
 
Important!
Plants growing in acidic soils are called as Oxalophytes.
Plants growing in sandy soils are called as Psammophytes.
Plants growing on rocks are called as Lithophytes.
Plants growing in high saline conditions such as mangroves are termed as Halophytes.
Soil contains air:
Air is possessed in the space between the soil particles, which gives the oxygen to roots of plants and other organisms in the soil for respiration.

For example, Sandy soil contains larger particle. It cannot fit closely together. So, naturally larger spaces form between the sand particles. The space between sand particles is occupied with air. Thus, sandy soil gives more air to the plant roots and organisms that live in the soil. But clay particles pack tightly together, which leaves little space for air. So, clayey soil cannot provide more air to the plant root and organisms. 
Presence of air in the soil - Activity
  • Collect some dry garden soil.
  • Take a jar and fill half of jar with garden soil.
  • Gently pour some water on the soil until the jar is full.
Observation: 
We can see bubbles burst out off the water surface. This is because thewater poured into the soil pushes out the air in the soil spaces from the water surface. Therefore, we can say that the soil contains air.
 
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