The different layers observed is due to the fact that soil is made up of different types of materials all of which have different sizes and weight. The lighter materials float on top and the heavier particles settle at the bottom.

Horizon O is a layer of partially decomposed organic matter lying above topsoil.
Horizon A is the topsoil. It is dark in colour due to the presence of large amount of humus. It makes the soil nutrient rich and fertile. The layer is soft, porous and can retain more water.

Horizon B is the layer below horizon A and has less quantity of humus but at the same time it contains more minerals.

Horizon C is the layer which is composed of partially eroded small lumps of rocks.

Soil on earth is formed as a result of continuous and long period of constant erosion and weathering of rocks. Large rocks break down to form soil. This is called weathering of rocks. Soil erosion breaks down large particles into smaller soil pieces.

Wind, rainfall, temperature, light and humidity are the factors which affects the soil and its type in a certain region. These factors also affects the soil profile and bring changes in the soil structure.

Clayey and loamy soil both have fine particles and therefore they retain more water as compared to other types of soil. In other words, these soil types have low percolation rates. Hence crops like wheat and gram grow well in clayey and loamy soil.

Clayey soil has an important characteristic that it can retain water and moisture. Paddy, wheat and gram need a lot of water for their growth. Therefore, clayey soil is suitable for growing cereals like wheat and gram. Clayey is also rich in humus and other minerals which is also ideal for paddy and wheat. 
So the statement is true. 

Wheat requires clayey soil which can hold large amounts of water.

Paddy requires clayey soil with lots of humus content.

Lentils require loamy soils which can hold an average amount of water

Cotton requires sandy-loams to grow.