There  are a great variety of soils in existence.  A number of parameters play a role:

• Type of bedrock,
• Climate,
• Topography,
• Biological factors,
• Weather.

Only the upper part of the soil is important for vegetation. This fine layer of less than 40 cm is the locale for the mixing of organic wastes at the surface (humus) and the deeper mineral base. High quality agricultural land has the following proportions:

• 25% air,
• 25% water,
• 45% mineral matter,
• 5% organic matter.