There is a big difference between soil and dirt. They are different regarding composition. Soil is alive- there are more species of organisms in the soil than there are above ground. A single handful of soil contains millions of individual living organisms.
Dirt is dead soil, void of any nutrients or living organisms that plants need to grow.
Basics of soil -
Soil is classified into four types based on their texture: sandy, silt, clay, and loamy. The different types of soil are categorized based on the size of the particles and the percentage of particles present in them. Loamy soil is a combination of sand, silt and clay and as a result, the beneficial properties of each are included. Loamy soil has a high content of organic matter and the ability to retain moisture and nutrients making it ideal for plant growth. Other types of soil are based on the percentage of particles, resulting in more compound types of soil: loamy sand, sandy clay, silty clay, etc.
What is topsoil? -
Literally, topsoil is the natural upper layer of soil and usually extends to a depth of two to ten inches. All soils are not created equal and not all topsoils are created equal. Topsoils can differ dramatically. The best topsoil has an adequate proportion of sand, silt, and clay, and has a high concentration of organic matter, as well as high levels of microbial activity. It is commonly referred to as loam soil or garden soil.
◆There is no legal definition of the word topsoil.
◆When you buy topsoil do you really know what you are getting?
“In the landscape materials industry, topsoil refers to earth that has gone through a screening process to remove debris and create a consistent texture,” aptly described on the company TheDirtBag website.
◆Topsoil and loam soil (garden soil) are not the same. Loam soil is topsoil that has been enriched to make it better suited for plant growth. This is a mix of local topsoil and organic matter. This is the healthy soil that is the foundation of a healthy garden.