There are three basic types of soil, which are categorized by their mineral particle sizes, and they are clay, silt and sand. Clay soil contains very fine mineral particles. Silt is also fine but to a lesser degree than clay, while sand contains large, coarse particles.
Soil that contains all three particle sizes in significant amounts is called loam. An ideal soil for plant growth consists of 45 percent mineral content, 5 percent organic matter, 25 percent air and 25 percent water. The basic soil type - clay, silt or sand - will influence the availability of nutrients, air and water that will be available for plant growth. The larger particles in sandy soil, for example, create more air spaces and will reduce the soil's ability to retain moisture. This not only limits the amount of water required for plant growth, but it also reduces the nutrient content that needs to be in a liquid form so that it can be absorbed by plant roots. Clay soil represents the opposite extreme. It can hold too much water and limit the amount of air that needs to be contained in the soil so that plant roots can exchange gases and nutrients. An equal amount of clay, silt and sand in the mineral portion of soil represents the ideal plant growth combination.