Soil Composition

Soil is a complex medium consisting of solids (inorganic rocks and organic material), as well as water, nutrients and gases. These factors play an important role in maintaining the plants that grow and feed on them.

Soil contains organic matter in various stages of decomposition, as well as a team of microorganisms, algae, and bacteria, that work around the clock to convert raw materials into products the plant can utilize.

The structure of soil is determined by its porosity (air space). Pores typically occupy 40 to 60 percent of soil by volume. After a watering by rainfall or irrigation, water percolates down (gravity) through the air spaces (pores) of the soil. This reservoir of water is then consumed by plants, and removed by evaporation, leaving behind gases.

Soil characteristics can be divided into three components in accordance to particle size:

Sand:

Large particles (2.00 to 0.02 mm in size) creating pores that act like pockets or chambers for gases, as well as allowing roots to easily network through the soil in search of nutrients. Sand has poor water retention, but provides excellent aeration.

Silt:

Medium sized particles (0.02 to 0.002 mm) providing good aeration as well as good water retention in the soil.

Clay:

Very small particles (less than 0.002 mm in size). Clay has excellent water retention, but poor aeration. Poor drainage can be caused by an excess of clay in soils; this can be alleviated with the use of compost.

...more on soil nutrients