The Soil Profile
The soil profile comprises two or more soil layers called horizons, one below the other, each parallel to the surface of the land. Important characteristics that differentiate the various horizons are:
- Color, texture, structure, consistency, porosity and soil reaction
- Thicknesses ranging from several feet thick to as thin as a fraction of an inch
- Generally, the horizons merging with one another and which may or may not be showing sharp boundaries
The uppermost layer in the soil profile or surface soil. It includes the mulch layer and plow layer. Living organisms are most abundant in this horizon, consisting of plant roots, bacteria, fungi and small animals. Organic matter is most plentiful, particularly in the mulch layer. When a soil is tilled improperly, the A Horizon may be eroded away.
Lies immediately beneath the A Horizon and above the C Horizon. It is called the subsoil. The B Horizon has properties of both A and C. Living organisms are fewer in number than in the A Horizon, but more abundant than in the C Horizon. Color is transitional between A and C as well. It is frequently higher in clay than either of the other horizons.
The deepest of the three. This is the material from which the mineral part of the soil forms. It is the parent material of soils. It may have accumulated in place by the breakdown of hard rock, or it may have been placed there by the action of water, wind or ice.
A fertile soil contains an adequate supply of all the nutrients required for plant growth. The full potential of crops is not realized if a shortage of nutrients occurs at any time during the growth cycle. This is true even though plants are capable of remarkable recovery from short periods of starvation.
A fertile soil is not necessarily a productive one. The second major requirement is that the soil must be adequate for plant growth. This soil is based on environmental factors including texture, structure, soil water supply, pH, temperature and aeration.