Soil Profile
The term "soil profile" is an important concept to learn. Soil profile is a side view or vertical cross-section of the soil as seen in a ditch bank or dug pit that allows the topsoil and subsoil to be examined. When we look beneath the surface of the soil, we see that the soil is divided into layers or "horizons." These layers differ in color, physical properties, chemical composition, and biological characteristics. This is the soil profile. It has three major parts or horizons: (1) the topsoil or "A" horizon, (2) the subsoil or "B" horizon, (3) the parent material or "C" horizon. A hypothetical soil profile is shown in Figure 1. Most land judging decisions are based on a soil profile that is at least 40 inches deep.

Organic horizon of undecomposed and decomposed organic matter. Absent in cultivated and many other soils.  Mineral surface soil which has accumulated decomposed organic matter and is usually darker colored than lower layers. It is also the horizon that has lost organic matter, clay, iron, and aluminum due to downward movement.  Mineral horizon that usually has a finer texture, or a darker, stronger, redder color and a distinctly different developed structure. Structure is often more distinct than in the "A" horizon.  Mineral horizon of weathered parent material like the material from which the soil developed or other substratum of unconsolidated material not related to the above soil.  Underlying consolidated bedrock. Absent under many soils.

Figure 1. Hypothetical soil profile showing the letter designation used in describing the major kinds of horizons usually present.

Coarse-textured soils are loose, very friable, and the individual grains can be readily seen or felt. When squeezed between thumb and forefinger, it feels gritty and will not ribbon or stain fingers. Squeezed when dry, it will fall apart as pressure is released. When moist, a mold may be formed which is unstable and crumbles as the soil is handled.

Moderately coarse-textured soils feel gritty but contain enough silt and clay to make moist soil hold together. The individual sand grains can readily be seen and felt. Squeezed when dry, it will form a mold which breaks readily upon handling. If squeezed when moist, a mold can be formed which can be carefully handled without breaking. It forms no ribbon or very poor ribbon.

Medium-textured soils have a slightly smooth or velvety feel when moist. Squeezed when dry, it forms a mold that will bear careful handling. The mold formed by squeezing when moist can be handled freely, without breaking. When the moistened soil is squeezed out between thumb and forefinger, it will form a poor ribbon with a dull surface.

Moderately fine-textured soils usually break into clods or lumps when dry. When the moist soil is squeezed out between thumb and forefinger, it crushes with some effort. It will form a short (1 inch to 2 inch) well-formed ribbon with a shiny surface which will tend to break or the ribbon will bend downward. The sandy clay loam texture has a slightly gritty feel when moist.

Fine-textured soils form very hard, massive lumps or clods when dry and are quite plastic and sticky when wet. When the moist soil is squeezed out between thumb and forefinger it crushes with considerable effort and will form a long (2 inch+) ribbon which will support itself. The sandy clay texture may also have a slightly gritty feel when moist.

Deep soils have over 40 inches of soil that can be penetrated by plant roots.

Moderately deep soils have over 20 inches of soil but less than 40 inches of soil that can be penetrated by plant roots.

Erosion
Soil erosion is the detachment and movement of soil materials by wind or water. Erosion consists of three distinct processes -- detachment, transport, and deposition. Raindrops falling on unprotected soil, wind striking unprotected soil particles, and the bombarding action of moving particles are detachment forces. Flowing water and air currents are the transportation forces. Four erosion classes are recognized in land judging.

None to slight --- Soils of this class show no obvious effect of erosion. The plow layer exhibits characteristics of the "A" horizon. Less than 25 percent of the surface soil has been removed and no gullies are present.

Moderate --- Soils of this class have 25 to 75 percent of the original surface layer present. The plow layer may consist of a mixture of the surface "A" horizon and underlying "B" horizon. Small rills and occasional, crossable gullies may be present. It may or may not change the land capability class but it is always considered a factor to keep an area out of Class I.

Severe --- Soils of this class have been eroded to the extent that over 75 percent of the original surface layer is removed. The plow layer exhibits characteristics predominately of "B" horizon. Frequent crossable gullies, or occasional uncrossable gullies, or occasional wind blow-out area may be present.

Very severe --- Soils of this class have over 75 percent of surface soil removed with frequent uncrossable gullies and/or severe accumulations by wind. The plow layer exhibits characteristics similar to severely eroded soils. If wind is the main erosion force, blow-outs are numerous and deep. In either case, areas are unfit for crop production without extensive reclamation.

The term "gullies" includes both crossable and uncrossable, unless otherwise specified. A crossable gully is one that can be crossed with normal, operating farm machinery. Frequent gullies are less than 100 feet apart. Occasional gullies are more than 100 feet apart.

Structure
Soil structure is not judged, however, it is very important because of its effect upon permeability. It also relates to how well crops can grow. It is necessary to know about this soil property. Structure means the shape and arrangement of soil particles into clusters or aggregates. Each aggregate has a particular shape or size and determines the type of soil structure. It is best to observe this property in the soil profile rather than in the sample box because of the disturbance. The various types are:

Single grained --- Each soil particle functions as an individual unit due to the lack of binding material. This structureless condition is usually found in coarse-textured soils.

Granular and/or subangular blocky --- Granular is sphere-like or rounded aggregate with no flat surfaces due to contact pressure from the faces of surrounding aggregates. Subangular blocky is block-like or tending toward six-faced aggregates having mixed, rounded and flat surfaces with many rounded vertices or corners.

Blocky --- Block-like or tending toward six-faced aggregates having flat surfaces with mostly sharp, angular vertices or edges that are mold casts formed by surrounding aggregates.

Prismatic --- Prism-like or vertically-oriented aggregates with the vertical axis much greater in length than the horizontal axis. Flat surfaces or faces are well defined.

Columnar --- Structure is a modified type of prismatic aggregate but with rounded surfaces. It usually suggests salty conditions.

Platy --- Plate-like or relatively thin horizontal plates or leaflets.

Massive --- Indistinct or no apparent aggregation. This type is characteristic of clayey, very slowly permeable soils.

Structure means the shape and arrangement of soil particles into cluster or aggregates. Each aggregate has a particular shape or size and determines the type of soil structure.