Breakdown of clods, crusts, and plant material by the impact of saltating soil particles moved by the wind in saltation. The impacting particles may also abrade. Abrasion causes soil aggregates to break down progressively as wind erosion continues.

The cementing or binding together of soil particles into a secondary unit, aggregate, or granule.

Air-Dry Weight

Weight of a substance after it has been allowed to dry to equilibrium with the atmosphere.

The angle between prevailing wind erosion direction and a line perpendicular to: (1) the long side of the field or strip, when determining unsheltered distance using a wind

erosion direction factor, or (2) row direction when determining effect of wind direction on the ridge roughness factor.

The capacity of a soil to hold water in a form available to plants, usually expressed in inches of water per inch of soil depth. Commonly defined as the amount of water held between field capacity and wilting point.

The increase in rate of soil flow with distance downwind across an area being eroded by wind.

Soil containing sufficient free calcium carbonate or

magnesium carbonate to effervesce visibly when treated with cold 0.1 N hydrochloric acid. High content of lime (up to about 5 percent), particularly in the clay fraction, appreciably increases erodibility by wind.

The relative influence of climate on field erodibility by wind in different regions, specifically the effects of average wind-speed and effective soil surface moisture.

Clod

A compact, coherent mass of soil greater than 2 millimeters in equivalent diameter, often created by tillage or other mechanical disturbance of the soil.

Coarse Fragments

Rock or mineral particles greater than2 millimeters in diameter.

Period of the year when the greatest amount of wind erosion can be expected to occur from a field under an identified management system. It is the period when vegetative cover and soil surface conditions, and expected erosive winds, result in the greatest potential for wind erosion.

Maintaining stubble, stalks, and other crop residue on the soil surface or partially incorporated into the surface layer to reduce erosion, conserve soil moisture, and improve

soil tilth.

The maximum wind erosion that a growing crop can tolerate, from crop emergence to field stabilization, without an economic loss to crop stand, crop yield or crop quality. Crops can be damaged by blowing soil particles, exposure of plant roots, burial of plants by drifting soil, or desiccation and twisting of plants by the wind.

Crust

A thin surface layer, where aggregates are bound together and the surface is sealed. It is more compact and mechanically stable than the soil material immediately beneath it. Crust is characterized by its dense, platey structure, which becomes less distinct with depth until it merges with the soil below. Crust is a transitory condition.

The accumulation of eroded soil material on the land surface when the velocity of the transporting agent (wind or water) is reduced.

A non-erodible soil surface devoid of erodible materials or consisting of gravel or stones left on the land surface. It occurs in desert regions as a result of the removal of fine materials by wind or water erosion. Desert pavement is virtually non-erodible.

The removal of transportable fragments of soil material from the soil mass by an eroding agent, usually falling raindrops, running water, wind, or windblown soil particles. Detachment is the process that makes soil particles or aggregates available for transport.

Any year when precipitation is less than 80 percent of the long-term normal.

A compound or secondary air-dry soil particle that is not destroyed by dry sieving.

Dust Storm

A strong turbulent wind carrying large amounts of soil particles in suspension.

The capacity of winds above the threshold velocity to cause erosion, based on the cube of wind-speed and the duration of erosive winds.

The distribution of erosive wind energy over time at any geographic location.

Tables, derived from computer solutions (WEROS) of the Wind Erosion Equation that display values of average annual wind erosion per acre (E) for various combinations of soil erodibility (I), ridge and random roughness (K), climate (C), unsheltered distance (L), and vegetative cover (V).

The least decomposed of all the organic soil materials containing very high amounts of fiber that are well preserved and readily identifiable as to botanical origin.

Intermediate in degree of decomposition between the less decomposed fibric and the more decomposed sapric materials.

A line on a map or chart along which there is a constant value of a variable such as wind velocity or climatic erosivity.

An abrupt change in topography, characterized by windward slope change greater than 3 percent and windward slope less than 500 feet long.

The increase in wind erosion potential resulting from the compression of wind flow-lines and accompanying increased velocity over the crest of knolls. A knoll erodibility factor is used to adjust estimated erosion where these conditions occur.

Soil material transported and deposited by wind, consisting predominantly of silt-sized particles.

A period of time during a cropping sequence when cover and management effects are approximately uniform or otherwise result in uniform rates of erosion during the period.

A soil that contains a high percentage (greater than 20 percent) of organic matter throughout the solum.

The weight of a substance after it has been dried in an oven at 105 degrees C, to equilibrium.

An index of the effectiveness of precipitation, calculated from mean monthly precipitation and mean monthly temperature at a specific geographical location. A modified P-E index is used to represent effective surface soil moisture in calculation of the WEQ climatic factor C.

The direction from which winds most commonly occur. This may not be the same as the prevailing wind erosion direction.

The direction of erosive winds where there is potential for the greatest amount of soil to be moved, relative to the erosive force of winds from other directions.

Random roughness is the non-oriented surface roughness that is sometimes referred to as cloddiness. Random roughness is described as the standard deviation (in inches) of the soil surface elevations, measured at regular intervals from a fixed, arbitrary plane above a tilled soil surface, after oriented (ridge) roughness has been accounted for. Random roughness is usually created by the action of tillage implements.

A standard wind tunnel condition for small grain equivalent determination where small grain stalks 10 inches long are lying flat on the soil surface in l0-inch rows which are perpendicular to the wind direction, with stalks oriented parallel to the wind direction.

An index of relative erodibility under field conditions. Wind tunnel erodibility is adjusted for the effect of unsheltered distance and of the resistance of soil textural classes to breakdown of surface crusts by abrasion and avalanching. Compared to the wind tunnel, erodibility of a field surface is greater because the longer unsheltered distance allows abrasion and avalanching to occur.

The degree of oriented roughness is determined by the height and width of ridges formed by tillage and planting implements or by any other means of creating systematically spaced ridges. Ridges provide sheltered zones that trap moving soil particles.

The most highly decomposed of the organic materials, having the highest bulk density, least amount of plant fiber, and lowest water content at saturation.

The wind erosion control equivalent of vegetative cover, compared to a small grain standard. The standard (reference condition) is defined as small grain stalks 10 inches long lying flat on the soil surface in l0-inch rows which are perpendicular to the wind direction, with stalks oriented parallel to the wind direction. The small grain equivalent value is a function of kind, amount, and orientation of growing plants or plant residues on the soil surface.

The potential soil loss, in tons per acre per year, from a wide, level, unsheltered, isolated field with a bare, smooth, loose, and non-crusted surface, under climatic conditions like those in the vicinity of Garden City, Kansas.

T is expressed as the average annual soil erosion rate (tons/acre/year) that can occur in a field with little or no long term degradation of the soil resource thus permitting crop productivity to be sustained for an indefinite period of time.

Adsorbed water films surrounding surface soil particles which increase the soil resistance to erosion. In developing

the climatic factor (C), soil surface moisture is assumed to be proportional to the Thornthwaite Precipitation-Effectiveness (P-E) Index.

Separation of various size classes of soil particles or aggregates during wind erosion. Soils tend to have an increased coarseness fraction in response to continued sorting by erosion.

A stable border defines the upwind boundary of an isolated field. It is an area with sufficient protection to prevent saltation from starting, and capable of trapping and holding incoming saltation from eroding areas upwind, thus preventing saltating soil particles from entering areas downwind.

A layer of coarse fragments or other non-erodible particles resistant to abrasion that remain on the soil surface after the removal of fine particles by erosion.

Soil movement in the wind whereby the coarser fractions are transported by rolling and sliding along the ground surface, primarily by the impact of particles in saltation rather than by direct force of the wind. Particles greater than 0.5 mm (0.02 in) in size are usually moved in this manner.

Soil movement in wind whereby the finer fractions are transported over long distances floating in the wind-stream. Suspension is usually initiated by the impact of saltating particles. Particles moving in this manner are usually less than 0.1 mm (0.004 in) in size. Many suspension-size particles are created by abrasion during erosion.

The minimum velocity at which wind will begin moving soil particles from a smooth, bare, non-crusted surface. The threshold velocity is usually considered to be 13 mph at 1 foot above the soil surface, or 18 mph at 30 feet height.

The movement of detached soil material across the land surface or through the air by wind or running water. Transport of soil particles in wind is by three modes: (l) saltation, (2) suspension, and (3) surface creep.

The maximum amount of soil material that can be carried by wind or running water under given conditions.

A strip of grass or other erosion-resisting vegetation, planted between cultivated strips or fields and having sufficient width, height, and density to trap and store incoming saltation. Trap strips are usually not tall enough to create significant barrier effects.

The distance across an erodible field, measured along the prevailing wind erosion direction, beginning at a stable border on the upwind side and continuing downwind to a non-erodible or stable area, or to the downwind edge of the area being evaluated.

A field or portion of a field characterized by the absence of windbreaks or barriers and fully exposed to open wind velocity.

Narrow strips of annual or perennial vegetation planted at intervals across fields for wind erosion control, snow management, or protection of sensitive crops. Barriers have sufficient height and density to create a sheltered zone downwind. In the protected zone, wind velocities are reduced enough to prevent saltation from beginning. Vegetative barriers may also trap incoming saltation, but this is a secondary function

Any field with sufficient width to allow the rate of saltation/creep flow to reach the maximum that an erosive wind can sustain. This distance is the same for any erosive wind. It varies only and inversely with erodibility of the field surface. That is, the more erodible the surface, the shorter the distance in which maximum flow is reached.

A living barrier of trees or combination of trees and shrubs designed to reduce wind erosion, conserve energy or moisture, control snow deposition, or provide shelter for livestock or wildlife. When used to control wind erosion, windbreaks deflect wind forces and reduce wind velocity in the downwind sheltered zone below the threshold required for initiation of soil movement.

A grouping of soils that have similar properties affecting their resistance to wind erosion.

The detachment, transport, and deposition of soil by wind.

A numerical factor used to calculate the equivalent unsheltered distance. The factor accounts for field shape (length/width ratio), field width, preponderance, and angle of deviation of the prevailing wind erosion direction from a line perpendicular to the long side of the field or strip.

A method of farming whereby erosion-resistant crop strips are alternated with strips of erosion- susceptible crops or fallow. Erosion-resistant strips reduce or eliminate saltation and act as soil traps designed to reduce soil avalanching. Strips are perpendicular, or nearly so, to the direction of prevailing erosive winds during critical periods.

A duct in which experimental situations are created and tested by exposure to air-streams under controlled conditions. Both laboratory and portable field wind tunnels are used in wind erosion research.

An index of relative erodibility under wind tunnel conditions. Tunnel erodibility accounts for the effect of wind tunnel percent clods >0.84 mm, and for crop residue and surface roughness factors. Because wind erosion is limited by the length of the tunnel, tunnel erodibility does not account for the resistance of soil textural classes to abrasion and avalanching.