The Mechanics of Wind Erosion on Prairie Soils
Wind erosion occurs when surface winds exceed the threshold velocity needed to move soil particles. On bare agricultural soils in the Canadian prairie, that threshold is highly variable and depends on particle size, soil moisture at the surface, aggregate stability, and the degree of surface roughness.
Three transport processes carry eroded material: creep (rolling of large particles along the surface), saltation (bouncing of medium particles in a ballistic trajectory), and suspension (fine particles carried aloft and transported over long distances). Saltation typically accounts for the largest share of total soil loss during an erosion event, and saltating particles dislodge additional material on impact — an effect that amplifies loss once a threshold velocity is crossed.
On flat prairie fields without vegetative cover, sustained winds at moderate speed can move meaningful amounts of topsoil. Loamy fine sands and very fine sandy loams are among the most erodible soil textures under prairie conditions. Heavier clay-loam soils are generally more resistant, though they can dry into large clods that break down into highly erodible aggregates during spring cultivation.
Wind Erodibility Groups in Saskatchewan and Alberta
Agriculture and Agri-Food Canada classifies soils into Wind Erodibility Groups (WEG) based on surface texture, organic matter, and aggregate size distribution. These classifications are embedded in the Canadian Wind Erosion Prediction System (CWEPS) and inform field-level management recommendations.
| WEG Class | Soil Texture Description | Relative Erodibility |
|---|---|---|
| 1 | Fine sand, loamy fine sand | Very High |
| 2 | Loamy sand, very fine sand | High |
| 3 | Sandy loam, fine sandy loam | Moderate–High |
| 4 | Very fine sandy loam, loam | Moderate |
| 5 | Silt loam, clay loam | Low–Moderate |
| 6 | Clay, silty clay | Low |
The WEG classification applies to tilled soils. Native prairie soils in the same texture categories are substantially more resistant to wind detachment because of intact surface crust, organic matter at the surface, and perennial root networks. Converting native prairie to cultivated annual crops moves a field from the most resistant category to a more erodible one, regardless of the underlying soil texture.
Role of Vegetative Cover in Erosion Control
Vegetative cover reduces wind erosion through two mechanisms: direct obstruction of wind flow near the soil surface, and anchoring of soil particles via root networks and organic residue. Even partial cover significantly reduces erosion rates compared to fully bare ground.
For annual crops, cover at the soil surface during spring — before germination — represents the highest-risk window. Stubble from the previous crop, if left standing, provides mechanical drag that increases surface roughness and raises the threshold wind velocity required for particle movement. Systems that incorporate tall-stemmed crops (such as winter wheat or barley) into rotations, leaving standing residue over winter, reduce spring erosion exposure compared to low-residue crops like pulse legumes without a cover crop component.
For marginal cropland being managed toward perennial cover, the transition period between cultivation and establishment of a perennial grass stand carries elevated erosion risk. Nurse crops — fast-germinating annuals seeded with the perennial mixture — reduce exposed soil during the first growing season while the perennials establish.
In the Great Plains wind erosion literature, a cover threshold of approximately 30–35% is frequently cited as the level below which erosion rates increase substantially. Below 20% cover, rates accelerate non-linearly. These thresholds apply to random cover distribution; concentrated cover (such as isolated stubble rows with bare lanes between) is less effective than uniformly distributed cover at the same total percentage.
Shelterbelts and Field Windbreaks
Perennial shelterbelts — typically planted as linear rows of trees and shrubs perpendicular to prevailing winds — reduce wind velocity in the zone immediately downwind of the barrier. The protected area on the leeward side extends roughly ten times the height of the barrier, with maximum protection in the range of two to five times barrier height.
Shelterbelt effectiveness depends on porosity. A very dense, solid barrier creates a sharp wind shadow with strong turbulence immediately beyond it. A moderately porous barrier (roughly 40–50% visual porosity) produces a gentler, wider zone of reduced wind speed. In Saskatchewan and Alberta, common shelterbelt species include green ash, Manitoba maple, Scots pine, and caragana.
The Prairie Farm Rehabilitation Administration (PFRA), now part of Agriculture and Agri-Food Canada, historically supported shelterbelt planting across western Canada. Documentation of shelterbelt performance under prairie wind conditions is available through AAFC publications.
Soil Moisture and Seasonal Erosion Risk
Moist soil particles are heavier and more cohesive than dry ones. Erosion risk is therefore highest during dry periods, particularly in late winter and spring before growing-season precipitation, and again in late summer following a drought period. Early spring, when snowmelt has drained but vegetation has not yet resumed growth, is often identified as the highest-risk window on Canadian prairie cropland.
Snowpack depth and distribution influence spring soil conditions. Fields sheltered from snowdrift tend to experience deeper frost penetration and slower spring thaw, which can extend the window of moist, frost-stabilised surface conditions. Open, wind-exposed fields with minimal snow retention may thaw and dry quickly, moving into the erodible range within days of snowmelt.
Restoring Perennial Cover on Marginal Cropland
Fields with repeated erosion events, declining soil organic matter, and low yield potential are candidates for conversion back to perennial cover. The term "marginal cropland" in the prairie context often refers to sandy-textured soils or highly irregular terrain where the cost of inputs for annual crop production exceeds returns in most years.
Native grass species mixtures — including blue grama, buffalo grass, and native wheatgrasses — can be established on these sites, though seeding success varies with year-of-seeding precipitation and soil preparation method. Government programs administered through AAFC and provincial agriculture ministries have at various times supported perennial cover conversion on marginal cropland.