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Universal Soil Loss Equation (USLE)

BS

Baljeet Singh

Transcript

Agro-Ecology

Soil#4-Sept 30

Universal Soil Losss Equation (USLE)

Baljeet Singh, Ph.D., P.Ag.

Assiniboine Community College

25-08-2020

Soil Loss

  • The removal of soil by water, wind and other factors, the process is limited on soils covered by dense grass compared to bare soils.
  • Erosion can be catastrophic for steep or poorly covered soils, especially when exposed to heavy rainfall or high winds.
  • When top soil erodes it exposes the B horizon, which is less fertile and harder to till.
  • The eroded topsoil comes to rest as sediment, which may be rich in minerals that upset the ecosystem.
  • Soil Loss = Soil Erosion ==> Types

Wind Erosion

Wind

Water Erosion

Water

Types of Erosion:

  • Splash
  • Sheet
  • Rills
  • Gulley
  • Slip
  • Stream bank
  • Sea Shore

Other Erosion

Others

Types of Erosion:

  • Humans
  • Equipment
  • Wild-Life
  • SNIRT
  • Crop Removal
  • Grazing

RUSLEFAC

  • A = R·K·LS·C·P
  • A represents the potential, long term average annual soil loss in tonnes per hectare per year. This is the amount which is compared to the “tolerable soil loss” limits.
  • R is the rainfall factor (MJ mm ha-1 h-1)
  • K is the soil erodibility factor (t h MJ-1 mm-1)
  • L and S are the slope length and steepness factors, respectively (dimensionless).
  • C is the cropping-management factor (dimensionless)
  • P is the support practice factor (dimensionless)

USLE

Visual

Visual

Output

  • Outputs = Soil Erosion Rates and Potential Erosion Classes
  • The following qualitative ranking system was developed, based on the soil loss tolerance rates. This class system places greater emphasis on the relative implications of soil loss (e.g. severe vs. negligible impact) and less on the actual calculated soil loss rate.
  • Five erosion classes have been identified, and are defined in Table on next slide.

Output

5 Erosion Classes

Classes

Factors Influencing Erosion

  • Rainfall: Dependent on the amount, duration, intensity and frequency of rainfall.
  • Slope of Topography: The slope accelerates erosion as it increases the velocity of the flowing water.
  • Vegetation: The vegetative cover protects the soil from the beating and dispersing action of the raindrops by forming a canopy over the soil surface (better structure, accelerating water absorption and reducing surface run-off).
  • Tillage: The infiltration and permeability of the soil is improved by the practice of proper tillage.

Factors

Factors Influencing Erosion...

Continue.

  • Nature of the Soil: Erodibility of the soil is influenced by the nature of the soil, particularly its texture, structure, organic matter, amounts and kinds of salts present, presence of hard pan in the soil and presence of high water table.
  • Soil Moisture: The presence of high water table checks the infiltration and permeability. At the same time, long continuous rainless periods cause loosening of soil and thus expose the soil to erosion by wind.
  • Wind Velocity: Wind velocity is directly proportional to intensity of erosion.

Management

Mgt

References

  • Read page#129-130 on the Agro-Ecology Course pack.
  • Bring the handout at page#134 with you for infield assessment of soil erosion.
  • Take Notes
  • Bring a calculator
  • Participate in discussion

References

Thank You!