The Universal Soil Loss Equation (USLE) is a widely used method for estimating average annual soil loss. It was initially proposed in 1958 and modified to its current form in 1978. The USLE estimates soil loss as a function of rainfall erosivity, soil erodibility, slope length and steepness, crop management practices, and conservation support practices. It is used to predict soil loss, guide crop and management selections, and determine conservation needs. However, the USLE is empirical and only estimates average annual soil loss from sheet and rill erosion without considering sediment deposition.

1. UNIVERSAL SOIL LOSS EQUATION
(USLE)
Lecture-6
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat (M.P.)
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. UNIVERSAL SOIL LOSS EQUATION (USLE)
 The most widely accepted method for estimating the average annual soil loss,
which is referred to as the Universal Soil Loss Equation, which is very popularly
known as USLE.
 It also helps in determining the adequacy of conservation measures.
 USLE was initially proposed by Wischmeier and Smith in 1958.
 Modified to its present form by Wischmeier and Smith in 1978.
 The definition of USLE–
“The USLE is an erosion prediction model for estimating long term
averages of soil erosion from sheet and rill erosions from a specified land
under a specified condition.”

3. UNIVERSAL SOIL LOSS EQUATION (USLE)
 Universal Soil Loss Equation (USLE):
Erosion = f (Climate, Topography, Land use, Soil)

4. UNIVERSAL SOIL LOSS EQUATION (USLE)
Rainfall Erosivity Factor/ Index (R)
 Rainfall erosivity refers to the intrinsic capacity of rainfall to cause soil erosion.
 It is the function of kinetic energy and intensity of rainstorm.
 It is expressed as a product of the kinetic energy of the storm and maximum 30
minute intensity of the storm.
R= 𝐸𝐼30= 𝐾𝐸 × 𝐼30
 Rainfall Erosivity Index R is also referred to as EI30, where E is the kinetic
energy, and I30 is the maximum 30-minute rainfall intensity during the storm. I30
value is estimated from rain gauge charts.

5. UNIVERSAL SOIL LOSS EQUATION (USLE)
Rainfall Erodibility Factor/ Index (K)
 Erodibility is the resistance of the soil to both detachment and transportation.
 It can be determined through the measurement of soil loss from a standard
runoff plot.
 A unit plot having 9% slope, or in degrees, it is 5.16o, and the length of the plot is
22.13 meters or 72.6 feet.
 This plot is kept fallow with periodic tillage up and downslope.
 In this case LS=C=P=1, hence soil loss f(R,K).
Note: Erosivity is the characteristic of rainfall, and Erodibility is related to soil.

6. UNIVERSAL SOIL LOSS EQUATION (USLE)
 Based on the runoff plot studies, certain values of erodibility factor (K) have been
recommended for different soils of India (Subramanya, 2008).

7. UNIVERSAL SOIL LOSS EQUATION (USLE)
Topographic Factor (LS)
 Slope length (L) and slope steepness (S) are taken together and written as LS.
 It represents a soil loss ratio under given conditions to that at a site with standard
slope steepness of 9 per cent and slope length of 22.13 m.
 The Steeper and longer the slope, the higher risk of erosion.
 Topographic factor LS is given by
Where L is the slope length in meters, θ is the angle of slope,
m is the exponent depending on the slope.
 The exponent, m, is taken as 0.5 for slope 5 per cent or more, 0.4 for slope
range 3.5 to 4.5 per cent, 0.3 for 1 to 3 per cent, and 0.2 for less than 1 per cent.

9. UNIVERSAL SOIL LOSS EQUATION (USLE)
Crop Management Factor (C)
 It is the soil loss ratio from a land
cropped under specified
conditions to corresponding loss
from clean tilled continuous
fallow land.
 It includes the effects of various
crops factors like crop cover,
crop sequence, tillage practices
and residue management.
 The value of C can also be
obtained from standard tables.
Table based on reports from different ICAR
research centres

10. UNIVERSAL SOIL LOSS EQUATION (USLE)
Conservation Practice Factor (P)
 This represents the ratio of soil loss from a land where conservation practices
like contouring, strip cropping and terracing, etc., are adopted to that where they
are not.
 The value of P is taken is 1 for no conservation practice.
 The value of P can also be obtained from standard tables.
Example Table

11. APPLICATION OF UNIVERSAL SOIL LOSS EQUATION (USLE)
 Predict average soil loss from a field with specific land use condition.
 Guide the selection of cropping and management system and conservation
practices for specific soils and slopes.
 Predict the change in soil loss that would result from a change in cropping or
conservation practices on a specific field.
 Estimate soil losses from land use area other than agricultural land.
 Provide soil loss estimates for conservationists to use for determining
conservation needs.

12. UNIVERSAL SOIL LOSS EQUATION (USLE)
 In India, soil loss rates have been classified into six categories.
 Based on 21 observations, 64 estimated erosion values by USLE at different
locations spread across the country

13. LIMITATIONS OF UNIVERSAL SOIL LOSS EQUATION (USLE)
 It is empirical in nature that means all coefficients are empirical. The values of R
or K or LS or C or P are applicable only for the areas for which we have
estimated those values.
 Prediction of average annual soil loss: It only predicts average annual soil
loss. If you want to determine the soil loss from a particular event, then USLE
cannot be used.
 USLE is only limited to sheet and rill erosion.
 Non-consideration of sediment deposition: it only talks about sediment loss.
There is no consideration of soil deposition in USLE.

14. Thank You