Universal Soil Loss Equation Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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The Universal Soil Loss Equation (USLE) is one of the most widely used empirical models for estimating long-term average soil loss. Wischmeier and Smith introduced this equation in 1978; the U.S. Soil Conservation Service first utilized USLE on a large scale. Soil erosion has for a long time been a major concern, particularly because of its negative impacts on agriculture and sedimentation of reservoirs. A range of natural and anthropogenic factors influence soil erosion processes, which occur in all landscape types and under a range of land use systems. USLE was intended for cropping systems, but is also applicable to nonagricultural conditions (such as construction sites). USLE was developed to predict annual soil loss rates from a particular field or single slope, where it is used to compare soil losses from a specific cropping and management system to “tolerable soil loss” rates. Moreover, USLE is used to evaluate the effectiveness of alternative cropping systems and management practices in reducing soil loss, and determining optimal levels of cropping and maximal tolerable slope.

The USLE consists of six factors reflecting effects of precipitation patterns, topography, vegetation, land management, and soil characteristics. Specifically, USLE computes expected surface erosion on a particular slope as:

A = R x K x LS x C x P

A represents the potential long-term average annual soil loss in tons per acre per year; R is the rainfall and runoff factor (erosivity); K is the soil erodibility factor; LS is the slope length-gradient factor; C is the crop/vegetation and management factor; and P is the support practice factor.

USLE is used worldwide and has come under increasing criticism. However, every model makes assumptions that limit its usefulness to certain conditions. First, USLE is intended to estimate sheet and rill erosion only. It is not calibrated to account for soil loss from gully and channel erosion, or wind erosion. It does not identify areas susceptible to landslides. Second, USLE was designed to estimate average annual soil loss from a particular field. Its predictive capability is best at evaluating soil loss at that scale and less applicable to others. Particularly in areas of high spatial and temporal variability of input parameters, uncertainty associated with results may be high. Third, USLE does not identify areas of sediment deposition. Fourth, USLE requires judgment in applying values for the variables. Differences in judgment will account for differences in the assessment of field conditions, making the comparison of estimates difficult. Fifth, USLE was designed for use in the Midwestern United States, but has been widely used and misused throughout the world.

Revisions of USLE, which more accurately predict soil loss, have been implemented since the 1990s. The revised USLE (RUSLE) was released in the early 1990s and afterwards underwent several revisions. These revised models take advantage of new research about soil erosion processes and relationships between the variables, and of the capability of computer technology and geographic information systems. In spite of its limitations, which are well known, USLE remains a widely accepted model. USLE is easy to apply for assessing relative erosion potentials under different site conditions and land management practices. However, it is a best available estimate of annual average soil loss, rather than an absolute value.

Bibliography:

G. Renard et al., “RUSLE: Revised Universal Soil Loss Equation,” Journal of Soil and Water Conservation (v.46, 1991);
G. Renard et al., “Predicting Soil Erosion by Water. A Guide to Conservation Planning with the Revised Universal Soil Loss Equation (RUSLE),” in Agriculture Handbook No. 703 (U.S. Department of Agriculture, Agricultural Research Service, 1997);
T.J. Toy, R. Foster, and K.G. Renard, Soil Erosion: Processes, Prediction, Measurement and Control (Wiley & Sons, 2003);
United Nations Environment Programme (UNEP), “Guidelines for Sediment Control Practices in the Insular Caribbean,” CEP Technical Report 32 (UNEP, 1994);
W.H. Wischmeier and D. Smith, “Predicting Rainfall Erosion Losses: A Guide to Conservation Planning,” in Agriculture Handbook 537 (U.S. Department of Agriculture, Agricultural Research Service, 1978).