The Universal Soil Loss Equation (USLE) has been the most widely used erosion-prediction technology in the world since its introduction in the 1960's, and predicts average annual soil loss based on the product of 5 factors: rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), crop management (C), and supporting practices (P). Because the USLE was entirely an empirically-based equation, its application was limited to conditions where experimental data were available for deriving factor values. An enhanced and computerized version of the tool, the Revised USLE (RUSLE1) was released in the early 1990s. A major advancement in RUSLE1 was the use of subfactor relationships to compute C factor values from basic features of cover-management systems. This allowed RUSLE1 to be applied to far more conditions than the USLE. While RUSLE1 retained the basic structure of the USLE, process-based relationships were added where empirical data and relationships were inadequate, such as computing the effect of strip cropping for modern conservation tillage systems.

RUSLE2 is another major advancement over RUSLE1. While RUSLE2 uses the USLE basic formulation and predictions remain focused on average annual soil erosion rather than on individual events, the mathematics of RUSLE2 are on a daily basis. Many improvements have been introduced in RUSLE2, including carefully smoothed erosivity densities across the U.S., improved relationships for soil erodibility, and numerous enhancements to cropping management subfactor relationships. A new ridge subfactor has been introduced, new relationships for handling residues were added, and the deposition equations have been extended to consider sediment characteristics and how deposition changes these characteristics. A Windows-based graphical user interface was developed that makes RUSLE2 very simple to use (Fig. 1). Additional capabilities such as calculation the Soil Conditioning Index, Tillage Erosion, and various Phosphorus Indices have been added to the RUSLE2 interface.

The NRCS has embraced RUSLE2 and, working with ARS and collaborators, has compiled an extensive set of databases and developed over 22,000 management scenarios. NRCS uses RUSLE2 in conservation planning and also for determining eligibility of applicants for the Conservation Security Program (CSP) soil quality component and performs approximately 20,000 RUSLE2 runs per day.

RUSLE2 separately calculates “erosion for conservation planning,” which is an estimate reflecting the degradation of the soil resource, and “sediment yield,” which is an estimate of the amount and size distribution of sediment delivered to receiving waters. Future developments and enhancements planned for RUSLE2 include: adding ephemeral gully erosion computation, improving winter routines, and developing better technologies for very steep and very flat landscapes. RUSLE2 will be the cropland field erosion prediction tool of choice in the USA for the next several years.