Soil Erosion (RUSLE)

RUSLE (the Revised Universal Soil Loss Equation, USDA Agriculture Handbook No. 703, maintained by USDA-ARS and NRCS as RUSLE2) estimates long-term average annual soil loss from sheet and rill erosion by multiplying five independent factors together: rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C), and support practice (P). Because it's a straight multiplication, every factor matters proportionally — doubling any single one doubles the estimated soil loss, and a factor set to a very low value, like no-till corn's C-factor of roughly 0.05, can suppress erosion almost as effectively as a much larger reduction in slope or rainfall exposure, which is exactly why cover management is often the most practical lever a grower actually controls.

The calculator compares the result against a standard soil loss tolerance (T-value) of 5 tons per acre per year, the rate above which soil is generally considered to be eroding faster than it can naturally reform, and translates the annual loss into a rough estimate of how many years it would take to lose a full inch of topsoil at that rate, using the commonly cited benchmark of about 150 tons per acre per inch. Estimated sediment delivery assumes that only a portion of eroded soil, roughly 40% here, actually reaches a waterway rather than redepositing somewhere else in the field or landscape — sediment delivery ratios vary considerably with terrain and distance to the nearest stream, so this figure is a general planning estimate rather than a site-specific measurement. RUSLE itself is a well-established empirical model for sheet and rill erosion, but it doesn't capture gully erosion, streambank erosion, or wind erosion, so a field can pass a RUSLE check while still losing significant soil through other pathways.