CFR > Title 7 - Agriculture > SUBTITLE B—Regulations of the Department of Agriculture > CHAPTER VI—NATURAL RESOURCES CONSERVATION SERVICE, DEPARTMENT OF AGRICULTURE (parts 600 to 663) > SUBCHAPTER B—CONSERVATION OPERATIONS (parts 610 to 614) > PART 610—TECHNICAL ASSISTANCE > SUBPART B—Soil Erosion Prediction Equations (§610.11 to §610.14) > 610.12—Equations for predicting soil loss due to water erosion.

610.12—Equations for predicting soil loss due to water erosion.

(a) The equation for predicting soil loss due to erosion for both the USLE and the RUSLE is A = R × K × LS × C × P. (For further information about USLE see the U.S. Department of Agriculture Handbook 537, “Predicting Rainfall Erosion Losses—A Guide to Conservation Planning,” dated 1978. Copies of this document are available from the Natural Resources Conservation Service, P.O. Box 2890, Washington, DC 20013. For further information about RUSLE see the U.S. Department of Agriculture Handbook 703, “Predicting Soil Erosion by Water: A Guide to Conservation Planning with the Revised Universal Soil Loss Equation (RUSLE).” Copies may be purchased from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.)
(b) The factors in the USLE equation are:
(1) A is the estimation of average annual soil loss in tons per acre caused by sheet and rill erosion.
(2) R is the rainfall erosivity factor. Accounts for the energy and intensity of rainstorms.
(3) K is the soil erodibility factor. Measures the susceptibility of a soil to erode under a standard condition.
(4) LS is the slope length and steepness factor. Accounts for the effect of length and steepness of slope on erosion.
(5) C is the cover and management factor. Estimates the soil loss ratio for each of 4 or 5 crop stage periods throughout the year, accounting for the combined effect of all the interrelated cover and management variables.
(6) P is the support practice factor. Accounts for the effect of conservation support practices, such as contouring, contour stripcropping, and terraces on soil erosion.
(c) The factors in the RUSLE equation are defined as follows:
(1) A is the estimation of average annual soil loss in tons per acre caused by sheet and rill erosion.
(2) R is the rainfall erosivity factor. Accounts for the energy and intensity of rainstorms.
(3) K is the soil erodibility factor. Measures the susceptibility of a soil to erode under a standard condition and adjusts it bi-monthly for the effects of freezing and thawing, and soil moisture.
(4) LS is the slope length and steepness factor. Accounts for the effect of length and steepness of slope on erosion based on 4 tables reflecting the relationship of rill to interrill erosion.
(5) C is the cover and management factor. Estimates the soil loss ratio at one-half month intervals throughout the year, accounting for the individual effects of prior land use, crop canopy, surface cover, surface roughness, and soil moisture.
(6) P is the support practice factor. Accounts for the effect of conservation support practices, such as cross-slope farming, stripcropping, buffer strips, and terraces on soil erosion.