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434 Subpart B—Soil Erosion Prediction Equations § 610.5 7 CFR Ch. VI (1–1–10 Edition) (3) Providing assistance for installing culture Handbook 537, ‘‘Predicting practices, and Rainfall Erosion Losses—A Guide to (4) Certifying that the work done is Conservation Planning,’’ dated 1978. in accordance with NRCS standards Copies of this document are available and specifications. from the Natural Resources Conserva- tion Service, P.O. Box 2890, Wash- [42 FR 38169, July 27, 1977, as amended at 47 FR 56473, Dec. 17, 1982] ington, DC 20013. For further informa- tion about RUSLE see the U.S. Depart- § 610.5 Interdisciplinary assistance. ment of Agriculture Handbook 703, Technical assistance is based on the ‘‘Predicting Soil Erosion by Water: A principle that soil, water, plant, and Guide to Conservation Planning with related resources are interdependent the Revised Universal Soil Loss Equa- and must be managed accordingly. Soil tion (RUSLE).’’ Copies may be pur- conservationists integrate the various chased from the National Technical In- technical fields in providing for the formation Service, 5285 Port Royal conservation of land and water re- Road, Springfield, VA 22161.) sources. Staff scientists and specialists (b) The factors in the USLE equation develop conservation standards, pre- are: pare necessary specifications, provide (1) A is the estimation of average an- training, and review work performance, nual soil loss in tons per acre caused by NRCS uses consultants for conserva- sheet and rill erosion. tion problems that require special ex- (2) R is the rainfall erosivity factor. pertise. Accounts for the energy and intensity of rainstorms. (3) K is the soil erodibility factor. Subpart B—Soil Erosion Prediction Measures the susceptibility of a soil to Equations erode under a standard condition. (4) LS is the slope length and steep- SOURCE: 61 FR 27999, June 4, 1996, unless ness factor. Accounts for the effect of otherwise noted. length and steepness of slope on ero- sion. § 610.11 Purpose and scope. (5) C is the cover and management This subpart sets forth the equations factor. Estimates the soil loss ratio for and rules for utilizing the equations each of 4 or 5 crop stage periods that are used by the Natural Resources throughout the year, accounting for Conservation Service (NRCS) to pre- the combined effect of all the inter- dict soil erosion due to water and wind. related cover and management vari- Section 301 of the Federal Agriculture ables. Improvement and Reform Act of 1996 (6) P is the support practice factor. (FAIRA) and the Food Security Act, as Accounts for the effect of conservation amended, 16 U.S.C. 3801–3813 specified support practices, such as contouring, that the Secretary would publish the contour stripcropping, and terraces on universal soil loss equation (USLE) and soil erosion. wind erosion equation (WEQ) used by (c) The factors in the RUSLE equa- the Department within 60 days of the tion are defined as follows: enactment of FAIRA. This subpart sets (1) A is the estimation of average an- forth the equations, definition of fac- nual soil loss in tons per acre caused by tors, and provides the rules under sheet and rill erosion. which NRCS will utilize the USLE, the (2) R is the rainfall erosivity factor. revised universal soil loss equation Accounts for the energy and intensity (RUSLE), and the WEQ. of rainstorms. (3) K is the soil erodibility factor. § 610.12 Equations for predicting soil Measures the susceptibility of a soil to loss due to water erosion. erode under a standard condition and (a) The equation for predicting soil adjusts it bi-monthly for the effects of loss due to erosion for both the USLE freezing and thawing, and soil mois- and the RUSLE is A = R × K × LS × C ture. × P. (For further information about (4) LS is the slope length and steep- USLE see the U.S. Department of Agri- ness factor. Accounts for the effect of 434 VerDate Nov<24>2008 10:23 Feb 17, 2010 Jkt 220017 PO 00000 Frm 00444 Fmt 8010 Sfmt 8010 Y:\SGML\220017.XXX 220017 erowe on DSK5CLS3C1PROD with CFR Natural Resources Conservation Service, USDA § 610.14 length and steepness of slope on ero- (5) C is the climatic factor. It is a sion based on 4 tables reflecting the re- measure of the erosive potential of the lationship of rill to interrill erosion. wind speed and surface moisture at a (5) C is the cover and management given location compared with the same factor. Estimates the soil loss ratio at factors at Garden City, Kansas. The an- one-half month intervals throughout nual climatic factor at Garden City is the year, accounting for the individual arbitrarily set at 100. All climatic fac- effects of prior land use, crop canopy, tor values are expressed as a percent- surface cover, surface roughness, and age of that at Garden City. soil moisture. (6) L is the unsheltered distance. It is (6) P is the support practice factor. the unsheltered distance across an Accounts for the effect of conservation erodible field, measured along the pre- support practices, such as cross-slope vailing wind erosion direction. This farming, stripcropping, buffer strips, distance is measured beginning at a and terraces on soil erosion. stable border on the upwind side and continuing downward to the nonerod- § 610.13 Equations for predicting soil ible or stable area, or to the downwind loss due to wind erosion. edge of the area being evaluated. (a) The equation for predicting soil (7) V is the vegetative cover factor. It loss due to wind in the Wind Erosion accounts for the kind, amount, and ori- Equation (WEQ) is E = f(IKCLV). (For entation of growing plants or plant res- further information on WEQ see the idue on the soil surface. paper by N.P. Woodruff and F.H. Siddaway, 1965. ‘‘A Wind Erosion Equa- § 610.14 Use of USLE, RUSLE, and tion,’’ Soil Science Society of America WEQ. Proceedings, Vol. 29, No. 5, pages 602– 608, which is available from the Amer- (a) All Highly Erodible Land (HEL) ican Society of Agronomy, Madison, determinations are based on the for- Wisconsin. In addition, the use of the mulas set forth in 7 CFR § 12.21 using WEQ in NRCS is explained in the Nat- some of the factors from the USLE and ural Resources Conservation Service WEQ and the factor values that were (NRCS) National Agronomy Manual, contained in the local Field Office 190-V-NAM, second ed., Part 502, Technical Guide (FOTG) as of January March, 1988, which is available from 1, 1990. In addition, this includes the the NRCS, P.O. Box 2890, Washington, soil loss tolerance values used in those DC 20013.) formulas for determining HEL. The soil (b) [Reserved] loss tolerance value is used as one of (c) The factors in the WEQ equation the criteria for planning soil conserva- are defined as follows: tion systems. These values are avail- (1) E is the estimation of the average able in the FOTG in the local field of- annual soil loss in tons per acre. fice of the Natural Resources Conserva- (2) f indicates the equation includes tion Service. functional relationships that are not (b) RUSLE will be used to: straight-line mathematical calcula- (1)(i) Evaluate the soil loss estimates tions. of conservation systems contained in (3) I is the soil erodibility index. It is the FOTG. the potential for soil loss from a wide, (ii) Evaluate the soil loss estimates level, unsheltered, isolated field with a of systems actually applied, where bare, smooth, loose and uncrusted sur- those systems were applied differently face. Soil erodibility is based on soil than specified in the conservation plan surface texture, calcium carbonate adopted by the producer or where a content, and percent day. conservation plan was not developed, (4) K is the ridge roughness factor. It in determining whether a producer has is a measure of the effect of ridges complied with the HEL conservation formed by tillage and planting imple- provisions of the Food Security Act of ments on wind erosion. The ridge 1985, as amended, 16 U.S.C. 3801 et seq., roughness is based on ridge spacing, set forth in 7 CFR part 12; and height, and erosive wind directions in (2) Develop new or revised conserva- relation to the ridge direction tion plans. 435 VerDate Nov<24>2008 10:23 Feb 17, 2010 Jkt 220017 PO 00000 Frm 00445 Fmt 8010 Sfmt 8010 Y:\SGML\220017.XXX 220017 erowe on DSK5CLS3C1PROD with CFR.
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