i (190-V-NAM, 3rd Ed., July 2001) 

# National Agronomy Manual United States Department of Agriculture Natural Resources Conservation Service(190-V-NAM, 3rd Ed., October 2002 ) ii 

### October 2002

The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternate means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410, or call (202) 720-5964 (voice or TDD). USDA is an equal opportunity employer. National Agronomy Manual500–i (190-V-NAM, 3rd Ed., October 2002) Contents: Subpart 500A Authority 500–1 500.00 Soil Conservation and Domestic Allotment Act of 1935 ................................. 500–1 500.01 Purpose of the Agronomy Manual .................................................................... 500–1 Subpart 500B Agronomic policies 500–2 500.10 Location of policy

............................................................................................. 500–2 500.11 Amendments to NAM

....................................................................................... 500–2 Subpart 500C Responsibilities of agronomists 500–2 500.20 Responsibilities of national, State, area, and field agronomists ........................ 500–2 500.30 Technical information—preparing, transferring, and training .......................... 500–3 500.40 Certification

...................................................................................................... 500–3 500.50 Affiliation with professional organizations

...................................................... 500–3 

# Part 500 Authorities, Policies, and Responsibilities190-V-NAM, 3rd Ed., October 2002) 500–1 

# Part 500 Authorities, Policies, and Responsibilities

Subpart 500A Authority

500.00 Soil Conservation and Domestic Allotment Act of 1935The basic legislation for soil and water conservation programs by the Natural Resources Conservation Service (NRCS) is the Soil Conservation and Domestic Allotment Act, Public Law 74–46 of 1935 (16 U.S.C. 590a-590f). This original act recognized that agronomy, the science of field crop production, is essential in fulfilling the agency’sresponsibilities. The Buchanan Amendment to the Agricultural Appropriations Bill for FY 1930 (Public Law 70-769) led to the enactment of Public Law 74-46. In 1933, the Soil Erosion Service was established as a temporary agency of the Department of the Interior. The agency was transferred to USDA in 1935 and named the Soil Conservation Service (SCS). In 1994, the Natural Resources Conservation Service was established by Public Law 103–354, the Depart ment of Agriculture Reorganization Act (7 U.S.C. 6962).The NRCS combines the authorities of the former Soil Conservation Service as well as five natural resource conservation cost-share programs previously administered by other USDA agencies. The mission of the NRCS is to provide leadership in a partnership effort to help people conserve,maintain and improve our natural resources and environment. NRCS provides technical assistance through local conservation districts on a voluntary basis to land users, communities, watershed groups, Federal and State agencies,and other cooperators. The agency’s work focuses on erosion reduction, water quality improvement, wetland restoration and protection, fish and wildlife habitat improvement, range management, stream restoration, water management, and other natural resource problems. 

## 500.01 Purpose of the AgronomyManual The National Agronomy Manual (NAM) contains policy for agronomy activities and provides technical procedures foruniform implementation of agronomy tools and applications.National Agronomy Manual Authorities, Policies, and Responsibilities Part 500

500–2 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 500B Agronomic policies

500.10 Location of policyAgronomic policies are contained in specific parts and subparts of this National Agronomy Manual as appropriate.


## 500.11 Amendments to NAMThe NAM will be amended as needed, as additional research is completed, existing methods or procedures are updated, or as new technology is developed and approved for use in the NRCS. The national agronomist is responsible for updating this manual. 

# Subpart 500C Responsibilities of agronomists

500.20 Responsibilities of national, State, area, and field agronomists The national agronomist, nutrient management, and pest management specialists at the national level, cooperating scientists for agronomy, and agronomists on the institutesand center staffs provide staff assistance in all NRCS programs and provide national leadership on NRCS agronomy related activities. They are responsible for: • assisting upper management in formulating and recommending national policies, procedures, and standards; • technical leadership and guidance; quality control; • national coordination of agronomy with other NRCS technical fields; and • promoting and maintaining relations with groups and agencies that have common interest in agronomy.State agronomists provide staff assistance to the State Conservationist for all agronomy and related functions. They are responsible for: • Assisting in developing State policies, procedures, and instructions, and coordinating them with other States within the region. • Providing technical leadership and guidance to other agronomists and appropriate personnel within the State. • Collaborating with other State staff members to ensure interdisciplinary action in all NRCS programs. • Training field personnel. • Participating in agronomy components of appraisals and reviews. • Maintaining working relations with research centers and other cooperating agencies. • Developing and revising of all aspects of Field Office Technical Guides related to agronomy. • Providing assistance in interdisciplinary technical reviews of project plans, environmental impact statements, and other technical materials. • Coordinating agronomy functions with other States inthe region and across regional boundaries as appropriate.500–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Authorities, Policies, and Responsibilities Part 500



### Area or zone agronomists provide staff assistance in all NRCS programs. They are responsible for carrying out the requirements of conservation agronomy consistent with technical proficiency, training, interdisciplinary action, and quality control within their administrative area. In somecases, these agronomists may carry out some of the responsibilities of the state agronomists if so delegated. Field office agronomists are usually in training positions. Training is provided by agronomists at the area or State level. Agronomists in the above positions may provide specific functions through team or ad hoc assignments at a national, regional, or State level. Each agronomist has the responsibility to develop their training needs inventory and to work with their supervisorto obtain technical training to improve their overall agronomic expertise. Standards of performance for agronomists are contained in the NRCS Personnel Manual.


## 500.30 Technical information—preparing, transferring, and trainingAgronomists use technical information that has been developed at centers, institutes, national, or State level and maintain technical materials for the administrative area theyserve. State staff agronomists develop and review field office technical guide materials and ensure materials are technically correct, comprehensive, and useful to the end user. NRCS policy on preparing and maintaining technical guides is in Title 450-GM, Part 401. In addition, state agronomists are responsible for technical notes and other agronomy technical materials that are applicable to the State. Agronomists issue technical information at the area, state,or national level. This may include original information, research notes, papers, or excerpts of such material. Agronomists are encouraged to submit articles for publication orpresentation at professional meetings. Technical information presented or prepared for publication shall have an appropriate technical and or administrative review and include crediting of appropriate references. Agronomists receive and provide training necessary to maintain technical competency at all administrative levels. Training includes but is not limited to National EmployeeDevelopment Courses, workshops, conferences, and university courses.


## 500.40 Certification Agronomists at all levels of the agency are encouraged toobtain professional certification(s). Examples of certification programs include the Certified Crop Adviser (CCA) and Certified Professional Agronomists (CPAg) underARCPACS of the American Society of Agronomy, Certified Professional in Erosion and Sediment Control (CPESC) of the Soil and Water Conservation Society, and state pesticide applicator licenses. Continuing educationalrequirements of most certification programs provide excellent opportunities to stay abreast of advances in technology.


## 500.50 Affiliation with professional organizationsAgronomists at all levels are encouraged to be active members of professional scientific societies, such as the American Society of Agronomy, Soil Science Society of America,Crop Science Society of America, the Soil and Water Conservation Society. These organizations provide opportunities to interact with researchers at the national and State level and to stay current on the latest technology.501–i (190-V-NAM, 3rd Ed., October 2002) Contents: Subpart 501A Introduction 501–1 501.00 Overview of Content in Part 501 Water Erosion

.............................................. 501–1 Subpart 501B Water erosion 501–1 501.10 Forms of water erosion ..................................................................................... 501–1 501.11 The water erosion process ................................................................................. 501–1 Subpart 501C Estimating sheet and rill erosion 501–2 501.20 How, why, and by whom water erosion is estimated

........................................ 501–2 501.21 Methods of estimating sheet and rill erosion

.................................................... 501–2 501.22 The Revised Universal Soil Loss Equation

....................................................... 501–3 501.23 Limitations of the equation

............................................................................... 501–3 501.24 Alternative methods of applying RUSLE ......................................................... 501–3 501.25 Data needed to support RUSLE ........................................................................ 501–3 501.26 Tools for using RUSLE .................................................................................... 501–4 Subpart 501D RUSLE factors 501–4 501.30 The average annual soil loss estimate, A .......................................................... 501–4 501.31 The rainfall and runoff erosivity factor, R ........................................................ 501–4 501.32 The soil erodibility factor, K

............................................................................. 501–4 501.33 The slope length and steepness factors, L and S ............................................... 501–5 501.34 The cover-management factor, C ...................................................................... 501–5 501.35 The support practice factor, P

........................................................................... 501–5 Subpart 501E Principles of water erosion control 501–6 501.40 Overview of principles

...................................................................................... 501–6 501.41 Relation of control to RUSLE factors

............................................................... 501–6 Subpart 501F References 501–7

Exhibits Exhibit 501–1 Acceptable class and half-class factor K values for use in 501–8 RUSLE where K values are adjusted for seasonal variability 

# Part 501 Water Erosion(190-V-NAM, 3rd Ed., October 2002) 501–ii190-V-NAM, 3rd Ed., October 2002) 501–1 

# Part 501 Water Erosion

Subpart 501A Introduction

501.00 Overview of Content in Part 501 Water Erosion Part 501 presents Natural Resources Conservation Service (NRCS) policy and procedures for estimating soil erosion by water. It explains the types, the method used to estimate, and the control of soil erosion by water. NRCS technical guidance related to water erosion shall conform to policy and procedures set forth in this part.The Agricultural Research Service (ARS) has primary responsibility for erosion prediction research within the U.S. Department of Agriculture (USDA). ARS is the lead agency for developing erosion prediction technology, including theRevised Universal Soil Loss Equation (RUSLE). The technology in RUSLE is documented to the publication Predicting Soil Erosion by Water: A Guide to Conservation Planning With Revised Universal Soil Loss Equation, U.S. Department of Agriculture Handbook 703, hereafter referred to as Agriculture Handbook 703. 

# Subpart 501B Water erosion

501.10 Forms of water erosion Forms of soil erosion by water include sheet and rill,ephemeral gully, classical gully, and streambank. Each succeeding type is associated with the progressive concentration of runoff water into channels as it moves downslope. Sheet erosion, sometimes referred to as interrill erosion, is the detachment of soil particles by raindrop impact and the removal of thin layers of soil from the land surface by the action of rainfall and runoff. Rill erosion is the formation of small, generally parallel channels formed by runoff water. Rills usually do not re-occur in the same place. Ephemeral gullies are concentrated flow channels formed when rills converge to form shallow channels. They are alternately filled with soil by tillage operations and re-formed in thesame general location by subsequent runoff events. Classical gullies are also concentrated flow channels formed when rills converge. These are well defined, permanent incised drainageways that cannot be crossed by ordinary farming operations. Other forms of erosion that are related to soil erosion by water include stream channel and geologic. Stream channelerosion refers to the degradation of channels and waterways. Geologic erosion refers to long-term erosion effects, as opposed to accelerated erosion events discussed in the Subpart.No reliable methods exist for predicting the rate of ephemeral gully, classical gully, stream channel, or geologic erosion. The remainder of this part deals only with prediction and control of sheet and rill erosion.


## 501.11 The water erosion process The processes of sheet and rill erosion are detachment,transport, and deposition of soil particles caused by raindrop impact and surface runoff. Detachment is the removal of particles from the soil mass and is expressed in units, such as tons per acre. When soil particles are removed from the mass, they are referred to as sediment.501–2 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Erosion Part 501



### The movement of sediment downslope is sediment transport. A measure of sediment transport is sediment load. Sediment load on a slope increases with distance downslope as long as detachment is occurring. That is, detachment adds to the sediment load. Where runoff is slowed at the base of a slope or by densevegetation, deposition occurs, which is the transfer of sediment from the sediment load to the soil mass. That is, deposition removes sediment from the sediment load, and accumulates on the soil surface. Two types of deposition, remote and local, occur. Remote deposition occurs some distance away from the origin of the sediment. Deposition at the toe of a concave slope, on the uphill side of vegetative strips, and in terrace channels are examples of remote deposition. Local deposition is where sediment is deposited near, within several inches, of where it is detached. Deposition in microdepressions and in low gradient furrows are examples of local deposition. 

# Subpart 501C Estimating sheet and rill erosion

501.20 How, why, and by whom water erosion is estimatedNRCS estimates soil erosion by water as part of its technical assistance to land users. In conservation planning, erosion estimates are made for an existing management system and compared with alternative systems and with soil loss tolerance, T, values. In addition, soil loss estimates are used to inventory naturalresources, evaluate the effectiveness of conservation programs and land treatment, and estimate sediment production from fields that might become sediment yield in watersheds. In March 1995, NRCS adopted RUSLE as the official tool for predicting soil erosion by water. NRCS continues to use USLE for certain provisions of Farm Bill programs and for the NRCS National Resources Inventory (NRI).


## 501.21 Methods of estimating sheet and rill erosion Efforts to predict soil erosion by water started in the1930’s. Cook (1936) identified the major variables that affect erosion by water. Zingg (1940) published the first equation for calculating field soil loss. Smith and Whitt(1947) presented an erosion-estimating equation that included most of the factors present in modern soil loss equations. The Musgrave equation (Musgrave 1947) was a soilloss equation developed for farm planning. Finally, an effort was initiated to develop a national equation from the various state and regional equations that existed in the1950’s. In 1954, the Agricultural Research Service established the National Runoff and Soil Loss Data Center atPurdue University in West Lafayette, Indiana, to consolidate all available erosion data. Using the data assembled at the Data Center, Wischmeier and Smith (1965) developed the Universal Soil Loss Equation (USLE). The USLE was a consolidation of several regional soil loss equations, and was based on summarizing and statistical analyses of more than 10,000 plot-years of basic runoff andsoil loss data from 49 U.S. locations (Agriculture Handbook 703, 1997; Wischmeier and Smith 1965, 1978).National Agronomy Manual Water Erosion Part 501

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### The USLE was designed to provide a convenient workingtool for conservationists. It quantifies soil erosion as a product of six factors representing rainfall and runoff erosiveness, soil erodibility, slope length, slope steepness, covermanagement practices, and supporting practices.


## 501.22 The Revised Universal Soil Loss EquationSince March 1995, the Revised Universal Soil Loss Equation (RUSLE) has been used by NRCS to estimate soil loss by water (Agriculture Handbook 703.). RUSLE predicts long-term average annual soil loss from sheet and rill erosion. RUSLE is an update of the Universal Soil Loss Equation (USLE) as described in AgricultureHandbook 537 (Wischmeier and Smith 1978). RUSLE utilizes a computer program to facilitate the calculations. RUSLE technology reflects the analysis of research data that were unavailable when Agricultural Handbook 282 (Wischmeier and Smith 1965) and Agriculture Handbook 537 were completed.


## 501.23 Limitations of the equation The term Universal distinguishes the USLE and RUSLE from State and regionally based models that preceded them. However, the use of the USLE and RUSLE is limited to situations where factors can be accurately evaluated and to conditions for which they can be reliably applied (Wischmeier 1978; Agriculture Handbook 703, 1997). RUSLE predicts long-term average annual soil loss carried by runoff from specific field slopes under specified cover and management systems. It is substantially less accurate for the prediction of specific erosion events associated with single storms and short-term random fluctuations. RUSLE also estimates sediment yield for the amount of eroded soil leaving the end of a slope with certain support practices (see 501.35). It does not predict sediment yield for the amount of sediment that is delivered to a point in a watershed, such as the edge of a field, that is remote from the origin of the detached soil particles. Nor does RUSLE predict erosion that occurs in concentrated flow channels. 

## 501.24 Alternative methods of applying RUSLE ARS released RUSLE in 1992 as a computer program in the DOS environment. The model calculates soil loss from afield slope using values for each factor and using data elements from climate, plant, and field operation data bases. Since 1993, RUSLE has been implemented in many NRCS field offices in hardcopy form in the Field Office Technical Guide (FOTG). State and area agronomists have developed tables and charts containing values for each of the RUSLEfactors. Since the RUSLE module in Field Office Computing System (FOCS) is no longer supported by the Information Technology Center, NRCS will continue to implement RUSLE technology using charts and tables in the FOTG.


## 501.25 Data needed to support RUSLE RUSLE uses soil erodibility, K, values from the NASIS Soils Database. Climatic data is obtained from National Weather Service weather stations with reliable long-term data. State and area agronomists have developed cover andmanagement factor, C, values for common cropping systems. The crop data base in the DOS RUSLE program contains plant growth and residue production parameters. These variables for key crops are listed in chapter 7 of Agriculture Handbook 703. Values for many of these parameters are available in a data base for a wide variety of plants. A user interface, the Crop Parameter Intelligent Data System (CPIDS) (Deer-Ascough et al. 1995), allows the user tosearch the data base. The USDA, ARS, National Soil Erosion Research Laboratory, West Lafayette, Indiana, maintains CPIDS. Development and maintenance of data bases used by NRCS in erosion prediction models are the responsibility of NRCS agronomists at the State and national levels. Refer to Part 509 in this Manual for more detailed information on data base management and instructions. The national agronomist maintains a data base management plan that identifies the process of developing and maintaining data bases needed to support RUSLE. Data bases for some States are available in electronic format on the Fort Worth server.501–4 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Erosion Part 501



## 501.26 Tools for using RUSLE Maps of rainfall and runoff factors, R and R eq 

### (see part 501.31) for the continental United States plus Hawaii are available in Agriculture Handbook 703, figures 2-1 to 2-5 and figures 2-15 and 2-16. Additional climate-related dataand inputs are available in this chapter. Most states and Basin Areas have developed county-based climatic maps for their areas. These contain the greater detail that is desired when applying RUSLE to specific field situations, and are available in NRCS State offices. Soil erodibility factor, K, values for RUSLE are available in the NASIS Soils Database and in other soils data bases andtables. In areas of the United States where K values are adjusted to account for seasonal variability, (Agriculture Handbook 703) tables are available in State offices that show how the values are rounded to the nearest class and subclass. Four slope length and steepness, L and S, table options are available in RUSLE. LS values can be obtained from tables4-1 to 4-4 in Agriculture Handbook 703. The RUSLE computer program also calculates LS factor values for both uniform and complex slopes. Cover and management factor, C, values are available in electronic table format in tables in most State offices and in the Field Office Technical Guide. Hardcopy tables are available in most State offices. Support practice factor, P, values are calculated using tablesavailable in the FOTG in many states. Copies, where available, can be obtained from the State office. Table values forcommon stripcropping and buffer strip systems are available in the FOTG of some states. 

# Subpart 501D RUSLE factors

501.30 The average annual soil loss estimate, A The long time average annual soil loss, A, is the computed spatial average soil loss and temporal average soil loss per unit of area, expressed in the units for K and for the period selected for R. As applied by NRCS, the units for K and the period for R are selected so that A is expressed in tons per acre per year.RUSLE predicts the soil loss carried by runoff from specific field slopes in specified cover and management systems.


## 501.31 The rainfall and runoff erosivity factor, R The rainfall and runoff erosivity factor, R, is the product of total storm energy times the maximum 30-minute intensity. Stated another way, the average annual total of the storm energy and intensity values in a given location is the rainfall erosion index, R, for the locality. The R factor represents the long-term average annual summation of the Erosivity Index (EI) for extended period of record. In dryland cropping areas of the Northwest Wheat and Range Region, the effect of melting snow, rain on snow, and/or rain on thawing soil poses unique problems. An equivalent R value, R eq 

### , is calculated for these areas to account for this added runoff.


## 501.32 The soil erodibility factor, K The soil erodibility factor, K, is a measure of erodibility for a standard condition. This standard condition is the unit plot, which is an erosion plot 72.6 feet (22.1 ) long on a 9 percent slope, maintained in continuous fallow, tilled up and down hill periodically to control weeds and break crusts that form on the soil surface. The erodibility factor K represents the combined effect of susceptibility of soil to detachment, transport of sediment and the amount and rateof runoff caused by a particular rainfall event. Soil properties that affect soil erodibility include texture, structure, per-National Agronomy Manual Water Erosion Part 501

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### meability and organic matter content. Values for K shouldbe selected from those given in the NRCS soil survey database in NASIS or in published reports the RUSLE soilerodibility nomograph can also be used to estimate K values for most soils. Soil erodibility K varies by season. Ittends to be high in early spring during and immediately following thawing, and other periods when the soil is wet.NRCS further modifies the seasonally adjusted K by rounding the value to the nearest K factor class or half-class (exhibit 501-1). Rock fragments in the soil profile affect the soil erodibility factor 1 / 

### . The K value is adjusted upwards to account for rock fragments in the soil profile of sandy soils that reduce infiltration. No adjustment to the K value is recommendedby NRCS for rocks in the profile of medium and heavy textured soils.


## 501.33 The slope length and steepness factors, L and S The slope length factor, L, is the ratio of soil loss from the field slope length to soil loss from a 72.6-foot length under identical conditions. The slope steepness factor, S, is the ratio of soil loss from the field slope gradient to soil loss from a 9 percent slope under otherwise identical conditions. In erosion prediction as used by NRCS, the factors L and S are evaluated together, and LS values for uniform slopescan be selected from tables 4–1, 4–2, 4–3, and 4–4 in Agriculture Handbook 703. The slope length is defined as the horizontal distance fromthe origin of overland flow to the location of either concentrated flow or deposition. Slope lengths normally do not exceed 400 feet because sheet and rill flows will almost always coalesce into concentrated flow paths within that distance. Lengths longer than 1,000 feet should not be used in RUSLE. Slope length and steepness determinations are best made inthe field. In conservation planning, the hillslope profile representing a significant portion of the field having the mostsevere erosion is often chosen. Slope lengths are best determined by pacing out flow paths and making measurements directly on the ground. Steep slopes should be converted to horizontal distances. Slope steepness determinations are best made in the field using a clinometer, Abney level orsimilar device. Chapter 4, Agriculture Handbook 703 contains additional guides for choosing and measuring slopes. Most naturally occurring hillslope profiles are irregular inshape. When the slope profile is significantly curved (convex or concave, or sigmoid.convex at the shoulder and concave at the toe), the conservationist should represent it as aseries of slope segments, using the irregular slope procedure in the RUSLE computer program.


## 501.34 The cover-management factor, C The cover-management factor, C, is the ratio of soil loss from an area with specified cover and management to soil loss from an identical area in tilled continuous fallow.The C factor is used most often to compare the relative impacts of management options on conservation plans.The impacts of cover and management on soil losses are divided into a series of subfactors in RUSLE. These include the impacts of previous vegetative cover and management,canopy cover, surface roughness, and in some cases the impact of soil moisture. In RUSLE, these subfactors are assigned values, and when multiplied together yield a soil loss ratio (SLR). Individual SLR values are calculated for each period over which the important parameters are assumed to remain constant. Each SLR value is then weighted by the fraction of rainfall andrunoff erosivity, EI, associated with the corresponding period, and these weighted values are combined (summed) into an overall C factor value.


## 501.35 The support practice factor, P The support practice factor, P, is the ratio of soil loss with a support practice like contouring, stripcropping, or terracing to soil loss with straight-row farming up and down the slope. The contour P subfactor accounts for the beneficial effects of redirected runoff that modifies the flow pattern becauseof ridges or oriented roughness that are partially or completely oriented along the contour. 1/ Rock fragments on the soil surface are accounted for in the C factor.501–6 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Erosion Part 501



### The contour P subfactor includes the effects of storm severity, ridge height, off-grade contouring, slope length and steepness, infiltration, and soil cover and roughness. The stripcropping P subfactor is a support practice wherestrips of clean-tilled or nearly clean-tilled crops are alternated with strips of close growing vegetation, or strips with relatively smooth tilled soil surfaces are alternated with strips with rough tilled surfaces. The stripcropping P subfactor evaluates what are variously described as contour stripcropping, cross-slopestripcropping, field stripcropping, buffer strips and vegetated filter strips. Terraces in RUSLE are support practices where high andlarge ridges of soil are constructed across the slope at intervals. These ridges and their accompanying channels intercept runoff and divert it around the slope or into a closed outlet. Terraces can affect sheet and rill erosion by reducing slope length and cause deposition in the terrace channel.Tile drainage, under optimum conditions, can reduce erosion by reducing runoff. Because of a lack of support data, NRCS does not use the tile drainage subfactor in RUSLE, except in the Willamette Valley in the Oregon and Puget Sound basin in Washington.In addition to the support practice factor, P, used in conservation planning, RUSLE estimates sediment yield for contour strips and terraces. The sediment yield, or delivery ratio, used in RUSLE is the ratio to the amount of sedimentleaving the end of the slope length to the amount of sediment produced on the slope length. 

# Subpart 501E Principles of water erosion control

501.40 Overview of principles The principle factors that influence soil erosion by water are climate, soil properties, topography, vegetative cover, and conservation practices. Climate and soil properties areconditions of the site and are not modified by ordinary management measures. Conservation treatment primarily involves manipulation of vegetative cover, modification of topography, and manipulation of soil conditions in the tillage zone. The greatest deterrent to soil erosion by water is vegetative cover, living or dead, on the soil surface. Cover and cultural practices influence both the detachment of soil particles and their transport. Growing plants and plant residue absorb the energy of raindrops, decrease the velocity of runoff water, and help create soil conditions that resist erosion. Cultural practices that affect vegetative cover include crop rotations,cover crops, management of crop residue, and tillage practices. 

## 501.41 Relation of control to RUSLE factors In conservation planning, the cover and management factor, C, and the support practices factor, P, can be manipulated in RUSLE to develop alternatives for erosion reduction. In addition, where slope length is reduced with some terraceand diversion systems, the slope length and steepness factor, LS, will be reduced. Using RUSLE technology, estimates of erosion reduction are illustrated in the subfactors of factor C. Benefits to erosion control are achieved in the: • prior land use subfactor by increasing the mass of roots and buried residue and increasing periods since soil disturbance, • canopy cover subfactor by increasing the canopy cover of the field area and low raindrop fall height from the canopy, • surface cover subfactor by increasing the ground cover of plant residue, and by permanent cover such as rock fragments, • surface roughness subfactor by increasing the random surface roughness that ponds water, and thereby reduces the erosive effect of raindrops and traps sediment, andNational Agronomy Manual Water Erosion Part 501

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### • soil moisture subfactor by growing moisture-depleting crops. This benefit is only applied in RUSLE inthe Northwest Wheat and Range Region of the western United States. When support practices are applied, they become integral parts of a resource management system for controlling soil erosion by water. Contour farming, contour stripcropping, and conservation buffers form ridges on or near the contour that slow runoff and trap sediment. Terraces and diversions intercept concentrated runoff flows and, in many cases, shorten the length of slope. Some erosion control practices, such as grassed waterways and water control structures, do not substantially reduce sheet and rill erosion. While these can be effective erosion control practices in a resource management system, they are not a part of the soil loss reduction that is estimated by RUSLE. 

# Subpart 501F References

Cook, H.L. 1936. The nature and controlling variables of the water erosion process. Soil Sci. Soc. Am. Proc. 1:60-64. Deer-Ascough, L.A., G.A. Weesies, J.C. Ascough II, andJ.M. Laflen. 1995. Plant Parameter Database for Erosion Prediction Models. Applied Engineering in Agriculture, 11(5):659-666. Foster, G.R., G.A. Weesies, D.K. McCool, D.C. Yoder, and K.G. Renard. 1997. Revised Universal Soil LossEquation User’s Manual. U.S. Department of Agriculture, Natural Resources Conservation Service. (unpublished draft). Musgrave, G.W., and R.A. Norton. 1937. Soil and water conservation investigations at the Soil Conservation Experiment Station Missouri Valley Loess Region,Clarinda, Iowa, Progress Report, 1931-35. U.S. Department of Agriculture Tech. Bull. 558. Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder, coordinators. 1997. Predicting Soil Erosion by Water: A Guide to Conservation Planning With the Revised Universal Soil Loss Equation (RUSLE). U.S. Department of Agriculture Handbook No. 703, 404 pp. Smith, D.D., and D.M. Whitt. 1947. Estimating soil losses from field areas of claypan soil. Soil Sci. Soc. Am. 12:485-490.Wischmeier, W.H., and D.D. Smith. 1965. Predicting rainfall-erosion losses from cropland east of the Rocky Mountains: Guide for selection of practices for soiland water conservation. U.S. Department of Agriculture Handbook No. 282.Wischmeier, W.H., and D.D. Smith. 1978. Predicting rainfall erosion losses: A guide to conservation planning. U.S. Department of Agriculture Handbook No. 537.Zingg, A.W. 1940. Degree and length of land slope as it affects soil loss in runoff. Agric. Eng. 21:59-64.501–8 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 501G Exhibit

1/ Original K value from the soils data base for a specific map unit or soil component. 2/ Minimum value is 80% of the original K value, and is the cap for acceptable minimum class and half-class va lues. 3/ Maximum value is 120% of the original K value, and is the cap for the acceptable maximum class and half-class values. 4/ Acceptable class and half-class K factor values, were approved 4/15/94 by a joint committee of NRCS soil scientists and agro nomists, under the leadership of H.R. Sinclair, lead soil scientist. K l a n i g i r O e u l a v 1 / m u m i n i M e u l a v 2 / m u m i x a M e u l a v 3 / s e u l a v r o t c a f K s s a l c
- f l a h d n a s s a l c e l b a t p e c c A 4 /


### 2 0

. 0 6 1 0

. 0 4 2 0

. 0 2 0

. 0
5 0

. 0 4 0

. 0 6 0

. 0 5 0

. 0
0 1

. 0 8 0

. 0 2 1

. 0 8 0

. 0 0 1

. 0 2 1

. 0
5 1

. 0 2 1

. 0 8 1

. 0 2 1

. 0 5 1

. 0 7 1

. 0
7 1

. 0 6 3 1

. 0 4 0 2

. 0 5 1

. 0 7 1

. 0 0 2

. 0
0 2

. 0 6 1

. 0 4 2

. 0 7 1

. 0 0 2

. 0 2 2

. 0 4 2

. 0
4 2

. 0 2 9 1

. 0 8 8 2

. 0 0 2

. 0 2 2

. 0 4 2

. 0 6 2

. 0 8 2

. 0
8 2

. 0 4 2 2

. 0 6 3 3

. 0 4 2

. 0 6 2

. 0 8 2

. 0 0 3

. 0 2 3

. 0
2 3

. 0 6 5 2

. 0 4 8 3

. 0 6 2

. 0 8 2

. 0 0 3

. 0 2 3

. 0 5 3

. 0 7 3

. 0
7 3

. 0 6 9 2

. 0 4 4 4

. 0 0 3

. 0 2 3

. 0 5 3

. 0 7 3

. 0 0 4

. 0 3 4

. 0
3 4

. 0 4 4 3

. 0 6 1 5

. 0 5 3

. 0 7 3

. 0 0 4

. 0 3 4

. 0 6 4

. 0 9 4

. 0
9 4

. 0 2 9 3

. 0 8 8 5

. 0 0 4

. 0 3 4

. 0 6 4

. 0 9 4

. 0 2 5

. 0 5 5

. 0

5 5

. 0 4 4

. 0 6 6

. 0 6 4

. 0 9 4

. 0 2 5

. 0 5 5

. 0 0 6

. 0 4 6

. 0
4 6

. 0 2 1 5

. 0 8 6 7

. 0 2 5

. 0 5 5

. 0 0 6

. 0 4 6

. 0 0 7

. 0 6 7

. 0 Exhibit 501-1 Acceptable class and half-class factor K values for use in RUSLE where K values are adjusted for seasonal variability.502–i (190-V-NAM, 3rd Ed., October 2002) 

# Wind Erosion

Contents: 

# Part 502

Subpart 502A Introduction 502–1 502.00 Overview

....................................................................................................... 502–1 Subpart 502B Wind erosion 502–1 502.10 The wind erosion problem ............................................................................ 502–1 502.11 The wind erosion process ............................................................................. 502–2 Subpart 502C Estimating wind erosion 502–3 502.20 How, why, and by whom wind erosion is estimated ..................................... 502–3 502.21 Methods of estimating wind erosion ............................................................. 502–3 502.22 The wind erosion equation ............................................................................ 502–3 502.23 Limitations of the equation ........................................................................... 502–5 502.24 Alternative procedures for using the WEQ ................................................... 502–5 502.25 Data to support the WEQ .............................................................................. 502–6 502.26 Using WEQ estimates with USLE or RUSLE calculations .......................... 502–6 502.27 Tools for using the WEQ .............................................................................. 502–6 Subpart 502D WEQ Factors 502–7 502.30 The wind erosion estimate, E ........................................................................ 502–7 502.31 Soil erodibility index, I ................................................................................. 502–7 502.32 Soil roughness factor K, ridge and random roughness ................................ 502–10 502.33 Climatic factor, C

........................................................................................ 502–12 502.34 Unsheltered distance, L

............................................................................... 502–14 502.35 Vegetative cover factor, V .......................................................................... 502–16 Subpart 502E Principles of wind erosion control 502–17 502.40 General

........................................................................................................ 502–17 502.41 Relation of control to WEQ factors ............................................................ 502–17 502.42 Tolerances in wind erosion control ............................................................. 502–18 Subpart 502F Example problems 502–19 Subpart 502G References 502–99

Figures Figure 502-1 The wind erosi on process 502–2 Figure 502–2 Graphic of knoll erodibility 502–9 Figure 502–3 Detachment, transport, and deposition on ridges and furrows 502–10(190-V-NAM, 3rd Ed., October 2002) 502–ii National Agronomy Manual Wind Erosion Part 502

Figure 502–4 Chart to determine soil ridge roughness factor, Krd, from ridge 502–10 roughness, Kr, (inches) Figure 502–5 Unsheltered distance L 502–14 Figure 502–6 Unsheltered distance L, perennial vegetation (pasture or range) 502–14 Figure 502-7 Unsheltered distaqnce L – windbreak or barrier 502–14 Figure 502–8 Unsheltered distance L, stripcropping system 502–15

Exhibits Exhibit 502–1 Example E table 502–21 Exhibit 502–2 Wind erodibility groups and wind erodibility index 502–22 Exhibit 502–3 Sieving instructions 502–23 Exhibit 502–4 Ridge roughness factor, Krd, graphs 502–26 Exhibit 502–5 Ridge roughness factor, K rd , tables 502–31 Exhibit 502–6 Random roughness factor, K rr , graph 502–47 Exhibit 502–7a Example of erosive wind data available for specific locations 502–49 Exhibit 502–7b Example of wind erosion calculation using the management period 502–50 procedure Exhibit 502–8 C factor map, United States 502–51 Exhibit 502–9 Procedures for developing local C factors 502–52 Exhibit 502–10 Flat small grain equivalent charts 502–57 Exhibit 502–11 Estimating small grain equivalents for untested vegetation 502–95 Exhibit 502–12 Estimating small grain equivalents of mixed vegetative cover that has two 502–97 or more components Exhibit 502–13 Crop yield-residue conversion (Reserved, to be developed) 502–98 Exhibit 502–14 Residue reduction by tillage (Reserved, to be developed) 502–98 Exhibit 502–15 E Tables; Soil loss from wind erosion in tons per acre per year 502–98 (Insert appropriate E tables for local values of climatic factor, C) Exhibit 502–16 Wind physics (Reserved to be developed) 502–98 Exhibit 502–17 Wind erosion control exhibits ( Reserved, to be develo ped) 502–98

Tables Table 502–1 Knoll erodibility adjustment factor for I 502–8 Table 502-2 I adjustment guidelines for crusts 502–8 Table 502-3 Wind erosion direction factors 502–15 Table 502-4 Crop tolerance to blowing soil 502–19 Table 502–5A Angle of deviation = 0 degrees; I = <134 502–32 Table 502–5B Angle of deviation = 22.5 degrees; I = <134 502–32502–iii (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5C Angle of deviation = 45 degrees; I = <134 502–33 Table 502–5D Angle of deviation = 67.5 degrees; I = <134 502–33 Table 502–5E Angle of deviation = 90 degrees; I = <134 502–34 Table 502–5F Angle of deviation = 0 degrees; I = 134 502–34 Table 502–5G Angle of deviation = 22.5 degrees; I = 134 502–35 Table 502–5H Angle of deviation = 45 degrees; I = 134 502–35 Table 502–5I Angle of deviation = 67.5 degrees; I = 134 502–36 Table 502–5J Angle of deviation = 90 degrees, I = 134 502–36 Table 502–5K Angle of deviation = 0 degrees; I = 160 and 180 502–37 Table 502–5L Angle of deviation = 22.5 degrees; I = 160 and 180 502–37 Table 502–5M Angle of deviation = 45 degrees; I = 160 and 180 502–38 Table 502–5N Angle of deviation = 67.5 degrees; I = 160 and 180 502–38 Table 502–5O Angle of deviation = 90 degrees; I = 160 and 180 502–39 Table 502–5P Angle of deviation = 0 degrees; I = 220 502–39 Table 502–5Q Angle of deviation = 22.5 degrees; I = 220 502–40 Table 502–5R Angle of deviation = 45 degrees; I = 220 502–40 Table 502–5S Angle of deviation = 67.5 degrees; I = 220 502–41 Table 502–5T Angle of deviation = 90 degrees; I = 220 502–41 Table 502–5U Angle of deviation = 90 degrees; I = 250 502–42 Table 502–5V Angle of deviation = 22.5 degrees; I = 250 502–42 Table 502–5W Angle of deviation = 45 degrees; I = 250 502–43 Table 502–5X Angle of deviation = 67.5 degrees; I = 250 502–43 Table 502–5Y Angle of deviation = 90 degrees; I = 250 502–44 Table 502–5Z Angle of deviation = 0 degrees; I = 310 502–44 Table 502–5AA Angle of deviation = 22.5 degrees; I = 310 502–45 Table 502–5BB Angle of deviation = 45 degrees; I = 310 502–45 Table 502–5CC Angle of deviation = 67.5 degrees; I = 310 502–46 Table 502–5DD Angle of deviation = 90 degrees; I = 310 502–46 Table 502–6 Table converts random roughness heights (standard deviation in inches) 502–47 to WEQ K subfactors (Krr) for random roughness. Krr values vary by I factors assigned to soil Wind Erodibility Groups Table 502–7 Random roughness (standard deviation) core values 502–48 Table 502–8a Wind erosion direction factor; angle of deviation 1/ = 0 degrees 502–54 Table 502–8b Wind erosion direction factor; angle of deviation 1/ = 22.5 degrees 502–54 Table 502–8c Wind erosion direction factor; angle of deviation 1/ = 45 degrees 502–55 Table 502–8d Wind erosion direction factor; angle of deviation 1/ = 67.5 degrees 502–55 Table 502–8e Wind erosion direction factor; angle of deviation 1/ = 90 degrees 502–56502–1 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 502A Introduction

502.00 Overview Part 502 presents Natural Resources Conservation Service (NRCS) policy and procedures for estimating wind erosion. It explains the Wind Erosion Equation (WEQ) and providesguidance and reference on wind erosion processes, prediction, and control. NRCS technical guidance related to wind erosion conforms to policy and procedures in this part. This part will be amended as additional research on winderosion and its control is completed and published. The national agronomist is responsible for updating this chapter and coordinating wind erosion guidance with Agricultural Research Service (ARS). NRCS cooperating scientists may supplement this manual. However, appropriate supplements prepared by cooperating scientists are to be submitted to the national agronomist for review and concurrence before issuance. State supplements are to be reviewed and approved by the national agronomist before being issued to field offices. Understanding the erosive forces of wind is essential to the correct use of the Wind Erosion Equation and interpretation of wind erosion data. NRCS predicts erosion rates, assesses potential damage, and plans control systems for wind erosion.The Agricultural Research Service has primary responsibility for erosion prediction research within the U.S. Department of Agriculture (USDA). Wind erosion research isconducted by the Wind Erosion Research Unit at Manhattan, Kansas, and the Cropping Systems Research Unit at Big Spring, Texas. 

# Subpart 502B Wind erosion

502.10 The wind erosion problem Wind is an erosive agent. It detaches and transports soil particles, sorts the finer from the coarser particles, and deposits them unevenly. Loss of the fertile topsoil in erodedareas reduces the rooting depth and, in many places, reduces crop yield. Abrasion by airborne soil particles damages plants and constructed structures. Drifting soil causes extensive damage also. Sand and dust in the air can harm animals, humans, and equipment.Some wind erosion has always occurred as a natural landforming process, but it has become detrimental as a result of human activities. This accelerated erosion is primarily caused by improper use and management of the land (Stallings 1951). Few regions are entirely safe from wind erosion. Wherever the soil surface is loose and dry, vegetation is sparse or absent, and the wind sufficiently strong, erosion will occur unless control measures are applied (1957 Yearbook of Agriculture). Soil erosion by wind in North America is generally most severe in the Great Plains. The NRCS annual report of wind erosion conditions in the Great Plains shows that wind erosion damages from 1 million to more than 15 million acres annually, averaging more than 4 million acres per year in the 10-state area. USDA estimated that nearly 95 percent of the 6.5 million acres put out of production during the 1930’s suffered serious wind erosion damage (Woodruff 1975). Other major regions subject to damaging wind erosion are the Columbia River plains; some parts of the Southwest and the Colorado Basin, the muck and sandy areas of the Great Lakes region, and the sands of the Gulf, Pacific, and Atlantic seaboards. In some areas, the primary problem caused by wind erosionis crop damage. Some crops are tolerant enough to withstand or recover from erosion damage. Other crops, including many vegetables and specialty crops, are especially vulnerable to wind erosion damage. Wind erosion may cause significant short-term economic loss in areas where erosion rates are below the soil loss tolerance (T) when the crops grown in that area are easily damaged by blowing soil (table 502–4). 

# Part 502 Wind Erosion502–2 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



## 502.11 The wind erosion process The wind erosion process is complex. It involves detaching, transporting, sorting, abrading, avalanching, and depositing of soil particles. Turbulent winds blowing over erodiblesoils cause wind erosion. Field conditions conducive to erosion include • loose, dry, and finely granulated soil; • smooth soil surface that has little or no vegetation present; • sufficiently large area susceptible to erosion; and • sufficient wind velocity to move soil. Winds are considered erosive when they reach 13 miles per hour at 1 foot above the ground or about 18 miles per hour at a 30 foot height. This is commonly referred to as the threshold wind velocity (Lyles and Krauss 1971).The wind transports primary soil particles or stable aggregates, or both, in three ways (fig. 502–1): Saltation— Individual particles/aggregates ranging from 0.1 to 0.5 millimeter in diameter lift off the surface at a 50- to 90-degree angle and follow distinct trajectories under theinfluence of air resistance and gravity. The particles/aggregates return to the surface at impact angles of 6 to 14 degrees from the horizontal. Whether they rebound orembed themselves, they initiate movement of other particles/aggregates to create the avalanching effect. Saltating particles are the abrading bullets that remove the protective soil crusts and clods. Most saltation occurs within 12 inches above the soil surface and typically, the length of a saltating particle trajectory is about 10 times the height. From 50 to 80 percent of total transport is by saltation. Suspension

— The finer particles, less than 0.1 millimeter in diameter, are dislodged from an eroding area by saltation and remain in the air mass for an extended period. Some suspension-sized particles or aggregates are present in the soil, but many are created by abrasion of larger aggregates during erosion. From 20 percent to more than 60 percent of an eroding soil may be carried in suspension, depending onsoil texture. As a general rule, suspension increases downwind, and on long fields can easily exceed the amount of soil moved in saltation and creep. Surface creep —Sand-sized particles/aggregates are set in motion by the impact of saltating particles. Under high winds, the whole soil surface appears to be creeping slowly forward as particles are pushed and rolled by the saltation flow. Surface creep may account for 7 to 25 percent of total transport (Chepil 1945 and Lyles 1980). Saltation and creep particles are deposited in vegetated strips, ditches, or other areas sheltered from the wind, as long as these areas have the capacity to hold the sediment. Particles in suspension, however, may be carried a great distance. The rate of increase in soil flow along the wind directionvaries directly with erodibility of field surfaces. The increase in erosion downwind (avalanching ) is associated with the following processes: • the increased concentration of saltating particles downwind increases the frequency of impacts and the degree of breakdown of clods and crusts, and • accumulation of erodible particles and breakdown ofclods tends to produce a smoother (and more erodible) surface. The distance required for soil flow to reach a maximum for a given soil is the same for any erosive wind. The more erodible the surface, the shorter the distance in which maximum flow is reached. Any factor that influences the erodibility of the surface influences the increase in soil flow. Figure 502-1 The wind erosion process

Saltation Creep SuspensionNational Agronomy Manual Wind Erosion Part 502

502–3 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 502C Estimating wind erosion

502.20 How, why, and by whom wind erosion is estimated Using the Wind Erosion Equation (WEQ), NRCS estimates erosion rates to • provide technical assistance to land users, • inventory natural resources, and • evaluate the effectiveness of conservation programs and conservation treatment applied to the land. Wind erosion is difficult to measure. Wind moves across the land in a turbulent, erratic fashion. Soil may blow into, within, and out of a field in several directions in a single storm. The direction, velocity, duration, and variability of the wind all affect the erosion that occurs from a wind storm. Much of the soil eroding from a field bounces or creeps near the surface; however, some of the soil blown from a field may be high above the ground in a dust cloud by the time it reaches the edge of a field (Chepil 1963).


## 502.21 Methods of estimating wind erosion No precise method of measuring wind erosion has been developed. However, various dust collectors, remote and in-place sensors, wind tunnels, sediment samplers, and microtopographic surveys before and after erosion have been used. Each method has its limitations. Research iscontinuing on new techniques and new devices, on modifications to older ones, and on means to measure wind erosion. Estimates of wind erosion can be developed by assigning numerical values to the site conditions that govern wind erosion and expressing their relationships mathematically. This is the basis of the current Wind Erosion Equation (WEQ) that considers soil erodibility, ridge and random roughness, climate, unsheltered distance, and vegetative cover. 

## 502.22 The wind erosion equation The Wind Erosion Equation (WEQ) erosion model is designed to predict long-term average annual soil lossesfrom a field having specific characteristics. With appropriate selection of factor values, the equation will estimate average annual erosion or erosion for specific time periods. 

### Development of the wind erosion equation Drought and wind erosion during the l9th century caused wind erosion to be recognized as an important geologic phenomenon. By the late 1930’s, systematic and scientificresearch into wind erosion was being pioneered in California, South Dakota, Texas, and in Canada and England. This research produced information on the mechanics of soil transport by wind, the influence of cultural treatment on rates of movement, and the influence of windbreaks on windflow patterns. The publication, The Physics of Blown Sand and Desert Dunes , (Bagnold 1941), is considered a classic by wind erosion researchers. In 1947, USDA began the Wind Erosion Research Program at Manhattan, Kansas, in cooperation with Kansas State University. That program was started under the leadership of Austin W. Zingg, who was soon joined by W.S. Chepil, a pioneer in wind erosion research in Canada. The research project’s primary purposes were to study the mechanics of wind erosion, delineate major influences on that erosion, and devise and develop methods to control it. By 1954, Chepil and his coworkers began to publish results of their research in the form of wind erosion prediction equations (Chepil 1954; Chepil 1957; Chepil et al. 1955; Woodruff and Chepil 1956). In 1959, Chepil released an equation E = IRKFBWD where:

E = quantity of erosion I = soil cloddiness R = residue K = roughness F = soil abradability B = wind barrier W = width of field D = wind direction Wind velocity at geographic locations was not addressed in this equation (Chepil 1959).502–4 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### In 1962, Chepil’s group released the equation E ACKLV

= 

## ( )



# ∫

E IKCLV

= 

## ( )



# ∫ where:

A = percentage of soil fractions greater than 0.84 millimeter. Factors C, K, L, and V were the same as in the present equation although they were not handled the same (Chepil 1962). A C-factor map for the western half of the United States was also published in 1962 (Chepil et al. 1962). In 1963, the current form of the equation, E= ƒ(ICKLV) was first released (Chepil 1963). In 1965, the concept of preponderance in assessing wind erosion forces was introduced. See 502.34 for details onpreponderance (Skidmore 1965 and Skidmore and Woodruff 1968).In 1968, monthly climatic factors were published (Woodruff and Armbrust 1968). These are no longer used by NRCS. Instead, NRCS adopted a proposal for computing soil erosion by periods using wind energy distribution which was published in 1980 (Bondy et al. 1980). (See 502.24.) In 1981, the Wind Erosion Research Unit provided NRCS with data on the distribution of erosive wind energy for the United States and in 1982 provided updated annual C factors. (See exhibit 502-8.) Although the present equation has significant limitations (see 502.23), it is the best tool currently available for making reasonable estimates of wind erosion. Currently, research and development of improved procedures for estimating wind erosion are underway. The present Wind Erosion Equation is expressed as:

where:

E = estimated average annual soil loss in tons per acre per year ƒ = indicates relationships that are not straight-line mathematical calculations I = soil erodibility index K = soil surface roughness factor C = climatic factor L = the unsheltered distance V = the vegetative cover factor The I factor, expressed as the average annual soil loss in tons per acre per year from a field area, accounts for theinherent soil properties affecting erodibility. These properties include texture, organic matter, and calcium carbonate percentage. I is the potential annual wind erosion for a given soil under a given set of field conditions. The given set of field conditions for which I is referenced is that of an isolated, unsheltered, wide, bare, smooth, level, loose, andnon-crusted soil surface, and at a location where the climatic factor (C) is equal to 100. (For details on the I factor see 502.31). The K factor is a measure of the effect of ridges and cloddiness made by tillage and planting implements. It is expressed as a decimal from 0.1 to 1.0. (For details on the K factor see 502.32.) The C factor for any given locality characterizes climatic erosivity, specifically windspeed and surface soil moisture. This factor is expressed as a percentage of the C factor for Garden City, Kansas, which has a value of 100. (For details on the C factor see 502.33.) The L factor considers the unprotected distance along the prevailing erosive wind direction across the area to be evaluated and the preponderance of the prevailing erosive winds. (For details on the L factor see 502.34.) The V factor considers the kind, amount, and orientation of vegetation on the surface. The vegetative cover is expressed in pounds per acre of a flat small-grain residue equivalent. (For details on the V factor see 502.35.) Solving the equation involves five successive steps. Steps 1, 2 and 3 can be solved by multiplying the factor values. Determining the effects of L and V (steps 4 and 5) involves more complex functional relationships. Step 1: E I 1 

### = Factor I is established for the specific soil. I may be increased for knolls less than 500 feet long facing into the prevailing wind, or decreased to account for surface soil crusting, and irrigation. Step 2: E IK 2 

### = Factor K adjusts E 1 

### for tillage-induced oriented roughness, K rd 

### (ridges) and random roughness, K rr

### (cloddiness). The value of K is calculated by multiplying K rd 

### times K rr. 

### (K = K rd 

### x K rr 

### ).National Agronomy Manual Wind Erosion Part 502

502–5 (190-V-NAM, 3rd Ed., October 2002) 

### Step 3: E IKC 3 

### =

E IKCL

4 

### =

E IKCLV

5 

### = Factor C adjusts E 2 

### for the local climatic factor. Step 4: Factor L adjusts E 3 

### for unsheltered distance. Step 5: Factor V adjusts E 4 

### for vegetative cover.


## 502.23 Limitations of the equation When the unsheltered distance, L, is sufficiently long, the transport capacity of the wind for saltation and creep is reached. If the wind is moving all the soil it can carry across a given surface, the inflow into a downwind area of the field is equal to the outflow from that same area of the field, for saltation and creep. The net soil loss from thisspecific area of the field is then only the suspension component. This does not imply a reduced soil erosion problem because, theoretically, there is still the estimated amount of soil loss in creep, saltation, and suspension leaving the downwind edge of the field. Surface armoring by nonerodible gravel is not usually addressed in the I factor. The equation does not account for snow cover or seasonal changes in soil erodibility. The equation does not estimate erosion from single storm events.


## 502.24 Alternative procedures for using the WEQ The WEQ Critical Period Procedure is based on use of the Wind Erosion Equation as described by Woodruff and Siddoway in 1965 (Woodruff and Siddoway 1965). The conditions during the critical wind erosion period are used to derive the estimate of annual wind erosion. • The Critical Wind Erosion Period is described as the period of the year when the greatest amount of wind erosion can be expected to occur from a field under an identified management system. It is the period when vegetative cover, soil surface conditions, and expected erosive winds result in the greatest potential for wind erosion. • Erosion estimates developed using the critical period procedure are made using a single set of factor values (IKCL & V) in the equation to describe the critical wind erosion period conditions. • The critical period procedure is currently used for resource inventories. NRCS usually provides specific instructions on developing wind erosion estimates for resource inventories. The WEQ Management Period Procedure was published by Bondy, Lyles, and Hayes in 1980. It solves the equation for situations where site conditions have significant variation during the year or planning period where the soil is exposed to soil erosion for short periods, and where crop damage is the foremost conservation conern, rather than the extent of soil loss. The management period procedure is described as being more responsive to changing conditions throughout the cropping year but is not considered more accurate than the critical period procedure. Comparisons should not be made between the soil erosion predictions made by the management period procedure and the critical period procedure. In other words, where a conservation system has been determined to be acceptable by the management period procedure and placed in a conservation plan or the FOTG, then only the managementperiod procedure will be used to determine if other conservation sys tems, planned or applied, provide equivalent treatment. Factor values are selected to describe management periods when cover and management effects are approximately uniform. The cropping system is divided into as many management periods as is necessary to describe the year or planning period accurately

. Erosive wind energy (EWE) distribution is used to derive a weighted estimate of soil loss for the period. The general procedure is as follows: • Solve for E in the basic equation (E = ƒ(IKCLV)) using management period values for I, K, L, and V, and the local annual value for C. • Multiply the annual soil loss rate E obtained from management period values by the percentage of annual erosive wind energy that occurs during the management period to estimate average erosion for that management period. • Add the management period amounts for the crop year, or add the period amounts for a total crop sequence and divide by the number of years in the sequence to estimate average annual wind erosion

.502–6 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### Exhibit 502–7a is an example of tables showing the expected monthly distribution of erosive wind energy at specific locations. The complete table is available for downloading at http://www.weru.ksu.edu/nrcs/windparm.doc Exhibit 502–7b shows how these values are used in the management period method computations. Erosive windenergy values are entered on the form in the column identified % EWE

. Estimates for management periods less than 1 year induration are often useful in conservation planning. Examples include • When crop damage (crop tolerance) during sensitive growth stages is the major concern. • When a system or practice is evaluated for short-term effects. States will use critical period or the management period procedure, within published guidelines, for conservation planning. The management period procedure will not be used for resource inventories unless specifically stated in instructions. Refer to individual program manuals for morespecific instructions pertaining to the use of the Wind Erosion Equation. Adjustments to the WEQ soil erodibility factor, I , can be made for temporary conditions that include irrigation or crusts, but such adjustments are to be used only with themanagement period procedure. The use of monthly preponderance data to determine equivalent field width is also applicable only to the management period procedure.


## 502.25 Data to support the WEQARS has developed benchmark values for each of the factors in the WEQ. However, the NRCS is responsible for developing procedures and additional factor values for use of the equation. Field Office Technical Guides will include the local data needed to make wind erosion estimates. ARS has computed benchmark C factors for locations where adequate weather data are available (Lyles 1983). C factors used in the field office are to reflect local conditions as they relate to benchmark C factors. Knowledge of local terrain features and local climate is needed to determinehow point data can be extended and how interpolation between points should be done. See 502.33 for guidance. ARS has developed soil erodibility I values based on size distribution of soil aggregates. Soils have been grouped bytexture classes into wind erodibility groups. Wind erodibility group numbers are included in the soil survey data base in NASIS. For further discussion of benchmark data supporting factor values, refer to subpart 502D, WEQ factors.


## 502.26 Using WEQ estimates with USLE or RUSLE calculationsThe WEQ provides an estimate of average annual wind erosion from the field width along the prevailing wind erosion direction (L) entered in the calculation; USLE or RUSLE provide an estimate of average annual sheet and rill erosion from the slope length (L) entered into the model. Although both wind and water erosion estimates are in tons per acreper year, they are not additive unless the two equations represent identical flow paths across identical areas.


## 502.27 Tools for using the WEQ Graphs and tables for determining factor values are in Subpart 502G Exhibits. 

### E tables The ARS WEROS (Wind Erosion) computer program has produced tables that give estimated erosion (E values) formost of the possible combinations of I, K, C, L, and V. Exhibit 502–1 is an example. See 502.30 for procedures to download E tables. Use of the management period procedure can be simplified through the use of worksheets on which information for each management period is documented. Subpart 502F is toinclude sample wind erosion computations using the Management Period Procedure. An acceptable WEQ calculator has been developed in Microsoft Excel, and is being adapted for use in many states. A copy of this spreadsheet can be obtained from theNRCS state agronomist in Albuquerque, New Mexico. Exhibit 502.7B shows an example of this spread sheet.
Trade names mentioned are for specific information and do notconstitute a guarantee or warranty of the product by the Department of Agriculture or an endorsement by the Department over other products not mentioned.National Agronomy Manual Wind Erosion Part 502

502–7 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 502D WEQ Factors

502.30 The wind erosion estimate, EThe wind erosion estimate, E, is the estimate of average annual tons of soil per acre that the wind will erode from an area represented by an unsheltered distance L and for the soil, climate, and site conditions represented by I, K, C, andV. The equation is an empirical formula. It was initially developed by relating wind tunnel data to observed field erosion for 3 years in the mid 1950’s (Woodruff et al. 1976). The field data was normalized to reflect long-term average annual erosion assuming given conditions during the critical period without reference to change in those conditionsthrough the year. The estimate arrived at by using the critical period procedure for estimating wind erosion does not track specific changes brought about by management and crop development; nor does it assume that critical periodconditions exist all year. The calibration procedure accounted for minor changes expected to occur during a normal crop year at that time in history. The WEQ annual E is based on an annual C and field conditions during the critical wind erosion period of the year. This procedure does not account for all the effects of management.The management period procedure for estimating wind erosion involves assigning factor values to represent field conditions expected to occur during specified time periods. Using annual wind energy distribution data, erosion can be estimated for each period of time being evaluated. The periodestimates are summed to arrive at an annual estimate. Cropping sequences involving more than 1 year can be evaluated using this procedure. It also allows for a more thorough analysis of a management system and how management techniques affect the erosion estimate. The new E tables can be downloaded from the WERU server, Manhattan, Kansas. These tables can be accessed in two ways: • Through your WWW browser. To view, direct your web browser to: http://www.weru.ksu.edu/nrcs Download the Adobe Acrobat Reader (if not already installed on your computer) by clicking on the icon and installing per the installation instructions. (Trade names mentioned are for specific information and do not constitute a guarantee or warranty of the product by the Department of Agriculture or an endorsement by the Department over other products not mentioned.) When the Adobe Acrobat Reader is running on your browser you can click the PDF icon to view and print the table. When on the WERU Web page, copies of the files can be downloaded by clicking on the hypertext for the following: etab.pdf for PDF or etab.wpd (for WordPerfect) or etab.ps for Postscript • Through FTP—For those without a web browser but have FTP access, FTP to: ftp.weru.ksu.edu go to the appropriate directory, for example cd pub/nrcs/etables Be sure that you are in binary mode. To download the table format of your choice, type: get etab.pdf for PDF or get etab.wpd for WordPerfect or get etab.ps for Postscript The appropriate E table will download to your computer. Exhibit 502-1 shows an example of an E table.


## 502.31 Soil erodibility index, I
I is the erodibility factor for the soil on the site. It is expressed as the average annual soil loss in tons per acre that would occur from wind erosion, when the site is:

– Isolated – incoming saltation is absent

– Level – knolls are absent

– Smooth – ridge roughness effects are absent and cloddiness is minimal

– Unsheltered – barriers are absent. – At a location where the C factor is 100

– Bare – vegetative cover is absent

– Wide – the distance at which the flow of eroding soil reaches its maximum and does not increase with field size

– Loose – and non-crusted, aggregates not bound together, and surface not sealed.
The I factor is related to the percentage of nonerodible surface soil aggregates larger than 0.84 millimeters in diameter. For most NRCS uses, the I value is assigned for named soils based on wind erodibility groups (WEG). The WEG is included in the soil survey data base in NASIS. If the soil name is not known, exhibit 502–2 can be used to determine the WEG from the surface soil texture.502–8 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### To determine erodibility for field conditions during various management periods throughout the year, follow the sieving instructions in exhibit 502–3. (Do not use this procedure to determine average annual I values.) A soil erodibility index based solely on the percentage of aggregates larger than 0.84 millimeters has several potential sources of error. Some of these follow: • Relative erodibility of widely different soils may change with a change in wind velocity over the surface of the soil. • Calibration of the equation is based on the volume of soil removed, but the erodibility index is based on weight. • Differences in size of aggregates have considerable influence on erodibility but no distinction for this influence is made in table 1, exhibit 502–3. • Stability of surface aggregates influences erodibility; large durable aggregates can become a surface armor ; less stable aggregates can be abraded into smaller, more erodible particles. • Surface crusting may greatly reduce erodibility;erodibility may increase again as the crust deteriorates (Chepil 1958). Knoll erodibility— Knolls are topographic features characterized by short, abrupt windward slopes. Wind erosion potential is greater on knoll slopes than on level or gently rolling terrain because wind flowlines are compressed and wind velocity increases near the crest of the knolls. Erosion that begins on knolls often affects field areas downwind. Adjustments of the Soil Erodibility Index ( I ) are used where windward-facing slopes are less than 500 feet long and the increase in slope gradient from the adjacent landscape is 3 percent or greater. Both slope length and slope gradient change are determined along the direction of the prevailing erosive wind (fig. 502–2). Table 502-1 contains knoll erodibility adjustment factors for the Soil Erodibility Index I . The I value for the Wind Erodibility Group is multiplied by the factor shown in column A. This adjustment expresses the average increase in erodibility along the knoll slope. For comparison, column B shows the increased erodibility near the crest (about the upper 1/3 of the slope), where the effect is most severe. No adjustment of I for knoll erodibility is made on level fields, or on rolling terrain where slopes are longer and slope changes are less abrupt. Where these situations occur, the wind flow pattern tends to conform to the surface and does not exhibit the flow constriction typical of knolls. Surface crusting —Erodibility of surface soil varies with changing tillage practices and environmental conditions (Chepil 1958). A surface crust forms when a bare soil is wetted and dried. Although the crust may be so weak that it has virtually no influence on the size distribution of dry aggregates determined by sieving, it can make the soil less erodible. The resistance of the crust to erosion depends on the nature of the soil, intensity of rainfall, and the kind and amount of cover on the soil surface. A fully crusted soil may erode only one-sixth as much as non-crusted soil. However, a smooth crusted soil with loose sand grains on the surface is more erodible than the same field with a cloddy or ridged surface.

Table 502–1 Knoll erodibility adjustment factor for I

Percent slope change in A B prevailing wind Knoll Increase at erosion adjustment crest area direction of I where erosion is most severe 

### 3 1.3 1.5 4 1.6 1.9 5 1.9 2.5 6 2.3 3.2 8 3.0 4.8 10 and greater 3.6 6.8 Table 502-2 I adjustment guidelines for crusts

WEG I Max. adj. Calculated Rounded mgt prd. I I factor 1/ 

### 1 310 .7 217 220 1 250 .7 175 180 1 220 .7 154 160 1 180 .7 126 134 1 160 .7 112 134 2 134 .7 67 86 3 86 .4 34 38 4 86 .4 34 38 4L 86 .4 34 38 5 56 .3 17 21 6 48 .3 14 21 7 38 .3 11 12 1/ The management period adjustment to I has not been validated by research and is based on NRCS judgment.National Agronomy Manual Wind Erosion Part 502

502–9 (190-V-NAM, 3rd Ed., October 2002) 

### Under erosive conditions, the surface crust and surface clods on fine sands and loamy fine sands tend to break down readily. On silt loams and silty clay loams the surface crust and surface clods may be preserved, and the relative erosion may be as little as one-sixth of I . Other soils react somewhere between these two extremes (Chepil 1959). Because of the temporary nature of crusts, no adjustment for crusting is made for annual estimates based on the critical wind erosion period method (Woodruff and Siddoway 1973). However, crust characteristics may be estimated and adjustment to I may be made for management period estimates when no traffic, tillage, or other breaking of crusts is anticipated. Such adjustments may be up to, but may not exceed the percentages shown in table 502–2. Irrigation adjustments —The I values for irrigated soils, as shown in exhibit 502–2, are applicable throughout the year. I adjustments for irrigation are applicable only where assigned I values are 180 or less. Adjustments based on dry sieving —Temporal changes in the surface fraction > 0.84 millimeter may be measured by dry sieving. These measurements may be used to establish a basis for adjusting I for conservation planning when sieving has been performed for each management period and for 3 years or more. The adjustment to I applies only to the respective time periods when the soil surface is influenced by changes in the nonerodible fraction. Therefore, theadjustment is used only with the management period procedure of estimating wind erosion. The procedure does expand the applicability of the equation to a management effect not previously addressed. When the I factor is adjusted based on the results of sieving, no additional adjustment to I will be made for irrigated fields. Adjustments to I , based on sieving, should not be used without adequate supporting data. These adjustments reflect specific soil and management conditions and are only applicable in the area(s) from which samples were obtained and in areas that have similar soil and management conditions. Use of adjusted soil erodibility I factor, arrived at by using standard rotary sieving procedures, is warranted provided it represents soil surface conditions during the appropriate management period. Adjustments may be made up to, but should not exceed, limits assigned for crusting in table 502-2. The I factor adjustment may be used where applicable in determining whether an adequate conservation system is being followed. However, I factor adjustments are not to be used in the erodibility index (CI/T) when determining highly erodible land because this index is the potential erodibility and not an estimate of actual erosion. Current instructions for the National Resources Inventory (NRI) are to be followed. These instructions do not allow for any adjustment of the I factor. This ensure s uniformity between States and allows for trend analysis. Studies to adjust I should be made systematically and include all related soil in a given area. Multiple-year soilsieving data is required before adjustments are to be considered. The National Soil Survey Center must review and concur in any proposal to adjust I and arrange for laboratory assistance. Adjustments to I must also be approved by the National Soil Survey Center and correlated across state and regional boundaries before implementation. Any adjustment to I must be within the framework of the existing E tables. Surface stability —A significant limitation of the I factor is that it does not account for changes in the soil surface over time that are caused by the dynamics of wind erosion. The erodibility of a bare soil surface is based on the interaction of the following:• Soils that have both erodible and nonerodible particles on the surface tend to stabilize if there is no incoming saltation. As the wind direction changes, the surface is disturbed, or the wind velocity increases, erosion may begin again.• Saltation destroys crusts, clods, and ridges by abrasion. Figure 502–2 Graphic of knoll erodibility

Knoll erodibility adjustment applies here

Slope change 3 percent Windward slope 500 feet Greatest erodibility occurs here Compressed air flow Deposition occurs here Prevailing wind erosion direction502–10 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### • Fields tend to become more erodible as finer soil particles, which provide bonding for aggregation, are carried off in suspension. • If the surface soil contains a high percentage of gravel or other nonerodible particles that are resistant toabrasion, the surface will become increasingly armored as the erodible particles are carried away. Desert pavement is the classic example of surface armoring. A surface with only nonerodible aggregates exposed to the wind will not erode further except as the aggregates are abraded. • A surface may be virtually nonerodible and yet allowsaltation and creep to cross unabated. A paved highway is an example. Other surfaces may be relatively stable and trap some, or all, of zthe incoming soil flow. Examples of this type of stability usually relate to some roughness, sheltering, or vegetative cover. A ridged field may trap a significant portion of the incoming soil flow until the furrows are filled and the surface loses its trapping capability. A vegetated barrier will provide a sheltered area downwind until the barrier is filled with sediment. 

## 502.32 Soil roughness factor K, ridge and random roughness
K rd 

### is a measure of the effect of ridges made by tillage and planting implements. Ridges absorb and deflect wind energy and trap moving soil particles (fig. 502–3). The K r 

### value is based on a standard ridge height to ridgespacing ratio of 1:4. Because of the difficulty of determining surface roughness by measuring surface obstructions, a standard roughness calibration using nonerodible gravel ridges in a wind tunnel was developed. This calibration led to the development of curves (fig. 502–4 and exhibit 502–

Figure 502–3 Detachment, transport, and deposition on ridges and furrows

Zone of removal
Zone of accumulation Area of forward

movement Area of backward

and downward

movement



### K h h s r 

### = × 

### ( ) 4 Figure 502–4 Chart to determine soil ridge roughness factor, K rd, from ridge roughness, K r , (inches). Only this chart, representing an angle of deviation of 0°, will be used for the WEQ critical period procedure . When using the management period procedure , see exhibit 502–4 for graphs representing additional angles of deviation. Note: This graph represents erosive wind energy 60% parallel and 40% perpendicular to the prevailing erosive wind. —Hagen 1996



### where: h = ridge height in inches s = ridge spacing in inches 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20
0.10 0.00 0 2 4 6 81 0 1 2Soil ridge roughness factor, Krd

Soil ridge roughness K r (inches) Kr=4 ( hxh ) /s h=rid g

e hei g ht in inches s=rid g

e s p acin g in inches I=310 I=250 I=220 I=180 I=134 I<134National Agronomy Manual Wind Erosion Part 502

502–11 (190-V-NAM, 3rd Ed., October 2002) 

### 4) that relate ridge roughness, K r 

### , to a soil ridge roughness factor, K r d 

### , (Skidmore 1965; Skidmore and Woodruff 1968; Woodruff and Siddoway 1965; and Hagen 1996). The K r 

### curves are the basis for charts and tables used to determine K rd 

### factor values in the field (exhibits 502–4 and 502–5). The effect of ridges varies as the wind direction and erodibility of the soil change. To take into account the change in wind directions across a field, we consider the angle of deviation. The angle of deviation is the angle between the prevailing wind erosion direction and a line perpendicular to the row direction. The angle of deviation is 0 (zero) degrees when the wind is perpendicular to the row and is 90 degrees when the wind is parallel to the row. Following is an example of how the angle of deviation affects K rd 

### values: when evaluating a soil with an assigned I value of <134, and the prevailing erosive wind direction is perpendicular to ridges 4 inches high and 30 inches apart, then K rd 

### is 0.5. But when the prevailing erosive wind direction is parallel to those ridges, the K rd 

### value is 0.7. Random roughness, particularly in the furrows, significantly reduces wind erosion occurring from erosive winds blowing parallel to the ridges. In 1996, ARS scientists provided a method for adjusting the WEQ K rd 

### factor with consideration for preponderance (erosive wind energy 60% parallel and 40% perpendicularto prevailing erosive wind direction) when using the Management Period Procedure. The use of preponderence recognizes that during the periods when the prevailing erosive winds are parallel to ridges, there are other erosive winds during the same period which are not parallel, thusmaking ridges effective during part of each period. Preponderance keeps the K factor value less than 1.0, when the I factor values are 134 or less. When estimating wind erosion rates by management periods, without the aid of a computer model, the prevailing wind erosion direction and a default preponderance are used for each period. This procedure more adequately addresses the effects of the ridges in wind erosion control since erosive wind directions may vary within each management period. Note: When using the WEQ Excel spreadsheet model, the actual preponderance, up to and including a value of 4, for the period will be used, rather than a default value. The WEQ K rr 

### factor accounts for random roughness. Random roughness is the nonoriented surface roughnessthat is sometimes referred to as cloddiness. Random roughness is usually created by the action of tillage implements. It is described as the standard deviation (in inches) of the soil surface elevations, measured at regular intervals from a fixed, arbitrary plane above a tilled soil surface, after oriented (ridge) roughness has been accounted for. Random roughness can reduce erosion significantly. Note: The random roughness factor will only be used with the WEQ management period procedure. Random roughness values have been developed for various levels of WEQ I factor values and surface random roughness (exhibit 502–6). Random roughness curves only adjust the K factors of a soil that has an I factor value of 134 and less. The random roughness values used in the WEQ are the same random roughness values used in RUSLE. Random roughness (inches) from the machine operations data base in RUSLE can b e used to determine WEQ random roughness values (table 502–7). However, keep in mind that these RUSLE random roughness values were determined for medium textured soils tilled at optimum moisture conditions for creating random roughness. Under most circumstances random roughness is determined by comparing a field surface to the random roughness (standard deviation) photos in the RUSLE handbook (Agriculture Handbook 703, appendix C).

The photos in Agriculture Handbook 703, appendix C, may be downloaded from: http://www.nrcs.usda.gov/technical/ECS/agronomy/ roughness.html State agronomists should download, reproduce, and distribute the photographs to field offices. When both random roughness and ridge roughness are present in the field, they are complimentary. When both are present, the K rd 

### factor for ridges and K rr 

### factor for random roughness will be multiplied together to obtain the total roughness K-factor. Example problem: Take into consideration just one WEQ management period. The soil in the field being evaluated has an I value of 86. The field has just been fertilized with anhydrous ammonia using a knife applicator. Considering the height and spacing of the oriented roughness, the ridge roughness K rd 

### factor was determined to be 0.8. Usingtable 502–7, under random roughness (inches), the anhydrous applicator has a core value of 0.6. Going into the random roughness (inches) graph (exhibit 502–6), on the hori-502–12 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### zontal axis to 0.6, and then vertically to the line representing an I factor of 86, the K rr 

### factor is rounded to 0.8. The total roughness value (K factor) is 0.8 x 0.8 = 0.64, then rounded to 0.6. The major effects of random roughness on wind erosion are to raise the threshold wind speed at which erosion begins and to provide some sheltered area among the clods where moving soil can be trapped. Hence, when the effectiveness of random roughness increases the total K-value decreases. Random roughness, particularly in the furrows, significantly reduces wind erosion occurring from erosive winds blowing parallel to the ridges. Random roughness is subject to much faster degradation by rain or wind erosion than large tillage ridges. Therefore theWEQ management period, where random roughness is effective, may be of short duration. For fields being broken out of sod, such as CRP, random roughness will be credited for erosion control. The field surface is usually covered with the crowns of plants, theirassociated roots, and adhering soil. The total random roughness of the field should be compared to the photos in the RUSLE handbook and credited appropriately. Surface roughening (emergency tillage) —In some situations, there is a need to control erosion on bare fields where the surface crust has been destroyed or where loose grains are on the surface and can abrade an existing crust. Onemethod to reduce the erosion hazard on such fields is emergency or planned tillage to roughen the surface or increase nonerodible clods on the surface (random roughness). This may be accomplished by one or more of the following: • Soil that characteristically forms a crust with loose sand grains on the surface may be worked to create clods. The loose grains fall into the crevices between clods. This is the principle of sand fighting used in some emergency tillage. • The soil may be deep tilled to bring up finer textured soil material that will form more persistent clods. • Irrigation increases the nonerodible fraction of a soil (exhibit 502–2). • The surface may be worked into a ridge-furrow configuration that will trap loose, moving soil. • The soil may be tilled in strips or in widely spaced rows to provide some degree of ridge and random roughness to break the flow of saltation and creep. 

## 502.33 Climatic factor, C The C factor is an index of climatic erosivity, specifically windspeed and surface soil moisture. The factor for anygiven location is based on long-term climatic data and is expressed as a percentage of the C factor for Garden City, Kansas, which has been assigned a value of 100 (Lyles 1983). In an area with a C factor of 50, for example, the IKC value would be only half of the IKC for Garden City, Kansas. The climatic factor equation is expressed as:
C v PE = × 

### ( )

34 48 3
2 

### . where: C = annual climatic factor V = average annual wind velocity PE = precipitation-effectiveness index of Thornthwaite 34.48 = constant used to adjust local values to a common base (Garden City, Kansas) The basis for the windspeed term of the climatic factor is that the rate of soil movement is proportional to windspeed cubed. Several researchers have reported that when windspeed exceeds threshold velocity, the soil movement is directly proportional to friction velocity cubed which, in turn, is related to mean windspeed cubed (Skidmore 1976). The basis for the soil moisture term of the climatic factor is that the rate of soil movement varies inversely with the equivalent surface soil moisture. Effective surface soil moisture is assumed to be proportional to the Thornthwaite precipitation-effective- ness index (PE) (Thornthwaite 1931). The annual PE index is the sum of the 12 monthlyprecipitation effectiveness indices. The formula is expressed as follows:


### PE P T = ×

− 

# ( )       

# ∑ 12 10 9 

### 115 10
where: PE = the annual precipitation effectiveness index P = average monthly precipitation T = average monthly temperature The C factor isoline map developed by NRCS in 1987 can accessed at: http://data4.ftw.nrcs.usda.gov/website/c-valuesNational Agronomy Manual Wind Erosion Part 502

502–13 (190-V-NAM, 3rd Ed., October 2002)

### Complete instructions for viewing the map are given in exhibit 502-8. The map displays C factors for all areas of the conterminous United States and Alaska. The isolines were drafted to conform with local C factors calculated from 1951–80 weather data and were correlated across state andregional boundaries. Procedures for developing local C factors are explained in exhibit 502–9. 1. Interpolation of WEQ climatic factors (C)— States may interpolate between county assigned C values to the nearest 5 units based on the National C Factor Isoline Map or the state C Factor Isoline Map in theField Office Technical Guide (FOTG). When interpolating between values, knowledge of the local climatic and topographic conditions is extremely useful since climatic conditions can vary disproportionately between C factor value isolines. 2. Where WEQ soil loss (E) tables have been developed with C factor increments greater than 5 units, a straight line interpolation to the nearest C factor value of 5 may be made from existing E tables. Straight line interpolations can also be made from the soil losses(E) calculated with approved WEQ computer software, when C factors programmed into the model are in increments greater than 5 units.3. C factor interpolations are for the purpose of conservation planning only and are NOT to be used in determining or adjusting previous highly erodible land (HEL) designations. However, they may be used during status reviews to determine if an individual is actively applying a conservation system. Previous national policy, regarding the changing of prior HEL designations, remains in effect. Effects of irrigation water on the C factor—When irrigation water is applied to a dry soil surface, a reduction in wind erosion can be expected. A specific procedure to directly adjust the climatic factor C for irrigation is not available. However, a procedure has been developed by researchers to adjust the Erosive Wind Energy (EWE) by the fraction of time during which the soil is considered wet and nonerodible because of irrigation. See 502.31 and exhibit 502–2. The procedures that follow adjust the Erosive Wind Energy (EWE) value which planners are to use when estimating wind erosion on irrigated fields. This adjustment is for the WEQ Management Period Procedure. States where wind erosion is a concern should replace previous methods usedto adjust for the effects of irrigation and utilize this procedure and the procedure for adjusting the I factor, for allplan revisions or new planning activities. This new procedure, however, does not impact designated highly erodible lands (HEL) or new determinations since management practices are not considered in the HEL formula. Note: Irrigation adjustments to EWE and to the I factor, apply to fully irrigated fields and to fields that receive supplemental irrigation water. • Research scientists have developed an Irrigation Factor (IF) that adjusts the EWE or period erosion loss to account for the effect of irrigation wetting the soil surface and making it less erodible. The IF takes into account the number of days in a managementperiod, number of irrigation events during a management period, and a Texture Wetness Factor (TWF). • To account for the nonerodible wet condition of various soil textures after irrigation, a TWF of 1, 2, or 3 is assigned to coarse, medium, and fine texturedsoil, respectively. See exhibit 502.2 for values assigned to the various soil groups. • The IF is calculated with the following equation: IF = number of days in period minus (–) nonerodible wet days in period (NEWD), divided by the number of days in period. Nonerodible Wet Days (NEWD) are equal to the Texture Wetness Factor (TWF) times the number of irrigation events in the period. • When using the WEQ to account for the effects of irrigation, multiply the EWE for the period by the IF. • Example: A fine textured soil was irrigated three times during 45 days. Twelve percent of the annual EWE occurs during this period. Therefore: TWF = 3 for fine textured soil Number of irrigations during the period = 3 NEWD = (3)(3) = 9 IF = (45 days – 9)/45 = 0.80 The adjusted EWE for 45 days is then determined by multiplying IF times the percentage of annual erosion wind energy during the period being evaluated. Adjusted EWE = (.80)(12%) = 9.6 % Note: The EWE shall not be adjusted for any management period where irrigation does not occur. • The WEQ factors (C & I) used to determine the Erodibility Index (EI), will not be adjusted when determining highly erodible land (HEL) on cropland that is irrigated.502–14 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



## 502.34 Unsheltered distance, L The L factor represents the unsheltered distance along the prevailing wind erosion direction for the field or area to be evaluated. Its place in the equation is to relate the isolated, unsheltered, and wide field condition of I to the size and shape of the field for which the erosion estimate is beingprepared. Because V is considered after L in the 5-step solution of the equation (502.22), the unsheltered distance isalways considered as if the field were bare except for vegetative barriers. 1. L begins at a point upwind where no saltation or surface creep occurs and ends at the downwind edge of the area being evaluated (figure 502–5). The pointmay be at a field border or stable area where vegetation is sufficient to eliminate the erosion process. An area should be considered stable only if it is able to trap or hold virtually all expected saltation and surface creep from upwind. If vegetative barriers, grassed waterways, or other stable areas divide an agricultural field being evaluated, each subdivision will be isolated and shall be evaluated as a separate

Figure 502–5 Unsheltered distance L

Stable area

L Prevailing wind erosion direction

Isolated field

L begins at stable boundary

Stable area Incoming saltation Prevailing wind direction L

Field not isolated 

### field . Refer to the appropriate NRCS Conservation Practice Standards to determine when practices are of adequate width, height, spacing, and density to create a stable area. 2. When erosion estimates are being calculated for cropland or other relatively unstable conditions, upwind pasture or rangeland should be considered a stable border. However, if the estimate is being made for a pasture or range area, L should be determined by measuring from the nearest stable point upwind of the area or field in question (figure 502–6). The only case where L is equal to zero is where the area is fully sheltered by a barrier. 3. When a barrier is present on the upwind side of a field, measure L across the field along the prevailing wind erosion direction and subtract the distance sheltered by the barrier. Use 10 times the barrier height for the sheltered distance (figure 502–7).

Figure 502–6 Unsheltered distance L, perennial vegetation (pasture or range)

L Adjacent area stable

Unsheltered distance “L” perennial vegetation (pasture or range) Prevailing win

d erosion direc
tio n

Figure 502-7 Unsheltered distaqnce L – windbreak or barrier

L Windbreak

Sheltered area L = 0 10 H Prevailing wind erosion directionNational Agronomy Manual Wind Erosion Part 502

502–15 (190-V-NAM, 3rd Ed., October 2002) 

### 4. When a properly designed wind stripcropping system is applied, alternate strips are protected during critical wind erosion period s by a growing crop or by crop residue. These strips are considered stable. L is measured across each erosion-susceptible strip, along the prevailing wind erosion direction (figure 502–8). The prevailing wind erosion direction is the direction from which the greatest amount of erosion occurs during thecritical wind erosion period. The direction is usually expressed as one of the 16 compass points. When predictingerosion by management periods, the prevailing wind erosion direction may be different for each period (exhibit 502–7a). Preponderance is a ratio between wind erosion forces parallel and perpendicular to the prevailing wind erosion direction. Wind forces parallel to the prevailing wind erosion direction include those coming from the exact opposite direction (180°). A preponderance of 1.0 indicates that as much wind erosion force is exerted perpendicular to the prevailing direction as along that direction. A higher preponderance indicates that more of the force is along theprevailing wind erosion direction. Wind patterns are complex; low preponderance indicates high complexity and as a result, less wind will be from the prevailing erosive wind direction than locations that have a high preponderance. L can be measured directly on a map or calculated using a wind erosion direction factor: • For uses of the Wind Erosion Equation involving a single annual calculation, L should be the measured distance across the area in the prevailing wind erosion direction from the stable upwind edge of the field to the downwind edge of the field. When the prevailing wind erosion direction is at an angle that is not perpendicular to the long side of the field, L can be determined by multiplying the width of the field by the appropriate conversion factor obtained from table 502-3. • For management period calculations, wind erosion direction factors based on preponderance are to be used instead of a measured distance to determine L except – Where irregular fields cannot be adequately represented by a circle, square, or rectangle. – Where preponderance data are not available. Steps to determine L for management period estimates: 1. Obtain local values for prevailing the wind erosion direction and preponderance (exhibit 502–7a). 2. Measure actual length and width of the field and determine the ratio of length to width. 3. Determine angle of deviation between prevailing wind erosion direction and an imaginary line perpendicular to the long side of the field. Using data from steps 1 through 3, determine the wind erosion direction factor from wind erosion direction factor tables, tables 502–81a-e. These are adjustment factors thataccount for prevailing wind erosion direction, preponderance of wind erosion forces, and size and shape of the field. Multiply the width of the field by the wind erosion direction factor. This is the L for the field. If a barrier is on the upwind side of the field, reduce L by a distance equal to 10 times the height of the barrier. For circular fields, L = 0.915 times the diameter, regardless of the prevailing wind erosion direction or preponderance.

Figure 502–8 Unsheltered distance L, stripcropping system Table 502-3 Wind erosion direction factors 1/

Angle of deviation 2/ Adjustment factor 

### 0 1.00 22.5 o 

### 1.08 45 o 

### 1.41 67.5 o 

### 2.61 90 o 

### L = Length of field 1/ These adjustment factors are applicable when preponderance is not considered. L cannot exceed the longest possible measured distance across the field. 2/ Angle of deviation of the prevailing erosive wind from a direction perpendicular to the long side of the field. Protected strip (stable)

Planning area (field) L Prevailing wind erosion direction Stable area502–16 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



## 502.35 Vegetative cover factor, VThe effect of vegetative cover in the Wind Erosion Equation is expressed by relating the kind, amount, and orientation of vegetative material to its equivalent in pounds per acre of small grain residue in reference condition Small Grain Equivalent (SGe). This condition is defined as 10 inch long stalks of small grain, parallel to the wind, lying flat in rows spaced 10 inches apart, perpendicular to the wind. Several crops have been tested in the wind tunnel todetermine their SGe. For other crops, small grain equivalency has been computed using various regression techniques (Armbrust and Lyles 1985; Lyles and Allison 1980; Lyles 1981; Woodruff et al. 1974; Woodruff and Siddoway 1965). NRCS personnel have estimated SGe curves for other crops. SGe curves are in exhibit 502–10. Position and anchoring of residue is important. In general, the finer and more upright the residue, the more effective it is for reducing wind erosion. Knowledge of these and other relationships can be used with benchmark values to estimate additional SGe values. Research is underway to develop a method of estimating the relative erosion control value of short woody plants and other growing crops. Several methods are used to estimate the kind, amount, and orientation of vegetation in the field. Often the task is to predict what will be in the field in some future season orseasons. Amounts of vegetation may be predicted from production records or estimates and these amounts are then reduced by the expected or planned tillage. It may be desirable to sample and measure existing residue to determinequantity of residue. Local data should be developed to estimate surface residue per unit of crop yield and crop residue losses caused by tillage. The crown of a plant, its associated roots, and adhering soil should also be credited when doing transects to determineresidue cover. Employees will need to use their best judgment when deciding which crop curve to use when converting from percent ground cover to mass and then selecting a curve to convert the residue mass to SGe. If you encounter a crop, residue, or a type of vegetation for which an SGe curve has not been developed. exhibits 502– 11 and 502–12 give procedures to develop an interim SGecurve. Any SGe curve developed in this way must be submitted to the National Agronomists or the Cooperating Scientist for wind erosion for approval.National Agronomy Manual Wind Erosion Part 502

502–17 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 502E Principles of wind erosion control

502.40 General Five principles of wind erosion control have been identified (Lyles and Swanson 1976; Woodruff et al. 1972; and Woodruff and Siddoway 1965). These are as follows: • Establish and maintain adequate vegetation or other land cover. • Reduce unsheltered distance along wind erosion direction. • Produce and maintain stable clods or aggregates on the land surface.• Roughen the land with ridge and/or random roughness. • Reshape the land to reduce erosion on knolls where converging windflow causes increased velocity and shear stress. The cardinal rule of wind erosion control is to strive to keep the land covered with vegetation or crop residue at all times (Chepil 1956). This leads to several principles that should be paramount as alternative controls are considered: • Return all land unsuited to cultivation to permanent cover. • Maintain maximum possible cover on the surface during wind erosion periods. • Maintain stable field borders or boundaries at all times.


## 502.41 Relation of control to WEQ factors The Wind Erosion Equation (WEQ) was developed to relate specific field conditions to estimated annual soil loss. Of the five factors, two ( I and C) are often considered to be fixed while the other three (K, L, and V) are generally considered variable or management factors. This is not precisely true.
The I factor is related to the percentage of dry surface soil fractions greater than 0.84 millimeters. Its derivation is usually based on the Wind Erodibility Group. However, if a special management condition is going to be maintained, such as crusts or irrigation, a modification of I is appropriate. Also, I is increased by a knoll erodibility factor where appropriate. See 502.31. This adjustment is not appropriate if the knoll condition is modified through landforming or use of barriers to protect the knoll. Knoll erodibility adjustments to I relate to wind direction; low preponderance indicates that knoll erodibility will vary widely as wind direction changes. Total K reflects the tilled ridge roughness and random roughness in a field. This is a management factor. Stability of tilled roughness is related, however, to soil erodibility, climate, and the other erosion factors. Ridge roughness relates to ridge spacing in the wind erosion direction. Even with optimum orientation of rows, some ofthe winds will be blowing parallel to the rows when preponderance is low. Random roughness relates to the nonoriented surface roughness that is often referred to as cloddiness. Randomroughness is described as the standard deviation of elevation from a plane across a tilled area after taking into account oriented (ridge) roughness.The C factor is based on long-term weather records. Conservation treatment should be planned to address the critical climatic conditions when high seasonal erosive wind energy is coupled with highly erodible field conditions. The unsheltered distance L is a management factor that can be changed by altering field arrangement, stripcropping, or establishing windbreaks or other barriers. L is a function of field layout as it relates to prevailing wind direction and preponderance of erosive winds in the prevailing direction. When preponderance values are high (more than 2.5 andapproaching 4.0), conservation treatment should be concentrated on addressing potential erosion from the prevailing wind erosion direction. When preponderance values are low (approaching 1.0), knowledge of local seasonal wind patterns becomes more important in planning treatment. Conservation treatment should be planned to allow for the effect of seasonal changes in the prevailing wind erosion direction.502–18 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### A stable strip across an agricultural field divides the area into separate fields. Examples of stable areas include grass waterways, hedges and their sheltered area, brushy draws or ravines, roadways with grass borders, grass strips, and drainage or irrigation ditches. To be considered stable, an area must be able to stop and hold virtually all of the expected saltation and surface creep. Be aware that an area may be stable during one crop stage, but not stable in other seasons. V is the equivalent vegetative cover maintained on the soil surface. It is directly related to the management functions of crop establishment , tillage, harvesting, grazing, mowing, or burning

.


## 502.42 Tolerances in wind erosion control In both planning and inventory activities, NRCS compares estimated erosion to soil loss tolerance (T). T is expressed as the average annual soil erosion rate (tons/acre/year) that can occur in a field with little or no long-term degradation of the soil resource, thus permitting crop productivity to be sustained for an indefinite period. Soil loss tolerances for a named soil are recorded in the soil survey data base in NASIS. The normal planning objective is to reduce soil loss by wind or water to T or lower. In situations where treatmentfor both wind and water erosion is needed, soil loss estimates using the WEQ and USLE or RUSLE are not added together to compare to T.Additional impacts of wind erosion that should be considered are potential offsite damages, such as air and water pollution and the deposition of soil particles. Crop tolerance to soil blowing may also be an important consideration in wind erosion control. Wind or blowing soil, or both, can have an adverse effect on growing crops. Most crops are more susceptible to abrasion or other wind damage at certain growth stages than at others. Damage can result from desiccation and twisting of plants by the wind. Crop tolerance can be defined as the maximum wind erosion that a growing crop can tolerate, from crop emergence to field stabilization, without an economic loss to crop stand, crop yield, or crop quality. 

### (a) Blowing soil effects on crops Some of the adverse effects of soil erosion and blowing soil on crops include: • Excessive wind erosion that removes planted seeds, tubers, or seedlings. • Exposure of plant root systems. • Sand blasting and plant abrasion resulting in – crop injury – crop mortality – lower crop yields – lower crop quality – wind damage to seedlings, vegetables, and orchard crops. • Burial of plants by drifting soil. 

### (b) Crop tolerance to blowing soil or wind Many common crops have been categorized based on their tolerance to blowing soil. These categories of some typical crops are listed in table 502-4. Crops may tolerate greater amounts of blowing soil than shown in table 502–4, but yield and quality will be adversely affected. 

### (c) The effects of wind erosion on water quality Some of the adverse effects of wind erosion on water quiality include: • Deposition of phosphorus (P) into surface water • Increased Biochemical Oxygen Demand (BOD) in surface water • Reduced stream conveyance capacity because of deposited sediment in streams and drainage canals Local water quality guidelines under Total Maximum Daily Loads (TDML) for nutrients may require that wind erosion losses be less than the soil loss tolerance (T) in order to achieve local phosphorus (P) or other pollutant reduction goals. For a phosphorus (P) intrapment estimation procedure, see the Core 4 manual, chapter 3C, Cross Wind Trap Strips.National Agronomy Manual Wind Erosion Part 502

502–19 (190-V-NAM, 3rd Ed., October 2002) 

# Subpart 502F Example problems (Each state should develop example problems, common to their state, and insert in this section.) See exhibit 502–7b.

Table 502-4 Crop tolerance to blowing soil

Tolerant Moderate tolerance Low tolerance Very low tolerance T 2 ton/ac 1 ton/ac 0 to 0.5 ton/ac 

### Barley Alfalfa (mature) Broccoli Alfalfa seedlings Buckwheat Corn Cabbage Asparagus Flax Onions (>30 days) Cotton Cantaloupe Grain Sorghum Orchard crops Cucumbers Carrots Millet Soybeans Garlic Celery Oats Sunflowers Green/snap beans Eggplant Rye Sweet corn Lima beans Flowers Wheat Peanuts Kiwi fruit Peas Lettuce Potatoes Muskmelons Sweet potatoes Onion seedlings (<30 days) Tobacco Peppers Spinach Squash Strawberries Sugar beets Table beets Tomatoes Watermelons502–20 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502502–21 (190-V-NAM, 3rd Ed., October 2002) 

# Exhibit 502–1 Example E table

“E” tables for each combination of C & I factors are on the www browser: http://www.weru.ksu.edu/nrcs. Click on the hypertext for: etable.doc (for MS Word) and etable.wpd (for Word Perfect). (E)* SOIL LOSS FROM WIND EROSION IN TONS PER ACRE PER YEAR JANUARY, 1998 C = 100 SURFACE - K =1.00 I = 86 (L) (V)** - FLAT SMALL GRAIN RESIDUE IN POUNDS PER ACRE UNSHELTERED DISTANCE 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 IN FEET 10000 86.0 75.3 60.7 46.4 28.4 16.8 8.8 4.6 2.5 1.1 0.3

8000 86.0 75.3 60.7 46.4 28.4 16.8 8.8 4.6 2.5 1.1 0.3 6000 86.0 75.3 60.7 46.4 28.4 16.8 8.8 4.6 2.5 1.1 0.3 4000 86.0 75.3 60.7 46.4 28.4 16.8 8.8 4.6 2.5 1.1 0.3 3000 85.6 74.9 60.4 46.1 28.2 16.6 8.7 4.6 2.5 1.1 0.3 2000 82.7 72.3 58.1 44.2 26.9 15.7 8.1 4.2 2.3 1.0 0.3 1000 76.4 66.5 53.1 40.0 24.0 13.7 6.9 3.5 1.9 0.7

800 74.2 64.6 51.5 38.6 23.0 13.0 6.6 3.3 1.8 0.7 600 69.3 60.1 47.7 35.4 20.9 11.6 5.7 2.8 1.5 0.5 400 62.2 53.7 42.2 31.0 17.9 9.6 4.6 2.2 1.1 300 57.6 49.6 38.7 28.1 16.0 8.4 4.0 1.9 0.9 200 51.4 44.1 34.1 24.4 13.6 6.9 3.2 1.4 0.7 150 45.6 38.9 29.8 21.0 11.4 5.6 2.5 1.1 0.3 100 39.8 33.8 25.6 17.7 9.4 4.5 1.9 0.8 0.3

80 36.6 31.0 23.3 16.0 8.4 3.9 1.6 0.5 60 31.4 26.4 19.6 13.2 6.7 3.0 1.2 0.4 50 27.9 23.4 17.2 11.4 5.7 2.4 0.9 40 24.4 20.4 14.8 9.7 4.7 1.9 0.7 30 21.0 17.4 12.5 8.0 3.8 1.5 0.5 20 15.9 13.0 9.1 5.6 2.5 0.9 10 9.4 7.5 5.1 2.9 1.2 0.3
(E)* SOIL LOSS FROM WIND EROSION IN TONS PER ACRE PER YEAR JANUARY, 1998 C = 100 SURFACE - K =0.90 I = 86 (L) (V)** - FLAT SMALL GRAIN RESIDUE IN POUNDS PER ACRE UNSHELTERED

DISTANCE 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000

IN FEET 10000 77.4 67.5 54.0 40.7 24.4 14.0 7.1 3.6 2.0 0.7

8000 77.4 67.5 54.0 40.7 24.4 14.0 7.1 3.6 2.0 0.7 6000 77.4 67.5 54.0 40.7 24.4 14.0 7.1 3.6 2.0 0.7 4000 76.8 66.9 53.5 40.3 24.2 13.8 7.0 3.6 1.9 0.7 3000 75.8 66.0 52.7 39.6 23.7 13.5 6.8 3.5 1.9 0.7 2000 73.4 63.9 50.8 38.1 22.6 12.8 6.4 3.2 1.7 0.6 1000 67.2 58.2 46.0 34.1 19.9 11.0 5.4 2.6 1.4 0.5 800 64.7 56.0 44.1 32.5 18.9 10.3 5.0 2.4 1.3 600 59.7 51.5 40.3 29.4 16.8 8.9 4.3 2.0 1.0 400 55.0 47.3 36.7 26.5 14.9 7.8 3.6 1.7 0.8 300 51.0 43.7 33.8 24.2 13.4 6.8 3.1 1.4 0.7 200 44.7 38.1 29.1 20.5 11.1 5.4 2.4 1.0 0.3 150 39.1 33.2 25.1 17.4 9.2 4.3 1.8 0.8 0.2 100 34.5 29.1 21.8 14.8 7.7 3.5 1.4 0.5

80 31.2 26.3 19.5 13.1 6.7 2.9 1.2 0.4 60 25.9 21.7 15.8 10.4 5.1 2.1 0.8 50 23.1 19.2 13.9 9.0 4.3 1.8 0.7 40 20.7 17.1 12.3 7.8 3.7 1.5 0.5 30 17.2 14.1 10.0 6.2 2.8 1.1 20 12.7 10.3 7.1 4.3 1.9 0.4 10 6.2 4.9 3.2 1.7 0.6502–22 (190-V-NAM, 3rd Ed., October 2002) 

# Exhibit 502–2 Wind erodibility groups and wind erodibility index

Soil EWE Predominant soil texture Wind Soil Soil texture 1 texture class of surface layer Erodibility Erodibility Erodibility wetnes s Group Index ( I ) Index ( I ) factor 2 (WEG) 3 (ton/ac/yr) 4, 5 for irrigated soils (ton/ac/yr) 4



### C 1 Very fine sand, fine sand, 1 310 4 310 sand, or coarse sand 250 250 220 220 180 160 160 134 C 1 Loamy very fine sand, loamy fine sand, 2 134 104 loamy sand, loamy coarse sand, sapric organic soil materials, and all horizons that meet andic 6 soil properties as per Criteria 2 in Soil Taxonomy, regardless of the fine earth texture C 1 Very fine sandy loam, fine sandy loam, 3 86 56 sandy loam, coarse sandy loam, and noncalcareous silt loam with 35 to 50% very fine sand and <10% clay
F 3 Clay, silty clay, non-calcareous clay loam, 4 86 56 or silty clay loam with more than 35% clay
M 2 Calcareous 7 loam and silt loam or 4L 86 56 calcareous clay loam and silty clay loam
M 2 Non-calcareous loam and silt loam with 5 56 38 more than 20% clay (but does not meet WEG 3 criteria), or sandy clay loam, sandy clay, and hemic organic soil materials
M 2 Non-calcareous loam and silt loam with 6 48 21 more than 20% clay, or non-calcareous clay loam with less than 35% clay or silty clay loam with less than 35% clay
M 2 Silt and fibric organic soil material 7 38 21

— — Soils not susceptible to wind erosion 8 — — because of surface rock and pararock fragments or wetness 1/ Soil texture, C = Coarse; M = Medium; F = Fine 2/ Texture wetness factor for adjustment of Erosive Wind Energy (EWE) for the period (Irrigated fields only). 3/ For all WEGs except sand and loamy sand textures, if percent rock and pararock fragments (>2mm) by volume is 15-35, reduce I value by one group with more favorable rating. If percent rock and pararock fragments by volume is 35-60, reduce I value by two favorable groups except for sands and loamy sand textures which are reduced by one group with more favorable rating. If percent rock and pararock fragments by volume is more than 60, use I value of zero for all textures except sands and loamy sand textures which are reduced by three groups with more favorable rati ng. 4/ The wind erodibility index is based on the relationship of dry soil aggregates greater than 0.84 millimeters to potential soil erosion. Value for irrigatedsoils is applicable throughout the year. Values for irrigated soils determined by Dr. E.L. Skidmore, USDA, ARS, Wind Erosion Research Unit, Manhattan, Kansas. 5/ The I factor for WEG 1 vary from 160 for coarse sands to 310 for very fine sands. Use an I value of 220 as an average figure. 6/ Vitrandic, Vitritorrandic, and Vitrxerandic Subgroups with ashy textural modifiers move one group with less favorable rating

. 7/ Calcareous is a strongly or violently effervescent reaction of the fine-earth fraction to cold dilute (IN) HCL.502–23 (190-V-NAM, 3rd Ed., October 2002) 

# Exhibit 502–3 Sieving instructions

Soil sieving has become increasingly important because of USDA’s emphasis on advancing erosion prediction technology. Soil samples can be sieved using either a flat or a rotary sieve. The flat sieve method is useful in making onsite field determ inations. However, the results are not as consistent as those achieved by the electric motor-driven rotary sieve. If the objecti ve is to gather scientific data, consistency is important, and rotary sieving should be the chosen method. (a) Equipment needs • A standard number 20 flat sieve or access to a properly designed rotary sieve. • A device for weighing samples. • A square-nosed scoop or shovel. • Worksheet for sieving of dry aggregates (example follows). (b) Procedure 1. Take samples only when the soil is reasonably dry. If the soil sticks to the scoop, postpone the sampling until the soil dries sufficiently. If sieving is being done to verify the I factor assigned to a soil, samples should be taken during the normal wind erosion period in an area that is smooth, bare, not crusted, not sheltered by windbreaks or barriers, and at a location in the field far enough downwind for avalanching to occur. If the objective is to estimate erodibility for a specific field condition, select a smooth, bare, unsheltered area with the desired conditions. In all cases, avoid compacted or vegetated areas.2. Use the square-nosed scoop to collect a sample from the soil surface. Try to avoid sampling more deeply than approximately 1 inch. Several small scoops may be more representatives than one larger scoop of soil.3. Gently place the sample (about 2 lb) into a padded container for transporting to a sieving location. Fill in the appropriate blanks on the form to specify field conditions and other data. If the soil sample will be done in the field with a flat sieve, proceed. 4. Weigh the sieve (including receiver) and record for later use. Place about 2 pounds of the sample on the No. 20 sieve. Remove loose vegetation without fracturing soil aggregates. 5. Determine gross weight of the sample and sieve. Subtract the weight of the sieve to determine net weight of the sample. 6. Remove the receiver and shake the sieve 50 times using moderate force. Do not bounce the sample or shake so hard that you break down the clods. Place the sieve over the receiver and shake again 50 times. If more than 0.5 ounce collects in the receiver, empty the receiver and repeat the process. If more than 0.5 ounce is again in the receiver, repeat the process again. Do not exceed a total of 200 shakes. Discard material in the receiver and weigh the sieve, receiver, and remaining aggregates in the sieve. Determine the weight of soil aggregates greater than 0.84 millimeter in diameter. Divide the weight of the sieved sample by the total weight of the soil sample to determine percentage of aggregates that exceed 0.84 millimeter. 7. Refer to table that follows to arrive at soil erodibility when using the percentage of nonerodible aggregates.502–24 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–3 Sieving instructions–continued 

### Soil erodibility Index I in tons/acre determined by percentage of nonerodible fractions

% units—> 0 1 2 3 4 5 6 7 8 9 Tens ton/ac ton/ac ton/ac ton/ac ton/ac ton/ac ton/ac ton/ac ton/ac ton/ac 0 — 310 250 220 195 180 170 160 150 140 10 134 131 128 125 121 117 113 109 106 102 20 98 95 92 90 88 86 83 81 79 76 30 74 72 71 69 67 65 63 62 60 58 40 56 54 52 51 50 48 47 45 43 41 50 38 36 33 31 29 27 25 24 23 22 60 21 20 19 18 17 16 16 15 14 13 70 12 11 10 8 7 6 4 3 3 2 80 2 — — — — — — — — —502–25 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502– 3 Sieving instructions–continued 

## ARS and NRCS Data Worksheet for Sieving of Dry Aggregates Cooperative Soil Sieving Project 1. Field Office: _________________________________ 2. Date:___________________________________ 3. County:_____________________________________ 4. Sampled by: _______________________________ 5. Sample site number:_____________________________ 6. Soil Survey Sheet number:___________________ 7. Site location:____________________________________________________ 8. Symbol and map unit name:_______________________________________ 9. Erosion: (yes/no) ___________________________ 10. Tillage: __________________________________ 11. Ridge height (inches):_______________________ 12. Ridge spacing:______________________________ 13. Crust thickness:___________________________ 14. Date(s) and amount(s) of precipitation:______________________________ 15. Total precipitation:______________________________________________ 16. Kind of ground cover:____________________________________________ 17. Status of ground cover:__________________________________________ 19. Amount (lb):_______________________________ 20. Percent ground cover: _____________________ 21. Percent canopy: ____________________________ 22. Row pattern: _______________________________ Row direction (Azimuth): _____________________ 23. Is field irrigated: (yes/no) ____________________ 24. Type of irrigation: ________________________ 25. Annual irrigation applied (inches):___________________________________ 26. Samplers comments:
To be completed by ARS Sieving date: _______________ Sieved by: ______________________________ Soil weight, wet:_________; Soil weight, dry; __________; Percent moisture _________

Resulting I value: _______________ Siever’s comments 

### ) m m ( e z i s e v e i S 2 4

. 0 < 4 8

. - 2 4 . 3 8

. 2

- 4 8 . 4

. 6

- 3 8

. 2 7

. 2 1

- 4

. 6 7

. 2 1 > 4 8

. 0 > %

g n i v i e s t s 1 t h g i e w ( l a t o t f o t n e c r e P g n i v i e s d n 2 t h g i e w ( ) l a t o t f o t n e c r e P502–26 (190-V-NAM, 3rd Ed., October 2002) 

# Exhibit 502–4 Ridge roughness factor, K rd 

# , graphs

Note: Erosive wind energy is assumed to be 60% parallel and 40% perpendicular to prevailing erosive wind.

where: h = ridge height in inches s = ridge spacing in inches K h h s r 

### = × 

### ( ) 4 1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10 12Soil ridge roughness factor, Krd

Soil ridge roughness, K r (inches) Angle of deviation=0 degrees

I=310 I=250 I=220 I=180 I=134 I<134502–27 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–4 Ridge roughness factor, K rd , graph—Continued

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10 12Soil ridge roughness factor, Krd

Soil ridge roughness, K r (inches) Angle of deviation=22.5 degrees

I=310 I=250 I=220 I=160 & 180 I=134 I<134



### Note: Erosive wind energy is assumed to be 60% parallel and 40% perpendicular to prevailing erosive wind.

where: h = ridge height in inches s = ridge spacing in inches K h h s r 

### = × 

### ( ) 4502–28 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–4 Ridge roughness factor, K rd , graph—Continued

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10 12Soil ridge roughness factor, Krd

Soil ridge roughness, K r (inches) Angle of deviation=45 degrees

I=310 I=250 I=220 I=160 & 180 I=134 I<134



### Note: Erosive wind energy is assumed to be 60% parallel and 40% perpendicular to prevailing erosive wind.

where: h = ridge height in inches s = ridge spacing in inches K h h s r 

### = × 

### ( ) 4502–29 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–4 Ridge roughness factor, K rd , graph—Continued



### Note: Erosive wind energy is assumed to be 60% parallel and 40% perpendicular to prevailing erosive wind.

where: h = ridge height in inches s = ridge spacing in inches K h h s r 

### = × 

### ( ) 4 1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10 12Soil ridge roughness factor, Krd

Soil ridge roughness, K r (inches) Angle of deviation=67.5 degrees

I=310 I=250 I=220 I=160 & 180 I=134 I<134502–30 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–4 Ridge roughness factor, K rd , graph—Continued



### Note: Erosive wind energy is assumed to be 60% parallel and 40% perpendicular to prevailing erosive wind.

where: h = ridge height in inches s = ridge spacing in inches K h h s r 

### = × 

### ( ) 4 1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 2 4 6 8 10 12Soil ridge roughness factor, Krd

Soil ridge roughness, K r (inches) Angle of deviation=90 degrees

I=310 I=250 I=220 I=160 & 180 I=134 I<134502–31 (190-V-NAM, 3rd Ed., October 2002) 

### Table 502–5A Angle of deviation = 0 degrees; I = <134 Table 502–5B Angle of deviation = 22.5 degrees; I = <134 Table 502–5C Angle of deviation = 45 degrees; I = <134 Table 502–5D Angle of deviation = 67.5 degrees; I = <134 Table 502–5E Angle of deviation = 90 degrees; I = <134 Table 502–5F Angle of deviation = 0 degrees; I = 134 Table 502–5G Angle of deviation = 22.5 degrees; I = 134 Table 502–5H Angle of deviation = 45 degrees; I = 134 Table 502–5I Angle of deviation = 67.5 degrees; I = 134 Table 502–5J Angle of deviation = 90 degrees; I = 134 Table 502–5K Angle of deviation = 0 degrees; I = 160 and 180 Table 502–5L Angle of deviation = 22.5 degrees; I = 160 and 180 Table 502–5M Angle of deviation = 45 degrees; I = 160 and 180 Table 502–5N Angle of deviation = 67.5 degrees; I = 160 and 180 Table 502–50 Angle of deviation = 90 degrees; I = 160 and 180 Table 502–5P Angle of deviation = 0 degrees; I = 220 Table 502–5Q Angle of deviation = 22.5 degrees; I = 220 Table 502–5R Angle of deviation =45 degrees; I = 220 Table 502–5S Angle of deviation = 67.5 degrees; I = 220 Table 502–5T Angle of deviation = 90 degrees; I = 220 Table 502–5U Angle of deviation = 0 degrees; I = 250 Table 502–5V Angle of deviation = 22.5 degrees; I = 250 Table 502–5W Angle of deviation = 45 degrees; I = 250 Table 502–5X Angle of deviation = 67.5 degrees; I = 250 Table 502–5Y Angle of deviation = 90 degrees; I = 250 Table 502–5Z Angle of deviation = 0 degrees; I = 310 Table 502–5AA Angle of deviation =22.5 degrees; I = 310 Table 502–5BB Angle of deviation = 45 degrees; I = 310 Table 502–5CC Angle of deviation = 67.5 degrees; I = 310 Table 502–5DD Angle of deviation =90 degrees; I = 310 

# Exhibit 502–5 Tables502–32 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5A Angle of deviation = 0 degrees; I = <134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 30 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 36 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 38 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 40 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5B Angle of deviation = 22.5 degrees; I = <134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 30 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 36 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 38 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 40 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–33 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5C Angle of deviation = 45 degrees; I = <134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.8 0.7 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 0.9 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 30 0.9 0.8 0.6 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 36 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 38 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 40 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5D Angle of deviation = 67.5 degrees; I = <134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 0.8 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 18 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 20 0.9 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 24 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 30 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 36 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 38 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 40 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–34 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5E Angle of deviation = 90 degrees; I = <134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 18 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 20 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 24 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 30 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 36 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 38 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 40 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5F Angle of deviation = 0 degrees; I = 134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 36 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 38 1.0 0.9 0.8 0.6 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 40 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–35 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5G Angle of deviation = 22.5 degrees; I = 134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 36 1.0 0.9 0.8 0.6 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 38 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 40 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.



### .

Table 502–5H Angle of deviation = 45 degrees; I = 134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches)


### 7 0.9 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 0.9 0.8 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 20 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 36 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 38 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 40 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–36 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5I Angle of deviation = 67.5 degrees; I = 134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.9 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 0.9 0.8 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 18 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 20 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 24 1.0 0.9 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 30 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 36 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 38 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 40 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind


### .

Table 502–5J Angle of deviation = 90 degrees, I = 134

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 18 1.0 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 20 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 24 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 30 1.0 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 36 1.0 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 38 1.0 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 40 1.0 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–37 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5K Angle of deviation = 0 degrees; I = 160 and 180

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.8 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 36 1.0 0.9 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 38 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 40 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5L Angle of deviation = 22.5 degrees; I = 160 and 180

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches)


### 7 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.8 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 36 1.0 0.9 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 38 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 40 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–38 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5M Angle of deviation = 45 degrees; I = 160 and 180

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 30 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 0.4 36 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 38 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 40 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5N Angle of deviation = 67.5 degrees; I = 160 and 180

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 1.0 0.8 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 1.0 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 18 1.0 0.9 0.8 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 20 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 24 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 30 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 36 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 38 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 40 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–39 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5O Angle of deviation = 90 degrees; I = 160 and 180

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 1.0 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 18 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 20 1.0 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 24 1.0 0.9 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 30 1.0 1.0 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 36 1.0 1.0 0.9 0.8 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 38 1.0 1.0 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 40 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5P Angle of deviation = 0 degrees; I = 220

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 30 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 36 1.0 1.0 0.9 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 0.4 38 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 40 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–40 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5Q Angle of deviation = 22.5 degrees; I = 220

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches)


### 7 1.0 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 30 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 36 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 38 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 40 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5R Angle of deviation = 45 degrees; I = 220

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 0.9 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.4 30 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 0.4 36 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 38 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 40 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–41 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5S Angle of deviation = 67.5 degrees; I = 220

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 1.0 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 18 1.0 1.0 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 20 1.0 1.0 0.9 0.8 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 24 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 30 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 36 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 38 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 40 1.0 1.0 1.0 0.9 0.8 0.7 0.7 0.6 0.5 0.5 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5T Angle of deviation = 90 degrees; I = 220

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 1.0 1.0 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 18 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 20 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 24 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 30 1.0 1.0 1.0 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 36 1.0 1.0 1.0 0.9 0.8 0.8 0.7 0.6 0.6 0.6 0.6 0.6 38 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 40 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–42 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5U Angle of deviation = 90 degrees; I = 250

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.8 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 30 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 36 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 38 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 40 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5V Angle of deviation = 22.5 degrees; I = 250

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.8 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.8 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 30 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 0.4 36 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 38 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 40 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.4 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–43 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5W Angle of deviation = 45 degrees; I = 250

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 0.9 0.9 0.7 0.6 0.5 0.4 0.4 0.4 0.4 0.4 24 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.5 0.4 0.4 0.4 0.4 30 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.4 36 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 38 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.4 40 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5X Angle of deviation = 67.5 degrees; I = 250

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 1.0 1.0 0.8 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 1.0 1.0 0.9 0.8 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 18 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 20 1.0 1.0 1.0 0.9 0.7 0.6 0.5 0.5 0.5 0.5 0.5 0.5 24 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.5 0.5 0.5 30 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.6 0.5 0.5 0.5 0.5 36 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 38 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.5 0.5 0.5 40 1.0 1.0 1.0 1.0 0.9 0.8 0.8 0.7 0.6 0.5 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–44 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5Y Angle of deviation = 90 degrees; I = 250

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 0.9 0.8 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 1.0 1.0 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 18 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 20 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.6 24 1.0 1.0 1.0 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 30 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 0.6 36 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.6 0.6 0.6 38 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 40 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.7 0.6 0.6 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5Z Angle of deviation = 0 degrees; I = 310

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 1.0 0.9 0.7 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 1.0 0.9 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 1.0 0.9 0.8 0.6 0.4 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 24 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 30 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.7 0.6 0.5 0.4 0.4 36 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 38 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 40 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.5 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–45 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5AA Angle of deviation = 22.5 degrees; I = 310

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 1.0 0.9 0.7 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 1.0 0.9 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.4 0.4 0.4 0.4 0.4 20 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 24 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 30 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.7 0.6 0.5 0.4 0.4 36 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 38 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.7 0.6 0.5 0.4 40 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.5 0.4 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5BB Angle of deviation = 45 degrees; I = 310

Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches) 

### 7 1.0 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.4 10 1.0 1.0 1.0 0.9 0.7 0.5 0.4 0.4 0.4 0.4 0.4 0.4 14 1.0 1.0 1.0 1.0 0.8 0.6 0.5 0.4 0.4 0.4 0.4 0.4 18 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 0.4 20 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.5 0.5 0.4 0.4 0.4 24 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.4 0.4 0.4 30 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.5 0.5 0.4 36 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 38 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.5 0.5 40 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.5 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.502–46 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–5CC Angle of deviation = 67.5 degrees; I = 310 Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches)


### 7 1.0 1.0 0.9 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 10 1.0 1.0 1.0 0.9 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 14 1.0 1.0 1.0 1.0 0.9 0.7 0.5 0.5 0.5 0.5 0.5 0.5 18 1.0 1.0 1.0 1.0 0.9 0.8 0.6 0.5 0.5 0.5 0.5 0.5 20 1.0 1.0 1.0 1.0 0.9 0.9 0.7 0.6 0.5 0.5 0.5 0.5 24 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.5 0.5 0.5 0.5 30 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.5 0.5 36 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.6 0.6 0.5 38 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.5 40 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.5 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.

Table 502–5DD Angle of deviation = 90 degrees; I = 310 Ridge - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ridge height (inches) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - spacing 1 2 3 4 5 6 7 8 9 10 11 12 (inches)



### 7 1.0 1.0 1.0 0.8 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 10 1.0 1.0 1.0 0.9 0.8 0.6 0.6 0.6 0.6 0.6 0.6 0.6 14 1.0 1.0 1.0 1.0 0.9 0.7 0.6 0.6 0.6 0.6 0.6 0.6 18 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 0.6 20 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 24 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 0.6 30 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6 36 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.7 0.6 0.6 38 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.7 0.7 0.6 40 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.8 0.7 0.6 These values are based on conditions in which erosive wind energy is 60% parallel and 40% perpendicular to prevailing erosive w ind.(190-V-NAM, 3rd Ed., October 2002) 502–47 

### Graph to convert random roughness heights (standard deviation in inches) to WEQ K-subfactors for random roughness. K subfactors vary by I factors assigned to soil groups. Random roughness is defined as the standard deviation (in inches) of the soil surface elevations, measured at regular intervals from a fixed arbitary plane above a tilled soil surface, after oriented roughness has been considered. Random roughness photos and associated random roughness (standard deviation) values are in Predicting Soil Erosion byWater: A Guide to Conservation Planning With Revised Universal Soil Loss Equation (RUSLE), 1997, Agriculture Handbook 703, appendix C, or can be downloaded at http:/www.nrcs.usda.gov/technical/ECS/agronomy/roughness.html 

# Exhibit 502–6 Random roughness factor, K rr 

# , graph

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Krr, Factor for random roughness



### Random roughness, std. deviation (inches) 134

104

86

56 I-Factors

Table 502–6 Table converts random roughness heights (standard deviation in inches) to WEQ K subfactors ( K rr ) for random roughness. K rr values vary by I factors assigned to soil Wind Erodibility Groups.
Random roughness (standard deviation, inches) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 I Factors K rr values 

### >134 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 134 1.00 0.99 0.98 0.96 0.93 0.91 0.98 0.96 0.85 0.84 104 1.00 0.94 0.88 0.82 0.78 0.74 0.71 0.69 0.67 0.66 86 1.00 0.87 0.76 0.67 0.61 0.57 0.54 0.52 0.50 0.48 56 or less 1.00 0.71 0.50 0.38 0.31 0.27 0.25 0.23 0.23 0.22502–48 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–7 Random roughness (standard deviation) core values

### This information on core values is from Predicting Soil Erosion by Water: A Guide to Conservation Planning With the Revised Universal Soil Loss Equation (RUSLE), 1997, Agriculture Handbook 703. Parameter values of core cropland field operations may be used in the Wind Erosion Equation for random roughness. However the use of the random roughness photos in Agriculture Handbook 703, in appendix C, may be preferable, especially where roughness is caused by residual sod material such as the crowns of plants that has attached roots and soil. The following core values are typical and representative for field operations in medium textured soils tilled at optimum moisture conditions. Many of the machines may differ by cropping region, farming practice, soil texture, or other conditions.Refer to the random roughness photos in the handbook and adjust to values that seem most appropriate. The photos and associated random roughness (standard deviation) values in the Agriculture Handbook 703 can be downloaded at: http:// www.nrcs.usda.gov/technical/ECS/agronomy/roughness.html State agronomists can reproduce and distribute copies of the photographs to Field Offices. Field operations Random roughness (standard deviation in inches) Chisel, sweeps 1.20 Chisel, straight point 1.50 Chisel, twisted shovels 1.90 Cultivator, field 0.70 Cultivator, row 0.70 Cultivator, ridge till 0.70 Disk, 1-way 1.20 Disk, heavy plowing 1.90 Disk, tandem 0.80 Drill, double disk 0.40 Drill, deep furrow 0.50 Drill, no-till 0.40 Drill, no-till into sod 0.30 Fertilizer applicator, anhyd knife 0.60 Harrow, spike 0.40 Harrow, tine 0.40 Lister 0.80 Manure injector 1.50 Moldboard plow 1.90 Mulch treader 0.40 Planter, no-till 0.40 Planter, row 0.40 Rodweeder 0.40 Rotary hoe 0.40 Vee ripper 1.20502–49 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–7a Example of erosive wind data available for specific locations


### This information is found at: http://www.weru.ksu.edu/nrcs/windparm/
KS CHANUTE JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 180 0 180 180 180 180 180 180 180 180 180 180 PREPONDERANCE 4.0 2.3 2.5 3.5 4.6 4.2 3.6 3.7 4.5 4.8 5.2 3.4 EROSIVITY (EWE) 7.9 7.3 17.5 30.2 17.9 2.5 .7 1.5 1.6 2.0 5.6 5.1 CUMULATIVE EWE 7.9 15.3 32.8 63.0 81.0 83.4 84.1 85.6 87.2 89.3 94.9 100.0 KS CONCORDIA JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 0 0 338 158 180 180 180 180 180 180 338 338 PREPONDERANCE 3.4 2.7 2.7 2.0 2.8 3.4 3.8 4.1 5.8 5.3 3.0 2.5 EROSIVITY (EWE) 8.9 9.5 19.8 18.4 7.4 5.4 3.7 3.3 3.8 6.2 5.9 7.6 CUMULATIVE EWE 8.9 18.4 38.2 56.6 64.0 69.5 73.1 76.5 80.3 86.5 92.4 100.0 KS DODGE_CITY JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 0 0 0 180 180 180 180 180 180 180 0 0 PREPONDERANCE 6.6 3.4 2.7 3.1 3.6 5.8 4.1 4.7 5.7 5.5 3.4 3.8 EROSIVITY (EWE) 7.3 8.5 17.3 16.5 9.1 7.7 4.5 3.2 5.6 6.5 6.5 7.4 CUMULATIVE EWE 7.3 15.8 33.1 49.6 58.7 66.4 70.9 74.1 79.6 86.2 92.6 100.0 KS FT.RILEY JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 180 180 180 180 180 180 180 180 202 180 180 202 PREPONDERANCE 5.2 3.6 3.9 3.0 6.0 7.9 5.4 4.1 4.8 4.9 3.6 1.9 EROSIVITY (EWE) 5.3 6.3 20.6 18.5 10.1 4.9 2.2 3.1 5.4 10.0 5.7 7.8 CUMULATIVE EWE 5.3 11.7 32.3 50.8 60.9 65.8 68.0 71.1 76.4 86.4 92.2 100.0 KS GOODLAND JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 338 338 338 338 158 180 158 158 180 338 337 337 PREPONDERANCE 3.3 3.8 3.4 3.6 2.3 2.4 2.1 2.9 3.2 3.6 3.6 4.4 EROSIVITY (EWE) 5.1 7.4 19.2 16.9 9.7 8.8 4.4 4.1 6.0 5.2 7.3 6.0 CUMULATIVE EWE 5.1 12.5 31.7 48.5 58.2 67.0 71.4 75.5 81.5 86.7 94.0 100.0 KS HUTCHINSON JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 0 0 0 180 180 180 180 180 180 180 0 0 PREPONDERANCE 4.5 3.4 3.2 2.9 3.8 5.1 4.9 3.5 4.5 5.1 4.1 4.3 EROSIVITY (EWE) 7.9 10.2 12.3 15.5 9.5 10.1 3.9 3.5 6.2 7.6 6.8 6.6 CUMULATIVE EWE 7.9 18.1 30.4 45.9 55.3 65.4 69.3 72.8 79.0 86.6 93.4 100.0 KS OLATHE JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 180 338 180 202 180 180 202 202 202 180 180 180 PREPONDERANCE 2.4 1.8 1.8 2.2 2.7 3.6 3.7 4.4 5.5 2.6 1.9 2.0 EROSIVITY (EWE) 8.3 7.4 27.9 26.7 7.7 1.9 .7 .6 1.0 4.9 4.9 7.9 CUMULATIVE EWE 8.3 15.7 43.6 70.4 78.1 80.0 80.7 81.3 82.3 87.2 92.1 100.0 KS RUSSELL JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 0 0 0 0 202 202 202 202 202 180 0 0 PREPONDERANCE 3.3 2.9 2.6 1.9 2.7 3.0 3.1 3.4 4.2 3.1 2.8 2.4 EROSIVITY (EWE) 6.9 8.9 14.8 14.5 8.4 5.9 4.8 6.2 7.3 7.2 8.2 6.9 CUMULATIVE EWE 6.9 15.8 30.7 45.1 53.5 59.4 64.2 70.4 77.6 84.8 93.1 100.0 KS SALINA JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC PREV WIND EROS DIR 0 0 0 180 180 180 180 180 180 180 180 0 PREPONDERANCE 5.8 2.4 3.0 2.9 4.6 5.4 3.7 4.6 6.4 4.6 4.0 3.0 EROSIVITY (EWE) 7.4 8.8 19.6 19.8 11.5 4.2 2.2 5.2 6.5 4.9 5.8 4.2 CUMULATIVE EWE 7.4 16.2 35.8 55.6 67.1 71.3 73.4 78.6 85.1 90.0 95.8 100.0502–50 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502NRCS - WEQ CALCULATIONS, Version 5Producer: Iam Windy Planner: mas Location: Mose Lake Tract: 123 Field: 1Crop Rotation: Corn Climate Data Station: WA, MOSES LAKE, oldSite "C" Value:50Tillage Direction (NS/EW): ns Length/width ratio: 1 Field Direction (NS/EW): ew Field Width (Ft.): 2640Irrigation (Y or N): y Soil "I": 134 Wind Erodibility Group: 2 (1-7) TWF: 1 (see instr.)Sum Period Erosion (t/ac): 6.9 No. Yrs in Rotation: 1.0 Av. Annual Wind Erosion: 6.9 (t/ac/yr)Mgt Periods Irr. Soil Ridge Roughness R Roug Unsheltered Distance SGe ErosionDates No. of"I"Dev. Ht. Sp. "Krd" "Krr" Dev. Prep. WED "L" "V" "E" EWE "IF" LossBegin End (#) (t/ac) (deg) (in.) (in.) (factor) (factor) (deg) (factor) (factor)(ft)(lbs/ac) (t/ac) (%) (%) (t/ac)1/1/99 1/2/99 0 104 90.0 0 0 1.0 0.99 0.0 2.5 1.02 2693 3422 0.0 0.3 1.00 0.001/2/99 3/15/99 0 104 90.0 0 0 1.00 1.00 0.0 2.5 1.02 2693 2703 0.0 24.9 1.00 0.003/15/99 3/15/99 0 104 45.0 0 0 1.00 0.98 45.0 1.3 1.03 2719 1437 4.0 0.0 1.00 0.003/15/99 4/1/99 0 104 45.0 0 0 1.0 1.00 45.0 1.3 1.03 2719 1361 5.3 8.5 1.00 0.454/1/99 4/1/99 0 104 45.0 0 0 1.0 0.88 45.0 1.1 1.03 2719 57 43.8 0.0 1.00 0.004/1/99 4/10/99 0 104 45.0 0 0 1.0 0.99 45.0 1.1 1.03 2719 54 49.8 4.3 1.00 2.124/10/99 4/15/99 0 104 45.0 3 30 0.7 0.98 45.0 1.1 1.03 2719 34 33.8 2.4 1.00 0.804/15/99 4/30/99 2 104 45.0 3 30 0.7 0.99 45.0 1.1 1.03 2719 33 34.5 7.1 0.87 2.124/30/99 5/15/99 6 104 45.0 3 30 0.7 1.00 45.0 1.1 1.03 2719 37 34.6 4.4 0.60 0.925/15/99 5/15/99 0 104 0.0 3 30 0.7 0.97 90.0 1.1 1.03 2719 26 33.2 0.0 1.00 0.005/15/99 5/30/99 12 104 0.0 3 30 0.7 1.00 90.0 1.1 1.03 2719 114 32.5 4.3 0.20 0.285/30/99 6/14/99 12 104 0.0 3 30 0.7 1.00 90.0 1.1 1.03 2719 448 23.7 4.5 0.20 0.216/14/99 6/29/99 12 104 45.0 3 30 0.7 1.00 45.0 1.2 1.03 2719 5291 0.0 4.6 0.20 0.006/29/99 10/15/99 38 104 45.0 3 30 0.7 1.00 45.0 1.2 1.03 2719 6999 0.0 17.2 0.65 0.0010/15/99 11/1/99 0 104 90.0 0 0 1.0 1.00 0.0 1.6 1.03 2719 6999 0.0 3.7 1.00 0.0011/1/99 11/1/99 0 104 90.0 0 0 1.0 0.98 0.0 1.6 1.03 2719 3613 0.0 0.0 1.00 0.0011/1/99 12/31/99 0 104 90.0 0 0 1.0 1.00 0.0 1.6 1.03 2719 3422 0.0 13.7 1.00 0.00 Exhibit 502–7b Example of wind erosion calculation using the management period procedure502–51 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–8 C factor map, United States 

### An interactive version of the C factor map is located at http://data4.ftw.nrcs.usda.gov/website/ On this page, click on the link for “C-Values”, and the map will load. The icons below will be displayed in the upper left hand corner of the screen. Fol

lowing each one is a short description of what that icon allows you to do. - Toggles between Layer list and the Map Legend (in upper right hand corner of screen). - Toggles the overview map (in the upper right hand corner) on and off. - After clicking this icon, you can zoom in on a specific area of the map. - After clicking this icon, you can zoom out from a specific area of the map. - Zooms the U.S. map so that it fills the entire viewing area. - Zooms to the active layer - Returns zoom level to the last one viewed. - Cursor becomes cross-arrows. As you zoom in on the map, click and hold the left mouse button and move the map in the desired direction. - Cursor becomes crosshairs. Click on an attribute to find its value. For example, when the “WEQ” layer is active, click on a C factor isoline to find its value. When the “County Boundaries” layer is active, click on a county to find its name and area in acres.- Brings up a query box at the bottom of the screen. Allows you to query the data for the active layer for specific attribute values. Uses SQL (Structured Query Language) - Brings up a query box that allows you to search for a specific value in the active data layer.- Allows you to measure the distance between two points. The cursor becomes crosshairs; click on two different locations on the map, and the distance between them will be displayed. - Brings up a box at the bottom of the screen that allows you to change the units of distance used on the map. - After selecting a line or polygon, click on this icon to set a buffer of a given width around it. - Cursor becomes crosshairs. Hold down the left mouse button and select a rectangular area. Displays values of attributes in and immediately adjacent to the area selected. Attributes displayed will vary with the active layer. - Cursor becomes crosshairs. Allows you to describe a line or a polygon. Displays values of attributes touched by the line or polygon. Attributes displayed will vary with the active layer - Clears the current selection - Prints the current selection502–52 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### The Wind Erosion Research Unit, ARS, Manhattan, Kansas, published new wind erosion C factors in 1983. This information, based on 1941-80 recorded weather data, updated previously published maps. Agriculture Research Service provided calculated values of C at benchmark locations—sites where available weather data included average monthly precipitation and temperature and average annual wind velocity. Data was obtained from the National Climatic Center at Asheville, North Carolina, from the Wind Energy Resource Atlas, and from other sources. To supplement the benchmark C values provided by ARS, NRCS extended the estimation of C to many more local weatherstations. Where recorded precipitation and temperature data were available, including 1951-80 NOAA weather data. An estimate of average annual wind velocity was used to calculate C . Wind velocity isoline maps were prepared from available data, and used as supporting information to estimate local wind velocities. The influence of topography on local climate was also considered. Precipitation and temperature data was used to calculate the precipitation-effectiveness (PE) index at various locations, using the equation:

PE P T = ×

− 

## ( )       

# ∑ 12 10 9 

### 115 10 where: PE = precipitation-effectiveness index P = average monthly precipitation l/ 

### (inches) T = average monthly temperature 2/ 

### (°F) 1/ When the average monthly precipitation is less than 0.5 inches, use 0.5 2/ When average monthly temperature is less than 28.4 °F, use 28.4

### The PE index was used to represent surface soil moisture, together with estimated local wind velocities, in the general equation to calculate C: C V PE = × 

### ( )

34 48 3 2



### .


### where: C = annual climatic factor V = average annual wind velocity
Estimated local C values, calculated as described above, were recorded on state and regional maps and used as a basis to locate C value isolines. The benchmark values provided by ARS were not changed unless there was reason to believe that station data was not reliable. The mathematical formulas can be solved manually or by use of computer software available for wind erosion from the NRCS cooperating scientist and most State Offices. The following page shows an example of the calculations. Exhibit 502–9 Procedures for developing local C factors502–53 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Exhibit 502–9 Procedures for developing local C factors–continued


### Constraints: Monthly P => 0.5 inches Monthly T => 28.4 degrees F LOCATION: Norton, Kansas COUNTY: Norton DATE: 09/26/97

Month P adj P T adj T T - 10 PE 

### January 0.41 0.5 26.7 28.4 18.4 2.1 February 0.6 0.6 32.6 32.6 22,6 2.0 March 1.33 1.33 39.7 39.7 29.7 3.7 April 1.83 1.83 52.4 52.4 42.4 3.5 May 3.42 3.42 62.3 62.3 52.3 5.6 June 3.68 3.68 72.2 72.2 62.2 5.0 July 3.35 3.35 77.8 77.8 67.8 4.1 August 2.61 2.61 76.3 76.3 66.3 3.2 September 2.16 2.16 66.8 66.8 56.8 3.1 October 1.41 1.41 55.7 55.7 45.7 2.4 November 0.73 0.73 40.3 40.3 30.3 1.8 December 0.46 0.5 31.1 31.1 21.1 1.8 Average 21.99 52.8 38.3 annual
Estimated V = 13 Estimated C = 51.8502–54 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–8A Wind erosion direction factor; angle of deviation 1/ = 0 degrees
Prepon- Field length/width ratio dence 1:1 2:1 4:1 8:1 10:1 12:1 16:1


### 1.0 1.03 1.46 1.70 1.85 1.88 1.90 1.95 1.2 1.03 1.30 1.45 1.53 1.56 1.58 1.62 1.4 1.03 1.20 1.28 1.32 1.35 1.37 1.40 1.6 1.03 1.14 1.18 1.20 1.22 1.23 1.25 1.8 1.03 1.10 1.11 1.12 1.13 1.14 1.15 2.0 1.02 1.07 1.07 1.07 1.08 1.08 1.08 2.2 1.02 1.05 1.05 1.05 1.05 1.05 1.05 2.4 1.02 1.04 1.04 1.04 1.04 1.04 1.04 2.6 1.01 1.03 1.03 1.03 1.03 1.03 1.03 2.8 1.01 1.02 1.02 1.02 1.02 1.02 1.02 3.0 1.01 1.02 1.02 1.02 1.02 1.02 1.02 3.2 1.01 1.01 1.01 1.01 1.01 1.01 1.01 3.4 1.01 1.01 1.01 1.01 1.01 1.01 1.01 3.6 1.00 1.01 1.01 1.01 1.01 1.01 1.01 3.8 1.00 1.01 1.01 1.01 1.01 1.01 1.01 4.0 1.00 1.01 1.01 1.01 1.01 1.01 1.01 See footnote at end of table.

Table 502–8B Wind erosion direction factor; angle of deviation 1/ = 22.5 degrees
Prepon- Field length/width ratio dence 1:1 2:1 4:1 8:1 10:1 12:1 16:1


### 1.0 1.03 1.46 1.70 1.85 1.88 1.90 1.95 1.2 1.03 1.37 1.50 1.61 1.64 1.66 1.70 1.4 1.03 1.27 1.36 1.44 1.46 1.47 1.50 1.6 1.03 1.22 1.26 1.30 1.32 1.33 1.35 1.8 1.03 1.18 1.20 1.21 1.22 1.23 1.24 2.0 1.04 1.16 1.16 1.16 1.16 1.16 1.17 2.2 1.05 1.14 1.14 1.14 1.14 1.14 1.14 2.4 1.06 1.13 1.13 1.13 1.13 1.13 1.13 2.6 1.06 1.13 1.13 1.13 1.13 1.13 1.13 2.8 1.07 1.12 1.12 1.12 1.12 1.12 1.12 3.0 1.07 1.12 1.12 1.12 1.12 1.12 1.12 3.2 1.07 1.12 1.12 1.12 1.12 1.12 1.12 3.4 1.08 1.12 1.12 1.12 1.12 1.12 1.12 3.6 1.08 1.11 1.11 1.11 1.11 1.11 1.11 3.8 1.08 1.11 1.11 1.11 1.11 1.11 1.11 4.0 1.08 1.11 1.11 1.11 1.11 1.11 1.11 See footnote at end of table502–55 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–8C Wind erosion direction factor; angle of deviation 1/ = 45 degrees
Prepon- Field length/width ratio dence 1:1 2 :1 4:1 8:1 10:1 12:1 16:1


### 1.0 1.03 1.46 1.70 1.85 1.88 1.90 1.95 1.2 1.03 1.44 1.63 1.72 1.75 1.77 1.81 1.4 1.03 1.42 1.57 1.62 1.65 1.67 1.70 1.6 1.03 1.42 1.52 1.55 1.57 1.58 1.61 1 8 1.03 1.42 1.49 1.51 1.52 1.53 1.55 2 0 1.03 1.42 1.48 1.49 1.49 1.49 1.50 2.2 1.02 1.42 1.48 1.48 1.48 1.48 1.48 2.4 1.02 1.42 1.48 1.48 1.48 1.48 1.48 2.6 1.01 1.42 1.48 1.48 1.48 1.48 1.48 2.8 1.01 1.42 1.48 1.48 1.48 1.48 1.48 3.0 1.01 1.42 1.48 1.48 1.48 1.48 1.48 3.2 1.01 1.42 1.48 1.48 1.48 1.48 1.48 3.4 1.01 1.42 1.48 1.48 1.48 1.48 1.48 3.6 1.01 1.42 1.48 1.48 1.48 1.48 1.48 3.8 1.01 1.42 1.48 1.48 1.48 1.48 1.48 4.0 1.01 1.42 1.48 1.48 1.48 1.48 1.48 See footnote at end of table.

Table 502–8D Wind erosion direction factor; angle of deviation 1/ = 67.5 degrees
Prepon- Field l ength/width ratio dence 1:1 2 :1 4:1 8:1 10:1 12:1 16:1


### 1.0 1.03 1.46 1.70 1.85 1.88 1.90 1.95 1.2 1.03 1.49 1.80 1.94 1.98 2.00 2.04 1.4 1.03 1.52 1.90 2.03 2.07 2.08 2.12 1.6 1.03 1.55 1.98 2.13 2.15 2.16 2.20 1.8 1.03 1.58 2.08 2.23 2.25 2.26 2.30 2.0 1.04 1.62 2.17 2.35 2.36 2.37 2.40 2.2 1.05 1.65 2.27 2.48 2.49 2.49 2.50 2.4 1.06 1.68 2.37 2.61 2.61 2.61 2.61 2.6 1.06 1.71 2.42 2.71 2.71 2.71 2.71 2.8 1.07 1.72 2.44 2.77 2.77 2.77 2.77 3.0 1.07 1.73 2.45 2.82 2.82 2.82 2.82 3.2 1.07 1.74 2.46 2.85 2.85 2.85 2.85 3.4 1.08 1.75 2.47 2.87 2.87 2.87 2.87 3.6 1.08 1.75 2.48 2.89 2.89 2.89 2.89 3.8 1.08 1.76 2.48 2.90 2.90 2.90 2.90 4.0 1.08 1.76 2.49 2.91 2.91 2.91 2.91 See footnote at end of table.502–56 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Table 502–8E Wind erosion direction factor; angle of deviation 1/ = 90 degrees
Prepon- Field length/width ratio dence 1:1 2:1 4:1 8:1 10:1 12:1 16:1


### 1.0 1.03 1.46 1.70 1.85 1.88 1.90 1.95 1.2 1.03 1.50 1.90 2.10 2.16 2.23 2.32 1.4 1.03 1.55 2.10 2.40 2.50 2.60 2.75 1.6 1.03 1.66 2.30 2.70 2.87 3.00 3.25 1.8 1.03 1.80 2.55 3.10 3.32 3.50 3.85 2.0 1.02 1.96 2.78 3.50 3.84 4.08 4.56 2.2 1.02 2.00 3.06 4.05 4.47 4.80 5.40 2.4 1.02 2.00 3.35 4.63 5.12 5.60 6.40 2.6 1.01 2.00 3.56 5.30 5.93 6.50 7.60 2.8 1.01 2.00 3.74 5.85 6.64 7.50 8.90 3.0 1.01 2.00 3.92 6.51 7.60 8.80 10.6 3.2 1.01 2.00 4.00 6.89 8.20 9.30 11.5 3.4 1.01 2.00 4.00 7.08 8.40 9.60 11.8 3.6 1.00 2.00 4.00 7.26 8.60 9.90 12.3 3.8 1.00 2.00 4.00 7.45 8.91 10.3 12.8 4.0 1.00 2.00 4.00 7.64 9.20 10.6 13.3 1/ Angle of deviation is the difference between prevailing wind erosion direction and a line perpendicular to thelong side of the field or strip (0 degrees is perpendicular to the long side). Multiply the Wind Erosion Direction Factor times the width of the field to determine L distance. For circular fields L = .915 times the diameter regardless of direction or preponderance.190-V-NAM, 3rd Ed., October 2002) 502–57 

# Exhibit 502-10 Flat small grain equivalent charts

Index to flat small grain equivalent charts
Vegetation Figure Vegetation Figure Alfalfa b-l Needleandthread d-1, 4, 8 Barley a-1, 2 Oats a-1, 2 Beans, dry b-2 Pe anuts b-12, 13, 14 Beets, sugar b-15 Potato b-15 Big bluestem d-1, 3, 4, 5 Range grasses and d-1–8 Blue grama d-1, 3, 4, 6, 7, 8 mixtures Buckwheat b-5 Rape b-16 Buffalograss d-1, 2, 4, 5, 7, 8 Rye a-1, 2 Corn a-3, 4, 5, 6 Safflower b-17 Cotton b-6, 7, 8, c-l Sesame b-12 Dry beans b-2 Sideoats grama d-1, 4 Flax b-9 Sorghum a-4, 5, 6, 8 Guar b-12 Soybeans b-2, 3, 4 Lentils b-2 Sudan a-9 Little bluestem d-1, 3, 4, 6 Sugar beets b-15 Manure c-2 Sunflower b-18 Millet a-7 Switchgrass d-3, 6 Mint b-10 Turnip b-10 Mustard b-ll Western wheatgrass d-1, 2, 4, 5, 8 Wheat a-1, 2 Winter peas b-2

Figure Chart a–1 Small grain residue (use for wheat, barley, rye, and oats) a–2 Growing small grain a–3 Corn residue a–4 Corn and grain sorghum silage stubble a–5 Growing corn and grain sorghum a–6 Growing corn and grain sorghum; days after emergence a–7 Millet stubble and residue a–8 Grain sorghum and residue a–9 Sudangrass stubble and residue b–1 Alfalfa residue b–2 Dry bean, lentil, soybean, and winter pea residue b–3 Growing soybeans b–5 Buckwheat residue b–6 Cotton residue b–7 Growing cotton b–8 Growing cotton; days after emergence b–9 Flax residue b–10 Reserved for turnip and mint residue) Figure Chart b–11 Mustard residue b–12 Peanut, guar, and sesame residue b–13 Growing peanuts b–14 Growing peanuts; days after emergence b–15 Potato or sugar beet residue b–16 Rape residue b–17 Safflower residue b–18 Sunflower residue c–1 Cotton burs c–2 Manure d–1 Overgrazed range mixtures d–2 Overgrazed big bluestem, western wheatgrass, and buffalograss d–3 Overgrazed little bluestem, switchgrass, and blue grama d–4 Properly grazed range grass mixtures d–5 Properly grazed big bluestem, etc d–6 Properly grazed little bluestem, etc d–7 Ungrazed blue grama and buffalograss d–8 Undergrazed western wheatgrass, needleandthread, blue grama, and buffalograss mixtures502–58 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Flat small g rain (ref erenc e condition) Flat winter wheat residue, 10-inch long ra ndomly distr ibuted Standing wint er wheat stubble, 10-inch rows perpendicular to wind 10,000 8,000 7,000 6,000 5,000 4,000 3,000
2,000

1,000

800 700 600 500 400 300

200

100 20 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 6,000 10,000 Small grain residue (lb/ac)Equivalent flat small grain residue(lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Residue is washed, air dried, and placed as described for the wind tunnel tests. Source: Lyles and Allison- — Trans. ASAE 1981, 24 (2): 405-408. Figure a–1 Flat small grain equivalents of small grain residue (use for wheat, barley, rye, oats)502–59 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Days after emergence 4/

_

Flat small gr ain (ref erenc e condition—dr y) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 20 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 4,000Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction.
1/ Siddway, F.H., W.S. Chepil, and D.V. Armburst 1965. 2/ Estimates by best judgment of SCS personnel. 3/ Air-dry weights of growing winter wheat from emergence to winter dormancy. 4/ Crop growth, in days after emergence, from Central SD, 1996. Growing sm all gr a in—ridged surface 2/ Growing small grain—fl a t s

urface 1/

10 1 7 15 20 30 40 45 1 7 16 21 30 35 48 60 Spring Wheat Winter Wheat

Growing small grain (lb/ac) 3/ _

_

_ Figure a–2 Flat small grain equivalents of growing small grain502–60 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–3 Flat small grain equivalents of corn residue

10,000 8,000 7,000 6,000 5,000 4,000 3,000
2,000

1,000

800 700 600 500 400
300

200

100 200 300 400 100 1,000 700 500 2,000 4,000 3,000 10,000 6,000 20,000 Corn residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Lyles and Allison, Transcript ASAE 1981, 24 (2): 405-408. 1/ Flat to 2,000 lbs, standing to 3,500 lbs. Extended by NRCS. Flat corn stalks 1/ Flat corn residue (60% st alk, 40% f ines) Standing corn (40% st alks, 60% finer residue) Flat small grain (reference condition—dry)

_502–61 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–4 Flat small grain equivalents of corn and grain sorghum silage stubble

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

100 100 200 300 400 500 700 1,000 3,000 5,000 7,000 10,000 Corn and grain sorghum silage stubble (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Lyles and Allison- — Trans. ASAE 1981, 24 (2): 405-408. Residue weights are washed, air dried, and placed as described for the wind tunnel tests. 1/ Field experience in the Northern Plains indicates the ratio of residue to grain is higher when crops, such as forage sorghum , are grown in narrow row seedings. Research is not available at this time to confirm this observation. Until research is available, the residue production values may be increased 30 percent when crops are planted in rows less than 20 inches apart. The line for standing forage sorghum 6.25 inches high with 10 inch rows includes an increase of 30 percent over the values for 30 inch rows

. Standing forage sorghum stubble 6.25 inches high, 30 inch rows perpendicular to wind.

Standing corn silage stubble 6.25 inches high, 30 inch rows perpendicular to wind. Standing forage sorghum 6.25 inches high, 10 inch rows perpendicular to the wind 1/

Flat small grain (reference condition — dry)

200

2,000 _502–62 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–5 Flat small grain equivalents of growing corn and grain sorghum

Fl

at smal l grain (refere nce condition—dr y) 10,000 8,000 6,000 5,000 4,000 3,000 2,000

1,000

800 600 500 400 300
200

80

2 40 50 70 100 200 300 400 600 1,000 2,000 4,000 

### Growing corn and grain sorghum (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Armburst and Lyles, 1984—unpublished. 1/ Natural Resources Conservation Service data from Central South Dakota, 1996. 100

60 50 40 30
20

10 1 3 4 5 6 7 8 10 20 30 Gr owing co rn—ro ws

paral lel

to wind

Grow ing gr ain sorghum — rows perpendicular to w ind Growing corn—rows perpendicular to wind 1 7 15 20 30 38 45 60 

### Days after emergence 1/

_502–63 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–6 Flat small grain equivalents of growing corn and grain sorghum; days after emergence Growing corn—rows paralell to wind (24,000 per acre) 1,000

200

100 80

40

20

10 20 30 40 50 60 80 100 Time after emergence (days)Equivalent flat small grain residue (lb/ac)

Source: Armburst and Lyles, 1984—unpublished. Growing grain sorghum—rows perpendicular to wind (38,500 per acre)

G row

ing corn— r ows pe

rpend

icu

lar to w ind (24,000 per acre)

15 10 8 7 6 5 4 3 2 1 30 50 60 70 150 300 400 500 600 700 1,500 2,000 3,000 4,000502–64 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–7 Flat small grain equivalents of millet stubble and residue

Flat small grain (re ference con

dition)

Flat millet—random Standing millet stubble 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 60 40 50 70 80 100 200 300 400 500 700 1,000 2,000 3,000 7,000 10,000 Millet residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Leon Lyles- — ARS memorandum, January 25, 1985. 5,000502–65 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–8 Flat small grain equivalents of grain sorghum and residue Standing grain sorghum residue 1/ Flat grain sorghum with leaves 1/ 10,000 8,000 7,000 6,000 5,000 4,000 3,000
2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 6,000 10,000 Sorghum residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Lyles and Allison- — Trans. ASAE 1981, 24 (2): 405-408. 1/ Leafy residue estimates by NRCS North Central agronomists. (Flat to 2,500 lbs. standing stalks to 3,500 lbs.) November 1984

. Flat small gr a in

(ref. con )

20,000 4,000 _ _
Flat grain s orghum s talks Standing grain sorghum stalks502–66 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure a–9 Flat small grain equivalents of sudangrass stubble and residue

Fla

t sma ll grain (refere nce condition ) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Sudan residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Leon Lyles, ARS, Memorandum, January 25, 1985. 7,000 Flat

sudan r esidue Standing sudan stubble502–67 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–1 Flat small grain equivalents of alfalfa residue Flat small grain (reference conditi on) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 70 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Standing alfalfa residue in field (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Unpublished coefficients provided by Leon Lyles- , ARS. Wind Erosion Research Unit, Manhattan, Kansas. 1/ Data from central South Dakota, 1996 Alfalfa , swee tclover flat 1 Standing alfalfa residue; stalks only

7,000502–68 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–2 Flat small grain equivalents of dry bean, lentil, soybean, 1/ and winter pea residue

10,000 8,000 7,000 6,000 5,000 4,000

3.000

2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Residue in field (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Best Judgment Estimates by NRCS, North Central Agronomists, November 1984. 1/ Soybeans—Lyles and Allison, Trans. ASAE. 1981, 24(2) 405-408. 7,000 10% standing 2 1/2 in. high 90% flat ra ndom Random flat residue Flat small grain (refe rence condi tion)502–69 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–3 Flat small grain equivalents of growing soybeans

100

40 30
20

10 1 Growing Soybeans (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Armburst and Lyles, 1984–unpublished. Soybeans—growing in rows perpendicular to the wind Soybeans— grow ing in row s parallel to the w ind.

Flat s mall grain (ref erence condition) Days after emergence 1/

2 4,000 2,000 1,000 600 400 300 200 100 70 50 40 30 20 10 8 7 6 5 4 3 50 60 80 200 300 400 500 600 800 1,000 2,000 3,000 4,000 5,000 6,000 8,000 10,000 7 15 22 27 31 37 45 52 60 _502–70 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–5 Flat small grain equivalents of buckwheat residue

Fla

t sma ll grain (refere nce condition) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 70 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Buckwheat residue in field (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Best judgment estimates by NRCS, North Central agronomists, November 1984. 7,000 Standing buckwheat residue Flat buckwhe at res idue—random502–71 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–6 Flat small grain equivalents of cotton residue

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 4,000 10,000 Cotton residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Lyles and Allison- , Trans ASAE, 1981, 24(2): 405-408. Residue weights are washed and dried, placed as described for wind tunnel test. 6,000 Flat s mall gra in (referen ce condition—dry) Standing cotton stubble—13.5 inches high —30 inch rows—perpendicular to wind Flat cotton residue, 10 inches long —randomly distr ibuted

20,000502–72 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–7 Flat small grain equivalents of growing cotton

10,000 8,000 6,000 5,000 4,000 3,000 2,000

1,000

200

40 30
20

10 70 30 40 50 10 100 200 300 400 600 1,000 2,000 4,000 Growing cotton (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Armburst and Lyles, 1984 — unpublished. Growing cotton—rows perpendicular to wind Growing cotton— rows parallel to wind Flat small grain (ref erence c ondi tion—dry)

7 6 5 4 3 2 1 50 60 80 100 800 600 500 400 300

20502–73 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–8 Flat small grain equivalents of growing cotton; days after emergence

Growing cotton — r ows perpe ndic

ular t

o wind (48,500 plants per acre) Growing cotton — rows parallel to w ind (48,500 plants per acre) 6,000 4,000 3,000 2,000

1,000

700 600 500 400 300
200

10 40 1 2 50 60 80 100 Time after emergence — daysEquivalent flat small grain residue (lb/ac)

Source: Armburst and Lyles- , ARS, 1984 —unpublished. 1,500

150
100 80 70 60 50 40 30
20

30 20 15 10 5 34 7 6 9502–74 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–9 Flat small grain equivalents of flax residue

Flat small g rain ( refere nc

e condition) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 70 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Flax residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Best judgment estimates by NRCS, North Central agronomists. November 1984. 7,000 Standing flax Flat flax — ran dom502–75 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–10 Turnip and mint residue


### (Reserved)502–76 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–11 Flat small grain equivalents of mustard residue

10,000 8,000 7,000 6,000 5,000 4,000
3,000

2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Mustard residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Best judgment estimates by NRCS West agronomists, 1983. 7,000 Flat mustar d residue, ra ndom ly distri buted Flat small grain (referenc e co

ndition — dry) Standing mustard stubble, perpendicular to wind502–77 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–12 Flat small grain equivalents of peanuts, guar, and sesame residue

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 6,000 10,000 Guar, peanuts, or sesame residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Best judgment estimates by NRCS. Flat small grain (referenc e co

ndition — dry)

20,000 4,000 Peanuts Guar or sesa me502–78 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–13 Flat small grain equivalents of growing peanuts

10,000 8,000

4,000 6,000 5,000

2,000 3,000

600

300 400 500

200

50 40 30
20

10 1 10 70 100 400 1,000 Growing peanuts (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long lying flat on the soil surface in 10-inch rows, rows perpendicular t o wind direction, stalks oriented to wind direction. Source: Armburst and Lyles, 1984 — unpublished. 600 Flat small grai n (ref erence co

ndition — dry)

4,000 200 2,000 300 50 40 30 20 8 7 6 5 4 3 2 60 80 100 800 1,000 Growing peanuts—rows perpendicular to wind502–79 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–14 Flat small grain equivalents of growing peanuts; days after emergence

5,000 4,000 3,000 2,000 1,500 1,000

300
200

80 70 150
100

40 30
20

10 20 30 40 50 60 80 100 Time after emergence (days)Equivalent flat small grain residue (lb/ac)

Source: Armburst and Lyles- , 1984 — unpublished. Growing peanuts — rows perpendicular to wind (4 8,500 per acre)

15 10 8 7 6 5 4 3 2 1 50 60 400 500 600 700502–80 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–15 Flat small grain equivalents of potato or sugar beet residue

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400

300

200

100 80 100 200 300 400 500 700 1,000 2,000 5,000 7,000 10,000 Potato or sugar beet residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Best judgment estimates by NRCS, North Central agronomists, November 1984. 3,000 1,500

150 Flat potato or sugar beet residue Flat sm all grain (reference co ndition)502–81 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–16 Flat small grain equivalents of rape residue

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 200 100 300 400 500 700 1,000 2,000 3,000 4,000 6,000 10,000 20,000 Rape residue (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Lyles and Allison- — Trans. ASAE 1981, 24 (2): 405-408. Residue weights are washed, air dried, and placed as described. Standing rape stubble 10 inches high in

10 inch rows perpendicular to wind

Flat small grain (reference condition) Flat rape residue 10 inches long rand omly distributded502–82 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–17 Flat small grain equivalents of safflower residue Flat small grain (reference condition) 10,000 8,000 7,000 6,000 5,000 4,000
3,000

2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 5,000 10,000 Safflower residue in field (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Best judgment estimates by NRCS, North Central agronomists, November 1984. Flat safflowe r resi due Standing safflower residue

7,000502–83 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure b–18 Flat small grain equivalents of sunflower residue

Fla

t sm al

l grain (refere nce con dition -dr

y) Standing sunflower stubb le - 17" high - 30" ro w s - perpendicular to wind

Flat sunf low

er residue - 17"

long - rand o mly di stributed 8,000 10,000

7,000 6,000 5,000

3,000

2,000

1,000 4,000

800

100 100 2,000 3,000 4,000 6,000 10,000 20,000 Sunflower residue (lb/ac)Equivalent flat small grain residue (lb/ac)

700 600 500
400 300

200

1,000 700 500 200 300 400

Source: Lyles and Allison, Trans. ASAE 1981, 24(2): 405-408. Residue wts. are washed, air dried, and placed as described for wind tunnel test.502–84 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure c–1 Flat small grain equivalents of cotton burs

10,000 8,000 7,000 6,000 5,000 4,000 3,000
2,000

1,000

800 700 600 500 400
300

200

100 100 200 300 400 500 700 1,000 2,000 3,000 6,000 10,000 Cotton burs (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Research by D.W. Fryear, ARS, Big Spring, Texas. Flat sm all grain (reference condition - dry) Cotton burs – flat surface

20,000 4,000502–85 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure c–2 Flat small grain equivalents of manure

Wet manure – tilled Dry manure – tilled Wet manure – surface a pplied Dry manure – s urfa

ce applie d 10,000 8,000 7,000 6,000 5,000 4,000
3,000

2,000

1,000

800 700 600 500 400
300

200

100

1,000 2,000 3,000 4,000 6,000 10,000 20,000 30,000 60,000 100,000 Manure (lb/ac)Equivalent flat small grain residue (lb/ac)

Source: Woodruff, N.P., L. Lyles, J.D. Dickerson, and D.V. Armbrust. 1974 Journal Soil and Water Conservation 19(3), pages 127–129. 40,000 Flat small grain (reference condition – dry)502–86 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–1 Flat small grain equivalents of overgrazed range mixtures—big bluestem, little bluestem, sideoats grama, western wheatgrass, needleandthread, blue grama, and buffalograss

Fla

t small gr ain

(refere nce c ondition ) 10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 20 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 Overgrazed range mixtures (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Lyles and Allison- — 1980 Journal Range Management, 33(2), pages 143–146. 70 10 Blue grama 45%, buffalograss 30%, western wheatgrass 25% — 1 inch tall

Western wheat 45% needle andthread 30%, b lue grama 25% — 1 inch tall

Bi

g bluestem 60 %, l

ittle blues tem 30%, side-oats g rama 10

% — 1 inch tal l502–87 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–2 Flat small grain equivalents of overgrazed big bluestem, western wheatgrass, and buffalograss

Fla

t sm all gr ain

(ref ere

nce c ondition ) 10,000 8,000 7,000 6,000 5,000 4,000 3,000
2,000

1,000

800 700 600 500 400 300

200

100 20 30 40 50 60 80 100 200 300 400 500 700 1,000 2,000 3,000 Overgrazed big bluestem, western wheatgrass and buffalograss (lb/ac)Equivalent flat small grain residue (lb/ac)

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soil surface in 10-inch rows, rows perpendicular to wind direction, stalks oriented to wind direction. Source: Lyles and Allison- — 1980 Journal Range Management, 33(2), pages 143–146. 10 4,000 Buffalograss — 1 inch Western wheatgrass — 1 i

nch Big bluestem —1 inc h502–88 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–3 Flat small grain equivalents of overgrazed little bluestem, switchgrass, and blue grama

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 10 20 30 40 50 70 100 200 300 600 1,000 Overgrazed little bluestem, switchgrass, and blue grama (lb/ac)Equivalent flat small grain residue (lb/ac)

Flat sm al

l grain (refe rence condition)

2,000 400 Little Bluestem 1 inch Switchgrass 1 inch Blue grama 1 inch

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10 inch rows perpendicular to wi nd direction, stalks oriented to wind direction. Source: Lyles and Allison – 1980 Journal Range Management, 33(2), pages 143–146.502–89 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–4 Flat small grain equivalents of properly grazed range grass mixture

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 10 20 30 40 50 80 100 200 300 700 1,000 Properly grazed range grass mixtures (lb/ac)Equivalent flat small grain residue(lb/ac) Flat small grain (reference condition)

2,000 500

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10-inch rows perpendicular to wind direction, stalks oriented to wind direction. Source: Lyles and Allison – 1980 Journal Range Management, 33(2), pages 143–146. Little B

lue

stem 60%

, little bluestem 30% , side-oats g ram a 10%

, all 6 in

ches Blue grama 45%, buffalograss 30%, western wheatgrass 25%, all 2 inches

Wester n wheatgrass 45%, ne edleandthread 30%, blue grama 25%, all 4 inches either mix

400 70 60502–90 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–5 Flat small grain equivalents of properly grazed big bluestem, western wheatgrass, and buffalograss

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 10 20 30 40 50 80 100 200 300 700 1,000 Properly grazed big bluestem, western wheatgrass, buffalograss (lb/ac)Equivalent flat small grain residue (lb/ac)

Flat sm all grain (refere nce condition )

2,000 500

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10 inch rows perpendicular to wi nd direction, stalks oriented to wind direction. Source: Lyles and Allison, 1980, Journal Range Management, 33(2), pages 143–146. 400 70 60 Big bluestem —6 inches (shor t er tha n “properly grazed”) Western wheatgr ass—4 inches

B uffalograss— 2 inches

3000502–91 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–6 Flat small grain equivalents of properly grazed little bluestem, blue grama, and switchgrass

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 30 40 50 80 100 200 300 700 1,000 Properly grazed little bluestem, blue grama, and switchgrass (lb/ac)Equivalent flat small grain residue (lb/ac) Flat small grain (reference condition )

2,000 500

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10 inch rows perpendicular to wi nd direction, stalks oriented to wind direction. Source: Lyles and Allison, 1980, Journal Range Management, 33(2), pages 143–146. 400 70 60 3,000 5,000 7,000 10,000 Switchgrass—6 inc he

s (shorter than “properly grazed”) Blue grama—2 inches Little bluestem—4 in ches502–92 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–7 Flat small grain equivalents of ungrazed blue grama and buffalograss

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 30 40 50 80 100 200 300 700 1,000 Ungrazed blue grama and buffalograss (lb/ac)Equivalent flat small grain residue (lb/ac)

Flat sm al

l grain (refe rence condit io

n)

2,000 500

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10 inch rows perpendicular to wi nd direction, stalks oriented to wind direction. Source: Lyles and Allison, 1980, Journal Range Management, 33(2), pages 143–146. 400 70 60 Buff

alograss 4 inches Bluegr ama 1 3 inches

20 10502–93 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Figure d–8 Flat small grain equivalents of ungrazed western wheatgrass, needleandthread, blue grama, and buffalograss mixtures

10,000 8,000 7,000 6,000 5,000 4,000 3,000

2,000

1,000

800 700 600 500 400
300

200

100 30 40 50 80 100 200 300 700 1,000 Ungrazed mixtures of grass (lb/ac)Equivalent flat small grain residue (lb/ac) Flat small grain (reference conditi on)

2,000 500

Reference condition: Dry small grain stalks 10 inches long, lying flat on the soils surface in 10 inch rows perpendicular to wi nd direction, stalks oriented to wind direction. Source: Lyles and Allison, 1980, Journal Range Management, 33(2), pages 143–146. 400 70 60 20 10 3,000 45%

13 inches—blue grama; 30% 4 inches— buffa lograss ; 25% 17 inches—we stern wheat grass

45% 17 inches—western wheatgrass ; 30% 17 inches needl eandthread; 25% 13 inc hes blue grama