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

National

Agronomy

Manual

United States

Department of

Agriculture

Natural

Resources

Conservation

Service
ii (190-V-NAM, 3rd Ed., October 2002)

October 2002

The United States Department of Agriculture (USDA) prohibits

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an equal opportunity employer.

National

Agronomy

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

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 Responsibilities

 190-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 1935

The 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’s

responsibilities. 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 Department 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 for

uniform 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 policy

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

500.11 Amendments to NAM

The 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 institutes 

and 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 in 

the region and across regional boundaries as appropriate. 
(190-V-NAM, 3rd Ed., October 2002) 500–3 

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 some 

cases, 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 supervisor 

to 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 training

Agronomists use technical information that has been developed at centers, institutes, national, or State level and maintain technical materials for the administrative area they 

serve. 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 or 

presentation 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 Employee 

Development Courses, workshops, conferences, and university courses. 

500.40 Certification

Agronomists at all levels of the agency are encouraged to 

obtain professional certification(s). Examples of certification programs include the Certified Crop Adviser (CCA) 

and Certified Professional Agronomists (CPAg) under 

ARCPACS 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 educational 

requirements of most certification programs provide excellent opportunities to stay abreast of advances in technology. 

500.50 Affiliation with professional organizations

Agronomists 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. 

(190-V-NAM, 3rd Ed., October 2002) 501–i 

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
501–ii (190-V-NAM, 3rd Ed., October 2002) 
190-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 the 

Revised 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 the 

same 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 channel 

erosion 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 

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Part 501 Water Erosion

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 dense 

vegetation, 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 estimated

NRCS 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 natural 

resources, 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 the 

1930’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 soil 

loss 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 the 

1950’s. In 1954, the Agricultural Research Service established the National Runoff and Soil Loss Data Center at 

Purdue 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 and 

soil loss data from 49 U.S. locations (Agriculture Handbook 703, 1997; Wischmeier and Smith 1965, 1978). 
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The USLE was designed to provide a convenient working 

tool 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

Equation

Since 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 Agriculture 

Handbook 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 a 

field 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 RUSLE 

factors. 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 and 

management 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 to 

search 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 

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Part 501 Water Erosion

501.26 Tools for using RUSLE

Maps of rainfall and runoff factors, R and Req (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 data 

and 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 and 

tables. 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 tables 

4-1 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 tables 

available in the FOTG in many states. Copies, where available, can be obtained from the State office. Table values for 

common 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, Req, 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 rate 

of runoff caused by a particular rainfall event. Soil properties that affect soil erodibility include texture, structure, per-
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Part 501 Water Erosion

190-V-NAM, 3rd Ed., October 2002) 501–5 

meability and organic matter content. Values for K should 

be selected from those given in the NRCS soil survey database in NASIS or in published reports the RUSLE soil 

erodibility nomograph can also be used to estimate K values for most soils. Soil erodibility K varies by season. It 

tends 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 recommended 

by 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 slopes 

can 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 from 

the 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 in 

the field. In conservation planning, the hillslope profile representing a significant portion of the field having the most 

severe 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 or 

similar device. Chapter 4, Agriculture Handbook 703 contains additional guides for choosing and measuring slopes. 

Most naturally occurring hillslope profiles are irregular in 

shape. 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 a 

series 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 and 

runoff 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 because 

of 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) 

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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 where 

strips 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-slope 

stripcropping, field stripcropping, buffer strips and vegetated filter strips. 

Terraces in RUSLE are support practices where high and 

large 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 sediment 

leaving 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 are 

conditions 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 terrace 

and 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, and 
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Agronomy 

Manual 

Part 501 Water Erosion

190-V-NAM, 3rd Ed., October 2002) 501–7 

• soil moisture subfactor by growing moisture-depleting crops. This benefit is only applied in RUSLE in 

the 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, and 

J.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 Loss 

Equation 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 soil 

and 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 values. 

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 agronomists, under the leadership of H.R. Sinclair, lead soil scientist. 

Original K

value 1/

Minimum

value 2/

Maximum

value 3/ Acceptable class and half-class K factor values 4/

0 6 .02 0 4 .01 0 2 .02 0.0

0 4 .05 0 6 .0 0 5 .0 0.0

0 8 .10 0 2 .0 0 8 .1 0 0 .0 0 2 .1 0.1

0 2 .15 0 8 .1 0 2 .1 0 5 .1 0 7 .1 0.1

0 6 .17 0 4 .13 0 5 .20 0 7 .1 0 0 .1 0.2

0 6 .20 0 4 .1 0 7 .2 0 0 .1 0 2 .2 0 4 .2 0.2

0 2 .24 0 8 .19 0 0 .28 0 2 .2 0 4 .2 0 6 .2 0 8 .2 0.2

0 4 .28 0 6 .22 0 4 .33 0 6 .2 0 8 .2 0 0 .2 0 2 .3 0.3

0 6 .32 0 4 .25 0 6 .38 0 8 .2 0 0 .2 0 2 .3 0 5 .3 0 7 .3 0.3

0 6 .37 0 4 .29 0 0 .44 0 2 .3 0 5 .3 0 7 .3 0 0 .3 0 3 .4 0.4

0 4 .43 0 6 .34 0 5 .51 0 7 .3 0 0 .3 0 3 .4 0 6 .4 0 9 .4 0.4

0 2 .49 0 8 .39 0 0 .58 0 3 .4 0 6 .4 0 9 .4 0 2 .4 0.5 0.55

0 4 .55 0 6 .4 0 6 .6 0 9 .4 0 2 .4 0 5 .5 0 0 .5 0 4 .6 0.6

0 2 .64 0 8 .51 0 2 .76 0 5 .5 0 0 .5 0 4 .6 0 0 .6 0 6 .7 0.7

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

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

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

National

Agronomy

Manual

Part 502 Wind Erosion

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, Krd, tables 502–31

Exhibit 502–6 Random roughness factor, Krr, 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 developed) 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 = <134 502–32
(190-V-NAM, 3rd Ed., October 2002) 502–iii

National

Agronomy

Manual

Part 502 Wind Erosion

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 502–56

(190-V-NAM, 3rd Ed., October 2002) 502–1 

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 provides 

guidance 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 wind 

erosion 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 is 

conducted 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 eroded 

areas 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 erosion 

is 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 Erosion
502–2 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 erodible 

soils 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 the 

influence 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 or 

embed 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 on 

soil 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 direction 

varies 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 of 

clods 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

Suspension
National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

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 is 

continuing 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 losses 

from 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 scientific 

research 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 

Part 502 Wind Erosion

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 on 

preponderance (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 the 

inherent 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, and 

non-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 E1 for tillage-induced oriented 

roughness, Krd (ridges) and random roughness, Krr

(cloddiness). The value of K is calculated by multiplying Krd times Krr. (K = Krd x Krr). 
National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

Step 3: E IKC 3 =

E IKCL 4 =

E IKCLV 5 =

Factor C adjusts E2 for the local climatic factor. 

Step 4: 

Factor L adjusts E3 for unsheltered distance. 

Step 5: 

Factor V adjusts E4 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 this 

specific 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 management 

period procedure will be used to determine if other conservation systems, 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 

Part 502 Wind Erosion

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 wind 

energy values are entered on the form in the column identified % EWE. 

Estimates for management periods less than 1 year in 

duration 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 more 

specific 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 the 

management 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 WEQ

ARS 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 determine 

how 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 by 

texture 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 calculations

The 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 acre 

per 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) for 

most 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 to 

include 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 the 

NRCS 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 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. 
National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

Subpart 502D WEQ Factors

502.30 The wind erosion estimate, E

The 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, and 

V. 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 conditions 

through 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 period 

conditions 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 period 

estimates 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 

Part 502 Wind Erosion

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 

Part 502 Wind Erosion

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

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, the 

adjustment 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 ensures 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 soil 

sieving 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 direction
502–10 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

• 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 to 

abrasion, 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 allow 

saltation 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

Krd 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 Kr value is based on a standard ridge height to ridge 

spacing 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, Krd, from ridge roughness, Kr, (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 6 810 12

Soil ridge roughness factor, Krd

Soil ridge roughness Kr (inches)

Kr=4(hxh)/s h=ridge height in inches s=ridge spacing in inches

I=310

I=250 

I=220 

I=180 

I=134 

I<134 
National

Agronomy

Manual

Part 502 Wind Erosion

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

4) that relate ridge roughness, Kr, to a soil ridge roughness 

factor, Krd, (Skidmore 1965; Skidmore and Woodruff 1968;

Woodruff and Siddoway 1965; and Hagen 1996).

The Kr curves are the basis for charts and tables used to 

determine Krd 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 Krd 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 Krd is 0.5. But when the prevailing erosive wind

direction is parallel to those ridges, the Krd 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 Krd factor with consideration for preponderance 

(erosive wind energy 60% parallel and 40% perpendicular 

to 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, thus 

making 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 Krr factor accounts for random roughness. 

Random roughness is the nonoriented surface roughness 

that 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 be 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 Krd factor for ridges and Krr 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 Krd factor was determined to be 0.8. Using

table 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 

Part 502 Wind Erosion

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

WEQ 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, their 

associated 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. One 

method 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 any 

given 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 monthly 

precipitation 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-values
National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

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 and 

regional 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 the 

Field 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 used 

to adjust for the effects of irrigation and utilize this procedure and the procedure for adjusting the I factor, for all 

plan 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 management 

period, 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 textured 

soil, 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 

Part 502 Wind Erosion

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 being 

prepared. Because V is considered after L in the 5-step solution of the equation (502.22), the unsheltered distance is 

always 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 point 

may 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 wind

erosion direction

Figure 502-7 Unsheltered distaqnce L – windbreak or barrier 

L

Windbreak

Prevailing wind

10 H Sheltered area L = 0

erosion direction
National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

4. When a properly designed wind stripcropping system 

is applied, alternate strips are protected during critical 

wind erosion periods 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 the 

critical wind erosion period. The direction is usually expressed as one of the 16 compass points. When predicting 

erosion 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 the 

prevailing 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 that 

account 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 

22.5o 1.08 

45o 1.41 

67.5o 2.61 

90o 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 area
502–16 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

502.35 Vegetative cover factor, V

The 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 to 

determine 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 or 

seasons. 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 determine 

quantity 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 determine 

residue 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 SGe 

curve. 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 

Part 502 Wind Erosion

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

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 of 

the 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. Random 

roughness 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 and 

approaching 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 

Part 502 Wind Erosion

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 treatment 

for 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 

Part 502 Wind Erosion

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

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 

Watermelons 
502–20 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion
(190-V-NAM, 3rd Ed., October 2002) 502–21 

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 0.6 
502–22 (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 

wetness 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 rating. 

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 irrigated 

soils 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. 
(190-V-NAM, 3rd Ed., October 2002) 502–23 

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 determinations. However, the results are not as consistent as those achieved by the electric motor-driven rotary sieve. If the objective 

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 

Part 502 Wind Erosion

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 — — — — — — — — — 
(190-V-NAM, 3rd Ed., October 2002) 502–25 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 

S 2 ieve size (mm) < 4 0.4 . 3 42-.8 . 4 84-2.8 2 7 .83-6. 6 7 .4-12. > 4 12. %>0.8

1st seiving

(weight

Percent of total

2nd seiving

( ) weight

Percent of total
502–26 (190-V-NAM, 3rd Ed., October 2002)

Exhibit 502–4 Ridge roughness factor, Krd, 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 12

Soil ridge roughness factor, Krd

Soil ridge roughness, Kr (inches)

Angle of deviation=0 degrees

I=310

I=250

I=220

I=180

I=134

I<134
(190-V-NAM, 3rd Ed., October 2002) 502–27

National

Agronomy

Manual

Part 502 Wind Erosion

Exhibit 502–4 Ridge roughness factor, Krd, 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 12

Soil ridge roughness factor, Krd

Soil ridge roughness, Kr (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 = 4( ) ×
502–28 (190-V-NAM, 3rd Ed., October 2002)

National

Agronomy

Manual

Part 502 Wind Erosion

Exhibit 502–4 Ridge roughness factor, Krd, 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 12

Soil ridge roughness factor, Krd

Soil ridge roughness, Kr (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 = 4( ) ×
(190-V-NAM, 3rd Ed., October 2002) 502–29

National

Agronomy

Manual

Part 502 Wind Erosion

Exhibit 502–4 Ridge roughness factor, Krd, 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 12

Soil ridge roughness factor, Krd

Soil ridge roughness, Kr (inches)

Angle of deviation=67.5 degrees

I=310

I=250

I=220

I=160 & 180

I=134

I<134
502–30 (190-V-NAM, 3rd Ed., October 2002)

National

Agronomy

Manual

Part 502 Wind Erosion

Exhibit 502–4 Ridge roughness factor, Krd, 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 12

Soil ridge roughness factor, Krd

Soil ridge roughness, Kr (inches)

Angle of deviation=90 degrees

I=310

I=250

I=220

I=160 & 180

I=134

I<134
(190-V-NAM, 3rd Ed., October 2002) 502–31 

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 Tables
502–32 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–33 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–34 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–35 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

. 

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 wind. 
502–36 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–37 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–38 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–39 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–40 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–41 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–42 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–43 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–44 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(190-V-NAM, 3rd Ed., October 2002) 502–45 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
502–46 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion 

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 wind. 

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 wind. 
(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 by

Water: 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, Krr, 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 2

Krr, 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 (Krr) for random roughness. Krr 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 Krr 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 0.22
502–48 (190-V-NAM, 3rd Ed., October 2002)

National

Agronomy

Manual

Part 502 Wind Erosion

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 1.20
(190-V-NAM, 3rd Ed., October 2002) 502–49

National

Agronomy

Manual

Part 502 Wind Erosion

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 95.8 100.0
502–50 (190-V-NAM, 3rd Ed., October 2002)

NRCS - WEQ CALCULATIONS, Version 5 Producer: Iam Windy Planner: mas Location: Mose Lake Tract: 123 Field: 1 Crop Rotation: Corn Climate Data Station: WA, MOSES LAKE, old Site "C" Value: 50 Tillage Direction (NS/EW): ns Length/width ratio: 1 Field Direction (NS/EW): ew Field Width (Ft.): 2640 Irrigation (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 Erosion Dates No. of "I" Dev. Ht. Sp. "Krd" "Krr" Dev. Prep. WED "L" "V" "E" EWE "IF" 

Begin End (#) (t/ac) (deg) (in.) (in.) (factor) (factor) (deg) (factor) (factor) (ft) (lbs/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 1/2/99 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 

3/15/99 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 3/15/99 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 

4/1/99 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 4/1/99 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 

4/10/99 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 4/15/99 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 4/30/99 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 5/15/99 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 5/15/99 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 5/30/99 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 6/14/99 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 6/29/99 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 

10/15/99 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 

11/1/99 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 11/1/99 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 
(190-V-NAM, 3rd Ed., October 2002) 502–51

National

Agronomy

Manual

Part 502 Wind Erosion

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. Following 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 selection
502–52 (190-V-NAM, 3rd Ed., October 2002)

National

Agronomy

Manual

Part 502 Wind Erosion

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 weather

stations. 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 factors
(190-V-NAM, 3rd Ed., October 2002) 502–53

National

Agronomy

Manual

Part 502 Wind Erosion

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 = 51.8
502–54 (190-V-NAM, 3rd Ed., October 2002)

National

Agronomy

Manual

Part 502 Wind Erosion

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 table
(190-V-NAM, 3rd Ed., October 2002) 502–55

National

Agronomy

Manual

Part 502 Wind Erosion

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 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 1.49 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

Part 502 Wind Erosion

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 the

long 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 Peanuts 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 mixtures 
502–58 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Flat small grain (reference condition)

Flat winter wheat residue, 10-inch long randomly distributed

Standing winter 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) 
(190-V-NAM, 3rd Ed., October 2002) 502–59 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Days after emergence 4/_

Flat small grain (reference condition—dry)

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 4,000

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.

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 small grain—ridged surface 2/

Growing small grain—flat surface 1/

10

1 7 15 20 30 40 45

Spring Wheat 1 7 16 21 30 35 48 60

Winter Wheat

Growing small grain (lb/ac) 3/

_

_

_

Figure a–2 Flat small grain equivalents of growing small grain 
502–60 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

100 200 300 400 500 700 1,000 2,000 3,000 4,000 6,000 10,000 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% stalk, 40% fines) 

Standing corn (40% stalks, 60% finer residue)

Flat small grain (reference condition—dry)

 _
(190-V-NAM, 3rd Ed., October 2002) 502–61 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 

Part 502 Wind Erosion

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

Flat small grain (reference condition—dry)

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

Growing corn—rows parallel to wind

Growing grain sorghum — rows

perpendicular to wind

Growing corn—rows perpendicular to wind

1 7 15 20 30 38 45 60

 

Days after emergence _1/
(190-V-NAM, 3rd Ed., October 2002) 502–63 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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)

Growing corn—rows perpendicular to wind (24,000 per acre)

1 2 3 4 5 6 7 8 10 15

30

50

60

70

150

300

400

500

600

700

1,500

2,000

3,000

4,000
502–64 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

Flat small grain (reference condition)

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

40 50 60 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.

5,000
(190-V-NAM, 3rd Ed., October 2002) 502–65 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 grain (ref. con)

4,000 20,000

 _

_

Flat grain sorghum stalks 

Standing grain sorghum stalks 
502–66 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

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 residue

Standing sudan stubble
(190-V-NAM, 3rd Ed., October 2002) 502–67 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Figure b–1 Flat small grain equivalents of alfalfa 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

30 40 50 60 70 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, sweetclover flat1

Standing alfalfa residue; stalks only

7,000
502–68 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 random

Random flat residue

Flat small grain (reference condition)
(190-V-NAM, 3rd Ed., October 2002) 502–69 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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—growing in rows parallel to the wind.

Flat small grain (reference condition)

Days after emergence 1/

2 3 4 5 6 7 8 10 20 30 40 50 70 100 200 300 400 600 1,000 2,000 4,000

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 

Part 502 Wind Erosion

Figure b–5 Flat small grain equivalents of buckwheat 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

40 50 60 80 70 100 200 300 400 500 700 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 buckwheat residue—random

 
(190-V-NAM, 3rd Ed., October 2002) 502–71 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 small grain (reference condition—dry)

Standing cotton stubble—13.5 inches high —30 inch rows—perpendicular to wind

Flat cotton residue, 10 inches long —randomly distributed

20,000
502–72 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

10 100 200 30 40 50 70 300 400 600 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 (reference condition—dry)

1 2 3 4 5 6 7

50

60

80

100

800

600

500

400

300

20
(190-V-NAM, 3rd Ed., October 2002) 502–73

National

Agronomy

Manual

Part 502 Wind Erosion

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

Growing cotton — rows perpendicular to wind (48,500 plants per acre)

Growing cotton — rows parallel to wind (48,500 plants per acre)

6,000

4,000

3,000

2,000

1,000

700

600

500

400

300

200

10

1 2 40 50 60 80 100

Time after emergence — days 

Equivalent flat small grain residue (lb/ac)

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

1,500

150

100

80

70

60

50

40

30

20

34 7 5 6 9 10 15 20 30

 
502–74 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Figure b–9 Flat small grain equivalents of flax 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

30 40 50 60 80 100 200 300 400 500 700 1,000 70 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 — random
(190-V-NAM, 3rd Ed., October 2002) 502–75 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Figure b–10 Turnip and mint residue 

 (Reserved)
502–76 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 mustard residue, randomly distributed 

Flat small grain (reference condition — dry)

Standing mustard stubble, perpendicular to wind

 
(190-V-NAM, 3rd Ed., October 2002) 502–77 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 (reference condition — dry)

4,000 20,000

Peanuts

Guar or sesame
502–78 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 to wind direction,

stalks oriented to wind direction.

Source: Armburst and Lyles, 1984 — unpublished.

600

Flat small grain (reference condition — dry)

2 3 4 5 6 7 8 20 30 40 50 200 2,000 300 4,000 

60

80

100

800

1,000

Growing peanuts—rows perpendicular to wind 
(190-V-NAM, 3rd Ed., October 2002) 502–79 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 (48,500 per acre)

1 2 3 4 5 6 7 8 10 15

50

60

400

500

600

700

 
502–80 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 small grain (reference condition)
(190-V-NAM, 3rd Ed., October 2002) 502–81 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

100 300 400 500 700 1,000 2,000 3,000 200 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 randomly distributded
502–82 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 safflower residue

Standing safflower residue

7,000
(190-V-NAM, 3rd Ed., October 2002) 502–83 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Figure b–18 Flat small grain equivalents of sunflower residue 

Flat small grain (reference condition-dry)

Standing sunflower stubble - 17" high - 30" rows - perpendicular to wind 

Flat sunflower residue - 17" long - randomly distributed

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

200 300 400 500 700 1,000

 

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 

Part 502 Wind Erosion

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 small grain (reference condition - dry)

Cotton burs – flat surface

4,000 20,000

 
(190-V-NAM, 3rd Ed., October 2002) 502–85 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Figure c–2 Flat small grain equivalents of manure 

Wet manure – tilled

Dry manure – tilled

Wet manure – surface applied

Dry manure – surface applied

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 

Part 502 Wind Erosion

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

wheatgrass, needleandthread, blue grama, and buffalograss 

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

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.

10 70

Blue grama 45%, buffalograss 30%, western wheatgrass 25% — 1 inch tall

Western wheat 45% needleandthread 30%, blue grama 25% — 1 inch tall

Big bluestem 60%, little bluestem 30%, side-oats grama 10% — 1 inch tall
(190-V-NAM, 3rd Ed., October 2002) 502–87 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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

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

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 inch

Big bluestem —1 inch
502–88 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 small grain (reference condition)

400 2,000

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 wind 

direction, stalks oriented to wind direction.

Source: Lyles and Allison – 1980 Journal Range Management, 33(2), pages 143–146. 
(190-V-NAM, 3rd Ed., October 2002) 502–89 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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)

500 2,000

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 Bluestem 60%, little bluestem 30%, side-oats grama 10%, all 6 inches

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

Western wheatgrass 45%, needleandthread 30%, blue grama 25%, all 4 inches

either mix

60 70 400

 
502–90 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 small grain (reference condition)

500 2,000

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.

60 70 400

Big bluestem—6 inches (shorter than “properly grazed”) 

Western wheatgrass—4 inches

Buffalograss—2 inches

3000
(190-V-NAM, 3rd Ed., October 2002) 502–91 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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)

500 2,000

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.

60 70 400 3,000 5,000 7,000 10,000

Switchgrass—6 inches (shorter than “properly grazed”)

Blue grama—2 inches

Little bluestem—4 inches

 
502–92 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 small grain (reference condition)

500 2,000

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.

60 70 400

Buffalograss 4 inches

Bluegrama 13 inches

10 20
(190-V-NAM, 3rd Ed., October 2002) 502–93 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

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 condition)

500 2,000

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.

10 20 60 70 400 3,000

45% 13 inches—blue grama; 30% 4 inches— buffalograss; 

25% 17 inches—western wheat grass

45% 17 inches—western wheatgrass; 30% 17 inches needleandthread;

25% 13 inches blue grama