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DU1L CONSERVATION ASSESSING THE NATIONAL RESOURCES INVENTORY Volume ~ Committee on Conservation Needs and Opportunities Board on Agriculture National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1986
National Academy Press 2101 Constitution Avenue, NW Washington, DC 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Insti- tute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to proce- dures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medi- cine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the princi- pal operating agency of both the National Academy of Sciences and the National Acad- emy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. This project was supported under Agreements No. 59-3A75-~57, Soil Conservation Service, and No. 59-32U44045, Science and Education, between the U.S. Department of Agriculture and the National Academy of Sciences. Preparation of the publication was supported by funds from the W. K. Kellogg Foundation. Library of Congress Catalog Card Number 86-60330 International Standard Book Number 0-309-03649-9 Cover photograph courtesy of the U.S. Department of Agriculture, Soil Conservation Service. Printed in the United States of America
Comnu~ee on Conservation Needs and Opportunities M. GORDON WOLMAN (Chairman), The Johns Hopkins University GEORGE W. BAILEY, U.S. Environmental Protection Agency, Athens, Georgia SANDRA S. BATIK, Virginia Polytechnic Institute and State University THOMAS E. FENTON, Iowa State University WILBUR W. FRYE, University of Kentucky WILFORD R. GARDNER, University of Arizona GEORGE W. LANGDALE, U. S. Department of Agriculture, Watkinsville, Georgia WILLIAM E. LARSON, University of Minnesota DONALD K. McCOOL, U.S. Department of Agriculture and Washington State University FRANCIS J. PIERCE, Michigan State University PAUL E. ROSENBERRY, Iowa State University LEO M. WALSH, University of Wisconsin Staff Charles M. Benbrook, Project Officer Carla Carlson, Editor Kenneth Cook, Consultant . . .
Board onA~iculture WILLIAM L. BROWN (Chairman), Pioneer Hi-Bred International, Inc. JOHN A. PINO (Vice Chairman), Inter-American Development Bank PERRY L. ADKISSON, Texas A&M University C. EUGENE ALLEN, University of Minnesota LAWRENCE BOGORAD, Harvard University ERIC L. ELLWOOD, North Carolina State University JOSEPH P. FONTENOT, Virginia Polytechnic Institute and State University RALPH W. F. HARDY, BioTechnica International, Inc., and Cornell University ROGER L. MITCHELL, University of Missouri CHARLES C. MUSCOPLAT, Molecular Genetics, Inc. ELDOR A. PAUL, Michigan State University VERNON W. RUTTAN, University of Minnesota JAMES A. TEER, Welder Wildlife Foundation JAN VAN SCHILFGAARDE, U.S. Department of Agriculture, Fort Collins, Colorado VIRGINIA WALBOT, Stanford University CHARLES M. BENBROOK, Executive Director tv
Preface New information on resource conservation has become available in the last few years that will facilitate the analytical assessment of several important conservation issues. The basic source of much of this new information the 1982 National Resources Inventory (NRI) is the sub- ject of this report. The 1982 NRI, a nationwide U.S. Department of Agriculture (USDA) survey of all nonfederal lands, contains data on approximately 22 parameters, including physical characteristics of the land and the effects of agronomic practices on soil erosion. The survey was teased on observations of approximately one million sites. (The first NRI was completed in 1977. The second was completed in 1982, follow- ing the mandate contained in the Soil and Water Resources Conserva- tion Act of 1977. Throughout this report the term NRI surveys refers to the 1977 and 1982 inventories.) In early 1984, the USDA's Soil Conservation Service (SCS) asked the National Research Council's Board on Agriculture to facilitate the establishment of discussion between the SCS and natural resource experts by providing analyses and recommendations on high-priority conservation issues. The board was asked to evaluate the potential applications of the 1982 NRI, and more specifically to address the fol- lowing: · Identification and classification of erodible and fragile soils; · Identification, methods of measurement, and effects of ephemeral gully erosion; v
vt . sloe; PREFACE Erosion-productivity models and the on-farm total costs of ero- · Need for onsite and offsite soil loss tolerance limits; · Methods to inventory, monitor, and appraise offsite erosion effects; · Definitions and methods for inventorying urban built-up land and potential cropland; · Changes in natural resource use and management since the 1977 NRI; and · Effects and distribution of erosion-control practices. As part of this evaluation the board convened a workshop in July 1984 on technical aspects of the statistical design and content of the 1982 NRI and a national convocation in December 1984, "Physical Dimensions of the Erosion Problem." The project, including development of this report, was executed by the Committee on Conservation Needs and Opportunities under the auspices of the Board on Agriculture. The USDA requested this evaluation project, in part, to ensure that maximum use is made of the 1982 NRI data. The committee foresees a wide variety of potential uses for the data. The range of recommenda- tions in the committee's report also suggests that extensive analysis is required to advance conservation. Some of this new work will come under the category of research, some under policy analysis, and some under program evaluation. All such efforts will contribute additional insights into the effective use of public expenditures in support of conservation. The companion volume to this report, Soil Conservation: Assessing the National Resources Inventory, Volume 2, contains 11 technical papers that were presented at the convocation. The papers and accompanying discussion- all based on data from the 1982 NRI contribute new infor- mation on analytical results and methods, specific applications of con- servation planning and practice, and innovative uses of data in resource policy and decision making. This volume contains the committee's major findings, conclusions, and recommendations on the potential uses of the NRI as well as sug- gestions for future improvements and complementary activities. (The reader should note that in technical discussions throughout this vol- ume, measures are expressed in English rather than metric units. This usage is consistent with the most commonly used NRI data and with erosion prediction models and equations used in soil management.) Chapter 1 identifies five important applications of NFl data and sum- marizes major findings based on the 1982 NR1. Chapter 2 presents
PREFACE . . v'' discussion and recommendations reflecting the committee's conclu- sion that several aspects of NRI data compilation and dissemination should be improved. It also includes recommendations on the use of remote sensing and related technologies in future NRIs, the expansion of NRI coverage to federal lands, and the inclusion of data of potential value in the evaluation of water quality. The last three chapters of the report include more detailed discus- sions on technical aspects of data gathering, analysis, and application. Chapter 3 contains information on the process of erosion and the use of equations to estimate erosion. In Chapter 4 the use of erosion-produc- tivity models and on-farm and off-farm erosion damages are discussed. Chapter 5 includes discussions of the application of conservation prac- tices and the need for an improved land classification system. The committee has commented and made recommendations on a variety of areas involving research, coordination, and administration relating to the NRI and to activities in the field of conservation and land use. Because work related to improvements in the NRI necessitates involvement of a number of agencies, the committee recommends interagency cooperation and coordination. There is much already, but can efforts be improved? The committee also recognizes that many of its suggestions require money and people; both are in short supply. The Executive Summary calls attention to a few particularly important rec- ommendations. The committee is not, however, in a position to evalu- ate priorities in detail. But it has called attention to a broad spectrum of issues, because they warrant attention, despite the reality of con- straints to some immediate solutions. Much remains to be learned about the processes of erosion and sedi- mentation, yet what is now known needs wide application. The com- mittee's goal in issuing this statement is to encourage the widest possible use, consistent with good science, of this important new data set the 1982 NRI. M. Gordon Wolman Chairman
Acknowledgments The committee wishes to express its appreciation to the many indi- viduals who participated in the July 1989= planning workshop and in the convocation "Physical Dimensions of the Erosion Problem," which was held the following December. Their formal presentations, discus- sions, and informal exchanges provided the foundation of this report. In undertaking this project, the perspective and insights of Ralph I. McCracken, former deputy chief for Assessment and Planning, Soil Conservation Service (SCS), were invaluable. The cooperation of Gary Nordstrom, director of the Resources Inventory Division of the SCS, also was of great aid to the committee throughout all stages of the project. In addition, the committee expresses its appreciation to William E. Larson, University of Minnesota at St. Paul, and Robert H. Dowdy, U.S. Department of Agriculture-Agricultural Research Service and University of Minnesota at St. Paul, for quickly and efficiently generat- ing and formatting tables based on data from the 1982 National Resources Inventory. The committee members wish to express special thanks to Carla Carlson and Kenneth Cook for their hours of writing and editing to fashion this report, and particularly to Charles M. Benbrook for his unwavering encouragement and enthusiasm. zx
Contents EXECUTIVE SUMMARY 1. SCOPE AND CONTENT OF THE 1982 NRI Uses of the 1982 NRI Information from the 1982 NRI 2. IMPROVING FEDERAL RESOURCE ASSESSMENT EFFORTS Compilation and Dissemination of NRI Data Use of Sensing Technologies in Future NRIs Expansion of NRI Coverage to Federal Lands Inclusion of Data Related to Water Quality . 3. THE MEASURES OF SOIL EROSION NRI Estimates of Sheet and Rill Erosion: The USLE Wind Erosion Estimates Erosion by Concentrated Flow: Ephemeral Gullies Xl · · . X111 1 2 7 19 21 . 26 30 31 34 . 35 54 . 59
Xlt 4. ON-FARM AND OFF-FARM CONSEQUENCES OF SOIL EROSION Effects of Erosion on Production Costs Erosion-Procluctivity Models Soil Erosion and Water Quality 5. ASSESSING CONSERVATION PRACTICES AND LAND CLASSIFICATION SCHEMES Conservation Practices The Lanct Capability Class System Alternative Land Classification Schemes REFERENCES APPENDIX INDEX CONTENTS 62 . . 63 68 72 75 75 85 91 95 99 111
Executive Summary The wearing away of the surface of the land by water and wind can be a gradual but accelerating process. Erosion removes imperceptibly thin layers of fertile soil, rich in nutrients and organic matter, and reduces the ability of plants to thrive in the soil. A reduction in plant growth results in less protective cover for the soil and less plant residue to enrich it. Further erosion occurs, and the process continues. The dan- ger is that erosion can reduce soil productivity so slowly that the seri- ousness of the problem might not be recognized until the land is no longer economically suitable for growing crops. Congress first appropriated funds to study soil erosion in 1928. Research stations were located on the most erodible land in the country. Data were collected on soil characteristics, the effects of erosion on crop yield, and the effects of sediments on water bodies. At the same time drought, depression, and the drama of the Dust Bowl combined to focus public attention on soil conservation. The Soil Conservation Service (SCS) was created in 1935 with the passage of the Soil Conser- vation Act. Much has been learned about soil and the process of erosion during the past 50 years. But as farming and land management methods con- tinue to change with the advance of technology and new demands on agricultural production, our knowledge of erosion must be put into the perspective of these newer methods and technologies. Progress requires that new information be collected by more refined techniques. This information must be applied to new problems and new situations. . . . X27!
xtv EXECUTIVE SUMMARY Analysis of data with more precise and reliable methods will provide an increased scientific and technical understanding of soil erosion, trans- port, and deposition and their effects on crop productivity and water systems an understanding that can be the basis for control of the process of erosion and conservation of the natural resources of the United States. A Basic Conclusion The 1982 National Resources Inventory (NRI) is the most recent of a series of national resource surveys and inventories performed by the SCS. It includes computerized data that represent a statistical sampling of all nonfederal land in the United States. The 1982 NRI and its imme- diate predecessor, the 1977 NRI, are valuable sources of data. While there are limitations of data and analytical equations in the 1982 NRI, the Board on Agriculture's Committee on Soil Conservation Needs and Opportunities emphasizes that these limitations do not significantly constrain the validity or accuracy of many important applications of the NRI. Creative use of the NRI allows conservation analysts and planners to project the degree of erosion control that would be achieved by a wide range of combinations of land use and management practices. It is also valuable in identifying the nature and degree of erosion problems that exist across various production regions. The value to society of soil conservation programs, research, and data compilation efforts stems from the contributions that these activities make to protecting environmental quality and encouraging better man- agement of national resources within agricultural production systems. A continued NRI series has the potential to contribute greatly toward achievement of this basic goal. Some Priorities Given the great potential value of the NRI, the committee believes that considerable effort is warranted to ensure that the NRI be made as strong as possible to best serve its various uses. To this end, the report includes a number of recommendations. While detailed priorities can- not be established, four broad areas are emphasized in the recommen- dations: the scientific teases of the equations used to predict erosion, the enhanced use of the NRI, the relationships between erosion and pro- ductivity and erosion and water quality, and the scope of future NRIs. While each is elaborated in subsequent chapters of the report, the thrusts of these four major areas are briefly stated here.
EXECUTIVE SUMMARY XV Improvements in the scientific bases of the estimates of erosion will enhance future policy decisions. The magnitude of erosion by wind and by ephemeral gullies requires special attention. Attention must also be given to the way that factors in the soil loss equations are evaluated in the field. Research, analysis, and evaluation by the scien- tific community in and out of government are needed. The fruits of such work need to be continually included in the policy process. Supplemental documentation of the 1977 and 1982 surveys, includ- ing details of statistical design and measures of reliability and evalua- tions of the data, is needed to increase the accessibility and potential use of the NRI. Appropriate studies would involve analyses of the data illustrating the applicability at varying spatial scales as well as evalua- tion of the sources and magnitude of statistical variability inherent in the sampling and collection of the vast amount of data assembled in the NRI. Estimates of erosion achieve their greatest value when they can be related to the potential effects of erosion on the productivity of the land and on the potential impact of erosion on water bodies. While models have been developed to evaluate where and how erosion affects the potential productivity of the land, additional work is essential to extend and apply such evaluations. Use of the NRI in estimating potential offside impacts of erosion requires development and verification of links between erosion, transport, and deposition of sediments and associated pollutants in runoff. Evaluations of potential onsite and offsite effects in different areas are essential to the precise delineation of policy choices in conservation. To achieve maximum value, a national resources inventory should encompass the country as a whole. The inclusion of appropriate data on federal landslands that were not included in earlier NRIswill provide the broader data base essential in addressing national needs and priorities. New observational techniques and data-handling capa- bilities may enhance future national surveys. Analytical Applications to Support Conservation Program Development The NRI is being used by U.S. Department of Agriculture (USDA) scientists and others as a basic data source in carrying out many impor- tant analyses. The committee has reviewed much of the on-going research using the NRI and recommends that further research using the NRI be applied to
xv' EXECUTIVE SUMMARY · The geographic distribution of the inherent erosion potential of cropland, measured by the physical factors of the Universal Soil Loss Equation (USLE). This work is essential to characterize and understand the severity of erosion-control problems across geographic regions and to evaluate the range of viable solutions; · The distribution and effectiveness of conservation practices cur- rently used by farmers and ranchers; · The development of improved land classification schemes appro- priate to specific uses based on criteria and data derived from USLE data in the 1982 NRI; · The relationship of different land classification schemes and con- servation measures to alternative policy options designed to conserve the land. Erosion Prediction Equations The 1982 NFI has advanced knowledge of conservation needs and, at the same time, highlighted gaps in data collection and empirically based estimation models such as the USLE and the Wind Erosion Equa- tion (WEE). It has raised new questions and has provided a major new data source to use in searching for answers. To support more cost-effective conservation investments, there is a need for an improved understanding of erosion and more accurate data on all its basic forms. Knowledge of erosion by wind and the concen- trated flow of water is particularly limited. Wind erosion estimates in the 1982 NRI must be used with consider- ably more caution than the estimates of sheet and rill erosion based on the USLE. While the wind erosion data can be useful relative indicators of wind erosion hazard, at least in the 10 Great Plains states, estimates of wind erosion losses in many regions are not sufficiently reliable for many uses, such as delineating the degree of erosion hazard as a func- tion of estimated rates of wind erosion. A major commitment, guided by a systematic research strategy' will be necessary to correct method- ological and empirical shortcomings in the WEE. There is a need to use the NRI results in gaining a better understand- ing of another form of erosion known as ephemeral gully erosion, which occurs within natural drainageways and swales. The NRIs con- tain no quantitative data on ephemeral gully erosion the erosion by concentrated flow in gullies that appear intermittently during runoff events. Such erosion, however, may be significant, adversely affecting portions of most sloping fields. For this reason, the committee recom-
EXECUTIVE SUMMARY . . XVlt mends that more accurate and widely applicable measures of ephem- eral gully erosion be developed, with a goal of incorporating new concepts and data into future inventories. Several important refinements are needed in the USLE to further improve its reliability and extend its range of application. Specifically, the committee recommends that accelerated research efforts be directed to · Ensuring that C factors (representing soil cover and management practices in the USLE) accurately predict the erosion control benefits of crop rotation and cover and management practices; · Improving the accuracy of field-level determinations of C factors by measuring and/or predicting the actual extent of soil cover provided by crop residues in each year of rotation; · Developing data and practical methods for incorporating adjust- ments into the USLE for application to areas of the country where frozen soils, snowmelt, or irrigation substantially alter runoff or erod- ibility and, subsequently, the estimated rates of erosion using the USLE. Leveraging Beneficial Uses of the NRI The committee believes that the NRIs have been underutilized. The USDA is to be commended, however, for steps it has already taken to ensure that the 1982 NRI is accessible and useful to a diversity of ana- lysts and institutions. The USDA's efforts would be more cost-effective and successful if a number of additional steps were taken, including · Publication of supplemental documentation on both the 1977 and 1982 NRIs addressing in detail survey design and content, methods to test statistical reliability, and caveats associated with common applica- tions of the raw data files; · Provision of a supplemental tape containing the individual factors of the WEE not recorded on the basic data tapes and the codes needed to cross-reference NRI sample points with other key data sources; at a minimum, these sources should include the SCS Soils-5 file and the hydrogeological data base; · Publication of a supplemental volume of 1977 and 1982 NRI statis- tics utilizing a variety of table formats based on ranges of inherent erodibility rather than the Land Capability Class System.
XVII! EXECUTIVE SUMMARY U n ~ e r s t a n ~ i n g t h e E r o s i o n - P r o ~ u c t i v i ~ y R e Z a ~ i o n s h i p Previous recommendations will enhance the ability of researchers to more fully employ the NRI as a basic data source. In particular, the NRI can make possible significant methodological and empirical advances in research that will explore the relationship between erosion and pro- ductivity. This work is vital, because the susceptibility of soils to ero- sion-induced damage is variable; at times it is highly variable. The control of erosion on all cropland, where desirable, can be a basic goal; but efforts are most critically needed to identify those soils now incur- ring accelerating or, perhaps, permanent damage from erosion. New erosion-productivity models, some of which are heavily reliant on the NRI, may soon reach a level of refinement adequate to make possible a long-overdue reassessment of soil loss tolerance limits (T). Better T values should, in turn, directly improve USDA's ability to more accu- rately classify cropland according to its susceptibility to erosion dam- age. Assessing AgncuZlural Runoffin Relation to Water Quality Conservation challenges have changed during the last 50 years as a result of progressive technological change in production methods and the change from diversified to specialized agriculture. The change from rotational cropping involving cover crops to monoculture or row crops only, for example, can significantly alter runoff and erosion. Most tech- nological advances to improve yields have had, in different regions and for different crops, both positive and negative effects on erosion-con- trol efforts. By increasing yields and making possible denser plantings, technology has reduced erosion by contributing to more complete soil cover. Some of the same technologies, however, have introduced land use practices that have been very damaging to soils ill-suited to inten- sive, continuous row-crop production. Perhaps the most important, relatively new conservation challenge is the need to much more carefully monitor, understand, and mitigate water pollution from agricultural sources. As scientists and farmers improve techniques to keep water on the land, infiltration may enhance the recharging of groundwater. However, such an improvement may increase the opportunity for undesirable chemicals and nutrients to move into groundwater. Technological changes in farming methods involving more widespread, intensive uses of inorganic fertilizers and agricultural chemicals have transformed the types of pollutants that agriculture contributes to surface water and groundwater. For exam-
EXECUTIVE SUMMARY XIX pie, nitrates have been found in drinking water supplies in several major farming regions, and scattered reports of herbicides and insecti- cides in groundwater add a new motivation to agricultural manage- ment and conservation efforts. Ample evidence indicates that agricultural sources of water pollution pose significant environmental problems. Better information on the effects of agricultural practices on water quality is essential in devising and implementing strategies for control of these nonpoint sources of pollution. Runoff from the land surface contributes sediments and chemical constituents to water bodies. Both are often considered pollu- tants. The 1982 NRI contains information on land use and conservation practices that are important in estimating the magnitude of these sources of pollution. The NRI can potentially contribute to research and evaluation of offsite as well as onsite effects of erosion. However, nei- ther in the 1982 NRI nor elsewhere is adequate information yet available to translate with confidence measures of eroding soil and related con- stituents to impacts on watercourses. The committee recommends that steps be taken to fully explore ways to more effectively use the 1982 NRI in water quality research. The committee foresees the need and some opportunities to incorporate into future inventories additional data designed to enhance the use of the NRI in conjunction with other data sources and models in the evaluation of offsite effects such as sedimentation and pollution caused by erosion of the land. Magnitude and Scope of Future NR7s The practical application of future NRIs would be expanded by incor- porating improved analytical tools and additional data. The committee has highlighted the need for an improved WEE, incorporation of data and equations to estimate the severity of ephemeral gully erosion on cropland, improved measures relating erosion and productivity, and data necessary to analyze how agricultural management practices affect water quality. In addition to these extensions, the committee believes that future inventories should include appropriate data on federal lands lands that were not included in the 1982 NRI or earlier surveys. The committee believes that the costs incurred by including new data in future NRIs might eventually be offset by cost savings made possible by incorporation of new satellite-based sensing technologies into natu- ral resource-monitoring programs. For example, remote sensing infor- mation can be used as input data to calibrate and run water quality
xx EXECUTIVE SUMMARY models. While recognizing the shortcomings of current technologies, the committee anticipates an expansion in the capability to use remote sensing and other technologies in conjunction with computer-based cartographic systems. It might be possible to develop highly refined, analytical capabilities using a combination of field-level surveys such as the NRI to ensure ground truth and new data from satellites that will be available several times each growing season. New technology should become available to accurately and cost- effectively monitor cropping patterns, rainfall, and erosion occur- rences; assess net recharge to groundwater and the effects of agricultural management practices on groundwater quality; and assess the flow of sediment and other constituents off fields and into water- ways. Efficient and effective acquisition and use of information from a variety of integrated data bases will require close cooperation among a number of agencies in the federal government.
OL ~ CONSE~1ON _ ING THE NATION ~ RESOURCES lNVENlT]RY Abe ma 1