USDA Soil Conservation Service Research Articles

Simulation of Long-Term Water Erosion in Rainfed Croplands of Eastern Washington

Highlights Water erosion in the inland Pacific Northwest was modeled with WEPP for the past (1940–1982) and present (1983–2020). Water erosion decreased from past to present in the study watersheds. Major factors are increased adoption of conservation practices and decrease in large precipitation events. Abstract. Water erosion is an ongoing problem in eastern Washington due to its hilly terrain, highly erodible silt loam soils, rain on thawing soil, and the prevalence of conventional tillage. The region is characterized by a Mediterranean-type climate with warm, dry summers and cool, wet winters. Three distinct precipitation zones, with annual totals low (<380 mm), intermediate (380–460 mm), and high (>460 mm), dictate the area’s crop rotations. A unique 43-year (1940–1982) dataset of winter erosion measured on multiple agricultural fields in Whitman County, eastern Washington, by Verle Kaiser, a USDA Soil Conservation Service agronomist, showed annual erosion rates averaging 53.8 Mg ha-1, far exceeding the current Natural Resources Conservation Service tolerable limit of 11 Mg ha-1 yr–1 for the soils in the area. Kaiser’s field data allowed us to compare the historical field-measured erosion rates with those simulated by the WEPP (Water Erosion Prediction Project) model. Anthropogenic factors, such as tillage and crop rotation, change with time. Conservation tillage, including reduced- and no-till, has been increasingly adopted in eastern Washington since the mid-1980s. The specific objectives of this study were to (1) apply the WEPP model to simulate soil erosion in eastern Washington and evaluate the interactive effects of climate and management, in addition to topography and soil, on water erosion in the study area, and (2) compare the simulation results with Kaiser’s historical field dataset and elucidate the long-term soil erosion trend. The WEPPcloud interface was used to delineate a watershed within each precipitation zone of the study area. Climate inputs were divided into two periods: the past (1939–1982) and the present (1983–2020). Erosion has noticeably decreased from the past to the present, with WEPP simulated annual erosion averaging 13.5, 34.5, and 52.6 Mg ha-1 for the past, and 9.5, 14.1, and 15.5 Mg ha-1 for the present, in the selected watersheds in the low-, intermediate-, and high-precipitation zones, respectively. The decreasing trend was primarily due to the increased adoption of conservation tillage and crop rotation, as well as a decrease in the number of high-intensity precipitation events in the present climate. Keywords: Inland Pacific Northwest, Soil erosion by water, Temporal trend, WEPP.

Estimating WEPP Cropland Erodibility Values From Soil Properties

Highlights Very fine sand is the single most important variable for predicting rill and interrill erodibility values. Slope steepness is the most important property for predicting critical shear for rill erosion. Erodibility prediction equations with the best goodness-of-fits have both soil texture and mineralogy terms. Equations to predict erodibility from texture, organic carbon, cation exchange, slope, and taxonomy are proposed. Abstract. In the late 1980s, the USDA Agricultural Research Service, along with other federal agencies and multiple universities, collaborated to develop a new physically based soil erosion model, the Water Erosion Prediction Project (WEPP) Model. The WEPP model was intended to replace the Universal Soil Loss Equation and was to include estimates for upland runoff and erosion, sediment delivery to first order channels, and runoff and sediment routing through a downstream channel network. The WEPP technology estimated erosion from raindrop splash and sheet flow (interrill erosion) and concentrated channel flow (rill erosion). To make these erosion estimates, WEPP required new soil erodibility values for interrill erodibility (Ki). rill erodibility (Kr), and critical shear (𝜏c) for concentrated flow erosion. The WEPP Core team determined that they needed to estimate these three erodibility values from measurable soil properties for a wide range of soil conditions. To develop relationships between WEPP soil erodibility variables and other soil properties, a field study was carried out using rainfall and runoff simulation to measure the three erodibility values for 36 soils. Sites were identified on croplands from Washington to Georgia and Maine to California, USA for erodibility measurement. Concurrently, the USDA Soil Conservation Service (SCS) carried out detailed soil surveys and laboratory analyses for all sites to provide a large database of soil physical, chemical, and engineering properties. Correlation and regression analyses were carried out to develop relationships between SCS measurable soil properties and WEPP soil erodibility values. This article provides a summary of the field procedures, data analyses, and subsequent predictive equations that were developed. The predictive equations that were finalized in the WEPP User Summary used sand, very fine sand, clay, and organic carbon contents to predict cropland soil erodibility, but the Coefficient of Determination (r2) values were 0.55 or less. More complex predictive equations were developed with soil physical, chemical, mineralogical, and geomorphic properties, with r2 values up to 0.81. Most of the better predictive equations included terms for soil texture and clay mineralogy, often with additional chemical properties. A set of simplified erodibility equations using only the readily available properties of soil texture, organic carbon, cation exchange capacity, slope steepness, and taxonomic order were derived for use within the WEPP Model, with r2 values greater than 0.5 for all three equations for estimating soil erodibility from measurable soil properties. Keywords: Critical Shear, Interrill Erodibility, Rill Erodibility, Soil Properties, WEPP.

Kajian Kebutuhan Air Irigasi Tanaman Jagung (Zea mays L.) Berdasarkan KP-01 dan Metode Thornthwaite-Mather

<p class="JudulAbstrakInggris">Two different methods for determining irrigation water requirement for corn, is KP-01 and Thornthwaite-Mather method. Two Methods have different parameter such as reference crop evapotranspiration (ETo) and effective rainfall. The average ETo value using Penman-Monteith for Thornthwaite-Mather was lower (82,5%) than using Penman Modification method (KP-01) . The ratio of effective rainfall between KP-01 and Thornthwaite-Mather was 33,02%. Corn water irrigation requirement for a pattern planting based on KP-01 is 806,96 mm, while corn water irrigation requirement based on Thornthwaite-Mather method is 254,4125 mm. Corn water irrigation requirement using KP-01 is higher than Thornthwaite-Mather because effective rainfall method for KP-01 (using USDA Soil Conservation Service) is lower than rainfall effective for Thornthwaite-Mather.</p>

Assessment of hydrological response as a function of LULC change and climatic variability in the catchment of the Wular Lake, J&K, using geospatial technique

The present study aims to identify the relationship and effect of various hydrological processes on the Wular Lake ecosystem. The study focused on assessment of combined hydrological response of LULC change and climatic variability in the upper catchment of Wular Lake. Multi-temporal satellite data were used for assessment of temporal dynamics of the lake catchment. The spatiotemporal pattern of annual soil loss and sediment yield has been assessed using the Revised Universal Soil Loss Equation approach and sediment delivery ratio adopted from USDA Soil Conservation Service in GIS environment. The runoff was estimated in the watershed using SCS curve number. The main impelling forces that led to the changes in land use/land cover in the catchment is mainly due to increased human activities, which ultimately leads to the increased erosion and sediment yield. The anticipated mean annual soil loss which was found 123.23 t ha−1 year−1 in the year 1992 increased to 942.52 t ha−1 year−1 in the year 2013. Similarly, estimated mean annual sediment yield also indicated an increase from 34.7 t ha−1 year−1 in the year 1992 to 233.4 t ha−1 year−1 in the year 2013. In addition, the decrease in rainfall from the last 35 years has led to the decline in runoff and consequent reduction in the surface water supply. The results of the present study indicate due to the changes in LULC and consequent hydrological changes like decreased runoff, increased erosion and sedimentation reduce the water holding capacity of lake day by day, thus leading to its deterioration.

Evaluation of Three Models for Simulating Pesticide Runoff from Irrigated Agricultural Fields.

Three models were evaluated for their accuracy in simulating pesticide runoff at the edge of agricultural fields: Pesticide Root Zone Model (PRZM), Root Zone Water Quality Model (RZWQM), and OpusCZ. Modeling results on runoff volume, sediment erosion, and pesticide loss were compared with measurements taken from field studies. Models were also compared on their theoretical foundations and ease of use. For runoff events generated by sprinkler irrigation and rainfall, all models performed equally well with small errors in simulating water, sediment, and pesticide runoff. The mean absolute percentage errors (MAPEs) were between 3 and 161%. For flood irrigation, OpusCZ simulated runoff and pesticide mass with the highest accuracy, followed by RZWQM and PRZM, likely owning to its unique hydrological algorithm for runoff simulations during flood irrigation. Simulation results from cold model runs by OpusCZ and RZWQM using measured values for model inputs matched closely to the observed values. The MAPE ranged from 28 to 384 and 42 to 168% for OpusCZ and RZWQM, respectively. These satisfactory model outputs showed the models' abilities in mimicking reality. Theoretical evaluations indicated that OpusCZ and RZWQM use mechanistic approaches for hydrology simulation, output data on a subdaily time-step, and were able to simulate management practices and subsurface flow via tile drainage. In contrast, PRZM operates at daily time-step and simulates surface runoff using the USDA Soil Conservation Service's curve number method. Among the three models, OpusCZ and RZWQM were suitable for simulating pesticide runoff in semiarid areas where agriculture is heavily dependent on irrigation.

Development of a Modified SMA Based MSCS-CN Model for Runoff Estimation

The Soil Conservation Service Curve Number (SCS-CN) method developed by the USDA-Soil Conservation Service (SCS, 1972) is widely used for the estimation of direct runoff for a given rainfall event from small agricultural watersheds. The initial soil moisture plays an important role in re-structuring of the SCS-CN method and enables us to prevent unreasonable sudden jump in runoff estimation and this has prompted the concept of soil moisture accounting (SMA) procedure to develop improved SCS-CN based models. Applying the concept of SMA procedure and changed parameterization, Michel et al. Water Resour Res 41(2):1–6 (2005) developed an improved SCS-CN model (MSCS-CN), which could be thought of an improvement over the existing SCS-CN method; however, their model still inherits several conceptual limitations and inconsistencies. Therefore, in this study an attempt is made to propose an improved SMA based SCS-CN-inspired model (MMSCS-CN) model incorporating a continuous function for initial soil moisture and test its suitability over the MSCS-CN and SCS-CN model using a large dataset from US watersheds. Using, Nash and Sutcliffe efficiency (NSE) and root mean square error (RMSE) of these models, the overall performance is further evaluated using rank grading system, and it is found that the MMSCS-CN scores highest mark (95; overall rank I) followed by MSCS-CN with 61 (overall rank II), and SCS-CN model with 51 mark (overall rank III) out of the maximum 105. This study shows that the proposed MMSCS-CN model has several advantages and performs better than the MSCS-CN and the existing SCS-CN model.

Profiles in History

1971 & 1996 2014 Dr. Victor Carlisle stands at the graduated concrete post near Belle Glade, FL, demonstrating soil subsidence between 1971 and 1996. Dr. Victor W. Carlisle (1922–2006), Soils Professor at the University of Florida (UF), taught several summer soil courses during his career. One of these courses encompassed field trips covering Florida soils from the southern tip of the peninsula to the panhandle. Many soils were observed on these field trips. A stop was always made in the Belle Glade area in southern Florida to see organic soils. Retired soil scientist Kenneth Johnson at age 90 in Red Bluff, California on May 31, 2014. When the organic soils, or Histosols, of the Everglades were drained for agricultural use in the early 1900s, subsidence was initiated and has continued to the present time. In 1924, a graduated concrete post was driven to the underlying bedrock at the University of Florida/IFAS Everglades Research and Education Center near Belle Glade. When it was installed, the soil surface was level with the top of the post, which is 9 feet in length. Dr. Carlisle, shown at the landmark post in 1971 and in 1996, always took his students to the post to demonstrate how oxidation of organic matter has resulted in soil subsidence. Since 1924 the soil has subsided more than seven feet. The once deep organic soils, Torry muck (euic, hyperthermic Typic Haplosaprists) are now moderately deep organic soils over limestone bedrock, probably Lauderhill muck (euic, hyperthermic Lithic Haplosaprists). Dr. Carlisle was featured as the “Father of Pedology in Florida” in SSSA's book Soils of Florida, as he was the coordinator of the Soil Characterization Laboratory at the UF, which sampled the soils above. Contributed by Frank Watts, Pedologist, CPSC, AAA Soil Consultants, Hilliard, FL Kenneth Everett Johnson, known to many as Ken Johnson, passed away on July 23, 2014. The following is a personal contribution from SSSA member Kerry Arroues. In the summer of 1970 Ken Johnson helped a young Soil Conservation Service student employee by introducing him to a couple of days of soil survey field work in the arid parts of Modoc and Lassen Counties in northeastern California. I was that young employee who Ken Johnson exposed to the incredible world of soils and the potential for a fulfilling career as a soil scientist in the National Cooperative Soil Survey Program. Many decades later, after a long soil science career working for the USDA–Soil Conservation Service and the Natural Resources Conservation Service, I understand the importance of being a mentor to future generations of soil scientists. Shortly after graduating from high school, Ken first served his country in the US Army during the Korean War, where he developed his mechanical aptitude working on airplanes in the Civil Air Patrol. After military service, Ken graduated from Oregon State University in Corvallis, majoring in agriculture and soil science. Upon graduating from OSU, Ken started his career as a soil scientist with the USDA–Soil Conservation Service. Ken and his wife raised five children as he worked in Oregon and Alabama before settling down in Susanville and eventually in Redding, CA. Ken worked for both the Soil Conservation Service and the Forest Service as a soil scientist. Working on old cars was one of his favorite past times. While out in the field he was able to find old car parts and, eventually, he had enough to complete his 1920 Model T Ford. He had a very unique ability to fix cars and was always willing to tinker with anything broken. He also loved to sing in his church choir and tell and retell endless jokes. I am indebted to Ken Johnson for his influence on me long ago and the subsequent rewarding and fulfilling career that his guidance helped me find. Contributed by Kerry Arroues, CPSS, retired USDA-NRCS Soil Scientist, Hanford, CA.

Profiles in History

1883 1949 Agricultural Map of California, 1883. The origins of the Soil Survey in California trace back beyond the first soil surveys of the US Bureau of Soils in 1899 to the founding of soil science itself. California's Eugene W. Hilgard at the University of California at Berkeley was a pioneer in many areas of soil science and is referred to as the cofounder of soil science by Hans Jenny and others. Hilgard also developed an original vision for soil surveys in California. A Conservation Survey of Stanford University's Agricultural Lands in 1949. The first soil survey map produced in California depicts the agricultural soil regions of the state. Shown here as “Agricultural Map of California,” this product was “compiled from many sources by R.H. Loughridge, Ph.D., Special Agent, under the direction of Eug. W. Hilgard, Ph.D., Special Agent in charge of cotton production” in 1883. The map was in essence a depiction of major land resource areas (MLRAs) in the state. Hilgard speculated that California's Great Central Valley would be good for growing cotton and was in charge of helping develop cotton production the state. This generalized map depicts the marsh and tule lands in the Delta and along rivers in light green. The alluvial lands of the Great Central Valley are shown in medium green. Note the lakes in the southern part of the valley at the time, which no longer exist today. Prominent adobe lands are shown in dark brown, lower Sierra foothills in red, the upper Sierra foothills in light pink, and the Sierra Nevada Mountains in dark pink. The Coast Ranges are in orange-brown with their chief valleys in yellow. The deserts are in light tan. Dark green areas depict redwood forests. The marsh lands around the San Francisco bay are not identified, possibly because they were too small in scale. The map displays remarkable knowledge of the soils and landforms of California for 1883. Contributed by Terry D. Cook and William R. Reed, Professional Soil Scientists Association of California. The formation of the USDA-Soil Conservation Service (SCS) under the New Deal in 1935 brought many changes to the Soil Survey in California. SCS set up headquarters for California and Nevada in Berkeley, CA and hired Dr. Stanley Cosby from the university to be the Regional Soil Scientist. Leonard Wholetz was hired as his assistant. One of his first assignments was a demonstration project in Santa Paula where erosion was severe. Many similar projects using conservation surveys would be produced through the early 1950s. The SCS quickly changed to making conservation needs surveys from standard soil surveys. These were quickly done and delivered to the conservationists for immediate use. The surveys were generally small areas with severe erosion problems. Twelve Civilian Conservation Corps camps were set up in California to implement conservation practices. Most were in central and southern California and in coastal areas. Many soil scientists went to work for the SCS. The work of the UC Division of Soils and the Bureau of Chemistry and Soils continued standard soil surveys, but there were fewer areas mapped than in the 1920s. The map shown here is one of the few remaining conservation maps from California. It included the Stanford University property and was made to assist Stanford in management of the lands. Soil depth, slope, erosion level, and capability unit were the extent of the information gathered. It was rapidly assembled and put to use immediately. From 1935 to 1952 there were likely thousands of these conservation maps made in California alone. They were used extensively to control serious erosion, mostly on private lands. Apparently an order was sent out by SCS around 1960 to dispose of them. Very few conservation maps remain, and the ones that do remain are maps of larger areas like this one at Stanford University. It was bound in a small book, rather than as a loose map, allowing it incidentally to survive on a shelf with other materials. Contributed by Terry D. Cook and William R. Reed, Professional Soil Scientists Association of California.

Curve Number Method: Time to Think Anew?

As most hydrologists know, the curve number method is popular, enduring, ubiquitous, versatile, and widely used to calculate event rainfall-runoff volumes. To many, it is quite comforting. It is also badly in need of some updating. Originally created on short notice in the mid 1950s for the ad hoc needs of Public Law 566, the curve number method was targeted at and developed for agricultural uplands and overland flow. With its origins in the USDA, PL566 (a USDA program) was preordained for acceptance, and its handbook-guided use in planning and design led to millions of dollars of cost sharing and grants. Thus it was accepted without much question. Happily, it also fit nicely into a waiting technologic niche in the emerging science and profession of hydrology. It had an assuring aura of cutting edge. In this setting, it was too big to fail. As a working man’s hydrology, it is simple, transparent, and appealing, and it is true to its USDA origins in that soils and land condition play major roles. At that time, an alternative model with the benefits of the curve number method was not available, and there still is not. Within its genus, it is monotypic. It serves as the poster boy and hypothesis for rainfall-runoff, and its terms and concepts (however approximate) serve a vocabulary role for the general hydrology case. The curve number concept was developed in the “quiet past” of Lincoln’s statement and may be “inadequate for the stormy present” of modern hydrologic engineering. It is overdue for an overhaul for several compelling reasons. Experiences with the procedure and comparisons with other rainfall runoff studies over the past 50 years have been both eyeopening and unsettling. Many tables and assumptions posted in the foundation documents [NEH4/630; USDA Soil Conservation Service (1954); USDA Natural Resource Conservation Service (2003)] are not matched by on-the-ground data or supported by critical analysis. Curve numbers (CN) tables based on soils and cover are often wide of the mark, a condition exacerbated by the model’s demonstrated primary sensitivity to the choice of the CN. Furthermore, some watersheds were found to perform quite differently from the basic CN runoff response patterns, leading to great differences between the model and reality. The inferred internal infiltration sequence is questionable. The hydrologic soils classifications, a supposed strong point considering the source agency, seem internally inconsistent and vague. These observations, and a host of others like them, become more common as applications depart from the rain-fed, agricultural upland, large-storm settings that spawned the original development. The expository literature continues to mount (Hawkins et al. 2009). At the same time, temptations to apply it well beyond its simple upland agriculture origins have grown in response to modern needs. It has been an easy off-the-shelf filler hydrology for rainfall-runoff and other targets, such as urban and river basin hydrology and agricultural and water quality models. Many of the latter apply creative extensions of the CN method to daily time-step continuous models. It is now comfortably embedded in flood control, environmental impact, and sediment-erosion methodologies world-wide. Finally, times and expectations have changed. There are now five decades more data upon which to base methodologies, much better means of analyses, and a greater variety of recognized lands and land uses. Equally important, as a profession, more is expected now than was expected in the mid 1950s. In its birth years, the CN method did not experience professional peer review, and most of the foundation data and calculations have since been lost. Alas, it was established by administrative fiat. This is now an age that values open communications, scientific cross-pollination, freedom of information, consilience, stakeholder participation, data sharing, and intellectual honesty. Is it not time to nudge quality and credibility up a notch? How and under what auspices might such needed renovations occur? Considering its development, origins, and history, and in a spirit of noblesse oblige, an unavoidable onus of leadership rests with the USDA. Via the image and authority of the USDA, the user world has followed its lead for over 50 years, but in the 21st century the user community should be an active contributor, too, perhaps through professional societies such as ASCE, American Society of Agriculture and Biological Engineers (ASABE), and American Water Resources Association (AWRA). It is no small task and promises to create discomfort. These issues are raised here to provide food for thought, grist for discussion, and, hopefully, reader feedback in these pages.

Profiles in History

2012 Members of the Professional Soil Classifiers Association of Alabama (PSCAA) convened on the Gulf Coast in Baldwin County for their 37th annual meeting and field tour in June 2012. The field tour was developed by USDA-NRCS District Conservationist and PSCAA President Joey Koptis along with members Greg Brannon and Jerome Langlinais, USDA-NRCS soil scientists, and Frank Cochran, USDA-NRCS soil conservationist. One of the field tour stops was to a pitcher plant bog where small spade holes were excavated and Joey Koptis led discussions on hydric soil indicators and the formation of a spodic horizon in one of the pedons. (left to right) Sanderson Page, Joey Koptis, and Jerome Langlinais examining hydric soil indicators. Other stops on the field tour included backhoe pits in a Malbis soil and a soil similar to the Robertsdale series. Discussions at these sites focused on plinthite, fragic properties and soil drainage. PSCAA Members Examine Hydric Soil Indicators The Professional Soil Classifiers Association of Alabama was organized by a small group of soil scientists in 1975 to promote the profession of soil classification and to further the increase and dissemination of information concerning all aspects of soil science. For more information on PSCAA, visit their website at www.alabamasoilclassifiers.org. Photo and information courtesy of PSCAA. 2011 In 2011, field work in the 48 contiguous states of the United States was completed for the Rapid Assessment of U.S. Soil Carbon (RaCA), a project initiated by the USDA-NRCS Soil Science Division in 2010. The project was a huge undertaking that involved the collection of 144,833 samples that were collected from the upper one meter of 32,084 soil profiles at 6,017 randomly selected locations. National Resources Inventory (NRI) sites were used as the basis for random selection of sample sites stratified by soil group and land use/land cover. At each location soil morphology and landscape characteristics were described, and limited vegetation and management information was collected. The collection and analysis of the many samples involved more than 300 soil scientists working in the National Cooperative Soil Survey Program, including 24 universities across the nation. A Toast to the Completion of RaCA Fieldwork Pictured above are Bev Harben and Phil Smith, USDA-NRCS soil scientists, “toasting” with bulk density sampling cores while celebrating the completion of their final sampling site in Solano County, California. Source: USDA-NRCS Soil Science Division, http://soils.usda.gov/survey/raca/. Photo courtesy of MLRA Soil Survey Office 2-TEM, Templeton, CA. 2004 Careers that span 60 years are a rarity, and Terry Cook is that rare soil scientist who has worked in the field from 1953 through 2013. In 1953, he was one of three crew members selected from Cal Poly, San Luis Obispo by a National Park Service Ranger to work on severely eroding Ellis Meadow at an elevation of 2,792 meters. This meadow in Kings Canyon National Park was beginning to rapidly erode as a result of past grazing practices. In 1955, he was the crew chief who selected his own crew from the Cal Poly Soils Department. Erosion control measures, all installed by hand, included basket dams, posts and anchors, chicken wire, branches and thatch, and even large logs on the eroding edge of the meadow, as shown in the photo, that were successfully placed to slow the water down and trap sediment. Terry Cook Stands on Log He Placed in 1955 Terry Cook has led a very diverse career and has provided superb leadership in soil science for many individuals and groups. From 1955 to 1983, Terry Cook worked for the Soil Conservation Service (SCS) in California as a Soil Survey Party Leader, Area Soil Specialist, and State and Regional Correlator. From 1983 through 1990, he worked as an International Training Specialist for USDA Soil Conservation Service with Soil Management Support Services (SMSS). This work took him to many different countries where he conducted workshops, meetings, and training forums. He has been a soil consultant in Davis, CA since he retired from SCS in 1990. He has been an active participant and field trip organizer in many soil-related organizations. Photo and information courtesy of Kerry Arroues, retired USDA-NRCS Soil Scientist, Hanford, CA.

A history of Wind Erosion Prediction Models in the United States Department of Agriculture: The Wind Erosion Prediction System (WEPS)

Development of the Wind Erosion Prediction System (WEPS) was officially inaugurated in 1985 by United States Department of Agriculture-Agricultural Research Service (USDA-ARS) scientists in response to customer requests, particularly those coming from the USDA Soil Conservation Service (SCS), for improved wind erosion prediction technology. WEPS was conceived to address deficiencies in the then-20-yearold, predominately empirical Wind Erosion Equation (WEQ) widely used by SCS, and it sparked an endeavor that relied on novel laboratory wind tunnel research as well as extensive field studies to adequately uncover the physical relationships between surface properties and their susceptibility to and influence on wind erosion. The result is that WEPS incorporates many process-based features and other capabilities not available in any other wind erosion simulation model today. The USDA Natural Resource Conservation Service (NRCS) has now implemented WEPS as a replacement for WEQ within their agency. However, the road to achieve that replacement required years of close interaction between ARS and NRCS. NRCS had to ensure they had suitable national-scale WEPS databases before implementation. User input simplifications were required as well as modifications to the reports. Run-time concerns also arose during the lengthy testing and evaluation process. Many of these were strictly nonwind erosion science issues that had to be addressed before NRCS could officially implement and begin using WEPS within their agency. The history of the development of WEPS, its unique features and its solutions to selected critical issues encountered by NRCS prior to implementation are presented and discussed. Published by Elsevier B.V.

A history of wind erosion prediction models in the United States Department of Agriculture prior to the Wind Erosion Prediction System

The Great Plains experienced an influx of settlers in the late 1850s–1900. Periodic drought was hard on both settlers and the soil and caused severe wind erosion. The period known as the Dirty Thirties, 1931– 1939, produced many severe windstorms, and the resulting dusty sky over Washington, DC helped Hugh Hammond Bennett gain political support for the Soil Conservation Act of 1937 that started the USDA Soil Conservation Service (SCS). Austin W. Zingg and William S. Chepil began wind erosion studies at a USDA laboratory at Kansas State University in 1947. Neil P. Woodruff and Francis H. Siddoway published the first widely used model for wind erosion in 1965, called the Wind Erosion Equation (WEQ). The WEQ was solved using a series of charts and lookup tables. Subsequent improvements to WEQ included monthly magnitudes of the total wind, a computer version of WEQ programmed in FORTRAN, small-grain equivalents for range grasses, tillage systems, effects of residue management, crop row direction, cloddiness, monthly climate factors, and the weather. The SCS and the Natural Resources Conservation Service (NRCS) produced several computer versions of WEQ with the goal of standardizing and simplifying it for field personnel including a standalone version of WEQ was developed in the late 1990s using Microsoft Excel. Although WEQ was a great advancement to the science of prediction and control of wind erosion on cropland, it had many limitations that prevented its use on many lands throughout the United States and the world. In response to these limitations, the USDA developed a process-based model know as the Wind Erosion Prediction System (WEPS). The USDA Agricultural Research Service has taken the lead in developing science and technology for wind erosion prediction. Published by Elsevier B.V.

Comparison of Synthetic Design Storms with Observed Storms in Southern Arizona

Historical storms with a 24-h rainfall depth exceeding 50.8 mm (2 in.) recorded in southern Arizona were compared with design storms developed both locally and by the USDA Soil Conservation Service (SCS). This study aims to evaluate if those design storms can be representative to southern Arizona. These storm depths represent the return-period storms that pose hazards considered in design. The temporal rainfall distributions, pattern index (PI), and intensity-duration relationships of the observed and design storms were compared. The comparison of the distributions and PIs of 3- or 24-h storms showed that the observed storms were diverse, and it was not clear which design storm fits best with the observed storms. The comparison of the intensity-duration relationships showed that most of the observed storms were less intense than any design storms, especially for short duration. This suggests that the application of any of the 3- or 24-h design storms would result in overestimating rainfall intensities for...

Origin of the Flax Cultivar ‘Appar’ and Its Position within the Linum perenne Complex

The ‘Appar’ flax germplasm was originally released by the USDA Soil Conservation Service as a cultivar of Linum lewisii. The observation that ‘Appar’ is heterostylic, a key taxonomic character distinguishing Lewis flax from other members of the Linum perenne complex, created a need for further study in order to resolve the taxonomic position of both Lewis flax and the ‘Appar’ cultivar. We grew 10 plants each of nine European, nine North American, and three putative ‘Appar’ seed sources, measured 18 morphologic variables on each plant, and examined genetic variation using randomly amplified polymorphic DNA (RAPD). We also performed self‐ and cross‐pollinations within and among source groups. North American collections differed from European collections for 12 of the 18 morphologic variables. ‘Appar’ collections were morphologically similar to European collections and differed from North American collections for 13 of the 18 variables. RAPD data also showed that ‘Appar’ sources clustered with European, and both were distinct from North American sources. European and ‘Appar’ collections were self‐sterile and interfertile, whereas North American collections were self‐fertile but reproductively isolated from European and ‘Appar’ collections. We conclude that L. lewisii is a distinct species within the L. perenne complex and that ‘Appar’ should be classified as L. perenne. This study provides an example of how questions regarding origin and/or taxonomy of plant materials developed for restoration can be resolved.

Simulation of an Agricultural Watershed Using an Improved Curve Number Method in SWAT

The USDA Soil Conservation Service (SCS) curve number (CN) method has been the foundation of the hydrology algorithms in commonly used continuous simulation models, including the Soil and Water Assessment Tool (SWAT). This expanded use of the SCS-CN method has proven successful for many applications. However, because the SCS-CN method was originally developed to determine design peak discharges of synthetic storm events under an average antecedent moisture condition, research is needed to address the controversy over the use of this method to represent continuous precipitation runoff processes. In addition, poor results obtained for some conditions indicate the necessity to improve the method to provide a more realistic and accurate representation of water flow amounts, paths, and source areas upon which erosion and water quality predictions depend. Thus, the objectives of this study were to: (1) propose a modified curve number (MCN) method, and (2) assess the MCN method relative to the existing SWAT method with an Ia/S value either equal to 0.2 or 0.05. The equations that formulate the MCN method were coded into the SWAT 2005 framework. A SWAT model implementing the MCN method was evaluated along with the models implementing the existing SWAT method with Ia/S values of 0.2 and 0.05. The evaluation was conducted in the 870 km2 upper portion of the Forest River watershed located in northeastern North Dakota. The results revealed that the total streamflows predicted by the three models were comparable, as indicated by similar values for the Nash-Sutcliffe coefficient. However, the MCN approach resulted in the most accurate prediction of the streamflow components (i.e., baseflow versus direct flow) as well as water yields. For the study area, the MCN method was judged to be superior to the existing commonly used curve number methods in terms of mimicking the precipitation runoff processes.

Practical results of a water budget estimation for a constructed wetland

An experimental water treatment plant was established to verify the effectiveness of constructed wetlands to improve water quality in the Venice Lagoon watershed. The wetland comprised three different subsystems, ranging from a riparian swamp to a marsh ecosystem. As a first step, monitoring was conducted over three years to evaluate the efficacy and efficiency of the system. Here, we report an analysis of the water budget resulting from routinely collected hydraulic and meteorological data. We used independent estimates of the water-budget terms, rather than budgetary residual estimation, because we wanted to estimate the water-budget error. Surface-water inflow, surface-water outflow, and direct precipitation were measured. Daily potential evapotranspiration values were estimated using the FAO Penman Monteith equation; runoff was estimated using the USDA Soil Conservation Service curve number model; indirect precipitation that flows toward the wetland via subsurface flow was estimated from the soils field capacity; and seepage was estimated using Darcy's law. The objectives of the research were to establish the best way to develop a water budget useful for application and design purposes, to determine the term that most influences the water-budget error, and to perform a sensitivity analysis on the parameters affecting this term. Surface flow dominated the wetland system, precipitation and evapotranspiration contributed about 10% to the water budget, and changes in water storage and the seepage flow contributed less than 5% to the water budget. The seepage flow term had the highest uncertainty, and the frequency of ground-water level measurements had the greatest impact on the water-budget error (ranging from 10.0%-28.6%). Therefore, in a free-water surface wetland with a shallow ground-water system, the main effort in field measurement should be to ensure a measurement frequency of less than five days.

The Original USDA-ARS Experimental Watersheds in Texas and Ohio: Contributions from the Past and Visions for the Future

The USDA Soil Conservation Service (USDA-SCS) realized the importance of understanding hydrologic processes on agricultural fields and watersheds in the mid-1930s. Based on this realization, the research program of the Hydrologic Division of SCS established three experimental watersheds across the U.S. to analyze the impact of landuse practices on soil erosion, flood events, water resources, and the agricultural economy. Two of the original watersheds remain in operation today within the USDA Agricultural Research Service (USDA-ARS): the Blacklands Experimental Watershed (now the Grassland, Soil and Water Research Laboratory) near Riesel, Texas, and the North Appalachian Experimental Watershed near Coshocton, Ohio. These original watersheds were designed for collection of hydrologic data on small watersheds and evaluation of hydrologic and soil loss response as influenced by various agricultural land management practices. A major contribution of these experimental watersheds is the quantification of soil loss reduction under conservation management, which has led to a drastic reduction in soil loss from cultivated agriculture in the 20th century. Riesel watershed studies produced the scientific basis for several watershed models that are now used worldwide to manage water quality and also facilitated fundamental analysis of the agronomic and environmental effects of tillage, fertilizer, and pesticide alternatives. Coshocton watershed studies led to the development of no-till and pasture management practices to control runoff, erosion, and chemical loss and were instrumental in understanding water quality and hydrologic effects of soil macropores and mining and reclamation activities. The long-term hydrologic records at each site have also improved understanding and management of water resources in their respective geographic regions. Because of their historical and future value, the USDA-ARS has a unique responsibility to maintain these long-term experimental watersheds, which are vital for addressing emerging research needs to meet future water availability, environmental quality, and food and fiber demands.

Early Investment in Soil Conservation Research Continues to Provide Dividends

Current soil conservation programs are built upon an established research legacy. Hugh H. Bennett, chief of the USDA Soil Conservation Service from 1935 to 1951, was instrumental in the establishment of a network of 35 soil conservation experiment stations (SCES). Research projects were initiated at the SCES in the 1930s to investigate the principal factors causing erosion and to identify the most effective and practical methods of controlling soil loss from agricultural areas. Information obtained from the SCES, and selected other locations, was assembled at the National Runoff and Soil Loss Data Center (NRSLDC) established on the campus of Purdue University in 1954. Data gathered at the NRSLDC was used to develop the Universal Soil Loss Equation (USLE). The USLE is recognized as one of the most important developments in soil and water conservation in the 20th century. The Revised Universal Soil Loss Equation was released in 1997 as an updated, computerized version of the USLE. Several soil conservation practices currently used on agricultural areas were developed, refined, tested, and adopted at the SCES. Data obtained from the SCES have been an essential component in the development and testing of several erosion and water quality models. It is a tribute to the early soil conservation researchers that information they collected in previous decades continues to be used by successive generations of conservationists and modelers.

Applicability of an empirical runoff estimation method in central Greece

In order to assess the water runoff on the sloping cultivated fields of Central Greece, an experiment was carried out from 1997 to 2000. The following treatments were used: three tillage methods, viz. conventional tillage, reduced tillage with heavy cultivator and disk-harrow; two with or without winter cover crop; two parallel and perpendicular to the contour tillage and planting directions. An existing methodology for predicting runoff was evaluated and improved, which is based on the estimation of ponding time for the different tillage systems in the study area under rainfall. An equation predicting the time to ponding was used obtaining data from infiltration experiments using double-cylinder infiltrometers in the field. The surface runoff of each rain storm was estimated by combining the appropriate infiltration equation with the rain intensity data, taking into consideration not only the excess rainfall rate over the infiltration rate, but also the surface detention. Measured runoff was used to test the validity of the USDA-Soil Conservation Service (SCS) curve number method in the region. The results from this test indicated that this prediction runoff method may not be used in the region without the proper modifications to suit the rainfall in the region. The developed model could be used to successfully estimate runoff and erosion in the area. It was found that the combination of equations of time to incipient ponding and the maximum surface storage capacity of topsoil, could explain about 85% of the existing runoff variation.

STAO: a component architecture for raster and time series modeling

Implementation of spatially distributed models using Geographic Information System (GIS) involves accessing and processing of spatial and time series data. Most of the GIS software do not provide an explicit functionality to support handling of time series data in modeling and also requires exclusive client storage of one-dimensional array for raster data access. This paper describes an attempt to overcome such short comings by developing Spatial and Time series data Access Objects (STAO) using Microsoft's Component Object Model (COM ®). STAO has advanced enough modeling objects which are developed for the raster and time series data access and analysis while they are simple enough for the user to implement them in spatial models in a variety of native proprietary formats. The STAO architecture defined in this study has multiple advantages in terms of interoperability, reusability, and extendibility. The usefulness of these objects has been demonstrated by implementing: (1) the USDA's Soil Conservation Service (SCS) method of rainfall runoff estimation and (2) an algorithm for finding time area diagram at sub-watershed level. The results of implementing SCS using STAO in Kolli Hills watershed is discussed and the computed runoff values are in good agreement with field observed values.