NSSH Part 630

Benchmark Soils

Definition and Purpose (630.00)

(a) Definition

A benchmark soil is one of large extent, one that holds a key position in the soil classification system, one for which there is a large amount of data, or one that has special significance to farming, engineering, forestry, ranching, recreational development, urban development, wetland restoration, or other uses. The cost of investigation and the large number of combinations of soil uses and management practices preclude laboratory and field studies of all soils; therefore, studies of benchmark soils are essential. A benchmark soil represents other soils. Knowledge of the properties and behavior of benchmark soils contributes to the understanding and interpretation of other soils with similar properties. This knowledge is important to soil technology and the use of soil surveys.

(b) Purpose

Benchmark soils help to focus the investigative effort on soils that have the greatest potential for extending collected data and resultant interpretations to other soils. Lists of benchmark soils are useful in planning many kinds of soil studies.

(c) Use

Example uses for benchmark soils:

• assessing conservation effects
• evaluating soil interpretations
• studying macro/micronutrient and trace elements
• monitoring dynamic soil property changes
• measuring saturated hydraulic conductivity
• determining soil quality
• verifying and testing soil erodibility factors
• collecting crop and range plant adaptation and yields
• assessing soil fertility
• locating sources for training materials and onsite training activities
• modeling crop/soil/pesticide scenarios for surface water and groundwater assessments
• modeling pedotransfer functions
   

(d) Access to Benchmark Soil List

Use the online Soil Series Classification (SC) or Official Soil Series Descriptions (OSD) data access through search routines to access and sort benchmark soils. These files are on the soils Web site by selecting View OSD by Query at http://soils.usda.gov/technical/classification/osd/index.html or by selecting Create Report by Query at http://soils.usda.gov/technical/classification/scfile/index.html.

Policy and Responsibilities (630.01)

(a) MLRA Office Responsibilities

• exchanging information on benchmark soils with state offices,
• maintaining the benchmark status of soil series in the soil classification database,
• maintaining a file of data for benchmark soils that are on the major land resource area list,
• coordinating benchmark soils with the state soil scientist in states that share the major land resource area, and
• focusing long-range plans for soil survey investigations on benchmark soils and their characteristics.

(b) State Soil Scientist Responsibilities

The state soil scientist is responsible for:

• proposing changes and additions to the benchmark soils list,
• ensuring input from cooperators and interdisciplinary specialists in the selection of benchmark soils, and
• encouraging the use of benchmark soils in organizing and planning the research by state agricultural experiment stations and other agencies.

(c) National Soil Survey Center Responsibilities

• providing guidance in the selection of benchmark soils,
• assuring the internet access and query routines for benchmark soils are available to researchers in experiment stations, highway departments, and other organizations,
• performing laboratory characterization, and
• maintaining the laboratory database.

(d) National Geospatial Development Center Responsibilities

• developing web-based geospatial analysis tools for use in analyzing and revising benchmark soils by major land resource area, and
• developing web-based map display products.

Criteria for Selecting Benchmark Soils (630.02)

(a) Criteria

The soil series that represent the range of soil conditions within a major land resource area serve as benchmark soils. The criteria are:

1. Extent. The soil series that are selected as benchmark soils are commonly of large extent (>100,000 acres) in the Land Resource Region (LRR), and of moderate or large extent in the major land resource area (> 10,000 acres). Not all series of moderate or large extent are benchmark soils. Generally, the combined total extent of benchmark soils should comprise about 20 to 25 percent of the total soil area of the major land resource area. Since benchmark soils represent the soil series in classes of the higher categories of soil taxonomy, the soils selected as benchmark should collectively be considered representative of 60 to 80 percent of all soils in the major land resource area. This kind of representation ensures that any collected data are widely applicable.
    
2. Key soils. Certain soils occupy key positions in soil taxonomy, and research on these can be easily applied to other soils. Benchmark soils represent the extensive soil series in classes of the higher categories of the soil classification system. They typically do not share the same family.
    
3. Important soils. Certain soils are especially important because of their use for specialty crops or engineering purposes. If these soils are essential to the understanding of and interpretations for specialty crops, engineering, or other uses, they become benchmark soils. The number of these soils is small, perhaps two or three per major land resource area.
    
4. Existing data. Soil series for which there are large amounts of data have preference over equally suitable series for which there are less data. Data-completeness of correlated pedon data must be evaluated concurrently with analyses of series extent and taxonomic significance. The national soil characterization database, maintained by the National Soil Survey Center, includes laboratory data for benchmark soils. In addition, soil survey investigations reports identify benchmark soils. This will optimize the identification of potential benchmark candidates.

(b) General Guidance

Select the fewest number of soils required to adequately reflect the criteria. The number of benchmark soils in a major land resource area varies according to the size of the area and the diversity and complexity of soils. In highly diverse and complex major land resource areas, do not construct a benchmark list solely on the basis of soil series extent. An unmanageable number of benchmark soils may otherwise result. Oftentimes, many of the series share the same taxonomic family and are expected to behave similarly. Therefore, there is little advantage in assigning more than one series from a given family as a benchmark soil. Instead determine which series is most representative for the family, and assign benchmark status to that series only (e.g., dominant extent or the series having the most complete laboratory dataset). This will keep the number of benchmark soils in the major land resource area relatively small and minimize research expenditures.

Maintaing a Record of Benchmark Soil Data Needs (630.03)

(a) Maintenance

Soil surveys are dynamic; consequently the adequacy of the current benchmark soils status needs to be evaluated during any maintenance activity. Evaluate benchmark soils status at any time, regardless of whether active soil surveys are being conducted. There is no automated procedure for evaluating and revising the current list of benchmark soils. Make judgments in deciding which key taxonomic positions are represented as benchmark, and which similar soils in closely related classes are associated with the benchmark soil.

(b) Development of a Comprehensive Report

Each MLRA office leader, in consultation with the state soil scientists and research institutions, develops a comprehensive report of the kinds of data and information available and needed to predict the behavior of soils in each major land resource area. This report compares existing data and information on benchmark soils with needs to determine the adequacy of information for the major land resource area. This comparison helps plan for studies of soil properties, qualities, and behavior.

(c) Narrative Record of Each Benchmark Soil

Based on the comprehensive report, a narrative record of each benchmark soil is provided to state soil scientists for distribution. The record helps to facilitate long range planning and to encourage cooperative ventures with research institutions. Discuss the kinds of special studies and soil properties needed. Include literature references of research studies on the benchmark soil. Refer to Exhibit 630-1 for an example of a narrative record.
 

Sample Narrative for Benchmark Soils (Exhibit 630-1)

BETA SERIES -- a member of the fine-loamy, mixed, superactive, frigid Typic Argiustolls family. It dominantly occurs in the Rolling Soft Shale Plains, Major Land Resource Area (MLRA) 54, but it also extends into the Southern Dark Brown Glaciated Plains, MLRA 53C. The Beta series is about 105,000 acres in extent.

Beta soils are 100 to 150 centimeters deep to soft bedrock and formed in material weathered from sandstone, siltstone, and shale.

Information needs: In MLRA 54, knowledge of the properties, qualities, and behavior of the Beta soils is useful in understanding (1) the effect of cropping systems and management practices on dynamic soil property change, (2) the penetration of roots and the movement of water into the soft bedrock, (3) pesticide and nutrient fate and transport for surface water and groundwater assessment, (4) the use of soils with soft bedrock for septic tank absorption fields, (5) the Silty range site, (6) and the use of soils with soft bedrock for building sites. The Beta soils are underlain by strippable coal, and the knowledge of soil properties, qualities, and behavior is important for the development of effective soil reclamation measures.

Data needs: The following dynamic properties and morphological attributes are needed across the common crop management systems: saturated hydraulic conductivity, soil bulk density, organic carbon, surface roughness, consistence, structure, and macropore characteristics (geometry, frequency, distribution, and continuity). The purpose is to integrate the macropore characteristic with structure, particle-size distribution, and mineralogy in order to develop a pedotransfer function that predicts saturated hydraulic conductivity.

Laboratory data: NRCS NSSC Soil Characterization Database:

User Pedon ID
82STATEFIPS031005
84STATEFIPS021002
87STATEFIPS005001
91STATEFIPS007007
97STATEFIPS013011

ANYSTATE University pedon data
(List sources and contacts where information can be acquired)

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