Soil Genesis and Classification Volume 143 (Buol/Soil Genesis and Classification) || Interpretations of Soil Surveys and Technical Soil Classification

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<ul><li><p>425</p><p>Soil Genesis and Classification, Sixth Edition. S. W. Buol, R. J. Southard, R. C. Graham and P. A. McDaniel. 2011 John Wiley &amp; Sons, Inc. Published 2011 by John Wiley &amp; Sons, Inc.</p><p>Interpretations of Soil Surveys and Technical Soil Classification</p><p>Interpretations of soil surveys are the proof of the pudding as the theories, hypotheses, and knowledge expressed in taxonomic systems are put to the test through applied, practical uses. The best test of our principles and technologies of soil genesis, classification, and surveys is how well they can be applied in the generalization of useful, easily understood descriptions of soil qualities and behavior important for various uses. Technical soil classifications are designed for a specific use and purpose, using criteria and characteristics appropriate for that purpose. These criteria and characteristics are generally a restricted subset of the properties used in the natural classification system.</p><p>Soil properties can be interpreted in the context of soil quality. Soil quality is a basic, intrinsic characteristic of a soil that is a reflection of several soil properties and cannot be directly characterized in one measurement, but ordinarily is estimated from a number of different measurements and/or observations. The concept of soil quality continues to evolve, but soil properties and environmental factors that are often included in an assessment of soil quality include soil fertility, potential productivity, resource sustainability, environmental quality, contaminant levels and their effects on use, the environmental cost of agricultural production, and the potential for reclamation of degraded soil (Kellogg 1961; Singer and Ewing 2000).</p><p>Soil Survey InterpretationsSoil survey interpretations help predict potentials, limitations, problems, and management needs for soils (Kellogg 1966; Soil Survey Division Staff 1993). Aandahl (1958) defined soil survey interpretation as the organization and presentation of knowledge about characteristics, qualities and behavior of soils as they are classified and outlined on maps. Soil survey interpretations are prepared to help land users, planners, policy makers and analysts, legislative officials, engineers, and other scientists to transfer technology about the use and management of soilsboth agricultural and nonfarmmore accurately. These interpretations are made to accompany or be used with detailed soil surveys and larger-scale maps prepared by the generalization process previously described (Chapter 20), or they are made to be </p><p>21</p><p>Buol_c21.indd 425Buol_c21.indd 425 7/1/2011 1:26:18 PM7/1/2011 1:26:18 PM</p></li><li><p>426 Soil Genesis and Classification</p><p>used with the schematic or technical single-purpose maps (Soil Survey Staff 1978, 1983a; USDA-NRCS 2009).</p><p>Interpretations of detailed soil surveys (those that have not been generalized) have a number of uses (USDA-NRCS 2009): indicating soil potentials for various land uses, pointing out limitations and potential problems with soil qualities (especially for conservation and environmental protection), predicting potential production of soils under various management systems, indicating types of management needed for different soils, and recasting the technical soil information into forms and terminology useful in other scientific disciplines and to land users. The soil information used for these detailed interpretations is contained in published county soil surveys, in digital soil surveys at the NRCS Web Soil Survey site (http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm), or in the USDA-NRCS Soil Survey Geographic (SSURGO) Data Base (http://soildatamart.nrcs.usda.gov). For statistical evaluation of crop response on adjacent mapping units, experimental designs that consider the soil patterns within fields are required (Nelson and Buol 1990).</p><p>Interpretations of generalized large-scale maps are usually designed for uses such as regional planning, setting priorities for action programs, depicting regional problems in conservation and environmental protection, estimating productivity on a regional basis, preparing and implementing regional development programs, determining feasibility and potential benefits of proposed irrigation and watershed programs, and assessing regional environmental protection needs and concerns. The soil information used for these regional interpretations is contained in soil maps generalized from county soil survey maps or in the USDA-NRCS State Soil Geographic (STATSGO) Data Base (http://soildatamart.nrcs.usda.gov/USDGSM.aspx).</p><p>Interpretations are prepared for taxonomic soil components of soil map units or of the soil map unit as a whole. Most commonly they are prepared for phases of taxonomic units (such as slope and eroded phases) if used with a detailed survey or with maps generalized according to the graphic generalization strategy. If used with taxonomically generalized, schematic, or technical maps, interpretations are generally prepared for mapping units, but may also be prepared from the properties of dominant taxonomic components identified in the map unit. As indicated in Chapter 20, both the preparers and the users of soil interpretations need to be aware of, and cautioned about, the differences between taxonomic units and soil mapping units. This is especially true if taxa with different interpretation requirements are included in a soil map unit. This is particularly important when the interest focuses on small sites such as house lots smaller than 1 ha.</p><p>Interpretive Uses of Taxonomic Information and Soil MapsSome interpretations are for specific soil materials present in soil horizons, but most soil uses involve an area of land. For these uses, the nature and composition of map units, as discussed in Chapter 20, are the basis of soil interpretations. Soil map and </p><p>Buol_c21.indd 426Buol_c21.indd 426 7/1/2011 1:26:18 PM7/1/2011 1:26:18 PM</p></li><li><p> 21 / Interpretations of Soil Surveys and Technical Soil Classification 427</p><p>taxonomic information is put to a number of agricultural and nonagricultural interpretive uses (Bartelli et al. 1966; Simonson 1974). For agricultural uses these include recommended conservation practices; identification of prime farm land; predictions of erosion losses under various cropping systems; development of productivity ratings of soils; soil potentials and crop yield; land evaluations and tax assessments; soil and farm management recommendations, including those on application of fertilizer; programs for protection of environmental quality from damage by sedimentation and agricultural chemicals; and improvements in agricultural energy conservation. Nonagricultural interpretations of soils are many, and include forest, range, and wildlife management; mined land reclamation; local, state, and regional planning, zoning, and other land use concerns; identification of hydric soils, suitability for locating septic tank filter fields and for municipal sewage effluent and sludge disposal; environmental quality protection with respect to off-farm sediment, dust, and pollution control; local road and highway route location, location of pipelines and power lines; building and real estate development site location; suitability as sources of building materials; valuation of land for tax assessment purposes; and planning the location and layout of outdoor recreation facilities, including parks, campgrounds, paths, and trails.</p><p>For these purposes it is more desirable and economical to prepare comprehensive soil maps as a base from which the interpretations can readily be made. If a single-purpose technical classification were to be used as the basis for soil mapping, it is highly probable that such a classification would not be suitable for other types of planning and site evaluation, such as the kinds we have described. Then the mapping and classification would need to be redone at considerable unnecessary expense to satisfy each new purpose. A well-prepared soil map, based on a sound general classification system that has quantitatively defined taxa, is useful over a long period of time as a base for a number of interpretation activities for technical and specific objectives, including those not yet foreseen. Such an approach allows (even forces) consideration and description of the dynamic aspects of each soil and the relating of the soils to various uses.</p><p>Technical Soil Maps and Classifications. We distinguish between technical soil maps, classifications, and surveys on the one hand and comprehensive standard soil classification, maps, and surveys on the other. The technical maps and classifications, prepared either by interpretation from the standard maps and classifications or spe-cially and separately prepared, are designed for a specific use and purpose, using criteria and characteristics appropriate for that purpose. The comprehensive standard maps and classifications are general and multipurpose in nature with criteria and char-acteristics selected according to scientific and taxonomic principles. They are capable of being interpreted for any number of specific, single-purpose objectives and uses.</p><p>It is important to understand that there are an almost infinite number of technical systemsone for each particular use of soil. Anyone can make a technical map and classificationeither by interpreting existing standard comprehensive scientific </p><p>Buol_c21.indd 427Buol_c21.indd 427 7/1/2011 1:26:18 PM7/1/2011 1:26:18 PM</p></li><li><p>428 Soil Genesis and Classification</p><p>surveys and classifications or by a separate soil survey with accompanying technical classification. In order to be useful and sound, such technical systems must, however, use a quantitative nomenclature with class limits based on measurable properties of the soils and/or of the environmental factors that influence soil behavior. The discussion that follows relates to preparation of technical systems interpreted from the comprehensive scientific classification and accompanying standard soil mapsthe process that we recommend over special purpose technical soil surveys.</p><p>Development of Technical Soil Interpretations. The preparation of interpretations by soil scientists of the National Cooperative Soil Survey ordinarily involves the following four steps (Soil Survey Division Staff 1993): (1) assembling information about the soils and landscapes, (2) modeling other necessary soil characteristics from existing soil data, (3) deriving inferences, rules, and guides for predicting behavior under specific land uses, and (4) integrating these predictions into generalizations for the map unit.</p><p>The essential ingredients in the development of soil interpretations are a clear definition of the specific soil use and quantitative expression of the influence of each applicable soil property on the evaluation or interpretation of a soil, or mapping unit, for that specific use. Each technical soil use (of which there is an infinite number) can and should have its own technical classification in order to facilitate communication between soil scientists and the specialists in the particular subject matter area of the soil use. The soil data used to develop the interpretations are contained in the National Soil Information System (NASIS) as described in the National Soil Survey Handbook (USDA-NRCS 2009). The NASIS database is managed by the USDA-NRCS and is the repository of the attributes of the taxonomic components of soil map units and the geo-referenced site information and pedon data. The database is populated with actual soil property data from pedon descriptions, laboratory characterization, and map unit characteristics, and with inferred soil properties derived from the actual data. Most of the NASIS data are available via the Soil Data Mart (http://soildatamart.nrcs.usda.gov). Laboratory data and pedon descriptions of sampled and characterized pedons are from a separate database maintained by the National Soil Survey Center in Lincoln, Nebraska (http://soils.usda.gov or http://ssldata.nrcs.usda.gov/).</p><p>Because it is not possible for anyone to anticipate all of the possible uses of soils information, the following example of a soil interpretation based on criteria outlined in the National Soil Survey Handbook (USDA-NRCS 2009) and on data contained in NASIS, is presented to illustrate the procedure for developing a soil interpretation.</p><p>Consider that you are confronted with the question: What makes a good picnic area? In order to address the question clearly, a number of broad criteria must be established first. For example, will only hikers use the picnic area or will vehicles bedriven to the area? Are garbage facilities to be provided for on the site, or will the garbage be exported? Will extensive revegetation of the site be required following construction activities? Thus, providing a clear definition of the use must be addressed first. In this example, we will use the following definition of picnic areas: picnic areas </p><p>Buol_c21.indd 428Buol_c21.indd 428 7/1/2011 1:26:18 PM7/1/2011 1:26:18 PM</p></li><li><p> 21 / Interpretations of Soil Surveys and Technical Soil Classification 429</p><p>are natural or landscaped tracts used primarily for preparing meals and eating out-of-doors. These areas are subject to heavy foot traffic, and vehicular traffic is confined to access roads and parking lots. The soils are rated on the basis of soil properties that influence development costs of shaping sites or building access roads and parking areas, trafficability, and growth of vegetation after development.</p><p>The soil properties of concern would appear to be those providing good trafficability: the surface soil in the picnic area should absorb rainfall readily, remain firm to heavy foot traffic, and not be dusty when dry. The second step is to place quantitative limits on the soil properties that should be considered as restrictive. Table 21.1 illustrates one guide to this soil use. The severity of the limitations is given, as well as a common or general expression of the problem. Perhaps most important, however, are the quantitative critical limits that will document the basis for the interpretation should the soil scientist or user be called upon to defend his or her decisions. In this example, the three categories of limitationsslight, moderate, or severeare used. The implication is that the relative cost of developing a picnic area would probably be least for locations with slight limitations and greatest for locations </p><p>Table 21.1. Evaluation of sites for plenic areas</p><p> Limits Restrictive</p><p>FeatureProperty Slight Moderate Severe </p><p>Slope (%) 08 815 &gt; 15 SlopeFlooding None to </p><p>occassionalFrequent Flood hazard</p><p>Depth to high water table (cm)</p><p>&gt; 75 3075 &lt; 30 Wetness</p><p>Fraction 275 mm (i.e., wt % of surface layer)</p><p>&lt; 25 2550 &gt; 50 Small stones</p><p>USDA texturea,c (surface layer)</p><p> SC, SIC, C Too clayey</p><p>USDA texture (surface layer)</p><p> LCOS, LS, LFS, VFS</p><p>COS, S, FS Too sandy</p><p>USDA texture (surface layer)</p><p> Muck, peat Excess humus</p><p>USDA textureb (su...</p></li></ul>

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