2012-03-30_REVISION - M1987013 (3)

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How Soil Surveys Are Made Sod surveys are made to provide information about the soils and miscellaneous areas in a specific area. They include a descnption of the soils and miscellaneous areas and their location on the landscape and tables that show sod properties and limitations affecting vanous uses. Soil scientists observed the steepness, length, and shape of the slopes, the general pattem of drainage; the kinds of crops and native plants; and the kends of bedrock_ They observed and described many soil profiles. A soil profile is the sequence of natural layers, or horizons, in a sal. The profile extends from the surface down into the unconsolidated matenal in which the sal formed or from the surface down to bedrock. The unconsolidated matenal is devoid of roots and other Irving organisms and has not been changed by other biological activity. Currently, sods are mapped according to the boundaries of major land resource areas (MLRAs)_ MLRAs are geographically associated land resource units that share common characteristics related to physiography, geology, climate, water resources, soils, biological resources, and land uses (USDA, 2006). Sal survey areas typically consist of parts of one or more MLRA. The soils and miscellaneous areas in a survey area occur in an orderly pattern that is related to the geology, landforms, relief climate, and natural vegetation of the area. Each kind of soil and miscellaneous area is associated with a particular kind of landfam or with a segment of the landform By observing the sods and miscellaneous areas in the survey area and relating their position to specific segments of the landform, a soil scientist develops a concept, or model, of how they were formed. Thus, during mapping, this model enables the sod scientist to predict with a considerable degree of accuracy the kind of soil or miscellaneous area at a specific location on the landscape Commonly. individual sods on the landscape merge into one another as their characteristics gradually change. To construct an accurate sod map, however, sal scientists must determine the boundaries between the sods. They can observe only a limited number of sod profiles Nevertheless. these observations, supplemented by an understanding of the soil - vegetation- landscape relationship, are sufficient to venfy predictions of the kinds of sod in an area and to determine the boundanes. Sod scientists recorded the charactenstics of the soil profiles that they studied_ They noted sal color, texture, size and shape of soil aggregates. kind and amount of rock fragments, distnbution of plant roots, reaction, and other features that enable them to identify sods. After descnbing the sods in the survey area and determining their properties. the sal scientists assigned the soils to taxonomic classes (units) Taxonomic Gasses are concepts. Each taxonomic class has a set of sal charactenstics with precisely defined limits. The lasses are used as a basis for cornpanson to classify soils systematically. Sal taxonomy. the system of taxonomic classification used in the United States, is based mainly on the kind and character of soil properties and the arrangement of horizons within the profile After the sod scientists classified and named the sods in the survey area, they compared the 5