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