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 surrey 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