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Custer Soil Resource Report <br />individtad sobs with similar sobs in the same taxonomic class in other areas so that <br />they Could confirm data and assemble additional data based on experience and <br />research. <br />The objWM Of soil mapping is not to delineate pure map unit components: the <br />objective is to separate the landscape, into WFWOfmS orlordfonn segments that have <br />similar use and marragemant requirements. Each map unit is defined by a unique <br />combination of son Components and/or miscellaneous areas in predictable <br />Proponti". Some compo may be highly Contrasting to the other components of <br />the map unit. The presence of minor components in a map unit in no way diminishes <br />the usefulness or accuracy of the data. The delineation of such tandorms and <br />landform segmerds an the map proms suf meat mfurmation for the development of <br />resource plans. ff "intensive use of smal areas is planned, onsite investigation is <br />needed to define and locate the Sills end miscellaneous areas. <br />Sal scientists make marry fwd observations in the process of producing a soil map. <br />The frequency of observation is dependent upon several factors. including scale of <br />mapping, intensity of mapping, design of map units, complexity of the landscape, and <br />experience of the soil scieritist Observations are made to test and refire the soil- <br />landscape model and predictions and to verify the classification of the soft at specific <br />locations. Once the soil-landscape model is refined, a significantly smaller cumber of <br />measurements of individual soil properties are made and recorded- These <br />measurements may include field measurements, such as those for eoor, depth to <br />bedrock, and texture, and laboratory measurements. such as those for content of <br />sand, silt day. salt. and other components. Properties of each soil typically vary from <br />one point to another across the landscape. <br />Observations for map unit components are aggregated to develop ranges of <br />characteristics for the components. The aggregated values are presented. Direct <br />measurements do not exist for every property presented for every map unit <br />component. Values for some properties are estimated from combinations of other <br />properties. <br />While a sod survey is in progress, samples of some of the sons in the area generally <br />are collected for laboratory analyses and for engineering tests. Sod scientists interpret <br />the data from these analyses and testis as well as the field-observed diaraderistics <br />and the sod properties to determine the expected behavior of the soils under drfferent <br />uses. Interpretations for all of the soils are field tested through observation of the soils <br />in different uses and under different levels of manogemer. Some interpretations are <br />modified to fit local chanditeons, and some new interpreh aons are developed to meet <br />local needs. Data are assembled from other sources. such as research information, <br />production records. and field experience of specialists. For example. data on crop <br />yields under defined levels of management are assembled from farm records and from <br />field or plot experbnerrts an the some kinds of soil <br />Predictions about sod behavior are based not only on soil properties but also on such <br />variables as dims and biological activity. Sal conditions are predictable over long <br />periods of time. but they are not predictable from year to year. For example, soil <br />scientists can predict with a fairly high degree of accuracy that a given soil will have <br />a high water table within certain depths in most years, but they cannot predict that a <br />high water table will always be at a specific level in the sod an a specfhc date. <br />After soil scientists located and identified the sigrificert natural bodies of soil in the <br />survey area, they drew the boundaries of these bodies on aerial photographs and <br />identified each as a specific map unit. Aerial photographs showtrees, buildings, fields, <br />roads, and rivers, all of which help in locating boundaries accurately.