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HOW THIS SURVEY WAS ~~DE Soil scientists made this survey to learn what kinds of soil are in Otero County. where they are located, and how they can be used. The soil scientists went into the county knowing they likely would find many soils they had already seen and per- haps some they had not. In the county, they ob- served the steepness, length, and shape of slopes, the size and speed of streams, the kinds of native plants or crops, the underlying materials, and many facts about the soils. They dug many holes to ex- pose soil profiles. A profile is the sequence of natural layers OT horizons, in a soil; it extends from the surface down into the parent material that has not been changed much by leaching or by the action of plant roots. The soil scientists made comparisons among the profiles they studied, and they compared these pro- files with those in counties nearby and in places more distant. They classified and named the soils according to nationwide, uniform procedures. The soil series and the soil phase are the categories of soil classification most used in a local survey. Soils that have profiles almost alike make up a soil series (7) 1/. Except for different texture in the surface layer, all the soils of one series have major horizons that are similar in thickness, arrangement, and other important characteristics. Each soil series is named for a town or other geographic feature near the place where a soil of that series was first observed and mapped. Rocky Ford and Minnequa, for example, are the names of two soil series. All the soils in the United States having the same series name are essentially alike in those characteristics that affect their behavior in the undisturbed landscape. Soils of one series can differ in texture of the surface soil and in slope, st~niness, or some other characteristic that affects use of the soils by man. On the basis of such differences, a soil series is divided into phases. The name of a soil phase in- dicates a feature that affects management. For example, Nurna clay loam, 0 to 1 percent slopes, is one of several phases within the Numa series. After a guide for classifying and naming the soils had been worked out, the soil scientists drew the boundaries of the individual soils on aerial photographs. These photographs show woodlands, buildings, field borders, trees, and other details that help in drawing boundaries accurately. The soil map in the back of this publication was pre- pared from the aerial photographs. The areas shown on a soil map are called mapping units. On most maps detailed enough to be useful in planning the management of farms and fields, a mapping unit is nearly equivalent to a soil phase. 1/ - Underscored numbers in parentheses refer to Literature Cited... p. 80 2 It is not exactly equivalent, because it is not practical to show on such a map all the small, scattered bits of soil of some other kind that have been seen within an area that is dominantly of a recognized soil phase. Some mapping units are made up of soils of dif- ferent series, or of different phases within one series. Three such kinds of mapping units are shown on the soil map of Otero County: soil com- plexes, undifferentiated soil groups, and soil variants. A soil complex consists of areas of two or more soils, so intricately mixed or so small in size that they cannot be shown separately on the soil map. Each area of a complex contains some of each of the two or more dominant soils, and the pattern and relative proportions are about the same in all areas. The name of a soil complex consists of the names of the dominant soils, joined by a hyphen. Glenberg-Bankard sandy loams, 0 to 1 percent slopes, is an example. An undifferentiated group is made up of two or more soils that could be delineated individually but are shown as one unit because, for the purpose of the soil survey, there is little value in separ- ating them. The pattern and proportion of soils are not uniform. An area shown on the map may be made up of only one of the dominant soils, or of two or more. The name of an undifferentiated group con- sists of the names of the dominant soils, joined by Iland. U Kim and Wi ley loams, 1 to 9 percent slopes, is an example. A soil variant has properties different enough to justify a new soil series but is of such limited known extent that establishing a new series is not considered practical. An example in this county is Numa loam~ gravel subsoil variant, 5 to 9 percent slopes. While a soil survey is in progress, soil scien- tists take soil samples needed for laboratory mea- surements and for engineering tests. Laboratory data from the same kinds of soil in other places are also assembled. Data on yields of crops under defined practices are assembled from farm records and from field or plot experiments on the same kinds of soil. Yields under defined management are esti- mated for all the soils. The soil scientists set up trial groups of soils on the basis of yield and practice tables and other data they have collected. They test these groups by further study and by consultation with farmers, agronomists, engineers, and others. Then they adjust the groups according to the results of their studies and consultation. Thus~ the groups that are finally evolved reflect up-to-date know- ledge of the soils and their behavior under pres- ent methods of use and management.