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Soil Survey

soil surveySoils vary considerably across the country, region, landscape, field, and sometimes even a backyard. Each soil may have markedly different land use capabilities. While the soil in Carolina Bays makes prime wetland wildlife habitat, they are miserable places to build a home. The land use suitability of a soil is usually not this obvious, however. Knowing how to use the information in a soil survey can save people from costly and, in some cases, dangerous mistakes.

A soil survey is a book of maps delineating the different types of soil that can be found across a landscape. A soil survey also includes soil profile descriptions, a series of tables describing each soil’s suitability for an assortment of uses, definitions and explanations of terms and concepts used in the survey, and often a summary of the area’s geology and land use history.

Each county that comprises the ACE Basin study area has its own soil survey. They are available free of charge from local Soil and Water Conservation District offices, and can also be checked out from many libraries. In the case of older surveys, like the one for Charleston County, books may no longer be available for distribution. However, individual map sheets can be obtained at the Conservation District office.

The soil surveys of South Carolina have all been digitized and may be downloaded from the Department of Natural Resources web site exit. A Suitable GIS software application, such as ArcView, is required to make use of these data. The soil surveys for the ACE Basin study area can be obtained through this website or from the data folder in the GIS directory located on disc two.

The first step in using a soil survey is to locate the parcel of land on one of the soil maps in the second half of the book. At the very beginning of the map section of the book is a colorful general soil map of the entire survey area. This map gives the reader an idea of the kind of landscapes found in the survey area, but is not intended as a guide for land use. The next map is an index to the individual soil maps that follow. Find the name of a town, waterway or road number that is near the land you are investigating, and take note of the map sheet numbers in that area. If the land is not close to any of these landmarks, you may have to look at several adjoining map sheets before locating the right one. Turn to the map sheet you think is closest to the land you have in mind.

The soil map sheets are drawn on aerial photos, so you should look for a known landmark on them to orient yourself. The photos in the surveys of these counties were taken in the 1960s and '70s, and land use patterns may have changed. What appears to be forest may now be an open field or a subdivision. A knowledge of the area’s landmarks is important in locating the land in which you are interested. Thicker black lines indicate major roads. Minor roads are not delineated but are often easy to see on the photos. In many surveys, buildings in rural areas are shown in black, but newer surveys are omitting them.

After locating the parcel of land, write down the letters, numbers, or combination that labels the mapping units on the map sheet. At the beginning of the map section, on the back of the index map, is a legend that includes the soils and their corresponding labels as found on the map sheets. At this point, refer to the summary of tables in the table of contents to find the land use for which you are interested. In addition to agricultural information (suitability rating for various crops, pasture and trees), you will find suitability information for building sites, sanitary facilities, wildlife habitat, etc. Most tables are easily understood by anyone, but some are specifically targeted toward civil engineers and soil scientists.

A few cautions are in order—the most important being a matter of scale. Due to the scale of the maps (typically 1:20,000 in the printed surveys, and 1:24,000 on the digitized data), the soil mappers cannot delineate areas smaller than five acres. This is adequate for most agricultural and wildlife purposes, but may not be enough detail for someone interested in a one acre home site. The mapping units usually have inclusions of other soils within them, so on-site inspections of the land are important.

Another consideration is that soil survey maps could contain some errors. For example, if a survey indicates that the land use capability of a field is limited because of soil wetness, but you know from experience that the site is always dry, there may be a mapping error. Keep in mind that a single site inspection by someone unfamiliar with soil wetness indicators is not enough to identify such an error. Seasonal weather fluctuations and drought conditions must be taken into consideration. Only someone trained in soil classification or someone with long-term knowledge of the particular site can make this determination. Soil surveys remain valuable sources of information that is available for anyone’s use. Further assistance can be obtained from the USDA Natural Resource Conservation Service (NRCS), the South Carolina Department of Natural Resources, and the local Soil and Water Conservation District . Using the information costs nothing, ignoring it costs dearly.

Back to Soil Composition and Formation

Author

R. Scharf, SCDNR Land, Water, and Conservation Division

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