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Soil Survey Manual SIZE 8 BY 10 Agriculture Handbook No. 18 February 2018 The Soil Survey Manual, USDA Handbook No. 18, provides the major principles and practices needed for making and using soil surveys and for assembling and using related data. The term “soil survey” is used here to encompass the process of mapping, describing, classifying, and interpreting natural three-dimensional bodies of soil on the landscape. This work is performed by the National Cooperative Soil Survey in the United States and by other similar organizations worldwide. The Manual provides guidance, methodology, and terminology for conducting a soil survey but does not necessarily convey policies and protocols required to administer soil survey operations. The soil bodies contain a sequence of identifiable horizons and layers that occur in repeating patterns in the landscape as a result of the factors of soil formation as described by Dokuchaev (1883) and Jenny (1941). Soil scientists gain an understanding of the factors of soil formation in their area, along with the resulting expression of their interaction in the soil, and are then able to make maps of the natural soil bodies quite efficiently (Hudson, 1992). The maps of soil bodies are related to, but different from, maps of single soil properties, such as organic matter or pH. The latter are made by sampling and statistical modeling to show how these properties vary over the landscape.