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Map of the Month

The value of soil survey maps and the influence they have on the health and wealth of planet Earth are often overlooked. Simply put, the world’s population takes for granted the importance of the “ground” we stand on. This page is designed to generate awareness about the relationship between historic maps and today’s environmental triumphs. Soil maps have always been critical for conservation and “Helping People Help the Land.” 

Each of these maps has historical significance. Some illustrate the work of noteworthy soil scientists; others show information that provided insight and direction for doing the right thing for the land. Whether the scientific community is addressing erosion or global warming, soil survey maps and the story they tell are foundational for how we treat the land.

Click on each image below to open a PDF file.

The USDA Soil and Plant Science Division recently developed a set of images and map layers to communicate the complexity, variability, and magnificence of soils and soil colors. In nature, soils occupy a three-dimensional space. This recent effort affords the opportunity to observe changes in soils and inherent soil properties both horizontally (across the landscape) and vertically (with depth). These maps and images present technical value for scientists, geographers, and educators but also have significance for anyone who simply appreciates the beauty that unfolds as art within the medley of colors.

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Soil surveys are evolving from the polygon-based format to the raster-based (pixel-based) format. These maps show the striking contrast in the consistency and detail of information between the two formats.

Raster soil surveys are the next generation of soil information and can be generated from both update projects and initial mapping projects. Raster soil surveys compliment traditional scale-dependent soil surveys by depicting soil types, properties, and ratings at higher resolution.

This map shows the suitability of soils to be imaged using ground penetrating radar. The map was made by evaluating properties derived from soil mapping by the National Cooperative Soil Survey. This suitability rating is a “soil survey interpretation.” Interpretations predict soil behavior for specified soil uses and under specified soil management practices.

Modern soil surveys are both scientific publications and sources of practical advice in the form of soil interpretations. Currently, the USDA-NRCS Soil and Plant Science Division provides over 500 soil-based interpretations.

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This map shows the distribution of soil series in the USDA Soil Survey Regions in the continental United States. Soil series are a level in the soil classification system. Soil Survey Regions are administrative units responsible for the quality of soil survey information.

The soil series is the most homogeneous 3-D body in the U.S. system of soil taxonomy. Soil maps show the locations of 3-dimensional soil bodies. Like a body of water, a soil series has a mappable surface area, lateral boundaries, and depth. A detailed soil map can show not only where series occur on the landscape but also the phases of the series. Phases are based on rockiness, depth to bedrock, slope, and amount of erosion.

By comparing USDA soil survey maps of varying ages, you can discern relationships that are not otherwise apparent. These maps of a single county from 1909, 1938, and 1980 illustrate this point.

Early soil maps were largely a reflection of a region’s geology. Modern soil maps, while still retaining information about geology, are based on Soil Taxonomy. They contain greater information about the multitude of properties within a soil. This classification system is useful because it groups and organizes soil properties based on (1) soil horizons and (2) long-term soil temperature and moisture.

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Block diagrams reduce the innumerable details of a crowded landscape to a relatively few simple lines. As such, they are very effective for communicating how and why soils differ from one place to another.

Block diagrams have been a routine part of the USDA soil survey program because they work so well for communicating soil patterns. Their use was especially widespread in the soil surveys of the 1970s, ‘80s, and ‘90s. During that era, professional illustrators employed by USDA worked with soil scientists to create the block diagrams. Currently, over 3,000 block diagrams are available online.

The U.S. produces a vast variety of crops on diverse soils in different climates, ranging from citrus in the south to cranberries in the north. How can we make such vastness intelligible? Or more specifically, how can we divide the U.S. into large regions for purposes of resource conservation and water quality improvement? The answer to this question began evolving in the early 20th Century as soil conservationists began working with scientists to create large map units with similar land, water, and biological resources. It continues today with the concept of Major Land Resource Areas (MLRAs).

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Soils differ from each other based on color, mineralogy, age, depth, and lateral boundaries with neighboring soils. But soils also differ for utilitarian purposes. Some soils have a greater ability than others to produce high crop yields, provide firm building foundations, purify contaminated water, or sequester carbon dioxide from the atmosphere.

This 1931 map provided a major step for understanding the meaning of “soils differ.” It identified soils as part of nature, showing how soil types are linked to the major biomes of grassland, forest, and desert.

By the late 1890s, when USDA was taking form, agricultural scientists and legislators widely recognized that more information was needed about the nation’s soils. To address that need, the USDA Division of Agricultural Soils and the National Cooperative Soil Survey were formed. They combined the expertise of the Division with land-grant universities and State and local agencies for the purpose of making soil maps. The aesthetic turn-of-the-century maps generated by the soil survey not only show soil patterns across the landscape, they also show features that are of interest to both historians and scientists.

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International soil scientists, including Europeans, Chinese, Africans, and Latin Americans, have been essential in the development of the current USDA soil classification system.

Modern networks of communication, transportation, global agriculture, and environmental issues have made international communication about soils more important than ever. Consequently, staff of the NRCS World Soil Resources branch have created maps that capture and display the state of world soils. This map shows where soils have been greatly modified by human activity, both in modern and ancient times.

The map shows the concentration of calcium carbonate in the soils of Nebraska. Calcium carbonate (CaCO3), like soil organic matter, stores carbon dioxide from the atmosphere. This is important because excess carbon dioxide is a major driver for climate change.

In the past, research has focused on using no-till agriculture and other management techniques to remove excess carbon dioxide from the air and store it in soils as organic matter. Currently, research includes how to remove excess carbon from the atmosphere and store it in soils as CaCO3.

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Hugh Hammond Bennett is most widely known as a champion for making the Nation and the world aware of the perils of soil erosion. During the first part of his career, however, he was a mapper, a soil scientist, and a pedologist.

Although most of his work was in the southeastern United States, he made some of the first soil maps of Alaska, as shown by this 1914 soil map of the Kenai Peninsula, Alaska. This map not only shows the soils (including some organic soils, some alluvial soils, and many Cryic soils), it also shows the extent of the glaciers in 1914.