Introduction

Washington Soil Atlas

This Washington Soils Atlas is designed to present information about Washington State soils in an organized format to a nontechnical audience.  The intention is to assist readers understand the importance of soil.  Soil is a vital natural resource to residents of Washington because it serves numerous functions that assist residents to live and to earn an income.  It also produces food and fiber for populations of the world.

Soil serves to regulate, partition, and filter air and water. It supports the projects built into and onto it and serves as a building material for other projects. Soil nourishes the plants that produce food and fiber for animal and human consumption. The soil assists in decomposing and recycling organic materials, and it preserves natural and cultural history. Therefore, soil is complex and it is also a fundamental material for all life. 

Soil, in its usual state, is made up of about 25 percent air, 25 percent water, 5 percent organic matter, and 45 percent mineral matter.  When compacted those percentages change and hence so do the soil’s properties.  When compacted, water intake is reduced, there is less air for plant use, and because water can’t infiltrate, soil erosion increases.  It is important to take care of Washington’s soil resources.

The soils presented in this atlas were selected from several hundred soil series recognized, mapped, and correlated in Washington State. Each of the soil series has a distinctive set of characteristics that make it a unique individual just as each person is a unique individual. The selected group of soils represents most of the unique soil features that occur within Washington. This was done because it is impractical to demonstrate each mapped and correlated Washington soil but the soils of this atlas can represent most all Washington State soils. Soil series are named after geologic formations, geographic locations, and some soil names are “coined” or made up by soil scientists who describe, map, and correlate soils from within the National Cooperative Soil Survey (NCSS) program. Soil series are correlated by NCSS soil scientists so that anywhere a particular soil individual occurs it is identified and called by the same name.

Photographs of the soils show the various layers or soil horizons and they also show a representative landscape where each soil series occur. Along the left side of each soil profile is a scale in inches. Along the right side of each soil profile are labeled the major genetic horizons of the soil using letters and numbers. These letters and numbers are used by soil scientists to show the soil forming process that has taken place in the development of each soil horizon.

The genetic soil horizons have been simplified for this atlas. As one can easily see in the photographs, each “A” horizon and each “B” horizon do not look alike. The soil scientist who described these soil profiles, used knowledge gained in university studies and experience gained from identifying, describing, mapping, and correlating soil in many locations in Washington State or other states to help determine how each horizon has developed from the original soil parent material. The soil horizon designators are useful in making comparisons among soils. A brief discussion or definition of each genetic soil horizon designator is found in the glossary of this atlas. The subscript identifiers are defined in Appendix 1 of this atlas. Appendix 2 provides a map and brief description of the Land Resource Regions in Washington.

The glossary terms may be helpful to assist users to understand certain words that are used to describe each soil. The definitions have been simplified to help more users understand them. More detailed definitions and information can be found in soil survey documents and publications like the Soil Survey Manual (http://soils.usda.gov/technical/manual) and Soil Taxonomy (http://soils.usda.gov/technical/classification/taxonomy) .

All soils are classified according to a recognized international system (Soil Taxonomy). This taxonomic classification system was developed to classify the hundreds of thousands of soils that occur in the world. It is a dynamic system that can be adjusted or added to when new kinds of soils are recognized that don’t fit within the framework of the existing system. The soil classification system resembles the systems that are used for classifying plants and animals. The soil classification system is mainly used by soil scientists to identify a soil individual, compare one soil to another, and to group soils together that have similar properties and uses.

Other information that is included for each soil series contained in the Washington Soils Atlas is the soil classification at the family level. It includes several items which describe soil depth, drainage class, parent material, arrangement of soil horizons, and other information. Also included is information on climate, topography, elevation, natural plant community, soil use(s), and management considerations. Management considerations are based on soil properties that impact the soil’s use. In many cases, mitigation measures must be used to modify the soil to modify it for a specific purpose. A map that shows where the soil series is located within the state is also included for each soil series. A link is also provided for the official soil series description that is maintained for each soil series in the NCSS database.

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