You’ve Got Soil Questions, and We’ve Got Answers

If you want to know how to access soil information for your property, work with multiple soils, or learn how to adapt your forest management for the soils you have, the USDA has online resources available to all that can help guide you through those processes.

Q: How can I access soil information for my property?

A: The U.S. Department of Agriculture publishes soil survey data online through a platform called Web Soil Survey. Although some areas are still undergoing initial mapping, the vast majority of private lands in the Pacific Northwest have soil survey data available. The data is available to the public, and best of all, it’s free! The following steps will help you obtain soils information for your property:

Step 1: Start Web Soil Survey by going to websoilsurvey.sc.egov.usda.gov/App/HomePage.htm. Click the large green “START WSS” button.

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Step 2: Define your area of interest (AOI). This is the area for which you will be obtaining soil survey data. You can simply enter an address or select a state/county, click “view”, and then zoom to your desired location on the map. Other navigation options are also available, although these methods are the most common and user-friendly.

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Once you are zoomed to your property or desired location, click the rectangular AOI tool to drag a box or use the polygon AOI tool to click around your select your AOI.

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The rectangle or polygon you select should then look like this:

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Step 3: View your soil map. Click the “Soil Map” tab at the top of your screen to see the soil survey map for your AOI. The map unit legend will appear on the left side of your screen. Clicking on the name of a map unit in the legend will open a window containing a description of that map unit and its individual soil components.

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Q: The soil map unit covering my property has multiple soils in it. How do I know which one I am working with?

A: In order to answer this question effectively I first need to clarify what exactly a “map unit” is, as well as explain the different types of map units used in soil surveys.

A map unit is a collection of areas defined and named the same in terms of their soil components (unique soil types) and/or miscellaneous (“non-soil”) areas. Each polygon delineated on a soil map is assigned a label or symbol that corresponds to a map unit. There are four general types of map units, however, for the purpose of this discussion I will focus on the three most commonly seen in soil survey products.

Consociations are map units dominated by a single soil component. A consociation may include minor components that occupy a relatively small (< 15%) percentage of the map unit area, but the map unit name will contain only the name of the dominant soil. Complexes and associations are map units consisting of two or more dissimilar components that occur in a consistent repeating pattern. The soil components comprising a complex cannot be separated at the mapping scale, while the components of an association can be; however, due to land use or user needs, they are not. Both of these map unit types may also include minor components. The map unit names for complexes and associations will contain the names of multiple soils.

Now to answer the original question: The map unit description (accessible by following step 3 above) will provide descriptions of typical site the soil characteristics for each component in the map unit. The type of map unit covering your property can be inferred from the map unit name. If the map unit is a consociation, the soil component that you are most likely working with is going to be the single dominant component for that map unit. However, if the specific area on your property is not representative of the map unit’s typical landscape/landform, you may be working with a minor component.

If the map unit covering your property is a complex or association, you will have to look at the map unit description to determine the component(s) you are working with. Soils tend to correlate strongly with topography, so focusing on the “setting” category for each component’s description is recommended. If the setting details alone don’t allow you to confidently determine your soil, the “properties and qualities” category under each component’s description would be the next best place to look. The goal is to find the component that has both a setting and soil characteristics that best match the point on your property that you are interested in. If that area on your property is rather large and not uniform, there is a high probability that multiple soils will exist in that area, especially if the map unit is a complex.

Q: How can soil information help me make management decisions?

A: Having a basic understanding of the distribution and characteristics of your soils can be extremely beneficial to you as a landowner. Knowledge of soil properties such as texture, drainage class, depth to a restrictive layer, and flooding or ponding frequency can influence management decisions including road and structure placement, as well as species selection and planting density strategies.

The summary information found in the map unit description provides a great overview of site and soil properties. However, the Web Soil Survey platform also contains hundreds of interpretations and thematic maps specifically designed to aid in the making of management decisions. Again, these tools are free and available to the public! The following steps will walk you through how to access and use these valuable tools.

Step 1: Define your AOI and access your soil map, as shown in steps 1-3 above. Click on the “Soil Data Explorer” tab. Then click either the “Suitabilities and Limitations for Use” or “Soil Reports” tab.

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Step 2: Both the “Land Management” and “Vegetative Productivity” categories have several interpretations concerning various aspects of forestry operations. Click the downward facing arrow for these categories and then click the downward facing arrow for any interpretation you would like to run. Look through the options and customize them to best apply to your situation. For example:

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Step 3: Once you have your options selected, click the “View Rating” button to see your customized interpretive map. Click the yellow “Legend” tab on the upper-left side of the map to see the map legend. Below the map will be tables containing more detailed results for the selected interpretation.

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Step 4: Explore the many reports and interpretations available under the “Suitabilities and Limitations for Use” and “Soil Reports” tabs. You may save the results of any report or interpretation by clicking the “Add to Shopping Cart” button located in the upper-right of the screen.  You can save numerous interpretations and reports by adding them to your cart. When you are finished, simply click on the “Shopping Cart (Free)” tab, review the table contents, and then click “Check Out” to download a PDF copy of your comprehensive report.

Max Ross, Soil Scientist, USDA Natural Resources Conservation Service, max.ross@wa.usda.gov