USDA Soil Mapper: How to Use Web Soil Survey Step by Step

The USDA soil mapper you are probably looking for is Web Soil Survey (WSS), the online map run by the USDA Natural Resources Conservation Service. The WSS home page says NRCS has soil maps and data online for more than 95 percent of US counties. You draw a boundary around your land, read the soil types inside it, and download a report at no charge.

This guide walks through the four tabs, shows how to read the results, and explains where the map stops being reliable. It also has a calculator that turns the numbers from your soil report into inches of water and days between irrigations, plus charts of what those ratings mean on US farmland.

What the USDA soil mapper shows

“USDA soil mapper” is a search phrase, not an official product name. The official tool is WSS, and the data behind it comes from the National Cooperative Soil Survey. The home page calls the site the single authoritative source of soil survey information.

According to the NRCS guide, WSS gives you a soil map over colour imagery or a topographic map, tables of soil properties and ratings, and data you can download for your own GIS software.

For any area you draw, you can look up:

• Soil types: each map unit, its acreage and its share of your area.
• Physical properties: texture, drainage class, depth to bedrock and available water capacity.
• Chemical properties: typical pH, organic matter and cation exchange capacity.
• Ratings by land use: suitabilities and limitations, with a list that changes according to the land use you pick.
• Ecological sites: information linked to the soils in each map unit, useful on rangeland.

How to use the USDA soil mapper in four tabs

The site works through four tabs, used from left to right. The steps below follow the NRCS how-to guide for version 3.0. Screens may differ slightly from its pictures.

1. Area of Interest

Find your land first. You can navigate by street address, state and county, soil survey area, latitude and longitude, PLSS township-range-section, federal land boundary or hydrologic unit. Zoom in until you can see your field edges on the imagery.

Then use the rectangle or polygon tool to draw around the land. The guide gives the maximum area as 100,000 acres. For odd-shaped fields, the polygon tool gives a closer fit, so the acreage table will not include your neighbour’s soils.

Before you leave, export the boundary as a shapefile from AOI Properties. You can load that file in a later session and return to the same area without drawing it again.

2. Soil Map

Click the Soil Map tab. WSS draws the map unit boundaries over the imagery and lists each unit with its symbol, name, acres and percent of your area. Click a unit name to read its full description.

Look at the percent column first. If one unit covers most of the field, a single management plan may be reasonable. If three or four units split the field, those lines are a good starting point for separate soil sampling zones.

3. Soil Data Explorer

This tab holds the ratings, properties and reports. It has three parts worth knowing:

• Suitabilities and Limitations: choose a land use, open a category folder, select a rating and click View Rating. You get a colour map and a table of the limiting features for each soil.
• Soil Properties and Qualities: choose one property, such as pH or drainage class, and view it as a map.
• Soil Reports: ready-made tables by topic, such as chemical soil properties, for your area.

Read the description under each rating. It explains which assumptions and options sit behind the result, and changing an option can change the map.

4. Shopping Cart

Despite the name, nothing is for sale. Add any map or table you want while you browse, then open the cart. WSS bundles your choices into one custom soil resource report as a PDF. The soil map, legend and map unit descriptions are included by default. You can get the report straight away or download it later.

Download data for GIS

Use the Download Soils Data tab when you need raw data. You can get SSURGO data clipped to your area, SSURGO for a whole soil survey area, or STATSGO2 for a state or the entire United States.

▶ How to draw a field boundary in the Farmonaut platform, the same idea as setting an area of interest. · 3:50

SSURGO, STATSGO2 and other ways to read the data

Pick the dataset that matches the size of your decision. The USDA catalog entry describes SSURGO as generally the most detailed level of soil geographic data from the National Cooperative Soil Survey. STATSGO2 is a broad inventory, mapped at 1:250,000 in the continental US, Hawaii, Puerto Rico and the Virgin Islands, and at 1:1,000,000 in Alaska.

Soil Data Access exists for needs that WSS does not meet. Its home page lists requests by SQL query or spatial filter, selected attributes, and results that do not have to follow the structure of the source database.

SoilWeb comes from the California Soil Resource Lab at UC Davis. It reads USDA-NCSS detailed data for most of the United States and runs in a browser on a desktop, tablet or smartphone. It suits a quick check at the edge of a field. Use WSS itself when you need a dated report.

How to read a soil map unit: a worked example

A map unit name usually gives a soil series, a surface texture and a slope range. Take Clarion loam, an upland soil of the Midwest. The Official Series Description says Clarion soils are very deep and moderately well drained, formed in glacial till, on slopes from 1 to 9 percent. They are extensive in north-central Iowa and south-central Minnesota.

That one description already answers useful questions. The same source reports a frequently saturated zone at 4 to 6 feet between March and June in normal years. That matters more for a basement or a septic field than for a corn root in July. The description is the place to look when a rating surprises you.

You can read any series the same way. Ask four questions:

1. How deep can roots go before they meet bedrock, a dense layer or water?
2. How fast does water leave, and is there a wet season?
3. How much water does the root zone hold?
4. What limits this soil for my planned use, and can I change that limit?

Soil properties that change farm decisions

Available water capacity

Texture strongly affects how much water a soil can store for a crop. The FAO Irrigation and Drainage Paper 56 gives typical ranges by texture, shown in the chart below. Its figures are volume fractions, so 0.15 means about 0.15 inches of water per inch of soil.

Chart

Typical available water, selected soil textures

Field capacity minus wilting point, as a volume fraction (inches of water per inch of soil)

At the middle of each range, sand holds less than half of what silt holds. A field that crosses from sandy loam to silt loam may therefore need different irrigation timing, even under one pivot. FAO notes that these are typical values; use the figure for your own map unit when you have it.

Drainage class and depth

Drainage class tells you how often and how long the soil stays wet. On a poorly drained unit, planting dates, traffic and crop choice all come under pressure. Options include tile drainage, raised beds or crops that tolerate short flooding. Check local rules before you change drainage, because wetland rules can apply.

Depth to bedrock or a dense layer sets the real root zone. A shallow soil cannot be fixed with fertilizer, and it holds less water no matter how good the texture is.

PH, organic matter and CEC

WSS gives typical values for each soil, and these are useful for planning. They help you predict how a soil may respond to lime or how well it can hold nutrients. They are not a measure of your field today, because past lime, manure and tillage are not in the map.

Land capability class on a soil map

Land capability is the quickest summary of a soil’s limits. Classes run from I to VIII, and higher numbers mean greater limitations and narrower choices. The 2022 National Resources Inventory explains that subclasses name the main problem: e for erosion, w for wetness, s for root zone limits and c for climate.

The chart below shows where US cropland sits. Class II and III together hold about 76% of non-Federal cropland, so a class II or III rating is ordinary for farmland and does not mean poor land. The letter tells you what to manage.

Chart

US cropland by land capability class

Million acres of non-Federal cropland, 2022

Prime farmland and erosion

Prime farmland is land with the best mix of physical and chemical traits for food, feed, forage, fiber and oilseed crops, which is also available for those uses. The same inventory counts about 312 million acres in 2022. If you are buying or valuing land, ask how the parcel is classed and confirm it with your local NRCS office.

Chart

How US prime farmland is used

Million acres of non-Federal rural prime farmland, 2022

Erosion ratings deserve attention too. The inventory reports that cropland erosion rates fell 34 percent between 1982 and 2022, but most of that fall came early. The chart shows both water and wind erosion have been almost flat since about 2002. Sloping class e soils still need residue, cover crops, contour work or terraces where these fit the farm.

Chart

Cropland erosion rates in the US

Tons per acre per year, estimated average on non-Federal cropland

Turn soil report numbers into an irrigation interval

Here is one practical use of your AOI table. Take the acres and available water capacity of your two largest map units. The calculator below finds the weighted average and estimates how much water you can use before the crop may start to feel stress.

The method comes from FAO 56: total available water is the water content range multiplied by rooting depth, and readily available water is a share of that total. FAO’s table gives a depletion fraction of 0.50 for soybeans and 0.55 for field corn, wheat and alfalfa hay under its reference conditions. Adjust for your crop, and check the result against soil moisture readings or local extension advice.

Try the numbers for your own farm below.

What the USDA soil mapper cannot tell you

WSS is the official soil map, but it has limits that matter for farm and site decisions.

• It is not a soil test. WSS does not report the nitrogen, phosphorus or potassium in your field now. NC State Extension’s gardener handbook advises testing before planting and every two to three years after that. Base fertilizer rates on a lab test, and follow local rules.
• Map units are generalised. The catalog entry explains that map units link to the proportionate extent of their component soils, so a unit can hold more than one soil. A special features layer marks some spots too small to draw at the mapping scale.
• Some jobs need a site visit. The home page says onsite investigation is needed in some cases, including soil quality assessments and certain conservation and engineering work.
• Updates are yearly. Official soil survey data are generally updated only on October 1 each year, with exceptions for newly completed datasets and critical fixes. Note the survey version date on any report used for a permit or sale.
• Coverage is not complete. The 95 percent figure means some counties do not yet have online data. The Status Maps link on the home page shows what is available.
• It does not show this season. The map shows the soil, not the crop growing on it. Compaction from last harvest or a drowned corner will not appear.

For questions the map cannot settle, contact your local USDA Service Center or NRCS state soil scientist. For a permit, sale or building project, get advice from a licensed professional too.

Using soil survey data beyond the farm

The Suitabilities and Limitations list changes with the land use you select, so the same steps serve other users. The aim stays the same in each case: find the limit early, then confirm it on site.

Best practices for soil map users

• Draw tight boundaries. Follow the true field edge, or import a boundary file, so the percentages describe your land.
• Save your area. Export the shapefile so next year’s check uses the same boundary.
• Use the map to plan sampling. Sample each main soil type on its own, rather than mixing unlike soils into one lab sample.
• Add other layers. Combine soils with slope, hydrology, weather and yield history to build a full site profile.
• Dig a few holes. A soil probe or spade check at several points shows if the mapped soil matches your field.
• Date your report. Keep the PDF, and download a new one after the next October update if the decision is still open.

▶ A walkthrough of reading NDVI maps and pulling a report for your own field. · 19:36

Adding satellite data to a soil map

A soil map changes slowly, while a crop changes week by week. Comparing the two can be useful. If one part of a field keeps showing weak vegetation, and the same area sits on a different map unit, soil is one possible cause worth checking. The satellite image cannot tell you the cause on its own, so walk the spot and test it.

Farmonaut Satellite + AI Farm Monitoring System offers satellite vegetation maps for fields you draw, on the web or in the mobile app. It adds a season view and does not replace a soil survey or soil test.

Related pages on our site: farm fleet management, satellite data API, API developer docs, carbon footprint tracking, crop loan and insurance checks and product traceability.

▶ A tutorial on monitoring crops with satellite maps in the Farmonaut web app. · 8:43

FAQ

Is there a charge for the USDA soil mapper?

No. NRCS provides maps, tables, the custom PDF report and the data downloads at no charge. The guide even describes the shopping cart as carrying no cost, and no purchase takes place.

What is the difference between WSS and SSURGO?

WSS is the website you use. SSURGO is the detailed soil database behind its maps and ratings. You can read SSURGO through WSS or download it for GIS software.

How large an area can I map?

The how-to guide gives a limit of 100,000 acres per area of interest. For a larger area, download whole soil survey areas, use STATSGO2 for broad work, or use Soil Data Access.

How often is the soil data updated?

Generally once a year, on October 1, with exceptions for newly completed datasets and critical fixes. RSS notices of updates by state are available, according to the guide.

Can I use the map instead of a soil test?

No. The map gives typical properties for a soil type. A lab test measures the nutrients and pH in your field now, and it should guide fertilizer and lime rates.

Does the map cover land outside the United States?

WSS covers US soil surveys, including support for the Pacific Island Area. Readers in Canada, the UK, Europe, Australia or New Zealand should use their own national or state soil agency.