Soil Survey Observations
What official soil surveys document about particular places — and what kind of fact each number is.
A soil survey does not measure fields. It maps soil bodies and publishes a representative value for each named component of one: the surveyor’s characterisation, informed by field description and laboratory work, of a polygon on a map. A measurement taken on one farm can differ from the representative value of the map unit containing it, and nothing here should be read as describing a particular field.
Every value carries the scale it belongs to. A number for a mapped soil body is not a number for a county, and a county’s map units are not a number for a state — so what is shown below is the spread across a state’s soil bodies, never a single figure standing in for the state.
For what a soil type is — a chernozem, a clay soil, a podzol — see the soils reference. This page is about what a survey has documented on particular ground.
- Observations
- 91,620
- Mapped soil bodies
- 13,390
- Jurisdictions
- 13
- Surveys read
- 1
What is documented, and where
| Jurisdiction | Soil bodies | pH across those bodies | Organic matter | Clay |
|---|---|---|---|---|
| CaliforniaUS-CA | 3,774 | 3.2–10.1 | 0.0–100.0% | 0–70% |
| FloridaUS-FL | 482 | 3.0–8.7 | 0.1–87.5% | 0–85% |
| IowaUS-IA | 543 | 4.6–8.2 | 0.0–75.0% | 0–60% |
| IllinoisUS-IL | 575 | 4.3–8.4 | 0.1–87.0% | 0–65% |
| IndianaUS-IN | 599 | 4.2–8.2 | 0.3–87.0% | 0–68% |
| KansasUS-KS | 412 | 4.3–9.6 | 0.2–69.0% | 1–60% |
| MinnesotaUS-MN | 1,032 | 3.5–8.2 | 0.1–98.0% | 0–70% |
| North DakotaUS-ND | 376 | 6.0–8.8 | 0.3–95.0% | 0–63% |
| NebraskaUS-NE | 417 | 5.0–9.2 | 0.0–85.0% | 0–58% |
| South DakotaUS-SD | 716 | 4.4–8.8 | 0.0–85.0% | 0–68% |
| TexasUS-TX | 1,565 | 3.4–9.0 | 0.0–85.0% | 0–86% |
| WashingtonUS-WA | 2,032 | 3.8–10.1 | 0.1–95.0% | 0–53% |
| WisconsinUS-WI | 867 | 3.1–8.2 | 0.0–95.0% | 0–60% |
Each range is the spread of the survey’s representative values across that jurisdiction’s mapped soil bodies. It is not a range of measurements, and no single value in it describes the jurisdiction.
How the survey classifies them
These are orders of the USDA Soil Taxonomy, the system this survey uses. No crosswalk to the World Reference Base is applied: the two systems classify the same ground differently, and matching an Order to a Reference Soil Group by name would produce confident nonsense.
| Order | Soil bodies |
|---|---|
| Mollisols | 4,419 |
| Alfisols | 2,585 |
| Entisols | 1,878 |
| Inceptisols | 1,437 |
| Aridisols | 678 |
| Andisols | 555 |
| Ultisols | 338 |
| Spodosols | 331 |
| Vertisols | 316 |
| Histosols | 230 |
| Alfisols to Mollisolsthe survey records both within the state | 153 |
| Entisols to Inceptisolsthe survey records both within the state | 64 |
| Inceptisols to Mollisolsthe survey records both within the state | 63 |
| Entisols to Mollisolsthe survey records both within the state | 55 |
| Alfisols to Inceptisolsthe survey records both within the state | 25 |
| Mollisols to Vertisolsthe survey records both within the state | 25 |
| Alfisols to Ultisolsthe survey records both within the state | 19 |
| Aridisols to Entisolsthe survey records both within the state | 12 |
| Andisols to Inceptisolsthe survey records both within the state | 12 |
| Alfisols to Aridisolsthe survey records both within the state | 12 |
| Alfisols to Entisolsthe survey records both within the state | 10 |
| Aridisols to Inceptisolsthe survey records both within the state | 10 |
| Alfisols to Vertisolsthe survey records both within the state | 6 |
| Inceptisols to Vertisolsthe survey records both within the state | 6 |
| Andisols to Mollisolsthe survey records both within the state | 5 |
| Aridisols to Mollisolsthe survey records both within the state | 4 |
| Entisols to Vertisolsthe survey records both within the state | 4 |
| Entisols to Ultisolsthe survey records both within the state | 2 |
| Alfisols to Andisolsthe survey records both within the state | 2 |
| Andisols to Aridisolsthe survey records both within the state | 1 |
| Ultisols to Vertisolsthe survey records both within the state | 1 |
| Inceptisols to Ultisolsthe survey records both within the state | 1 |
| Andisols to Entisolsthe survey records both within the state | 1 |
| Aridisols to Vertisolsthe survey records both within the state | 1 |
| Entisols to Histosolsthe survey records both within the state | 1 |
| Histosols to Mollisolsthe survey records both within the state | 1 |
| Histosols to Inceptisolsthe survey records both within the state | 1 |
| Entisols to Spodosolsthe survey records both within the state | 1 |
| Inceptisols to Spodosolsthe survey records both within the state | 1 |
| Gelisols | 1 |
| Alfisols to Spodosolsthe survey records both within the state | 1 |
500 soil bodies are classified into more than one order within a single state, and 1,522 into more than one drainage class. Both are shown as they are recorded. Choosing one would invent a certainty the survey does not have.
What is not here
- Crop suitability
- AgricultureID does not infer crop suitability from soil observations. That a crop is grown where a soil occurs is not evidence that the soil suits it, and no such link is published without a source that makes it.
- Subsoil
- Only the surface horizon is read. The survey publishes deeper horizons and they are not represented here.
- Laboratory measurements
- No laboratory characterisation dataset is ingested. The USDA Kellogg Soil Survey Laboratory publishes one and it is a separate source from SSURGO’s tabular data.
- Modelled soil maps
- ISRIC SoilGrids was examined and not ingested. It predicts properties for 250 m raster cells, and placing those beside a survey’s mapped soil bodies as though both described the same thing is exactly the scale conflation this layer refuses. It needs its own spatial basis and its own contract, not a column next to SSURGO.
- Derived values
- Nothing here derives a soil property from other properties. A pedotransfer function would produce this class and none is applied.