Soil series profile
Irwin soil series
Irwin is a moderately well drained soil with a silty clay loam surface, mapped on 1,062,444 acres in 45 counties across 2 states. Hydrologic group D.
- Drainage class
- Moderately well drained 100% of mapped acres
- Hydrologic group
- D 100% of mapped acres
- Typical topsoil pH
- 6.5 slightly acidic · range 6.5–6.5
- Mapped area
- 1.1M acres in 45 counties, 2 states
Typical Irwin profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–7 in (Ap) | Silty clay loam | 6.5 | 33% | 8% | 3% |
| 7–30 in (Bt) | Silty clay | 7.2 | 45% | 5% | 1% |
| 30–41 in (Btk) | Silty clay | 7.8 | 40% | 6% | 0.9% |
| 41–67 in (2Bt) | Silty clay | 7.9 | 42% | 6% | 0.7% |
| 67–79 in (2C) | Silty clay | 8.0 | 43% | 5% | 0.5% |
What this means
What Irwin soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Irwin soils is slightly acidic: pH 6.5, the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 100% of mapped Irwin acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silty clay loam (100% of mapped Irwin acres).
100% of mapped Irwin acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
On 100% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.
For a septic system
For conventional septic absorption fields, NRCS rates 100% of the acres in mapped Irwin soils very limited, 0% somewhat limited and 0% not limited.
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Irwin soil is found
Mapped acres
Irwin is mapped in Kansas and Nebraska.
| County | Acres | Share of county land |
|---|---|---|
| Dickinson County, KS | 215,682 | 39.7% |
| Butler County, KS | 207,354 | 22.7% |
| Marion County, KS | 169,881 | 28.1% |
| Morris County, KS | 108,868 | 24.5% |
| Wabaunsee County, KS | 58,968 | 11.6% |
| Riley County, KS | 56,602 | 14.5% |
| Cowley County, KS | 43,094 | 6.0% |
| Sedgwick County, KS | 41,995 | 6.6% |
| Chase County, KS | 37,890 | 7.7% |
| Geary County, KS | 30,763 | 12.5% |
| Harvey County, KS | 26,916 | 7.8% |
| McPherson County, KS | 18,611 | 3.2% |
| Saline County, KS | 18,601 | 4.1% |
| Lyon County, KS | 3,823 | 0.7% |
| Brown County, KS | 3,382 | 0.9% |
| Lancaster County, NE | 3,156 | 0.6% |
| Greenwood County, KS | 2,657 | 0.4% |
| Otoe County, NE | 2,084 | 0.5% |
| Sumner County, KS | 1,989 | 0.3% |
| Marshall County, KS | 1,981 | 0.3% |
| Shawnee County, KS | 1,722 | 0.5% |
| Pottawatomie County, KS | 1,403 | 0.3% |
| Atchison County, KS | 1,394 | 0.5% |
| Pawnee County, NE | 805 | 0.3% |
| Elk County, KS | 622 | 0.2% |
| Jackson County, KS | 566 | 0.1% |
| Cass County, NE | 441 | 0.1% |
| Washington County, KS | 206 | 0.0% |
| Woodson County, KS | 161 | 0.1% |
| Clay County, KS | 145 | 0.0% |
| Jefferson County, KS | 124 | 0.0% |
| Nemaha County, KS | 94 | 0.0% |
| Osage County, KS | 82 | 0.0% |
| Doniphan County, KS | 79 | 0.0% |
| Cloud County, KS | 77 | 0.0% |
| Saline County, NE | 77 | 0.0% |
| Republic County, KS | 57 | 0.0% |
| Seward County, NE | 31 | 0.0% |
| Reno County, KS | 30 | 0.0% |
| Chautauqua County, KS | 25 | 0.0% |
| Rice County, KS | 3 | 0.0% |
| Ottawa County, KS | 3 | 0.0% |
| Kingman County, KS | 1 | 0.0% |
| Jewell County, KS | 0 | 0.0% |
| Coffey County, KS | 0 | 0.0% |
Septic absorption fields
NRCS rating, share of Irwin acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 100.0% |
Drainage, water table and flooding
Share of Irwin acres
- Depth to seasonal high water table
- About 2.5 feet (30 in) (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 2–5% (median 2%).
- Topsoil organic matter
- Median 3%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 0.0% |
| Moderately well drained | 100.0% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 0.0% |
| C: slow infiltration | 0.0% |
| D: very slow infiltration (clayey, shallow or wet) | 100.0% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.0% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- All map unit components named Irwin (component kind "Series") in SSURGO: 1,062,444 acres.
- Method
- Shares are by mapped acres of Irwin components. The profile comes from the single largest Irwin component. Full methodology.