Soil series profile

Belknap soil series

Belknap is a somewhat poorly drained soil with a silt loam surface, mapped on 637,595 acres in 71 counties across 4 states. Hydrologic group B/D.

#392 by mapped area coarse-silty Fluventic Endoaquepts (Inceptisols)

Drainage class
Somewhat poorly drained
>99% of mapped acres
Hydrologic group
B/D
81% of mapped acres
Typical topsoil pH
5.9
moderately acidic · range 5.9–5.9
Mapped area
638k
acres in 71 counties, 4 states

Typical Belknap profile

Texture and pH by depth

Typical Belknap soil profile by depth 0 in 20 in 40 in 60 in 80 in 100 in 0–3 in · Ap · pH 5.9 · 13% clay Silt loam 3–9 in · Bw · pH 5.0 · 14% clay Silt loam 9–77 in · Bg · pH 5.0 · 15% clay Silt loam 77–100 in · BCg · pH 5.6 · 17% clay Silt loam
Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).
Show as a table
Typical Belknap horizons (representative values)
Depth Texture pH Clay Sand Organic matter
0–3 in (Ap) Silt loam 5.9 13% 9% 2%
3–9 in (Bw) Silt loam 5.0 14% 10% 0.75%
9–77 in (Bg) Silt loam 5.0 15% 11% 0.5%
77–100 in (BCg) Silt loam 5.6 17% 12% 0.25%

Representative values from the most extensive Belknap map unit (Belknap silt loam, 0 to 2 percent slopes, occasionally flooded, survey area KY631). Other map units of this series vary within the series range.

Hands holding dark garden soil
Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Belknap soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Belknap soils is moderately acidic: pH 5.9. Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.

Loamy topsoil (loam, silt loam and similar) covers 99% of mapped Belknap acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (99% of mapped Belknap acres).

>99% of mapped Belknap acres is somewhat poorly to very poorly drained, so soil stays soggy for long spells after rain and in wet seasons. Raised beds, plants that tolerate wet feet, and not working the soil while wet all help.

For lawns and yards

On 99% 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.

A seasonal high water table comes within 18 inches of the surface on 81% of mapped acres, often in spring. Basements, sump pumps and lawns in low spots feel it first.

For a septic system

For conventional septic absorption fields, NRCS rates 99% of the acres in mapped Belknap soils very limited, 0% somewhat limited and 0% not limited (1% not rated, such as urban land, pits or water).

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.

Flooding is mapped on >99% of the acres (53% occasional, 45% frequent).

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Belknap soil is found

Mapped acres

Belknap is mapped in Illinois, Kentucky, Missouri and Indiana. The 60 counties with the most Belknap acres:

Counties with the most mapped Belknap soil
County Acres Share of county land
Hamilton County, IL 37,167 13.4%
Hopkins County, KY 36,134 10.4%
Jefferson County, IL 34,530 9.7%
Daviess County, KY 34,466 11.7%
Wayne County, IL 31,488 7.0%
Williamson County, IL 28,667 11.0%
Franklin County, IL 26,370 10.2%
Webster County, KY 24,906 11.6%
Saline County, IL 21,798 8.9%
Muhlenberg County, KY 21,488 7.2%
Henderson County, KY 20,146 7.2%
McLean County, KY 20,134 12.4%
Audrain County, MO 20,124 4.5%
Edwards County, IL 18,520 13.1%
Pike County, IN 18,103 8.5%
Richland County, IL 17,794 7.8%
Perry County, IL 17,244 6.4%
White County, IL 17,128 5.6%
Massac County, IL 15,065 10.6%
Montgomery County, MO 14,919 4.3%
Lawrence County, IL 14,828 6.3%
Marion County, MO 14,335 5.1%
Johnson County, IL 14,099 7.0%
Jackson County, IL 11,122 3.1%
Pike County, MO 10,603 2.5%
Pulaski County, IL 9,663 8.2%
Wabash County, IL 9,296 6.5%
Caldwell County, KY 8,445 3.8%
Hancock County, KY 8,405 6.9%
Pope County, IL 8,377 3.9%
Ralls County, MO 7,781 2.6%
Marion County, IL 6,035 1.7%
Clay County, IL 5,717 1.9%
Callaway County, MO 5,383 1.0%
Gallatin County, IL 3,442 1.7%
Hardin County, IL 2,873 2.8%
Warren County, MO 2,838 1.0%
Alexander County, IL 2,806 2.0%
Crittenden County, KY 2,505 1.1%
Christian County, KY 2,376 0.5%
Fayette County, IL 974 0.2%
Warrick County, IN 941 0.4%
Washington County, IL 826 0.2%
Union County, KY 802 0.4%
Ohio County, KY 703 0.2%
Macoupin County, IL 584 0.1%
Gibson County, IN 562 0.2%
Shelby County, IL 531 0.1%
Effingham County, IL 473 0.2%
Owen County, IN 446 0.2%
Montgomery County, IL 444 0.1%
Bond County, IL 391 0.2%
Madison County, IL 390 0.1%
Lewis County, MO 341 0.1%
Jasper County, IL 279 0.1%
Clinton County, IL 245 0.1%
Cumberland County, IL 244 0.1%
Randolph County, IL 232 0.1%
Clark County, IL 223 0.1%
Daviess County, IN 204 0.1%

Septic absorption fields

NRCS rating, share of Belknap acres

Not limited 0%
Somewhat limited 0%
Very limited 99%
Not rated 1%
Septic tank absorption field rating across mapped Belknap acres. Scale 0 to 100% of mapped land.
Show as a table
Septic tank absorption field rating across mapped Belknap acres.
CategoryShare of acres
Not limited0.0%
Somewhat limited0.0%
Very limited98.6%
Not rated1.4%

Drainage, water table and flooding

Share of Belknap acres

Depth to seasonal high water table
About 1.2 feet (14 in) (median where reported); within 18 inches on 81% of acres.
Flooding
Mapped as flooding on >99% of acres (53% occasional, 45% frequent).
Slope
Typically 0–1% (median 1%).
Topsoil organic matter
Median 2.5%.

Drainage class

Excessively drained 0%
Somewhat excessively drained 0%
Well drained 0%
Moderately well drained 0%
Somewhat poorly drained >99%
Poorly drained 0%
Very poorly drained 0%
Not rated <1%
Drainage class across mapped Belknap acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Belknap acres.
CategoryShare of acres
Excessively drained0.0%
Somewhat excessively drained0.0%
Well drained0.0%
Moderately well drained0.0%
Somewhat poorly drained99.9%
Poorly drained0.0%
Very poorly drained0.0%
Not rated0.1%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%
B: moderate infiltration 0%
C: slow infiltration 18%
D: very slow infiltration (clayey, shallow or wet) 0%
A/D: D as is, A if drained 0%
B/D: D as is, B if drained 81%
C/D: D as is, C if drained 0%
Not rated 1%
Hydrologic soil group across mapped Belknap acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Belknap acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)0.0%
B: moderate infiltration0.0%
C: slow infiltration18.1%
D: very slow infiltration (clayey, shallow or wet)0.0%
A/D: D as is, A if drained0.0%
B/D: D as is, B if drained80.5%
C/D: D as is, C if drained0.0%
Not rated1.4%

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 Belknap (component kind "Series") in SSURGO: 637,595 acres.
Method
Shares are by mapped acres of Belknap components. The profile comes from the single largest Belknap component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Belknap.