Soil series profile

Zook soil series

Zook is a poorly drained soil with a silty clay loam surface, mapped on 966,469 acres in 189 counties across 7 states. Hydrologic group D.

#191 by mapped area fine Cumulic Vertic Endoaquolls (Mollisols)

Drainage class
Poorly drained
>99% of mapped acres
Hydrologic group
D
63% of mapped acres
Typical topsoil pH
6.1
slightly acidic · range 5.7–6.5
Mapped area
966k
acres in 189 counties, 7 states

Typical Zook profile

Texture and pH by depth

Typical Zook soil profile by depth 0 in 10 in 20 in 30 in 40 in 50 in 0–4 in · A1 · pH 5.7 · 32% clay Silty clay loam 4–40 in · A2 · pH 6.6 · 35% clay Silty clay loam 40–60 in · Bg · pH 6.7 · 35% clay Silty clay 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 Zook horizons (representative values)
Depth Texture pH Clay Sand Organic matter
0–4 in (A1) Silty clay loam 5.7 32% 16% 4.3%
4–40 in (A2) Silty clay loam 6.6 35% 16% 2.6%
40–60 in (Bg) Silty clay loam 6.7 35% 15% 2.2%

Representative values from the most extensive Zook map unit (Zook silty clay loam, 1 to 4 percent slopes, occasionally flooded, survey area MO063). 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 Zook soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Zook soils is slightly acidic: pH 6.1 (most land between 5.7 and 6.5), the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers 95% of mapped Zook acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silty clay loam (83% of mapped Zook acres).

100% of mapped Zook 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 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.

A seasonal high water table comes within 18 inches of the surface on 93% 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 100% of the acres in mapped Zook 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.

Flooding is mapped on 98% of the acres (78% occasional, 19% 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 Zook soil is found

Mapped acres

Zook is mapped in Missouri, Iowa, Nebraska, Illinois, Kansas, Minnesota and South Dakota. The 60 counties with the most Zook acres:

Counties with the most mapped Zook soil
County Acres Share of county land
DeKalb County, MO 45,015 16.6%
Daviess County, MO 43,692 12.1%
Harrison County, MO 42,375 9.2%
Adams County, IA 30,131 11.2%
Wayne County, IA 23,827 7.1%
Grundy County, MO 23,319 8.4%
Caldwell County, MO 23,138 8.4%
Ringgold County, IA 21,210 6.2%
Dodge County, NE 21,032 6.2%
Johnson County, MO 20,829 3.9%
Warren County, IA 20,781 5.7%
Lucas County, IA 19,860 7.2%
Nodaway County, MO 19,392 3.5%
Putnam County, MO 17,531 5.3%
Richardson County, NE 17,048 4.8%
Cass County, IA 16,941 4.7%
Otoe County, NE 15,850 4.1%
Sullivan County, MO 15,371 3.7%
Schuyler County, MO 14,822 7.5%
Decatur County, IA 13,758 4.1%
Mercer County, MO 13,543 4.7%
Mahaska County, IA 13,516 3.7%
Cuming County, NE 12,515 3.4%
Gentry County, MO 12,390 4.0%
Johnson County, NE 12,272 5.1%
Clark County, MO 12,113 3.7%
Colfax County, NE 12,071 4.6%
Jasper County, IA 11,236 2.4%
Audubon County, IA 11,195 3.9%
Madison County, IA 10,933 3.1%
Livingston County, MO 10,829 3.2%
Adair County, MO 10,294 2.8%
Clarke County, IA 10,273 3.7%
Davis County, IA 10,138 3.2%
Adair County, IA 10,125 2.8%
Pottawattamie County, IA 10,005 1.6%
Cass County, MO 9,895 2.2%
Macon County, MO 9,813 1.9%
Carroll County, MO 9,733 2.2%
Nemaha County, NE 9,217 3.5%
Lancaster County, NE 8,968 1.7%
Burt County, NE 8,480 2.7%
Keokuk County, IA 8,418 2.3%
Ray County, MO 8,329 2.3%
Montgomery County, IA 8,324 3.1%
Shelby County, IA 8,234 2.2%
Marion County, IA 7,956 2.3%
Jackson County, KS 7,866 1.9%
Chariton County, MO 7,225 1.5%
Andrew County, MO 7,084 2.5%
Iroquois County, IL 6,613 0.9%
Guthrie County, IA 6,576 1.7%
Iowa County, IA 6,392 1.7%
Page County, IA 6,109 1.8%
Butler County, NE 6,059 1.6%
Linn County, MO 5,491 1.4%
Mills County, IA 5,020 1.8%
Washington County, IA 4,897 1.4%
Monroe County, IA 4,814 1.7%
Buchanan County, MO 4,684 1.8%

Septic absorption fields

NRCS rating, share of Zook acres

Not limited 0%
Somewhat limited 0%
Very limited 100%
Septic tank absorption field rating across mapped Zook acres. Scale 0 to 100% of mapped land.
Show as a table
Septic tank absorption field rating across mapped Zook acres.
CategoryShare of acres
Not limited0.0%
Somewhat limited0.0%
Very limited100.0%

Drainage, water table and flooding

Share of Zook acres

Depth to seasonal high water table
About 0 inches (median where reported); within 18 inches on 93% of acres.
Flooding
Mapped as flooding on 98% of acres (78% occasional, 19% frequent).
Slope
Typically 1–2% (median 1%).
Topsoil organic matter
Median 4.5%.

Drainage class

Excessively drained 0%
Somewhat excessively drained 0%
Well drained 0%
Moderately well drained 0%
Somewhat poorly drained 0%
Poorly drained >99%
Very poorly drained <1%
Drainage class across mapped Zook acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Zook acres.
CategoryShare of acres
Excessively drained0.0%
Somewhat excessively drained0.0%
Well drained0.0%
Moderately well drained0.0%
Somewhat poorly drained0.0%
Poorly drained99.2%
Very poorly drained0.8%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%
B: moderate infiltration 0%
C: slow infiltration 4%
D: very slow infiltration (clayey, shallow or wet) 63%
A/D: D as is, A if drained 0%
B/D: D as is, B if drained 0%
C/D: D as is, C if drained 33%
Hydrologic soil group across mapped Zook acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Zook acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)0.0%
B: moderate infiltration0.0%
C: slow infiltration3.6%
D: very slow infiltration (clayey, shallow or wet)63.3%
A/D: D as is, A if drained0.0%
B/D: D as is, B if drained0.0%
C/D: D as is, C if drained33.1%

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 Zook (component kind "Series") in SSURGO: 966,469 acres.
Method
Shares are by mapped acres of Zook components. The profile comes from the single largest Zook component. Full methodology.

Independent reference site. No government affiliation or endorsement.

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