Johnson County Soil Data
Johnson County, Illinois
Avg pH
5.9
Texture
Silt loam
Drainage
Well drained
Organic Matter
1.8%
Hydrologic Group
C
Data Story
About Soil in Johnson County, Illinois
The Acidic Alfisols of Johnson
Johnson County is dominated by Alfisols, which are forest-derived soils with an average pH of 5.92. This is significantly more acidic than the national median of 6.5, requiring careful management for most traditional field crops.
Silt Loam Textures and Workability
The dominant texture is silt loam, characterized by 67.5% silt and 20.8% clay. While easy to till, the low sand content of 11.7% means these soils can become compacted if worked when too wet.
Lower Fertility and Water Capacity
Organic matter sits at 1.77%, trailing the state average of 2.94% by a wide margin. The available water capacity of 0.201 in/in is also slightly below the state average, necessitating consistent irrigation in dry seasons.
Well-Drained but Slow Infiltration
The soil is classified as well-drained, yet it falls into Hydrologic Group C, which indicates a slow rate of water transmission when thoroughly wet. This combination is common in the rolling hills of southern Illinois where runoff is a concern.
Warm Climate Gains in Zone 7a
As a Zone 7a region, Johnson County enjoys a long growing season perfect for heat-loving okra and peppers. Acid-loving plants like blueberries and azaleas will naturally thrive in this soil's low pH environment.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Group C — Moderate-High Runoff
Soils with slow infiltration rates, often with a layer that impedes downward water movement. Higher clay content restricts drainage.
Drainage Class
Well drained
Water is removed from the soil readily but not rapidly. Optimal for most plants and construction.
Soil Profile
Dominant texture: Silt loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Frequently Asked Questions
What type of soil does Johnson County have?
Johnson County's soil is classified as Silt loam. This indicates the relative proportions of sand, silt, and clay — 12% sand, 68% silt, and 21% clay. Loamy soils hold moisture well and support a wide range of plants.
Is Johnson County's soil acidic or alkaline?
Johnson County's soil has a pH of 5.9, which is moderately acidic. This range suits many crops and is common across much of the eastern US.
What is the drainage class for Johnson County?
Johnson County has a dominant drainage class of "Well drained." Well-drained soils allow excess water to move through quickly, reducing waterlogging risk and supporting most field and garden crops.
What crops or plants grow well in Johnson County's soil?
Based on Johnson County's Silt loam texture, pH of 5.9, and Well drained, the soil is well suited for vegetables, grains, and most field crops, row crops and vegetable gardens, most annual and perennial crops.
What USDA soil order is found in Johnson County?
Johnson County's dominant soil order is Alfisols. Alfisols are moderate to high base-status soils with a clay-enriched subsoil. They support productive forests and cropland across temperate regions.
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Other Counties in Illinois
Soil data sourced from USDA SSURGO via Soil Data Access. Data is informational only and should not be used as a substitute for on-site soil testing. Contact your local NRCS office for site-specific soil information.