Iowa Soil pH GIS Data
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Author: emlemke
This is an archived story. The content, links and information may have changed since the publication date.
Soil pH expresses acidity or alkalinity on a 0–14 scale and controls nutrient availability, microbial activity, and chemical reactivity. Values in these maps come from gSSURGO horizon data (standard laboratory/field methods such as 1:1 soil–water or CaCl₂), depth-weighted within components, aggregated to map units, and summarized as the representative pH for each depth interval. Parent material, carbonate presence, organic matter, climate, and drainage all influence pH. Management—especially liming, fertilization, and drainage—can shift conditions locally, so the maps portray expected background pH rather than field-specific, moment-to-moment readings.
Applied Relevance
Use the pH maps to target lime applications, set realistic crop and variety choices, and anticipate fertilizer efficiency and micronutrient issues. Low pH tends to limit phosphorus availability and can increase aluminum or manganese toxicity; high pH reduces availability of iron, zinc, and other micronutrients and affects herbicide performance. Depth-resolved pH helps interpret rooting-zone constraints, predict carbonate layers that influence water movement, and prioritize variable-rate management and reclamation.
Available Depths
Intervals provided are 0–5 cm, 5–20 cm, 20–50 cm, 50–100 cm, 100–150 cm, and 150–200 cm. Composite summaries are also included for 0–20 cm, 0–50 cm, 0–100 cm, and 0–200 cm.
GIS Map Folder Download
Click the button below to access the GIS data.
GIS Map Details
Data originate from USDA-NRCS gSSURGO. Horizon pH values were depth-weighted within components, generalized to map units, and gridded statewide at 10-m resolution to be consistent with SSURGO cartography. Symbology is standardized for cross-county comparison. Because these products reflect mapped soils at the SSURGO scale (about 1:12,000–1:31,680) and do not capture recent liming or disturbance, they are best used for regional to county-level screening and planning; verify site-level decisions in the field.
Metadata – Sources – Limitations
Produced by: Meyer Bohn, Joshua McDanel, and Bradley Miller January (2019)
Created with the gSSURGO mapping toolset for ArcGIS for Desktop 10.6. Available for download at:
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/geo/?cid=nrcs142p2_053628
Raster Format: 10-m resolution GeoTIFF, 32-bit floating point
Projection: NAD83 UTM Zone 15N
Extent – West: -96.801571 East: -90.007463 North: 43.644364 South: 40.302683
Soil Survey Staff. 2018. Natural Resources Conservation Service. United States Department of Agriculture. Gridded Soil Survey Geographic (gSSURGO) Database for Iowa. Accessed 27 Oct 2018.
Use limitations: See “Sources of Apparent Error on Existing Soil Maps”. Soil Survey Staff. 2018. Soil Survey Manual – Ch. 4: Soil Mapping Concepts. Natural Resources Conservation Service. United States Department of Agriculture. Available at:
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054254#quality
Scale Range: Not intended for use at scales larger than an order 2 Survey (1:12,000 to 1:31,680).