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Corn Suitability Ratings

A wide rural field with a dirt path running through harvested farmland under a cloudy sky.

CSR2 (Corn Suitability Rating 2) is an index used in Iowa to rate the productivity potential of soils for row-crop agriculture, especially corn. It ranges from 5 to 100, with higher values indicating better soil quality and yield potential. CSR2 is based on soil properties, climate, slope, and landscape position, and provides a standardized way to compare farmland productivity across the state. It replaced the original CSR system to improve consistency and transparency using updated soil data and models.

CSR2 Equation & Explanation 

CSR2 = S-M-W-F-D ± EJ 

Where: 

S – is the taxonomic subgroup class of the series of the soil map unit (MU), 

M – is the family particle size class, 

W – relates to available water holding capacity of the series 

F – is the field condition of a particular MU, for example, slope, flooding, ponding, erosion class and topsoil thickness, 

D – is the soil depth and tolerable rate of soil erosion, 

EJ – is an expert judgment correction factor. EJ is normally used with parent materials that have very high bulk density and/or are unusually clayey or sandy. 

Restored 1950 Allis-Chalmers WD tractor parked in front of a cornfield.

CSR2 (Corn Suitability Rating 2) measures a soil’s potential for corn production, with 100 being ideal and 5 being poor. It’s based on six soil factors and calculated per map unit using data from the Iowa Cooperative Soil Survey. There are two versions: CSR2-ISU, which assumes the dominant soil series, and CSR2-NRCS, which averages all included soils. Values are usually similar, but differences arise when map units contain many soil inclusions, steep slopes, or inconsistent data.

County Area-Weighted Average CSR2

County-by-county breakdown of CSR2 values based on NRCS 2022 data. The county means are calculated as an area-weighted zonal statistic

Iowa State University manages the CSR2 equation, which provides a transparent, repeatable index of natural soil productivity calculated from mapped soil properties. The soil properties used as inputs for that equation come from the SSURGO (Soil Survey) database managed by the USDA-NRCS. Soil Survey staff make edits to that map annually for a mixture of reasons that usually include some combination of wanting to update or correct problems from the past versions of that map.

Iowa CSR2 Distribution

CSR2 distribution across Iowa based on NRCS-weighted data, highlighting regional differences in soil productivity.

This map displays the 2016 Corn Suitability Rating 2 (CSR2) values across Iowa, which estimate the potential soil productivity for row crops, particularly corn. CSR2 ratings range from 5 to 100, with higher values indicating greater potential productivity. This dataset helps farmers, landowners, and planners evaluate land value and suitability for agricultural use.

CSR2 and Related Resources

CSR2 Equation and Methodology

CSR2 Equation and Component Values – Equation (Mar 2015)
CSR2 Equation Update (April 2015)

Guides and Articles

ISU Extension: Computing the Iowa Corn Suitability Rating for Your Farm – Article (Jun 2014)
Iowa Farmer Today: ISU Tweaks CSR – Article (May 2015)
Integrated Crop Management News: CSR2 Equation Updated – Article (Apr 2015)

Comparison and Background

A Comparison of Iowa’s Original CSR Index to the New CSR2 Index – Poster (Apr 2015)
CSR2 Background, Update, and Frequently Asked Questions – FAQ (May 2013)
ISU CALS: ISU Updates Method for Rating Soil Productivity – News Release (May 2013)

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