Iowa State University Soil Productivity Rating System Updated

AMES, Iowa — Iowa State University researchers have released the equation for calculating Iowa’s Corn Suitability Ratings, the updated soil productivity index for the state’s soils.

The updated Corn Suitability Rating 2 (CSR2) provides an index to the inherent soil productivity of each kind of soil for row-crop production. The index, which is measured on a scale of 5-100, with 100 as the most productive soils and 5 as the least.

“Our goal is to provide Iowa producers with a tool that allows users a transparent method to calculate the CSR2 for all Iowa soils,” said Lee Burras, Iowa State agronomy professor. 

Advances in soil science necessitated an update of the Corn Suitability Rating, a system published in 1971 for determining the crop-growing productivity of Iowa soil. It was created for county assessors who needed a measure to help assess the productivity of farmland.

In the mid-1970’s, the State of Iowa established legislation that required agricultural land be assessed on the basis of productivity and the net earning capacity to ensure equitable assessment. Today, the CSR is used in many other ways, including to develop land-use plans, determine land values, predict yields and negotiate cash rents.

The CSR2 equation and description of the six components used to calculate the productivity of each soil map unit is posted on the Soil and Land Use website under “CSR2 Equation and Component Values (Updated March 2015).”

A major difference between the original CSR and CSR2 is the deletion of a rainfall correction factor in CSR2. The original CSR was based on normal rainfall for the period 1931-1960, which experienced reductions in some parts of the state.

In most situations the differences in CSR2 are minimal although in a few cases could be significant, especially for those areas of north central, northwest and western Iowa where the rainfall factor is no longer relevant.

Beginning in 2012 soil survey updates are made at the multiple county Major Land Resource Area scale and posted on the USDA-NRCS site at USDA-NRCS is expected to update the site annually along with a listing of CSR2.