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Iowa State University Updates Corn Suitability Rating SystemIowa State University Updates Corn Suitability Rating System

Popular CSR system for rating productivity of Iowa soils, used to determine land values and develop land use plans, will be replaced by CSR2.

Rod Swoboda 1

May 23, 2013

5 Min Read

Advances in soil science have necessitated an update in the Corn Suitability Rating system, a method for rating the crop-growing productivity of Iowa soil. That was the message Iowa State University agronomist Lee Burras delivered in his presentation to the crowd of lenders, appraisers, farm management professionals and others attending the 2013 Iowa Soil Management and Land Valuation Conference on May 22 at Ames. This was the 86th year the conference has been held, and the introduction of the new CSR2 rating system was a hot topic.


"Advances in soil-mapping techniques and the adoption of the national soil classification system during the past 50 years provides improved methods for calculating the CSR when compared to its original formula," said Burras, a professor of soil science.

ISU releasing a new method to determine Corn Suitability Rating for Iowa soils 

The Corn Suitability Rating system was first developed and published in 1971 by ISU agronomy professor Tom Fenton and several colleagues at Iowa State. It reflected their expertise and a multiyear detailed analysis on the productivity of Iowa's 30 million acres of farmland, making the CSR system the most sophisticated and complete quantitative soil productivity rating available.~~~PAGE_BREAK_HERE~~~

CSRs have been, and arguably remain, the most sophisticated and complete quantitative soil productivity ratings available in the world. As a resource, they certainly have been the most trusted.

CSR was originally established for use by county assessors to help rate the value of farmland for property tax purposes

The CSR system was originally established in response to county assessors who needed a measure to help assess the productivity of farmland. In the mid-1970s the State of Iowa established legislation that requires agricultural land be assessed on the basis of productivity and the net earning capacity to ensure equitable assessment. Today, the CSR values are used in many additional ways, including to develop land use plans, determine land values when farms are being sold, to predict yields and to help negotiate cash rents.

"The goal of the new system, called CSR2, is to provide a transparent system for calculating CSR such that a county assessor, farmer, realtor and any other interested person readily understands the mathematics underlying CSR," Burras says. The new CSR2 values are meant to be proportional to the existing CSR values, he says, although that is not always possible given the responsibility for transparency and consistency.

The CSR2 values of any given soil map unit, or SMU, is a function of five parameters, says Burras:

(a) the soil properties captured within a soil series classification 

(b) the specific field conditions captured by each SMU 

(c) the soil depth 

(d) local climate and environment

(e) expert judgment

A secondary goal is the creation of a framework for CSR2 evolution, which is necessary to ensure rapid and transparent updates of CSR2 as new soil series and new classifications are created.

Burras presented and explained the updated CSR2 at the Soil Management and Land Valuation Conference on May 22. A recording of his presentation will soon be available at the Iowa State Land Use Web page, which also includes frequently asked questions about the change.

The new CSR2 values are to be added to Iowa State Land Use Web page by July 1

* Burras said the new CSR2 values would be added to the Iowa State Land Use Web page by July 1.~~~PAGE_BREAK_HERE~~~

* The USDA Natural Resources Conservation Service will make CSR2 available Oct. 1 through the USDA-NRCS Web Soil Survey, which is the nation's official source of soil survey information. CSR is the source used by the federal government for soil maps and the data and interpretations associated with soil maps.

* Sometime in 2015 is the projected date that the new CSR2 values will be used by county assessors for property tax purposes in Iowa.

What has changed since the CSR system was introduced in the early 1970s?

Since 1971, from a technical point of view, the knowledge base of soil properties has been significantly enhanced and expanded, says Rick Bednarek, state soil scientist with NRCS in Iowa. He shared the podium with Burras as they explained the new CSR2 soil rating method at the May 22 meeting at Ames.

The science for calculating CSRs has changed and become more robust. The current system for soil classification was not in place 40 years ago. Today, more than 500 soil series are recognized in Iowa, 150 more than when the CSR was first published. Another example is the percentage of different soil series within a specific soil map unit. That percentage can now be recognized and recorded, which was not the case in earlier years.

Will the new CSR2 change the current CSR values for my farmland?

That was a common question asked by farmers and others attending the May 22 session. Burras and Bednarek say noticeable increases in CSR2 will occur for farmland in parts of north central, west central, western and northwest Iowa. Due to annual rainfall increases in these areas of the state the rainfall adjustment factor is dropped from CSR2. However, this applies to all soils, so the increase will be relative and uniform. This will not affect how CSR is used to equalize assessment of agricultural land, they say. For more information and answers to other questions, they refer people to the FAQs posted on the ISU website.

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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