Crop productivity index ratings from the Natural Resources Conservation
Service provide a relative ranking of soils based on their potential for
intensive crop production. An index can be used to rate the potential
yield of one soil against that of another over a period of time. Ratings
range from 0 to 100. The higher numbers indicate higher production
CPI ratings do not take into account climatic factors, such as the
differences in precipitation or growing degree days across Minnesota.
The ratings are based on physical and chemical properties of the soils
and on such hazards as flooding or ponding. Available water capacity,
reaction (pH), slope, soil moisture status, cation-exchange capacity
(CEC), organic matter content, salinity, and surface fragments are the
major properties evaluated when CPI ratings are generated. The soil
properties selected are those that are important for the production of
All soil component mapping phases in Minnesota were evaluated using the Cropland Productivity rule in the National Soil Information System (NASIS), and a CPI was generated for each phase. A statistical mean CPI value was created for each soil component mapping phase. All map units were populated with each component’s mean CPI value, and a weighted average CPI was created for each soil map unit in the state. An individual map unit (for example, Canisteo clay loam, 0 to 2 percent slopes) will have the same CPI value wherever that map unit occurs throughout the state.
When the soils are rated, the following assumptions are made:
Even though predicted average yields will change with time, the
productivity indices are expected to remain relatively constant in
relation to one another over time.
The Natural Resources Conservation Service provides maps and tables of crop productivity index ratings via the Web Soil Survey. After choosing your Area of Interest and creating your soil map, go to the Soil Data Explorer tab, choose Vegetative Productivity, choose Crop Productivity Index, and then check "View Rating". Click on graphic to the right for a larger view of a sample map.
Spreadsheets of values in Excel (.xls) format are available by county in the Electronic Field Office Technical Guide (once you are at the eFOTG site, click on the map to navigate to Minnesota and then to a specific county. In the eFOTG menu, go to Section II, then section A. County Soils Information, then the county folder, then section e. Cropland Interpretations).