Comparing Soil Productivity Indices Used in the North Central Region of the United States.

Since 1815, attempts to determine agriculturally productive soils in the United States have been made.  Today, soil productivity indices (SPI) are used in several states of the USA, generally for the purpose of land valuation and taxation of agricultural lands.  A review of published literature describing SPI currently used in the North Central Region of the United States (NRCUS) was conducted.  Similarities and differences in how each SPI uses inherent soil properties and crop yields were identified.  Additionally, each SPI calculation was performed on four soil taxonomic subgroups commonly found across the NRCUS to compare how these four soils rate in each SPI.