I want to compare previous year's numbers since I have inherited a farm in Marshall County.
Iowa has updated the soil productivity system from Corn Suitability Rating (CSR) to Corn Suitability Rating 2 (CSR2) in 2013, and the USDA NRCS Web Soil Survey tool allows you to compute the new CSR2 for your farm (google ISU Extension Ag Decision Maker information file C2-87). However, the USDA Natural Resource Conservation Service (NRCS) has historical records with CSR value for previous years. For example, the ISU agronomy website has a map (https://www.extension.iastate.edu/soils/sites/www.extension.iastate.edu/files/soils/Iowa_CSR_Distribution_Map.pdf) of the old CSR across Iowa based on NRCS data. You could contact your local NRCS or FSA office, or contact Dr. Lee Burras at ISU Agronomy who is the expert behind CSR and CSR2. His email is at firstname.lastname@example.org