Zone Forge reads your Iowa soil test against Iowa's own publication — the printed crop-category cells come straight from Iowa State University Extension — PM 1688: A General Guide for Crop Nutrient and Limestone Recommendations in Iowa, not a national average. Lime has its own live calculator for Iowa with method-specific lab inputs.
ISU PM 1688 uses fixed category tables. Philosophy, build years, target overrides and hybrid settings are ignored; the printed category cell determines the rate.
ISU PM 1688 fixed P/K category tables, February 2023. Select the laboratory P method and potassium sample handling. The printed Optimum cells are used unchanged; harvested-yield footnotes are disclosed where printed, while Table 13 bluegrass cells are approximate estimates. Forages require the printed hay/pasture and stand choices.
Iowa State University Extension — PM 1688: A General Guide for Crop Nutrient and Limestone Recommendations in Iowa rates these crops in Iowa:
Published source: Iowa State University Extension — PM 1688: A General Guide for Crop Nutrient and Limestone Recommendations in Iowa
Iowa State University Extension — PM 1688: A General Guide for Crop Nutrient and Limestone Recommendations in Iowa. Zone Forge cites the publication on every recommendation.
Yes — the Iowa soil-test recommendation calculator is free and needs no signup. Enter your lab values for source-cited P and K; Iowa's live lime calculator is available separately with its own required lab inputs.
Yes — the free soil-test calculator covers source-cited P and K. Iowa also has a live lime calculator on Zone Forge that uses the state's published method. Open the Iowa lime guide or lime calculator for tons of CaCO3-equivalent per acre.
Zone Forge reads every Iowa soil test in its own state's language, then builds source-cited fertilizer and a live lime calculator and full variable-rate prescriptions. See the science →