Advances in soil-testing research have led Iowa State University Extension and Outreach agronomists to reviserecommendations for phosphorus, potassium and lime. “Field research is conducted continuously to assure that nutrient management suggestions are up to date,” says AntonioMallarino, an extension agronomist and professor of agronomy. “This research has indicated some recommendations should notbe changed, but other recommendations needed significant change to optimize nutrient management in order to improve theprofitability and sustainability of crop production.”

He and John Sawyer, agronomy professor and extension agronomist, have updated the extension publication "A General Guidefor Crop Nutrient and Limestone Recommendations in Iowa" (PM 1688). It is available online for free.

Mallarino said the most significant changes include:

  • Interpretations for the new moist- and slurry-based test for potassium
  • Changes to soil-test interpretations categories for potassium using dried soil samples
  • Adjustments to both crop nutrient concentrations and default crop yields needed to estimate nutrient removal formaintaining soil-test levels in the optimum category
  • Discontinued use of the P and K subsoil categories for interpretations

Read more about the changed and updated nutrient recommendations from Iowa State University.

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