Advances in soil-testing research have led Iowa State University Extension and Outreach agronomists to revise recommendations for phosphorus, potassium and lime. “Field research is conducted continuously to assure that nutrient management suggestions are up to date,” says Antonio Mallarino, an extension agronomist and professor of agronomy. “This research has indicated some recommendations should not be changed, but other recommendations needed significant change to optimize nutrient management in order to improve the profitability and sustainability of crop production.”
He and John Sawyer, agronomy professor and extension agronomist, have updated the extension publication "A General Guide for 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 for maintaining soil-test levels in the optimum category
- Discontinued use of the P and K subsoil categories for interpretations
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