AMES, Iowa — Advances in soil-testing research has 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,” said 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 to download at no charge from the Extension Online Store https://store.extension.iastate.edu/.
Mallarino said the most significant changes are:
He indicated recent research showed the moist- and slurry-test for K is more reliable at assessing K fertilization needs of crops than the commonly used test based on dried soil samples, even with the improved interpretations for the dry test.
The agronomists maintained many of the current recommendations farmers use to determine soil fertility, including: