New ISU guidelines for application of phosphorus, potassium on farm fields

(Radio Iowa) – Iowa State University Extension agronomists have updated charts which spell out how much phosphorus and potassium are recommended for Iowa farm fields.

“The key issue of this update is essentially the economic impact of fertilizer management,” says Iowa State University agronomy professor Antonio Mallarino.

The researchers were under a time crunch to get these new recommendations published.

“At least half or more of the phosphorus and potassium is applied in the fall, so that’s why were really in a hurry to try to get all done,” Mallarino says.

After farmers complete the harvest, they’ll collect soil samples, make calculations and then apply these soil supplements.

Mallarino says the new Iowa State University Extension guidelines call for a “little bit less” phosphorus for corn and soybean fields and “a little bit more” phosphorus is recommended for fields where alfalfa will be grown. Plus there’s a new soil test for potassium. The soil is moist rather than completely dry when it’s tested and Mallarino says that makes the test slightly more accurate when farmers use it to calculate how much potassium to apply to their fields.

“Potassium, of course, is all imported to the state,” Mallarino says. “There are no potassium mines in the state, so the fact now that we have a better method and updated recommendations and interpretations should result in better potassium management by farmers and, of course, more profitable crop production.”

The Iowa State University Extension recommendations for the application of lime were reviewed and Mallarino says the research shows they’re working.