Iowa State College agronomists are now making alternative fertilizer recommendations available for Iowa soils. Through these, it's possible to "tailor" fertilizer recommendations more closely to your individual situation.
Hanway, John H. and Bennett, William F.
"Fertilizer Rates to Suit Your Soil and You,"
Iowa Farm Science: Vol. 11
, Article 3.
Available at: https://lib.dr.iastate.edu/farmscience/vol11/iss10/3