Nitrogen fertilizers have been accepted very rapidly in Iowa - so rapidly that on-farm knowledge of nitrogen fertilizers and how they act hasn't kept pace with use. There are different types of nitrogen fertilizers as well as barnyard manure and legumes that supply nitrogen.
Stritzel, J. A.
"Know Your Nitrogen Fertilizers,"
Iowa Farm Science: Vol. 10
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol10/iss4/2