Right on the heels of the rapid acceptance and use of fertilizers in general- and of straight nitrogen fertilizers in particular- has come the development of liquid sources of nitrogen containing from 21 to 82 percent nitrogen.
Stritzel, J. A.
"Liquid Nitrogen for Your Farm?,"
Iowa Farm Science: Vol. 7
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol7/iss6/2