In agriculture, nitrogen (N) fertilizer recommendations historically have been based on the producer's yield goal. N supplied from legumes (soybeans and alfalfa) and manure is usually estimated conservatively to avoid any possible shortage. In Iowa, it has been generally assumed that N not used by the crop during a given growing season is denitrified (converted from nitrate, or NO3, to nitrite) or leached into the groundwater before the following growing season.
Stewart Melvin, James Hultgren
Year of Grant Completion
Kohl, Kris; Melvin, Stewart; and Hultgren, James, "Implementing nitrogen management to protect Iowa's groundwater" (1993). Leopold Center Completed Grant Reports. 8.