With organic fertilizers, such as cow manure or poultry litter, much of the nitrate and ammonium becomes available through decomposition of organic nitrogen. Regardless of the source, plants must have nitrate or ammonium forms of N available so they can grow and reproduce.
Some plants prefer the ammonium form of N, and others like to take up nitrate first.
The majority appear to show no real preference, or research has not been completed that shows a preference exists. Collected data included plant height, leaf N concentration, and yield. Harvested tomatoes were separated into marketable and non-marketable segments based on fruit size and quality. Different N sources had varying and inconsistent effects on yield and quality of fruit. Although plant height and stem diameter of tomatoes from UAN treatments were always smaller than those from other N sources, this effect did not lead to decreased total marketable yield.