Thunderstorms do supply N but not enough. In the NT where there are 80 to 90 thunderstorms a year, the fertilzer guide for mangoes is pretty sophisticated and draws on N % in foliage in which optimal range varies between varieties but also canopy area.the amount of N available in the soil in plantations also is known and influences application rates of N. Keitt by the way has lower requirements than the more glamorous and prized honey gold.It advises that N is the most important nutrient for fruit volume and quality and that excess or deficient application strongly influences the crop. It is lost from the system relatively faster than other macros and is in the soil in a few forms.
The pre-flowering dormancy is needed as is the pre harvest root flushing but vegetative flushing during flowering isn't. So what does that all mean? Most people have no idea how much N is needed in any season but it is pretty volatile. Anyway fertliser application around harvest time and a second period around flowering and fruit set is recommended for the best crop. Nearly always dominates other nutrients in terms of volume applied but is reduced in some seasons and years when the soil has plenty and leaf concentrations are over about 1.4% N.