Interaction of Nitrogen Nutrition and Photoperiod as Expressed in Bulbing and Flower-Stalk Development of Onion

Abstract

Effects of photoperiod and N nutrition upon the bulb and flower stalk development of onion were studied. Plants grown on photoperiods substantially longer than that critical for bulb formation showed no difference in bulb development when supplied different amts. of N. Plants grown on a photoperiod at or near that critical for bulb formation exhibited the greatest bulb development with the lowest N concentration and the least with the highest conc. Under certain environmental conditions N and photoperiod can interact to influence bulb development of certain onion vars. Onion plants of sister lines gave similar bulbing response on photoperiods of identical duration, but the 2 lines differed in their production and development of visible floral stalks'', especially on the shorter of the photoperiods; Development of floral stalks was favored by long photoperiods. In a hybrid line unrelated to the sister lines, long photoperiods also favored flower-stalk development, but low temps. applied during the early growth of these plants were without measurable effect. Onion plants were grown from seed to seed without an intervening dormant bulb stage by controlling the photoperiod and conc, of N available for growth.