Effect of Varying Nitrogen Form and Concentration During Growing Season on Sweet Pepper Flowering and Fruit Yield

Flowering and fruit set of sweet pepper (Capsicum annum L.) is sensitive to environmental condition and nitrogen (N) nutrition status. To clarify the N fertilization effect, four levels of total N concentrations and four nitrate-nitrogen (NO3─N) and ammonium-nitrogen (NH4─N) ratios were supplied in three distinct physiological stages of sweet pepper: Stage I—vegetative; Stage II—fruit set during cross-pollination; and Stage III—fruit developing period. The plants were grown hydroponically during two seasons. In the season of short photoperiod progressing from autumn to winter with 10.9 to 10.2 light h day−1, gradually increasing the total N concentration with the progressing physiological stages from 3 to 6 and 9 mM increased the total set of flowers and fruits, and produced the highest total fruit yield (3444 g plant−1). During the increasing day length season from spring to summer (12.3–12.8 h day−1), supply of 9 mMN and 30% NH4─N before fruit set produced the larger amount of early ripening fruits. When the NH4─N percent rose from 0 to 15 and 30 in the autumn-winter season, the highest amount of early ripening fruits was obtained. In both seasons, the highest total fruit yields was obtained when NH4─N was 30% of the total N (6 mM) during the vegetative stage and NO3─N as sole N source during fruit filling stage.