In passion fruit, little information is available about the effect of the form of N fertilizer on vegetative growth and flowering. Nutrient solutions containing 5, 10, 25, or 50 mM N with an NH
4-N:NO
3-N ratio of 100:0, 75:25, 50:50, 25:75, or 0:100 were applied to passion fruit grown in sand to determine the appropriate ratio for vegetative growth and flowering. Vegetative growth, SPAD value, photosynthetic and transpiration rates, flower number, and leaf mineral contents were examined. SPAD value and photosynthetic rate decreased and necrosis was observed following the pure application of 25 and 50 mM NH
4-N; in addition, the vine dry weight decreased at 50 mM. With additional NO
3-N, the plants were able to avoid the detrimental effects of NH
4-N. The N ratio did not affect vegetative growth except for the application of NH
4-N alone, and no visible damage was observed, while the photosynthetic rate increased as the NO
3-N ratio increased at N concentrations of ≥25 mM. At less than 10 mM N, symptoms of N deficiency were observed. The flower number increased as the NH
4-N ratio increased. NH
4-N should not be applied alone to passion fruit; however, an NH
4-N-dominant fertilizer consisting of ≥50% NH
4-N is recommended to promote reproductive growth without reducing vegetative growth.
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