Effects of Nitrogen Form and Concentration in Fertilizer on Vegetative Growth, Flowering, and Leaf Mineral Contents of Passion Fruit

Abstract

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 NH4-N:NO3-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 NH4-N; in addition, the vine dry weight decreased at 50 mM. With additional NO3-N, the plants were able to avoid the detrimental effects of NH4-N. The N ratio did not affect vegetative growth except for the application of NH4-N alone, and no visible damage was observed, while the photosynthetic rate increased as the NO3-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 NH4-N ratio increased. NH4-N should not be applied alone to passion fruit; however, an NH4-N-dominant fertilizer consisting of ≥50% NH4-N is recommended to promote reproductive growth without reducing vegetative growth.