Effects of Nitrogen Form in Nutrient Solution on Passion Fruit Quality

Abstract

High-quality passion fruit, with low acidity and an aesthetic appearance, is important for fresh consumption. Thus, the effects of nitrogen (N)-form in nutrient solution on the juice quality and external appearance were examined. Passion fruit plants were grown in 10-L pots filled with river sand. Nutrient solutions containing 25 mM N with different NH₄-N:NO₃-N ratios of 100:0, 75:25, 50:50, 25:75, or 0:100 were applied. The numbers of flowers and fruits per bearing-vine were counted and fruit-set percentage was recorded. After harvest, fruit weight, dimensions, and peel color were measured. After a 10-day storage, total soluble solid (TSS), titratable acidity (TA), juice content, peel color, and wrinkle degree were measured. TA was the lowest at NH₄-N only, and the sugar/acid ratio increased as the NH₄-N ratio increased. TSS was not significantly affected by the N-form. Therefore, high NH₄-N ratio, such as NH₄-N alone or 75 % NH₄-N, was beneficial for juice palatability, while juice content decreased as the NH₄-N ratio increased. High NH₄-N ratio could improve not only the juice palatability but also the fruit’s external appearance. Fruit at high NH₄-N ratio wrinkled less and had deeper color on the peel. However, with NH₄-N solely, leaf necrosis appeared, and the SPAD index, photosynthetic rate, and total dry weight were lowest; thus, NH₄-N should not be applied alone. With NO₃-N solely, flower number, fruit size, and yield were smallest among the treatments. These results indicated that NH₄-N-dominant fertilizer can be used to produce high-quality passion fruit while NH₄-N should not be applied alone.