Optimizing nitrogen, phosphorus and potassium fertilization for pomegranate fruit and juice quality

Studies investigating the effects of NPK fertilization on pomegranate have focused mainly on growth and yield, and less on fruit-quality attributes. Therefore, the major objective of this study was to examine the effects of different concentrations of NPK fertilization on fruit, aril, and juice quality of pomegranate cultivars ‘Emek’ and ‘Wonderful’. Low N and high K fertilizer rates decreased fruit and aril weights for ‘Emek’ but did not affect ‘Wonderful’. High K rates also decreased the number of arils in ‘Emek’ fruit. Low N rates increased the risk of sunburn in ‘Wonderful’ fruit, but reduced peel roughness in ‘Emek’. Increased P rates decreased the proportion of rough peel in ‘Wonderful’ and of black rot disease in ‘Emek’, but somewhat hindered red color development of ‘Emek’ fruit peel. High K rates resulted in a lower proportion of ‘Emek’ fruit with rough peel and increased red color development. In general, low P and high N reduced the proportion of marketable ‘Wonderful’ and ‘Emek’ fruit, respectively. Low NPK increased the TSS-to-acid ratio of ‘Emek’ juice by reducing its acid content. Low N also decreased anthocyanin content in ‘Emek’ juice. Insufficient P rates enhanced the concentration of phenols and flavonoids in ‘Wonderful’ and ‘Emek’ juices, respectively. Mg and S concentrations in the juices of both cultivars decreased when the trees were grown under low P, but Cu content was higher. Overall, the effects of different fertilizer-application rates varied between the two cultivars. Lower N and P and excessive K significantly influenced fruit quality, especially for ‘Emek’, an early-maturing cultivar that is harvested 2 months before ‘Wonderful’ and may therefore accumulate less mineral nutrients during fruit ripening. The fertilization regime of pomegranates should be adjusted to cultivar characteristics and maturity period.