An experiment was conducted to assess the effects of foliar sprays of a calcium fertilizer containing nanoparticles (nano-Ca) and calcium chloride (CaCl2.2H2O) on the yield and quality of pomegranate fruits cv. Ardestani, during two consecutive years, 2014 and 2015. The nano-Ca fertilizer was sprayed at concentrations of 0.25 and 0.50 g Ca L−1, and CaCl2.2H2O was used at concentrations of 1 and 2% (2.73 and 5.45 g Ca L−1), with treatments being applied twice, first at full blooming and then one month later. Calcium foliar fertilization did not have significant effects on yield, number of fruits per tree and average fruit weight, whereas it increased fruit length only in the case of the CaCl2 1% treatment in the first season. The untreated trees in the orchard were moderately affected by fruit cracking, with 6–7% of the fruits being affected. Calcium foliar treatment with the nano-Ca fertilizer at 0.50 g Ca L−1 and 1% CaCl2 (in the both seasons) and also 2% CaCl2 (only in the second season) decreased significantly fruit cracking when compared with the control treatment, resulting in increases in marketable fruit yield. Foliar sprays with CaCl2 1% increased TSS by 7.6% only in the second season. Moreover, foliar nano-Ca fertilization at 0.50 g Ca L−1 led to minor decreases (approximately 1%) in total phenolics only in the first season. Other chemical properties, including titratable acidity, fruit maturity, total sugar, antioxidant activity and total anthocyanin contents were not affected by Ca foliar fertilization. Leaf analyses show that Ca foliar treatments increased leaf Ca concentrations in the first season, with the exception of the low dose of nano-fertilizer, whereas the leaf concentrations of N, P, K, Fe, Zn and Mn were unaffected. In summary, fertilization with a low (0.50 g Ca L−1) Ca concentration in the form of a nano-Ca formulation resulted in similar decreases in pomegranate fruit cracking than those obtained with higher doses of CaCl2 (2.73 and 5.45 g Ca L−1).
Pomegranate (Punica granatum L.) is one of the oldest known edible fruits, which is native of Iran and is currently cultivated in many countries, including Spain, Morocco, Egypt, Afghanistan, Burma, China, Japan, USA, Russia, Bulgaria and Italy. Pomegranate is mainly consumed as a fresh fruit and also used in form of jams, juices, wines, vinegars and jellies (Heber et al., 2006; Kingsly and Singh, 2007; Sheikh and Manjula, 2012; Gumienna et al., 2016).
Results obtained from the present study show that Ca fertilization as foliar sprays at full bloom and one month later decreased significantly fruit cracking in an orchard moderately affected by this disorder (6–7% of the fruits). Results show that Ca fertilization lead to 26–52% decreases in fruit cracking in two different seasons in comparison with the control, with the best effect being found with the nano-Ca fertilizer at 0.50 g Ca L−1 . Foliar Ca fertilization did not have any effects on pomegranate fruit yield, number of fruits per tree, average fruit weight, TA, fruit maturity, total sugars, antioxidant activity and total anthocyanins. Fruit length increased by 9% with the CaCl2 1% treatment in the first season, and minor effects on total phenolics (by 1% with the nano-Ca2 treatment in the first season) and TSS (by 8% with the CaCl2 1% in the second season) were also observed. Results obtained indicate that foliar applications of Ca fertilizers led to decreases in fruit cracking, which is still a relevant problem in well-managed pomegranate orchards in Iran. In particular, results indicate the potential of low doses of Ca in new formulations for reducing fruit cracking in pomegranate. Additional studies would be necessary to further optimize the concentration and timing of the Ca applications with these new formulations, with the aim to reduce the incidence of this physiological disorder in crops such as pomegranate, where it limits fruit quality and yield every year.