Foliar calcium fertilization reduces fruit cracking in pomegranate (Punica granatum cv. Ardestani)

An experiment was conducted to assess the effects of foliar sprays of a calcium fertilizer containing nanoparticles (nano-Ca) and calcium chloride (CaCL2 center dot 2H(2)O) 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 and CaCL2 center dot 2H(2)O 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).