Effect of drip irrigation and fertilizer regimes on fruit quality of a pomegranate (Punica granatum (L.) cv. Rabab) orchard

Abstract

We investigated the effect of different drip irrigation strategies including irrigating one side of trees with 50% and 75% of ETC (DI50, DI75); irrigating alternate sides of trees with 50% and 75% of ETC (PRD50, PRD75), and full irrigation (FI) that received 100% ETC and three prevalent fertilizers type including manure (M), chemical (CF) and foliar (FF) fertilizers on quality of pomegranate fruit in a semi-arid area. Results showed that the values of measured attributes varied from 64.4 to 71.2% in aril, 28.8 to 35.6% in peel, 49.0 to 55.7% in juice percentage, 1.055–1.064gcm−3 in juice density, 12.4 to 15.7 in maturity index (MI), 1.14 to 1.53% citric acid in titratable acidity (TA), 17.5 to 19.2°Brix in total soluble solids (TSS), 10.8 to 12.3mg per 100mL of juice in vitamin C and 3.12 to 3.26 in pH. On average, PRD strategies increased the juice percentage, MI and decreased the TA in comparison with FI while the results of DI strategies were in contrast to PRD. Furthermore, higher level of water stress (PRD50 and DI50) increased the TSS and decreased the vitamin C in comparison with other irrigation strategies. CF fertilizer showed the lower values in MI, TSS, peel percentage and juice density and the higher values in aril percentage, TA and vitamin C in comparison with other fertilizer types. Among the irrigation strategies, PRD50, PRD75 and DI75 strategies is recommend due to the positive impact on fruit quality attributes; however, it is important to consider the negative effect of PRD50 on fruit yields. For fertilizer types, the fertilizers including microelements (M and FF) are preferred in comparison with CF (including NPK). Based on the results, correct harvest maturity and ripening for pomegranate fruit can be determined when TA is reached lower than 1.32% citric acid, MI is increased to higher than 13.95 and TSS is greater than 18.25°Brix.