Water use and irrigation management of pomegranate trees - A review

Global warming-induced climatological changes, limited water resources and water restrictions for agriculture during drought force producers to invest in crops more suited to the potential future climate, such as drought-tolerant pomegranate trees. Skilful management of limited and poorer quality water resources is critical to optimize production and fruit quality for a total farm unit and requires appropriate knowledge regarding the crop. The review focuses on irrigation methods, water requirements of the crop, water use efficiency and productivity and water management strategies under limited water supply (irrigation and orchard management). With regard to irrigation systems, drip irrigation appears to be favoured above the more conventional types of irrigation. Management challenges of subsurface drip irrigation systems though should be taken into account if this type of irrigation is considered. The evapotranspiration of subsurface irrigated pomegranate orchards in arid regions ranged from 53 to 953?mm for one to six-year-old trees and orchard water requirements may increase depending on the irrigation system used and whether weeds are present in the orchard. Comparison of mathematical relationships to determine crop coefficients from fractional ground cover indicated that the pomegranate cultivar 'Wonderful' tended to have lower crop coefficient values than grapevine, peach and other deciduous fruit at comparable canopy cover. A comparison of advantages and disadvantages of several irrigation strategies identified potential of some to optimise farmer profitability and to comply with customer requirements. Water deficits during flowering and fruit set may increase aril red colour for some cultivars without detrimental effects on marketable yield, fruit size and chemical composition. Water deficits during ripening and sustained deficit irrigation throughout the season in some cases resulted in improved red colour of fruit peel and/or juice, but with a negative effect on fruit weight and economic income. Sustained deficit irrigation at low levels of evapotranspiration replacement is not considered a sustainable strategy for pomegranate orchards over the long term. In terms of orchard management, olive pomace mulch increased yield and decreased orchard water use. Different types of mulches can be considered to reduce soil evaporation water losses. Variable results with different systems and different cultivars in different countries clearly indicate that results from one study cannot simply be transferred to another area where conditions and cultivar types may not be the same. This underscores the necessity of conducting research under local conditions.