Diurnal irrigation timing affects fruit growth in late-ripening nectarines

Little is known about the best diurnal irrigation timing for maximum fruit growth in stone fruit, despite fruit size being the most important focus for growers to achieve maximum marketable yield. This study investigated the effects of morning and afternoon irrigation on nectarine fruit growth in stage I (cell division) and stage III (cell expansion). In the 2017/18 season, ‘September Bright’ trees were subjected to morning (Iam) and afternoon (Ipm) irrigations. Fruit diameter was monitored continuously (15-min intervals) using fruit gauges and converted into fruit weight, relative growth rate (RGR) and fruit growth efficiency (FGE), with the latter representing RGR per unit of crop water supply (irrigation + rainfall). Irrigation timing affected FGE in opposite fashions during stage I and III. In stage I, maximum FGE occurred in days of Iam, whereas in stage III in days of Ipm. The different observations in the two stages were strongly influenced by the effect of crop evapotranspiration on FGE but were likely dependent on other factors such as stage-specific vascular activity, sugar and starch content and fruit advancement in phenology phases. Overall, this study suggests that optimal irrigation management needs to consider irrigation timing at sub-daily scales in conjunction with stage-specific irrigation strategies.