Exploring six reduced irrigation options under water shortage for ‘Golden Smoothee’ apple: Responses of yield components over three years

Water for irrigation is in short supply worldwide, therefore reduced irrigation options will have to be explored. We did this for ‘Golden Smoothee’ apple over the growing seasons of 2003–2005 at the IRTA-Estaciò Experimental de Lleida (41°37′ N; 0° 52′ E; 260 m a.s.l.), Catalonia, Spain. This region has a temperate climate with winter-dominant rainfall. Averages of annual rainfall and reference evapotranspiration over 2000–2009 were, respectively, 371 and 1023 mm. The treatments were: Control (C), receiving full irrigation; spring irrigation (SI), where at the budbreak 80 mm of water was applied followed by watering so that the total water applied in the season was either at 33% of C (SI-33) or at 50% of C (SI-50); and deficit irrigation (DI), where trees were irrigated either with 33% of C (DI-33) or with 50% of C (DI-50). Water in DI was applied either through one dripper per tree (DI-33-1d and DI-50-1d) or through two drippers per tree (DI-33-2d and DI-50-2d). Trees showed biennial bearing with 2004 being an ‘off-year’ when treatment effects on yield were largely masked by the higher values of stem water potential associated with lower crop loads. SI-50 and SI-33 performed poorly and cannot be recommended. For each of the DI treatments, the one-dripper version increased fresh market yield and fruit size. For example, although DI-50 performed better than DI-33, DI-33-1d was similar in performance to DI-50-2d. Under water shortage, we recommend whole-season application of DI-50-1d and DI-33-1d depending on the availability of water supply.

Research highlights▶ Apple tree responds positively to deficit irrigation if judiciously applied. ▶ Apple trees can be irrigated with 50% less water than they normally are. ▶ In an ‘off-year’ in the biennial bearing cycle, less water can be applied.