The Impact of Long-Term Evapotranspiration-Based Water Scheduling in Various Irrigation Regimes on Tree Growth, Yield, and Fruit Quality at Harvest in 'Fuji' Apple

In a long-term study between 2002 and 2007, the use of crop evapotranspiration (ETc), when a precise crop coefficient value (Kc) was used, provided a reliable tool (irrigation scheduling) for determination of water requirement for 'Autumn Rose Fuji' apple (Malus x domestica Borkh). In this process, the crop coefficient was modified by percentage of ground shade (GS) and tree canopy maturity (M). Water use, tree growth, yield, and fruit quality attributes at harvest were examined under various irrigation systems that were scheduled using ETc. The average rainfall during the irrigation periods of 2004-2005, when trees were immature or at an early stage of maturity, was 66.0 mm, while during 2006-2007 irrigation periods, when trees were fully grown, it was 55.1 mm. Application of water through a drip system resulted in significantly lower water consumption as compared to applications through micro-jet sprinkler. When trees were mature, each tree with a micro-jet full sprinkler system (FS) received an average of 6461.7 L (994 mm) while each tree with a full drip system (FD) received 3996 L (614.1 mm) of irrigation water per growing season. Using a partial root zone drying regime through a micro-jet sprinkler system (PRS) reduced fruit size but slightly improved fruit color. In general, any deficit drip irrigation regime (65% of full-drip) initially increased yield due to induction of stress and the production of higher number of fruit spurs. However, production declined when the water-deficient treatment was repeatedly applied to the trees over several years. Application of water at 65% of full drip rate, applied on both sides of the tree row (DD), reduced fruit weight. However, when 65% of full drip rate was applied to only one of the alternating sides of the tree every other week (PRD), fruit was heavier than those with the DD treatment. Averaging values over all years indicated that fruit from trees with PRS had higher SSC and the difference was highly significant in 2004 when trees were young. However, trees with FS systems had slightly lower SSC when trees were mature (after 2005). Considering tree growth, yield, and quality attributes in this study, a well-calculated ETc-based full drip irrigation system (FD) is recommended over any other irrigation regime.