A study of the soil water potential threshold values to trigger irrigation of ‘Shimizu Hakuto’ peach at pivotal fruit developmental stages

Water management is an important practice that affects fruit size and quality. Effective implementation of irrigation scheduling requires knowledge of the appropriate indicators and thresholds, which are established manly based on the effects of water deficits on final fruit quality. Few studies have focused on the real-time effects of water status on fruit and shoot growth. To establish soil water potential (ψsoil) thresholds to trigger irrigation of peach at pivotal fruit developmental stages, photogrammetry, 13C labelling, and other techniques were used in this study to investigate real-time changes in stem diameter, fruit projected area, net leaf photosynthetic rate (Pn), and allocation of photoassimilates to fruit under soil water potential conditions ranging from saturation to stress in 6-year-old ‘Shimizu hakuto’ peach. Stem growth, fruit growth, and Pn exhibited gradually decreasing sensitivity to water deficits during fruit developmental stages I, II, and III. Stem diameter growth was significantly inhibited when ψsoil dropped to −8.5, −7.6, and −5.4 kPa, respectively. Fruit growth rate was low, reaching zero when the ψsoil was −9.0 to −23.1, −14.9 to −21.4, and −16.5 to −23.3 kPa, respectively, and Pn decreased significantly when the ψsoil reached −24.2, −22.7, and −20.4 kPa, respectively. In addition, more photoassimilates were allocated to fruit under moderate ψsoil conditions (−10.1 to −17.0 kPa) than under other ψsoil values. Our results revealed three ψsoil thresholds, −10.0, −15.0, and −15.0 kPa, suitable for triggering irrigation during stages I, II, and III, respectively. These thresholds can be helpful for controlling excessive tree vigor, maintaining rapid fruit growth and leaf photosynthesis, and promoting the allocation of more photoassimilates to fruit.