Scheduling deficit subsurface drip irrigation of apple trees for optimizing water use

The impact of four different irrigation strategies on soil and plant water status and fluxes of photosynthesis (A) and chamber transpiration (E) has been studied under continental climate on field-grown apple trees ( Malus domestica ‘Gala’) in 2010 and 2011. The non-irrigated treatment resulted in a decrease in soil water content (SWC) throughout the season in comparison with irrigated treatments. Non-irrigated trees showed more negative values of predawn leaf water potential (Ψ P ), which decreased to − 0.2 MPa, reflecting a moderate water stress during the fruit ripening period. A decrease (15 to 25%) of stomatal conductance (g s ), leaf photosynthesis (A), and transpiration (E) were observed in these water-stressed trees (T1). Well-irrigated trees during the whole season (T2) showed the highest rates of g s , A, E, as well as of Ψ P values, which were around − 0.1 MPa. Trees irrigated only during the fruit cell division period (stage I) and the ripening period (stage III) (T3) showed a small decrease (10%) in leaf gas exchanges. A regulated deficit irrigation (RDI) applied only during the fruit cell growth (stage II) on trees and well-irrigated during the fruit cell division period and the ripening period (T4) seems to have little effects on gas exchanges and no effects on yield and fruit quality before and after storage. Therefore, the results showed that with the exception of RDI treatment, increasing water stress reduced the physiological parameters due to stomatal and non-stomatal limiting factors. However, such regulated deficit irrigation saved 45% of water compared to the comfort irrigation. Considering these results, regulated deficit subsurface drip irrigation applied during the fruit growth II is a sustainable strategy for saving water, increasing water use efficiencies, and preserving the physicochemical quality of the apple fruits before and after storage.