Optimization of irrigation on walnut through the IRRIFRAME water balance model

In recent years, reduced summer precipitation frequencies related to climate change have raised the probability of waterscarcity, even in the Po Valley of Italy, thus requiring an optimization of the irrigation management for walnut cultivationwhich has become very present in the area. The aim of the present study was to evaluate, during four consecutive sea-sons (2018–2021), the physiological (stem water potential Ψw, leaf photosynthesis A and stomatal conductance gs), yield(nut weight, shelled yield, kernel colour) and water use efficiency (WUE) responses of walnut trees to different irrigationlevels (100% ETc, 75% ETc, and 50% ETc) in order to obtain an improved water balance model, fit for walnut produc-tion under Emilia Romagna conditions. Water supply in 100% ETc (CTRL) was managed according to the IRRIFRAMEwater balance model. CTRL trees generally showed higher stem Ψw at midday, than those irrigated at 75% (DI75) and50% ETc (DI50). Less sensitivity was found for gs and A, than for Ψw, to the different water regimes: in fact, differencesamong treatments occurred only in the first two years, when yield was reduced by 50% ETc irrigation, compared to 100%and 75% ETc. No differences were registered for shelled yield and kernel colour during the experimental period. On thecontrary, irrigation treatments affected WUE in all the seasons, with CTRL being the less efficient treatment, followed byDI75 and DI50.