Physiological, yield and nut quality responses of walnut tree subjected to different irrigation regimes following IRRIFRAME water balance model

In the last years commercial walnut orchards plantation is increasing in Emilia-Romagna, an Italian region renowned for its excellence in fruits cultivation. Despite the expansion of walnut plantations in this region, there is scarcity of studies focusing on the water demand of this crop. This research aims to assess the response of an adult walnut orchard (cv. 'Chandler') to three distinct irrigation treatments (100% ETc, 75% ETc, and 50% ETc). Water supply was managed according to the IRRIFRAME water balance model. Plant water status (stem water potential, SWP), leaf gas exchanges (leaf photosynthesis, A; stomatal conductance, gs), yield, nut quality (e.g., nut weight, shelled yield, kernel colour) and water use efficiency (WUE) were measured for four consecutive seasons (2018-2021). Differences in plant water status were detected only in half of the performed measurements and trees irrigated at 100% ETc generally showed more positive SWP values compared to 75% and 50% ETc trees. Gs and A were less sensitive than SWP to the different water regimes, showing limited differences among treatments only in the first two years. Yield and main nut quality parameters were slightly affected by irrigation treatments mainly in 2018 and 2019, with the 50% ETc showing a reduced productivity compared to 100% and 75% ETc. No differences where registered for shelled yield and kernel colour for all the four consecutive years. On the contrary, irrigation treatments highly affected WUE in all the considered years, with 100% ETc being the less efficient treatment, followed by 75% and 50% ETc.