Improving water productivity in Walnut (Juglans regia L.): effects of spring regulated deficit irrigation and sustained irrigation rates under semi-arid conditions

Abstract

The increasing water scarcity and rising irrigation costs in semi-arid regions like Mendoza, Argentina, threaten the sustainability of high-density walnut orchards, requiring irrigation strategies that balance yield with water productivity. This study assessed the effects of four irrigation treatments on vegetative growth, yield, and nut quality of the ‘Chandler’ cultivar over three consecutive seasons (2022–2025). Treatments consisted of: (i) full irrigation replacing 100% of crop evapotranspiration throughout the season (T100); (ii) sustained deficit irrigation at 75% ETc (T75); (iii) over-irrigation at 125% ETc (T125); and (iv) a regulated deficit irrigation strategy applying 50% ETc during spring followed by full irrigation thereafter (T50/100). The experiment was arranged in a randomized complete block design with four replicates per treatment, and data were analyzed using analysis of variance followed by LSD’s test for mean comparisons. Results indicated that T125 and T100 treatments (125 and 100% ETc, respectively) maximized yield, maintaining stem water potential (SWP) around -6 bar throughout the growing season. These treatments produced heavier and bigger nuts than deficit irrigation treatments. Over-irrigation (T125) did not significantly enhance yield or nut quality compared to T100 and resulted in lower agronomic water productivity. In contrast, moderate (T75) and spring-regulated (T50/100) deficit irrigation significantly reduced yield by 25% and 29%, respectively, also limited trunk vegetative growth and reduced kernel size and weight, although kernel color remained unaffected. While the T50/100 strategy caused a sharp decline in stem water potential during spring, recovery was rapid once full irrigation resumed. Nevertheless, the temporary reduction in growth and yield highlights the high sensitivity of walnut trees to water stress during early phenological stages. Overall, this study provides novel multiseason evidence that full irrigation at 100% ETc optimizes the trade-off between yield and agronomic water productivity, offering practical guidance for irrigation management in walnut orchards grown under semi-arid environments with limited winter rainfall and spring high atmospheric demand.