Peach yield and fruit quality is maintained under mild deficit irrigation in semi-arid China

Abstract We conducted a two-year study of deficit irrigation impact on peach yield and quality in semi-arid northwest China. Over two years, four-year-old peach trees were irrigated at 100, 75, 50 and 25% of peach evapotranspiration (ET c ), here, ET c = Coefficient (K c )×Local reference evapotranspiration (ET o ). During the April–July fruit production season we measured root zone soil water depletion, sap flow velocity, net photosynthetic rate ( P n ), transpiration rate ( T r ), stomatal conductance ( G s ), water use efficiency (WUE= P n / T r ), fruit quality, and yield under a mobile rain-out shelter. Increased soil water depletion reasonably mirrored decreasing irrigation rates both years, causing progressively greater water stress. Progressive water stress lowered G s , which in turn translated into lower T r as measured by sap flow. However, mild deficit irrigation (75% ET c ) constricted T r more than P n . P n was not different between 100 and 75% ET c treatments in both years, and it decreased only 5–8% in June with higher temperature than that in May with cooler temperature. Concurrently under 75% ET c treatment, T r was reduced, and WUE was up to 13% higher than that under 100% ET c treatment. While total fruit yield was not different under the two treatments, because 75% ET c treatment had fewer but larger fruit than 100% ET c trees, suggesting mild water stress thinned fruit load. By contrast, sharply decreased T r and P n of the driest treatments (50 and 25% ET c ) increased WUE, but less carbon uptake impacted total fruit yield, resulting 13 and 33% lower yield compared to that of 100% ET c treatment. Irrigation rates affected fruit quality, particularly between the 100 and 75% ET c trees. Fewer but larger fruit in the mildly water stressed trees (75% ET c ) resulted in more soluble solids and vitamin C, firmer fruit, and improved sugar:acid ratio and fruit color compared to the 100% ET c treatment. Overall, trees deficit irrigated at 75% ET c maintained yield while improving fruit quality and using less water.