Water use efficiency is improved by alternate partial root-zone irrigation of apple in arid northwest China

Apple is an important fruit tree in semiarid and arid areas, but increasing water scarcity limits apple productivity. Earlier studies have reported that alternate partial root-zone irrigation (APRI) can increase water use efficiency (WUE), but the effects of APRI with different irrigation frequencies on fruit yield and WUE are still unknown or contradictory. To close this knowledge gap, a two-year field experiment was conducted including two irrigation amounts (400 and 500 mm) and three irrigation methods (i.e. conventional irrigation with low frequency, APRI with low and high frequencies) in an apple orchard of the arid region of northwest China. Soil water content, sap flow, soil evaporation, leaf area index (LAI), fruit yield and components, and WUE on the basis of irrigation amount and tree evapotranspiration were evaluated. Results showed that (1) compared with low irrigation amount, high irrigation amount improved apple yield and significantly increased tree evapotranspiration and LAI; (2) in comparison of conventional irrigation, APRI could increase apple yield significantly and reduce tree evapotranspiration, so it enhanced WUE; (3) compared with low frequency, APRI with high frequency could improve apple yield and WUE. Our results demonstrated that alternate partial root-zone irrigation with high irrigation frequency has the potential to increase fruit yield and water use efficiency on the basis of tree evapotranspiration in arid northwest China.