Optimizing surge-root irrigation parameters to enhance apple yield and water productivity in arid regions

Although various irrigation strategies are used in arid regions, approximately 75 % of apple orchards still experience drought stress. Surge-root irrigation (SRI) has shown potential in enhancing root-zone water supply, but the precise alignment of fruit trees’ water demand with key irrigation parameters remains unclear. Therefore, this study, conducted in apple orchards in Yan’an, Shaanxi Province, China, systematically evaluated the effects and comprehensive benefits of nine flow rate and sleeve/burial depth configurations of SRI and subsurface drip irrigation (SDI) on soil moisture, canopy physiology, and root characteristics. The results showed that long-term SRI significantly improved the uniformity and content of soil moisture in the root zone. The combination of a 40 cm sleeve/burial depth and a 4 L h⁻¹ flow rate resulted in the most uniform soil moisture distribution, which in turn promoted root penetration into the 60–80 cm soil layer, where the root length density reached 2.57 cm cm⁻³, accounting for 37.8 % of the total root distribution. Meanwhile, the 40–60 cm sleeve/burial depth and a 4 L h⁻¹ flow rate improved the canopy physiological performance of the fruit tree. SRI increased yield by 14.0 % compared with SDI. The fruit quality (transverse diameter is 75.86 mm) and irrigation water productivity (WP_I, 156.12 kg m⁻³) were high at 40 cm sleeve/buried depth and 4 L h⁻¹ flow rate. Path analysis indicated that SRI significantly affected the root system and canopy, and soil moisture and canopy were key factors influencing fruit quality and yield. The optimal water consumption for apple trees over the entire growth period was 454.7 mm determined using a binary nonlinear model (R² = 0.61). The 40 cm sleeve/burial depth and 4 L h⁻¹ flow rate could balance water-saving efficiency and sustainable development in approximately 5.5 years by regulating soil moisture distribution, root architecture and canopy physiology. This study provides a significant reference for optimizing SRI parameters in apple orchards on the Loess Plateau and similar arid regions.