Optimizing subsurface drip irrigation to enhance root-zone environment and pear orchard productivity in arid regions

Subsurface drip irrigation (SSDI) has the potential to alleviate root-zone water and salt stress in orchards, but the mechanisms by which SSDI regulates root-zone water–heat–salt dynamics and enhances productivity remain insufficiently understood. A three-year field experiment (2021–2023) was conducted in a salinity-affected fragrant pear (Pyrus sinkiangensis T. T. Yu) orchard in southern Xinjiang, China, to examine the combined effects of irrigation amount (I1: 3750, I2: 5250, I3: 6750 m3 ha−1) and lateral depth (L1: 20, L2: 30, L3: 40 cm). Surface drip irrigation (SDI, 6750 m3 ha−1) and flood irrigation (FI, 9750 m3 ha−1) were used as farmer-practice controls. The I3L2 treatment significantly improved soil conditions in the 30–60 cm root-active layer, increasing soil moisture by 20–24% and reducing electrical conductivity and soil temperature by 10–30% and 7–9%, respectively. These changes enhanced root traits, increasing root length density, specific root length, specific root area, and root mass density by 17–33%. While FI promoted vegetative growth, I3L2 enhanced reproductive performance, increasing fruit diameters by 10% and 13%. Mantel tests revealed strong soil–plant correlations, and partial least squares structural equation modeling (PLS-SEM) identified root traits as the primary driver of overall benefits (total effect = 0.67). Multi-objective optimization indicated that irrigation amounts of 4870–4940 m3 ha−1 and lateral depths of 30–33 cm could achieve ≥ 70% of maximum yield, water productivity, fruit quality, and net profit. These findings demonstrate that SSDI enhances orchard productivity through improved root-zone environment, providing a basis for precision irrigation management in arid orchards.