The role of proper deep tillage in balancing soil aggregate stability, salinity, and crop yield in the early stages of salinized farmland improvement

Deep tillage can reduce soil salinity, improve soil health, and enhance productivity. However, the effects of deep tillage on soil aggregate stability and the mechanisms underlying salinity mitigation remain poorly understood during the early stages of salinized farmland reclamation. This study conducted a two-year experiment (2022–2023) in southern Xinjiang, China, with three tillage treatments: conventional tillage (CT, 20 cm depth), and two deep vertical rotary tillage (DVRT) treatments: continuous DVRT (CDT) and alternating DVRT with CT (DT) at three depths (20, 40, 60 cm). Deep vertical rotary tillage (DVRT) effectively disrupts the plow pan, significantly reducing soil bulk density and enhancing pore connectivity throughout the soil profile. This structural improvement promotes irrigation-driven downward salt migration. Desalination was most pronounced under the CDT40 and CDT60 treatments, with the largest reductions observed in soluble sulfate and chloride ions. DVRT shifted the aggregate-size distribution toward finer fractions, resulting in reduced macro-aggregate proportions and lower mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates. These changes were primarily driven by mechanical fragmentation and irrigation-induced salt leaching, which reduced root-zone ionic strength and weakened salt-induced flocculation. Electrical conductivity (EC) and salt stock were significantly negatively correlated with crop yield, whereas effective desalination was associated with reduced MWD and GMD and increased yield. However, continuous deep disturbance (CDT), although enhancing early-stage desalination, reduced root-zone water storage due to excessive soil loosening and induced salt re-accumulation during the late growing season. Post-harvest EC in the 0–60 cm soil profile increased by 20% and 35% under CDT40 and CDT60, respectively, and EC under CDT60 exceeded that under DT60, ultimately resulting in yield reduction. Overall, the agronomic benefits of DVRT depend on balancing salt removal with root-zone water conservation, and moderate deep tillage is more conducive to achieving stable yield improvement during the early stages of salinized farmland reclamation.