Effects of deep tillage and pre-irrigation on soil salinity, water use and performance of cotton in a saline soil

Soil salinization poses a serious threat to agricultural sustainability in arid regions, particularly in Xinjiang, China, a major cotton-producing area. Although deep tillage and pre-irrigation are widely used for saline soil reclamation, their interactive effects on seasonal water–salt regulation and crop performance remain insufficiently understood. This study evaluated the combined effects of deep tillage depth (F1: 20 cm, F2: 40 cm, and F3: 60 cm) and pre-irrigation volume (W1: 2400, W2: 3000, and W3: 3600 m³·ha⁻¹) on soil salinity, soil physical properties, and cotton productivity in a saline cotton field. A two-year split-plot field experiment was conducted, and a four-stage analysis of soil salt storage was used to characterize seasonal salt transport in the 0–60 cm profile. Results showed that deep tillage was the dominant factor regulating the soil water–salt environment. Compared with F1W3, F3W3 reduced soil salt storage in the 0–20 cm layer by 32.50%. Deep tillage also improved soil physical properties, decreasing bulk density by 4.70%, increasing total porosity by 6.20%, and enhancing soil water retention by 18.30% during the growing season. The recalculated stage-based analysis showed that the greatest reduction in profile salt storage occurred during the rapid-leaching period immediately after pre-irrigation, whereas only limited net changes occurred during the growing season. By contrast, the non-growing season was the principal period of salt re-accumulation, and this re-accumulation was clearly suppressed by deeper tillage. For cotton production, F2W2 achieved stable and relatively high yield, whereas F2W1 provided the highest water productivity, representing a 57.60–78.20% increase over F1W1. Overall, F2W2 is recommended as the most suitable treatment for balancing salinity control, crop performance, and water productivity, whereas F2W1 can serve as a practical water-saving alternative under water-limited conditions. • Deep tillage dominated salinity regulation and soil physical improvement in saline cotton fields. • A four-stage soil salt storage analysis clarified seasonal salt leaching and re-accumulation. • Deep tillage reduced bulk density by 4.70% and increased porosity by 6.20%. • F2W2 gave stable high yield, whereas F2W1 achieved the highest water productivity. • F2W2 is recommended overall, with F2W1 as a practical water-saving alternative.