Optimizing conjunctive use of on-farm water storage and groundwater to enhance sunflower productivity and rhizosphere health in saline-alkaline agroecosystems

Soil salinization and water scarcity severely threaten agricultural sustainability in arid and semi-arid regions. Conjunctive water use (CWU) of on-farm water storage (OFWS) and groundwater (GW) is a promising strategy, however, its synergetic impacts on the soil-microbe-plant system remain inadequately explored. A field experiment was conducted in the Hetao Irrigation District, China to evaluate six irrigation regimes: one non-irrigation (I0), and five CWU ratios (I1: 100% OFWS; I2: 75% OFWS + 25% GW; I3: 50% OFWS + 50% GW; I4: 25% OFWS + 75% GW; and I5: 100% GW). Results showed that OFWS and GW exhibited distinct physicochemical signatures. OFWS featured higher temperature, pH, dissolved oxygen (DO), and K + , whereas GW maintained consistently low temperature and elevated Ca 2+ . These differences drove divergent microbial successions and higher α-diversity. Notably, the I2 regime (75% OFWS + 25% GW) emerged as the optimal strategy, significantly outperforming single-source and non-irrigated treatments. It increased 100-seed weight, size, and plumpness by 2.1–11.6%, as well as elevating rhizosphere total nitrogen (TN) and phosphorus (TP) by 4.6–18.6%. Mechanistically, I2 mitigated soil salinization by reducing Na + and the sodium adsorption ratio (SAR) by 11.4–43.8%, thereby improving structural stability and enriching beneficial taxa such as Actinobacteriota and Proteobacteria. Bacterial communities were primarily regulated by hydrochemical (temperature, DO, K + ) and edaphic (SAR, nutrients) factors, whereas fungal communities exhibited functional niche differentiation specifically linked to water-borne NH 4 + and soil pH/EC. This study demonstrates that a 75:25 OFWS-to-GW ratio maximizes sunflower productivity and rhizosphere health, providing evidence-based guidance for sustainable irrigation and agricultural resilience in saline-alkaline arid regions.