Response of soil properties and water use efficiency to straw-based amendments and irrigation rates in a saline soil

Reducing irrigation water utilization and improving water use efficiency (WUE) are critical for sustainable agriculture in arid areas with saline soils. However, reduced irrigation exacerbates salt stress in saline soils, presenting a paradoxical challenge for increasing WUE. To address this issue, three straw-based composite amendments, including a liquid film combined with a straw layer (LFSG), biochar combined with straw (SBSH), and polyacrylamide combined with straw (PAMSH), were selected to evaluate their effects on saline soil properties and WUE under normal irrigation (NI, 75 % water holding capacity) and deficit irrigation (DI, 55 % water holding capacity) through a pot experiment. The results demonstrated that the LFSG treatment significantly increased WUE regardless of NI or DI, primarily through dual regulation of soil water and salinity redistribution, with minimal association with nutrient availability or enzymatic activities. The spatial‒temporal analysis revealed divergent patterns in the upper straw layer of the LFSG treatment: NI decreased salinity by 25 %, whereas DI elevated both the soil water content and salinity, suggesting buried layer-driven water and salinity mobilization. The SBSH treatment resulted in irrigation-dependent outcomes. Under NI, the SBSH treatment achieved the highest WUE by increasing salinity leaching and improving the soil nutrient transformation efficiency (increasing the activities of C-, N-, and P-related enzymes). Conversely, the SBSH treatment triggered synergistic water and salinity stress under DI, thereby reducing the WUE. The PAMSH treatment significantly increased soil water retention and reduced crop water consumption but paradoxically suppressed WUE, likely due to low water effectiveness and salinity leakage. This adverse effect of PAMSH on WUE under DI was partially mitigated through extended growth cycles. These results show that the effect of amendments on WUE is irrigation-dependent and is governed by competing water-salinity-nutrient interactions. This study emphasizes the importance of integrating amendment selection with hydrological conditions to achieve synergistic water-salinity management and WUE improvement in arid saline soil agroecosystems.