Synergistic amelioration of saline soils by a superabsorbent carbon-based material and flue gas desulfurization gypsum: Enhanced soil health, crop yield, and underlying drivers

Superabsorbent carbon-based materials (CB) have been shown to ameliorate saline soils in arid regions; however, their synergistic effects with flue gas desulfurization gypsum (FGD) on soil health and seed cotton yield remain poorly understood. A field experiment was conducted with six treatments: control, FGD, biochar (BC), BC + FGD, CB, and CB + FGD to evaluate the individual and combined effects of these amendments on soil properties and cotton performance. The results showed that all amendment treatments improved soil aggregate structure, water retention capacity, salt suppression, and nutrient availability, thereby promoting cotton growth and increasing seed cotton yield. Although treatment advantages varied among individual indicators, CB + FGD showed the greatest overall improvement. Compared with the control, CB + FGD increased the mean weight diameter (MWD) of soil aggregates by 73.33% and decreased total soluble salts (TSS) by 21.37% in the 0–20 cm plow layer, while achieving the highest seed cotton yield of 6125.7 kg ha−1. Other indicators, including geometric mean diameter (GMD), water-stable macroaggregates, Na+ concentration, electrical conductivity (EC), soil nutrients, soil moisture, plant growth, and root traits, also improved markedly. Random forest analysis identified soil aggregates and salinity as core drivers of soil health. Partial least squares path modelling further revealed that CB + FGD enhanced aggregate structure and moisture, which in turn drove salt suppression and nutrient retention, indirectly promoting cotton growth and seed cotton yield. These findings suggest that improving soil structure and alleviating salt stress should be prioritized in saline-alkali drylands. Combining CB with FGD offers a promising strategy for sustainable agriculture in arid regions.