## 4 Discussion  
### Short-Term Improvement Enhances the Physicochemical Properties of Saline-Alkali Soil  
Under the 2-year short-term soil improvement involving gypsum, straw, and other amendments, notable changes occurred in the physical and chemical properties of the soil. Specifically, the soil pH and exchangeable sodium decreased significantly over the years, while the electrical conductivity (EC) value exhibited an annual increase. The total alkalinity  
Figure 6: Effects of different improvement treatments on seedling dry weight (**a**), plant root length (**b**), seedling height (**c**), and leaf age (**d**). Control (JCK): with no amendments; straw + gypsum treatment (JCW); straw + gypsum + sulfuric acid treatment (JCWH); straw + gypsum + chemical fertilizer treatment (JCWF); the farmer ’s seedling-raising soil (ZCK). The symbol notation is the same as in Figure 2.  
Figure 7: Pearson correlation analysis of seedling quality parameters with indicators relative to soil salinity, alkalinity, and fertility under different improvement treatments. SH, seedling height; RL, root length; LA, leaf age; SDW, seedling dry weight; EC, electrical conductivity; TA, total alkalinity; ES, exchangeable sodium; SOC, soil organic carbon; HAC, humic acid carbon; FAC, fulvic acid carbon; HA\(\_\)lgiK, color tone coefficient of humic acid; FA \(\_\)lgiK, color tone coefficient of fulvic acid; PQ, humination coefficient. displayed a trend of initially decreasing and then increasing (Figure 2). In alignment with the experimental findings of [PERSON] [23] and [PERSON] [24], this study also observed a significant reduction in the soil pH and exchangeable sodium. The observed decrease in pH could be attributed to the presence of acidic substances and acidifications generated due to the amendments [6; 15], as well as the macromolecular carboxyl groups formed through the humification of straw [25; 26], which exerted neutralizing effects on alkaline ions. The reduction in exchangeable sodium primarily resulted from the enhancement of the Ca-Na exchange process facilitated by gypsum [27]. Moreover, Ca\({}^{2+}\) ions reduced the electrokinetic potential of the soil colloid surfaces, promoting colloid coagulation, which subsequently increased soil hydraulic conductivity and enhanced the leaching of sodium [28; 29]. The extent of the decrease in pH and exchangeable sodium across treatments was ranked as follows: JCWH > JCWF > JCW (Figure 2a,c), with JCWH demonstrating the most effective results. While sulfuric acid lowered the pH of saline-alkali soil, it also facilitated the dissolution of deposited calcium in the soil, thereby enhancing Ca-Na replacement [15]. Similar to the research trends observed by [PERSON] [30], [PERSON] [31], and others, this study found that the EC values of all amendment treatments were higher than those of the control group (Figure 2b). This phenomenon can be attributed to the extended cultivation time of the soil, which facilitates a more complete dissolution of soluble salts [32]. [PERSON] et al. [30] also reported that the application of gypsum and straw to saline-alkali soil resulted in decreases in the soil pH and exchangeable sodium percentage (ESP), while the EC increased by 31.79% compared to the control group. Furthermore, the concentrations of ions detrimental to plant growth, such as Na\({}^{+}\) and Cl\({}^{-}\), were significantly reduced, whereas the levels of beneficial ions, such as Ca\({}^{2+}\) and SO\({}_{4}\)\({}^{2-}\), were significantly increased. These outcomes resulted from the effective improvement process. In this study, the total alkalinity of all amendment treatments in 2021 was significantly reduced. However, an upward trend was observed in 2022 (Figure 2d). The total input of straw carbon was identified as a key driving factor [33]. In carbon-rich and alkaline soils, the continuous application of substantial amounts of straw promoted the mineralization of soil organic carbon (SOC) and resulted in the accumulation of calcium bicarbonate, thereby increasing total alkalinity.