## 3 Results
### Soil Organic Carbon Components and Humification Degree  
In this study, we applied the improved soil obtained over two years to rice-seedling raising. We investigated the organic carbon content and the degree of humification of the seedling-raising soil, comparing it with the farmer's seedling-raising soil (ZCK). The average soil organic carbon (SOC) of the seedling-raising soil across all improved treatments ranged from 10.42 to 19.39 g\(\cdot\)kg\({}^{-1}\) (Figure 3). Overall, the average SOC for each treatment in 2022 was 24.4% to 31.4% higher than that in 2021. Compared to JCK, the amendment treatments significantly increased the SOC by 23.3% to 78.9% (\(p<0.05\)). Among all of the amendment treatments, the JCWH treatment, which included additional sulfuric acid, exhibited the highest SOC levels over the two years, measuring 14.76 and 19.39 g\(\cdot\)kg\({}^{-1}\), respectively. Notably, we found no significant difference in the SOC content between the JCWH-treated soil over the two years and the ZCK soil. All amendment treatments resulted in a year-on-year increase in both humic acid carbon (HAC) and fulvic acid carbon (FAC) in the soil (Figures 4 and 5). Compared to the control group (JCK), the HAC increased by 46.3%, reaching 137.2%, while the FAC rose by 26.4% to 86.0%. As is shown in Figure 4, the increases in HAC for JCW and JCWH were more pronounced than that of JCWF over the two-year period. However, despite these improvements, a notable disparity remained when comparing the HAC of the farmer's seedling-raising soil (ZCK), which was 3.38 g\(\cdot\)kg\({}^{-1}\), with that of the amendment treatments. In 2022, the HAC/SOC ratios for both JCW and JCWH increased compared to 2021, while that of JCWF experienced a slight decrease. Figure 5 illustrates that among the various improved treatments, the increases in FAC for JCWH and JCWF were more significant than that of JCW. Nevertheless, the FAC/SOC ratio for JCWH exhibited a downward trend, decreasing by 7.7% over the two years, whereas the FAC/SOC ratios for JCW and JCWF showed upward trends, increasing by 5.8% and 8.2%, respectively. Importantly, after two years, the FAC of all amendment treatments significantly exceeded that of the ZCK soil. Figure 2: Effects of different improvement treatments on soil pH (**a**), EC (**b**), exchangeable sodium (**c**), and total alkalinity (**d**). Control (JCK): with no amendments; straw + gypsum treatment (JCW); straw + gypsum + sulfuric acid treatment (JCWH); straw + gypsum + chemical fertilizer treatment (JCWF). The different lowercase and uppercase letters above the column indicate the significant differences among different treatments in 2021 and 2022, respectively (\(p<0.05\)). Bars are means, with standard errors (n = 3). In comparison to JCK, the PQ values of all amendment treatments exhibited an increase over the two-year period (Table 2). The JCW treatment recorded the highest PQ value, with measurements of 50.46% and 50.30% in the respective years, followed by JCWH. Notably,  
Figure 4: Effects of different improvement treatments on soil HAC content and HAC/SOC ratio. 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 5: Effects of different improvement treatments on soil FAC content and FAC/SOC ratio. 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 3: The effect of different improvement treatments on soil organic carbon content. 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).