## 3 Results and Discussion
### The Impact of Amendments on Soil Physicochemical Properties and the Bioavailability of Cu  
The utilization of soil amendments has manifested improvements in soil physicochemical attributes to varying extents (Table 2). In contrast to the control (CK), the application of vermicompost and steel slag has exerted a salutary influence on soil pH. Notably, in the plot treated with vermicompost (L1), the pH has ascended from 3.78 to 5.17. In the plots ameliorated with steel slag (L2) and a composite of vermicompost and steel slag (L3), a more conspicuous augmentation in soil pH has been observed, reaching 6.76 and 6.86, respectively, from the baseline of 3.78. The escalation in soil pH is ascribed to the alkaline nature of steel slag, fostering the generation of hydroxides and the precipitation of carbonates [28]. Furthermore, the electrical conductivity (EC) within the soil across all treatment cohorts (L1, L2, and L3) has undergone diverse increments vis a vis CK, registering increments of 17.1%, 44.6%, and 34%, respectively. Concurrently, the cation exchange capacity (CEC) has undergone a notable surge, escalating from 17.2 cmol kg\({}^{-1}\) to 30.6, 28.2, and 23.2 cmol kg\({}^{-1}\). Vermicompost and steel slag conduce to the augmentation of soil EC via the precipitation of soluble ions [29]. The heightened pH implies an accentuation of negative surface charges (OH\({}^{-}\)), thereby instigating a heightened CEC [30]. Moreover, both the singular and concomitant application of amendments has signally elevated soil organic matter (SOM), particularly in the vermicompost-treated cohort (L1), where SOM has burgeoned by 147.9% compared to CK. The substantial augmentation in soil SOM is ostensibly attributable to the constituents bequeathed by vermicompost, with organic amendments serving as a direct four for the amplification of SOM in the soil [31]. Intriguingly, post-amendment application, there was a marginal decrement in soil Eh. The inverse correlation between soil Eh and pH values substantiates this phenomenon [32]. Figure 2: SEM images (**A**) and XRD patterns (**B**) of steel slag. Due to the pronounced acidity inherent in the acidic soil derived from copper sulfide, characterized by a pH value of 3.78, the copper (Cu) within the soil manifests a heightened degree of bioavailability [33]. The application of vermicomopost in isolation (L1), exclusive application of steel slag (L2), and the co-application of vermicomopost and steel slag (L3) collectively yield a discernible reduction in both total and bioavailable Cu content within the soil matrix (Figure 3). Relative to the control group (CK), there is a notable decline in total Cu content of 43.2-44.7%, alongside an analogous decrease in bioavailable Cu content by 79.6-88.9%. Furthermore, the Cu bioavailability (Cu-BI) in soils subjected to L1, L2, and L3 applications exhibits a reduction of 64.2%, 80.3%, and 72.6%, respectively. These outcomes underscore the efficacy of steel slag application in enhancing Cu sequestration within the soil. The integration of SEM and XRD spectra unveils the substantial presence of alkaline oxides within the steel slag. This substantiates its robust acid-neutralizing capacity, thereby markedly elevating the concentration of hydroxide ions (OH\({}^{-}\)) in the soil milieu. Consequently, this heightened OH\({}^{-}\) concentration facilitates the precipitation of Cu\({}^{2+}\) as insoluble Cu(OH)\({}_{2}\)[34]. Furthermore, SEM and FTIR analyses of vermicomopost corroborate the abundance of organic functional groups. The undissociated functional groups form coordination bonds with liberated Cu\({}^{2+}\) to promote the formation of less reactive metal complexes, thus significantly mitigating the toxicological impact of heavy metals [35].