# The Effect of Slow-Release Fertilizer on the Growth of Garlic Sports and the Soil Environment
## 3 Results and Analysis
### Regulation of the Soil's Heavy Metal Content by the Slow-Release Fertilizer  
As shown in Figure 7, compared with that in the CK group, the metal content in the T1 treatment group increased slightly overall, whereas the metal contents in the T2 and T3 groups generally decreased. Specifically, the Cd content in the T2 and T3 groups decreased by 15.56% and 16.25%, respectively, compared with that in the CK group; the Cr content decreased by 1.18% and 6.79%; the Ni content decreased by 13.53% and 19.54%; and the Zn content decreased by 3.11% and 14.14%, respectively. These reductions are  
Figure 6: Principal component analysis of soil’s chemical properties by different treatment groups. primarily attributed to the addition of bentonite, a material widely used in slow-release fertilizers due to its large specific surface area, strong ion exchange capacity, stable effects, and abundant availability [66]. Bentonite exhibits an effective remediation capacity for soils contaminated with heavy metals. Its ion exchange properties enable the fixation of heavy metal ions in the soil, thereby reducing their bioavailability and limiting their uptake by plants [67]. This makes bentonite a suitable material for the remediation of heavy-metal-contaminated soils. The negatively charged surfaces of clay minerals allow them to adsorb cations, and montmorillonite (a 2:1-type clay mineral) facilitates ion exchange due to the absence of interlayer ion bonds [68]. Additionally, the migration of heavy metals in the soil involves rapid exchange and precipitation-dissolution reactions. The sulfate ions present in phosphogypsum can form insoluble sulfate precipitates with heavy metal ions, thus reducing their mobility and bioavailability [69]. Moreover, phosphogypsum is rich in Ca\({}^{2+}\), which competes with heavy metals for adsorption sites on soil colloids, promoting the transformation of heavy metals from adsorbed states into precipitated forms [70]. [PERSON] et al. [71] investigated the effects of phosphogypsum (PG) and its combination with compost (CP) at a wet-to-weight ratio of 1:1 on the fixation of heavy metals in contaminated soil. The results indicated that the application of PG alone had a more pronounced effect on heavy metal immobilization, whereas the combined use of PG and CP exhibited a slightly weaker fixation capacity. Although the addition of CP contributed to improved plant growth, the fixation of heavy metals was most effective with PG alone. [PERSON] et al. [72] demonstrated that the application of 2.5% columnar fixed bentonite significantly improved plant growth while reducing the bioavailable heavy metal content in the soil. This finding suggests that columnar fixed bentonite is effective in remediating heavy-metal-contaminated soils by immobilizing metal ions. In a related study, [PERSON] et al. [73] further showed that the biological concentration factor (BCF) of heavy metals was significantly reduced by improving the soil with 2.5% bentonite. Specifically, in the first and second harvests, the BCF of zinc decreased by 74% and 28%, that for copper was reduced by 38% and 36%, and that for nickel was reduced by 44% and 34%, respectively, due to bentonite's ability to immobilize heavy metals in contaminated soils. Therefore, the application of slow-release fertilizers in this study effectively reduced metal ion leaching and decreased the extent of soil metal contamination. The T3 group demonstrated a supe  
Figure 7: Soil metal content in different treatment groups. rior performance, attributed to the higher fertilizer application rate, which enhanced the synergistic fixation effects of phosphogypsum and bentonite. Although the data on the heavy metal content in the soil in this experiment was based on a single measurement and could not be statistically analyzed, the measurement results are consistent with the relevant literature, indicating that slow-release fertilizers do not increase the soil's heavy metal load and may even reduce their bioavailability through physical and chemical fixation.