## 3 Results and Discussion
### Vegetable Growth  
Growth data for the vegetables were obtained in all groups to evaluate whether the growth of vegetables was affected by metal contamination. The growth rate of water spinach and sweet potato leaf in the experimental groups was slower than that in the control group from the third week to harvest time. The harvest quantity for potato and sweet potato in the control groups was significantly higher than in the experimental groups  
Figure 1: The comparison of metal levels in soils of control, group 1 and group 2: (**a**) Cd level; and, (**b**) Cu level.  
(Table 1). The greatest negative effect on growth was in tomato during the last period before harvesting time (\(p<0.05\)). In the Cu contamination group, we found that all of the vegetables in the control groups grew higher than all of the experimental groups by harvest time (Table 2).  
The crop weights at harvest for potatoes, sweet potatoes, and tomatoes were greater in the control group than the experimental groups. This result is consistent with [PERSON] et al. (2017), who reported that growth declined in carrot and packhoi under greenhouse cultivation conditions with exposure to metals in the soil. Additionally, the harvest weight of water spinach and sweet potato leaf were lower in group 1 as compared to the control group, and similarly for sweet potato (\(p<0.05\)).  
To monitor Cd accumulation in vegetables grown in Cd-contaminated soils, [PERSON] et al. (2017) planted _Solanum nigrum_ L. in soils that were contaminated with Cd at different concentrations. They found that the concentration of Cd in the vegetables ranged from 122 (standard deviation (SD): 38.2) to 387 (SD: 84.9) mg/kg. The height and quantity of vegetables did not decrease if the Cd concentration was <10 mg/kg in soil, while there was a reduction in the plant height and shoot dry biomass when the plants were grown at Cd concentration >25 mg/kg ([PERSON] et al., 2017; [PERSON] et al., 2017). In the current study, there was a negative impact of Cd contamination on the growth (height) and quantity of vegetables at harvest for soil concentrations in the range 8.24-20.6 mg/kg. [PERSON] et al. (2017) also demonstrated that the yield of rice decreased with an increase in Cd concentration in each group using artificially heavy metal-contaminated soils in China; comparing plant growth with Cd- and Cu-contaminated irrigation water at same dose, Cu produced a slight decrease in growth parameters, but Cd had a high impact on plant growth ([PERSON] et al., 2017), and Cd exposure seriously inhibited the root growth as compared to other metals ([PERSON] et al., 2017).  
Overall, heavy metal-polluted soils have a significant effect on the growth of plants or vegetables. In this study, in addition to soil texture and species, we also found that the soil organic matter, electrical conductivity, and total nitrogen content of each soil differed among the three soil groups (Supplementary Materials Table S1). All of these factors may affect the nutrient content and water transport capacity of vegetables in different groups, which results in differences in the growth and development of each vegetable ([PERSON] et al., 2017).