Objective The aims were to investigate the efficacy of planting various green manure crops to control the levels of lead, chromium, and zinc in citrus orchard soil as well as the impacts of enrichment and transit on these elements under typical field management practices.

Method In the field runoff plot, three types of green manure were planted: vetch, white clover and ryegrass. A control group was also established (Citrus plot without green manure). Throughout the experiment, measurements of the physical and chemical characteristics of the soil as well as the concentrations of lead, chromium, and zinc in the soil and plants in various treatment plots were made in order to assess the impact of green manure on heavy metals.

Result ① Compared with the clean tillage treatment, planting green manure reduced the average of soil pH and increase the average contents of soil organic matter, total nitrogen, alkali-hydrolyzed nitrogen and available potassium. Among them, the average pH of the soil planted with ryegrass was the smallest (6.34), and the average contents of soil organic matter, total nitrogen, alkali-hydrolyzed nitrogen and available potassium in the soil planted with vetch were the highest. ② After one year of green manure planted, the concentrations of lead, chromium and zinc in soil were dropped. Compared with the clear tillage treatment, the average lead and chromium contents in the soil planted with ryegrass dropped the most, with 7.77% and 10.88%. Secondly, they could be decreased 9.42%, 6.91% in the soil planted with vetch. ③ The following three types of green manure have varying capacities for enhancing heavy metals: Vetch > Ryegrass > White clover. The abilities of ryegrass and vetch enriching lead, chromium and zinc increased over the course of the experiment.

Conclusion Planting green manure could decrease the amount of heavy metals in the soil and increase its nutrient content compared to clean tillage. Vetch had the highest concentration of heavy metals and the strongest capacity to increase soil nutrients. Vetch could be chosen as the best green manure crop in the purple soil citrus slope garden combined with the management practices of plowing and clearing the green manure in the orchard in August.