Trace elements are found in small concentrations in soil, yet plants require them for physiological functions. The runoff process leads to soil fertility loss by shifting soil particles and elements, and deposits them to a different position. However, there is a lack of information about the amount of trace elements that flow in tobacco-growing red soil during the natural rainy seasons due to runoff. In this study, runoff discharge was collected from two different soil mulching conditions (straw and no straw) at 15˚, in Miyi county of Sichuan province, to evaluate the characteristics of trace elements in runoff discharge. The runoff discharge was filtered to separate water (runoff) from sediment. The concentrations of the elements were analyzed in samples obtained from 9 erosive rainfall events, with 3 replications for every sample. The considered trace elements were Zinc (Zn), Copper (Cu), and Molybdenum (Mo). In addition, the total amount of each element loss per unit area (total loss) was also calculated statistically. The results revealed different concentrations and total losses for the selected trace elements. The total loss in runoff ranged from 10.82 to 194.05 mg/ha, 0.62 to 18.91 mg/ha, and 0.32 to 2.37 mg/ha for Zn, Cu, and Mo, respectively.

Green manure (GM) is widely adopted for agricultural productivity and sustainability. The present study supplemented the GM effect with that of water retaining agent (WRA) to enhance the sustainability of tobacco planting purple soils in Sichuan Province, China. The study employed three GM legumes varieties (Trifolium repens, Vicia villosa and Medicago sativa), while the WRA used was polyacrylamide at different application rates (0, 30, 90, 150 and 210 kg/ha). The results revealed that the average concentration of trace elements ranged from 0.86 to 1.18 mg/kg, 22.2 to 26.5 g/kg, 78 to 426 mg/kg, 16 to19 mg/kg, and 69 to 76 mg/kg for Mo, Fe, Mn, Cu, and Zn, respectively. Compared to actual soil concentration, Mn was increased by adding 150 or 210 kg/ha to M. sativa fertilized soil. Zn was increased by combining any WRA rate with V. villosa or 150 kg/ha WRA with T. repens. The combination of 90 kg/ha WRA with M. sativa, and 30 kg/ha WRA with either T. repens or V. villosa decreased Fe. Then, all the treatments reduced soil Mo and Cu. Therefore, these GM and WRA affected the soil environmental conditions associated with different responses of individual soil trace elements.