Combined effects of water retaining agent and green manure on trace elements concentration in tobacco farming purple soils

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.