Effect of Planting Density on Marigold (Tagetes erecta L.) Biomass and Cadmium and Lead Accumulation

PurposeTo determine the optimal density for planting marigold in a heavy metals polluted farmland around a lead-zinc mine, Lanping County, Yunnan Province.

MethodA marigold variety F1 was planted to study the effects of different planting densities (27 800, 33 300, 41 700 and 55 600 plants/hm²) on the growth and the accumulation characteristics of cadmium and lead in marigold.

Result (1) The stem biomass was the largest among marigold plant. The cadmium content in marigold was stem>root>leaf≈flower at the flowering stage, as well as root≈stem>leaf>flower at the maturity stage. The lead content in marigold was root≈leaf>stem>flower at the flowering and maturity stages. Cadmium and lead were mainly accumulated in the stem. (2) For the four planting densities, the biomass per plant and the cadmium and lead content per plant were the highest at 27 800 and 33 300 plants/hm², and the accumulation of cadmium and lead per unit area was 55 600 plants/hm². (3) The chemical forms of cadmium are mainly oxidizable and acid extractable, and the chemical forms of lead are mainly oxidizable, reducible and residual in soil. But there was no significant correlation between cadmium and lead content in marigold with chemical forms of cadmium and lead in soil.

ConclusionMarigold can be used for alternative planting on the polluted farmland in the lead-zinc mining area of Yunnan Plateau, and providing a new method for agricultural safe use of polluted farmland in the mining area.