Growth and Cu and Zn uptake of two forage grasses affected by application of vermicompost spiked with different metal contents

To identify environmental risks of vermicompost-borne pollutants after consecutive application for different times, pot experiments were conducted to evaluate the effects of application of polluted vermicompost produced by Eisenia fetida on growth and Cu and Zn uptake of Mexico corn (Euchlaena mexicana) and Sudan grass (Sorghum hybrid Sudangrass) as well as soil characteristics. The results showed that application of vermicompost significantly increased shoot biomass of the two forage grasses, but decreased Mexico corn root biomass. Tissue Cu and Zn contents and soil bio-available fractions of Cu and Zn were significantly increased as the increase of application times, while soil pH and water soluble organic carbon (DOC) decreased. A significantly positive correlation was obtained between soil exchangeable and reducible fractions of Cu and Zn and forage grass tissue metal contents, whereas DOC performed a significantly negative correlation. So, application of polluted vermicompost could contribute to accumulate of soil Cu and Zn exchangeable and reducible fractions, and pose a potential threat to increase tissue Cu and Zn contents of the cultured plants.