Changes in Chemical Forms and Bioavailability of Zinc by Distance from Rhizosphere of Single and Mixed Culture

Heavy metals behavior in soil is complicated due to their different chemical forms. To investigate the effects of single and mixed rhizosphere of canola and corn on chemical forms and DTPA extractability of zinc, this experiment is set up using a rhizobox system. The rhizoboxes divided into four different parts and canola and corn were seeded in the middle part mixed or separately. The plants were harvested after the growth period and the soil samples were taken from different parts of the rhizoboxes. The results showed that, due to the decrease in pH and increase in dissolved organic carbon, the distribution of different forms of zinc changed in rhizosphere as compared to the bulk soil. The DTPA extractability of Zn is increased in the rhizosphere, while decreased with distance from the root. The soil pH increased and the DOC decreased from rhizosphere toward the bulk soil while the exchangeable, organic bound and oxide forms of zinc changed differently. There was a positive correlation between DOC and DTPA extractable, exchangeable, and organic and carbonate bound forms of zinc while the correlation between these forms and soil pH and oxide bound Zn was negative. Zinc concentrations in corn and canola shoot decreased while zinc uptake increased over corn in mixed culture. The Zn transport factor from root to shoot in mixed culture was greater than corn but lower than canola in single culture.