Assessment of lead extractable changes with different extractants in rhizosphere and bulk soil of corn (Zea mays) and canola (Brassica napus) and lead amounts in these two plants

Biological, physical and chemical characteristics of rhizosphere, especially chemical forms of elements are different in bulk soil. This experiment was conducted to compare different chemical forms of lead and their availability in rhizosphere and bulk soil, in two plants (corn and canola) at two times, (three and six weeks after planting) using planting boxes separated into three zones S1 (rhizosphere), S2 (rhizosphere affected area) and S3 (bulk soil) in green house condition. For assessment of metal fraction changes and their bioavailability, various methods of extraction (distilled water, Ca (NO3)2, DTPA and HNO3) were used. Results showed that water soluble forms of lead in cultivated corn and canola soil were greater than control three weeks after planting. Rhizosphere had no significant effect on Pb extractable with Ca(NO3)2. DTPA extractable Pb in corn and canola rhizosphere, was greater than bulk soil three weeks after planting. Extractable Pb with HNO3 in corn rhizosphere, was greater than other zones and for canola was less than bulk soil six weeks after planting. Amounts of Pb uptake in corn shoot were significantly higher than roots. Changes in lead forms in rhizosphere could be as a result of soil properties and plant species. Lead movement in the rhizosphere showed that increase in exchangeable fraction of metal was due to induced solubility of this element in the rhizosphere compared with bulk soil.