The residual effects of applying compost on the amount of lead and cadmium (total and available) in soil and rice plant

In order to investigate the residual effects of continuous many-years application of compost on the amount of lead and cadmium (total and available) in soil and rice plant, an experiment was conducted in split plot based on randomized complete block design with three replications in 2010. Main plot, was application three levels of compost (0, 20 and 40 ton/ha) and also sub plot was effects of 4, 3 and 2 continuous years of without using compost after their use in 2006, 2006 and 2007, 2006-2008 years, respectively. Results showed that, the maximum concentration of available lead (2.58 mg kg-1) and cadmium (0.1 mg kg-1) in soil belonged to 40 ton ha-1 compost treatment. Also, with increasing the levels of applying compost and years of applying of 1 to 3 continuous years, concentration of lead and cadmium (total) in soil increased 85.40 and 58.24 percent compared to control treatment, respectively. Meanwhile, the interaction effect between levels of applying compost and years without applying compost had no significant effect on the amount of lead (available) in soil, shoots and seeds. Also, with continuous 3-year application of 40 ton ha-1 compost after 2 years since the last fertilization, the highest concentration of roots, shoots and seeds with about 3.61, 2.96 and 3 times increase were obtained compared to control treatment, respectively.