Effect of municipal waste compost and zeolite on reduction of cadmium availability in a loamy soil (A case study: Arak municipal waste compost)

Application of organic amendments as a cheap material is increasing to modify soil physical, chemical and biological properties of arid and semi-arid regions. Applying municipal waste compost can probably increase soil pH, organic carbon percent and cation exchange capacity and thereby decreaseing heavy metal availability such as cadmium. On the other hand, applying soil natural clay such as zeolites can probably increase cation exchange capacity that decreases the heavy metal availability in soil and plant. However, this may be affect soil nutrition availability. This research was done to investigate the effect of applying Arak municipal waste compost and zeolite on decreasing cadmium availability in a loamy soil.
A loamy, non-saline soil with low organic carbon percent was sampled from soil surface layer (0–15 cm) in the research field of Arak Azad University. A factorial experiment with a randomized complete block design with 3 replications was conducted in greenhouse conditions.. Treatments were consisting of applying Arak municipal waste compost at the rates of 0, 15 and 30 Mg ha-1. The soil was polluted with cadmium from cadmium chloride source at the rates of 0,5,10, 15 and 20 mg Cd kg-1 soil and incubated for one month. On the other hand, zeolite clay (clinoptilolite) was added to the soil at the rates of 0 and 10 % (W/W). Then, corn (Zea mays L. single grass 704) seeds were sown. After 60 days from the experiment, soil physio-chemical properties and soil and plant Cd concentration were measured.
The results showed that increasing application of municipal waste compost from 0 to 30 Mg ha-1 significantly increased CEC (3 units) and pH in the soil under growth of corn. Increasing the amount of Arak municipal waste compost from 0 to 15 and 30 Mg ha-1 in a 20 mg Cd kg-1 soil without applying zeolite, caused a significant decrease in DTPA-extractable Cd by 19 and 30 %, respectively. Similar to this result, root and shoot Cd concentration were decreased, as, applying 30 Mg ha-1 Arak municipal waste compost (in a soil polluted with 20 mg cd kg-1 soil) without receiving zeolite caused a significant decrease in root and shoot Cd concentration by 37 and 66%, respectively. In addition, applying 10 % (W/W) zeolite clay in a cadmium polluted soil (20 mg Cd kg -1soil) without municipal waste compost decreased the DTPA-extractable Cd by 7%. Root and shoot Cd concentration was also decreased by 16 and 23%, respectively.
The lowest DTPA-extractable Cd was in a 5 mg cadmium polluted soil treated with 30 Mg ha-1 municipal waste compost and 10% (W/W), white the greatest amount of DTPA-extractable Cd was observed in a polluted soil with 20 mg cd kg-1 soil without receiving municipal waste compost and zeolite. The result of this experiment showed that applying zeolite and Arak municipal waste compost can increase the cation exchange capacity and thereby decreasing cadmium concentration in soil or plant. However, the other effect of applying organic amendments cannot be ignored.