ALLEVIATION OF CADMIUM STRESS ON RADISH BY HUMIC ACID an‎d CHITOSAN AS SOIL ADDITIVES

Two pot experiments were conducted to study the effect of humic acid (HA) or chitosan (CHI) as soil additives at concentrations of 100 and 200 mg kg-1 soil on counteracting the harmful effects of cadmium ions at levels of 100 and 150 mg kg-1 soil on radish plant. Results showed that, Cd at 100 and 150 mg kg-1 decreased significantly length, fresh and dry weights of shoot and root organs as well as leaves number per plant in both seasons. Chlorophyll, total sugars, nitrogen, phosphorus, potassium, relative water content, soluble proteins and total amino acids content were also decreased. Meanwhile, Cd concentration in plant tissues was increased. On the other hand, application of HA or CHI at levels of 100 or 200 mg kg-1 increased all the above mentioned parameters and decreased Cd concentration in plant tissues. In conclusion, both natural chelating compounds, in particular, CHI at 200 mg kg-1 dry soil can increase the capability of radish plant to survive under cadmium stress due to chelating Cd2+ ions and reducing Cd bio-availability.