Cadmium phytotoxicity in spinach with or without spent wash in a vertisol

The phytotoxicity due to cadmium (Cd) and its likely contamination of the food chain-resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) in spinach (Spinacia oleracea L.) - was studied in a pot culture experiment. Twelve levels of Cd (0, 2, 4, 8, 10, 20, 40, 60, 80, 120, 160, 200 mg kg(-1) soil) were applied singly and in combination with two doses (0 and 2.5 cm) of spent wash. Above 80 mg Cd kg(-1) soil, there was very slow growth of spinach after germination. Spinach crop suffering from severe Cd toxicity had small roots and narrow yellowish leaves, covered in small necrotic spots. Higher levels of Cd inhibited the growth and biomass of the crop. However, application of spent wash alleviated the toxic effect of Cd to some extent. The concentration of Cd in plant parts increased when Cd was applied singly but decreased considerably when used in combination with spent wash. Cd concentration in spinach root ranged from traces (control) to 120 mg kg(-1) dry matter and was directly related to soil Cd concentration. At 40 mg kg(-1) soil, yield of spinach was reduced to 38% of control plants. A laboratory study was also conducted in the soils collected from treated pots after harvest in order to know the different operationally defined fractions of Cd that control the availability of Cd to spinach and that were correlated with dry-matter yield of spinach crop.