Sorption Characteristics of Chromium and Its Phytotoxic Effect with or without City Compost on Maize and Spinach in a Vertisol of Central India.

Phytotoxicity, due to chromium [Cr (VI)] additions from low to very high levels in a swell-shrink clayey soil (Haplustert), in maize and spinach was studied in a pot culture experiment. Six levels of Cr (VI) (0, 5, 10, 25, 50, and 75 mg kg-1 soil) for maize and five levels for spinach (0, 2, 5, 10, and 25 mg kg-1 soil) were applied singly and in combination with two doses (0 and 20 t ha-1) of city compost. At levels of more than 75 mg Cr (VI) kg-1 soil for maize there was virtually no growth after germination, whereas 25 mg Cr (VI) kg-1 soil hindered the germination of spinach crop. Initial symptoms of Cr (VI) toxicity appeared as severe wilting of the tops of treated plants. Maize plants suffering from severe Cr (VI) toxicity had smaller roots and narrow brownish red leaves covered with small necrotic spots. In spinach, severe chlorosis was observed in leaves. Higher levels of Cr (VI) inhibited the growth and dry-matter yield of the crops. However, application of city compost alleviated the toxic effect of Cr (VI). The concentration of Cr (VI) in plant parts increased when Cr (VI) was applied singly but decreased considerably when used in combination with city compost. There was evidence of an antagonistic effect of Cr (VI) on other heavy-metal (Mn, Cu, Zn, and Fe) concentrations in plant tops. Thus, when Cr (VI) concentration increases, the concentration of other beneficial metals decreases. Chromium (VI) concentration in maize roots ranged from traces (control) to 30 mg kg-1and were directly related to soil Cr (VI) concentration. At 25 mg Cr (VI) kg-1 soil, yield of maize was reduced to 41% of control plants, whereas in spinach, 10 mg Cr (VI) kg-1 soil caused a 33% yield reduction. Experimental results revealed that the maize top (cereal) is less effective in accumulating Cr (VI) than spinach (leafy vegetables). Laboratory studies were also conducted to know Cr (VI) sorption capacity of a swell-shrink clayey soil with and without city compost, and it was found that Cr (VI) sorption reaction was endothermic and spontaneous in nature. [ABSTRACT FROM AUTHOR]