Cadmium Accumulation and Its Effects on Uptake of Micronutrients in Indian Mustard [Brassica juncea (L.) Czern.] Grown in a Loamy Sand Soil Artificially Contaminated with Cadmium

A pot experiment was conducted in a greenhouse to evaluate the effects of different levels of cadmium (Cd) on Cd accumulation and their effects on uptake of micronutrients in Indian mustard [Brassica juncea (L.) Czern.]. Cadmium accumulation in shoots and interactions among other metals [manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn)] were investigated. Ten levels of Cd ranging from 0 to 200 mg kg–¹ soil were tested. The crop was grown for 60 days in a loamy sand soil with adequate basal fertilization of nitrogen (N), phosphorus (P), and potassium (K), and dry-matter yield (DMY) was recorded. The plants were analyzed for total Cd and micronutrients, and the soil was analyzed for diethylenetriaminepentaacetic acid (DTPA)–extractable Cd. Experimental results showed that the DTPA-extractable Cd in the soil increased consistently and significantly with increase in rates of Cd application up to 200 mg Cd kg–¹ soil. Significant reduction in the DMY of Indian mustard occurred with application of 5 mg Cd kg–¹ soil and greater. The content as well as uptake of Cd by Indian mustard increased significantly over the control at all rates of its application. It increased from 5.95 μg pot–¹ in the control to 150.6 μg pot–¹ at Cd application of 200 mg kg–¹ soil. Application of Cd to soil though decreased the content of micronutrients in plants, but significant reduction occurred only for Fe at rates beyond 50 mg Cd kg–¹ soil. However, the total removal of Fe, Zn, and Cu registered a significant decline over the control at and above Cd application of 10 mg kg–¹ and that of Mn beyond 10 mg kg–¹. In loamy sand soil, a DTPA-extractable Cd level of 3.8 mg kg–¹ soil and in plant content of 28.0 μg Cd g–¹ DMY was found to be the upper threshold levels of Cd for Indian mustard. Considerable residual content in the soil suggests that once the soil is contaminated by Cd it remains available in the soil for decades, and food crops grown on these soils may be a significant source of Cd toxicity to both humans and grazing animals.