Cadmium, chromium and copper in greengram plants

Soils contaminated with heavy metals including cadmium, chromium and copper present a major concern for sustainable agriculture. We studied the effects of cadmium, chromium and copper used both separately and as mixtures, on plant growth, nodulation, leghaemoglobin, seed yield and grain protein in seeds, in greengram inoculated with Bradyrhizobium sp. (Vigna). Cadmium at 24 mg kg(-1) of soil reduced the dry matter accumulation and number of nodules by 27 and 38%, respectively. Chromium at 136 mg kg(-1)of soil increased the dry phytomass and nodule numbers by 133 and 100%, respectively. The average maximum increase of 74% in seed yield occurred at 136 mg Cr kg(-1) of soil. Cadmium and copper at 24 and 1338 mg kg- 1 soil decreased the seed yield by 40 and 26%, respectively. Chromium at 136 kg- 1 of soil increased the root and shoot N and leghaemoglobin content by 42, 31% and 50%, respectively. In contrast, the root and shoot N decreased by 22% at 24 mg Cd kg- 1 of soil, while a maximum decrease of 50% in leghaemoglobin content occurred at 12 and 669 and 24 and 1338 mg Cd with Cu kg(-1) of soil, relative to the control. The average maximum grain protein (283 mg g(-1)) was observed at 136 mg Cr kg(-1) of soil, while minimum grain protein (231 mg g(-1)) was recorded at 24 and 1338 mg kg- 1 of cadmium with copper. The metal accumulation in roots and shoots at 50 days after sowing and in grains 80 days after seeding differed among treatments. The degree of toxicity of heavy metals to the measured parameters decreased in the order Cd > Cu > Cr.