Soil contamination by chromium and its enzymatic activity and yielding

The effect of chromium (VI) on the activity of dehydrogenases, urease, acid and alkaline phosphatases and the yield of lupine was assayed in a pot experiment. Chromium was applied as K2Cr2O7 in the amounts of 0, 10, 20, 30, 40, 50, 100 and 150 in mg . kg(-1) of soil. The tests were conducted on brown leached soil from slightly dusty clay sand of pH in 1 M KCI 5.80. Soil was inoculated with nitragine containing Bradyrhizobium bacteria. Hexavalent chromium was found to inhibit the activity of dehydrogenases, urease, acid and alkaline phosphatases and to depress the yield of above-ground parts of lupine, yield of roots, number and weight of root nodules. The negative effect of chromium occurred in both inoculated and non-inoculated soil. The potential biochemical soil fertility index derived from the activity of the soil enzymes and organic carbon content was negatively correlated with the rate of chromium (VI) contamination of soil, On the other hand, the index was positively correlated with the yield of lupine.