Effect of chromate and organic amendments on the composition and activity of the microorganism flora in soil

Abstract

The effects of chromate and organic amendments on the composition and activity of the microbial flora in a soil were studied after the addition of rice straw and cow manure to a soil which was treated with Na2CrO4. At a 20 ppm level of chromate, CO2evolution was reduced and at a 100 ppm chromate level it was markedly depressed. Cow manure as a compost promoted the activity and multiplication of the microorganisms, and accelerated the decomposition of rice straw, and after 20 days the total CO2evolution increased 1.3–1.4 times compared with that in a soil which contained only rice straw. By the addition of 100 ppm chromate, the population of the fungi increased. It is assumed that the numbers of fungi sensitive to chromate decreased, which promoted the growth of the fungi tolerant to chromate. The bacterial number in the Cr-treated soils remained as high as that in the untreated soils, and the tolerant bacteria were considered to be dominant. As a whole it appeared that the fungi were more tolerant to chromate than the bacteria. In contrast, the population of actinomycetes decreased to less than 104per g soil by the addition of 100 ppm chromate, and all the species of actinomycetes were considered to be sensitive to chromate. The reduction of chromate from the hexavalent form to the trivalent form was promoted by the addition of rice straw or cow manure and further accelerated by the addition of both materials because the microbial activity was stimulated. © Taylor & Francis Group, LLC.