The Resistance Evaluation of Dry Subtropics Brown Soils to Heavy Metal and Oil Contamination by Biological Indicators

Contamination of brown calcareous soils with Cr, Cu, Ni, Pb and oil leads to deterioration of their biological properties. There is a reduction in activity of catalase and dehydrogenase, an abundance of Azotobacter genus bacteria, cellulolytic activity and the length of radish roots. As a rule, there is a direct relationship between the content of contaminant in the soil and degree of deterioration of biological properties of the soil. According to the degree of negative impact on the biological properties of brown soil heavy metals form the following series: Cr > Cu > = Pb > = Ni. The pattern that chromium is more toxic and copper, lead and nickel have less and similar to each other degree of toxicity was established earlier in research conducted by the same method, with other soils in southern Russia. According to the degree of resistance brown soils are close to chestnut soils, they are less stable than chernozems and more stable than brown semi desert soils. Regional standards of Cr, Cu, Ni, Pb and oil content in brown soils of Ciscaucasia dry subtropics Ciscaucasia are proposed.