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In order to understand the effect of industrial pollution in the Baotou industrial areas on heavy metal content in soils, correlation analysis was used to study the source of Cu, Zn, Pb, Cr, Cd, Mn, and Ni. The heavy metal pollution in the soils was assessed using the methods of Nemerow index and Hakanson's ecological risk index. The results show that the contents of these seven heavy metals are higher than the background values of soils in Inner Mongolia. The exceeding ratios of Cd, Mn, Ni contents in soil are 100%, and Cu, Pb, Zn, Cr were 97%, 93%, 93%, 53%, respectively. The pollution degree of single elements showed the order of Cd > Pb > Cu > Ni > Zn > Mn > Cr. Pb and Cd are strong pollution elements, whereas Cu, Zn, Ni are moderate pollution elements,Cr, Mn are minor pollution elements. The main sources of heavy metals (Cu, Zn, Cr, Mn, Ni) in soils of the industrial district were industrial pollutant discharge and transportation. Excluding the two sources mentioned previously, Pb and Cd are mainly attributed to the emissions of coal-fired flue gas. The potential ecological risk has the order of Cd > Pb > Cu > Ni > Cr > Zn > Mn. Among them, Cd is the most harmful heavy metal pollutant and should be addressed.

The application of nitrogen (N) fertilizer results in decreases of soil pH, but its effects on CO2 emission from soils with different inorganic carbon contents remain unclear. An closed-jar incubation experiment was conducted to examine the effects of N fertilizer and nitrification inhibitor (DCD) on soil pH and CO2 emissions from three soil types with different contents of soil inorganic carbon (SIC), including paddy soil (PS), lime concretion black soil (CS), and eum-orthic anthrosols (AS). There were three treatments for each soil type, including control (N0), 0.2 g•kg-1 N fertilizer (N0.2), and its combination with DCD (N0.2+DCD). Soil pH, contents of mineral N (NH4+, NO3-), and CO2 emissions were measured. The results showed that N fertilizer addition significantly reduced soil pH and increased soil CO2 cumulative emissions in each type of soil. Compared to control, the CO2 cumulative emissions after 49 days incubation from the three soil types were enhanced by 39.4%, 23.4%, and 71.8% for PS, CS, AS soils, respectively. The soil pH of N0.2+DCD for three soil types were significantly higher than N0.2 after 49 days incubation, indicating that DCD application inhibited soil nitrification process. There were no significant differences in the mean CO2 cumulative emissions of PS and CS soils between N0.2 and N0.2+DCD treatments; however, N0.2+DCD treatment significantly reduced cumulative CO2 emissions from AS soil by 12.5%. Soil inorganic carbon can effectively buffer soil acidification caused by N fertilizer addition. The CO2 emission in calcareous soil following N addition is not only derived from the mineralization of soil organic carbon, but also from the dissolution of inorganic carbon. Given the large differences in soil inorganic carbon content in different regions of China, the problem of soil acidification and soil inorganic carbon pool consumption caused by long-term large amount of N fertilizer inputs deserve more attention. [ABSTRACT FROM AUTHOR]

The application of nitrogen (N) fertilizer results in decreases of soil pH, but its effects on CO 2 emission from soils with different inorganic carbon contents remain unclear. An closed-jar incubation experiment was conducted to examine the effects of N fertilizer and nitrification inhibitor (DCD) on soil pH and CO 2 emissions from three soil types with different contents of soil inorganic carbon (SIC), including paddy soil (PS), lime concretion black soil (CS), and eum-orthic anthrosols (AS). There were three treatments for each soil type, including control (N 0 ), 0.2 g·kg -1 N fertilizer (N 0.2 ), and its combination with DCD (N 0.2+DCD ). Soil pH, contents of mineral N (NH 4 + , NO 3 - ), and CO 2 emissions were measured. The results showed that N fertilizer addition significantly reduced soil pH and increased soil CO 2 cumulative emissions in each type of soil. Compared to control, the CO 2 cumulative emissions after 49 days incubation from the three soil types were enhanced by 39.4%, 23.4%, and 71.8% for PS, CS, AS soils, respectively. The soil pH of N 0.2+DCD for three soil types were significantly higher than N 0.2 after 49 days incubation, indicating that DCD application inhibited soil nitrification process. There were no significant differences in the mean CO 2 cumulative emissions of PS and CS soils between N 0.2 and N 0.2+DCD treatments; however, N 0.2+DCD treatment significantly reduced cumulative CO 2 emissions from AS soil by 12.5%. Soil inorganic carbon can effectively buffer soil acidification caused by N fertilizer addition. The CO 2 emission in calcareous soil following N addition is not only derived from the mineralization of soil organic carbon, but also from the dissolution of inorganic carbon. Given the large differences in soil inorganic carbon content in different regions of China, the problem of soil acidification and soil inorganic carbon pool consumption caused by long-term large amount of N fertilizer inputs deserve more attention.