Study On The Soil Microbial Biomass And Enzyme Activity Of Farmland Soil In Tongling Mining District

Tongling is an important mine region in China and has the rich mineral resources of copper, iron, sulfur and gold mine. For long-term mining, large quantities of tailings waste water, waste residue produced by atmospheric precipitation, etc. In this way, the farmland soil near the mining area was polluted by heavy metals. Mining exploitation leads to the aggravation of heavy metal pollution in soil, then resulting in the sharp decline of agricultural productivity. Based on the research of the farmland soil microbial community near by the mining area, it can be better to understand the soil status of heavy metal pollution. Therefore, study the microbiological activity of farmland soil has great significance.The farmland surface soil is the object of this study, near Shizishan mine and Xinqiao mine, focusing on the distribution and influence factor of soil microbial biomass, basal respiration and enzyme activity in different farmland (including vegetable land, rapeseed land, wheat land and rice paddy). The result showed that:(1) The content of organic matter, TN, TP and available phosphorus in vegetable land was higher than other lands, and significantly higher than rapeseed land (P<0.05), but had no significant difference with grain land (wheat land and rice paddy)(P>0.05); Water-soluble carbon and water-soluble nitrogen were irregular in different lans, but the water-soluble nitrogen content was consistent with TN content. The order of heavy metals pollution from heavy to light was Cd> As>Cu>Zn>Pb, and Pb was not exceed the Environmental quality standard for soils (Pi<1), but Cd had reached extent of the severe pollution (Pi>2). The distribution of available heavy metals was similar to total heavy metals, rapeseed land was the most serious polluted area, wheat land was the least, and the difference between them was significant (P<0.05), but the difference was not significant compared with other lands(P>0.05).(2) Microbial biomass carbon and microbial biomass nitrogen varied in different soil; the maximum and minimum of microbial biomass appeared in wheat land soil (with high nutrient and low heavy metal pollution) and rapeseed land (with low nutrient and serious heavy metal pollution), respectively. The highest and lowest ratio of microbial biomass carbon and nitrogen present in paddy land and autumn vegetable land, respectively, and with significant difference (P<0.05); but the difference of paddy land with other lands was not significant (P>0.05). The variation of metabolic quotient and basal respiration differed from microbial biomass, the descending order was rapeseed land> spring vegetable land≈autumn vegetable land> wheat land> paddy land. Soil enzyme activity differed in various farmland soils and the difference also varied; Dehydrogenase and phosphatase in wheat land was the highest in all farmlands, highest content of urease and sucrose appeared in spring vegetable land and rapeseed land, respectively.(3) Correlation analysis of microbiological activity with nutrients showed that microbial biomass had significant positive correlation with organic matter and TN, between microbial biomass and TP had different degree of positive and negative correlation in all farmlands. Basal respiration enhanced with the increase of soil nutrient content. Phosphatase had significant or very significant positive correlation with organic matter, the correlation of dehydrogenase, urease and invertase with soil nutrients in different land had significant difference. This result displayed that organic matter had a great promoting effect on the soil microbial biomass, respiration and phosphatase.(4) Correlation analysis of microbiological activity with heavy metal revealed that microbial biomass had significant positive correlation with Cd and Zn in autumn vegetable land, while had significant negative correlation with As and Cu in rapeseed land. Ratio of microbial biomass carbon and nitrogen, metabolic quotient and basal respiration had significant or very significant positive correlation with As, Cd, Cu and Zn; Phosphatase had significant or very significant positive correlation with As, Cd and Zn in spring vegetable land, but in autumn vegetable land it had very significant negative correlation with As, Cd and Cu, and very significant positive correlation with Zn. This suggested that the content of heavy metals had important influence on soil microbial activity.(5) Cd, the hightest degree of contamination and was the major element of potential ecological risk in farmland soil in Tongling mining area. In different farmland, soil microbial biomass, basal respiration and enzyme activity varied. In natural ecological system, soil microorganisms affected greater by the compound pollution of soil environmental factors, and microbial biomass, basic respiration and phosphatase activity can be used as the important parameters of soil fertility and heavy metal pollution.