| Population boom and land over-exploitation sparked some problems of land degradation such as groundwater pollution, soil erosion, desertification, fertility and pollutants, so researches of soil health has become rather hot in modern soil science. In this paper, farmlands and orchards in central and southern ChangWuXian as representative of Wei Bei Plateau have been made a comprehensive research. with non- buffer several soil enzymes (invertase, urease, phosphatase, catalase, dehydrogenase )was determined to acquire sensitive enzymes of soil fertility; The microflora together with soil enzymes and microbial biomass is to set up the dynamic changes of soil quality index; At the same time changes of soil enzymes activity are discusses under specific concentration of Hg2+ stress and the relationship between the changes and other soil fertility factors are also analysed to construct the index of soil quality assessment. Main conclusions are obtained as follows:(1) Soil enzyme activities of farmland in this area change to a large extent. the variation coefficients of Urease, dehydrogenase, respiration intensity are larger than the others; Soil invertase, urease, phosphatase, dehydrogenase, respiration intensity were significantly or extremely significantly related to most soil physicochemical properties; The soil information system obtained by principal component analysis(PCA) and the newly constructed Total Enzyme Activity Index(TEI) could be better to reflect difference of soil fertlity levels; The twos are related to soil properties, they both can be used as index of soil fertility.(2) In this district overall level of organic matter content in orchard litter middle level, surface Layer is the 1.3 times of the below; Soil invertase, urease, phosphatase, in soil layer of 5-20 cm is respectively 1.25, 1.82, 1.54, 1.27 times in one of 20-40cm, and respectively 40%,93.33%,86.6 %,86.67% of soil samples reached significant or very significant difference; Catalase and dehydrogenase in surface soil are significant higher than the ones of the lower for 20% and 40% respectively, the latter are significant higher than the ones of the fromers for 40% and 40% respectively,the rest is not obvious; Soil enzymes of orchard and soil chemical properties is very close correlation in the region, this paper reveals dehydrogenase, phosphatase, invertase, urease and respiration intensity can be used as fertility index of orchard soil; Principal components analysis of chemical properties and soil enzyme shows that organic matter, dehydrogenase, invertase and phosphatase play leading role in soil fertility; Composite scores can reflect the soil fertility level of quality and can be used as the evaluation index of soil fertility.(3) Pour plate methed was used to study microflora, results shows the numbers of bacteria of farmland and orchard are respectively 85.67%, 70.56% of total number, actinomyces followe and the smallest one is fungi; The correlation analysis between the soil microorganism quantity,diversity and physicochemical properties show that, in the farmland soil ,bacteria and total number and organic, carbon, etc are close to characterize soil fertility, farmland urease and phosphatase and bacteria, total number and three diversity indexs reach a significant correlation, which can be used to be as characterization of biological activity, and in orchard, actinomycetes and soil invertase, phosphatase, dehydrogenase reach good correlative level; Respiration intensity in the farmland and orchard are both positive correlation with the microbial community; Soil microbial biomass in farmland and orchard barely achieve significant with physical and chemical properties, though with a certain degree of positive correlation; Soil respiration intensity and organic carbon, available nitrogen, phosphorus and phosphorus, phosphorus and potassium in farmland reach significant positive correlation, which shows soil respiration intensity can be used as a biological index of soil fertility.(4) Soil enzymes have different response under specific Hg2+concentrations,the changes of urease and dehydrogenase are larger, inhibiting rates of the former for 34.87% -100%,the later for 38.24% - 91.39%; Invertase and arejust opposite,only inhibition rate of the sample 18 is over 80%, the rest are less than 50%,only three soil samples is between 50 -80%, the rest of the 22 soil samples are less than 50%. Under specific concentrations of Hg2+, the changes of dehydrogenase activity and comprehensive score by principal component analysis have good linear relationship, R=0.509 at 0.01 level, therefore, we can use changes of soil enzyme activity under specific concentrations of Hg2+ to range different soil fertility. |
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