| With the speeding up of industrialization, the waste water were more and more irrigated in farmland, and led to more serious pollution in environment. The heavy metal was a kind of major pollutants, the area of land polluted makes up 1/5 of total arable land now. So it was one of the most important environmental researches to monitor and remediate soil polluted by heavy metal.Soil enzyme was one of the three principal components in soil, there was closely correlated between soil enzyme and nutriment recycling, energy metabolizing and pollutant remediation and monitoring to a certain degree. Many domestic and overseas scientists finished a lot of research on their relationships and acquired some better results. It was seldom to study the different species of metal influence on soil biochemical activity, for example Chromium (III) and Chromium (VI), although much research only focused on the relationships. So it is necessary and important to study on the relationships between different species chromium and soil enzyme activity in both theory and practice.By simulative method, we systematically studied not only the relationships between soil uresae, alkaline-phosphatase and the heavy metals [Cr(VI),Cr(Ш),Cu] in several major soil types of China, but also the reaction mechanism between enzymes and the metal by means of enzymatic kinetics. The results were as follows:1. Cr(VI) can decreased soil pH remarkably, their relationship reached the significant negative correlation, bigger decrease was observed in alkaline soils. Water-soluble Cr(VI) content were about 40.07% of total Cr added in soils. There was significant correlation between soil pH and water-soluble Cr(VI) content. Water-soluble Cr(VI) had the same changing law during the same type soils.2. The activities of urease and alkaline-phosphatase can be indicators of the soil fertility in the same ecological zones.3. Soil alkaline-phosphatase activities were inhibited by Cr(VI), their ecological dose ED10 values were 1487.12～2747.68 mg/kg. The alkaline-phosphatase were not sensitive to Cr(VI) because ED10 value was so higher. Enzymeatic reaction Km was the same and Vmax was reduced with increasing Cr(VI) concentrations, showed there was mechanism of no-competitive inhibition between Cr(VI) and the soil alkaline-phosphatase. Soil alkaline-phosphatase activity,Vmax and k values can be one of indexes to monitor soil polluted by Cr(VI).4. Cr(Ш) inhibited soil alkaline-phosphatase activity, their correlation coefficient reached 0.906～0.994;ED10 values were 542.92～746.58 mg/kg for Cr(III). By enzyme kinetics, there was mechanism of mixed inhibition because Cr(Ш) increased Km and decreased Vmax values of soil alkaline-phosphatase. Soil alkaline-phosphatase activity,Vmax,Vmax/Km and k values can be index to monitor soil polluted by Cr(Ш).5.Chromium remarkably inhibited soil urease activities of Red soil and Sandy soil. Soil urease of other alkaline soil varied increase at the beginning and then decrease. Vmax was the same changing law with soil urease activities. Km was a constant parameter with increasing Cr concentrations; Indicated enzyme reaction mechanisms were different between alkaline and acid soils. Soil urease activity was activated under lower Cr(VI) concentrations because soil had higher buffer capacity to heavy metal. Cr(Ш) decreased urease activity of Loessal soil.6.The urease activity was remarkably reduced by the introduction of copper into soil, Calculated copper ecological dose ED10 and ED50 values,that could be used as different polluted levels, were 94-151.75 and 470.40-759.28mg/kg in soils tested. Urea concentration showed little effect on ecological dose. The kinetic parameters such as Vmax,Vmax/Km and k were reduced with the increase of copper concentration, and their relationship was upto the significant correlation levels, except the Km value was increased. It was proved that the copper reaction mechanism was a mixed inhibition, including both competitive and non-competitive effect, while the non-competitive mechanism was more important.
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