| Soil enzyme is one of the major components in soil, playing important roles in transfer of nutrient and matter, shift of energy and remediation of pollutants. And meanwhile the relationship between soil enzyme and soil quality is a main scientific project to study. So, this experiment investigates the soil enzymes activities (such as invertase, cellulose, amylase, protease, urease, phosphatase, arylslphatase, dehydrogenase, catalase, uricase) by using no-buffer method and microbiota in Changwu where is as the representative of Loess Plateau gully region; studies the reaction mechanism of hydrolytic enzymatic activity, and also the relationship between it and soil properties by kinetic. It is expected to find some soil enzymes which can sensitively reflect the level of soil fertility, built soil enzymatic monitoring indicators and developed soil enzyme theory; and finally, provided the basis for soil quality assessment and laid the foundation for the sustaining development of agriculture in Loess Plateau from soil enzyme perspective. They will be showed as following:(1) In Loess Plateau gully region, biochemical activities of soil urease, invertase, dehydrogenase and respiration of farmland were more sensitive to environmental change among these ten biochemical activities. There was a significant correlation between urease, invertase, phosphatase, dehydrogenase and respiration, and also between these five soil biochemical activities and most of soil chemical properties. This indicated that these five soil biochemical activities can be used as indicators for soil fertility.(2)Invertase, urease, phosphatase, and dehydrogenase activities in surface soil were respectively 1.2, 1.5, 1.6, 1.3 times higher than that in subsoil in Loess Plateau gully region. And soil organic matter content in surface soil is 1.2 times higher than that in subsoil. It indicated that the four soil enzymes had the same regularity with soil organic matter. Soil enzyme spatial variation was different in different orchards. As the soil depth increased, phosphatase and urease activity significantly had proportion of 96% and 88% decreases, while invertase and dehydrogenase activities only had proportion of 60% and 52% decreases. There was no significant influence on hydrogen peroxide activity. The correlation coefficient showed that soil enzymes and soil chemical properties related significantly. This indicated that soil dehydrogenase, phosphatase, invertase, urease can be used as indicators of orchard soil fertility in this region. Construction of principal component analysis of soil enzymes - the chemical nature of the integrated information system can not only reflect soil enzymes and chemical properties had effects on soil fertility and their relationships, but also the comprehensive scores directly reflected soil fertility, it can be indicator to evaluate soil quality.(3)In Loess Plateau gully region, Km of hydrolase changed in the same rank quantitatively, but high fertility soil's was higher than low fertility.Vmax, Vmax/Km and k of urease were significant differences among different fertilizers. Vmax/Km and k of invertase could reflect the change of pH. There were significant positive correlation between urease kinetics and soil chemical characteristic, it was revealed that the Vmax,Vmax/Km and k of urease could be one of indexes to evaluate fertilizer of soil.(4)Pour plate method was used to study the soil microflora. The results showed bacteria, fungi and actinomyces accounted for 83.35%～93.47%, less than 0.02% and 6.51%～23.07% of the total of soil microorganism, respectively, indicating that the Shannon-Wiener index,Simpson index and Mcintosh index of this area were 0.24～0.56,0.12～0.36,0.80～0.94 respectively. the correlation analysis showed the diversity index could correctly describe the soil fertility of this area, and could be used as one of the biological indicators for the soil biological survey.(5)Among combinational parameters such as BIF, EAN, TEI and TEI5 obtained in this experiment, BIF, TEI and TEI5 had a significantly positive correlation with chemical properties with TEI5 as the most significant. This suggested that these three parameters can be used to monitor soil fertility. By processing the data of soil biochemical activities and chemical properties in principal component analysis and clustering analysis, the soil information system obtained in this experiment can better show the variation of soil fertility and the multiple scores were significantly positive correlated with BIF, TEIand TEI5, and this indicated that they can be used to monitor soil fertility levels. A simplified expression of the total enzymatic activity index may be more useful than individual soil enzyme activity to measures of soil quality.(6)Addition of the organic manure and bacterial manure on homestead caused significant increases in the activity of some enzymes (such as invertase, urease, phosphatase, arylslphatase, dehydrogenase) and the respiration rate and the number of actinomycete tested. The increases were much higher than a year of reclamation ago. But addition of fertilizer or compound fertilizer had little effect on soil enzymes and number of soil microorganisms. Catalase activity didn't change in different fertilization system. Total enzymatic activity index (TEI) can be a good evaluation of different fertilization on soil biological properties, and organic fertilizer is a appropriate soil improvement measures that can enhance soil biological activity and fertility in homestead.To sum up, our results confirm that enzyme activity can be determined more accurately by no-buffer method than by buffer method, and the total enzymatic activity index (TEI) is suitable indicator of soil fertility and monitoring soil status in Loess Plateau gully region. But to use this index to soil fertility in the region to grade, have to be studied further.
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