| Chinese fir is a fast-growing native species with valuable timber attributes in subtropical area of southern china. Because of it's own characteristics and unreasonable managements, it's land productivity has extreamly declined. Siol enzyme activity and nutrients contants and their relativity in the second rotation of Chinese fir plantation were studied by using field located sampling and indoor analysis in Sep.2007, Jan. Apr., and Jul. 2008. Comparing all above targets with different age, managements, and under different sites, we studied the soil quality of Chinese fir plantations by counting QI (quality index) which depend on both enzyme activity and nutrients.All six nutrients content in the second rotation of Chinese fir plantation at age of 20 are lower than that at age of 12. Differences of fast-acting phosphorus and humus carbon content were extremely significant. Organic matter and the hydrolisis nitrogen content were showed as:foot> summit> mountainside. Among various sites the organic matter does not have sigificant difference. Between foot and mountainside and between foot and summit, the differences of hydrolisis nitrogen are sinificant and extremely sinificant, respectively. Total nitrogen and the humus carbon content were ranked as that: Foot>mountainside>summit. Among the summit, the foot and the mountainside, the difference of the total nitrogen content is sinificant, the difference of the humus carbon is sinificant in various slope positions; Total phosphorus and fast-acting phosphorus content performanced as that:the mountainside> the foot> the summit, the total phosphorus content does not have the sinificant difference in various slopes position, and the difference of the fast-acting phosphorus content among foot,the mountainside and the summit was sinificant. All six nutrients in naturely restoration shrub land are obviously higher than those in second rotation of Chinese fir plantation at age of 20. Organic content definited as: winter> the spring> autumn> summer. Between winter, spring and summer, fall, the difference is sinificant; Total nitrogen content was showed as that:summer> winter> spring> autumn. Only between summer and fall, the difference is sinificant; The hydrolisis nitrogen content ranked as that:summer> the spring> the winter> the autumn, between various seasons the difference is sinificant, there is a extremely siginficant difference between summer and autumn; The total phosphorus content showed as:autumn> the summer> the winter> the spring, between autumn and other three seasons among which there are no significant differences, difference is sinificant; The fast-acting phosphorus content was showed as that:summer> the spring> the autumn> the winter. Between summer, the spring and autumn, the winter, differences are extremely sinificant. The humus carbon content was ranked as that:autumn> summer> spring> winter, between each season the differences achieved sinificant or the extremely sinificant level.All four enzymes activity in the second roatation of Chinese fir plantation at age of 20 are lower than that one at age of 12. Difference of catalase was significant. Both in 0-30cm and in 30-60cm soil layer, enzyme activity was ranked as that:Mountain torrent> the mountainside> the mountain ridge> the summit, but the difference of phosphatase activity was very small in different sites. all four enzymes activity and organic matter in naturely restoration shrub land are obviously higher than those in Chinese fir plantation at age of 20. Enzyme activity in spring, summer was higher than that in fall and winter, but under different managements and in different soil layer and slope positions, the change rules was different. In 0-30cm soil layer, each determination target was obviously higher than that in the 30-60cm. The soil nutrient contents and enzyme activity share a highly consistent space and time change tendency.The result indicated that there are very close relevances between two kinds of determination targets. The principal components analysis demonstrated enzyme activity play vital role in soil quality system. It can be extremely meaningful to use it as parameter to account the QI (quality index). Catalase activity and the organic matter, the total nitrogen, the hydrolisis nitrogen, the fast-acting phosphorus are extremely related, and it is obviously related with the humus carbon; The urease and all determiated nutrients content are extremely related; Phosphatase activeness and organic matter, total nitrogen, hydrolisis nitrogen and fast-acting phosphorus content are extremely obviously related; Invertase activeness and organic matter, total nitrogen, hydrolisis nitrogen and fast-acting phosphorus content are extremely related. The Organic matter content and total nitrogen content are extremely sinificant related. Organic matter and the total phosphorus are extremely sinificant related. Organic matter and the hydrolisis nitrogen and fast-acting phosphorus are sinificant related. Total nitrogen content and the hydrolisis nitrogen, fast-acting phosphorus content are sinificant related. Hydrolisis nitrogen content and the fast-acting phosphorus content are extremely sinificant related. There exist close relevance among various enzyme activity. Catalase activeness and urease activeness, oil urease and soil phosphatase, urease and the invertase are sinificant related, the phosphatase and the invertase are extremely sinificant related. Among four kinds of enzymes class, two pairs' relevances achieve extremely sinificant level。Function of individual enzyme is not isolated, each kind of targets mutual influent each other, regulating metabolism and the transformationm of soil material.Along with plantation development, soil fertility of the second rotation of Cinese fir plantation gots obvious degeneration. Soil enzyme activity and nutrients content have obvious drop. Quality index (%) of the second rotation of Chinese fir plantation at age of 12(43.268) is seriously bigger than that one at age of 20 (35.173). Under different managements, there are significant differences of quality index. In contrast to Chinese fir plantation at age of 20, the naturely restoration shrub land had better soil quality. Soil quality index of the former and the latter were 35.173 and 48.902, respectively. There existed big differences among different seasons' soil quality. Quality index (annual mean value) were ranked as:summer (54.95)> spring (46.15)> autumn (42.41)> winter (39.54). Quality index of naturely restores shrub land in summer (64.036) was the highest one. The result indicated that soil quality increases in summer, but obviously drops in winter.Taking the second rotation of Chinese fir plantation at age of 12 as the datum, it has been figured out that the degeneration index of the second rotation of chinese fir plantation at age of 20 and naturely restore shrub are-9.16% and 3.26% which are based on four season data, respectively. The result showed two informations:One is that soil quality of the second rotation of Chinese fir plantation presents great degeneration as increment of stand age. Another is soil quality of the second rotation of Chinese fir plantation is lower than that of naturally restoration shrub. Taking the autumn as the datum, we have accounted soil degeneration index which based on three (2,3,7) research area's annual data in the different season. The result showed that soil degradation index in winter is 5.08%, which is remarkablely higher than that in the autumn. Sping is 10.43%, which is obviously higher than the autumn, and it is also higher than the winter. Summer's degeneration index is 23.40%, which in the highest one among four seasons. This result is consistent with that one which came from using the quality quality as index.
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