| Chinese fir is one of the most important commercial timber tree species in the south of China, with fast growth, fine material quality, high yield and wide-range use. In the producing area of south china, Chinese fir accounts for46%of the total commercial timber yield. But with the requirements increased, more and more Chinese fir planted continuously at the same ground, which consumed much soil fertility and caused a decline in plantation productivity, so that it had a serious impact on the continued operation of Chinese fir plantation. However, the traditional operation disturbed by many human activities, such as controlled burning and intermediate cutting which also had a significant effect on soil fertility, and the controlled burning leaded to loss much soil organic matter and nutrient elements which disappeared by gaseous or ash, with the biomass decreasing, intermediate cutting also caused the loss of nutrients, which maybe the reasons for the soil degradation.Some study showed the scarcity of soil available phosphorus was one of the most important reasons for soil degradation, phosphorus is one of the essential elements for the growth of Chinese fir, which affected growth and continued operation of Chinese fir plantation. In order to describe the morpHology of phosphorus and transformation accurately, people classified the phosphorus based on similar chemical composition or the ability of same decomposition mineralization, which had the important significance to provide evidence for the utilization mechanism and afforestation patterns. At present, there were many studies on increment, soil erosion and species diversity of different forest management measures on Chinese fir, but it was few studies on the effect controlled burning and intermediate cutting brought to Chinese fir plantation, especially the distribution, content and the correlation between different phosphorus. In view of these, this paper based on a method of combining investigation and sampling with indoor experiment, used Chinese fir plantation of different thinning in shunchang and pushang, and compared soil nutrient in different depth and the influence of controlled burning and intermediate cutting, especially the characteristics of different phosphorus, so all of which master the characteristics of different phosphorus content and distribution clearly, and provide a reference to reveal the composition and source of available phosphorus in Chinese fir plantation, at the same time, it provided a theoretical basis for the cleaning,planting,tending and thinning in future.The main results were as follows:1.Tree height, DBH, and single timber volume of Chinese fir on thinned stands were greater than unthinned stands after7years, and the thinning had the greater influence than DBH. The largest increment of DBH, and single timber volume were on the top, and the maximum difference of height were on the downhill; but the volume was opposite, which had largest reduce in the middle.2.The species of underplant showed the different results between thinned and unthinned stands, the species increased quickly and even appeared the new ones after thinning, and the dicotyledon had the maximum influence, so which were good for light preferring plants, the bushes and improving community structure of Chinese fir plantation. But from the biomass of the underplant, which on thinned stands showed better than the unthinned stands in different periods, and with the growing of Chinese fir plantation, the biomasses of underplant were also growing quickly, especially the bushes.3.The results showed thinning was helpful to improve soil fertility of Chinese fir plantation, in which the soil bulk density and soil non-capillary porosity tended to decrease,, but on the contrary, soil capillary porosity and soil porosity increased, and the differences were obvious in surface soil. At the same time, the soil pH value, organic matter and total N tended to decrease with the increasing of soil depth, but the soil total K increased. Compared to the different stands, soil pH value, organic matter, total N and total K on unthinned stands were lower.4. The soil total P tended to decrease with the increasing of soil depth. However, it had the little differences between thinned and unthinned. The average content of available soil P had decreased with the increasing of soil depth, which in the thinned stands was higher than the unthinned stands, and the differences were obvious, especially in the surface.The study on classification of soil inorganic P showed O-P>Fe-P>Al-P>Ca-P, which tended to decrease with the increasing of soil depth. The influences of different P content between thinned and unthinned stands reached significant level, and Al-P,Fe-P in the thinned stands were higher than the unthinned stands, O-P,Ca-P showed opposite; although the soil tall inorganic P in thinned stands were significantly smaller than those in unthinned stands, on the contrary, the soil total organic phosphorus in thinned stands were more. With increasing of soil depth, the soil total organic phosphorus tended to decrease, and the differences of upper layers were much greater than those of lower layer between different thinning treatment. The labile organic P and moderately stable P of different depths in the thinned stands were much higher than those in unthinned stands, the moderately labile organic P increased by21.07%in L1,, but the difference of high stable organic P were not significant.5.Tree height, DBH, and single timber volume of Chinese fir and masson pine in controlled burning stands were lower than stands without burning, and controlled burning had the greater influence to Chinese fir than masson pine.6.The results showed, in the long run, controlled burning measure which had a greater impact on the soil surface was bad for soil fertility of Chinese fir plantation. It increased soil bulk density, on the contrary, soil non-capillary porosity, soil capillary porosity and soil porosity were decreased. Controlled burning also had a significant impact on the soil chemical properties. pH values, soil organic matter, total N, total K content were obviously lower. Among those indexes, soil organic matter content were affected most.In L1, L2, L3and L4layer, it in the stands without controlled burning were respectively higher than the burning one by107.56%,122.48%,42.75%and36.74%. So in the long run, the controlled burning measure is harmful to the maintenance of land capability.7.In the plot of controlled burning forest, the soil total P,available soil P tended to decrease with the increasing of soil depth,and those which in the controlled burning stands was sharply lower. Especially in L1and L2, soil available P content in the controlled burning stands decreased by50.94%and61.01%respectively.The soil A1-P,O-P was sharply lower in the controlled burning stands, especially in L1and L2layer, soil Al-P content in the control stands was hihger by30.15%and27.71%respectively; the O-P content in the L4layer of the controlled burning stands was lower than those without burning by52.10%.On the contray, the soil Ca-P in the controlled burning stands was significantly higher.After controlled burning, the Fe-P content in L1,L2was higher. The total inorganic P in the soil depends primarily on O-P content, so it was also lower in the controlled burning stands.In controlled burning stands, the total soil organic phosphorus were significantly reduced. The size of the relationship between different component of organic phosphorus shows that moderately stable P>moderately labile organic P> highly stable P> Labile organic P, and each of them tended to decrease with soil depth. After controlled burning, the difference of high stable organic P were not significant, but moderately stable P, moderately labile organic P, Labile organic P became lower, and this change were more significant in the surface of the soil. |
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