Study On Physical Properties Of Forest Soil Macropores Etc In The Upper Reaches Of Minjiang River, Sichuan Province

The soil layer of forest ecosystem plays major roles of water storage and adjustor in forest hydrological function, Macropore exists very commonly in forest soil and has very important impacts on the soil water flow. So it's necessary to investigate the macropore quantity and its distribution in the soil in order to understand the mechanism of water source conversation by forests and the process of forest hydrology. In this thesis, the author has studied the physical properties, the macropore situation and the content of soil water etc in four types of natural forest in western Sichuan, some main results are described as follows:(1) The contents of powder (0.05-0.002mm) and coarse clay (0.002-0.001mm) in the depth of 0-20cm to 80-100cm were high, and the mean values accounted for 74.50% and 19.73% respectively in four different types of forest communities. So was the content of gravel, and the mean value came up to 42.41%, and its distribution was relatively even in each layer of sail. The results showed that the penetrability of the soil was good. It was possibly caused by high contents of gravel with a diameter of more than 3 mm.(2) The root systems mainly distributed in the soil horizon of 0-40cm according to the investigation of soil profiles in four forest communities. There were few fine roots in the soil profiles below 40cm.(3) The water breakthrough curve and Poiseulle model were used to study the range and quantity of soil macropore diameter in four forest communities. The radius of soil macropores was mainly focused between 0.2-2.4mm and the mean values was 0.68mm.The standard deviation was 0.096. There were more macropores with bigger radius in the upper-layer than those in the lower-layer with the development of soil profile.(4) The amounts of macropores in four different forest communities were in the range of 134- 1261 and the average value was about 566 , The coefficient of variation was 59.6%. The results showed that the amount of macropores changed obviously with different sampling points. The coefficient of variation of the amounts of macropores in five soil layers was Shrub-bamboo forest66.19%,Fir forest56.02%,Oak forest39.56%, Hardwood forest38.59% respectively. It also showed that the amounts of macropores both in Shrub-bamboo and Fir forests changed obviously. There were much more roots in Shrub-bamboo and Fir forests , Therefore vegetation had important effects on the soil macropores.(5) The response of the soil water content was not accorded with the rainfall changes. The water contents were totally higher in the rain season (from July to August). The average soil water contents were Hardwood forest37.55%,Fir forest30.97%. Shrub-bamboo forest 37.54%, Oak forest29.33% respectively. The water contents of the upper soil layers were higher than those of the lower layer. Because of better crumb structure in the upper soil layer, richer...