tailieunhanh - Encyclopedia of Global Resources part 112

Encyclopedia of Global Resources part 112 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 1038 Rubber natural Global Resources of a rootstock. Upon a successful take the bud grows and the rootstock is topped or removed at the point of growth. The bud is then transplanted from the nursery to the field. The tree is ready for tapping in five to seven years when tree girth reaches 50 centimeters at meters from ground level. Crown budding may also be done before budded stumps are transferred to the field. This type of budding is used to provide a crown that is tolerant of or resistant to disease or wind damage. Stand density in rubber plantations ranges from 250 to 400 trees per hectare at an average spacing of about 6 square meters. Rubber performs best on deep well-drained soils with a pH of less than in the to range . However Hevea brasiliensis can be grown on a wide range of soils. Thus while in China rubber plantations are found on latosols and lateritic red soils in Brazil the primary center of diversity rubber grows on red yellow podosols. In Malaysia at one time the world s leading producer rubber grows on lateritic red soils. With regard to climatic requirements P. Sanjeeva Rao and K. R. Vijayakumar in Natural Rubber Biology Cultivation and Technology 1992 edited by M. R. Sethuraj and N. M. Mathew summarize the optimum conditions as follows a rainfall of 2 000 millimeters or more evenly distributed without any marked dry season and with 125 to 150 rainy days per year a maximum temperature of about 29 to 34 Celsius a minimum temperature of about 20 and a monthly mean of 25 to 28 Celsius. There should be high atmospheric humidity in the order of 80 percent with moderate wind and bright sunshine amounting to about 2 000 hours annually at the rate of 6 hours per day in all months. These conditions exist in the major rubber-producing countries of the world. Anatomy and Physiology of Latex Latex is obtained from latex vessels called secondary laticifers in Hevea. The quantity of laticiferous tissue in the tree is determined by a number of