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Environmental Soil Chemistry - Chapter 10

The Chemistry of Saline and Sodic Soils Đại dương có chứa khoảng 97,3% nước của Trái đất, các lục địa khoảng 2,8%, và bầu khí quyển khoảng 0,001% (Todd, 1970). Khoảng 77,2% của các nước liên quan đến lục địa xảy ra trong băng và sông băng và khoảng 22% là nước ngầm. 0,8% còn lại xảy ra như nước bề mặt (hồ và sông). Bề mặt đất của trái đất là 13,2 × 109 ha của khu vực này, 7 × 109 ha canh tác và chỉ 1,5 × ha 109 được trồng (Massoud, 1981). Trong số đất canh tác,. | The Chemistry of 1 1 Saline and Sodic Soils Introduction Oceans contain about 97.3 of the Earth s water continents about 2.8 and the atmosphere about 0.001 Todd 1970 . About 77.2 of the water associated with continents occurs in ice caps and glaciers and about 22 is groundwater. The remaining 0.8 occurs as surface waters lakes and rivers . The land surface of the Earth is 13.2 X 109 ha of this area 7 X 109 ha is arable and only 1.5 X 109 ha is cultivated Massoud 1981 . Of the cultivated land approximately 0.34 X 109 ha 23 is saline and 0.56 X 109 ha 37 is sodic containing excessive levels of Na . Salinity can be defined as the concentration of dissolved mineral salts present in waters and soils on a unit volume or weight basis Tanji 1990b . Figure 10.1 and Table 10.1 show the global distribution of salt-affected soils. Salt-affected soils can be classified as saline sodic and saline sodic soils. Briefly saline soils are plagued by high levels of soluble salts sodic soils have high levels of exchangeable sodium and saline sodic soils have high contents of both soluble salts and exchangeable sodium. These soils will be described more completely later. 285 286 10 The Chemistry of Saline and Sodic Soils FIGURE 10.1. Global distribution of salt-affected soils. Reprinted with permission from Szabolcs I. 1989 . Salt-Affected Soils. CRC Press Boca Raton FL. TABLE 10.1. Global Distribution of Salt-Affected Soilsa Continent Area in millions of ha Saline Sodic alkali Total North America 6.2 9.6 15.8 Central America 2.0 2.0 South America 69.4 59.6 129.0 Africa 53.5 27.0 80.5 South Asia 83.3 1.8 85.1 North and Central Asia 91.6 120.1 211.7 Southeast Asia 20.0 20.0 Australasia 17.4 340.0 357.4 Europe 7.8 22.9 30.7 Total 351.5 581.0 932.2 a From I. Szabolcs Review of Research on Salt-Affected Soils. Copyright 1979 UNESCO Paris. Salt-Affected Soils. Copyright 1989 CRC Press. Reprinted by permission of CRC Press. Salt-affected soils occur most often in arid and semiarid climates .