| Summary: | Typescript. Thesis (Ph. D.)--University of Hawaii, 1965. Bibliography: leaves [149]-157. viii, 157, 2 l mounted illus. (part col.), tables Arid regions make up a significant percentage of the total land surface of the world. It has been estimated (Dickson, 1957) that of the 57 million square miles of the exposed land surface, about 14 million, i. e., a quarter of the total, receive an annual rainfall of less than 10 inches in any given year. (This excludes the Arctic and Antarctic regions), Broadly speaking, it is this area which has been classified as the "Arid Region of the World" by UNESCO and is shown in Figure 1. Historians trace back the birth of the earliest civilization to arid environment requiring irrigated agriculture. In fact, ancient civilizations could flourish only where irrigation could flourish, and this was possible only along the banks of the big, perennial rivers like the Nile, the Tigris, the Euphrates, the Indus, and the Yang-tze. It has only been during the last 1500 to 2000 years that the scene of greater and greater agricultural activity has gradually shifted to the humid regions. The prime factor contributing to the decline of arid region agriculture has been the development of poor physical condition in the soil caused by the accumulation of soluble salts. This problem has been further aggravated by unwise methods of cultivation which could not be checked because of lack of technical know-how. With the re-emergence of independent nations in the arid regions since the Second World War, greater efforts are being made to study the nature, properties and management practices of the soils of these areas thoroughly. Also contributing to the amount of interest in these soils has been the rapid increase in the population of the world. With the cultivatable lands of the humid regions more or less completely utilized, it is becoming essential to turn to the arid regions to increase food production. The soils of the arid and semi-arid regions are quite different from those of the humid ...
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