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|Title:||Effects of adsorbed cations on the physical properties of soils under arid conditions|
Soils -- Hawaii
|Abstract:||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 temperate and humid tropic regions. Hilgard (1906) is attributed by Thorne and Peterson (1949) as being the first to recognize and record these differences. Broadly speaking, while the problems of the humid regions are due to excessive leaching, loss of bases, soil acidity and low lime content, those of the arid regions are due to restricted leaching, accumulation of bases, soil alkalinity and high lime content. The soluble salts accumulating most commonly in the arid region soils are the chlorides, sulphates, bicarbonates and carbonates of calcium, magnesium, sodium and potassium. These may be brought up to the surface from a saline water table at shallow depth, or may have been derived from a parent material high in them, or they may be brought in by irrigation water (United States Salinity Laboratory Staff, 1954) and ac cumulate in. those areas where enough "later is not applied to meet the leaching requirement (Wilcox and Resch, 1963). The processes of salt accumulation cause the soil solution to become highly saline. This saline solution is not removed from the soil because of the low precipitation and high evaporation rates, and consequently affects the exchange complex of the soil. Salts may also accumulate in low lying areas due to flooding by saline waters, particularly ocean water. Kelley and Brown (1925) have shown that an equilibrium exists between the cations in the soil solution and those on the exchange complex, and thus the soil will adsorb Ca, Mg, Na and K ions from the soil solution in proportion to its composition and the concentration of the cations therein (Kelley and Cummins, 1921). The physical and chemical properties of the soil are known to be greatly affected by the nature of the cations on the exchange complex. In soils of the arid and semi-arid zones Na is usually the dominant cation, while in the soils of the humid regions, Ca may be the dominant cation. The effects of these cations have been well studied in the literature. The effects of Mg and K have, however, received much less attention. The purpose of this investigation has been to study the effects of the different cations on the physical properties of soils, with special emphasis on the roles of magnesium and potassium. It will be worthwhile to mention that the effects of excess salts have not been investigated--only the effects of the cations, when adsorbed on the exchange complex, have been studied.|
Thesis (Ph. D.)--University of Hawaii, 1965.
Bibliography: leaves -157.
viii, 157, 2 l mounted illus. (part col.), tables
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|Appears in Collections:||Ph.D. - Soil Science|
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