Physics of drained paddy soils Paddy soils

Briones, Aurelio Aguila
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One way in which the tropical world can surpass the temperate regions in food and fiber production is to employ a system of continuous cropping. In tropical Asia for example large areas of paddy land remain idle during the dry season owing to a lack of water and inability of the farmers to obtain adequate soil tilth. When the water resources of these areas are fully developed soil tilth will become a limiting factor for implementing a system continuous cropping. In Southeast Asia alone 27 to 54 million hectares of additional land area can be planted to crops if the problem of water and soil tilth can be solved. This dissertation concerns itself with the problem of regenerating soil structure in paddy soils so that crops other than rice can be grown on these lands. It focuses its attention on the problem of obtaining adequate tilth so that non-paddy crops might be grown as a second, third or even fourth crop on an annual basis. In this study paddy soils are viewed as rheological bodies which behave viscously in the puddled and saturated state, plastically in the moist state and elastically in its driest state. Since this dissertation concerns itself with the physics of drained paddy soils the Hookian or elastic model finds the widest application. Procedures for obtaining elastic constants from sound velocity measurements are described. Physical models are employed to describe shrinking, strengthening and ultimate cracking in drying paddy soils. An attempt is made to explain how and why soil material breaks down into aggregates. Stress-strain relations in drying paddy soils are discussed and the resultant rupture at critical stresses is described by several failure criteria. Lastly, the structural regenerative capacity of a paddy soil is predicted on the basis of a number of soil physical parameters.
Bibliography: leaves 181-188.
xiv, 188 l illus., tables
Soil physics, Soil moisture
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