The shrinkage which a accompanies a reduction in the water content of a soil mass has long been recognized to be an important soil property affecting the economics of the irrigation water, especially in Vertisols of north Egypt. The potential linear extensibility (PLE), coefficient of linear extensibility (COLE), shrinkage ratio (SR) and total volume reduction (TVR) in a clayey Vertisols were measured and related to their physical and chemical properties. It is shown that the most important factors affecting PLE, COLE, SR and TVE are bulk density, clay content, organic matter and exchangeable sodium percentage. On the contrary, exchangeable calcium percentage gives a negative close correlation with PLE, COLE, SR and TVR. Multiple regression equations involving the bulk density, clay content and organic matter accounted for 93% of the variation in soil shrinkage. The regression equation for the relationship between PLE and both bulk density and clay content was found to be 0.9036 + 0.53574 (bulk density) + 0.50246 (clay content %). Because of restrictions on shrinkage imposed by factors such as climate, crops, groundwater and moisture release characteristics of soils, soils with a high PLE may not behave very differently to soils with a much lower potential. |
