HYDRAULIC PROPERTIES OF EGYPTIAN CALCAREOUS SOILS

Abstract

Calcareous soils are of a wide occurrence under arid and semiarid climates, where the presence of CaCo3,, are in considerable amounts. These soils cover more than one million feddan of agricultural soil and more than 30% of the desert soil in Egypt. The main objectives of this work are: 1) Characterize the hydraulic and the physical properties of the calcareous soils, 2) Studying the effect of CaCO3,content on the hydraulic properties of these soils and subsequently predict some equations that help in calculating the values of the hydraulic properties of the calcareous soils, and 3)Defining these calcareous soils in relation to the hydraulic and physical properties. The obtained results revealed the following: I- A clear variations was found in the total CaCO3, and active CaCO3, content in each fraction among the different soil texture classes. 2- The texture and CaCO3, content was found to have a major influence on the variations of water retained under different suction levels, especially in tlie fine and moderately textured soils. The increasing of active CaCO3, content increased the moisture retained under the different suction levels. 3- The study of the soil moisture constants (field capacity, wilting point and available moisture content), showed that these soil moisture constants increased by increasing the active CaCO3, content, and the CaCO3, in clay plus silt fractions. 4- The hydraulic properties values (infiltration rate, saturated hydraulic conductivity, and unsaturated hydraulic conductivity), decreased significantly with increasing each of total CaCO3,, active CaCO3, content and CaCO3,%in clay plus silt fraction. 5- The relationship between both of total CaCO3, and active CaCO3, and the hydraulic properties was fitted as exponential and power equations (with the highest correlation coefficient for predicting the relationships between CaCO3, % and these hydraulic properties. 6- The most affecting soil physical parameters on the hydraulic properties were found out by using the stepwise analysis programme, The results showed that the active CaCO3, % is the more affecting factor on the most of the hydraulic properties followed by the soil texture and the soil structure parameters. Moreover the contribution percentages of the soil physical parameters affecting the hydraulic properties were also calculated. 7- The simple correlation and the stepwise multiple regression equations between the soil hydraulic properties and each of total CaCO3, % and active CaCO3, % were also calculated. Consequently the hydraulic properties could be predicted from these multiple regression equations. 8- The relationship between the unsaturated hydraulic conductivity and the CaCO3, content show negative correlation within the range of 0.1-0.33 atm. suction, after that the relation was positive at the suction range from 0.33 to 0.66 at. suction, After 3.0 atm. suction the correlation was not significant. The best fitting equations between unsaturated hydraulic conductivity K(0) and both of total and active CaCO3, content were calculated for predicting the values of K(0). under the different suctions levels. 9- The calcareous soils can be defined from the hydraulic and physical point of view as the soils containing more than 16% total CaCO3, or 6% active CaCO3, in their relation for the whole studied soil hydraulic properties.