الفهرس | Only 14 pages are availabe for public view |
Abstract To study the moisture characteristics of some soiJIs in Kaliobia governorate, twenty soil profiles were selected from governorate soils to represent the different geomorphological units, .namely., natural levee, sedimentary basin, river terrace, overlapping and saline soils. The field morphological description as well as chemical and physical measurements were carried out using undisturbed and disturbed soil samples. The soil chemical analysis show that the soils under investigation are generally neutral to slightly alkaline. The soils are generally non saline with one exceptional cases which represent some patches of saline soils. The data of soluble salts show that calcium and sodium are the dominant soluble cations while the sulphates and chlorides are the dominant soluble anions. The cation exchange capacity of the investigated soils are widely different and mainly related to soil texture. The data show that each landform type is characterized by a special type of sedimentation and therefore the particle size distribution diners quite considerably. The organic matter content of the investigated soils is generally low with one exceptional case of El-Gabal El-Asfar soils which exhibit relatively high content of organic matter. Also the soils under consideration exhibit low content of carbonates with a maximum value of 6.0%. The aggregate states of the investigated soils are proportionally related to exchangeable calcium and magnesium, clay, and silt fractions and inversely related to tine and coarse sand tract ions. Regression equation is: A.S.= - 16.7431-0.6156 ESP + 1.3055 clay, with multiple R= 0.92. Also the mean weight diameter is affected by thc same soil properties affect the aggregate state, unless the effect of organic matter content on the mean weight diameter is dependent on the clay content .Thc multiple regression equation is : M.W.D =- 0.4923 + 0.0546 ECa, with multiple R ~-~0.82 The soil bulk density shows negative and significant correlations with clay; silt; carbonate; and organic matter content. The multiple regression Equation is : B.D = 1.3636-0.0343 a.M. + 0.0058 C.S., with multiple R= 0.9 The soil porosity is positively or negatively related to many soil properties. However, only exchangeable calcium, sodium adsorption ratio (SAR), organic matter content (O.M.), silt + clay; and tine sand are considered for multiple regression. The relationship can be summerized : TP. = 27.9136 + 0.2658 ECa + 0.4498 SAR -+- 0.9694 OM + 0.2266 Si + Cl + 0.1330 F.S.; with multiple R = 0.95 The pore size are classified to four categories, .narnely., quickly drainable, slowly drainable, water holding and fine capillary pores ~?~on useful pores. The data show that the quickly drainable pores are mainly affected by soil texture and to considerable extent by aggregate state and organic matter content. However only two variables are considered tor stepwise regression, namely, aggregate state and fine and coarse sand fractions to provide the following equation: Q.D.P. = 1.7176 + 0.0622 A.S. + 0.1535 (C.S.+F.S.), with multiple R = 0.73 However, another variables of exchangeable calcium, carbonate and silt + clay content are considered for slowly drainable pores. The regression equation can be written as : S.D.P. ~ 9.0763 -I- O.I048 ECa + 0.3506 CaC03 - 0.1113 (Si. Cl) with multiple R = 0.75 The results show that the water holding pores (W.H.P.) are mainly affected by organic matter content and partially by soil texture. The effect of soil texture is more evident in the subsurface and deeper layers which have less organic matter content. The multiple regression describes this relation in the following equation : W.H.P. = 12.048 + 0.2683 ECa + 0.9072 OM. - 0.1086 C.S., R = 0.91 The non useful pores (N.D.P.) are mainly affected by soil texture as well as exchangeable cations. The multiple regression equation may formulated as: N.U.P. = - 0.7592 + 0.1938 EMg I· 0.8435 ENa I 0.701 (Si I CI) + 6.0602 F.S., with multiple R’ 0.96 The moisture retention curves of the investigated soils show that the amount of water retained at relatively low matric suction depends primarily upon the capillary effect and the pore-size distribution. On the other hand , water retained at high suction range is due increasingly to adsorption and is thus influenced less by the pore-size distribution and more by the texture and specific surface of the soil material. As generally, the fine-textured soils exhibit greater water retention at any given suction and more gradual the slope of the curves. On the other hand, the coarse textured soils exhibit less water retention and more sharp and distinct curves. The results show that the values of soil moisture content at field capacity and wilting point are mainly related to the soil texture and soil salinity. Since the retained water at field capacity occupies two different types of soil porosity, ”namely” water holding and non useful pores, its value is mainly affected by the distribution pattern of the two types of porosity. The statistical analysis show many significant correlation between field capacity and soil components, unless only two them are considered for the step wise regression, .namely, silt + Clay and exchangeable sodium. The regression equation can be summerized as : F.C. = 6.3081 + 0.5494 ENa + 0.5201 (Si + CI), with multiple R= 0.95 The available water is mainly affected by both soil texture and organic matter content and partially by salt contents. One of the most soil properties related to saturated hydraulic conductivity is the particle size distribution. The coarser textured soils are, in the same time, the faster factors such as compaction and salinity are subsidiary affect the saturated hydraulic conductivity. The relationship between different soil properties and saturated hydraulic conductivity (K sat ) is statistically studied and provided the following multiple regression equation: Ksat = 9.0730 - 6.7031 OM + 1.5952 C.S., with multiple R = 0.84 The Van Genuchten equation reduced to four parameters, .namcly.O s, er , a and n, is used to predict the moisture retention characteristic of the soils under consideration. Principal factor analysis was used to reveal the structure in the data and to examine the relation between moisture retention characteristic (MRC) parameters and selected measured soil properties, .namely, bulk density, organic carbon, silt, clay, and mean weight diameter. Regression equations arc established between these MRC parameters and measured soil properties. It may be conclude that the moisture retention characteristic (MRC) can be estimated at a reasonable level of accuracy from simple soil properties such those mentioned above. The study further shows that for the prospected horizons the Van Genuchten model gives a good description over the entire range of the MRC. Finally the data show that the transition from saturation to unsaturation water flow entails a steep DROP in hydraulic conductivity. The decrease in hydraulic conductivity is steeper for coarse textured soils than the fine textured ones. |