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Downward water flow in the vadose zone occurs principally through the non-capillary pores, while the redistribution and lateral and upward flow occurs in the capillary pores. The purpose of this study was to propose equations to estimate water flow, Q(θ), and hydraulic conductivity, K(θ), in the capillary and non-capillary soil pores. The equations related K(θ) to soil pore radius (r) were based on soil hydraulic data, including water retention h(q), field basic infiltration rate, water sorptivity (S) and distribution density function f(r) of the soil pore size. Calcareous sandy loam and alluvial clay soils located at the Nile Delta were used to test the validity of the assumed equations. Data showed that the values of K(θ) calculated by the proposed equations were in the common ranges for such soils. The equations are therefore expected to be applicable for both coarse and fine textured soils. Also, an equation was derived to estimate the sorptivity at steady state infiltration. It was observed that S is decreased in going from the un-saturation condition to steady state infiltration by 15.1% and 45.9% in sandy loam and clay soils, respectively.

Water infiltration and storage under surface irrigation are evaluated, based on the initial soil water content and inflow rate as well as on the irrigation parameters and efficiencies. For that purpose, a field experiment was conducted using fruitful grape grown in alluvial clay soil at Shebin El-Kom in 2008 grape season. To evaluate the water storage and distribution under partially wetted furrow irrigation in comparison to the traditional border irrigation as a control method, two irrigation treatments were applied. They are known as wet (WT) and dry (DT) treatments, at which water was applied when the available soil water (ASW) reached 65% and 50%, respectively. The coefficient of variation (CV) was 6.2 and 10.2% for WT and DT respectively under the furrow irrigation system as compared to 8.5% in border. Water was deeply percolated as 11.9 and 18.9% for wet and dry furrow treatments respectively, as compared with 11.1% for control with no deficit. The application efficiency achieved was 86.2% for wet furrow irrigation achieving a high grape yield (30.7 t/ha). The relation between the infiltration (cumulative depth, Z and rate, I) and opportunity time (t₀) in minutes for WT and DT treatments was: Z_WT = 0.528 t₀^0.6, Z_DT = 1.2 t₀^0.501, I_WT = 19 t₀^–0.4, I_DT = 36 t₀^–0.498. Also, empirical power form equations were obtained for the measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion, and recession.

Six calcareous and alluvial soil profiles differing in their texture, CaCO3 and salinity were chosen from west and middle Nile Delta for the present study. The 1 st and 2 nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO3, while the 3 rd and 4 th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO3. The 2 nd and 4 th profiles were taken from cultivated area with maize. The 5 th profile from Epshan area was non-saline clay alluvial soil and the 6 th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content (W%) and water vapour pressure (P/Po) was established for the mentioned soils. Data showed that the specific surface area (S) values were 34-53 and 44-60 m 2 /g for calcareous soils of Borg El-Arab and Nubaria areas, 206-219 and 206-249 m 2 /g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of the external specific surface area (Se) were 16-21, 14-22, 72-86 and 92-112 m 2 /g. Submitting Wm + Wme as an adsorption boundary of moisture films (Wc) (where Wm is mono-adsorbed layer of water vapour on soil particles and Wme is the external mono-adsorbed layer), the maximum water adsorption capacity (Wa) was found to be Wc + Wme or Wm + 2Wme. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70-10.70% and 10.80 to 13.12% while the maximum hygroscopic water (MH) values were 2.43-3.78%, 2.91-4.65%, 16-17% and 18.30-21.9% for the studied soil profiles respectively. The residual moisture content (θr) at pF 7 and P/Po = 0 was ranged from 0.0005-0.0010%, 0.0007-0.0019% and 0.0043-0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles, respectively. The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were as follows: Calcareous soils; Wm = 0.40 MH, Wc = 0.55 MH, Wa = 0.70MH, S = 14 MH Non-saline soil; Wm = 0.35 MH, Wc = 0.49 MH, Wa = 0.63 MH, S = 13 MH Saline soil; Wm = 031 MH, Wc = 0.45 MH, Wa = 0.59 MH, S = 12 MH These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic water, which can be obtained through the experimental determination of water vapor adsorption isotherms.

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Soil water management and irrigation practices largely depend on a timely and accurate characterization of temporal and spatial soil moisture dynamics in the root zone. Consequently, measurements and detailed information about soil water sorption, water content, behavior, and potential are required. In that concern, water vapor adsorption is an important phenomenon in arid and semi-arid regions, as well as in dry periods of tropical soils. Therefore, quantifying adsorption is important for agricultural water management, surface energy balance studies, ecological studies, and remote sensing investigations changes in surface soil moisture content will affect land surface properties such as albedo, emissivity, and thermal inertia . The vapor pressure and isothermal adsorption of water vapor can be used to predict soil moisture adsorption capacity Wa , specific surface area, and hydro-physical properties of arid soils such as in Egypt and in the tropical soils in Ecuador. Theory of adsorption of water vapor on soil particles is developed among the mono-molecular and poly-molecular adsorption with respect to "runauer, Emmett, and Teller "ET theory. Data of soil-water adsorption W% at different relative vapor pressures P/Po can be obtained for the soils, where the W% values are increased with increasing P/Po in general. The highest values of water adsorption capacity Wa , specific surface area S , and other hygrophysical properties such as adsorbed layers and maximum hygroscopic water are observed in the clay depths of soil profiles, while the lowest values can be found in coarse textured soils sandy and sandy loam soils profiles . Two equations were assumed to predict P/Po at water adsorption capacity Wa and to applyWa in prediction of soil moisture retention, i.e., ψ W function at pF < . .

Particle size distribution (PSD) in the soil profile is strongly related to erosion, deposition, and physical and chemical processes. Water cycling and plant growth are also affected by PSD. Material sedimented upstream of the dam constructions formed large areas of deposited farmland (DF) soils on the Chinese Loess Plateau (CLP), which has been the site of the most severe soil erosion in the world. Two DFs without tillage on the CLP were chosen to study the combined effect of erosion and check dams on PSD. Eighty-eight layers (each 10 cm thick) of filled deposited farmland (FDF) soils and 22 layers of silting deposited farmland (SDF) soils of each studied soil profile were collected and 932 soil samples were investigated using laser granulometry. The particle sizes were stratified in both DFs based on soil properties and erosion resistance. The obtained results of clay and silt fractions showed similar horizontal distribution, indicating parallel characteristics of erosion and deposition processes. Fine sand represented the largest fraction, suggesting the preferential detachment of this fraction. The most erodible range of particle sizes was 0.25-0.5 mm, followed by 0.2-0.25 mm in the studied soil profiles. The correlation between particle size and soil water contents tended to increase with increasing water contents in FDF. Due to the abundant shallow groundwater, the relationship between particle size and soil water content in SDF was lost. Further studies on PSD in the DF area are needed to enhance the conservation management of soil and water resources in this region.Index terms: soil texture, stratification, soil erodibility, dam construction, soil conservation.

The purpose of this study was (1) to find a matching factor (u) between infiltration rate and hydraulic conductivity during steady-state infiltration, and (2) to propose equations based on infiltration and soil moisture-retention functions for prediction of the hydraulic conductivity K(y) within the rapidly (non-capillary) drainable pores (RDP) and capillary-matrix pores of soils. The K(y) of capillary pores was divided into K(y) SDP , K(y) WHP and K(y) FCP within slowly drainable pores (SDP), water-holding pores (WHP) and fine capillary pores (FCP), respectively. Five soil profiles of calcareous sandy loam, alluvial saline and non-saline clay, located at the Nile Delta, were used to apply the proposed equations. The highest and the lowest values of K(y) RDP were observed in calcareous and saline clay soil profiles, respectively. Values of K(y) RDP remained higher than those for capillary pores in the studied soils. The predicted values of K(y) in capillary and non-capillary pores classes were in the expected range for unsaturated hydraulic conductivity. Water sorptivity (S) was determined at initial unsaturated soil water conditions and calculated at steady-state infiltration (S w ) using a derived equation. There was a decrease in S with an increase in soil water content; i.e. at steady-state infiltration, S decreased by 35-40% in calcareous soils and by 45-60% in alluvial clay soils. The parameter values of u and S w tended to be uniform in calcareous soils, but nonuniform in saline and non-saline clay soils.