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Abstract The study area (Assiut Governorate) is located 300 km south Cairo between 26° 20ʹ 00ʹʹ to 27° 40ʹ 00ʹʹ N latitude and 30° 30ʹ 00ʹʹ to 31° 40ʹ 00ʹʹ E longitude. The limestone plateau in Assiut region is a part of the major Eocene plateau that covers major parts of the western and the eastern desert of Egypt. During the last seven years, some investors started digging groundwater wells and cultivating some soils, of this plateau while some others just put their hands on the land as a sort of confirming positioning. So, the physical properties and water resources of these soils have been unknown. This study is an important step to investigate the physical properties, and water resources of these soils for agricultural use and their favorable management practices on the short and long terms. Therefore, the main objectives of this work were: 1. To assess some physical and hydrological properties as well as their interrelation of the studied soils. 2. To recognize the groundwater quality for irrigation purposes and initiates its contour map. So, four transect was chosen to represent various parts of the eastern and western limestone plateaus at Assiut, Egypt. The sites of each transect were carefully selected by GPS to represent most of the various soils; the average distance between each two consecutive soil profiles was about 5-8 km, with a total number of 40 profiles, number of 119 soil samples and a total number of 15 groundwater samples. Disturbed and undisturbed soil cores were collected from the profile layers, according to vertical morphological variations. Soil physical, hydraulic and chemical properties were measured and determined. Chemical properties and quality parameters of the groundwater samples were also, measured and determined. The obtained results revealed in the following: Soil properties: 1. The gravel content ranges from 1.18 to 73.43 % by weight. The highest amount of gravels occurs in the subsurface layer of most soil profiles. Soil texture is mostly coarse (mainly sand, loamy sand and sandy loam). Finer soil texture i.e. loam, and sandy clay loam is not frequently present. 2. The bulk density varies from 1.21 to 1.97 Mg/m3. A slight increase in the bulk density was observed with depth. This may be related to a high content of the sand fraction and to their lower contents of silt, clay and organic matter. Non-significant variations in bulk density values were found among soil samples. 3. Most of the studied soil samples have higher particle density (Dp) values than 2.60 Mg/m3. Non-significant variations were recorded in particle density values. 4. The studied soil moisture characteristics cure moisture content indicated a marked decrease of soil moisture content (50%) when the soils were subjected to suction above one atmosphere. Moisture content all transect profiles at all pressure heads has medium values of C.V. The obtained results indicated that soil texture and CaCO3 content have a major influence on the variations of water retained under different suction levels. 5. The studied saturated soil hydraulic conductivity indicated that soils can be categorized between low to excessive permeability. The C.V % for saturated hydraulic conductivity (Ks) was very high and ranges from 124 to 217.2%. These high variations may be attributed to the variability of soil deposition, pedogenic and hydrologic processes. The obtained results of Ks indicated that soil texture and CaCO3 content have a major influence on the variations of saturated hydraulic conductivity. 6. The unsaturated soil hydraulic properties, K (Ɵ) decreases greatly with decreasing soil moisture content. Also, the K (Ɵ) decreases nonsignificantly with increasing of total CaCO3 % content. The unsaturated hydraulic conductivity K (Ɵ) of the transect profiles have very high values of C.V. The K (Ɵ) DROP drastically from 0.1 atm. (suction) up to 0.33 atm., afterward, the curve starts to flatten with a minimum rate of change with increasing the suction head. 7. The soils have a high content of calcium carbonate ranging between 13.10 and 93.80%, with a coefficient of variation equal to 40.10% that it is classified as highly variable. The high content of CaCO3 in these soils is mainly attributed to the pedogenic carbonate formed from limestone parent material. Most of the soil profiles are classified as extremely calcareous in terms of CaCO3 content according to FAO (2006). 8. The organic matter content of the soil samples ranges between 0.03 and 0.83%. In most soil profiles, organic matter decreases with depth. This reflects the little effect of rainfall during winter and the prevailing dry climate. 9. The soil pH values range between7.5 to 9.4. In general, the results show relatively strong alkaline pH values for most studied samples. These soils are classified to have low variability with respect to pH values. 10. The salinity value (ECe) of the studied samples differs between 1.7 and 109.5 dS/m. Its CV value is considered highly variable for all transects. In general, most of these soil samples are relatively strongly saline (> 16 dS/m). This could be attributed to the barren nature of the soils and, also, to the ineffective role of leaching due to the scanty rainfall received. ii. Groundwater: The groundwater quality of the limestone plateau is strongly influenced by the water-rock interaction and anthropogenic activity. The rock dominance of the major ion chemistry in the basin provide, an insight of chemical weathering in the drainage basin since weathering of the different parent rocks (e.g., carbonates, silicates, an evaporates) yields a different combination to dissolve cations and anions to a solution. 1. The water depth in the study area varies from one place to another and is influenced by the surface level. The pH value of the groundwater in the study area is generally neutral and reflecting natural groundwater (slightly alkaline) type. 3. The TDS value in the study area is considered fresh water except well no. 12 (sample 14) that is considered slightly saline according to Hem, (1970). The TDS values of these waters are attributed to the dissolution of limestone and to leaching of halite and gypsum deposits. 4. The EC value of groundwater samples varies between 672 and 2321 μS/m. It fluctuates between moderate and high saline. The groundwater under this condition can be used for irrigation if a moderate amount of leaching occurs and crops with moderate salt tolerance can be grown in most instances without special practices for salinity control. 5. The cation concentration in the groundwater of the study area is in the order of Na+> Ca2+> Mg2+> K+ and that of the anions is in the order of Cl-> HCO3 2-> SO4 2-. Cation concentrations and aonion ratio can trace water-rock interaction processes, such as mineral weathering and cation exchange (Han et. Al, 2009). 6. According to the Piper classifications, about 53% of the groundwater samples are characterized by non-carbonate alkali (primary salinity) that exceeds 50%, where the chemical properties of alkalies and strong acids dominate properties. However about 27% of the groundwater samples are characterized by the strong acids where (SO4+Cl) > (HCO3+CO3). They are characterized by carbonate hardness (secondary alkalinity) that exceeds 50% and the chemical properties of the groundwater are dominated by alkaline earths and weak acids. 7. The following, six main groups of salt assemblage: group I : Ca(HCO3)2, MgSO4 and NaCl are noticed in samples no. 1 and 8. group II : Ca(HCO3)2, Mg(HCO3)2, MgSO4 and NaCl are detected in samples no. 2and 3. - group III: Ca(HCO3)2, Mg(HCO3)2 and NaCl are detected in samples no. 5, 6 and 7. - group IV: Ca(HCO3)2, MgCl2 and NaCl are detected in samples no. 12, 14 and 15. - group V: Ca(HCO3)2, CaSO4 and NaCl are detected in samples no. 9 - group VI: Ca(HCO3)2 and NaCl are detected in samples no. 4, 10, 11 and 13. 8. The sodium adsorption ratio (SAR), of the investigated groundwater samples ranges from 2.8 to 8.8. The groundwater in the study area can be used for irrigation on most of these soils with the advent of low levels of sodium hazard. 9. The sodium soluble percentage (SSP) of these groundwater samples lies between 40.9 to 62.3%. Most of these groundwater samples permissible for irrigation, except the sample no. 6 that is in doubtful for irrigation. 10. The total hardness in the groundwater of the investigated aquifer lies in the hard water category. These results due to the high percentage of calcium and magnesium in limestone. 11. The residual sodium carbonate (RSC) in the groundwater understudy varies from -2.80 to 0.20 meq/l. All groundwater samples of this study area are within the good categories for irrigation. 12. The residual sodium bicarbonate (RSCB) of these groundwater’s ranges from -0.52 to2.09 meq/l. All these samples are satisfactory for irrigation. 13. The magnesium hazard (MH) value in the groundwater of the study area varies between 29.28 to 49.09%, indicating that these waters are suitable for irrigation. 14. The permeability index (PI), of the groundwater in the study area range from 62.08 to 81.05 %. Most of these water samples are moderately suitable for irrigation. 15. According to Richards classification (US salinity diagram), the salinity hazard for the water samples of the study area is medium, high and very high. Most of these water samples belong to the high-salinity hazard (C3). 16. According to Wilcox classification, the water quality of the study 14 groundwater samples are acceptable for irrigation purpose but one sample is not suitable for irrigation under ordinary conditions due to its high salinity. iii. Conclusions: 1- According to soil hydrological characteristics, it is recommended to use pressurized irrigation systems (sprinkler-drip....). 2- Leaching is a must to get rid of soil salinity considering drainage system. 3- selection of appropriate crops based on the content of soil salts, total calcium carbonate and groundwater quality in the area. 4- It is essential to use the water resources wisely and efficiently as possible to optimize the soil plant relationships. 5- Further, detailed hydrological studies are required to know the groundwater situation in limestone. |