الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
Siwa Oasis represents one of the most important natural depressions in the western desert of Egypt. It covers an area of about 1100 km2; however the studied area is about 521 km2. It is located between latitudes 29o 6’ 10.14’’- 29o 18’ 36.24’’ N and longitudes 25o 16’ 2.36’’ to 25o 51’ 3.04’’ E. It is located at about 300 kilometers south of the Mediterranean Sea at the western borders with Libya. Soils in Siwa Oasis have a great potential for land reclamation projects due to the availability of water resources for crop irrigation. However, they are suffering from some land degradation problems such as soil salinity, sodicity, water logging and wind erosion. Accordingly, the main objectives of this work were to study these soils, evaluate their capability for agricultural production, and their suitability for some potential crops using remote sensing and GIS techniques. For that purpose, 20 geo-referenced soil profiles were randomly dug throughout the studied area and sampled based on their development. Forty six soil samples were collected from these profiles and analyzed for their physical, chemical, and fertility properties. Water samples were also collected from irrigation wells and drainage canals. These water samples were analyzed for their chemical properties. Land evaluation was carried out using the Agriculture Land Evaluation System for arid and semi-arid regions (ASLEarid), which is a GIS based land evaluation system. The results could be summarized as follows: The obtained results indicated that the majority of soils in the studied area were Sandy, which had a significant influence on the soil physical properties such as the saturation percentage (SP), bulk density (BD) and total porosity. The average values of SP, BD, and total porosity were about 34%, 1.58 g cm-1, and 41%; respectively. Also, the content soil organic matter was very low in the studied soils (about of 0.43% in average). On the other hand, there was a wide variability in calcium carbonates within the studied area depending on soil parent material, where they varied from 1.71 to 59.72% with an average of 27.04%. Chemical properties of the studied soils revealed that sodium was the prevalent cation in the soil solution followed by magnesium and calcium ions. Their average concentrations were about 17.01, 3.50 and 3.24 meq/100 g soil, respectively. In the contrary, chlorides were the dominant anions followed by sulfates and bicarbonates. Their average values were about 19.03, 4.24, and 0.70 meq/100 g soil; respectively. Soils in this oasis were moderately alkaline, where soil pH was about 8.41 in average. However, the majority of soils in the Oasis were highly salinity, where the EC values varied from 4.25 to 427.17 dS m-1 with an average value of 76.76 dS m-1. Cation exchange capacity (CEC) was highly affected by the soil texture and it value was about 31.13 meq/ 100 g soil in average. The higher values were associated with fine-textured soils, whereas the lower values were associated with the coarse-textured soils. Exchangeable sodium percentage (ESP) was about 14.55% in average; which indicates that the majority of the studied soils in the oasis were non-sodic soils. The average values of available NPK were about 62.00, 11.63, and 5185 ppm; respectively. Total nitrogen and organic carbon in the studied soils were very low about (about 0.07 and 0.25% in average, respectively). As a result, the C/N ratio ranged between 0.55 and 34.80%, with an average of 5.37%. The concentrations of cations and anions in collected water samples took a similar trend as those in soil solution. The EC values ranged between 2.28 to 5.45 dS m-1 (about 3.48 dS m-1 in average). These higher values could be attributed to the collection of these samples from the private wells, which usually have a shallower depth (about 100 to 150 m) than the governmental wells (> 1000 m). However, the sodium adsorption ratio (SAR) was about 5.73 in average and the residual sodium carbonates (RSC) had negative values (-14.60 meq l-1 in average). This reveals little possibility of soil conversion into sodic soils when irrigated with this water. Conclusions Land capability and suitability in Siwa Oasis were effectively evaluated using the ASLEarid. Soils in the studied area were fit into two capability classes. These classes are fair and poor. The fair class represented about 70% of the studied area. Poor land capabilities were mainly associated with high soil salinity, coarse texture and low fertility. On the other hand, land suitability for the selected field crops and vegetables ranged between suitable to currently unsuitable. However, suitability for fruit trees varied from suitable to permanently unsuitable. Unsuitable areas for fruit trees were mainly associated with shallow soil depth, poor drainage and high soil salinity. Most of these limitations for plant cultivation can be eliminated through the proper land management practices. In summary, soils in Siwa Oasis could have a promising future for agricultural reclamation and cultivation projects, where most of soil limitations for crop production are none permanent and can be improved through implementing of proper management practices.