Pedo- Chemical Studies On Some Soils Of North Western Coast Of Egypt:

Donya Mohamed Ibrahim

5. SUMMARYThis study points to the evaluation of the pedochemical characteristics of some soils representing the northwestern coast of Egypt. The studied area is bounded by longitudes 28° 15’ and 29° 00’ East and latitudes 30° 15’ and 31° 30’ North. These were by four physiographic units (aeolian plain, piedmont, alluvial plain and sabkha).Seventeen soil profiles were chosen to represent the different physiographic units and were morphological described their physical, chemical and mineralogical properties were evaluated. The obtained data could be summarized in the following: 1- Physical and chemical properties 1.1.Soils of Aeolian plainSoil texture of this physiographic unit ranges from sand to sandy clay loam. Calcium carbonate is commonly very high and ranges from 28.15 to 93.84% with no specific distribution pattern with depth. Organic matter content is very low and does not exceed 0.61%. pH values ranged from 8 and 9.1 indicating that the soils are moderately alkaline to very strongly alkaline. EC, values range between 0.59 to 32.7 dSnil indicating that the soils are non saline to strongly saline. Soluble cations are in the order: Na+> Ca++> Me.> IC, while in some layers Ca++ ion exceeds Na+. Soluble anions have the order C1-> SO4 > HCO3-.Summary -168-1.2. Soils of piedmontSoil texture of this physiographic unit varies from sand to clay. CaCO3 content varies from 24.8 to 66.47% and tends to decrease with depth. Organic matter content is very low and does not exceed 0.98%. Soils are slightly alkaline to strongly alkaline (pH 7.7 to 8.9). Soils are non saline to strongly saline and soluble cations are characterized by the dominance of Na+ followed by CC and/or Mg++, while K+ ions are the least abundant soluble cations. Soluble anions have the order C1-> SO4=> HCO3” while CO3- is absent. 1.3. Soils of alluvial plainSoils texture of this physiographic unit fluctuates between sand to sandy clay loam. CaCO3 content is very high and ranges from 27.73 to 68.42% with an irregular distribution pattern with depth. Organic matter content is extremely low it is not exceeding 0.52%. Soils reaction lies in the moderately alkaline to very strongly alkaline side. Soils are non saline to moderately saline as the EC, values varies between 0.7 and 9.13 dsm-1. Soluble cations are in the order Na+> CC> Mg++> K+, while soluble anions have the order CI-> SO4=> 1-1CO3”. 1.4. Soils of sabkhaThese soils have sandy clay loam and sandy loam textural class throughout the entire profile depth. CaCO3 content ranges from 20.8 to 68.81% indicating that these soils are calcareous. Organic matter content is very low and does not exceed 0.4%. Soil reaction is moderately alkaline and the soils are slightly saline to strongly saline. The dominant soluble cations are Na+Summary -169-followed by Mg’, Ca++ and K+ while soluble anions dominated by CL followed by SO4- and HCO3-. 1.5. Calcium carbonate distributionParticle size distribution of carbonate components in the sand sub fraction, indicating that the physical weathering predominates the chemical ones. The increase of carbonate in the sand size fraction may be possibly, due to lime segregation, nearest these sediments to parent rocks and soft nodule formations within the profile layers of these soils. Therefore, these carbonates could be considered as primary, i.e. inherted from parent materials forming these soils. 2.Grain size analysisfrom the grain size parameter, it can be noticed that the water action is the main factor affecting transportation and deposition of the studied soilsGenerally, the moderate differences of kurtosis value in the studied soils are corresponding to a relatively low energy environment. The (SK) values of these soils show bimodal or non normal distributions, indicating a mixing of two or more model fractions. 3.Trace element status 3.1. Total zincTotal Zn ranged between 0.1 to 57.0 mg kg-I, having negative correlation with clay %, silt %, OM % and fine sand %, and negative correlation with CaCO3 % and coarse sand.Summary -170-3.2. Total copperTotal Cu ranged between 2.0 and 27.4 mg kg-1, having positively correlation with clay %, silt %, and OM %, but negatively correlation with coarse sand % and CaCO3 %. 3.3. Total ironThe total Fe ranged widely between 1110.9 and 12698.6 mg kg-I, and was closely related to soil texture and CaCO3, giving positive correlation with each of OM %, clay %, silt % and fine sand and negatively with CaCO3 % and coarse sand. 3.4. Total manganeseTotal Mn ranged between 20.0 and 269.2 mg kg-1 having positively correlation with clay %, silt %, OM % and fine sand and negatively correlation with CaCO3 and coarse sand.The vertical distribution of total trace elements is discussed in light of the statistical measures, i.e. weighted mean, trend and specific range, suggested by Oertel and Giles (1963). 3.5. DTPA-ZnDTPA-extractable Zn ranged from. 0.012 to 0.62 mg kg-I, having positive correlation with fine sand %, silt % and clay % and negatively correlation with CaCO3 % and coarse sand. 3.6. DTPA-CuDTPA-extractable Cu ranged from. 0.004 to 0.82 mg kg-1, having positively correlation with clay %, EC, and CaCO3 %Summary -171-3.7. DTPA-FeDTPA-extractable Fe varied from 1.18 to 36.8 mg kg-1 and having positively correlation with ECe. 3.8. DTPA-MnDTPA-extractable Mn ranged between 1.11 to 36.59 mg kgi, having positively correlation with ECe. 5.4. Mineralogical composition of the studied soils 5.4.1. Mineralogical of the sand fractiona)Light mineralsQuartz predominate the light fraction with less pronounced amounts of feldspars of which orthoclase and plagioclase are the principal members, while microcline is the least abundant.b)Heavy mineralsHeavy mineral are dominated by opaques, non-opaque minerals are dominated by pyroboles (pyroxenes + Amphiboles) and altrastable minerals (zircon, rutile and tourmaline). Garnite, epidote, kyanite and silimanite minerals are present in moderate amounts, while the remaining minerals are detected in less pronounced occurrences.c)Uniformity of soil parent materials:The data of frequency distribution of resistant minerals and weathering ratios leads to the conculusion that the studied soils are heterogeneous either due to their multi-origin or due to multi-depositional regimes.Summary -172-5.4.2. Mineralogy of the clay fractionfrom x-ray identification of the clay minerals it can be generally noticed that palygorskite minerals are alternatively dominated in the studied physiographic units followed by kaolinite. Smectite, illite and chlorite minerals are the lowest abundant clay minerals in these soils.The identified accessory minerals are mainly dominated by quartz and feldspars followed by calcite, dolomite and apatite. 5.5. Soil classificationAccording to the previously mentioned field analytical results and soil abservation, the soil classification was performed on the basis of the USDA (1975) and the key of Soil Survey Staff (2001). The studied soils are generally classified in the one order namely, Aridisols down to the family level.1- order: AridisolsSuborder: Calcids•Subgroup: Haplocalcids•Subgroup: Petronodic Haplocalcids (profiles 6, 7,13, 15, 16, 1, 3, and 9)•Subgroup: Typic Haplocalcids (profiles 5, 8, 12,14, 4, 10, 11, 2 and 17) 5.6. Land evaluationApplication of the capability index for the studied soil profiles suggested by Sys et al (1991) shows that estimated current suitability of the studied soil profiles could beSummary -173-categorized into two classes between grade (III) and grade (VI) as follows:1-Grade (III): fair soils, represented by profiles 7, 13, 15 and 16 (Aeolian plain), profiles 1 and 9 (piedmont), profiles 8, 10, 11 and 14 (alluvial plain) and profiles 2 and 17 (sabkha).2-Grade (VI): Non agriculture soils, represented by profiles 6, 3, 4, 5 and 12The studied soil profiles are evaluated to determine its suitability for growing 12 crops. Results reveal that the studied soil profiles include the suitable classes (S2, S3 and N).Summary -174-