الفهرس 
SummaryOnly 14 pages are availabe for public view
 |  | from | 266 |  |  |
| | | from | 266 | | |
Abstract
The present investigation was undertaken to study the pedochemical characteristics of some representative soil profiles developed on the main physiograpkic units in Toshki region. The studied area is ,bounded by longitudes 29° 30’ , 30° 30’ East and latitudes 22° 30’ , 23° 30’ North , and this study aims to give a scientific idea about the importance of soil characteristics , potentialities and suitability crops , which used as a guide or more beneficial recommendations for a successful agricultural utilization of the studied area .
The studied area is characterized by the presence of six physiographic units namely:
a)Pediplain of sandstone .
b)Pediplain of clay stone.
c)Alluvial deposits derived from sandstone.
d)Alluvial deposits derived from claystone.
e)Aeolian plain.
f)Playa.
To achieve this target, sixteen soil profiles were chosen to represent the different physiographic units. These profiles were morphological described and their physical, chemical and mineralogical properties were discussed and evaluated. The obtained results could be summarized in the following :
(1) Soil morphological characteristics of the studied area :
** Soil relief: The soils under consideration are generally characterized by two classes of relief:
a)Gently undulating, which is dominated in the majority of soils developed on the geomorphic units, pediplain of clay stone, soils of alluvial deposits derived from claystone and aeolian plain?
b)Almost flat, which is dominated in the rest soils of physiographic units and previous excepted profiles.
**Gravel content: All the studied soil profiles have not gravel, except some soils of pediplain of sandstone, alluvial deposits derived from sandstone and soils alluvial deposits derived from claystone
** Soil texture: Soils of pediplain of claystone, alluvial deposits derived from clay stone and playa are characterized by medium to fine texture classes (clay loam and clay), while the other physiographic are characterized by coarse texture classes (sand, loamy sand and sandy loam).
**Calcium carbonate content: The majority of soils of pediplain of sandstone have relatively high CaCO3 content that enough to form a calcic horizon. Some soils of pediplain of claystone, alluvial deposits derived from sandstone, alluvial deposits derived from claystone and playa have higher CaCO3 content, while soils of the rest profiles have a relatively lower content.
** Gypsum content : The representative soil profiles have low content of gypsum , except soils of pediplain of claystone
that have a secondary gypsum content enough to form a gypsic horizon .
** Organic matter content: The studied area has very low content not exceeding 0.97 %. (2)-Soil chemical properties of the studied area:
**Soil reaction (pH) is generally almost neutral to moderately alkaline
(since pH values ranged between 6.7 and 8.3)
** Soil salinity (EC) fluctuates between non — saline to
extremely saline. In general, it tends to increase with depth in most of the studied soils.
**Soluble cations show an arrangement of: Na+ > Ca2+ >
Mg2+ > K+ , while the soluble anions show a general distribution pattern of S02- > C1”> HCO3” •
**Cation exchange capacity: It ranges between 3.59 and 50.86 cmolc/kg, the highest values are observed in soils of pediplain of claystone, alluvial deposits derived from claystone and playa, due to the occurrence of high clay contents.
**Exchangeable cations : In general , the studied soils show a sequence patter of : Ca2+ > Na+ > Mg2+ > K+ as well as
soils under consideration have ESP < 15 % , which indicate that these soils are non- alkaline .
(3)- Soil classification:
According to the previous soil characteristics, and applying the USDA (1999), the soils under considerationcould are classified into 12 taxonomic units (family level), as follow:
- Typic Haplocalcids, sandy, mixed, hyperthermic. - Typic Torriorthents, sandy, mixed, hyperthermic.
- Lithic Haplocalcids, coarse loamy, mixed, hyperthermic. - Gypsic Haplosalids, Clayey, mixed, hyperthermic.
- Lithic Haplogypsids, fine loamy, mixed, hyperthermic. - Typic Torriorthents, fine loamy, mixed, hyperthermic.
- Typic Haplocalcids, coarse loamy, mixed, hyperthermic. - Typic Torriothents, coarse loamy, mixed, hyperthermic.
- Typic Haplocalcids, loamy skeletal over sandy, mixed, hyperthermic.
- Gypsic Haplosalids, fine loamy, mixed, shallow, hyperthermic. - Gypsic Haplosalids, fine loamy, mixed, hyperthermic.
- Halic Haplotorrerts, clayey, montmorillonitic, hyperthermic. (4)-Total micronutrients and trace elements:
Total contents of some micronutrients , i.e., iron ,manganese ,zinc and copper are 6800-39900 ,109 -1020 ,45 -416 and 12 -146 mg/kg , respectively .These values show a positive and significant correlation with silt , clay and (silt + clay) %, while the reverse is true with coarse sand and total sand .Also , their
distribution pattern and homogeneity are discussed through weighted mean ,trend and specific range .