136
A. B. A. Belal et al.
In Upper Egypt CaCO 3 content in some soils found to be ranged from 0.15 to
49.00% (Ghoneim et al. 1984). Hamed and Khalafallah (2017) reported that soil
organic matter is ranged between 0.1 to 1.5%, where mean value of soil organic
matter is approximately 1%. Furthermore the low values of soil organic matter were
found in the sandy soil as the agricultural activities is very low. On the other hand
the high values were recognized in the cultivated land that charachtrized by fine
and medium texture (El-Sayed et al. 2016). The cation exchange capacity (CEC)
values were ranging between 10 to 38 cmol (+) kg
−1 . This result agrees with those
obtained by Reid and Dirou (2004). OM and clay content are considered as a source
of nutrients (Maji et al. 2005; Chude et al. 2011) by attracting more cations and
provide extra exchange sites to get the cations adsorbed in it. On the other hand, the
effect of soil tillage may be led to the low values of CEC which could be attributed to
the reduction of soil organic matter (Paz-Gonzalez et al. 2000). SAR values ranged
from 0.78 to 5.56, which showing that most of soils have values of less than 8,
the non-sodic soils cover about 77% of area soils. The soil depths of Dakhla are
varying between shallow to deep as they ranged between 70 to > 150 cm (Hamed
and Khalafallah 2017). Hamed and Khalafallah (2017) found that N values were with
a mean value of 99.37 mg/kg of total values that ranged from 70.31 to 170.22 mg/kg,
while P values were with a mean value of 31.32 mg/kg of total values that ranged
from 14.33 to 52.71 mg/kg, and K values were with a mean value of 121.93 mg/kg
of toatal values that ranged from 82.36 to 240.04 mg/kg for. The addition of plants
residual and organic fertilizers is the main practices in the area could be the reason
of founded high level of available N, P, and K as a result of providing a substrate for
microbial growth, and subsequent microbial activity (Suge et al. 2011)
6 Soil Classification of Dakhla Oasis
The examination of the soils provides the basis for placing them into taxonomic and
mapping units. Based on joint complication of the morphological features already
presented physical and chemical properties, we could explore the capability of these
soil properties to reply the requirements of different diagnostic horizons in order to
find the suitable taxonomic position of the different soil mapping units in the study
area. Soils belonging to the taxonomic units could be differentiated into orders,
suborders, great groups and subgroups (Soil Survey Staff 2014). According to ElSayed et al. (2016) two soil orders are dominated in the Dakhla Oasis, Aridisols and
Entisols, Aridisols are found throughout the world in desert environments. Salids,
Calcids and argids are the most common suborders belonging to Aridisols present
in the studied area. Soils of this order are classified according to morphological,
physical and chemical properties to three sub great groups, namely; Typic Natrargids,
Salic Natrargids and Sodic Haplosalids. Entisols order: they are characterized by
the lacking of diagnostic horizons. Psamments and Orthents are the most common
suborders belonging to Entisols present in the studied area. Soils of this order are
A. B. A. Belal et al.
In Upper Egypt CaCO 3 content in some soils found to be ranged from 0.15 to
49.00% (Ghoneim et al. 1984). Hamed and Khalafallah (2017) reported that soil
organic matter is ranged between 0.1 to 1.5%, where mean value of soil organic
matter is approximately 1%. Furthermore the low values of soil organic matter were
found in the sandy soil as the agricultural activities is very low. On the other hand
the high values were recognized in the cultivated land that charachtrized by fine
and medium texture (El-Sayed et al. 2016). The cation exchange capacity (CEC)
values were ranging between 10 to 38 cmol (+) kg
−1 . This result agrees with those
obtained by Reid and Dirou (2004). OM and clay content are considered as a source
of nutrients (Maji et al. 2005; Chude et al. 2011) by attracting more cations and
provide extra exchange sites to get the cations adsorbed in it. On the other hand, the
effect of soil tillage may be led to the low values of CEC which could be attributed to
the reduction of soil organic matter (Paz-Gonzalez et al. 2000). SAR values ranged
from 0.78 to 5.56, which showing that most of soils have values of less than 8,
the non-sodic soils cover about 77% of area soils. The soil depths of Dakhla are
varying between shallow to deep as they ranged between 70 to > 150 cm (Hamed
and Khalafallah 2017). Hamed and Khalafallah (2017) found that N values were with
a mean value of 99.37 mg/kg of total values that ranged from 70.31 to 170.22 mg/kg,
while P values were with a mean value of 31.32 mg/kg of total values that ranged
from 14.33 to 52.71 mg/kg, and K values were with a mean value of 121.93 mg/kg
of toatal values that ranged from 82.36 to 240.04 mg/kg for. The addition of plants
residual and organic fertilizers is the main practices in the area could be the reason
of founded high level of available N, P, and K as a result of providing a substrate for
microbial growth, and subsequent microbial activity (Suge et al. 2011)
6 Soil Classification of Dakhla Oasis
The examination of the soils provides the basis for placing them into taxonomic and
mapping units. Based on joint complication of the morphological features already
presented physical and chemical properties, we could explore the capability of these
soil properties to reply the requirements of different diagnostic horizons in order to
find the suitable taxonomic position of the different soil mapping units in the study
area. Soils belonging to the taxonomic units could be differentiated into orders,
suborders, great groups and subgroups (Soil Survey Staff 2014). According to ElSayed et al. (2016) two soil orders are dominated in the Dakhla Oasis, Aridisols and
Entisols, Aridisols are found throughout the world in desert environments. Salids,
Calcids and argids are the most common suborders belonging to Aridisols present
in the studied area. Soils of this order are classified according to morphological,
physical and chemical properties to three sub great groups, namely; Typic Natrargids,
Salic Natrargids and Sodic Haplosalids. Entisols order: they are characterized by
the lacking of diagnostic horizons. Psamments and Orthents are the most common
suborders belonging to Entisols present in the studied area. Soils of this order are