um and magnesium are precipitated; hence, the soil solutions of sodic soils usually contain only small amounts of these cations, sodium being the predominant one (US Salinity Laboratory 1954). Soils having pH 8.5, SAR 13, ESP 15, and ECe 4 dS/m are referred to as saline -sodic soils. Soils containing saline and saline -sodic categories may contain a salic horizon. In spite of high Na saturation, all of the studied soils did not showed a very high pH probably due to absence of Na2CO3. Consistent with this, the soils were classified as saline -sodic with pH 8.5, SAR 13, ESP 15, and ECe 4 dS/m into each profile (Figures of 4.1, 4.2, 4.3, and 4.4). Also, Figure 4.5 indicates the map of saline and sodic properties in the studied soils. Such conditions and properties were reported in other situations of Iran such as Khuzestan and Southern Coastal Plains in southwestern Iran (Qadir et al., 2008).
.

Fig. 4.1 The weighted mean of soil pH in the different profiles

Fig. 4.2 The weighted mean of soil EC in the different profiles

Fig. 4.3 The weighted mean of soil SAR in the different profiles

Fig. 4.4 The weighted mean of soil ESP in the different profiles

Fig. 4.5 The map of saline and sodic properties for the studied soils

*: S4, EC 32 dS/m; S3, Ec 16-32 dS/m A3, SAR 30-70; A4, SAR 70

4.1.2 Soil Salinity and Alkalinity Properties

The soil pH of the different horizons was alkaline, ranging from 7 to 7.9 in different horizons the studied profiles (Table 4.4). In salt-affected soils, Changes in pH become important when pH reaches values above 8.4. The results of this study suggest that pH changes do not indicate a shift towards extreme sodification of the soils studied mainly due to the absence of carbonate anions. For most of the studied soil profiles, the high soil reactions were formed at topsoil, where the values of SAR and ESP are in a high level.
The values of soil electrical conductivity (EC) showed a wide range, varying between 8 and 137 dS/cm (Table 4.4). The soil EC of all soils was more than 8 dS/m, indicating strong salinity in these soils. This pattern is probably due to saline water table, which acted as the main source of soluble salts the soils. The highest contents of EC were associated with Salic horizons mainly in soil surface (Table 4.4). In this region, the groundwater levels vary with the seasonal changes and the up and down movement of soil water is frequent, so the processes of soil salinization are very active. In the winter and spring, downward movement of the salt was occurred by leaching process, resulted in to the formation of salic horizon in the subsoil. In contrast, in the summer and autumn, downward movement of salts to the ground waters is impaired and salic horizon translate to topsoil following raises ground water table over time and by capillarity and later evaporates (from the soil surface) and salt crusts are formed (Rezapour et al., 2012). Therefore, the annual repetition moisture (in rainy seasons) – drought (in wormer seasons) cycle leads the accumulation of considerable amounts of salts that concentrate in the water fluctuation area, but not in the saturation area, which explains why the saline distribution pattern tends to be highest on the surface. As indicated in Fig. 4.6, soil pH shows a trend to decrease as the salinity increases which is in agreement to other author (Pisinaras et al., 2010).
Table 4.4 The soluble cation and anion of the studied soil profiles
Horizon
Depth (cm)
CO3-2

HCO3-1

Cl-1

So4-2

Na+1

K+1

Ca2+

Mg2+

meq/L
Profile1
Az
0-15
0.0
3.5
1260
9.0
3.25
0.55
8.75
2.00
Bgz
15-60
0.0
2.5
690
11.5
2.33
0.53
16.50
2.00
Cgz
60-110
0.0
2.5
505
16.0
1.90
0.34
8.50
3.00
Bgzb
110-150
0.0
3.0
425
27.5
1.82
0.29
6.00
3.50
Profile2
Az
0-20
0.0
4.0
92
1.2
5.19
1.27
9.00
3.50
Bg
20-60
0.0
2.5
145
2.4
1.76
0.40
8.00
7.00
Cg
60-110
0.0
3.5
81
0.9
0.86
0.20
1.75
1.00
Bgzb
110-140
0.0
3.0
147
1.8
2.79
1.14
3.50
1.50
Profile3
Az
0-20
0.0
2.5
1390
2.6
1.75
2.61
4.25
3.00
Bgz
20-40
0.0
3.0
1105
3.3
6.98
2.11
2.00
2.80
Bkgz
40-80
0.0
3.0
1230
3.0
3.00
0.98
3.00
5.00
Cgz
80-125
0.0
2.5
1690
4.2
4.16
0.61
3.25
2.25
Profile4
Az
0-20
0.0
3.0
1470
2.0
4.38
3.20
9.00
6.00
Bgz1
20-60
0.0
2.5
1102
0.8
3.93
1.90
8.00
4.50
Bgz2
60-100
0.0
2.5
1520
3.1
3.90
0.67
3.75
1.5
Cgz
100-130
0.0
3.0
1570
2.2
3.89
0.55
3.75
1.25
Profile5
A
0-10
0.0
5.0
185
26.0
1.61
0.41
8.50
0.75
Bg
10-40
0.0
4.5
185
31.5
1.60
0.35
3.75
0.25
Cz
40-90
0.0
4.5
145
21.0
1.36
0.14
2.50
2.50
Bgzb
90-140
0.0
3.5
545
28.5
3.04
0.39
5.25
0.50
Profile6
Az
0-20
0.0
4.0
1020
11.0
1.69
0.36
8.00
2.00
Cgz
20-90
0.0
3.5
1110
16.5
2.15
0.26
6.50
2.50
Bgzb
90-140
0.0
2.5
1540
6.5
0.96
0.37
6.50
4.50
Profile7
Az
0-20
0.0
4.0
1250
9.0
1.71
1.97
9.00
7.00
Bgz
20-60
0.0
2.5
840
12.5
1.37
0.48
9.50
3.00
Bkgz1
60-120
0.0
2.5
820
11.0
1.34
0.60
9.00
5.00
Bkgz2
120-160
0.0
2.5
935
4.7
1.53
0.38
11.50
6.00

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Fig. 4.6 A plot of pH versus EC in soil samples saturation extracts

The predominant salt type is important in the salt-affected soils because of the effect of individual ions on the soil properties and the possibility that they may be toxic to plants. For this, Cl-1, SO4-2, HCO3-1, Na+1, K+1, Mg+2, and Ca+2 concentrations were determined in the SP extract solution.
All ions concentrations showed a wide range (Table 4.4), with Cl-1, SO4-2, Na+1, and Ca+2 showing a much larger variation. The significant differences between the values of Cl-1, Na+1, K+1, Mg+2, and Ca+2 at each profiles indicated clearly a temporal distribution, which can be attributed to the variation in other soils properties (e.g., particle-size distribution) and the high soluble salt content of groundwater in the study area. Many authors have studied the possible relationship between ECe and the salt concentration of a soil, in an attempt to assess the validity of this parameter as an indicator of soil salinity. Richards (1974) established a linear relationship between EC and total dissolved salts, while other authors have demonstrated that a linear correlation does not always exist between the EC and the corresponding ionic species (Alvarez et al. 1997; Simon et al. 1994). The formation of ionic pairs, mainly Ca+2, Mg+2, and SO4-2 ions (Timpson and Richardson 1986), in highly saline solutions is the main cause of this anomaly, because ion mobility in the extract is decreased (Csillag et al. 1995; Sposito 1984). Therefore, the types of soluble salt and their concentration levels directly influence the correlation model. Based on this reason, it is difficult to find a general equation to relate EC in all cases.
Based on the analytical data shown in Table 4.4 and considering the total number of analyzed samples, the different saline parameters were correlated in an attempt to establish a relationship between different salts measured in the soil saturation extract and their influence on the EC values. The results show that most ions and especially Cl-1, Na+1, Mg+2, Ca+2, and K+1 demonstrate a linear behavior with EC. The highest linearity was observed for Cl-1 in anions and Ca+2 in cations, which are the major ions of SP extracts of the soil samples (Fig. 4.7). Other ions demonstrate a greater dispersion of the points and loss in linearity mainly for EC values greater than 5 dS/m where the saline soil samples are separated from the saline-sodic ones due to the different increase rate of Na+1 and Ca+2. Such behavior seems to be related to the formation of ionic pairs on the part of Ca+2, Mg+2, and SO4-2, which, unlike Cl-1 and Na+1, reduce the EC value (Timpson and Richardson 1986).

Fig. 4.7. Relation between EC values with Cl-1 and Ca+2 of soil saturation extracts

4.2 Soil chemical and Fertility Characteristics
The selected chemical and fertility properties of the soils are presented in Tables 4.5. Organic carbon content (OC) ranged from 0.04 (C-horizon of profile 2) to 1.02% (A-horizon of profile 3) and its highest values was occurred in the surface horizons. Soil organic carbon is a key resource owing to its ameliorative effect on nutrient supply, detoxification of harmful soil constituents, moisture and nutrient retention and its role in soil structure formation (Yao et al. 2010). However, the majority of soil samples were categorized as extremely poor ( 0.6% of OC), poor (0.6-1.2% of OC) probably due to poor plant growth and low input rates of organic matters.
The content of calcium carbonate equivalent (CCE) varied from 2.25% (A-horizon of profile 1) to 19% (B-horizon of profile 3) and increased with depth in profiles of 1, 2 and 7 mainly due to dissolution and translocation of the CaCO3 from topsoil in rainy seasons and precipitation during dry periods (Abtahi and Khormali 2001). In contrast, the values of CCE with depth in profiles of 3, 4, 5 and 6 (Table 4.5) which can

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