This study investigates the feasibility of utilizing drainage water for reclamation of saline and sodic soils in the Dosalagh plain of Khuzestan province, Iran. With significant drainage water generated in the region's irrigation networks, repurposing it for soil reclamation emerges is a low-risk strategy. Leaching, a practical technique for soil desalination, was examined using the double ring method at depths up to 150 cm. Four water qualities (electrical conductivities of 2.12, 7, 25 and 40 dS m−1) and depths (0, 25, 50 and 75 cm) were tested, with intermittent leaching over three cycles. Results indicate a substantial reduction in electrical conductivity (117.7 to 29 dS m−1) and sodium content (1415.9 to 39.83 mEq L−1) at the 0-25 cm depth with drainage water incorporation. The study highlights the beneficial impact on soil quality, emphasizing decreased sodium content, sodium adsorption ratio, and electrical conductivity. Overall, reusing drainage water proves advantageous for soils with high salinity levels, showcasing its potential for sustainable soil management in saline regions. This research underscores the importance of effective drainage water management for soil reclamation and agricultural sustainability in arid regions like Khuzestan province.

  • Soil electrical conductivity (EC) decreased by increasing the depth of leaching water.

  • By increasing the depth of water in the leaching process, the amount of soil sodium and chloride decreased.

  • The combination of saline drainage water and non-saline river water is suitable for irrigation and reducing soil salinity.

  • The amount of EC reduction was more than exchangeable sodium percentage reduction.

SAR

sodium adsorption ratio

EC

electrical conductivity

ECf

soil salinity after an application of a specified depth of leaching water

ECi

initial salinity of the soil (EC of saturated)

Dw

depth of leaching water that moves by gravity force after supplying soil moisture deficiency

Ds

soil depth

ECeq

soil salinity at the end of the reclamation process (EC of soil water at equilibrium)

ESP

exchangeable sodium percentage

ESPf

soil sodicity after an application of specified leaching depth

ESPi

initial sodicity of soil

ESPeq

sodicity of soil at the end of leaching (equilibrium).

The available global water sources cannot supply the increasing water demand, and climate change intensifies water scarcity. Furthermore, water scarcity magnifies food insecurity, and thus the irrigation system plays an essential role in food security and sustainable income (Molden et al. 2007; Corwin 2021). The surge in human population has increased the water demand for urban and agricultural uses. Water demand has increased worldwide, while the availability of fresh water decreased rapidly. Over 700 million people across 43 countries suffer from water scarcity, and the perceived limits to producing food for a growing global population have caused debate for ages (World Bank Land and Water Development Division 2011; Ebrahimi et al. 2020a, 2020b). Thus, the drainage and salinity problems must be addressed by better management of irrigation water. Some solutions in this field are to control groundwater levels and reduce subsurface drainage, to increase crop water use of shallow groundwater without yield reductions, and to reuse drainage water for irrigation (Hanson & Ayars 2002).

Salinity refers to the presence of dissolved inorganic solutes in aqueous samples, such as Na+, Ca2+, Mg2+, and K+ for the cations and Cl, , and for the anions. Salinity concentrations have direct effects on plants and soil physical properties. Excess salinity within the root zone reduces plant growth rate because it increases the energy that the plant must expend to acquire water from the soil by depressing external water potential and it also causes ion toxicity and nutrient imbalance (Bernstein 1975). Soil salinity reduces the agricultural potential of arid and semi-arid irrigated lands and so affects crop productivity and sustainability of irrigated agriculture worldwide (Corwin et al. 2007; Kahlon et al. 2013; Cao et al. 2023). The amount of leached water depends on the initial soil salinity level, applied water technique, and soil type. Suitable water for irrigation is ordinarily proper for reclamation. Therefore, it is crucial to have reliable estimates of the required amount of leached water needed to reduce soil salinity/sodicity to a desirable level (Mamoun et al. 2012). To overcome the soil salinity problems, some researchers recommended such methods as mixing agricultural drainage water with high-quality irrigation water, plant breeding (selection of salt-tolerant cultivars), and alternating high-quality irrigation water with saline water (Yurtseven et al. 2005). Initial soil salinity, desired salinity after leaching, depth of leaching salts, and physicochemical characteristics of soils are the main issues determining the amount of nutrients leached from the water (Abrol et al. 1988). Depth of leaching also plays a vital role in desalinization and desodification. The suitable depth for leaching depends on the initial salinity, soil texture, and plant species (Corwin et al. 2007). The physical and chemical properties of soil are the main factors determining the required amount of water for leaching. The leaching curves are used to detect how much water is needed for salt leaching and reaching the balance level of salinity (Pazira & Homaee 2010). Both farming communities and research studies have contributed to the existing body of information on saline water application. Kiani & Asadi (2008) in the Golestan province of Iran showed that irrigation with saline water (electrical conductivity (EC) = 14 dS m−1) reduced wheat grain yield by only 10% compared to irrigation with non-saline water.

In arid and semi-arid areas, due to lack of leaching, the concentrations of carbonates, gypsum, and soluble salts are usually high (Narimani & Manafi 2013; Naorem et al. 2023). This accumulation forms various soil types, such as calcareous, gypsum, saline, sodic, and saline–sodic soils. As a result, salinization commonly occurs in arid and semi-arid regions, and it is a severe problem for agricultural development management and sustainable use of soil and water resources (Valipoor et al. 2008; Hussain et al. 2019). Saline soils consist of soils in which the EC of soil saturated extract (ECe) is more than 4 dS m−1 at 25°C, the exchangeable sodium percentage (ESP) is less than 15, and under normal conditions, its acidity (pH) is less than 8.5 (US Salinity Laboratory Staff 1954). More than 6% of the world's soils, about 800 million ha, are affected by salinity and alkalinity (Munns & Tester 2008). Dajic (2006) stated that the area of saline and sodic soils worldwide is 397 and 434 million ha, respectively. In 1951, initial investigations were carried out in the form of a soil fertility project by the Institute of Soil Science of Iran, in collaboration with the World Food Organization (FAO 1973). The specific climatic conditions of Iran have led to the formation and extension of many saline soils with uneven distribution in most parts of this land; such soils are often dispersed in arid and semi-arid regions and generally have poor drainage or develop under such conditions (Dewan & Famuri 1964; Lees & Falcon 1952). It should be noted that a 23.5 million ha area of Iran, equal to 14.2%, has encountered different degrees of salinity, alkalinity, and water logging issues, and it is equivalent to 30% of the low plateau area and plains in Iran (Dewan & Famuri 1964).

Soil improvement is a method for controlling and removing harmful salts from the root zone to increase production and reduce runoff losses (Hogarth 2015; Mohanty et al. 2015). Improvement of saline soils involves extracting excess salts, particularly the disposal of sodium exchangeable to reach the desired amount (Mahday 2011). Lado et al. (2012) and Levy et al. (2014) mentioned that reusing low-quality and degraded water could be highly beneficial in agriculture. Additionally, Gupta & Khan (2009) stated that wastewater could be used to treat saline soils, and Sastre-Conde et al. (2015) used sewage sludge to recover saline soil in Mexico. Various methods are available for leaching salinity soil, such as accumulation of water on the farm surface (Cote et al. 2000), web-based (Shahrokhnia & Wu 2021) and use of water resources, and saline soil (Ghafoor et al. 2012). Disproportionate leaching not only wastes tons of water but also tends to remove essential nutrients and impedes aeration by waterlogging the soil (Hillel 2003). Nutrients such as nitrogen and phosphorous that are leached out to the ground water can contaminate surface waters from runoff by causing eutrophication (Carpenter et al. 1998). Thus, the application of excessive water during leaching can be detrimental for the environment and crop production, making it imperative to assess the optimum quantity of water that must be applied for leaching purposes. Soluble salts have substantial effects on plant growth, and exchangeable sodium affects the aggregates stability and causes toxicity in plants. Saline soils that are geographically expanding should be considered as both saline and sodic soils. This research was performed to study problems regarding the widespread extent of saline and sodic soils and the salty water table located at the depth of 90 to 120 cm in the Dosalagh plain in Ahwaz (Khuzestan province). To perform this study, an underground drainage system was installed on this land. Also, the purpose of this study is to investigate the effect of different treatments of water depths and EC on the sodium leaching process in saline soil.

Study area

The study area is located in the Dosalagh plain in the Khuzestan province in southwestern Iran. This plain is situated between 47°, 57′ to 48°, 14′ east longitude and 31°, 57′ to 32°, 13′ north latitude with an area of 5,450 ha (Figure 1).
Figure 1

Location of the Dosalagh plain in the Khuzestan province of Iran.

Figure 1

Location of the Dosalagh plain in the Khuzestan province of Iran.

Close modal

The average elevation of the region from sea level is 111 m. The highest point in the Abu-Salibi-Khat hills is about 165 m, while the lowest elevation is the outlet of the Karkheh river terraces. The current sediments include alluvial deposits and slope wash, cone deposits, and plain deposits (southeast). The region has a semi-arid desert climate, and the average annual rainfall over the 30-year period is 275 mm.

Treatment

The study employed a double-ring design by applying a combination of four different water qualities: 2.12 dS m−1 (freshwater that arises from the Karun River, M1 treatment), 7 dS m−1 (mixture of drainage water and the Karun River water, M2 treatment), 25 dS m−1 (mixture of drainage water and the Karun River water, M3 treatment), and 40 dS m−1 (drainage water, M4 treatment). The drainage water used in this study was obtained from the existing drainage systems in the region. Each water treatment quality included four different water depths: 0, 25, 50, and 75 cm. An intermittent leaching method (the total of 75 cm water was utilized in three 25 cm applications every 2 days) was implemented. The leaching experiment was carried out using a triangle layout in three repetitions. In order to prevent the evaporation of water, rings were covered with plastic sheets. This research was performed in 12 stations by digging and sampling soil profiles and using the intermittent leaching method. Then, Hordeum vulgare (barley) was cultivated in different treatments, and the effect of salinity changes on its growth was examined.

Physical and chemical properties of soil and water

Soil samples were obtained from four depths of 0–25, 25–50, 50–75, and 75–100 cm to investigate the soil's salinity variation after leaching. Different chemical and physical characteristics of water and soil samples before and after leaching are analyzed in Tables 1 and 2, respectively. Physical and chemical properties of soils then were measured, such as soil texture by the Bouyoucos hydrometric method (Gee & Bauder 1986), pH of soil and water using a saturation paste (McLean 1982), EC of soil and water using a saturation extract (US Salinity Laboratory Staff 1954), and calcium and magnesium cations of soil and water by titration with EDTA1 0.02 N (equipment needed: Burette, 20 mL pipette, 250 mL conical flasks, 100 mL volumetric cylinder) (Gupta 2007). Sodium of soil and water was determined by a flame photometer (Gupta 2007), chloride of soil and water was measured by titration with silver nitrate (Gupta 2007), calcium carbonate equivalent of soil was determined by neutralization with chloride acid (Spark 1996), and sodium adsorption ratio (SAR) was calculated (Equation (1)).
formula
(1)
Table 1

Results of water quality analysis

TreatmentEC (dS m−1)pHMg2+ (mEq L−1)Ca2+ (mEq L−1)Na+ (mEq L−1)Cl (mEq L−1) (mEq L−1) (mEq L−1)SAR (mEq L−1)Water Classa
M1 2.12 8.1 7.2 16.0 16.1 1.6 7.1 C3S1 
M2 7.7 73 13.5 62.5 48 33 9.5 C4S1 
M3 25 7.17 25 31 278.4 208 12 52.6 C4S4 
M4 40 8.23 44 35 410.2 344 16 65.3 C4S4 
TreatmentEC (dS m−1)pHMg2+ (mEq L−1)Ca2+ (mEq L−1)Na+ (mEq L−1)Cl (mEq L−1) (mEq L−1) (mEq L−1)SAR (mEq L−1)Water Classa
M1 2.12 8.1 7.2 16.0 16.1 1.6 7.1 C3S1 
M2 7.7 73 13.5 62.5 48 33 9.5 C4S1 
M3 25 7.17 25 31 278.4 208 12 52.6 C4S4 
M4 40 8.23 44 35 410.2 344 16 65.3 C4S4 

aC3:0.75 < EC < 2.25, C4: EC > 2.25, S1: SAR < 10, S4: SAR > 26.

Table 2

Some of the physical and chemical characteristic of soils before leaching

ParameterSoil depth (cm)
0–2525–5050–7575–100100–150
Clay (%) 11 10 10 11 
Sand (%) 57 38 30 28 29 
Silt (%) 34 51 60 62 60 
Texture Sandy loam Silt loam Silt loam Silt loam Silt loam 
pH 7.66 7.69 7.82 7.73 7.62 
EC (dS m−1117.7 69.1 76.2 88.3 83.9 
Na (mEq L−11,415.9 725.7 782.0 894.5 856.0 
Cl (mEq L−11,536 732 884 1,080 980 
HCO3 (mEq L−13.5 
Ca (mEq L−165 58 54 59 55 
CaSO4 (%) 25.5 13.2 14 16.5 23 
Mg (mEq L−1120.5 65 80.5 108 111.5 
SAR (mEq L−1147.0 92.5 95.4 97.9 93.8 
ParameterSoil depth (cm)
0–2525–5050–7575–100100–150
Clay (%) 11 10 10 11 
Sand (%) 57 38 30 28 29 
Silt (%) 34 51 60 62 60 
Texture Sandy loam Silt loam Silt loam Silt loam Silt loam 
pH 7.66 7.69 7.82 7.73 7.62 
EC (dS m−1117.7 69.1 76.2 88.3 83.9 
Na (mEq L−11,415.9 725.7 782.0 894.5 856.0 
Cl (mEq L−11,536 732 884 1,080 980 
HCO3 (mEq L−13.5 
Ca (mEq L−165 58 54 59 55 
CaSO4 (%) 25.5 13.2 14 16.5 23 
Mg (mEq L−1120.5 65 80.5 108 111.5 
SAR (mEq L−1147.0 92.5 95.4 97.9 93.8 

After drawing desalinization and desodification curves and determining the appropriate equation for each treatment, the necessary amount of water for initial leaching of 25 and 50 cm of soil was calculated to cultivate barley (H. vulgare) with high efficiency. The water quality results were classified as C3S1, C4S1, and C4S4, with problems of high to very high salinity and slight to very high sodicity (US Salinity Laboratory Staff 1954). Since the amount of salinity was more than 4 dS m−1 in the soil profile, the ESP and SAR of soil were more than 15 and 13, respectively; therefore, these soils were classified as saline–sodic. Then the laboratory and field results were evaluated according to soil taxonomy. These soils were classified as Coarse Loamy, Mixed, Hyperthermic, and GypsicAquisalids, which means soils with aridic soil moisture regime (soils in arid regions) have a salic and gypsic or petrogypsic horizon within 100 cm of the soil surface. Soils were saturated with water in one or more layers within 100 cm of the mineral soil surface for one month or more in normal years, and the mean annual soil temperature was 22°C or higher.

Desalinization and desodification curves

Based on Table 2 and using the EC figures of saturated soil extract and ESP calculated through the experimental relationship, the weighted average of ECe and ESP was calculated for different layers. It is possible that all the water used will not be used to wash the dissolved salts from the soil profile and some of it will be used to compensate for the lack of soil moisture; in this case even the use of large amounts of washing water will not lead to the creation of a chemical balance between the soil and the washing water. This means that the equilibrium EC of soil is slightly higher than the EC of irrigation water. For this purpose, in this research, the value of equilibrium EC was obtained as 1.15 times the salinity of irrigation water. Based on the values of ECe, ESP, ECeq, and ESPeq, different layers are defined as the following equations:
formula
(2)
formula
(3)
which ECi and ECf are, respectively, the electrical conductivity of saturated soil extract, before and after leaching (dS m−1), ECeq is the electrical conductivity of saturated soil extract at equilibrium (dS m−1), ESPi and ESPf are, respectively, the percentage of pre-exchanged sodium and after washing, ESPeq is the exchangeable sodium percentage in equilibrium, Dw is the depth of washing water (cm), and Ds is the depth of the soil layer (cm). Decreasing the value of ECeq and ESPeq from the numerator and denominator of the fractions of Equations (1) and (2) makes the results independent of the effects of external factors such as the amount of evaporation, the internal drainage conditions of the soil, the quality of the washing water, and the conditions of the experiment. In fact, with this work, the function becomes an implicit function from an explicit state. After obtaining all the figures of washing tests, the necessary analyses were performed using Excel software.

Fitting model

Datafit 9 software was used to fit various models of the irrigation curve. To achieve this goal, the outlier data were first evaluated. Then, the data were normalized and standardized, and finally, regression relationships were obtained.

Statistical

The statistical calculations were performed via SAS 9.4 software, and the charts were drawn by Excel 2013.

The results of the variance analysis (Table 3) showed the effect of changes in the volume of water, water type, and depth. According to Table 3, EC is affected by all the applied changes. However, acidity changed only at different depths, and the interaction effect of water depth and type, the amount of sodium, SAR, calcium, magnesium, chloride, and EC were affected by all changes.

Table 3

Variance analysis of studied characteristics as affected by changes in leaching conditions

Sources of variationdfMean square error
ECpHCa + MgNaClSAR
Water depth 3,144** 0.106ns 6,916** 104,364** 125,011** 1,221** 
Water type 4,221** 0.008ns 27,154** 136,151** 30,996** 318** 
Depth 12,083** 0.200** 33,633** 414,708** 1,285,064** 1,490** 
Depth × Type 384** 0.036** 1,078** 84,182** 72,478** 1,484** 
Error 50 11.12 0.003 37.77 666 427.37 36.29 
Coefficient of variation (%) – 5.61 0.78 5.46 4.41 3.44 7.82 
Sources of variationdfMean square error
ECpHCa + MgNaClSAR
Water depth 3,144** 0.106ns 6,916** 104,364** 125,011** 1,221** 
Water type 4,221** 0.008ns 27,154** 136,151** 30,996** 318** 
Depth 12,083** 0.200** 33,633** 414,708** 1,285,064** 1,490** 
Depth × Type 384** 0.036** 1,078** 84,182** 72,478** 1,484** 
Error 50 11.12 0.003 37.77 666 427.37 36.29 
Coefficient of variation (%) – 5.61 0.78 5.46 4.41 3.44 7.82 

**significant at 1%, ns not significant.

Electrical conductivity

Figure 2(a) represents the mean interactions between water depth and water type on the soil EC changes. In general, the results showed that water treatment with a higher depth of water and lower EC performed better than draining water, but using drainage water caused reduced soil EC values. EC is related directly to the sum of the anions and cations. Therefore, it is an appropriate indicator for identifying the total amount of salts in irrigation water and soil saturation extract (Alizadeh et al. 2001).
Figure 2

Mean comparison of (a) EC and (b) pH in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Figure 2

Mean comparison of (a) EC and (b) pH in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Close modal

The entry of calcium, magnesium, and other salts present in irrigation water into the soil increases the cation exchange capacity of the soil. As a result, exchangeable sites are saturated with calcium, magnesium, and potassium, preventing sodium from entering the soil exchange complex. In this situation, sodium increases in the solution phase, and ultimately, the soil's EC level decreases. The results obtained from this study are consistent with the study conducted by Jalali & Ranjbar (2009). Hao & Chang (2003) stated that changes in soil EC are affected by water flow in the soil profile. Rezayi-Sadr (2008) conducted leaching experiments using water from the mixing of the Karun River and drainage water (EC of 9.6 dS m−1) at Salman Farsi Culture & Industry in south Khuzestan. Results showed that after applying 25 cm of leaching water in three rounds (75 cm total), 88% of salts were removed from the root depth of the Karun River water, whereas only 81% of salts were removed from the root depth of the Karun River and drainage water mixture. Kameli et al. (2017) began to leach saline and sodic soils using sewage from sugar factories in Khuzestan. These researchers stated that using this sewage, which contained a large amount of organic matter, improved the quality of soil so that EC values decreased by 90% and sodium values declined anywhere from 30 to 71%. Organic matter contributes to the soil structure and improves soil porosity to leach elements (Becher et al. 2023; Garbowski et al. 2023). On the other hand, organic matter has positive and negative charges that can absorb many cations and anions, reducing their solubility in the solution phase and helping regulate the EC of the soil (Bansal & Kapoor 2000; Fennell et al. 2023; Liang et al. 2023).

Acidity

Figure 2(b) shows that the acidity changed due to the interaction of water depth and water type. Generally, the effect of depth and water type significantly changed compared with the blank sample, and the lowest acidity value was obtained in treatments with 25 cm of water by medium EC.

The significant changes in pH in this experiment are consistent with the results of Rezapour (2014). This phenomenon is due to the buffering capacity of the soil. In other words, the soil shows considerable resistance to changes in pH, which is called the soil buffering capacity. This resistance is due to the balance between active acidity and reserve acidity, which, in the case of soil pH reduction with the use of acidic materials such as sulfuric acid, releases alkaline agents stored in the soil such as lime from soil colloids. In sudden changes in soil pH, the soil resists and moderates the effects of soil acidification.

Calcium and magnesium

Figure 3(a) represents the interaction between depth and type of water on calcium and magnesium contents. As the figure shows, the highest amount of extracted calcium and magnesium from the soil is related to the conditions where water EC and the amount of water were high (D4M2 and D4M4).
Figure 3

Mean comparison of (a) Ca + Mg and (b) Cl in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Figure 3

Mean comparison of (a) Ca + Mg and (b) Cl in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Close modal

The accumulation of calcium and magnesium in the upper layer of the soil due to the cation exchange process reduces the amount of sodium. In the final stages of irrigation, the output of calcium and magnesium in the soil decreases. It seems that in soils, when an ion is washed out, the vacant site is usually occupied by another ion, which is why soil has the ability to recover. Therefore, it is justifiable that if the calcium and magnesium ions present in the water have replaced another ion (sodium) washed out of the soil, then their amount has also increased in the soil. It seems that with the continuation of irrigation, the amount of soil salts decreases, soil alkalinity decreases, and as a result, pH decreases and the pressure of carbon dioxide gas increases in the soil, increasing the solubility of gypsum and other sources containing calcium in the soil. Calcium and magnesium had a positive effect on the physical properties of the soil, but high concentrations of sodium chloride or sodium sulfate had a negative effect (FAO, UNESCO 1973). El-Boraie (1997) stated that by enhancement of irrigation water salinity level, sodium, magnesium, and calcium cations increased in soil solution while potassium values of soil solution decreased with increasing irrigation water salinity, so the amount of irrigated water used also had different effects on salinity levels.

Chloride

Figure 3(b) shows how the interaction of water depth and type affects the amount of chloride in the soil profile. The comparison of mean treatments showed that different treatments significantly changed the amount of chloride in the soil. The lowest amount (359 mEq L−1 was obtained from a treatment with higher water depth and medium EC (D4M2). Additionally, Figure 3(b) shows that there was no significant difference in treatments with 25 and 50 cm water depths and EC of 7 and 25 dS m−1. Chloride anion does not easily form a complex with soil particles and shows little tendency to be adsorbed to soil particles. The movement of chlorine in the soil is therefore largely determined by the flow of water (White & Broadley 2001).

Sodium

Figure 4(a) shows the interaction of mean comparison between water depth and water type on sodium variations. Ultimately, using different treatments improved soil conditions and decreased sodium significantly. The lowest amount of soil sodium was 341 mEq L−1 and was related to the treatment with the highest water depth (75 cm) and maximum EC (40 dS m−1). As shown in Figure 4(a), the highest amount of sodium was removed in the water treatment with the greatest depth and maximum EC; the interaction of these two parameters also indicates the same trend. Singh et al. (1980) concluded that using wastewater for leaching caused a decrease in pH, EC, and ESP in soil; their results showed that wastewater reduced ESP from 100 to 2%. Jalali et al. (2008) also stated similar results about the leaching of sodium. By increasing the water depth in leaching, the amount of sodium and EC decreases (Shaygan et al. 2017). Jalali & Ranjbar (2009) found that in the leaching process, sodium increased in the soluble phase; eventually, it was removed from the soil. Chaudhari (2001) and Quirk & Schofield (1955) said that by enhancing electrolyte concentration, the sodium leaching amount would increase.
Figure 4

Mean comparison of (a) Na and (b) SAR in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Figure 4

Mean comparison of (a) Na and (b) SAR in interaction of water depth and type. Means with common letters have no significant difference according to Duncan's multiple range test (p < 0.05) D1, water depth of 0–25 cm; D2, depth of 25–50 cm; D3, depth of 50–75 cm; D4, depth of 75–100 cm. M1, EC = 2.12 dS m−1; M2, EC = 7 dS m−1; M3, EC = 25 dS m−1; M4, EC = 40 dS m−1.

Close modal

Sodium adsorption ratio

Figure 4(b) indicates the mean comparison interaction of depth and type of water on SAR changes. Results revealed that the lowest amount of SAR occurred under conditions where the depth of water was high, and water had medium or high EC. Using water with high depth and moderate EC had a more significant impact than other treatments. Increasing sodium concentration disperses soil and increasing salinity flocculates soil (Hanson et al. 1999). The relationship between soil salinity and its flocculating effects and soil ESP and its dispersive effects dictate whether a soil will stay aggregated or become dispersed under various salinity and sodicity combinations (Nikos et al. 2002). Thus, the bulk solution salinity will have specific effects on soil physical and chemical properties.

Leaching of saline and alkaline soils using a stepwise dilution of saline water containing two capacity cations is an effective method to modify soils without consuming amendatory materials. At first, saline water flocculates soil particles and provides calcium to exchange with sodium (Gupta et al. 2019; Adeymo et al. 2022). It has also been reported that the leaching of saline and alkaline soils with low salinity water may disperse soil particles and limit the leaching process. For amending these soils, if the EC of leaching water is less than 2 dS m−1, it destroys the soil's physical structure and reduces or ceases the leaching efficiency (Naseri 1998). Gharaibeh et al. (2014) leached saline soils using water of medium quality, and their results showed that consumption of this kind of water also has the potential to diminish salinity. Unless soil properties are improper or soil texture is heavy, desalinization is easy; a large amount of high-quality water is enough to remove salts from the soil profile. Amending saline soil is not a complex process because using the necessary amount of good quality water can remove excess salts from the soil profile, unless the drainage properties of soil are poor or soil texture is heavy or very heavy. Accordingly, the prerequisite for the success of the amendatory programs and leaching of saline, alkaline, and both saline and alkaline soils depends on suitable drainage conditions of soils. If these conditions are not naturally provided, inevitably they must be artificially created (Pazira 1997; Rajabzadeh et al. 2009). Raj & Nath (1980) showed that applying one pore volume caused the leaching of 80% salinity from sandy soil. They reported that the high amount of salts removed caused the soil's light texture in that study area.

Leaching curves

Leaching curves are valuable tools to determine the efficiency of amendments and the depth of water needed for successful reclamation and are used to describe the relationship between soil salinity (desalinization) or sodicity (desodification) and the depth of leached water. Leaching curves (desalinization curves) are constructed by plotting relative changes in soil salinity ordinate and Dw/Ds on the abscissa (Figure 5).
Figure 5

(a) Desalinization and (b) desodification curves of soil salinity in various treatments. ECi and ECf are, respectively, electrical conductivity of soil saturated extract, before and after leaching (dS m−1), ECeq is the electrical conductivity of saturated soil extract in equilibrium (dS m−1), ESPi and ESPf are, respectively, the percentage of exchangeable sodium before and after leaching, ESPeq is the exchangeable sodium percentage in equilibrium, Dw is the depth of the leaching water (cm), and Ds is the depth of the soil layer (cm).

Figure 5

(a) Desalinization and (b) desodification curves of soil salinity in various treatments. ECi and ECf are, respectively, electrical conductivity of soil saturated extract, before and after leaching (dS m−1), ECeq is the electrical conductivity of saturated soil extract in equilibrium (dS m−1), ESPi and ESPf are, respectively, the percentage of exchangeable sodium before and after leaching, ESPeq is the exchangeable sodium percentage in equilibrium, Dw is the depth of the leaching water (cm), and Ds is the depth of the soil layer (cm).

Close modal

Similarly, desodification curves were constructed by plotting relative changes in soil sodicity represented on the ordinate and Dw/Ds on the abscissa (Figure 5). A comparison of desalinization and desodification graphs (Figure 5) shows that by increasing Dw/Ds, ECe and ESP were reduced. Application of 0.4 Dw/Ds of drainage water reduced soil salinity to 30%, whereas application of 0.4 Dw/Ds in other treatments reduced soil salinity to at least 35%. Using 0.4 Dw/Ds of drainage water also reduced soil sodicity to 35%, whereas applying 0.4 Dw/Ds in other treatments reduced soil salinity to 50% and higher. It can clearly be seen that the amount of EC reduction was more than ESP reduction. Saline drainage water (M4 treatment, EC = 40 dS m−1) most likely caused an increase in soil infiltration by flocculating soil particles, so more salts were removed from the soil.

The results of the salinity leaching curve indicate a rapid salt leaching at the beginning of irrigation, which shows that the soil in the region has a high potential for improvement. As the amount of irrigation water increases, the amount of washed salts per unit of irrigation water should decrease. This may be due to the high solubility of salts in the soil solution, meaning that the first irrigation has a high efficiency in moving half of the soil salts towards the bottom. The remaining salts that are retained in the surface layers and finer pores of the soil or have lower solubility will be washed out more slowly.

Modeling

Table 4 determines the necessary amount of water and suitable equations for the initial leaching of 25 and 50 cm soil for tolerant crops, such as H. vulgare (barley). The required amount of leaching water for M1 and M2 treatments (EC = 2.14 and 7 dS m−1, respectively) was relatively the same, but for M3 treatment, the amount was significantly more. It can clearly be seen that increased efficiency likewise increased the amount of necessary water. It is necessary to mention that these values have been obtained using only one treatment through the experiment. For example, the required amount of water can be decreased by initially applying water that is poor quality (M3 or M4) and then using better quality water (M1 or M2).

Table 4

Necessary water estimated for initial leaching of 25 and 50 cm soil for H. vulgare

TreatmentCrop typeExpected efficiency of crop (%)EquationR225 cm50 cm
M1 Salt-tolerant crop H. vulgare 100 Y = −0.202Ln(x) + 0.1968 0.85 73.8 78.8 
90 67.6 70.8 
75 59.3 60.4 
50 47.8 46.6 
M2 100 Y = −0.172Ln(x) + 0.173 0.71 124.4 152.0 
90 111.0 131.2 
75 93.6 105.4 
50 70.6 73.8 
M3 100 Y = −0.099Ln(x) + 0.176 0.46 540.6 828.3 
90 439.8 629.9 
75 323.0 418.4 
50 193.4 212.9 
TreatmentCrop typeExpected efficiency of crop (%)EquationR225 cm50 cm
M1 Salt-tolerant crop H. vulgare 100 Y = −0.202Ln(x) + 0.1968 0.85 73.8 78.8 
90 67.6 70.8 
75 59.3 60.4 
50 47.8 46.6 
M2 100 Y = −0.172Ln(x) + 0.173 0.71 124.4 152.0 
90 111.0 131.2 
75 93.6 105.4 
50 70.6 73.8 
M3 100 Y = −0.099Ln(x) + 0.176 0.46 540.6 828.3 
90 439.8 629.9 
75 323.0 418.4 
50 193.4 212.9 

Correlation

Table 5 represents the correlation between various water and soil parameters. As can be seen in Table 5, there is a positive correlation between EC-W and Ca-W, Na-W, Cl-W, and SAR-W, but a negative correlation with SAR-S. The results indicate that there is a positive relationship between EC-W and EC-S, but this relationship was not significant. The correlation results show that pH-W had no significant correlation with any of the water and soil characteristics. SAR-S is significantly and positively correlated with EC-S, calcium, sodium, and soil chloride. The key point in Table 5 is the negative correlation between SAR of water and soil. The reason for this positive correlation can be attributed to the amount of irrigation, which causes the washing out of salts from the soil and consequently reduces SAR in the soil, which can be observed in Figure 4.

Table 5

Correlation between water and soil parameters

EC-WpH-WMg-WCa-WNa-WCl-WHCO3-WSAR-W
EC-          
pH-0.056          
Mg-0.139 −0.076         
Ca-0.969* −0.191 0.150        
Na-0.998** −0.002 0.110 0.981*       
Cl-0.999** 0.078 0.115 0.964* 0.997**      
HCO3-0.021 −0.187 0.988* 0.061 −0.002 −0.005     
SAR-0.979* −0.091 0.010 0.986* 0.990** 0.979* −0.089    
EC-S −0.304 0.599 −0.811 −0.442 −0.314 −0.273 −0.836 −0.286    
pH-S 0.605 −0.741 −0.025 0.778 0.654 0.592 −0.014 0.731    
Mg-S 0.086 0.701 −0.749 −0.084 0.070 0.117 −0.828 0.082    
Ca-S −0.504 0.777 −0.445 −0.684 −0.538 −0.478 −0.468 −0.567    
Na-S −0.446 0.541 −0.793 −0.568 −0.454 −0.418 −0.796 −0.423    
Cl-S −0.261 0.591 −0.828 −0.397 −0.269 −0.230 −0.857 −0.238    
HCO3-S −0.373 0.645 0.529 −0.529 −0.433 −0.373 0.500 −0.553    
SAR-S −0.962* 0.454 −0.780 −0.660 −0.565 −0.535 −0.761 −0.927*    
Clay 0.115 −0.343 0.963* 0.192 0.103 0.086 0.981* 0.033    
Sand −0.839 0.340 −0.526 −0.906 −0.846 −0.821 −0.465 −0.825    
Silt 0.862 −0.331 0.483 0.927 0.870 0.846 0.420 0.853    
EC-SpH-SMg-SCa-SNa-SCl-SHCO3-SSAR-SClaySandSilt
EC-S           
pH-S −0.362          
Mg-S 0.828 −0.481         
Ca-S 0.833 −0.374 0.490        
Na-S 0.986** −0.360 0.733 0.872       
Cl-S 0.998** −0.318 0.833 0.820 0.980**      
HCO3-S 0.065 −0.610 −0.060 0.517 0.112 0.028     
SAR-S 0.941* −0.284 0.597 0.886* 0.983** 0.933* .125    
Clay −0.829 −0.211 −0.526 −0.705 −0.830 −0.851 0.218 −0.844   
Sand 0.754 −0.341 0.298 0.872 0.851 0.731 0.339 0.921* −0.648  
Silt −0.728 0.371 −0.274 −0.860 −0.830 −0.703 −0.370 −0.902* 0.605 −0.999** 
EC-WpH-WMg-WCa-WNa-WCl-WHCO3-WSAR-W
EC-          
pH-0.056          
Mg-0.139 −0.076         
Ca-0.969* −0.191 0.150        
Na-0.998** −0.002 0.110 0.981*       
Cl-0.999** 0.078 0.115 0.964* 0.997**      
HCO3-0.021 −0.187 0.988* 0.061 −0.002 −0.005     
SAR-0.979* −0.091 0.010 0.986* 0.990** 0.979* −0.089    
EC-S −0.304 0.599 −0.811 −0.442 −0.314 −0.273 −0.836 −0.286    
pH-S 0.605 −0.741 −0.025 0.778 0.654 0.592 −0.014 0.731    
Mg-S 0.086 0.701 −0.749 −0.084 0.070 0.117 −0.828 0.082    
Ca-S −0.504 0.777 −0.445 −0.684 −0.538 −0.478 −0.468 −0.567    
Na-S −0.446 0.541 −0.793 −0.568 −0.454 −0.418 −0.796 −0.423    
Cl-S −0.261 0.591 −0.828 −0.397 −0.269 −0.230 −0.857 −0.238    
HCO3-S −0.373 0.645 0.529 −0.529 −0.433 −0.373 0.500 −0.553    
SAR-S −0.962* 0.454 −0.780 −0.660 −0.565 −0.535 −0.761 −0.927*    
Clay 0.115 −0.343 0.963* 0.192 0.103 0.086 0.981* 0.033    
Sand −0.839 0.340 −0.526 −0.906 −0.846 −0.821 −0.465 −0.825    
Silt 0.862 −0.331 0.483 0.927 0.870 0.846 0.420 0.853    
EC-SpH-SMg-SCa-SNa-SCl-SHCO3-SSAR-SClaySandSilt
EC-S           
pH-S −0.362          
Mg-S 0.828 −0.481         
Ca-S 0.833 −0.374 0.490        
Na-S 0.986** −0.360 0.733 0.872       
Cl-S 0.998** −0.318 0.833 0.820 0.980**      
HCO3-S 0.065 −0.610 −0.060 0.517 0.112 0.028     
SAR-S 0.941* −0.284 0.597 0.886* 0.983** 0.933* .125    
Clay −0.829 −0.211 −0.526 −0.705 −0.830 −0.851 0.218 −0.844   
Sand 0.754 −0.341 0.298 0.872 0.851 0.731 0.339 0.921* −0.648  
Silt −0.728 0.371 −0.274 −0.860 −0.830 −0.703 −0.370 −0.902* 0.605 −0.999** 

The W and S indices in the parameters indicate water and soil, respectively.

*Correlation is significant at the 0.05 level.

**Correlation is significant at the 0.01 level.

The results of this research showed that using drainage water was very helpful and significantly decreased the amount of sodium and chloride, but it should be noted that this method is used for soils with high salinity. It is suggested that initially, applying drainage water with a depth of 25 cm, which causes more infiltration, and then applying water with lower salinity leads to lower freshwater consumption and lower volume of drainage water production. Drainage water with a depth of 25 cm equals 2,500 m3 ha−1. In general, the results showed that the increase in water depth and EC causes a decrease in EC and SAR in the soil profile. This is due to the increase in leaching of Na and Cl from the soil. In addition, using the other treatments after using 25 cm drainage water would create more efficiency. Cultivating salt-resistance crops, including barley, and leaving mulch and barley stalks over the ground during the warm season to prevent evaporation and capillary rise of salt, is helpful. Leaching salt from barely (H. vulgare) cultivated lands can prepare the ground for the next cultivations of the moderately tolerant crop. Generally, the results of this study showed that the use of drainage water for the reclamation of saline and sodic soils in Khuzestan province and similar conditions in other regions is possible. Moreover, the use of high-quality water (such as river water) for soil washing in these areas can reduce water consumption.

By reusing drainage water for leaching, two objectives are achieved simultaneously: managing excess drainage water and enhancing the condition of problematic soils. This approach offers several benefits:

  • Water resource management: The reuse of drainage water helps in optimizing water usage by repurposing water that would otherwise be discarded as waste.

  • Soil improvement: Leaching using drainage water aids in reducing the concentration of salts and sodium ions within the soil profile, making it more suitable for agricultural activities.

  • Sustainable agriculture: The practice contributes to sustainable agricultural practices by transforming non-productive or marginally productive land into arable land.

  • Cost efficiency: Reusing drainage water for leaching can be cost-effective compared to using freshwater resources, particularly in areas where water is scarce.

  • Environmental considerations: Properly managed leaching with drainage water can prevent soil degradation and minimize the negative environmental impacts associated with saline and sodic soils.

  • Soil fertility: Improved soil conditions resulting from leaching can lead to increased nutrient availability and better root growth, enhancing overall crop yields.

However, it is important to note that while this approach offers benefits, it requires careful planning and management to prevent potential drawbacks such as over-leaching, which might lead to waterlogging or further soil degradation. Monitoring water quality, soil response, and overall land management practices are crucial to ensure the success of this method. Reusing drainage water for leaching saline and sodic soils is a practical and sustainable approach that addresses both water management and soil improvement challenges, ultimately contributing to more productive and fertile agricultural lands.

The authors wish to thank Behzad Sobhani and Siavash Tatlari as well as the irrigation and soil science Departments of MahabGhodss Consulting Engineering Company for helping with soil sampling and valuable comments, respectively.

1

Disodium dihydrogen–ethylenediaminetetraacetate.

The subject of plagiarism has been considered by the authors and this article is without problem.

Yes.

E.S., E.E. and A.A.H. conceived the presented idea. E.S., E.E., T.K. and A. Asilianmahabadi developed the theoretical framework. E.S., A.A.H. and A. Amirinejad developed the theory and performed the computations. E.E., A. Asilianmahabadi and A. Amirinejad verified the analytical methods. E.S. and E.E. carried out the experiments. All authors discussed the results and contributed to the final manuscript.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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