Boron adsorption–desorption characteristics of irrigated soils in the Jordan Valley

Geoderma Regional 2–3 (2014) 50–59

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Boron adsorption–desorption characteristics of irrigated soils in the Jordan Valley T.M. Abu-Sharar ⁎, N. Bani Hani, S. Al-Khader Department of Land, Water and Environment, The University of Jordan, Amman, Jordan

a r t i c l e

i n f o

Article history: Received 8 April 2014 Received in revised form 23 September 2014 Accepted 25 September 2014 Available online 30 September 2014 Keywords: Jordan Valley soils Pachic Haplustolls Fluventic Haplustolls Fluventic Haplustept Ustic Torrifluvents Typic Torrifluvents Boron solubility and soil salinity Boron adsorption and regeneration

a b s t r a c t Increasing replacement of fresh water by saline or reclaimed wastewater in the predominantly drip-irrigated Jordan Valley (JV) soils poses a threat of boron (B) accumulation in these soils. Twenty nine composite soil samples in each of the two layers, surface (0–25 cm) and subsurface (25–50 cm), were collected from sites located along the entire JV. The samples were analyzed for major chemical and physical properties. Water soluble B was determined in both hot water and saturated paste extracts. Boron adsorption was carried out from 50 molc/m3 NaCl/CaCl2 background electrolyte solutions of SAR 5, but of increasing B concentration (0.25– 4.00 μg/mL). These solutions were arranged to percolate duplicate columns of three soil samples representing Northern JV of Shuna (Fluventic Haplustolls), Middle JV of Deir-Alla (Fluventic Haplustepts) and Southern JV of Sweimeh (Typic Torrifluvents). Regeneration of B from soil columns was determined. First, duplicate soil columns were permeated with solutions of constant B concentration of 1.0, 1.5, 2.0 or 4.0 μg/mL. Following soil–liquid B equilibrium, the columns were incubated at room temperature for one week then permeated with the background solution of 0 μg B/mL. The permeation continued until three successive effluent fractions showed the same B concentration. The process of incubation/permeation was repeated two more times. The results showed that, with the exception of a few outlier values from the Southern end of the JV, B in saturated paste or hot water extracts wasn't linearly correlated with soil salinity of the surface and subsurface samples. The reason for that was argued to be due to the anthropogenic factor of intensive agriculture that generated high demand on B as contrasted by high rate of salt accumulation in surface soil layers caused by the use of conservative irrigation systems with increasingly poor quality water. The low B levels in most samples marked the JV soils to be marginal to deficient in that nutrient. Soluble B in paste or hot water extracts followed a 1:1 relation between either fraction in surface and subsurface layers. However, the hot water extractable B was almost 4 times the corresponding levels of paste extract for both surface and subsurface samples. This implied that crop uptake of B takes place mainly from the paste extract fraction. Adsorption of B onto the three soil samples conformed to the Langmuir adsorption isotherm. These soil samples exhibited a similar affinity constant for B (0.12–0.21 mL/μg), but their maximum adsorption capacity decreased in the southward direction geographically; being the highest for the Northern Shuna (39.7 μg B/g soil) and the lowest for the Sweimeh (8.7 μg B/g soil). The similarity of the Langmuir affinity constant reflected the similarity of clay mineralogy. In addition, the decreasing adsorption capacity was consistent with the decreasing clay content and CEC of these samples. The three soil samples showed a tendency for B regeneration while this tendency decreased with the advancement of incubation/leaching cycles. Almost half of the adsorbed B was leached from the Shuna-North soil columns as contrasted by half of that quantity for the other two samples. © 2014 Published by Elsevier B.V.

1. Introduction The Jordan Valley (JV) extends 110 km from Lake Tiberias in the north to the Dead Sea in the south. Soil formation is influenced by more than one parent material including recent alluvium occupying a narrow flood plain along the Jordan River and lacustrine (Lisan Marl) deposits overlaid by more than one layer of colluvial sediments ⁎ Corresponding author. E-mail address: [email protected] (T.M. Abu-Sharar).

http://dx.doi.org/10.1016/j.geodrs.2014.09.007 2352-0094/© 2014 Published by Elsevier B.V.

transported as colluvial fans along the Eastern Escarpment edges. The moisture regime is Ustic in the north (N 250 mm annual rainfall) and Aridic in the south. The temperature regime is Hyperthermic in the entire JV. Traditionally, the JV has been the principle fruit (mainly oranges and banana) and vegetable production basket of the country. A subtropical climate prevails in the JV with decreasing rainfall and increasing temperature in the southward direction. Such geographically-driven climate change evolved soils with decreasing pedogenic development in the same south ward direction. Further characterization of the JV soils can be found in Taimeh (in press).

T.M. Abu-Sharar et al. / Geoderma Regional 2–3 (2014) 50–59

Jordan is a very water-poor country with annual per capita share of fresh water not exceeding 145 m3 (Al-Bakri et al., 2013). This fresh water supply shortage is mitigated by the supplemental use of reclaimed municipal waste water of inferior quality. Subsequently, soils in the Northern and Middle JV have become partially irrigated with the reclaimed wastewater. In the South, saline well water is the major irrigation water resource. Boron adsorption onto soil solids is controlled by clay content (Alleoni and De Camargo, 2000; Keren and Bingham, 1985), adsorbent surface area, which is highly correlated with clay type (Hatcher et al., 1959; John et al., 1967), soil content of Fe and Al oxides and hydroxyoxides (Alleoni and De Camargo, 2000; Beyrouty et al., 1984; Goldberg and Glaubig, 1985; Hatcher et al., 1959; Keren and Gast, 1983; Keren and Taplaz, 1984; Sims and Bingham, 1968), and organic matter content, especially in soils with acid pH (Beyrouty et al., 1984; Goldberg and Suarez, 2012; Gupta, 1968; Marzadori et al., 1991; Yermiyaho et al., 1988). Boron adsorption was found to increase in the soil pH range between 7.0 and 9.0 (Chen et al., 2009; Goldberg et al., 2008; Gupta, 1968; Keren and Bingham, 1985; Keren and Gast, 1981; Keren et al., 1981; Sartaj and Fernandes, 2005; Sims and Bingham, 1968). In addition, Chen et al. (2009) pointed out that the increase in B adsorption was more pronounced when Ca(OH)2, as opposed to NaOH, was used for pH adjustment. Soil salinity also enhances B adsorption by promoting the formation of borate ions available for reaction (Couch and Grim, 1968; Goldberg et al., 2008; Keren and Bingham, 1985). Mahler (2007) indicated that soil texture, soil organic matter content, and soil moisture (annual precipitation, irrigation) are the three most important factors affecting boron availability in soils. Subsequently, coarse textured soils (sands, loamy sands, sandyloams) that are low in organic matter are often low in plant-available boron. As a result of the use of low quality irrigation water, JV soils may become subjected to accumulation of B. In this regard, Evans and Sparks (1983), Mass (1984) and Goldberg and Suarez (2011) reported a narrow soil solution concentration range (0.05–0.5 mg/L) separating Bnontoxicity from B-toxicity with respect to plant nutritional needs. In addition, excessive soil B leaching processes require more water than what is needed for salinity leaching processes. For example, Elrashidi and O'Connor (1982) reported two-stage boron desorption. The first stage of adsorption–desorption was completely reversible, but the second one acquired a hysteresis tendency. This phenomenon was not associated with any soil property except equilibrium between solid and soil solution-B; the higher the B concentration in the soil solution the larger was the deviation. The ability of reclaimed B-enriched soils to re-establish elevated solution levels was also observed by Peryea et al. (1985a, 1985b). These authors indicated a successively decreasing soil tendency for Bregeneration with continuous leaching. However, such a tendency increased when soil was allowed to air-dry before the next leaching. Because of the gradual intensity decrease of pedogenic factors (e.g. climate and biota) of soil formation and the decreasing agricultural intensity along the North to South direction, soils of the JV may represent a typical global example of how these factors could affect soil B availability. Accordingly, this research was initiated with the following objectives: i) evaluation of the B status in surface and subsurface soil samples collected along the entire length of the JV, ii) studying the capacity of selected soil samples with different pedogenic characteristics to adsorb B from percolating solutions of increasing B concentrations, and iii) evaluation of the tendency of the B adsorbing soils to release that element when leached with a B-free solution. 2. Materials and methods 2.1. Soil characteristics Composite soil samples representing both surface (0–25 cm) and subsurface (25–50 cm) layers were collected from 29 sites along the entire length of the JV (Fig. 1). Further data on crop and agroclimatic zones

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Fig. 1. Map of Jordan Valley showing the major soil sampling sites.

of the JV is found in Abu-Sharar and Battikhi (2002) and Abu-Sharar et al. (2007). Collection of the soil samples took into consideration spacing between two successive sites, extent of the site representation to the neighboring farms, the site pedology, crop type, and irrigation water quality. Since irrigation water quality and cropping pattern adhered to the variation in the JV agroclimatic zones, these two variables were the first to be considered when collecting the soil samples. In the Northern JV, sampling was focused on citrus orchards irrigated with fresh water from the King Abdulla Canal, while reclaimed waste water or fresh water mixed with reclaimed waste water irrigating greenhousevegetable crops was the focus in the Middle JV, e.g. high tech and protected agriculture. Saline ground water irrigating banana orchards represented most of the farms in the South JV. Moreover, there was no fixed spacing interval in this study since such a priori criterion would cause overlooking of some farms that had one or more of the above sampling characteristics. The collected samples were air dried and ground to pass through a 2 mm sieve. Selected chemical and physical properties of these samples were determined according to the standard soil analysis methods (Page, 1982). Soluble B in saturated paste extracts or hot water extracts was determined colorimetrically using the curcumine method of Page (1982).

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Table 1 Salinity of the saturated paste extract (ECe) and boron concentration in these extracts and in hot water extracta for surface and subsurface Jordan Valley soil samples.b Site

Saturation %

Paste extract

Hot water extract

ECe

μg B/mL

1 — 4.0 km to the north of North Shuna 2 — Shuna North 3 — Al-Munsheyeh 4 — 1.5 km to the north of Waq'qas 5 — Waq'qas 6 — Al-Sheikh Hussein 7 — 1.5 km north of Al-Zumaleyeh 8 — Al-Zumaleyeh 9 — Al-Mashare'e 10 — WadiYabis 11 — Abu-Habeel 12 — Al-Qirin 13 — Abu-Seedo 14 — Kraimeh 15 — Balawneh 16 — Abu-Aubeida 17 — Dhirar 18 — Deir-Alla 19 — 1.0 km north of Sawalha 20 — Ardha 21 — 0.7 km south of Ardha 22 — 4.0 km north of Karama 23 — 2.0 km north of Karama 24 — 1.0 km north of Karama 25 — Karama 26 — 1.0 km south of Karama 27 — 3.0 km south of Karama 28 — Shuna South 29 — Sweimeh a b

dS/m

Surface

Subsur.

Surface

Subsur.

Surface

Subsur.

Surface

Subsur.

53.3 57.1 49.0 51.3 37.4 38.8 45.1 41.5 51.1 54.5 39.3 44.6 42.7 42.3 39.3 34.4 47.3 25.2 36.4 31.4 30.5 25.6 27.2 26.7 34.6 41.3 37.1 34.1 26.5

54.5 56.0 51.4 53.2 35.2 39.6 48.0 43.6 49.6 54.0 38.6 48.2 40.6 44.6 28.2 36.8 44.8 25.0 33.0 29.6 33.6 23.4 29.6 25.5 36.8 39.6 39.6 32.5 28.6

0.05 0.06 0.05 0.07 0.05 0.09 0.13 0.16 0.36 0.67 0.24 0.13 0.16 0.27 0.34 0.27 0.60 0.30 0.23 0.34 0.36 0.20 0.39 0.28 2.97 0.70 0.21 0.34 2.50

0.05 0.05 0.05 0.06 0.06 0.08 0.15 0.19 0.32 0.69 0.25 0.18 0.19 0.25 0.32 0.32 0.56 0.28 0.18 0.28 0.39 0.18 0.42 0.31 3.16 0.65 0.26 0.38 2.41

0.45 0.37 0.32 0.36 0.33 0.36 0.40 0.38 0.38 1.09 0.40 0.36 0.47 0.55 0.51 0.51 0.53 0.51 0.64 0.56 0.55 0.53 0.59 0.65 2.04 1.21 0.71 0.51 2.17

0.39 0.35 0.31 0.37 0.34 0.33 0.41 0.41 0.35 1.06 0.42 0.43 0.44 0.52 0.54 0.63 0.58 0.49 0.53 0.47 0.51 0.48 0.63 0.69 2.16 1.12 0.81 0.48 1.99

1.14 0.42 0.76 0.85 1.00 1.12 0.92 0.85 1.16 1.08 1.52 1.21 0.82 1.21 1.55 0.98 1.24 2.42 1.32 1.06 1.48 2.52 2.45 1.92 3.35 2.00 12.80 2.50 7.52

1.35 0.73 0.79 1.33 0.62 0.96 0.62 0.59 2.15 0.75 0.80 1.26 0.87 1.00 1.18 0.81 0.84 0.95 0.93 0.85 1.14 1.22 1.47 1.25 1.96 1.40 11.80 1.46 33.10

Filtrate of 20 g soil sample suspended in 40 mL 0.1 M CaCl2. Soil classification 1: Pachic Haplustolls, 2: Fluventic Haplustolls, 3–19: Fluventic Haplustept, 20–21: Ustic Torrifluvents and 22–29: Typic Torrifluvents.

2.2. Boron adsorption Glass cylinders with 5.0 cm internal diameter were filled with duplicate surface soil samples to a depth of 15 cm at bulk density of 1.25 Mg/m3. The samples represented soils of contrasting chemical

and physical properties (Northern JV of Shuna: Fluventic Haplustolls, Middle JV of Deir-Alla: Fluventic Haplustepts and Southern JV of Sweimeh: Typic Torrifluvents). A thin sand filter layer (1.0 cm) was placed in the bottom of each cylinder to prevent migration of soil particles and potential clogging of the draining tubes. A filter paper disc was

3.5

3.0

Subsurface Soil Sample

Saturated Paste: 2.5

Y =1.0176X (R² = 0.9948)

2.0

1.5

1.0

Hot Water: Y =0.9712X +0.0114(R² = 0.9784)

0.5

0.0 0.0

0.5

1.0

1.5 2.0 Surface Soil Sample

2.5

3.0

3.5

Fig. 2. Relation between B concentration (μg/mL) in extracts of saturated paste (▲) and hot water (•) of surface and subsurface soil samples collected from 29 sites along the Jordan Valley.

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25.0 Subsurface Soil: Y = 3.7292X + 0.6574 (R² = 0.9728)

Hot Water Extract

20.0

15.0

10.0 Surface Soil: Y = 3.6883X + 0.658 (R² = 0.971)

5.0

0.0 0.0

1.0

2.0

3.0 4.0 5.0 Saturated Paste Extract

6.0

7.0

Fig. 3. Relation between B concentration (μg/mL) in extracts of saturated paste and hot water for surface (▲) and subsurface (•) soil samples collected from sites along the entire Jordan Valley.

also placed on the surface of each soil column to prevent disturbance of soil aggregates when successively replacing one solution by another. Each soil column was vertically placed on the top of a fraction collector tray in such a way to facilitate collection of the permeating solution in the test tubes placed in the holes of the tray. The fraction collector was adjusted to move one position after siphoning an 80 mL leachate volume. Boron concentration in each leachate fraction was then determined. The soil columns were first saturated by capillary rise of a blank solution having 0 μg B/mL and 50 molc/m3 NaCl/CaCl2 total electrolyte concentration of SAR 5. The solution was then placed in a Marriott bottle device adjusted in such a way to provide a constant water head of 5 cm above the surface of each soil column. Permeation

Table 2 Selected physical and chemical properties of the three JV soila samples employed in the B retention study. Soil Parameter

pH Carbonate % Organic matter % CEC (cmol(+)/kg) SO4 (mmolc/L) Cl (mmolc/L) HCO3 (mmolc/L) CO3 (mmolc/L) Na (mmolc/L) Mg (mmolc/L) Ca (mmolc/L) K (mmolc/L) Sand % Silt % Clay % Texture a

Shuna-North

Deir-Alla

Sweimeh

Surface

Subsur.

Surface

Subsur.

Surface

Subsur.

8.4 57.1 1.9 31.3 0.7 1.0 2.7 0.0 0.8 1.3 2.7 0.2 17.9 36.1 46.0 Clay

8.2 56.0 1.3 29.6 0.8 3.6 3.0 0.0 0.9 1.7 4.7 0.2 18.4 33.6 48.0 Clay

8.4 28.2 1.3 15.6 14.9 5.8 5.0 0.0 3.5 8.0 13.0 1.0 30.6 29.9 29.5 Clay loam

8.5 27.0 0.8 16.2 1.3 5.0 3.8 0.0 0.8 3.0 6.0 0.7 19.1 44.4 36.5 Loam

8.1 28.2 0.1 8.3 5.9 68.0 1.2 0.6 29.4 15.2 26.0 4.6 50.5 35.5 14.0 Loam

7.7 26.2 0.1 7.9 71.6 256.0 1.6 1.0 126.3 52.0 136.0 8.2 48.0 34.0 18.0 Loam

Dominant clay minerals are mica followed by kaolinite. Only small amounts of montmorillonite can be detected in the northern section of the JV.

of the blank solution continued until steady state hydraulic conductivity (HC) was achieved. The selection of SAR 5 and 50 molc/m3 solution was aimed at maintaining stability of soil structure according to Abu-Sharar (1988) and eliminating the effect of background solution on B adsorption. In this regard, Majidi et al. (2010) showed that increasing electrolyte concentration (0.01 M NaCl) to 0.1 and 0.5 M increased B adsorption maximum by 30% and 75%, respectively. Moreover, at the equi-molar concentration, CaCl2 increased B adsorption more than NaCl. The positive effect of ionic strength was attributed to a better screening of surface charges and compaction of double layer thickness. Soil columns were then successively permeated with electrolyte solutions of the same SAR and total electrolyte concentration, but of increasing B concentration of 0.25, 0.50, 0.75, 1.00, 1.50, 2.00, and 4.00 μg/mL. The permeation of each solution was similar to the permeation of the blank solution, but the criterion for the replacement of one solution by its successor was the achievement of steady state B concentration in the leachate fractions as evidenced by constant B concentration in three successive effluents. Boron retention onto each soil column was calculated according to the following equation: Boron Retentionðμg=g soilÞ h

i ¼ Vps  Cps −ΣðVds  Cds Þ− Vfc  Cps =oven dry mass of soil:

Table 3 Volumes (mL/g soil) of percolating solutions required to reach B-steady state equilibrium with soil columns. Soil

Shuna-North Deir-Alla Sweimeh

Boron concentration in the permeating solution (μg B/mL) 0.25

0.50

0.75

1.00

1.50

2.00

4.00

15.49 9.58 4.23

12.39 5.47 3.06

6.42 5.75 2.97

5.23 5.75 2.75

6.42 4.38 2.14

6.65 4.65 1.99

5.86 5.20 1.99

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18.0 Shuna-North Deir-Alla Sweimeh

16.0

B-Adsorption (mg/kg Soil)

14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Equilibrium B Concentration (μg/mL) Fig. 4. Boron adsorption isotherm for three surface soil sample locations in the JV. A soil column was successively permeated with electrolyte solutions of constant salinity and SAR but of increasing B concentration.

Here:

week at room temperature. Boron regeneration was evaluated by permeating each column with the blank solution (0 μg B/mL). The permeation of the blank solution continued until B concentration in the effluent fractions reached a new steady state condition. The soil columns were again left standing for another week at room temperature before resuming the permeation of the blank solution as described before. The process of incubation, permeation and B determination in the effluent volumes was repeated for a third time.

Vps and Vds volume of permeating and draining solutions, respectively Cps and Cds concentration of B in the permeating and draining solutions, respectively volume of water at field capacity. Vfc

2.3. Boron regeneration 3. Results and discussion A duplicate set of four soil columns from each of the three soil samples were permeated with solutions of B concentration 1.0, 1.5, 2.0 or 4 μg/mL in a way similar to that employed in the adsorption study. When steady state B concentration in the permeating solution from each soil column was reached, the column was left standing for one

3.1. Status of B in Jordan Valley soils Soil sample sites and their respective salinity and water soluble B values are presented in Table 1. Higher salinity and B levels were

0.9 Shuna-North

Y = 0.548 + 0.1153X R² = 0.997

0.8

Deir-Alla Sweimeh

0.7

c/(x/m)

0.6 0.5 Y = 0.2469 + 0.0286X R² = 0.9691

0.4 0.3 0.2

Y = 0.1523 + 0.0252X R² = 0.9137

0.1 0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Equilibrium B Concentration μg/mL Fig. 5. Langmuir plot of adsorbed-B from three soil sample locations in the Jordan Valley. Each soil column was permeated with solutions of successively increasing B concentration.

T.M. Abu-Sharar et al. / Geoderma Regional 2–3 (2014) 50–59 Table 4 Langmuir's (K) and (b) parameters for B adsorption for the three JV soil samples. Soil

B (μg/g)

K (mL/μg)

Shuna-North Deir-Alla Sweimeh

39.7 35.0 8.7

0.16 0.12 0.21

observed in soil samples collected from the southern end of the JV. Low rainfall, high groundwater salinity usually used in conservative drip irrigation, the saline nature of lacustrine parent material from which these soils were derived and the subsequent limited soil development in that part of the JV are thought to be the major factors leading to such observations. No strong correlation between soil salinity and either paste extractable- or hot water extractable-B was observed, particularly when the outlier values from the southern end of the JV were not considered in the linear regression analysis. In the later case, R2 was very poor (0.0556 and 0.0916 for the correlations with B concentration in hot water and paste extracts, respectively). Most land area in the Southern JV was recently cultivated (~ 50 year history) as compared to the millennia of years of cultivation history in the majority of the Middle and Northern JV. Subsequently, we think that the human (anthropogenic) factor of soil–water management has obscured the naturally associated salinity with elevated levels of B (Couch and Grim, 1968; Goldberg et al., 2008; Keren and Bingham, 1985). In that regard, salts may accumulate in JV surface soil layers due to commonly practiced drip irrigation as contrasted by a high crop demand on B in such an intensive agriculture system (two vegetable crops in a year). For most crops, 1–4 μg/g soil B is sufficient to prevent nutrient deficiencies. Less than 0.5 μg/g soil B is rated as marginal to deficient (soilquality.org. au). The highest soil paste extractable B (~3.0 μg/mL) was reported in Karama, but most soil samples had much lower values (Table 1). The later figure corresponds to ~ 1.1 μg/g soil B meaning most soils of the JV may be classified as marginal to deficient in B. Fig. 2 shows almost a 1:1 functional relation between saturated paste-B for surface and subsurface soil layers. A similar relation was also observed for hot water extractable-B. Fig. 3 shows that B levels in hot water extracts were almost four times the corresponding values in the saturated paste extracts for the surface or subsurface soil samples. Given the results shown in Figs. 2 and 3, this finding indicates that B uptake by crops takes place from the paste extract fraction which also can be defined as the most labile fraction (Goldberg and Suarez, 2011). In addition, downward B transportation in the soil profile seemed very

55

limited. Such movement depends on the concentration of soluble B in the soil solution, the magnitude of adsorbed B, the number of adsorption sites per unit mass of soil, and the soil moisture content (Bingham et al., 1985; Hatcher et al., 1959). The predominance of drip irrigation in the JV may have enhanced the former conclusion as the meager quantity of irrigation water applied limits the downward leaching of soluble salts and B.

3.2. Boron adsorption onto soil solids Selected properties of the three soil samples employed in the adsorption study are presented in Table 2. The results show almost double the carbonate content in Shuna-North as compared to the other two soil samples. Very high salinity of the Southern soil sample of Sweimeh, especially for the subsurface sample, was associated with relatively elevated B levels in both extracts. High salinity in that location was a result of being much closer to the southern end of the JV where the Dead Sea starts and where highly saline lacustrine parent material is located. Due to the prevailing aridity, all soil samples had low organic matter content. Table 3 shows that reaching steady state equilibrium with solutions of low B concentration required permeating much higher volumes of these solutions in the case of Shuna-North soil as compared to the other two soils. This was mainly due to the higher clay content of that soil on the one hand, and to larger sizes of the dry aggregate and stronger wet aggregate stability on the other which in turn, maintained a relatively open soil structure. In such a case, most of the permeating solutions were expected to by-pass micro-aggregates and their associated micro-pores without allowing much of the percolating B to reach the adsorbing sites, and thus to establish equilibrium with the solid phase. This hypothesis was confirmed by observing a higher hydraulic conductivity, and thus a faster solution flux from Shuna-North soil columns relative to the other soil columns. The B adsorption isotherms onto the solids of the three soil columns are presented in Fig. 4. For the three soil columns, Fig. 4 shows almost an L-type of adsorption. Moreover, the magnitude of B adsorption was the highest in the case of Shuna-North and the lowest for Sweimeh. This sequence was consistent with the decreasing clay content, CEC and OM of the three soil samples as evidenced in Table 2. The correlation with clay content was reported by Elrashidi and O'Connor (1982). Moreover, Keren and Mezuman (1981) argued that if the amount of adsorbed B has to be expressed on a clay, not on a soil mass basis, then any differences that were reported among soils would have become much

5.0 4.5 4 μg/mL

B Concentation (μg/mL)

4.0

2 μg/mL 1 μg/mL

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

1000

2000

3000

4000

5000

6000

Cumulative Effluent Volume (mL) Fig. 6. Boron concentration in effluent volumes from Shuna-North soil columns successively permeated with three sets of solutions of constant B concentration separated by one week of standing time.

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T.M. Abu-Sharar et al. / Geoderma Regional 2–3 (2014) 50–59

B Concentration (μg/mL)

5.0 4.5

4.0 μg/mL

4.0

2.0 μg/mL

3.5

1.0 μg/mL

3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

1000

2000

3000

4000

5000

6000

Cumulative Effluent Volume (mL) Fig. 7. Boron concentration in effluent volumes from Deir-Alla soil columns successively permeated with three sets of solutions of constant B concentration separated by one week of standing time.

smaller. Their argument was based on the hypothesis that B adsorption takes place mainly on the clay fraction, especially in cases of soils in arid and semiarid areas. Adsorption data conformed to the Langmuir's linear type: c=ðx=mÞ ¼ ð1=KbÞ þ ðc=bÞ where: x/m K c b

is the amount of adsorbed B per unit mass of soil (μg/g) is the affinity coefficient of B for soil solids (mL/μg) is the equilibrium concentration of B in soil solution (μg/mL) is the maximum monolayer adsorption capacity (μg/g).

The linear plot of the adsorption data is presented in Fig. 5. Very high correlation coefficients of these linear relations were observed.

Accordingly, the two Langmuir parameters, K and b, were calculated for the three soils (Table 4). In this regard, the three soils had a similar affinity for B adsorption, but the maximum adsorption capacity varied consistently with clay and OM contents and CEC of these soils. Similarly, Arora and Chadal (2010) reported a high correlation between maximum B adsorption and these parameters. Moreover, Majidi et al. (2010) showed that removing CaCO3 from a soil sample (CaCO3-equivalent was 18%) lowered B adsorption maximum by 35%. These authors also showed that B was mainly adsorbed as an outer-sphere complex. In our study, the ShunaNorth surface soil sample had the highest CaCO3 concentration (57%) as compared to the other two surface soil samples (28%). 3.3. Boron regeneration Results of B concentration in effluent volumes from the three soil columns are presented in Figs. 6, 7 and 8. Data on leaching soil columns

B Concentration (μg/mL)

5.0

4.5

4.0 μg/mL

4.0

2.0 μg/mL

3.5

1.0 μg/mL

3.0 2.5

2.0 1.5 1.0 0.5 0.0 0

500

1000

1500

2000

2500

3000

3500

4000

Cumulative Effluent Volume (mL) Fig. 8. Boron concentration in effluent volumes from Sweimeh soil columns successively permeated with three sets of solutions of constant B concentration separated by one week of standing time.

T.M. Abu-Sharar et al. / Geoderma Regional 2–3 (2014) 50–59

57

0.30

50 Desorbed B %

45

Cumulative Desorbed B %

40 35

% Desorbed B

0.20

30

0.15

25

20

0.10

15

% Cumulative Desorbed B

0.25

10

0.05

5

0.00

0

5

10

15

20

25

30

35

0

Number of Pore Volumes Fig. 9. Boron desorption from Shuna-North soil column previously permeated with 4.0 μg/mL B as influenced by the volume of permeating water (pore volumes).

previously permeated with 1.5 μg/mL are not presented to avoid confusion. The figures show that all soil columns demonstrated a certain tendency to regenerate B in excess of the steady state concentration obtained from the soil columns that were left standing one week before resuming the permeation process using blank solution of 0.0 μg/mL B concentration. The additional B concentration was observed especially in the first leaching. A possible reason for this is the soil solution evaporation during the incubation period produced more concentrated B than was expressed in the elevated levels in the first effluent volumes. However, such a tendency decreased with the advancement in soil incubation/leaching cycles. Peryea et al. (1985a) pointed out the significance of short contact time between soluble B and soil solids which can promote B regeneration. These authors also argued that B regeneration in effluent volume can be reduced by maintaining low soil moisture content between the successive permeations. This could be attributed to limiting B diffusion from occluded micro-pores into the conducting

macro-pores. Boron in the bypass soil regions appears to be effectively isolated from the leaching solution. Quantities of B regeneration from the three soil samples are presented in Figs. 9, 10 and 11. The results indicated that the Shuna-North soil sample had the highest capacity to release almost 45% of the adsorbed B as compared to the other two soil samples which had a similar value of about 22% B regeneration. This finding conforms to the calculated Langmuir's affinity constants with the highest maximum adsorption capacity for the Shuna-North sample. However, all soil samples confirmed the early reported observation of the difficulty to leach B from soils enriched with that element. 4. Conclusion Saturated paste extractable- or hot water extractable-B wasn't correlated with JV soil salinity. A 1:1 relation was found between paste extract-B in surface and subsurface soil samples. Similar results were

0.14

25 Desorbed B %

Cumulative Desorbed B%

20

% Desorbed B

0.1 15

0.08 0.06

10

0.04

% Cumulative Desorbed B

0.12

5 0.02 0

0

5

10

15

20

25

0

Number of Pore Volumes Fig. 10. Boron desorption from Deir-Alla soil column previously permeated with 4.0 μg/mL B as influenced by the volume of permeating water (pore volumes).

58

T.M. Abu-Sharar et al. / Geoderma Regional 2–3 (2014) 50–59

25

0.14 Desorbed B %

0.12

Cumulative Desorbed B %

20

15

0.08

0.06

10

0.04

% Cumulative Desorbed B

% Desorbed B

0.10

5 0.02

0.00

0

5

10

15

20

25

0

Number of Pore Volumes Fig. 11. Boron desorption from Sweimeh soil column previously permeated with 4.0 μg/mL B as influenced by the volume of permeating water (pore volumes).

also reported for the hot water extracts. However, the hot water extractable B was almost 4 times greater than the paste extractable fraction. Adsorption of B conformed to the Langmuir model with similar affinity constants for the three soil samples employed in this study (ShunaNorth, Deir All and Sweimeh). B regeneration was observed when these soil samples were previously permeated with solutions of constant B level. However, the magnitude of cumulative B regeneration was relatively low with the Shuna-North soil sample having the maximum value 45% of the adsorbed B. This was most likely due to having the highest CEC, OM and clay contents, thus, the highest B adsorption capacity. Acknowledgment The authors are very thankful to Prof. Awni Taimeh for providing the soil classification and to Dr. Dale Rachmeler an International Development Expert who assisted with the final English language editing, his contribution wasn't limited to the language itself but went beyond that. Deep gratitude is also extended to anonymous reviewers for their valuable comments that substantially improved the quality of this manuscript. Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.geodrs.2014.09.007. These data include Google map of the most important areas described in this article. References Abu-Sharar, T.M., 1988. Stability of soil aggregates as inferred from optical transmission of soil suspension. Soil Sci. Soc. Am. J. 52, 951–954. Abu-Sharar, T.M., Battikhi, A.M., 2002. Water resources management under competitive demand: a case study from Jordan. Water Int. 27, 364–378. Abu-Sharar, T.M., Hussein, I., Al-Jayyousi, O., 2007. The use of treated sewage for irrigation in Jordan: opportunities and constraints. Water Environ. J. 17, 232–238. Al-Bakri, J.T., Salahat, M., Suleiman, A., Suifan, M., Hamdan, M.R., Khresat, S., Kandakgi, T., 2013. Impact of climate and land use changes on water and food security in Jordan: implications for transcending “the tragedy of the commons”. Sustainability 5, 725–748.

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