The effect of chemical and organic amendments on

Environ Monit Assess (2015) 187:683 DOI 10.1007/s10661-015-4894-7

The effect of chemical and organic amendments on sodium exchange equilibria in a calcareous sodic soil Faranak Ranjbar & Mohsen Jalali

Received: 28 July 2015 / Accepted: 22 September 2015 # Springer International Publishing Switzerland 2015

Abstract In this study, the reclamation of a calcareous sodic soil with the exchangeable sodium percentage (ESP) value of 26.6 % was investigated using the cheap and readily available chemical and organic materials including natural bentonite and zeolite saturated with calcium (Ca2+), waste calcite, three metal oxide nanoparticles functionalized with an acidic extract of potato residues, and potato residues. Chemical amendments were added to the soil at a rate of 2 %, while potato residues were applied at the rates of 2 and 4 % by weight. The ESP in the amended soils was reduced in the range of 0.9–4.9 % compared to the control soil, and the smallest and the largest decline was respectively observed in treatments containing waste calcite and 4 % of potato residues. Despite the reduction in ESP, the values of this parameter were not below 15 % at the end of a 40-day incubation period. So, the effect of solutions of varying sodium adsorption ratio (SAR) values of 0, 5, 10, 20, 30, 40, and 50 on sodium (Na+) exchange equilibria was evaluated in batch systems. The empirical models (simple linear, Temkin, and Dubinin-Radushkevich) fitted well to experimental data. The relations of quantity to intensity (Q/I) revealed that the potential buffering capacity for Na+ (PBCNa) varied from 0.275 to 0.337 ((cmolc kg−1) (mmol L−1)−1/2) in the control soil and amended soils. The relationship between exchangeable sodium ratio (ESR) and SAR was individually determined for the F. Ranjbar (*) : M. Jalali Department of Soil Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran e-mail: [email protected]

control soil and amended soils. The values of Gapon selectivity coefficient (KG) of Na+ differed from the value suggested by U.S. Salinity Laboratory (USSL). The PHREEQC, a geochemical computer program, was applied to simulate Na+ exchange isotherms by using the mechanistic cation exchange model (CEM) along with Gaines-Thomas selectivity coefficients. The simulation results indicated that Na+ exchange isotherms and Q/I and ESR-SAR relations were influenced by the type of counter anions. The values of KG increased in the presence of bicarbonate, sulfate, and phosphate in comparison with the presence of chloride, and the largest value was obtained in the presence of phosphate. So, it can be concluded that the presence of chloride anion is more favorable to reduce ESP compared to other anions, while the presence of phosphate anion makes the reclamation process more difficult. Furthermore, it is possible to reclaim sodic soils using inexpensive and readily available compounds such as potato residues and water management. Keywords Exchange isotherm . Sodicity . PHREEQC . Gaines-Thomas . Mechanistic simulation

Introduction The problem of soil salinity and sodicity is increasingly growing throughout the world. Soil properties may significantly be influenced by the accumulation of cations dispersing aggregates such as sodium (Na+) in the soil solution and exchangeable phases. Some detrimental

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effects of salinity and sodicity on physical (Hussain et al. 2001; Tejada et al. 2006), chemical (David and Dimitrios 2002; Ferreras et al. 2006), and biological properties of soil (Wong et al. 2008) as well as on the growth of plants (Qadir and Oster 2004) have been reported. The remediation of sodic soils is one of the essential management activities in agricultural production in order to meet the growing need for food and fiber in the world. The purpose of the reclamation is to convert a sodic soil into an arable soil with a high productivity by reducing the amount of the exchangeable Na+. There are two key factors in amending sodic soils as follows: (1) providing an adequately accessible source of calcium (Ca2+) and (2) maintaining a sufficient permeability through keeping a highly enough concentration of electrolytes in the soil solution. In other words, the reclamation of sodium-affected soils includes the replacement of exchangeable Na+ by Ca2+. A common method to reclaim the sodium-affected soils is to use chemical amendments such as gypsum and calcium chloride. Since the solubility of calcium carbonate is much less than that required to replace the exchangeable Na+ by Ca2+, sulfuric acid or acid-causing substances such as gypsum and organic matter are used for remediation of calcareous sodic in soils (Li and Keren 2009; Wong et al. 2009). However, chemical amendments are usually not easily accessible in many areas especially in developing countries (Qadir et al. 2001). In addition, the use of these amendments and the subsequent increase of electrolyte concentration in the drainage water can have adverse effects on the environmental protection (Qadir and Oster 2004). Calcium carbonate minerals found abundantly in soils of arid and semi-arid regions can act as a potentially important source of Ca2+ ions. As mentioned before, a very low solubility is the major obstacle to reclaim the sodic soils. The dissolution rate of calcium carbonate is dependent on pH, partial pressure of carbon dioxide (CO2), and its hydrolysis reaction in the soil solution. In alkaline conditions, the concentration of CO2 in the soil solution is the main factor controlling the dissolution of calcium carbonate (Plummer et al. 1978). Organic matter content, temperature, and soil moisture content are the parameters affecting the concentration of CO2 in the soil. The partial pressure of CO2 in the soil pore air is usually much higher than that of the atmosphere due to respiration of plant roots and soil microbial oxidation. The partial pressure of CO2 in

Environ Monit Assess (2015) 187:683

irrigated fields is in the range of 3.5–10.0 kPa (Buyanovsky et al. 1986). Increased partial pressure of CO2 in the root zone as well as the release of protons (H+) from roots of certain plant species can lead to an increase in the dissolution rate of calcium carbonate in the soil (Qadir et al. 2005) and the subsequent increase in replacing Na+ from the exchangeable sites. A new concept of environmental management is based on the recycling of waste and trash. The principles of sustainable agriculture are turned to use agricultural wastes to improve the physical, chemical, and biological properties of soils. The effect of organic materials on remediating salt- and sodium-affected soils has been proven. In addition, the importance of maintaining high levels of organic matter in the soil is well shown. The organic matter improves the soil structure and aggregate stability (Oades 1993) and the hydraulic conductivity (Hussain et al. 2001), and it increases the cation exchange capacity (CEC) and nutrient levels in the soil (Clark et al. 2007; Jalali and Ranjbar 2009). On the other hand, an increase in efficiency of chemical sources of Ca2+ such as calcium carbonate and gypsum in the presence of organic matter has been reported during amending saline and sodic soils (Qadir et al. 2005; Li and Keren 2009; Mahmoodabadi et al. 2013). Ca2+ and magnesium (Mg2+) are the most abundant divalent cations in soils of arid and semi-arid regions, and Na+ is the major cation in saline and sodic soils. Furthermore, potassium (K+) is an essential nutrient for plants, so a quantitative study of sorption of these cations in the soil can be significant. Since the accumulation of sodium salts as a result of irrigation and thereby the replacement of exchangeable Na+ by Ca2+ provide conditions for the formation of sodic and alkaline soils, the nature of Na+–Ca2+ and/or Na+–Mg2+ exchange equilibria in soils of arid and semi-arid regions is very important. Replacement of exchangeable Ca2+ by Na+ is dependent on the relative concentration of these ions in the soil solution. This caused to propose a statistically empirical equation by U.S. Salinity Laboratory (USSL 1954) for the calculation of exchangeable sodium percentage (ESP) using the sodium adsorption ratio in the saturated paste extract (SARe). The concept of the chemical potential and the equilibrium activity ratio (ARe) have been widely used for K+ as an essential nutrient for growing crops. Beckett (1964) suggested the exchange isotherm relating the amount of exchangeable ions and ARe in the solution referred as the quantity to intensity (Q/I) relationship.


Many studies have tried to develop predictive models to describe adsorption phenomenon for a wide range of systems. In studies of natural sediments and soils, empirical or semi-empirical models are often used to describe the partitioning of adsorbate between solutions and solid phases. However, partition coefficients depending on the composition of solution and solid phases cannot be utilized beyond the conditions for which they are measured. Furthermore, since partition coefficients do not consider mass balance, they can cause incorrect predictions concerning metal speciation and mobility (Bethke and Brady 2000). In contrast, thermodynamically based cation exchange and surface complexation models (CEMs and SCMs) comprise clear descriptions of reaction stoichiometries and the development of electrical charge at the solid surface (Dzombak and Morel 1990). These models have a significant benefit over empirical or semi-empirical models because of their accurate prediction of ion speciation under changing solution compositions (e.g., ionic strength, background electrolyte, competing ions, etc.), and thus they can be useful in predicting ion speciation in a wide variety of systems. Therefore, this study was aimed to (1) evaluate the effect of adding chemical and organic amendments on the reclamation of a saline-sodic soil; (2) investigate Na+ exchange isotherms, Q/I curves, and the potential buffering capacity for Na+ in the control soil and chemically and organically amended soils; (3) simulate mechanistically Na+ exchange isotherms in the presence of different counter anions by using CEM in PHREEQC as a geochemical computer program (Parkhurst and Appelo 1999); (4) obtain the relation between the exchangeable sodium ratio (ESR) and SAR in the control soil and amended soils and determine the quality of irrigation water suitable for soil remediation in the batch system.

Materials and methods Characterization and preparation of amendments Amendments used in this study consisted of bentonite saturated with Ca2+ (Ca-bentonite), zeolite saturated with Ca2+ (Ca-zeolite), metal oxide nanoparticles functionalized with the extract of potato residues, sludge collected from a power plant in Hamedan, western Iran, and potato residues.

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X-ray diffraction (XRD) analysis revealed that bentonite used in this study consisted mainly of montmorillonite (69.3 %) and quartz (30.7 %), while zeolite was a type of clinoptilolite with the purity of 53.5 % and showed the presence of a small percentage of quartz (22.7 %) (Moharami and Jalali 2013). It has also been reported that the average pore diameter of bentonite and zeolite was respectively 13.91 and 18.84 nm and the specific surface area was 84.98 and 13.83 m2 g−1, correspondingly (Moharami and Jalali 2013). In order to saturate the cation exchangeable sites of bentonite and zeolite with Ca2+, 500 mL of 1 M CaCl2 solution were added to 200 g of these particles. Then, the suspensions were alternatively shaken for 5 days. After removing the supernatants, particles were washed with distilled water so that the concentration of chloride in the suspension was near to zero (undetectable by titration with silver nitrate) (Lin et al. 2011). The mineral particles saturated with Ca2+ were then air-dried and passed through a 2mm sieve. The residues of potato, one of the main products cultivated in Hamedan, western Iran, were washed three times with distilled water, oven-dried at 60 °C for 24 h, and then ground to pass through a 2-mm sieve. Three types of metal oxide nanoparticles including copper oxide (CuO), magnetite (Fe3O4), and zinc oxide (ZnO) were used in this study. The nanoparticles (with purity of 99.5 %) were purchased from companies Tecnan of Spain and Nabond of China. The XRD and transmission electron microscopy (TEM) analyses of nanoparticles were previously carried out by Mahdavi et al. (2012). The size of crystalline particles of CuO, Fe3O4, and ZnO calculated using the result of XRD and Scherrer equation was 31.5, 36.9, and 16.7 nm, respectively. The TEM images showed that the mean diameter of the spherical-shaped CuO nanoparticles, sphericalshaped Fe3O4 nanoparticles, and rod-shaped ZnO nanoparticles was respectively 75, 50, and 25 nm. This difference could be due to the lack of consideration of particles with a poor crystallinity in XRD analysis. The extract of potato residues was used for surface functionalization of nanoparticles. Extraction of functional groups of potato residues was carried out based on the modified method of Kim et al. (2001). The potato residues, prepared as mentioned earlier, were extracted a day after exposure to 0.1 N nitric acid at the solid to solution ratio of 1:10. After filtration, pH was adjusted to 5 (higher pH leads to the deposition of soluble materials). The solution was then filtered through a 0.22-μm

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sieve and stored at 4 °C before being used for functionalization of nanoparticles. Then 0.5 g of nanoparticles was equilibrated with 30 mL of the extract at 70 °C for 6 h. After evaporation of the solvent, the functionalized nanoparticles were washed three times with a mixture of distilled water and ethanol, centrifuged (supernatant after each washing stage must be decanted as waste), air-dried, and stored in closed bottles for subsequent use. The XRD analysis showed that the sludge mainly contained calcite with Mg impurities (Merrikhpour and Jalali 2012). So, this material will be referred to as waste calcite in following parts. Analyses of pH and soluble cations and anions in a 1:5 extract of waste calcite to distilled water showed a pH value equal to 9.39 as well as the presence of Mg2+, Na+, carbonate, and bicarbonate at high levels (Merrikhpour and Jalali 2012). Since the purpose of this study was to reclaim or reduce the soil sodicity problem, the waste calcite was initially washed three times with distilled water and then airdried to be used as one of the amendments.

zeolite; 2 % of Ca-bentonite+2 % of potato residues; 2 % of Ca-zeolite+2 % of potato residues; 2 % of functionalized CuO+2 % of potato residues; 2 % of functionalized Fe3O4 +2 % of potato residues; 2 % of functionalized ZnO+2 % of potato residues; 2 % of waste calcite; 2 % of waste calcite+2 % of potato residues; 2 % of potato residues and 4 % of potato residues. The amendments were added to the soil sample on a dry-weight basis. The soil samples were thoroughly mixed with amendments and incubated for 40 days at field capacity moisture and room temperature (25±1 °C). The samples were weighed at the beginning of the experiment and re-weighed periodically to check for any significant loss of moisture. Lost moisture was compensated by adding distilled water to bring back the initial mass. After the incubation period, soils were airdried and passed through a 2-mm sieve. The pH, EC, and soluble cations were measured in a 1:5 soil to water extract and exchangeable cations were determined using 1 M NH4OAc solution (pH 7.0). The Na+ exchange isotherms were conducted on the control soil and amended soil samples.

Soil sampling and characterization A bulk surface (0–30 cm) soil sample was collected from an agricultural area in Tajarak, Hamadan, western Iran. The sample was air-dried, ground, and then passed through a 2-mm sieve. The pH, electrical conductivity (EC), and soluble cations and anions were analyzed in a 1:5 soil to water suspension (Rowell 1994). The particle size was determined by the hydrometer method and equivalent calcium carbonate (ECC) was measured by back titration. Ca2+, Mg2+, and bicarbonate were determined by complexometric titration, and Na+ and K+ were measured by flame photometry. The exchangeable Ca2+, Mg2+, Na+, and K+ were extracted using 1 M ammonium acetate (NH4OAc) solution buffered at pH 7.0. Effective CEC was estimated as the sum of exchangeable cations (Rowell 1994). The ESP was calculated based on the following equation: ESPð%Þ ¼

2þ

Ex: Ca

Ex: Naþ 100 þ Ex: Mg2þ þ Ex: Naþ þ Ex: Kþ

ð1Þ

Soil treatments and incubation A total of 12 treatments were used in this study: no amendment (control); 2 % of Ca-bentonite; 2 % of Ca-

Na+ exchange isotherms The Na+ exchange isotherms were performed in quaternary Na-Ca-Mg-K systems. The solutions used for the experiment were prepared using chloride salts of Ca2+, Mg2+, Na+, and K+. These solutions contained concentrations of 0.0, 13.7, 27.2, 54.8, 82.3, 109.7, and 137.1 mM Na+ in the presence of 3.76 mM Ca2+, Mg2+, and K+. Therefore, SAR of solutions was 0, 5, 10, 20, 30, 40, and 50 (mmol L−1)1/2, respectively. About 2 g of the control soil and amended soils in duplicate was equilibrated with 20 mL of isotherm solutions for 24 h at constant temperature. At the end of time considered for equilibration, extracts were separated from soils by centrifuging and the equilibrium concentration of cations was measured in supernatants. The difference between the concentration of Na+ in the initial and in the equilibrium solutions was considered as the amount of Na+ adsorbed or desorbed by exchangeable sites of soils (ΔNa) (cmolc kg−1): C i −C cor V e ‐1 ΔNa cmolc kg ¼ ð2Þ m 10 where Ci is Na+ concentration in initial solutions (mmol L−1), Cecor is corrected Na+ concentration in


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equilibrium solutions (mmol L−1), V is volume of the solution (L), and m is the mass of soil (g). In order to prevent the error of the soluble Na+ concentration of soils in calculating ΔNa, the concentration of this cation in 1:10 soil to water extract was subtracted from Na+ concentration in the equilibrium solution (Ce) to obtain Cecor. The ESP of soils following equilibration with solutions of varying SAR values was calculated using the following equation: ΔNa þ NaXi ESPð%Þ ¼ 100 CEC

ð3Þ

where NaXi is the initial exchangeable Na+ (cmolc kg−1) before isotherm experiments. The remaining soils in the tubes were air-dried and then separately extracted by 1 M NH4OAc and distilled water. The exchangeable Ca2+ and Mg2+ were obtained by subtracting the concentration of these cations in supernatants resulting from NH4OAc and distilled water extractions. The exchangeable K+ were calculated by subtracting CEC from the sum of exchangeable Ca2+, Mg2+, and Na+ (ΔNa+NaXi). The Na+ exchange isotherms in soils were investigated using the relationship between Cecor and ΔNa. Empirical equations used to describe the exchange isotherms were as follows: 1. Simple linear where ΔNa and Cecor have the same concepts previously mentioned and Kd is the linear distribution coefficient which can be expressed as liters per kilogram when multiplied by 10. This coefficient shows the distribution of the ions between the solid and liquid phases, and the larger the value, the more presence of ions is in the solid phase.

ΔNa ¼ K d C cor e

ð4Þ

2. Temkin This equation has a parameter that takes into the account of the interaction between the adsorbent and adsorbate. Regardless of extremely low and high concentrations, it is assumed that the heat of the sorption of all molecules (here the exchange of cations) in the layer adsorbed decreases linearly rather than logarithmically with

increasing coverage. The linear form of the equation is as follows: ΔNa ¼ B ln C cor e þ B lnK T

ð5Þ

where KT is Temkin isotherm equilibrium constant which can be expressed as liters per kilogram when multiplied by 10 and B is the constant related to the heat of the exchange calculated as follows: B¼

RT bT

ð6Þ

where R is the universal gas constant (8.314 J K−1 mol−1), T is the absolute temperature (K), and bT is the heat of the exchange (J mol−1). 3. Dubinin-Radushkevich This equation is commonly used to describe the adsorption mechanisms with a Gaussian energy distribution onto a heterogeneous surface. It has often successfully fitted to data obtained from solutions containing moderate to high ionic strength. The linear form of this equation is as follows: lnΔNa ¼ lnqs − K DR ε2

ð7Þ

where qs is the theoretical saturation capacity of adsorbent (cmolc kg−1) and KDR is the constant of equation (mol2 J−2). The parameter ɛ, Polanyi potential, is calculated as: 1 ε ¼ RT ln 1 þ cor ð8Þ Ce The energy of the sorption (here the exchange) (J mol−1) can be calculated using KDR based on the following equation: 1 E ¼ pffiffiffiffiffiffiffiffiffiffiffi 2K DR

ð9Þ

Q/I relations and determining the potential buffering capacity for Na+ The Q/I curves represent a relationship between the amount of Na+ adsorbed on the surface of the adsorbent (Q) and the equilibrium activity ratio of this cation in the

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solution phase (I). The slope of Q/I curve is considered as a potential buffering capacity of the soil for Na+ (PBCNa) ((cmolc kg−1) (mmol L−1)−1/2): ΔNa ¼ PBCNa SARe −ΔNa0

ð10Þ

The value of equilibrium sodium adsorption ratio, SARe, when no Na+ is adsorbed or desorbed, i.e., ΔNa=0, is obtained from the graph by interpolation. The ΔNa0 value, or the intercept at SARe =0, is obtained by extrapolation which represents the amount of exchangeable Na+ held in the soil. Determining ESR-SAR relations in the control soil and amended soils The ESR can be obtained using the amount of exchangeable Na+ (NaX) and CEC: ESR ¼

NaX CEC NaX

ð11Þ

On the other hand, several researchers have reported a very significant positive correlation between ESR and SAR in the saturated paste extract (SARe). For example, USSL (1954) suggested the following equation after analysis of 59 arid-zone soils from the western United States: ESR ¼ 0:01475 SARe −0:0126

ð12Þ

According to the ESR-ESP relation, the above equation can be expressed in the following way: ESP ¼ 0:015 SARe −0:013 100−ESP

ð13Þ

Because the ESR-SAR relation is influenced by some soil characteristics, it is essential to determine this relation for different soils in various areas. Thus, based on the results of exchange isotherms, the relations presented in Eqs. 11 and 12 were separately obtained for the control soil and amended soils. Furthermore, the values of SARe were calculated using the measured values for ESP in soils. Simulating Na+ exchange isotherms by using the mechanistic CEM in PHREEQC In order to simulate Na+ exchange isotherms in the control soil and amended soils, cation selectivity coefficients were calculated using Gaines-Thomas convention

(Gaines and Thomas 1953). For determining cation selectivity coefficients, 2.5 g of soil samples was equilibrated with 25 mL of two types of irrigation water (Table 1) synthesized in the laboratory. The composition of irrigation waters was selected according to Jalali (2007) who described the quality of waters used for irrigation of agricultural fields in Tajarak area (the control soil sample was collected from this area). After centrifugation and filtration, the concentrations of Ca2+, Mg2+, K+, and Na+ were measured in supernatants. The exchangeable cations of the soil samples remaining in the centrifuge tubes were extracted using 25 mL of 1 M NH4OAc solution (pH 7.0). The activity of soluble cations was obtained through the activity coefficient multiplied by the concentration. The activity coefficients were calculated using the form of WATEQ Debye-Hückel equation as proposed by PHREEQC capabilities: pffiffi I pffiffi þ bI logγ ¼ −AZ 2 ð14Þ 1 þ B a∘ I where γ is the activity coefficient of the ion, A (0.511 at the temperature of 25 °C) and B (0.33 at the temperature of 25 °C) are the temperaturedependant constants, I is the ionic strength, Z is the charge of ion, and å and b are the ion-specific parameters. The selectivity coefficients were calculated using Gaines-Thomas convention. This equation is based on the assumption that the cationic mixture on the exchanger phase behaves as an ideal mixture, i.e., the activity of each exchangeable species is equal to its equivalent fraction and its activity coefficient is equal to 1.0. For example, for the exchange reaction: 2 NaX þ Ca2þ ¼ CaX2 þ 2 NaHþ

ð15Þ

The Gaines-Thomas selectivity coefficient, KGT, is obtained as follows: K GT ¼

ECa mNa 2 γ2 Na ðE Na Þ2 mCa γCa

ð16Þ

where X is one equivalent of the anionic part of exchanger, ENa and ECa are the equivalent fractions of the total exchange capacity occupied by the ions specified, and mNa and mCa are the molar ion concentrations in the solution phase. As there were two types of irrigation water, an average selectivity coefficient for each cation was used in the


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Table 1 The chemical composition of irrigation waters (Jalali 2007) used in calculating Gaines-Thomas selectivity coefficients Irrigation water

pH

EC dS m−1

Ca2+ mM

Mg2+ mM

K+ mM

Na+ mM

SAR (mM)1/2

Cl− mM

CO32− mM

HCO3− mM

SO42− mM

Non-sodic

6.50

0.39

1.00

0.35

0.00

0.35

0.30

0.40

0.00

0.80

0.10

Sodic

8.76

8.90

11.30

9.25

4.54

63.13

13.93

54.00

1.50

11.70

20.00

simulation process. The Na+ exchange isotherms were simulated using the average cation selectivity coefficients calculated according to Gaines-Thomas convention and CEM in PHREEQC v.2.18 (Parkhurst and Appelo 1999). In addition to the graphical evaluation, the efficiency of CEM in simulating exchange isotherms was estimated by the root mean square error (RMSE) as a standard statistical measure widely used in the model evaluation: sffiffiffiffiffiffiffiffi 1 n RMSE ¼ ∑ðX m −X s Þ2 ð17Þ n i¼1 where xm and xp are respectively the measured and simulated values and n is the number of samples corresponding to the number of isotherm solutions. The smaller the RMSE (closer to zero), the less the systematical difference between measured and simulated data. The experiments were conducted in the presence of chloride anion and in order to show the effect of other counter anions, Na+ exchange isotherms in the presence of bicarbonate, sulfate, and phosphate were simulated in the control soil by using CEM in PHREEQC.

Results and Discussion The effect of addition of amendments on some chemical properties of a saline-sodic soil The selected physical and chemical characteristics of the control soil are presented in Table 2. The soil had a clay loam texture. ECC, CEC, and ESP was respectively 15.0 %, 26.3 cmolc kg−1, and 26.6 %. Table 3 shows the changes in pH, EC, and concentrations of cations in solution and exchangeable phases of amended soils relative to the control soil at the end of incubation. The pH of soils treated with amendments increased only slightly compared to the control soil. The greatest increase (at a level of half a unit) was observed in the treatment containing 4 % of potato residues. No drastic

changes in pH followed by the application of organic materials may be due to the presence of clay and calcium carbonate which lead to increased soil buffering capacity and resistance to significant changes in pH. Although often it is expected that organic materials reduce the soil pH due to the release of hydrogen ions through the decomposition process, they can increase soil pH by releasing organic anions mineralized to CO2 and water and consequently removing hydrogen ion or because of their alkaline nature (Helyar 1976). Xu et al. (2006) showed that the use of plant residues increased the soil pH. They suggested that the release of alkalinity

Table 2 The selected characteristic of the calcareous sodic soil sample (control soil) Parameters

Unit

Quantity

Sand

%

39.48

Silt

%

22.92

Clay

%

37.60

Textural class

–

Clay loam

pH

–

9.01

EC

dS m−1

0.62

Soluble Ca2+

mmol L−1

0.50

Soluble Mg2+

mmol L−1

0.20

Soluble K+

mmol L−1

0.40

−1

+

Soluble Na

mmol L

3.26

Soluble HCO3−

mmol L−1

1.20

Soluble Cl−

mmol L−1

2.80

Exchangeable Ca2+

cmolc kg−1

11.60

Exchangeable Mg2+

cmolc kg−1

6.20

+

−1

Exchangeable K

cmolc kg

1.50

Exchangeable Na+

cmolc kg−1

7.00

CEC

cmolc kg−1

26.30

ESP

%

26.60

SAR

(mmol L−1) 1/2

3.90

CaCO3

%

15.00

pH, EC, and soluble cations and anions were determined in a 1:5 soil to water extract

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Table 3 Some chemical properties of amended soils after a 40-day incubation duration Treatmentsb

Soluble cations

Exchangeable cations

pHa ECa Ca2+a Mg2+a K+a Na+a SARa Ca2+ Mg2+ K+ Na+ CEC ESP mM mM (mM)1/2 cmolc kg−1 cmolc kg−1 cmolc kg−1 cmolc kg−1 cmolc kg−1 % dS m−1 mM mM B

9.07 0.63

0.50

0.20

0.40 3.34 3.99

13.00

6.20

1.50

6.90

27.60

25.00

Z

9.04 0.62

0.50

0.50

0.32 3.34 3.34

13.40

6.80

1.60

6.90

28.10

24.60

B+P

9.17 1.11

0.70

0.50

3.82 4.04 3.69

14.60

6.80

1.40

6.60

29.40

22.40

Z+P

9.10 1.09

0.70

0.50

3.64 4.04 3.69

15.00

6.80

1.60

6.60

30.00

22.00

CuO+P

9.14 1.19

0.50

0.50

3.82 4.13 4.13

13.60

6.80

1.40

6.50

28.30

23.00

Fe3O4 +P

9.14 1.23

0.50

0.50

3.74 4.13 4.13

13.60

6.80

1.50

6.50

28.40

22.90

ZnO+P

9.14 1.27

0.50

0.50

3.64 4.24 4.24

13.80

6.80

1.60

6.40

28.60

22.40

W

9.06 0.64

0.50

0.20

0.40 3.42 4.09

12.00

6.20

1.50

6.80

26.50

25.70

W+P

9.17 1.14

0.80

0.50

3.78 3.95 3.46

13.40

6.80

1.50

6.70

28.40

23.60

P2

9.12 1.09

0.70

0.50

3.74 3.95 3.61

13.20

6.80

1.50

6.70

28.20

23.80

P4

9.21 1.64

1.00

0.90

7.02 4.52 3.28

14.60

7.20

1.60

6.50

29.90

21.70

a

Measured in a 1:5 soil to water extract

b

Treatments including B: 2 % of Ca-bentonite, Z: 2 % of Ca-zeolite, B+P: 2 % of Ca-bentonite+2 % of potato residues, Z+P: 2 % of Cazeolite+2 % of potato residues, CuO+P: 2 % of functionalized CuO nanoparticles+2 % of potato residues, Fe3O4 +P: 2 % of functionalized Fe3O4 nanoparticles+2 % of potato residues, ZnO+P: 2 % of functionalized ZnO nanoparticles+2 % of potato residues, W: 2 % of waste calcite, W+P: 2 % of waste calcite+2 % of potato residues, P2: 2 % of potato residues, P4: 4 % of potato residues

during the decomposition of organic residues and the ammonification of organic nitrogen can increase soil pH, while the nitrification process leads to reduce it. Therefore, the effect of organic residues on soil pH depends on the superiority of these processes. Clark et al. (2007) also reported the increased soil pH by adding organic amendments under incubation conditions. Table 3 indicates that EC of soils treated with amendments increased relative to the control soil and the largest enhancement (1 dS m−1) was observed in the treatment containing 4 % of potato residues. The increase in EC followed by the addition of organic compounds is mainly due to the production of organic acids (Wong et al. 2009), the release of cations and anions during the decomposition process, and an increase in the dissolution of carbonate minerals caused by the increment of partial pressure of CO2 (Li and Keren 2009). Jalali and Ranjbar (2009) and Ranjbar and Jalali (2011) also reported an increase in the soil EC following the addition of organic amendments at a rate of 5 % and a 1month incubation period. They showed that the greatest increase in EC compared to the control soil was about 4 dS m−1 in the treatment containing potato residues. Higher values obtained for EC in their study were due to the application of organic compounds at the higher rate

and not washing them before adding to the soil. Clark et al. (2007) demonstrated that the increase in the soil EC by adding organic amendments depends on the type of organic compounds and the electrolyte concentration released from them. The increased concentration of soluble cations occurred in treatments containing potato residues and the maximum amount was observed in the soil amended with 4 % of these components. The application of functionalized CuO, Fe3O4, and ZnO nanoparticles along with potato residues can also improve soil fertility through providing the essential micro- and major nutrients for crop growth. Values of SAR decreased in treatments containing Ca-bentonite+potato residues, Ca-zeolite+potato residues, waste calcite+potato residues, and 2 and 4 % of potato residues relative to the control soil, while increased in other treatments. The exchangeable Ca2+ increased in all treatments compared to the control soil, and the greatest increase was observed in the treatment containing 4 % of potato residues. In comparison with the control soil, the exchangeable Mg2+ also increased in all treatments except in Ca-bentonite and Ca-zeolite. The amount of exchangeable K+ in amended soils showed no significant difference relative to the control soil, while the amount of exchangeable Na+ was slightly reduced in amended


soils. The greatest decline compared to the control soil (0.6 cmolc kg−1) was observed in the treatments containing ZnO nanoparticles+potato residues. The CEC in amended soils increased in comparison with the control soil. The increase of CEC varied from 0.2 to 3.6 cmolc kg−1 and the smallest and the greatest increment was respectively observed in treatments containing waste calcite and 4 % of potato residues. Thus, the ESP in the amended soils was reduced in the range of 0.9–4.9 % compared to the control soil, and the smallest and the largest decrease was respectively observed in treatments containing waste calcite and 4 % of potato residues. The application of organic residues reduces not only the cost of remediation practices but also the adverse effects of the disposal of these components on the environmental quality in developing countries, where many crop residues are usually burned in the fields. Furthermore, the addition of organic residues to calcareous sodic soils prevents the use of acids or other chemical amendments and, hence, reduces the threat of remediation practices for environmental quality (Li and Keren 2009). At the same time, it should be noted that an excessive use of fresh plant residues may lead to some detrimental effects on the crop growth or plant disease occurrence. But these harmful effects can be reduced or minimized by an efficient management. For example, crop residues and organic compounds can be added in autumn and mixed with the soil by plowing (Li and Keren 2009). Thus, when soil is moistened following the rainfall occurrence, the decomposition of organic residues and the subsequent increment of the partial pressure of CO2 and the dissolution of calcium carbonate may lead to an increase in CEC and a reduction in ESP. In fact, incubation durations in vitro studies are designed for this purpose. Quedraogo et al. (2001) showed that the use of compost in agricultural fields at a rate of 10 Mg ha−1 resulted in an increase in CEC from 4 to 6 cmolc kg−1 as well as an increase in the soil pH. An increase in CEC of soils after application of compost and chicken manure has also been reported in previous studies (Lax 1991; Bernal et al. 1992; Walker and Bernal 2004). About 20– 70 % of CEC in many soils depends on organic matter. Walker and Bernal (2008) reported that the use of poultry manure at the rate of 2–3 % increases CEC as much as 3 to 5 units. They also showed that the increase in CEC resulted in more occupation of exchangeable sites by divalent cations including Ca2+

Page 9 of 21 683

and Mg2+ and preventing the entry of Na+ to the exchange complex. Clark et al. (2007) indicated that the reduction in ESP of a sodic clay soil was around 10 % after application of wheat, canola, and chickpea residues and chicken manure at a rate of 1 % by weight and a 174-day incubation period. The results showed that despite the positive impact of amendments in reducing ESP, the value of this parameter was still more than 15 %, and so, the amended soils were still classified in sodic soil group. The use of good quality water can be another way to solve the sodicity problem is these soils. Therefore, Na+ exchange isotherm experiment was conducted to determine the water quality suitable for improving soils. Na+ exchange isotherms and fitting empirical models The results of Na+ exchange isotherms in the control soil and amended soils are presented in Fig. 1. Negative values of ΔNa indicate the desorption of Na+ from exchangeable sites, while positive values represent the adsorption of Na+ by these places. The results showed that the use of solutions of SAR 0, 5, and 10 led to the release of Na+ from exchangeable sites in control soil and amended soils, whereas the release of Na+ was observed after application of solution of SAR 20 in treatments containing Ca-bentonite+potato residues, Ca-zeolite+potato residues, and 4 % of potato residues. Figure 1 shows that the maximum release or, in other words, the minimum adsorption of Na+ belongs to the treatment containing 4 % of potato residues, while the greatest amount of Na+ adsorbed is observed in the control soil. The results of fit of empirical isotherm models including simple linear, Temkin, and DubininRadushkevich to experimental data are given in Table 4. Three empirical models fitted well to the experimental data and the largest values of coefficient of determination (R 2 ) were obtained for Dubinin-Radushkevich model. The values of K d were in the range of 0.79–0.93 L kg−1 and the maximum and minimum value was respectively obtained in the control soil and 4 % potato-amended soil. The smaller the value of Kd, the more presence of ion in the solution phase and, therefore, the greater risk of transport by leaching process or the greater uptake by plants. In contrast, the larger value represents a reduction in mobility and an increment in adsorption and retention of ion by the solid phase.


Page 10 of 21

6

6

4

4

2 0 -2

0

50

100

150

0 -2 -4

-6

-6

6

6

4

4

2 0 -2

50

100

150

-2

-6

-6

8

2 0 0

50

100

150

∆ N a + (cm ol c kg -1 )

∆ N a + (cm ol c kg -1 )

50

100

150

Equilibrium Na+ conc. (mmol L -1 ) Soil + 2% CuO + 2% Potato residues RMSE=0.37

6

4

4 2 0 0

50

100

150

-2

-4

-4

-6 -8

0

8

6

-2

Soil + 2% Ca-bentonite + 2% Potato residues RMSE=0.38

-8

Soil + 2% Ca-zeolite + 2% Potato residues RMSE=0.36

150

0

-4

Equilibrium Na+ conc. (mmol L -1 )

100

2

-4

-8

50


8

Soil + 2% Ca-zeolite RMSE=0.45

0

0

-8


8

Soil + 2% Ca-bentonite RMSE=0.41

2

-4

-8

∆ N a + (cm ol c kg -1 )

8

Control RMSE=0.58

∆ N a + (cm ol c kg -1 )

∆ N a + (cm ol c kg -1 )

8

∆ N a + (cm ol c kg -1 )

683


-6


+

Fig. 1 Na exchange isotherms in the control soil and amended soils (the marker symbols and solid lines are respectively representing experimental and mechanistically simulated data)

The values of constant KT of Temkin equation ranged from 0.16 to 0.27 L kg−1 and, like Kd, the largest and the smallest value was obtained in the control soil and 4 % potato-amended soil, respectively. The parameter of the heat of the exchange estimated

by Temkin equation (bT) was in the range of 560.8– 636.6 J mol−1 and the minimum and maximum value was respectively observed in treatments containing ZnO nanoparticles+potato residues and 4 % of potato residues.

Environ Monit Assess (2015) 187:683 8

Soil + 2% Fe3O4 + 2% Potato residues RMSE=0.36

6

6

4

4

2 0 0

50

100

150

∆ N a + (cm ol c kg -1 )

∆ N a + (cm olc kg -1 )

8

Page 11 of 21 683

0

-4

-4 -6


0 0

50

100

150

∆ N a + (cm ol c kg -1 )

2

150

Soil + 2% Waste calcite + 2% Potato residues RMSE=0.30

2 0 0

50

100

150

-2 -4

-4

-6

-6 -8

-8


8


6

Soil + 2% Potato residues RMSE=0.33

6

Soil + 4% Potato residues RMSE=0.60

4

2 0 0

50

100

150

2 0 0

50

100

150

-2 -4

-4

-6

-6 -8

∆ N a + (cm ol c kg -1 )

4

-2

100

4

4

-2

50


6

Soil + 2% Waste calcite RMSE=0.43

6

∆ N a + (cm ol c kg -1 )

0 -2

8

∆ N a + (cm o lc kg -1 )

2

-2

-6

Soil + 2% ZnO + 2% Potato residues RMSE=0.40

Equilibrium Na+ conc. (mmol L-1)

-8


Fig. 1 (continued)

The theoretical saturation capacity predicted by Dubinin-Radushkevich varied from of 8.6 to 23.7 cmolc kg−1 and the smallest and the largest value was respectively observed in waste calcite- and Cazeolite-amended soils. The values of this parameter were less than CEC in the control soil and amended

soils due to the presence of other competitive cations (Ca2+, Mg2+, and K+) in the quaternary system used in exchange isotherm experiments. The values of the energy of the exchange, E, calculated on the basis of KDR were in the range of 12.9–23.4 J mol−1. It has been reported that magnitude of E is useful for estimating

683


Page 12 of 21

Table 4 The parameters obtained from fitting empirical models to Na+ exchange isotherms in the control soil and amended soils Treatments

Simple linear

Temkin

Kd ×10 L kg−1

R2

0.093

0.981**

B

0.088

**

0.945

Z

0.088

0.975**

0.091

**

C

B-P Z-P CuO-P

0.090 0.089

0.992

**

0.989

**

0.983

bT J mol−1

KT ×10 L kg−1

R2

580.50

0.027

567.21 582.96 564.24 566.43 583.78

qs cmolc kg−1

KDR mol2 J−2

E J mol−1

R2

0.941**

11.28

0.001

22.36

0.997**

0.023

**

0.976

8.59

0.001

22.36

0.990**

0.021

0.960**

23.69

0.003

12.91

0.962**

0.020

**

10.82

0.001

22.36

0.998**

**

10.16

0.001

22.36

0.999**

**

12.60

0.002

15.81

0.992**

**

0.020 0.023

0.930 0.935 0.924

Fe3O4-P

0.090

0.984

580.91

0.022

0.925

13.01

0.002

15.81

0.990**

ZnO-P

0.092

0.982**

560.79

0.022

0.932**

12.76

0.002

15.81

0.991**

0.086

**

0.024

**

8.56

0.001

23.36

0.997**

**

11.98

0.002

15.81

0.998**

**

12.11

0.002

15.81

0.998**

**

15.52

0.003

12.91

0.984**

W W-P P2 P4

0.087 0.088 0.079

**

Dubinin-Radushkevich

0.970

**

0.979

**

0.980

**

0.993

597.58 583.23 578.47 636.58

0.020 0.021 0.016

0.965 0.950 0.948 0.930

C control **

Significant at the level of 99 % (P