Time-dependent copper extraction in different soil orders as influenced by soil to extractant Ratio

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1 International Research Journal of Applied and Basic Sciences. Vol., 3 (8), , 2012 Available online at www. irjabs.com ISSN X 2012 Time-dependent copper extraction in different soil orders as influenced by soil to extractant Ratio Reza Ghasemi-Fasaei 1*, Abdolmajid Ronaghi 1, and Mahdi Najafi Ghiri 2 1- Department of Soil Science, College of Agriculture, Shiraz University, Shiraz, Iran 2- College of Agriculture and Natural Resources, Shiraz University, Darab, Iran *Corresponding Author ghasemif@shirazu.ac.ir Abstract In order to study and compare patterns of time-dependent copper (Cu) extraction in different soil orders and to investigate the effect of soil to extractant ratio (SER) on the rate of Cu release in different soil orders, a laboratory experiment was designed with ten soils from five orders. Soil samples were extracted using DTPA extractant for periods of 1, 10, 30, 60, 120, 240, 480, and 1440 min. Overall patterns of Cu extracted was characterized by a fast release reaction during the first two hours followed by a slower reaction and the pattern well fitted to power function, parabolic diffusion, and Elovich models. At SER = 1: 2 (SER 1/2 ) Cu release rates were in order: Vertisols Alfisols Inceptisols Histosols Mollisols. At SER = 1: 10 (SER 1/10), however, Cu release rates were in order: Histosols Vertisols Alfisols Inceptisols Mollisols. Results showed that the amounts of Cu released at SER 1/10 were 76 to 316% higher than those of SER 1/2 in different soil orders. The difference in the extraction capacity of the extractant between two SER was more considerable in Mollisols and Histosols and in all soils decreased with time. According to results of correlation coefficients between soil properties and percent increase in Cu extraction at SER 1/10 than those of SER 1/2, it is assumed that the higher extractant distributed to the soil per unit weight at SER 1/10 might be responsible for higher dissolution of Cu bound to carbonates and OM which are potentially available forms, besides other available forms. Keywords: copper, dynamics, soil to extractant ratio, soil orders. Introduction Copper (Cu) availability is low in some calcareous soils of southern Iran and optimum growth of crops depends usually on Cu application (Maftoun et al., 2002). It has been shown that sorption capacity and binding strength of Cu in calcareous soils were greater than other trace elements (Jalali and Moharrami, 2007). Ghasemi-Fasaei et al. (2011) observed that the rate and magnitude of Cu release in clay and sandy loam calcareous soils were the least among metal micronutrients. Release and availability of Cu is controlled by some soil properties including organic matter (OM), calcium carbonate equivalent (CCE), cation exchange capacity (CEC) Ghasemi-fasaei et al., 2006, 2007). McLaren et al. (1983) observed that sorption hysteresis was most conspicuous when Cu adsorbed onto soil organic compounds. Diethylenetriaminepentaacetic acid (DTPA) extractant (DTPA 0.005M + CaCl M + TEA 0.1M at ph 7.3) is useful for simultaneous extraction of available metal micronutrients including Cu in calcareous soils (Lindsay and Norvell, 1978). Application of this method provides only a static measure of nutrient availability to plants. Study of equilibrium conditions using thermodynamic approach is just useful to predict the final state of a soil system. Investigation of kinetics is, however, imperative to gain further information on the changes in nutrient availability with time (Dang et al., 1994). In order to assess and interpret the chemical characteristics of metals in soils, obtaining enough information on the nature of sorption/desorption processes is compulsory (Sing et al., 2006). In addition, release rate parameters calculated from the best fitted kinetic models can describe a higher portion of the variation in plant responses in comparison with results of nutrient soil tests (Dang et al., 1994). Pattern of Cu release has been described by different

2 mathematical models including power function, parabolic diffusion, and first order models (Khater and Zaghloul, 2002). Rupa and Shukla (1998) studied Cu adsorption-desorption characteristics of 40 soils from three orders and observed that Cu desorption was in the order: Alfisols Inceptisols Vertisols. According to findings of Lindsay and Norvell (1978) when soil to extractant ratio (SER) is 1: 2, the capacity of DTPA to complex Cu is 10 times its atomic weight, about 640 parts per million. Harter and Naidu (2001) believed that change in SER may influence the aqueous phase chemistry of native trace metal ions, and affect either one or both sorption and desorption processes. It appears that when SER increases the concentration of metal after desorption equilibrium increases and percent desorption decreases (Papassiopi ter and Naidu, 2001) probably since solution distributed to the soil per unit weight decreases (Wang et al., 2007). Fest et al. (2008) reported that extraction of dissolved organic matter and related metal concentrations were also affected by this ratio. Data on the study of time-dependent Cu extraction patterns in different soil orders and at different SER is limited. The main objectives of present study were to investigate (i) the patterns of time-dependent Cu extraction and (ii) the effect of soil to extractant ratio on the rate of Cu extraction in ten calcareous soils belonging to five different orders. Materials and Methods Ten surface (0-30 cm) soil samples were collected from different fields of Fars province located in southern Iran between longitudes to E and latitudes 27 3 to N. The soils were from five orders including two samples from each Alfisols, Histosols, Inceptisols, Mollisols, and Vertisols. Physiographic units, classification, moisture and temperature regimes of the soils were determined according to standard procedures (Soil Survey Staff, 2006 and 2009) (Table 1). The soil samples were air dried, crushed, and sieved. Particle size distribution was analyzed using Rowell' s procedure (1994) via dispersion of soil with sodium hexametaphosphate after removal of calcium carbonate and organic matter then separation of sand, silt, and clay by sedimentation, cation exchange capacity (CEC) by replacing exchangeable cations with NaOAc then displaced exchangeable Na +, which was determined to give the CEC (Sparks et al., 1996), calcium carbonate equivalent (CCE) by neutralization with HCl, organic matter (OM) by wet oxidation (Sparks et al., 1996). Electrical conductivity (EC) and ph were determined in saturated paste and extract, respectively (Table 1). Copper (Cu) was extracted using DTPA extractant (DTPA 0.005M + CaCl M + TEA 0.1M at ph 7.3) (Lindsay and Norvell, 1978). In order to study the effect of soil: extractant ratio (SER) on the rates of Cu extraction and the patterns of Cu release, two SER including 1: 2 (SER 1/2 ) and 1: 10 (SER 1/10 ) were used in the experiment. Extraction study was conducted for shaking periods of 1, 10, 30, 60, 120, 240, 480, and 1440 min at 25± 2 C. After shaking, samples were centrifuged at 2500 rpm for 10 min. The concentration of Cu in the filtrates was determined!"# "# Instruments Ltd. UK). The patterns of Cu release were investigated using five mathematical models. These models were zero-order (q t = q 0 k 0 t), first-order ( ln q t = ln q 0 k 1 t), Elovich (q t = 1/$ s ln % s $ s + 1/$ s ln t), parabolic diffusion (q t = q 0 + Kp t 0.5 ), and power function (q t = a t b ), where k 0 is zero-order rate constant (mg Cu kg -1 s -1 ), k 1 is first-order rate constant (s -1 ), kp is diffusion rate constant [(mg Cu kg -1 ) -0.5 ], % s is initial Cu release rate (mg Cu kg -1 s -1 ), $ s is Cu release constant [(mg Cu kg -1 ) -1 ], a is initial Cu release rate constant (mg Cu kg -1 s -1 ) b, b is release rate coefficient [(mg Cu kg -1 ) -1 ], q t and q 0 are the amount of soil Cu released (mg Cu kg -1 ) after t (s) period of extraction and at t = 0, respectively. The goodness of fits was evaluated by calculation of coefficient of determination (R 2 ) and standard error of estimate (SE). A relatively high values of R 2 and low values of SE were used as criteria for the selection of the best fitted models. Standard errors of estimate were calculated as follows: SE = [ &(q q*) 2 / (n 2)] 0.5. Where q and q* represent the measured and predicted Cu extracted, respectively and n is the number of observations. Coefficients values of the best fitted models were calculated for the studied soils. Correlation coefficients between these values and soil properties were also determined. Data were analyzed using SPSS and Excel software packages. Results and Discussion Characterization of the soils Physiographic units, classification, moisture and temperature regimes, and selected physical and chemical properties of the studied soils are given in Table 1. The soils represented wide ranges in some soil properties including CCE (3-61%), Clay content ( %), and OM ( %). Alfisols, Inceptisols, and Vertisols were located on piedmont plains, but Histosols and Mollisols were located on lowlands. All soils were developed under mesic temperature regime (except for soil 5 with a thermic temperature regime). Alfisols, Inceptosols, and Vertisols were developed under xeric moisture regime. Histosols were developed,

3 however, under aquic moisture regime. Mollisols 7 and 8 were developed under xeric and ustic moisture regimes, respectively (Table 1). Patterns of Cu release from different soil orders Patterns of Cu extracted in different soil orders at two SER are shown in Figures 1 and 2. Overall, patterns of Cu released were characterized by an initial fast rate during the first two hours, followed by a slower release rate. This is in agreement with results reported by Olama et al. (2010) for Cu, Ghasemi- Fasaei et al. (2009) for Mn, and Dang et al. (1994) for Zn. At SER = 1: 2 (SER 1/2 ) Cu release rates from soil orders were in the order: Vertisols Alfisols Inceptisols Histosols Mollisols. Study of Cu adsorptiondesorption characteristics of 40 soils from three orders of Andhra Pradesh by Rupa and Shukla (1998) showed that Cu desorption was in the order: Alfisols Inceptisols Vertisols. At SER = 1: 10 (SER 1/10 ), however, Cu release rates from different soil orders were in following order: Histosols Vertisols Alfisols Inceptisols Mollisols. The values of coefficient of determination (R 2 ) and standard error of the estimate (SE) for different kinetic models at SER 1/2 and SER 1/10 are given in tables 2 and 3, respectively. At SER 1/2, the best models fitting to Cu release data were, respectively, power function, parabolic diffusion, and Elovich. These results are in agreement with the findings of Ghasemi-Fasaei et al. (2006). Khater and Zaghloul (2002) investigated the influence of ph on the pattern of Cu release and found that Cu desorption data well fitted to power function, parabolic diffusion, and first order models. At SER 1/10, Cu release data well fitted to power function, Elovich, and parabolic diffusion models, respectively (Tables 2 and 3).

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5 Soil no Table 1. Physiographic unit, classification, moisture and temperature regimes, and selected physical and chemical properties of the studied soils. Classification Fine, smectitic, mesic, Typic Haploxererts Fine, smectitic, mesic, Typic Haploxererts Fine, carbonatic, mesic, Typic Haploxerepts Fine, carbonatic, mesic, Typic Calcixerepts Fine, carbonatic, thermic, Calcic Haploxeralfs Clayey-skeletal, smectitic, mesic, Calcic Haploxeralfs Fine-loamy, carbonatic, mesic, Entic Haploxerolls Fine, carbonatic, mesic, Typic Haploxerolls Very-fine, carbonatic, mesic, Hydric Haplofibrists Very-fine, carbonatic, mesic, Hydric Haplofibrists Physiographic unit Lowland Lowland Lowland Lowland Temperature regime Thermic Moisture regime Ustic Aquic Aquic Clay Silt Sand CCE OM...(%) ph CEC cmol c kg EC ds m Table 2. Coefficient of determination (R 2 ) and standard error of the estimate (SE) for different kinetic models (soil: extractant ratio = 1: 2). Power function Parabolic diffusion Elovich Zero order First order Soil no. R 2 SE R 2 SE R 2 SE R 2 SE R 2 SE Mean

6 Table 3. Coefficient of determination (R 2 ) and standard error of the estimate (SE) for different kinetic models (soil: extractant ratio = 1: 10). Power function Parabolic diffusion Elovich Zero order First order Soil no. R 2 SE R 2 SE R 2 SE R 2 SE R 2 SE Mean Soil order / number Vertisols Inceptisols Alfisols Mollisols Histosols Rate Soil : constants extractant ab 1 : (mg kg -1 S -1 ) b 1 : q 0 1 : (mg kg -1 ) 1 : Kp 1 : mg kg -1 S 0.5 ) 1 : Table 4. Rate constants of the best fitted models in different soil orders. Table 5. Correlation coefficients between soil properties and percent increase in Cu extracted at soil to extractant ratio = 1: 10 than those of soil to extractant ratio = 1: 2. OM ph EC CEC CCE sand silt clay PI PI ** * PI ** PI ** * PI ** * PI ** ** PI ** * PI ** *and **: Significant at p ' 0.05 and p ' 0.01, respectively. PI-1 to PI-1440: percent increase in Cu extracted at soil to extractant ratio = 1: 10 than those of soil to extractant ratio = 1: 2 for time intervals of 1 to 1440 min, respectively. Influence of soil to extractant ratio on Cu extraction Results showed that the amounts of Cu released at SER 1/10 were higher than those of SER 1/2 in all studied soil orders (Figure 3). These results are compatible with those reported by Papassiopi et al. (1999) and Harter and Naidu (2001). According to the findings of Harter and Naidu (2001) change in soil to solution ratio may influence the aqueous phase chemistry of native trace metal ions, and affect either or both sorption and desorption processes. Lindsay and Norvell (1978) reported that with a SER 1/2, the capacity of DTPA to complex Cu is 10 times its atomic weight, about 640 parts per million, which is higher than Cu extraction data in present study demonstrating that lower rates of Cu extracted at SER 1/2 is not related to the saturation of DTPA. Smaller rates of Cu extracted at SER 1/2 may be attributed to the lower extractant distributed to the soil per unit weight (Wang et al., 2007). The differences between Cu extracted at two SER are shown in Figure 3. The differences were more considerable in Mollisols and Histosols than the other soil orders (Figure 3). Ratio of Cu extracted at SER 1/10 to that of SER 1/2 varied at different shaking periods (Figure 4). The highest ratio was related to the first shaking period, 1 min, and decreased with time thereby the lowest ratio was related to the highest shaking period, 1440 min. The differences in the extraction capacity of the extractant

7 between the two SER decreased with time (Figure 4). A quadratic regression equation described the relationship between time (X) and Ratio of Cu extracted at SER 1/10 to that of SER 1/2 (Y) (Eq. 1). Y = X X R 2 = 0.79 p = (1) Some rate constants of the best fitted models including ab (initial release rate of Cu) (Dalal, 1985), q 0 (the amounts of Cu released at t = 0), and Kp (Cu diffusion rate constant) for different soil orders at two SER are given in Table 4. Rate constants of Cu at SER 1/10 were greater than those of SER 1/2 in all soil orders. Mean ab, q 0, and Kp values at SER 1/10 were about 3.6-, 4.1-, and 1.86-fold higher than those of SER 1/2, respectively (Table 4). Percent increase in Cu extracted at SER 1/10 than those of SER 1/2 ranged from 76 to 316% (Data not shown). Correlation coefficients between soil properties and percent increase in Cu extraction at SER 1/10 than those of SER 1/2 showed that among soil properties, OM and CCE were positively correlated with this increase in most extraction periods (Table 5). Lindsay and Norvell (1978) believed that DTPA with a SER 1/2, extracts available forms and prevents dissolution of micronutrients in forms which are normally not available to plants. Some chemical forms of Cu such as Cu bound to carbonates and OM are potentially available forms (Ma and Uren, 19(")*"+, higher extractant distributed to the soil per unit weight at SER 1/10 might be responsible for higher dissolution of Cu bound to carbonates and OM which are potentially available forms, besides other available forms. Conclusion Overall patterns of Cu extracted was characterized by a fast release reaction during the first two hours followed by a slower reaction and the patterns well fitted to power function, parabolic diffusion, and Elovich models. Results showed that the amounts of Cu released at soil to extractant ratio = 1: 10 (SER 1/10 ) were 76 to 316% higher than those of 1: 2 (SER 1/2 ) in different soil orders. The difference in the extraction capacity of the extractant between two SER was more sizeable in Mollisols and Histosols and in all soils decreased with time. According to results of correlation coefficients between soil properties with percent increase in Cu extraction at SER 1/10 than those of SER 1/2, it is assumed that the higher extractant distributed to the soil per unit weight at SER 1/10 might be responsible for higher dissolution of Cu bound to carbonates and OM which are potentially available forms, besides other available forms. Acknowledgment The authors would like to appreciate Shiraz University and Darab College of Agriculture and Natural Resources for providing some research facilities. References Dalal RC Comparative prediction of yield response and phosphate uptake from soil using anion and cation-anion exchange resins. Soil Sci. 139, Dang YP, Dalal R, Edwards DG, Tiller KG Kinetics of zinc desorption from Vertisols. Soil Sci. Soc. Am. J. 58, Fest EPMJ, Temminghoff EJM, Comans RNJ, Riemsdijk WH Partitioning of organic matter and heavy metals in a sandy soil: Effects of extracting solution, solid to liquid ratio and ph. Geoderma 146, Ghasemi-Fasaei R, Maftoun M, Ronaghi A, Karimian N, Yasrebi J, Assad MT, Ippolito JA Kinetics of copper desorption from highly calcareous soils. Commun. Soil Sci. Plant Anal. 37, Ghasemi-Fasaei R, Maftoun M, Olama V, Molazem B, Tavajjoh M Manganese-release characteristics of highly calcareous soils. Commun. Soil Sci. Plant Anal. 40, Ghasemi-Fasaei R, Ronaghi A, Farrokhnejad E Comparative study of metal micronutrients release from two calcareous soils. Arch. Agron. Soil Sci. (In Press). Ghasemi-Fasaei R, Tavajjoh M, Olama V, Molazem B, Maftoun M, Ronaghi A, Karimian N., Adhami E Copper release characteristics in selected soils from southern and northern Iran. Aust. J. Soil Res. 45, Harter RD, Naidu R An assessment of environmental and solution parameter impact on trace-metal sorption by soils. Soil Sci. Soc. Am. J. 65: Jalali M, Moharrami S Competitive adsorption of trace elements in calcareous soils of western Iran. Geoderma 140, Karaca A Effect of organic wastes on the extractability of cadmium, copper, and zinc in soil. Geoderma 122,

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