JWSS - Journal of Water and Soil Science

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Information about forms of zinc (Zn) is important for the evaluation of its status in soil and also understanding of the soil fertility and chemistry. To obtain such information, amounts and distribution of Zn in different fractions of 20 soil samples of Tehran province, Iran were determined by sequential extraction method and their relationships with each other and with soil characteristics were investigated. Total Zn of soils ranged from 70 to 169.9 mg/kg^-1. The amount of different Zn forms relative to the sum of forms was determined to be as follows: organic less than 0.1, soluble+exchangeable 0.1, manganese-oxide-associated 0.9, carbonate 1.6, crystalline iron-oxide-associated 3.8, amorphous iron-oxide-associated 4.2, and residual form 89.3%. Simple correlation coefficients showed that pH had a negative significant correlation with all forms of Zn except organic. Silt and clay contents had significant positive correlations with total, residual, and crystalline iron-oxide-asociated Zn but CEC had significant correlation only with total Zn. Calcium carbonate equivalent showed a significant correlation with soluble+exchangeable, manganese-oxide-associated and amorphous iron-oxide-associated Zn. DTPA-extractable Zn was significantly correlated with soluble+exchangeable, carbonate, and amorphous iron-oxide-associated Zn. A significant correlation was also observed between the Zn forms themselves, which is presumably a reflection of the existence of a dynamic relation between the chemical forms of an element in soil.

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Application of sewage sludge on the farmland as a source of crop nutrient had recently received considerable attention. Some management practices may be required to control the accumulation of toxic elements including Pb, Ni and Cd. Sequential extraction gives useful information on plant bioavailability of the elements. The objective of this study was to investigate the cumulative and residual effects of sewage sludge application on the chemical forms and mobility factor of Pb, Ni and Cd. Zero, 25, 50 and 100 Mg ha-1 of sewage sludge were applied for 1, 2 and 3 consecutive years in a split plot design, with three replications. Soil samples were taken from 0-20 cm at the end of the third year of application. Different chemical forms of Pb, Ni and Cd were measured. Results revealed that the soluble form (SOL) of Ni and Cd increased whereas Pb soluble form decreased with increasing levels and years of application. Exchangeable (EXC), carbonate (CAR) and organic (ORG) forms of the three elements increased as levels and years of application increased. Occluded (OCC) form decreased for Pb, Ni and increased for Cd. Residual form (RES) of Pb increased while that of Ni and Cd decreased. A gereral increase was observed for available (DTPA-extractable) concentration of Pb, Ni and Cd. Relative distributions of different chemical forms were in the following order: Pb: OCC > RES> ORG> CAR> EXC> SOL, Ni: RES> ORG> OCC> CAR>EXC> SOL and Cd: OCC> CAR> RES> ORG> EXC> SOL. The comparison of different forms of the metals showed the following orders: soluble Ni>Pb>Cd, exchangeable, carbonate and occluded Pb>Ni> Cd, organic and residual Ni> Pb>cd. Increasing the available (DTPA-extractable) concentration of the elements in such a calcareous soil showed that consecutive application of sewage sludge may increase the available (DTPA-extractable) concentration beyond critical levels. A significant corretation was observed between organic form and available (DTPA-extractable) concentration of the elements.

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Cadmium (Cd) and its rate in soil have received lots of attention because it is easily taken up by plant root, making it 20 times more toxic in comparison with other heavy metals. Knowledge about the factors affecting Cd availability and conversion of its chemical forms is, therefore, important. Sequential extraction has been used as a suitable method for identification of chemical forms and their relationship with plant availability, but in soils of Iran less attention has been paid to studying the change in chemical forms as affected by time. The present research was designed to study the change in Cd chemical forms as affected by application rate and time of incubation in two soil textural classes. A clay loam calcareous soil [Fine, mixed (calcareous), mesic Typic Calcixerepts] was converted to sandy loam soil by adding pure quartz sand and both soils were treated with 0, 5, 15, 30, and 60 mg Cd / kg soil as cadmium sulfate and incubated at room temperature near field capacity moisture. After 0, 1, 2, 4, 8, and 16 weeks, chemical forms of Cd were determined by sequential extraction. Results showed that, depending on the textural classes, about 82 and 87 % of applied Cd was converted to soluble+exchangeable, carbonate, and organic forms. In both soils carbonate fraction was dominant. Conversion of applied Cd to soluble+exchangeable and carbonate forms in sandy loam was higher than in clay loam. For organic, manganese oxide, amorphous iron oxide, and residual forms, the reverse was true. The crystalline iron oxide form was less than detection limit of atomic absorption in both textural classes. Increasing the application rate caused an increase in all forms of Cd but the percentage increase depended on the capacity of different soil components for Cd retention. Carbonate showed the highest capacity for retention. The effect of incubation time on conversion of Cd to different forms was significant. However, in almost all treatments more than 80 % of added Cd was converted to carbonate and organic forms immediately, and the proportion approximately stayed the same throughout the course of experiment.

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In order to investigate mineral manganese forms and their relations with plant responses, 22 soil samples from Fars province (0-20 cm) were in a greenhouse experiment filled in 3 liter pots, and soybean (Glycine max (L.) merr.,CV.Williams) was grown for 7 weeks. Chemical forms of manganese were determined in soils by warden and Reisenauer sequential extraction method (readily soluble, weakly adsorbed, carbonate bound and oxide bound extracted with Ca(No₃)₂, Ca DTPA +Na₂B₄O₇, HNO₃ and NH₂OH. HCl, respectively) after harvesting the plants. Results showed that the amount of Mn in different forms was in the following order: Carbonatic Mn >Mn Oxides >Weakly adsorbed Mn > Soluble Mn. Regression equations between soil properties and Mn forms showed a significant correlation between calcium carbonate equivalent and carbonate bound Mn. Significant correlation between Carbonate bound Mn and concentration of Mn in the aerial part of soybean showed that this fraction plays an important role in plant nutrition.

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This study was conducted to determine the effect of 3 extractants on K release from biotite, phlogopite and muscovite. The minerals were grouped to <60 and 60-100 µm size classes. Particles CEC were saturated with calcium. Sequential extraction up to 30 times was carried out using 0.01M HCl, 1M NH4OAc and 0.05M BaCl2 solutions and cumulative concentration of K was calculated for each extractant. There was a difference among the 3 extractants in cumulative K release values from the three minerals. The highest values of cumulative K release were obtained by 0.01M HCl and 1M NH4OAc for less than 60 and 60-100 µm particle sizes, respectively. The amount of K release from muscovite was even higher when 1M NH4OAc and 0.05M BaCl2 solutions were used as extractants. This might indicate that muscovite cannot be considered as an ineffective source of available K in soils. Furthermore, particle size had a great impact on nonexchangeable K release from micaceous minerals. Coarser particles released higher quantity of K as compared to that of finer particles. Therefore, particle size distribution of different micaceous minerals in soils may be a factor that causes a difference in the amount of K release from soils.

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Silver toxicity and its fate in the environment are currently being debated and are important as challenging research topics. Even though there are several studies on its total content in soils, fractionation of Ag especially in calcareous soils has not been investigated. Therefore, to provide fundamental information on the chemical behavior of Ag in calcareous and noncalcareous soils, we studied 8-step chemical fractions of Ag (i.e., EXCH, CARB, Me-Org, re-MeOx, H2O2-Org, am-MeOx, cr-FeOx, and RES) after 30 and 60 days of incubation in soils amended with Ag (0 and 15 mg kg-1), sewage sludge (0 and 20 t ha-1) and EDTA (0 and 0.5%). Experimental results showed that redistribution of Ag in spiked noncalcareous soils was EXCH (34%), H2O2-Org (33%) and RES (17%). In calcareous soils, after 30 days, EXCH- and RES-Ag increased but at the end of 60 days H2O2-Org-Ag increased. Based on our data, we could conclude that addition of Ag results in an increase of Ag mobility in soils but incubation and sewage sludge may have adverse effect on its mobility. In contrast to noncalcareous soil, EDTA in calcareous soil resulted in higher Ag mobility. This may have environmental implications in Ag polluted calcareous soils.

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The aim of this study was to investigate the effect of parent materials and pedogenic processes on distribution of Pb, Zn, Cu, and Ni in the residual soils derived from different parent materials in the Binaloud zone, western Mashhad. Two soil profiles on the summit of granitic, ultrabasic and metamorphic rocks were described and sampled from their genetic horizons. Pseudototal concentrations of selected heavy metals and fractions of these metals were determined using aqua-regia and sequential extraction methods, respectively. 178.1-419.7 mg kg-1of Ni in ultrabasic soil versus 0.7-27.5 mg kg-1 in the granitic soil make the Ni a distinctive element in the studied area. Cu with the average contents of 60 and 56.3 mg kg-1 in the ultrabasic and metamorphic soils respectively showed more concentration in comparison to granitic soils with 12.1 mg kg-1. The amount of Zn was not significantly different among the soils, although the average of this element in the granitic soil (55 mg kg-1) is slightly more than the other soils. Pb was only detectable in the surface layers of all pedons reaching up to 6 mg kg-1. Residual fraction except Ni and Cu in granitic soil was the main fraction for all of the studied heavy elements that was expectable according to the low weathering intensity of the soils. The eolain addition of gypsum and carbonates have influenced heavy metals concentration, especially in surface horizons. In conclusion, the amount of heavy metals was significantly affected by parent materials and the eolian deposition must be considered as the secondary influencing factor.

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In this research available iron was measured in 21 calcareous surface soil samples (0-30 cm) by five methods including DTPA, AB-DTPA, AC-EDTA, hydroxylamine, reference ammonium oxalate and rapid ammonium oxalate. Fe fractions were also determined by the modified sequential extraction procedures introduced by Singh et al. According to results, rapid ammonium oxalate and AC-EDTA methods extracted the maximum (856.03 mg.kg^-1) and minimum (4.46 mg.kg^-1) amounts of Fe, respectively. Rapid ammonium oxalate extraction method, in addition to Fe-Afeox, extracted other fractions of iron such as Fe-Ex, Fe-Om, Fe-CFeox and Fe-Res. Hydroxylamine method compared to other methods, ectracted Fe mostly from the amorphous oxides source. Regression analysis indicates that Fe-Ex, Fe-AFeox and Fe-Res fractions have major and Fe-Car and Fe-Mnox have minor role in releasing available Fe (with AB-DTPA and DTPA) in the studied soil. According to the statistical relationships, carbonates associated Fe, does not seem a potential source of available Fe in calcareous soils. Organic carbon content and cation exchange capacity of the soils appear the two most influential soil properties that predict available Fe in the studied soils.
 

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