Soil science
zahra movahedirad; Mohsen Hamidpour
Abstract
Introduction
Recently, layered double hydroxides (LDH) have attracted considerable attention. LDHs have found applications in numerous cases particularly slow-release fertilizers for essential nutrients for plants. Several studies have reported the release of nitrate and phosphorus from LDHs. The metal ...
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Introduction
Recently, layered double hydroxides (LDH) have attracted considerable attention. LDHs have found applications in numerous cases particularly slow-release fertilizers for essential nutrients for plants. Several studies have reported the release of nitrate and phosphorus from LDHs. The metal hydroxide layer can structurally incorporate micronutrients such as Zn, Cu, and Mn. According to recent research, LDHs have a suitable potential for releasing micronutrients. No information regarding ratios M2+/M3+ in LDHs and the influence of malic acid on the release of Zn, Mn, and Mg from LDHs is available. This study aimed to investigate the effects of malic acid and the ratio of divalent cation (M2+) to trivalent cation (M3+) on the kinetics release of Zn, Mn and Mg from Mg-Zn-Mn-Al-LDH intercalated with nitrate.
Materials and Methods
All chemicals used in this study including malic acid (C4H6O5), KCl, Zn (NO3)2.6H2O, Mn(NO3)2.4H2O Mg(NO3)2.6H2O and Al(NO3).9H2O were of analytical grades, purchased from Chem-Lab or Merck Chemical Corporations. The solutions were made with the decarbonated ultrapure water (electrical resistivity = 18 MΩcm). The LDHs were synthesized by co-precipitation method at constant pH = 9.2-9.6. Two types of LDHs were synthesized with varying the M+2(Zn+Mn+Mg)/M+3(Al) 3:1 and 4:1 in the precursor solution while being stirred vigorously in a nitrogen atmosphere. The pH was kept at 9.2-9.6 by adding volumes of 3 M NaOH. The crystals of LDH were ripened in the mixture for 2 h and after that, the precipitates were centrifuged at 3000 rpm for 20 min and washed several times with distilled water and placed in an oven at 70 °C for 8 hours to dry. The chemical composition of the synthesized LDHs was determined by furnace atomic absorption spectrophotometry (SavantAA, GBC) after acid digestion. The physical, chemical, and morphological characteristics of the LDHs were determined using X-ray diffraction analysis (Panalytical x Pert ProX-ray diffractometer), Fe-SEM (Sigma VP), FT-IR (Nicolet iS10 spectrometer), and BET (BELSORP Mini II) techniques.
A batch study was done to determine the effect of different ratios of M2+/M3+ in LDHs and the effect of malic acid on release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1). Briefly, 0.01 g of synthesized LDH were put in a centrifuge tube mixed with 10 ml background electrolyte (KCl 0.01 M) and 1.25 mM malic acid in initial pH=6-7 and constant temperature (25±0.5 °C). Blank samples (without ligand) were also considered. Suspensions were shaken at periods ranging from 5 to 720 min agitation (180 rpm). Then, the supernatant solution was separated using a centrifuge at a speed of 4000 rpm for 20 minutes. Zn, Mn, and Mg concentrations in supernatant solutions were determined by graphite furnace atomic absorption spectrophotometry. The effect of pH in the range of 5 to 10 on the release of Zn, Mn, and Mg from LDH was also studied. Two equations (pseudo-second-order and Elovich) were used to fit the kinetics data.
Results and Discussion
. The results showed that the calculated molar ratio of divalent cation to trivalent cation is similar to their molar ratio in the solution prepared for the synthesis of LDH samples. The X-ray diffraction patterns of LDH (3:1) and LDH (4:1) samples show the existence of strong and sharp peaks for 003 and 006 plates. Accordingly, the reflections of the 003 and 006 plates reveal the layered structure of the synthesized LDH materials. Two bands of FT-IR spectrums around 3480 and 1620 cm-1 for all synthesized LDH materials designate stretching vibrations of the O-H group of hydroxide layers and the interlayer water molecules. The sharp characteristic band around 1382 cm−1 in LDH (3:1) and band around 1354 cm-1 in LDH (4:1) is attributed to the antisymmetric stretching mode of nitrate anion in LDH. The specific surface area of LDH (3:1) and LDH (4:1) were 5.50 m2g-1 and 16.54 m2g-1 respectively. The average pore diameters in LDH (3:1) and LDH (4:1) were 1.92 nm and 2.55 nm, respectively.
Time-dependent cumulative release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1) in the presence and absence of malic acid was investigated. Time-dependent Zn, Mn, and Mg release from LDH (3:1) and LDH (4:1) was accelerated in the presence of malic acid. The Zn, Mn, and Mg release from the LDHs was likely to be separated into two stages. In the initial stage from 0 to 60 min, the release rate of Zn, Mn, and Mg was rapid, then either remained constant or slightly enhanced during 60–720 min. In this research, among the non-linear models used to determine the release kinetics of Zn, Mn, and Mg, the result with the highest R2 values was chosen. The R2 values were 0.91–0.99, 0.93–0.99, 0.93–0.99, 0.89-0.99, and 0.55–0.86 for pseudo-first-order, pseudo-second-order, Elovich, power function, and parabolic diffusion, respectively. So, pseudo-second-order and Elovich models were used to analyze kinetic data. The amounts of release of Zn, Mn and Mg were higher from LDH (4:1) than from LDH (3:1) because of greater specific surface area, volume, and pore diameter in LDH (4:1). On the other hand, the presence of divalent cations in this structure has increased its instability. A comparison of metal release versus time profiles exhibited that dissolution was greatly dependent on the pH.
Conclusions
The results of this research showed that the release of Zn, Mn, and Mg from LDHs was dependent on time, ligand, solution pH, and the type of LDH. Based on the results of fitting the kinetics models to the experimental data, the release rate of Zn, Mn, and Mg from LDH (4:1) was higher than LDH (3:1). In both types of LDH, the presence of malic acid led to an increase in the rate and amount of release of Zn, Mn, and Mg compared to the absence of malic acid. Although the results of this research showed that it is possible to influence the amount and rate of release of Zn and Mn by synthesizing these compounds in different ratios of divalent to trivalent cations, to confirm the efficiency of LDH as a slow-release fertilizer in calcareous soils, greenhouse studies are needed.
Soil science
M. Madahinasab; M. Mousavi nik; S.A. Ghanbari; A.R. Sirousmehr; Sh. Kouhestani
Abstract
Introduction: The use of sewage sludge, which is mixed locally with poultry waste and is available at a relatively low cost, improves the circulation of nutrients and organic matter in the soil, reduces the concentration of CO2 in the atmosphere, and increases the level of soil organic carbon. Fertilization ...
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Introduction: The use of sewage sludge, which is mixed locally with poultry waste and is available at a relatively low cost, improves the circulation of nutrients and organic matter in the soil, reduces the concentration of CO2 in the atmosphere, and increases the level of soil organic carbon. Fertilization with this method is of particular importance in soils of arid and semi-arid regions that face erosion and organic matter reduction. However, there are concerns about the presence of essential and unnecessary heavy metals such as Cd, Cr, Cu, Ni, Pb, and Zn that enter the environment from domestic, light industrial, commercial and municipal wastewater sources and can lead to soil contamination and eventually enters the food chain through absorption, transport, and accumulation in agricultural and non-agricultural products and has threatened human and animal health. Phytoremediation is the cleaning up of polluted terrestrial areas and aquatic sites from heavy metal and organic contaminants by green plants. An appropriate plant for phytoremediation should ideally have a high ability to translocate contaminants into the plant shoot. However, the toxicity of the remains of these plants has become a severe problem for human health. Iran is an arid and semi-arid country and many soils face the problem of using animal manure sources with sewage sludge and the possibility of contamination with heavy metals. Farmers cultivate the barley plant (Hordeum vulgare L.) in these areas widely, and it has a significant role in the food chain of livestock and humans. Therefore, in this study, we evaluated the barley plant in terms of lead and chromium accumulation by increasing drought levels in the field.Materials and Methods: It was a two-year field experiment with three irrigation levels (irrigation per 100 (control), 75 and 50% of field capacity). The amount of chromium and lead in soil and plant samples was measured using atomic spectroscopy with flame mode after extraction by digestion in acid. We used bio-concentration coefficients including root bioaccumulation factor ( ), shoot bioaccumulation factor ( ) and translocation factor ( ) to measure the plants bio-accumulation capacity. A plant with a root bioaccumulation factor bigger than one and a bio-translocation factor of less than one is suitable for plant stabilization of elements. In contrast, a plant with a shoot bioaccumulation factor and bio-translocation factor of more than one and root bioaccumulation factor of less than one is suitable for plant extraction of elements from the soil.Results and Discussion: After barley harvest, the average concentration of lead and chromium in soil decreased by 23% and 17% compared to before harvest. The results of the analysis of variance showed that the effect of experimental years was significant on the concentration of chromium in the soil and the aerial part of barley and shoot bioaccumulation and root bioaccumulation factor of the same elements in the barley (p<0.05). The effect of drought was significant on the shoot and root dry weight, chromium concentration in both shoots and roots, lead concentration in shoots, lead and chromium shoot bioaccumulation factor, chromium root bioaccumulation factor, and lead bio-translocation factor (p<0.01) and chromium bio-translocation factor (p<0.05) but the interaction effect of year and drought was not significant on any of these traits. In all cases, the concentration of elements in the roots was higher than the aerial part, and with increasing drought stress, the concentration of lead in the roots remained constant but increased in the aerial parts while the concentration of chromium decreased. As the amount of drought increased, the shoot bioaccumulation factor increased for the lead but decreased for the chromium. The root bioaccumulation factor of chromium also decreased while the translocation factor increased for both elements, but the increase was more pronounced for the lead. Lead shoot bioaccumulation factor decreased linearly with an increasing dry weight of aerial parts (β = -0.86), but chromium shoot bioaccumulation factor increased (β = 0.62). Root dry weight predicted chromium root bioaccumulation factor (β = 0.85). The total plant dry weight regression model could predict the lead translocation factor (β = -0.89) and chromium transfer factor (β = -0.67).Conclusion: In this experiment, the studied bioconcentration coefficients were all less than one. So, barley is an avoidant plant when encountered with lead and chromium in the soil, and in increasing drought conditions in the field, it does not translocate these toxic metals to the food chain.
H. Arfania; Abbas Samadi; F. Asadzadeh; E. Sepehr
Abstract
Introduction: Phosphorus (P) is an essential nutrient for all life forms. In aquatic environments, P is a double-edged sword. In some areas, habitat biodiversity is strongly limited by low P bioavailability, while in others, P inputs in excess of plant needs have led to pollution of water bodies and ...
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Introduction: Phosphorus (P) is an essential nutrient for all life forms. In aquatic environments, P is a double-edged sword. In some areas, habitat biodiversity is strongly limited by low P bioavailability, while in others, P inputs in excess of plant needs have led to pollution of water bodies and eutrophication. There is little information available on P status in river sediments by single chemical extraction and its correlation with algae growth in Iran. This study was performed to select proper single chemical extraction methods by algal bioassay. The quantity of P estimated by different extractions methods depends on sediment characteristics such as calcium carbonate, pH, clay and organic matter contents. Therefore, this study was conducted in western rivers of the Lake Urmia to get an insight into P status in sediments by using single chemical and biological P assay.
Materials and Methods: The lakeUrmia basin has the second largest water resources in Iran with Mediterranean climate. Italso has the largest hypersaline lake in the world. There is a significant phytoplankton growth and also some dense algal blooms occurring during years with low salinity in wetlands and lagoons. Thirty four river sediment samples from seven main rivers of the Lake Urmia basin were collected from depth of 0-10 cm to evaluate algae (SenedesmusObliquus) P bioavalability by single chemical extraction. Selection of extractantis based on different mechanism of extraction. Cluster analysis was conducted on 17 sediment samples selected for algal bioassay.Pearson simple correlation and multivariate analysis were also performed.
Results and Discussion:Average total P concentrations of the sediments were343-654, 456 mg kg-1. Sodium bicarbonate 0.5 Mextractable P (Olsen-P) varied from 0.48 to 8.42 mg kg-1. Sediments from upper reach had considerably higher total and bioavailable P concentration in comparison with lower reach sediment. The low reach sediments of two rivers had higher Olsen extractable P than the threshold value of 20 mg kg-1indicating possible release which poses a threat to aquatic environment.Upper reach sediments had higher restoration potential, but algal bloom was observed in low reach part of rivers, particularly Simineh and Mahabad Chai. Land use changes, discharge of sewage from rural and urban section, industrial activity and cycling of river borne P are the main reasons for algal bloom in wetlands and lagoons around the lake.Principal component analysis (PCA) performed on the data identified three PC which explained 83.3% of total variation and silt and sand had higher loading values. Active calcium carbonate equivalent (ACCE) was negatively correlated with sand in the first PC. Different extractions were positively correlated with each other. The Mehlich III and Olsen-P extraction methods were significantly correlated and the predicted values were same. The average rank order of P extraction by singleextractantswas Cowell >Mehlich III >NaOH 0.1 M > Olsen > Morgan > AB-DTPA > Bray II.Extractants had different long-term and short-term potential to extract algal available P. The Cowell extractable P concentrations of sediments varied from 1.44 to 88.0 mg kg-1.This extractant was correlated significantly with algal growth and selected as the best P single extraction method among allextractants. The high correlation between 0.1 M NaOH and algae growth indicates the sensitivity of P bioavailability to redox conditions in river system. Algae (SenedesmusObliquus) was able to use P from different sediment components because its growth was correlated with Cowell, Mehlich III, NaOH 0.1M, Olsen and Morgan.
Conclusion: Legacy P (sediment P) evaluation by chemical extractants gives new insight into P bioavailability in river sediments of the Urmia Lake. The results of this work showed that Cowell extractant could be used to estimate algal available P in studied river sediments. Similarity between Olsen-P and Mehlich-P in estimating bioavailable P suggests that Mehlich III-P can be substituted for Olsen-P in studied sediments.For sustainable P management, monitoring P status by single chemical extraction methods is necessary. Phosphorous fertilizer application around the Lake Urmia basin lands should be conducted based onthe P soil test to avoid any aquatic pollution. Care must be taken in lower reach river sediments because of fragile ecosystems such as wetlands and lagoons. Further investigations are also needed to evaluate legacy P bioavailability by temporal and spatial variability.
Somayeh Sefidgar; Mojtaba Barani Motlagh; farhad khormali; Esmael Dordipour
Abstract
Introduction: Soil pollution with heavy metals have become a global concern because of its damaging effects on the environment, including human health, toxicity in plants and long-term effects on soil fertility. Heavy metals stress in plants is characterized by decrease in photosynthesis, nutrient uptake, ...
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Introduction: Soil pollution with heavy metals have become a global concern because of its damaging effects on the environment, including human health, toxicity in plants and long-term effects on soil fertility. Heavy metals stress in plants is characterized by decrease in photosynthesis, nutrient uptake, damaging of roots and finally plant death. Lead (Pb) is found to be the most dangerous heavy metal, responsible for reduced soil fertility and elevated environmental pollution. Lead toxicity causes the inhibition of seed germination and exerts adverse effects on growth and metabolic processes of plants, which retards plant and crop production. The overproduction of reactive oxygen species (ROS) is the best indicator for secondary stress, which results in a number of toxic effects on biochemical processes in many plant cells. The overproduction of ROS due to Pb stress brings about changes in cellular membrane permeability, which in turn damages organelles such as nuclei, mitochondria, and chloroplasts in plant cells which decreased plant growth and yield. Chemical stabilization is an in situ remediation method that uses inexpensive amendments to reduce contaminant availability in polluted soil. The aim of this study was to investigate the immobilization of lead in a calcareous contaminated soil using two types of biochar as organic and Pumice, Leca, Zeolite and Bentonite as inorganic amendments.
Materials and Methods: In order to investigate the effect of organic amendments (biochar 640°C, and biochar 420°C) and inorganic amendments (Pumice, Leca, Zeolite and Bentonite) on Pb stabilization in a contaminated soil (1500 mg/kg), a greenhouse experiment using maize plant was carried out. This experiment was conducted in a completely randomized design consisting of 6 types of amendments (Pumice, Leca, Zeolite, Bentonite, Biochar 420°C, and Biochar 640°C) and at 1% and 5% levels of each amendment (12 amendments plus 1 control). The experimental treatments were incubated for 3 months. At the end of incubation time, the potential bioavailability of Pb in non-amended and amended soils was assessed by chemical extractions, as: extraction with DTPA, with ammonium acetate and with ethylenediaminetetraacetic acid (EDTA). After the end of incubation time, the pots were transferred to a greenhouse and in each pot five maize seeds were planted and then reduced to three seedlings in each pot after germination. After 3 months, all the plants were harvested. The Pb concentration in each plant, its biomass, its chlorophyll and its antioxidant enzyme activities levels were analyzed. All statistical analyses were performed using SAS software. Means of different treatments were compared using LSD (P ≤0.05) test.
Results and Discussion: The results indicated that the addition of amendments to soils reduced the concentration of Pb extracted with DTPA and EDTA. The 5% biochar 640 had the greatest reduction effect on DTPA-extractable Pb. The smallest concentration of Pb in the leaves and root of maize plant was observed in treated soil with organic amendments (biochar 640°C, and biochar 420°C) and treated with 5% zeolite, respectively. The highest increase in plant growth parameters like SPAD value, leaf area, plant height, number of leaves per plant, dry biomass yield and dry matter of roots were observed in organic amendments compared to the control. The application of 5% amendments in soil caused a significant increase in plant height and number of leaves as compared to control. The increase in growth and biomass of zea mays L. under various amendments might be due to decreased bioavailable Pb concentrations in soil amended which may be attributed to reduced Pb toxicity through improvement of soil fertility. Also, the application of amendments resulted in a significant increase in antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), peroxidase (PX), and ascorbate peroxidase (ASP) in maize plants compared to the control. The increase of leaves enzyme activities with addition amendments may be due to a lower Pb accumulation in leaves because excess Pb generates free radicals and reactive oxygen species (ROS) those causes oxidative stress in plants.
Conclusions: The results indicated that the application of amendments were successful in lowering the potential bioavailability of Pb in the soils. The 5% biochar 640 treatment had the greatest reduction effect on extractable Pb. The application of amendments decreased the uptake and accumulation of Pb in maize plants, via the reduction of DTPA- extractable Pb. The amendments also significantly increased leaves antioxidant enzyme activities and photosynthetic pigments compared to the control.
faeze lotfi; amir fotovat; reza khorasani; Mahdi Bahraini
Abstract
Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical ...
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Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical forms in the soil. According to Tessier (1979), heavy metals can be found in various chemical forms in soil including exchangeable, bound to carbonates, bound to iron and manganese oxides and bound to organic matter and residual. These fractions significantly influence the cadmium mobility and bioavailability. Distribution of metals in chemical forms in soil depends on soil pH, amount of organic matter, oxidation-reduction potential and ionic strength. Root exudation, soil texture, cation exchangeable capacity and amount of calcium carbonate may also impact chemical forms of cadmium. Many studies have showed that plant root may affect the chemistry of heavy metals in soil root zone. The objective of this study was to evaluate the effect of organic matter on the distribution of cadmium in corn root media.
Materials and Methods: To investigate the effect of organic matter (cow manure) and root activity on chemical forms of cadmium, a greenhouse experiment was conducted using rhizobox. The contaminated soil sample used in the study was collected from Zanjan. This greenhouse experiment was conducted in a factorial design, with 2 replications, two levels of organic matter (0 and 1.5%) and three zones classified based on their distance from root. The soil samples were air dried and crushed to pass through a 2-mm sieve. The cultivation was conducted using a rhizobox. The rhizobox consisted of three parts: 1.central compartment (rhizosphere), 2.close to rhizosphere, and 3. soil bulk. Soil samples were mixed with fertilizer and packed in rhizobox. Eight pre-germinated maize seedlings were transferred to the central compartment and five days after germination, thinned to four plants. Ten weeks after planting, corn plants were harvested for analysis. The compartments of rhizobox were separated. The collected plant samples (root and shoot) were rinsed with deionized water and oven-dried at 70 °C. Soil samples were also measured for pH, CEC and total organic carbon. The chemical forms of cadmium in the soil and plant samples were identified by the sequential extraction procedure proposed by Tessier (1979). Bioavailable cadmium in soil was also extracted by DTPA-TEA.
Results and Discussion: Results showed that the highest amount of soil cadmium was found in carbonate fraction. Adding organic matter increased the soil pH, CEC and organic carbon amount, whereas none of chemical forms of cadmium were significantly affected by adding organic matter. Bioavailability of cadmium, however, decreased by adding organic matter to soil, It can be therefore concluded that increment in cadmium uptake due to increased organic matter led to decreased cadmium bioavailability. The exchangeable cadmium was negatively correlated to soil organic carbon, while bioavailable cadmium was negatively correlated to soil pH, CEC and amount of soil organic carbon. Moreover, our results indicated that the fractions of cadmium were not significantly affected by distance from the root. Moreover, adding organic matter insignificantly increased concentration of cadmium in shoots, roots and total plants.
Conclusion: In this study, among different chemical forms of cadmium, only bioavailable cadmium was significantly affected by adding organic matter to soil. Additionally, soil pH, CEC and organic carbon were significantly increased by adding organic matter. These results indicate that addition of organic matter to soil may indirectly influence chemical forms of cadmium through impacting soil properties (soil pH, CEC and organic carbon). The addition of organic matter had the most influence on carbonate fraction of cadmium which may be potentially available to plant. It seems that addition of organic matter (cow manure) may result in increase of cadmium concentration in plant. Therefore, it can be concluded that addition of cow manure to calcareous soils with neutral to slightly alkaline pH may lead to increased cadmium uptake by the plant (corn) and reduced soil cadmium concentration.
