Soil science
B. Abolfazli Behrooz; S. Oustan; H. Mirseyed Hosseini; H. Etesami
Abstract
IntroductionCadmium (Cd) contamination has been a widespread concern in paddy soils because of its subsequent transfer to the food chain. Biochar amendment is proposed to stabilize Cd in the contaminated soils. However, the pristine biochar shows limited functionality towards Cd sorption in practice. ...
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IntroductionCadmium (Cd) contamination has been a widespread concern in paddy soils because of its subsequent transfer to the food chain. Biochar amendment is proposed to stabilize Cd in the contaminated soils. However, the pristine biochar shows limited functionality towards Cd sorption in practice. Recently, Mg-modified biochars have attracted much attention for their low toxicity. These biochars are coated by MgO or Mg(OH)2 precipitates during the pyrolysis process. Magnesium chloride (MgCl2)-modified biochars have been used widely in the removal of heavy metals from the aqueous solutions. However, there is little literature about their performance in soils. The present study therefore was conducted to investigate the effects of application of unmodified and MgCl2-modified rice husk biochars on the kinetics and isotherms of Cd sorption in a calyey paddy soil. Materials and MethodsThe unmodified and MgCl2-modified biochars were produced from rice husk at 600°C. Some relevant characteristics of the produced biochars (including elemental composition, pzc, pH1:10, ash content and BET surface area) were determined. Moreover, the studied soil was taken from a paddy field (0-20 cm) in the Qaemshahr region of Mazandaran province. The biochars (< 0.5 mm) were added to the soil samples at three levels (0, 3, and 5% w/w) and the amended soils were incubated at 25°C for 45 days. Then, the kinetic experiments of Cd sorption at a concentration of 375 mg Cd/L at times of 0.25, 0.5, 1, 2, 4, 8, 16, 24 and 48 hours and the isothermal experiments of Cd sorption at concentrations of 50, 100, 150, 200, 300, 350, 400, 600 and 800 mg Cd/L were performed. In both kinetic and isotherm experiments, a 0.01 M KCl solution was used as the background electrolyte. Finally, the relevant kinetic and isotherm models were fitted to the sorption data and their parameters were calculated. Results and DiscussionBiochar characterization indicated that modification with MgCl2 resulted in an increase of the O/C ratio (from 0.27 to 0.48) and pH (from 7.67 to 8.60). This modification also increased the H/C ratio (from 0.032 to 0.071) and the specific surface area (from 195.6 to 231.2 m2/g). As a result, the MgCl2-modified biochar was more hydrophilic and less carbonized than the unmodified one. Moreover, the characteristic peaks of the MgCl2-modified biochar (3700, 1428 and 500 cm-1) were present in its FTIR spectrum. The results revealed that about 74 to 89% of the Cd sorption by the soils occurred in times less than 2 hours. With MgCl2-modification, the sorption equilibration time was reduced from 48 hours to 24 hours. In contrast, the unmodified biochar had no considerable effect on the Cd sorption kinetics. Among the kinetic models, the Elovich model with lower SEE was the best to fit the Cd sorption kinetic data. The intra-particle diffusion model was not satisfactory for Cd sorption on the biochars. Freundlich model with lower SEE well described the Cd sorption isotherms. Application of 3% and 5% MgCl2-modified biochar increased the Freundlich KF parameter by 2.4 and 2.8 times as compared to the control. Moreover, the aforementioned treatments increased the heterogeneity parameter of the Freundlich model (n) from 3.48 to 6.08. The Temkin model could not reasonable fit the sorption data. In contrast, the unmodified biochar did not show any considerable effect on the Cd sorption capacity of the clayey soil used in this research. This finding means that the unmodified biochar could not improve the sorption performance of negatively charged soil clay particles. ConclusionAccording to the results obtained, it could be concluded that the Cd sorption behavior of the soil treated with unmodified rice husk biochar was similar to that of the untreated soil. Whereas, the MgCl2-modification improved both sorption rate and sorption capacity of the soil for Cd. Application of MgCl2-modified biochar improved the Cd sorption properties of a clayey soil with high intrinsic sorption ability. Thus, this may be a promising approach in remediation of Cd-contaminated paddy soils with the aim of reducing Cd mobility and availability. However, there is need to do more research to create awareness about the importance of biomass nature as well as pyrolysis temperature, the ratio of MgCl2 to biomass, the mechanism of Cd stabilization and the desorption of Cd from soils treated with MgCl2-modified biochars.
E. Shirmohammadi; H.A. Alikhani; Ahmad Ali Pourbabaee; H. Etesami
Abstract
Introduction: Stresses of drought, salinity and deficiency of nutrients especially phosphorus (P) are the most important challenges for wheat production in Iran. One of the ways to achieve more wheat yield production is increasing of this plants tolerance to stresses of water-deficit, salinity and deficiency ...
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Introduction: Stresses of drought, salinity and deficiency of nutrients especially phosphorus (P) are the most important challenges for wheat production in Iran. One of the ways to achieve more wheat yield production is increasing of this plants tolerance to stresses of water-deficit, salinity and deficiency of essential elements such as P; and/or alleviate destructive effects of these stresses. In this respect, use of PGPR can be useful. Research has shown that PGPR with multiple mechanisms reduces the negative effects of water-deficit and salinity stresses, and also increases the resistance of plants to these stresses, which ultimately leads to increase of plants growth. This study was designed and carried out to investigate the effect of three superior PGPR on qualitative and quantitative indices of wheat under water-deficit stress in saline soil. Materials and Methods: The soil used in this experiment was collected from longitude of 49° 26' 25'' E, latitude of 35° 52' 26'' N and elevation of 1534 m (located in the Qazvin province of Iran) from depth of 0-30 cm of soil. According to the experimental design, 3.5 kg of soil with applying P-fertilizers treatments was filled to the pots. The factorial arrangement based on completely randomized design (CRD) was used in this study. The treatments were replicated three times. The first factor: soil water content at two levels including 80% and 55% FC (W80 and W55); the second factor: Bacterial inoculants at four levels including control or non-inoculated seeds with bacterium (B0), inoculated seeds with Bacillus pumilus strain W72 (B1), inoculated seeds with B. safensis strain W73 (B2), inoculated seeds with Staphylococcus succinus strain R12N2 (B3); and the third factor: P-fertilizers at six levels including control or non-treated plants with P-fertilizers (F0), and plants treated with (rock phosphate) RP - (F1), RP + 19 mg triple superphosphate (TSP) / kg of soil (F2), RP + 38 mg TSP / kg of soil (F3), RP + 57 mg TSP / kg of soil (F4), with 57 mg TSP / kg of soil (F5), generally there were 144 experimental units (pots). Also, 192 mg RP (containing 13.8% P2O5 or 6.13% P) was mixed per kg of soil in each of RP treatments. Statistical analysis of data was performed using SAS software and comparison of means was evaluated by using the Tukey's test (HSD) at p < 0.05 level. There were 5 plants in each pot and irrigated up to 80% FC with distilled water. With the beginning of stem elongation stage, water-deficit stress was applied and continued until the harvest. During the experiment, pots were kept in greenhouse at 25/20±2°C day/night temperatures and 16 h photoperiod with 23,000 lux light intensity. At the end of the experiment, plants height, fertile clusters, root dry weight /shoot dry weight ratio, total dry weight of plant, grain number, thousand grain weight, also, root, shoot and grain P-concentration were measured. Results and Discussion: Generally, it can be said that the moisture level of W80 compared to W55 increased all of measured traits in wheat plant. Due to the unique properties of water and its role in biological and non-biological reactions, by reducing soil water content to near of the permanent wilting point (W55), water absorption by the plant hardly occurs. Therefore, the plant needs to consume more energy for water absorption or grow with less water than normal status, which these factors disturb the metabolism of cells and eventually decreases natural activity and growth of plant. Also, it seems that under water stress condition, wheat plant by formation of “Rhizosheaths” around of their own roots, enters to the defensive phase and by this strategy prevents expansion of their own rhizosphere. With attention to the special importance of the rhizosphere in the supply of water, nutrients and activity of microorganisms, as well as the effect of microorganisms secretion and root exudates on the solubility and availability of nutrients. Thus, it is reasonable that qualitative and quantitative traits of plants decrease by reduction of the rhizosphere diameter due to the water-deficit stress. There was no significant difference between application of rock phosphate and control (F0) for most of measured traits of soil and plant; but, application of RP with bacterial treatments (B1 and B2 at W80 and B3 at both level of W55 and W80) compared to the control, often increased measured traits. Also, each level of TSP compared to the control, often increased this trait. Research indicates that RP can be used as a P-fertilizer, but its efficiency depends on its reactivity in the soil. There is ample evidence that RP has not enough efficiency in neutral and alkaline soils; but, it can be used as the P-fertilizer with proper efficiency in acidic soils or alkaline soil with application of PGPR. Often, all of three bacterial treatments (B1, B2 and B3) at level of W80 and B3 treatment at level of W55, compared to control (without bacterial inoculation) improved qualitative and quantitative traits of plant. Research also shows that under stressful and non-stressful conditions, PGPR can improve plant growth by different strategies. However, this microorganism does not always improve plant growth under all conditions. It seems to be due to differences in genetic and function of bacteria and with conditions change, each bacterium may behave differently. Conclusions In general, for wheat cultivation that may get exposed to moisture stress at one or more stages of its growth (such as dry-farming of wheat), the use of B3 bacterial inoculant (Staphylococcus succinus strain R12N2) seems appropriate for crop management. Because in this study at both W80 (non-water-deficit stress) and W55 (severe water-deficit stress) levels of soil water content, B3 treatment increased qualitative and quantitative of wheat traits. In other words, because of the natural conditions of the dryland farming, the probability of precipitation is different; it seems that B3 treatment can increase wheat production under these conditions. However, the use of this bacterium as a biofertilizer for dryland wheat farming in Iran or other place of the world requires further testing and evaluation in dryland farms of that countries.
H. Etesami; H.A. Alikhani
Abstract
Abstract
Now, it’s completely proved that we can find strains among many strains of each rhizobial group that can also do effective process in plant growth promoting as plant growth hormones production (IAA), in addition of their ability in N2 fixation .therefore, the aim of this research is to determinate ...
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Abstract
Now, it’s completely proved that we can find strains among many strains of each rhizobial group that can also do effective process in plant growth promoting as plant growth hormones production (IAA), in addition of their ability in N2 fixation .therefore, the aim of this research is to determinate the ability of IAA production of some of the indigenous rhizobial strains by two quantitative and qualitative methods. The results obtained from this study show that Rhizobial bacteria enable to produce auxin hormone (IAA). Moreover, this ability is not the same among various rhizobial species and among the strains belonging to each rhizobial species (p3), Rhizobium leguminosarum bv. Viciae (with HD/CD = 2.5 – 3) and Sinorhizobium meliloti (with HD/CD = 2 – 2.5) had the same production ability in both methods and also the strains of Mesorhizobium ciceri (with HD/CD= 1.5 – 2) and Bradyrhizobium spp (with HD/CD= 1 – 1.5) produced the small amount of IAA in both two methods.
Keywords: Rhizobbium, PGPR, IAA, Auxin, Tryptophan
