Soil Chemistry and Pollution
Khosro Betyar; Neda Moradi; Abdolamir Moezzi; Shila Khajavi-Shojaei
Abstract
Introduction Phosphorus deficiency is one of the major problems of calcareous soils and a limiting factor for crop production in these soils and excessive use of phosphate fertilizers can cause pollution in soil and water. The use of organic amendments such as compost, biochar or a combination of them ...
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Introduction Phosphorus deficiency is one of the major problems of calcareous soils and a limiting factor for crop production in these soils and excessive use of phosphate fertilizers can cause pollution in soil and water. The use of organic amendments such as compost, biochar or a combination of them can be effective in improving the amount of available phosphorus of the soil. For this purpose, the effect of combined application of compost and biochar of sugarcane bagasse on phosphorus sorption and desorption were investigated.Materials and Methods Sugarcane bagasse and compost were provided from Debal Khozaei agro-industry Company. The oven-dried sugarcane bagasse 105 ºC were pass through 2 mm sieve and slow pyrolysed at 500 ºC using a laboratory muffle furnace with a heating rate of 5 ºC min-1 and presence of N2 flow to provide an anoxic condition. Some physico-chemical properties of samples were determined. The soil sample was collected from 0-30 cm of the campus of Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan province, SW Iran (48° 65′91.12′′E31°30′53.82′′N). The studied soil classified as a Typic Haplocalcids. The air-dried soil samples were sieved (˂ 2 mm) and used for physico-chemical analysis. The incubation experiment was conducted with 7 treatments. The treatments including (1) control (without any amendments), (2) 100% sugarcane bagasse, (3) 100% sugarcane bagasse compost, (4) 100% sugarcane bagasse biochar, (5) 50% compost +50% biochar, (6) 75% compost + 25% biochar, (7) 25% compost + 75% biochar were added as 2% w/w to soil. The 200 g air-dried soil and treatments were mixed and kept in poly-ethylene containers for 120 days. Samples were incubated in 25 2 ºC and soil moisture was adjusted to soil field capacity using distilled water during the incubation time. At the end of incubation time, soil phosphorus sorption isotherm was measured. A 2.5 g of each treatment was transferred to a 50 ml centrifuge tube. Then, a 25 mL of CaCl2 0.01 M containing 0, 10, 20, 40, 60, 80, and 100 mg P L-1 (prepared from KH2PO4) was added to each centrifuge tube. Two drops of chloroform were added to each centrifuge tube to inhibit microbial growth. Samples were equilibrated at 25 1 ºC for 24 h on shaker at 150 rpm, and then centrifuged for 5 min at 3000 rpm and pass through 0.45-μm filter paper. The phosphate desorption was conducted on soil remaining in the filter immediately after sorption experiment. For this purpose, each treatment was resuspended with 25 ml of CaCl2 0.01 M solution without phosphate and shaken for 24 h. after collecting the supernatant, desorbed phosphate was measured. For assessing the adsorbed phosphate, the difference between the initial phosphate concentration and the phosphate concentration at equilibrium was calculated. The Langmuir, Freundlich and temkin isotherm models were used to describe the sorption of phosphate. In addition, some phosphorus buffering indices including maximum buffering capacity (MBC), standard buffering capacity (SBC), equilibrium buffering capacity (EBC) and standard phosphorus requirement (SPR) were obtained from P sorption equations at 0.2 mg P L-1 concentration in soil solution. The experimental data were fitted by Microsoft Excel-SOLVER and graphs were plotted by Microsoft Excel.Results and Discussion The soil was had loam texture, with low SOC content and high pH and calcium carbonate content, also the results of the characteristics of sugarcane bagasse compost and biochar showed that the compost had high salinity and the biochar had high pH and C/N ratio. The amount of phosphorus absorption increased with increasing the initial concentration of phosphorus in the treated soils. The highest and lowest amount of phosphorus absorption were in the control in compost treatments, respectively. In general, different levels of biochar and compost treatments caused a decrease in phosphorus absorption compared to the control treatment. The results showed that P sorption and desorption are described well by the Freundlich and Langmuir equations with a high correlation coefficient; however, the Temkin equation described the P sorption and desorption in the soils poorly. Biochar and compost treatments significantly decreased the Freundlich n parameter. Results showed that the effects of compost and 75% compost + 25% biochar were significantly greater than the effects of other treatments on the n parameter exponential adsorption equation. Application of different treatments of sugarcane bagasse compost and biochar application caused a significant increase in MBC (25.4-70.7%) and EBC (33.1-69.4%). The standard P requirements (SPR) were lower in soils treated than in control soil.Conclusion The results showed that the combined application of biochar-compost of sugarcane bagasse reduced the sorption and increased desorption of phosphorus. The maximum buffering capacity (MBC) and equilibrium buffering capacity (EBC), standard buffering capacity (SBC) and standard phosphorus requirement (SPR) in compost and compost 75% + biochar 25% showed more decrease than the control. In general, the results of this study indicate that the combined application of biochar-compost of sugarcane bagasse reduces phosphorus sorption in soil in calcareous soils, which can increase the availability phosphorus for plants.
Soil Biology, Biochemistry and Biotechnology
Naeimeh Enayatizamir; A Moezzi; Shila Khajavi
Abstract
Introduction Biosurfactants or microbial surfactants are surface active molecules that are produced from a variety of microorganisms. Due to its amphiphilic nature, these biomolecules are capable of lowering the surface tension, interfacial tension and forming micro-emulsion to enable mixing of two immiscible ...
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Introduction Biosurfactants or microbial surfactants are surface active molecules that are produced from a variety of microorganisms. Due to its amphiphilic nature, these biomolecules are capable of lowering the surface tension, interfacial tension and forming micro-emulsion to enable mixing of two immiscible solutions. Such properties exhibit excellent detergency, emulsifying, foaming and dispersing traits, which can be applied in various industries. The features that make them commercially promising alternatives to chemically synthesized surfactants are their lower toxicity, higher biodegradability, better foaming properties, and greater stability towards temperature and pH. Limited full scale production has been realized for many biosurfactants due to expensive raw material, low production yield and high purification cost. In order to alleviate these problems, many studies have been carried out using cost-free or low-cost feed stocks or agricultural byproducts as substrates for biosurfactant production. Oil pollution and remediation technology has become a global phenomenon of increasing importance. Materials and Methods In this study, Potential strains of microorganism were isolated from various hydrocarbon polluted area on nutrient agar medium using sterile saline (0.85% NaCl) method and different bacterial isolates were selected based on the colony morphology on nutrient agar. The selected isolates were screened for the production of biosurfactants using following screening methods. Pure culture of bacterial isolates were streaked on the freshly prepared blood agar and incubated at 37°C for 48-72 h. Results were recorded based on the type of clear zone observed i.e. α-hemolysis when the colony was surrounded by greenish zone, β-hemolysis when the colony was surrounded by a clear white zone and γ-hemolysis when there was no change in the medium surrounding the colony. Surface tension reduction and emulsification index of isolates was determined by culturing the isolates in minimal mineral salt solution containing glucose as carbon source. Based on the screening test results, the positive isolates were inoculated into the mineral salt medium for the biosurfactant production and then identified by its microscopic appearance, biochemical tests based on Bergey’s manual of determinative bacteriology and molecular method. Bio-surfactant production by superior isolate was evaluated in minimal mineral salt medium containing different carbon sources (kerosene, sugar cane molasses, phenanthrane and glucose) at 30 and 37 °C within the incubation periods of 48 and 156 hours. Emulsification activity, oil spreading, drop collapse, cell hydrophobicity and surface tension activity of isolate were used to detect biosurfactant production. Results and Discussion Out of 13 isolates of microorganism, strain S10 showed positive response to biosurfactant tests (hemolytic activity, surface tension reduction and emulsification index) and was select for identification and considering the effect of different carbon sources on its biosurfactant production. The biochemical and molecular identification results showed isolate S10 belongs to Bacillus pumilus. Results showed that Bacillus pumilus was able to grow in all carbon sources. Based on bio-surfactant production, this strain had a positive or β hemolysis on blood agar medium. Results showed that this bacterium was able to grow in all carbon sources. The compound produced by this strain in each of carbon sources at both temperatures (30 and 37 °C) and incubation periods (48 and 156 hours) collapsed down. The maximum surface tension reduction was recorded in the samples containing molasses as carbon source incubated at 30 ° C for 48 hours, in which bacterium reduced surface tension to 20.33 mNm-1. The highest bacterial growth with a higher surface tension reduction selected this isolate as a potential biosurfactant producing microorganism. The maximum emulsifying and cell hydrophobicity were also recorded in molasses (28%) and kerosene (70%) respectively. Conclusion In conclusion, the study represented surfactant activity of the bacterial strain isolated from oil contaminated soils. This confirms that environment has an influence on the metabolism of the tested microbes. This study suggests that, Bacillus pumilus isolated from oil contaminated soil showed biosurfactant producing ability. Further study on the utilization of agro industrial wastes as substrates for the large-scale production of biosurfactants is recommended.
