نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم و مهندسی باغبانی، دانشکده کشاورزی و منابع طبیعی، دانشگاه ازاد اسلامی واحد کرج، کرج، ایران
2 گروه خاکشناسی، دانشکده کشاورزی و منابع طبیعی، دانشگاه ازاد اسلامی واحد کرج، کرج، ایران.
3 پژوهشکده فناوری تولیدات گیاهی، دانشگاه شهید باهنر کرمان، ایران
4 گروه زراعت و اصلاح نباتات، دانشکده کشاورزی و منابع طبیعی، دانشگاه ازاد اسلامی واحد کرج، کرج، ایران
5 گروه محیط زیست، پژوهشگاه علوم و تکنولوژی پیشرفته و علوم محیطی، دانشگاه تحصیلات تکمیلی صنعتی و فناوری پیشرفته، کرمان، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The present study investigates the effects of different humic substances—including humic acid, fulvic acid, and their combination—on the behavior of nickel (Ni) in a calcareous soil. In this research, humic substances were extracted from leonardite obtained from Kerman Province and separately applied to soil contaminated with Ni (at a concentration of 120 mg/kg). After a three-month incubation period under moist conditions, Ni desorption kinetics were assessed using EDTA extraction, and the chemical forms of Ni were evaluated through a sequential extraction method. The results showed that the application of humic acid led to a 52% increase in Ni desorption. In comparison, the application of the humic acid–fulvic acid combination and fulvic acid alone resulted in 13% and 35% decreases in Ni desorption, respectively, compared to the control. The two first-order kinetic model fit the Ni desorption data well, indicating its capability to describe the desorption process in the treated soils. Furthermore, the impact of humic substances on the chemical forms of Ni revealed that humic acid and the humic acid–fulvic acid combination significantly (at the 1% level) increased the exchangeable and carbonate-bound fractions of Ni. In contrast, fulvic acid significantly reduced these mobile forms compared to the control. Overall, the findings demonstrate the high potential of humic substances in altering the bioavailability of Ni in calcareous soils and highlight the influence of humic substance type on the behavior of this heavy metal in the soil environment. These results suggest the applicability of humic substances in developing sustainable strategies for managing heavy metal pollution, such as chemical immobilization or phytoremediation processes.
کلیدواژهها [English]
EXTENDED ABSTRACT
Heavy metals contamination, particularly from elements like nickel (Ni), poses significant risks to soil health and agricultural productivity. Ni is known for its toxic effects on plant growth and soil microbiota, leading to reduced crop yields and ecosystem degradation. Humic substances, such as humic acid and fulvic acid, have gained attention for their potential to improve soil conditions and mitigate the adverse effects of heavy metals. These natural organic compounds can enhance nutrient availability, promote soil structure, and interact with metal ions, influencing their mobility and bioavailability. Despite the promising characteristics of humic substances, the specific impacts of different types on Ni behavior in calcareous soils remain insufficiently explored. Therefore, this study aimed to investigate the effects of various humic substances, including humic acid, fulvic acid, and their combined form, on Ni behavior in a calcareous soil.
Humic substances were extracted from leonardite sourced from Kerman province, Iran. The extracted humic acid (HA), fulvic acid (FA), and their combination (HAFA) were then applied to Ni-contaminated soil at a concentration of 120 mg/kg. The contaminated soil was maintained under moisture conditions for 3 months to simulate field conditions. The kinetics of Ni desorption were assessed using EDTA as an extractor, and the chemical forms of Ni were evaluated through a sequential extraction procedure. For desorption kinetic process, 5 g samples of the treated soil were placed in centrifuge tubes and mixed with 25 mL of 0.01 M EDTA solution at pH 7 for various time intervals (30, 60, 120, 240, 480, 960, 1920, 3840, and 7680 minutes). After each interval, the samples were centrifuged, and the supernatant was analyzed for Ni concentration using atomic absorption spectroscopy. The effectiveness of the humic substances on the chemical forms of Ni was determined through a series of extraction steps aimed at isolating exchangeable, carbonate-bound, organically-bound, Mn-Oxid-bound, Fe-Oxid-bound and residual forms of Ni. The mobility coefficient of Ni was calculated as a ratio of the sum of exchangeable and carbonate-bound forms to the total Ni content.
The results indicated that the application of humic acid significantly enhanced Ni desorption, resulting in a 52.13% increase in Ni release. Conversely, the use of fulvic acid and the combination of humic and fulvic acids led to reductions of 13.91% and 35.25% in Ni desorption, respectively, compared to the control samples. The data were well-fitted to a two first-order reaction model, which highlighted the capacity of this model to accurately describe the Ni desorption process in the treated soils. Furthermore, the effectiveness of humic substances on the chemical forms of Ni demonstrated that humic acid and the humic-fulvic acid combination significantly increased both exchangeable and carbonate-bound forms of Ni by 37% and 25%, respectively, compared to the control treatment. In contrast, fulvic acid application resulted in an 18% decrease in these mobile forms.
The present study demonstrates that the use of various humic substance components can significantly influence Ni behavior in soil. Humic acid application enhanced Ni availability. Conversely, fulvic acid reduced nickel availability by decreasing both desorption and mobility factor of Zn. The combination of fulvic acid and humic acid also exhibited a substantial reduction in Ni accessibility, albeit with a slight increase in its mobility factor as revealed by chemical form analysis. These findings suggest that humic acid is a beneficial amendment for studies aimed at increasing the bioavailability of nutrients and heavy metals for applications such as phytoremediation or improving soil fertility. On the other hand, the use of fulvic acid could serve as a chemical stabilizer for nickel in the soil, which may be advantageous in preventing the potential toxicity of this heavy metal. However, further field studies are required to validate these results and explore the practical implications of using humic and fulvic acids in soil management practices.
Iman Seifollahi: conceptualization, methodology, formal analysis, software, data curation, investigation, writing—original draft preparation, and overall project administration; he also assisted in the data analysis and guided the modeling process. Ali Khanmirzaei: contributed to supervision, validation, and writing—review and editing; also supported the completion of numerical modeling and data analysis. Vahid Reza Saffari: contributed to data collection, validation, and writing—review and editing; also involved in numerical analysis. Peyman Foroozesh: provided expertise in data validation and analysis, and contributed to writing—review and editing. Mahboub Saffari: supported supervision, assisted in the final revisions, and helped complete the numerical modeling.
The data that support the findings of this study are available from the corresponding author upon reasonable request.
This work was partially derived from the Ph.D. thesis of the first author. The authors would like to acknowledge the support of the Department of Horticultural Sciences, College of Agriculture and Natural Resources, Karaj Branch, Islamic Azad University, Karaj, Iran.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare no conflict of interest.
)