Structural characterization of fulvic acids and their impact in the agricultural area of Palakkad, Kerala, India

Abstract

Structural characterization of fulvic acids (FAs) along with the essential heavy metals (Fe, Co, Zn, and Cr) was carried out in the surface soil samples of prominent mango orchards in Palakkad district, Kerala, India. The FAs were examined with the help of elemental analyzer, UV-Visible, and FT-IR spectroscopy. The heavy metal distribution in the soil was observed in the following order: Fe > Cr > Zn > Co. The statistical analysis indicated the lithogenic and agricultural origin of metals in the study area. The detected level of Fe from the sampling sites was higher than the WHO guideline, while Co and Cr concentration exceeded the USEPA guideline values. The influence of cation exchange capacity, clay content, and CaCO₃ of soil over the fate of heavy metals was identified through canonical correspondence analysis. The aliphatic and oxidation degree of FAs was examined using UV-Visible absorbance ratios, atomic ratios, and elemental composition. Results revealed that aliphatic moieties and polar functional groups enrich the FAs in the study area. Pearson correlation analysis exposed the dominant role of FAs in the fate of metals along with the other soil properties. These outcomes provide necessary information that might be useful in the assessment of risk/deficiency associated with the heavy metals in agricultural soils of the study region. It emphasizes the necessity of soil constituent evaluation before crop cultivation to attain sustainable farming practices.

Keywords:

• Trace metals
• soil
• fulvic acids
• agriculture
• correlation
• fate and transport

Acknowledgments

Authors are thankful to the Department of Chemical Oceanography, Cochin University of Science and Technology (CUSAT) for providing laboratory facility and the cooperation of the research scholars to complete the research work. Also, the authors gratefully appreciate the FTIR facilities provided by the Director, Inter-University Centre for Marine Biotechnology, School of Marine Sciences. Moreover, authors are grateful to Sophisticated Test and Instrumentation Centre (STIC), Cochin University, for providing the CHNS facility. AA is deeply indebted to Kerala Government for financial assistance in the form of e-Grantz fellowship. Authors also thank anonymous reviewers for helpful comments.