In recent years, new varieties of organic fertilizers such as vermi compost, sludge and sediment have been added as new sources of fertilizers, which have humic acid (HA) present in it. However, a systematic characterization of these substances and their comparison with cow dung has not been reported. This is essential to decide the relative merits and demerits of these substances as a fertilizer. The objective of this work was to extract and characterize the chemical compositions of various HA using various techniques such as UV-Vis, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1H-NMR), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), atomic absorption spectrophotometer (AAS) and X-ray diffractometer (XRD). Cow dung manure, vermi compost, sludge and lake sediment were used for this purpose. 1H-NMR show that all HA samples were rich in aliphatic groups. EDS analysis found HA rich in carbon and oxygen and poor in nitrogen and presence of elements such as Na, Ca, K, Mg, Al, S, P, Cu, Fe, Cr, Co and Pb in various proportions. It was supported by AAS analysis where elements such as Na, K, Ca, Mg, Fe, Cu and Co were found in all HA samples in various concentrations. SEM images and XRD analysis showed some crystal forms found in all HA samples. These results elucidate that the chemical composition and the molecular structure of HA samples varies as per the origin and environment where decomposition has occurred. Present study also documented that the spectroscopic and imaging techniques can be successfully used to bring out the finer differences among HA extracted from different sources. It brings out the relative merits and demerits of vermi compost, sludge and lake sediment as compared to cow dung manure. This analysis showed that out of the four HA samples extracted from different sources except HA-SD can be used as fertilizer with caution to Al, Co and Cr content.
alkaline extraction, fertilizer, humic acid, metal-crystal form, spectroscopic and imaging techniques
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