Spectroscopic and elementary characterization of humic substances in organic substrates

Abstract

The humic substances, major constituents of the organic matter of the substrates, play an important role in plant development, including: the availability of nutrients, the generation of negative charges (CEC) and the buffering effect. Based on this, this study aimed to use the molecular absorption spectroscopy in the ultraviolet-visible region (UV-VIS), the vibrational spectroscopy Fourier transform infrared (FTIR) and the elementary analysis CHN/O techniques to characterize the humic acid (HA) and fulvic acid (FA) fractions of the humic substances of five organic substrates, named as T1, T2, T3, T4, and T5, which were produced at the Federal University of Tocantins – Campus Gurupi. The molecular absorption spectra in UV-VIS and FTIR on the T1, T2, T3, T4 and T5 substrates showed humification, the formation of negative charges, which is related to the cation exchange capacity (CEC) and the complexation of metal ions that are considered nutrients. The biggest humification was shown for the T4 substrate, in function of its higher cabon-acid humic/carbon-acid fulvic ratio and the lower C/N ratio, allied to a negative charge generation, the low E4/E6 ratio found in the humic acid fraction. The complexation of metal nutrient ions indicates the greatest potencial of its use for seedlings production and the conservation of the chemical and physical properties of the organic substrate.

Humus horizon development during natural forest succession process in the Polish Carpathians

“…Comparing both methods used here, UV-VIS spectroscopy is useful in determining the absorbance of aromatic systems, which is related to the degree of humic substances' humification as well as the quality of soil (Da Silva et al 2018), whereas the ADI showed the diversity of the degree of organic matter stabilization. The ADI correlated with organic carbon content and is especially dependent on soil colour and the amount of material scattered as well as its exposure time (Mazurek et al 2016).…”

Zinc Binding to Fulvic acids: Assessing the Impact of pH, Metal Concentrations and Chemical Properties of Fulvic Acids on the Mechanism and Stability of Formed Soluble Complexes

“…FAs isolated from various soils differed significantly in terms of chemical and structural properties ( Table 1). The H/C atomic ratio showed the highest value for FA2 (0.94) while indicating the lowest degree of condensation of aromatic rings, and thus the greatest proportion of aliphatic structures in relation to FA3, which showed the lowest H/C value (0.85) [13,37]. The highest O/C and O/H ratios were determined for FA2 sample, while the lowest ones for FA3, which indicated a higher content of oxygen structures and as a higher humification degree of FA2 as compared to FA3.…”

“…Some exemplary FTIR characteristics are shown in Figure 5 (black, solid lines). Some of the observed signals can be considered important in terms of interaction with Zn(II): (a) wide intensive band at 3435 cm −1 attributed to the N-H stretch of amines and O-H of hydroxyl groups in hydrogen bonds, carboxylic acids, alcohols and phenols [5,13,16], (b) vibrations at~1710 cm −1 related to C=O stretching of protonated carboxyls, quinines, cyclic and acyclic aldehydes and ketones [42,68], (c) band at~1625 cm −1 refers to C=O bonds of deprotonated COO-, C-O and C-N stretching in amides [13,69] as well as vibrations of -C = C-on benzene rings [16,42], (d) peak at~1400 cm −1 reflecting aliphatic -C-H deformation, -COO-symmetric stretching and -O-H deformation [5], (e) vibrations at~1220 cm −1 corresponded to C-O stretching in phenols, carboxylic acids and ethers [68,70] and (f) band at~1070 cm −1 , indicating the presence of polysaccharides, ethers and alcohols attributed to the stretches of C-O bond [5,13]. The increase of pH caused a gradual reduction of the bands at~1710 cm −1 and at~1220 cm −1 and enhancement of the bands at~1625 and at~1400 cm −1 , which was associated with the successive deprotonation of surface COOH groups and, consequently, an increase of the COO − fraction.…”

“…FAs find a wide variety of applications, however the greatest potential of these compounds comes from their chelating properties due to a large number of carboxylic, phenolic and alcoholic hydroxyl functional groups (900-1400 cmol kg −1 ) [6,7] as well as others including quinines, semiquinones [8,9], amino and sulphydryl groups [5,10]. As a consequence, FAs exhibit a high sorption capacity to cationic substances, hence they can play a key role in controlling speciation, bioavailability, toxicity and mobility of metals [11][12][13]. According to Bertoli et al [14], the absence of chelates of metals, like Zn, Cu and Fe, makes these elements insufficient, thus causing deficiencies in the plant and inhibiting root growth.…”

Fulvic acid isolation and characterisation from water of a Ramsar Lake Mansar, J&K, India

“…During the present study, it was 0.65%. High O/C ratio observed presently suggested that the humic substances have undergone a low degree of condensation and are more aliphatic in nature with a higher proportion of carbohydrates (Mengchang et al 2008;Guéguen et al 2012;da silva et al 2018).…”