The chemistry of humic and fulvic acids extracted from argentine soils—II. Permanganate oxidation of methylated humic and fulvic acids

Five humic and three fulvic acids, extracted from Argentine soils, were methylated and oxidized with KMnO* solution. The oxidation products were extracted into ethyl acetate, remethylated, separated by preparative gas chromatography and identified by comparing their mass and micro-IR spectra with those of authentic specimens.The major oxidation products from the humic acids were benzenetetra, -penta-, and -tricarboxylic and hydroxybenepentacarboxylic acid. The major compounds isolated from the fulvic acid oxidation products were aside from benzenecarboxylic and phenolic acids, substantial amounts of ethyl-benzylsulfonate and N-methyl-benzylsulfonamide, one complex aromatic ester and two anhydrides. The origin of the S-containing compounds is uncertain; they could be impurities. Weight ratios of benzenecarboxylic to phenolic acids averaged 5·8 for humic acids but only 0·9 for fulvic acids, suggesting an enrichment in phenolic structures in the fulvic acids. Possible structural arrangements for humic and fulvic acids are discussed.     

The process of manganese depositton in paddy soils

Abstract

The changes in quality and quantity of phenolic substances in the decaying process of rice straw in a soil were compared under moist and flooded conditions for 200 days. The amounts of phenolic substances divided into fractions of humic acid and fulvic acid, ether- and butanol-extractable and organic solvent-unextractable fractions, then the amounts of individual phenolic acids were determined. The following results were obtained.

1) Alkali-extractable total phenolics as well as individual phenolic acids decreased more rapidly under moist, than under flooded, conditions as rice straw decayed in the soil. The phenolics present were mainly attributable to the straw, not to the soil.

2) The decrease in the level of total phenolics in the early stage of the decaying process was mainly due to the decrease in ether-extractable phenolic compounds in the fulvic acid fraction, and in the later stage, was mainly due to the decrease in butanol-extractable phenolics in the humic acid fraction.

3) The amounts of butanol-extractable phenolics and organic solvent-unextractable phenolics were larger in humic acid than in fulvic acid. On the other hand, a larger amount of organic solvent-extractable phenolics, especially ether-extractable phenolics, was present in fulvic acid.

4) The degradation patterns and pathways of individual phenolic acids in the decaying process of rice straw in soil were found to be the lame as those of decaying straw without soil which were reported previously.

5) The level of phenolic substances in the humic acid was not greatly changed during the decaying process, but the phenolic substances in fulvic acid rapidly increased for 30 days and then rapidly decreased to a constant level.     

Chromatographic behavior of humic materials extracted from Barberton sludge

Humic and fulvic acids extracted from alkali treated municipal sludge contain more higher molecular weight materials than from secondary wastewater effluents. This suggests that higher molecular weight materials (greater than 30 000)' are more easily entrapped on the proteinaceous surface of the biomass. About 28% of the sludge COD is humic material. The humic acid fraction is of a higher molecular weight than the fulvic acid fraction. The value of theE ₄:E ₆ ratio indicates that humic materials of raw sludges are of recent origin.     

Decomposition and distribution of residual activity of some 13C-microbial polysaccharides and cells,glucose, cellulose and wheat straw in soil

Studies were made to determine the rate of decomposition of some ¹⁴C-labeled microbial polysaccharides, microbial cells, glucose, cellulose and wheat straw in soil, the distribution of the residual ¹⁴C in various humic fractions and the influence of the microbial products on the decomposition of plant residues in soil. During 16 weeks from 32 to 86 per cent of the C of added bacterial polysaccharides had evolved as ¹⁴CO₂. Chromobacterium violaceum polysaccharide was most resistant and Leuconostoc dextranicus polysaccharide least resistant. In general the polysaccharides, microbial cells, and glucose exerted little effect on the decomposition of the plant products. Upon incubation the ¹⁴C-activity was quickly distributed in the humic. fulvic and extracted soil fractions. The pattern of distribution depended upon the amendment and the degree of decomposition. The distribution was most uniform in the highly decomposed amendments. After 16 weeks the bulk of the residual activity from Azotobacter indicus polysaccharide remained in the NaOH extracted soil. From C. violaceum polysaccharide both the extracted soil and the humic acid fraction contained high activity. About 50–80 per cent of the residual activity from the ¹⁴C-glucose, cellulose and wheat straw amended soils could be removed by hydrolysis with 6 n HCl. The greater part of this activity in the humic acid fraction was associated with the amino acids and that from the fulvic acids and residual soils after NaOH extraction with the carbohydrates. About 8 16 per cent of the activity of the humic acid fraction was present in substances (probably aromatic) extracted by ether after reductive or oxidative degradation.     

Effects of humic and fulvic acids on release of fixed potassium

Release of potassium fixed by expanding silicate clays is considered of practical importance in soil fertility. Humic and fulvic acids are expected to play a definite role in liberating this fixed K, because of their chelating power, but not much is known in this respect. The following investigation was conducted to study release of fixed K by montmorillonite and illite, using humic and fulvic acids isolated from the surface horizon of a Cecil soil (Typic Hapludult, Red Yellow Podzolic soil) as extractants. For comparison, extraction was also done with 1 N neutral NH₄ -acetate, a mixture of 0.05 N HCl and 0.025 N H₂SO₄ or H₂ O. Supporting analyses of clays were carried out with X-ray diffraction to establish changes, if any, in crystal structure due to fixation, release of K, or adsorption of humic compounds. The results indicated that humic and fulvic acids released some of the K fixed by montmorillonite or illite. In terms of percentage of the total K fixed, 9 to 28% were released by the various extractants. The percentages K released by humic and fulvic acids were similar from both montmorillonite and illite, but based on absolute values, humic and fulvic acids extracted less K (mg/100 g) from illite than montmorillonite. Although statistically significant at the 5% level of probability, the capacity of humic compounds to liberate fixed K was not different markedly from those of NH₄ -acetate and the double acid mixture. Differences in pH of humic solutions had no influence on extraction of fixed K. X-ray diffraction analysis yielded curves showing an increase in spacing from 10.4 Å for K-montmorillonite to 13.2 Å as a result of extraction with the double acid mixture.     

Analysis of polynuclear aromatic and aliphatic components in soil humic acids using ruthenium tetroxide oxidation

Although condensed aromatic components are considered to be one of the major structural units of soil humic acids (HAs) and to be responsible for the dark colour of HAs, their amount and composition remain largely unknown. In ruthenium tetroxide oxidation (RTO), condensed aromatic components are detectable as their degradation products, mainly benzenepolycarboxylic acids (BPCAs). We applied this technique to soil HAs with various degrees of humification (darkening). The yields of water‐ and dichloromethane‐soluble products from HAs upon RTO after methylation ranged from 210 to 430 mg g⁻¹ and 10–40 mg g⁻¹, respectively. Eight kinds of BPCAs with two to six carboxyl groups, and seven kinds of BPCAs with additional side chains (tentative assignment) were obtained as methylated counterparts. The yield of each BPCA and the sum of the yields of BPCAs (12–85 mg g⁻¹ HAs) increased with increasing degree of humification and aromatic C content. The compositions of BPCAs indicated that the degree of condensation was greater in the HAs with greater degrees of humification. The sum of the yields of aliphatic compounds ranged from 0.1 to 6.5 mg g⁻¹, and decreased with increasing degree of humification. The C₁₂ to C₃₀ monocarboxylic acid methyl esters accounted for > 56% of the aliphatic compounds assigned, which may be present mainly as end alkyl groups in the HA molecules. We also obtained the methylated counterparts of C₁₄ to C₂₄ dicarboxylic acids; these were possibly derived from polymethylene bridges between adjacent aromatic rings.     

Chemical heterogeneity of humic substances: characterization of size fractions obtained by hollow-fibre ultrafiltration

To investigate the chemical heterogeneity of humic substances in relation to molecular size, fulvic and humic acids were extracted and purified from the surface horizon of a Humic Gleysol in northern Switzerland. A fractionation scheme using hollow‐fibre ultrafiltration cartridges was developed and used to obtain four size fractions of the humic acid with nominal molecular weight ranges > 300 kDa, 100–300 kDa, 30–100 kDa, and 10–30 kDa. The fulvic acid and all humic acid fractions were characterized by size exclusion chromatography, elemental analysis (C, H, N, S), as well as spectroscopic techniques including UV‐VIS, CP‐MAS ¹³C‐NMR, FT‐IR, and fluorescence spectroscopy. Clear chemical differences between the humic acid size fractions were observed. Smaller size fractions of the soil humic acid contained more chargeable functional groups and a larger percentage of aromatic carbon than the larger size fractions. Conversely, the percentage of aliphatic carbon increased with increasing apparent molecular weight. The chemical composition of the smallest humic acid fraction differed clearly from the fulvic acid fraction, despite similar apparent molecular size and carboxyl carbon content. Small humic acids contained much more aromatic carbon and less aliphatic carbon than the fulvic acid fraction. Apparently, humic size fractions differ in their chemical composition, which can have important implications for their environmental behaviour.     

Chemical–structural information from solid-state 13C NMR studies of a suite of humic materials from a lower montane forest soil,Colorado, USA

Chemically and physically fractionated samples extracted from the surface horizon of a soil developed under a mix of coniferous and deciduous vegetation in southwestern Colorado were studied. ¹³C NMR data on this soil's organic matter and its HF(aq)-washed residue, as well as the classic acid/base-separated humic fractions (humic acid, fulvic acid, humin), were examined for chemical–structural detail, e.g., the various structural functionalities present (especially lipids, carbohydrates, aromatics, polypeptides and carbonyl/carboxyls). Among the humic fractions, it was found that the lipid concentrations are in the order humic acid>fulvic acid= humin; for carbohydrates the order is fulvic acid>humin>humic acid; for aromatic carbons the order is humic acid>humin>fulvic acid; for polypeptides it is humic acid>fulvic acid>humin and for carbonyl/carboxyl species it is humin>humic acid>fulvic acid, but the differences are small. ¹³C spin–lattice relaxation times indicate that at least two types of “domains” exist in each, corresponding to “higher” and “lower” concentrations of paramagnetic centers, e.g., Fe³⁺.     

Behavior of phenolic substances in the decaying process of plants

The behavior of phenolic substances in the decaying process of rice straw, ladino clover, and fanen leaves of red oak under moist conditions, and also of rice straw under various conditions were compared in the laboratory. The amounts of phenolic substances, divided into either humic acid and fulvic acid fractions, or ether-extractable, butanol-extractable and organic solvent-unextractable fractions, and the amounts of individual phenolic acids were periodically determined during incubation for 150 days. The following results were obtained.

1) The amounts and behavior of phenolic substances in various fractions differed considerably among the plant materials. The total amount of phenolic substances was remarkably larger in red oak leaves than in the others during the whole period of incubation. The amounts of phenolics in the fulvic acid fraction changed to a larger extent than those in the humic acid fraction during the decaying process of plant materials. The changes in total amount of phenolics in decaying red oak leaves and ladino clover were mainly due to changes in the level of relatively hydrophilic phenolics in the fulvic acid fraction, but the changes in decaying rice straw were mainly due to changes in the level of relatively lipophilic phenolics.

2) Rice straw and ladino clover, especially the former, contained large amounts of p-coumaric and ferulic acids, but these decreased rapidly in the early stage of the decaying process. The amounts in red oak leaves were small, but did not decrease markedly during incubation.

3) The changes in amounts of phenolics in both humic acid and fulvic acid fractions in the decaying process of rice straw were largely influenced by temperature, moisture, and pH, but not to a large extent by C/N ratio and the presence of soil. At higher temperatures under moist conditions, phenolic substances disappeared rapidly. Also, acidification of the system inhibited the degradation process.     

In-source pyrolysis-field ionization mass spectrometry and Curie-point pyrolysis-gas chromatography/mass spectrometry of amino acids in humic substances and soils

With the aid of in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) and Curie-point pyrolysis-gas chromatography/mass spectrometry (cPy-GC/MS) in the conventional electron impact mode, characteristic signals of 23 amino acid standards were described. Thermal and mass spectrometric fragmentation pathways of these amino acids differed with each method and complemented each other. Pyrolysis products assigned by Py-FIMS extended the range of signals for N-containing compounds in humic substances and soil organic matter and gave marker signals for free amino acids and their subunits in proteinaceous materials. These characteristic signals were correlated with the amino acid content in N-rich humic fractions consisting of seven fulvic acids and eight humic acids. The selected marker signals reflected 25–84% of the variances of the molar distribution of acidic, neutral, neutral aromatic, and basic amino acids in the humic fractions. In addition, a well described agricultural soil (0.08% amino acid N) was spiked with a standard amino acid mixture (0.08 mg amino acid N 100 mg^-1 dry soil) and produced enhancements of the relative abundances of the corresponding amino acid signals. Moreover, for 27 samples of whole agricultural soils of widely different origins, soil types, and vegetations, 15 selected amino acid indicators were correlated significantly with -amino N (r=0.76^***) and total N (r=0.65^***).     

THE ACCUMULATION OF SOIL ORGANIC MATTER AND ITS CARBON ISOTOPE CONTENT IN A CHRONOSEQUENCE OF SOILS DEVELOPED ON AEOLIAN SAND IN NEW ZEALAND

Soil organic matter was extracted by a mixture of O.IM Na₄P₂O: O.IM NaOH from a chronosequence of weakly weathered soils developed on aeolian sand, and fractionated into humin (non-extractable), humic acid, and fulvic acid. The mass of total organic carbon in the profiles, the ¹⁴C content and the ¹³C/12C ratios were also determined. The weight of total carbon increased rapidly at first and then gradually without attaining a steady state. This trend was also shown by the humin and fulvic acid fractions, but the humic acid fraction appeared to have reached a maximum after about 3000 years. The order of total weights of the organic fractions was humin > fulvic acid > humic acid. The evidence suggests that the proportions of the humic fractions formed by decomposition are related to soil differences but not to vegetation. The greater part of the plant material found in the soils appears in the humin and fulvic acid fractions.     

Long-term cultivation effects on the quantity and quality of organic matter in selected Canadian prairie soils

Sixteen Orthic Chernozemic surface soil samples, one half from virgin prairie and one half from adjacent cultivated prairie (cultivated for 31 to 94 years), were collected from eight sites throughout Southern Saskatchewan, Canada. Samples were analyzed for total organic C and a number of other chemical and physical properties. The virgin and cultivated soils at site No. 4 were selected for more detailed analysis by CP-MAS ¹³C NMR, Curie-point-pyrolysis-gas chromatography/mass spectrometry (Cp-Py-GC/MS), and by pyrolysis-field ionization mass spectrometry (Py-FIMS). Long-term cultivation resulted in large significant decreases in total SOM (soil organic matter), as represented by total soil organic C. There were significant increases in aromaticity of the SOM as a result of long-term cultivation as indicated by CP-MAS ¹³C NMR spectroscopy. This was mainly attributable to the result of cultivation-enhanced degradation of aliphatic C relative to aromatic C. Organic compounds identified in the Cp-Py-GC/MS spectra of the virgin and cultivated soils at site No. 4 consisted of n-alkanes (ranging from C₁₁ to C₂₂) and alkenes (ranging from C_7:1 to C_21:1), with the virgin soil being richer in alkenes than the cultivated soil. Other components identified were cyclic aromatics, carbocyclics, N-containing aromatics, N-heterocyclics, benzene and substituted benzenes, phenols and substituted phenols and substituted furans. The compounds identified appeared to originate from long-chain aliphatics, lignins, polyphenols, aromatics, polysaccharides, and N-containing compounds in the two soils. While qualitatively similar compounds were identified by Py-FIMS in the two soils, the total ion intensity (TII) of the virgin soil was almost 2.5 times as high as that of the cultivated soil. This suggests that cultivation made the organic matter less volatile, either by favouring the formation of higher molecular weight organic matter or by promoting the formation of non-volatile metal-organic matter complexes. The Py-FIMS spectra showed that the virgin soil contained relatively more lignin dimers, lipids, sterols, and n-C₁₆ to n-C₃₄ fatty acids than the cultivated soil. Thus, conversely, the cultivated soil was richer in carbohydrates, phenols and lignin monomers, alkyl aromatics and N-containing compounds, including peptides, than the virgin soil.     

日本常规耕作和有机耕作(翻耕与免耕)农田的动物区系(螨和线蚓)比较

Nitrogen forms of humic substances from a subalpine meadow soil,a lateritic red soil and a weathered cola and the effect of acid hydrolysis on N structures of soil humic substances were studied by using ^15N cross-polarization magic angle spinning nuclear magnetic resonance(CPMAS NMR) spectroscopy,Of the detectable ^15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups ,10%-18% to aromatic/aliphatic amines and 6%-11% to indole-and pyrrole-like N.Whereas in the spectrum of the fulvic acid from weathered coal 46%,at least,of the total ^15N-signal intensity might be assigned to pyrrole-like N,14% to aromatic/aliphatic amines,and the reamining intensities could not be assigned with certainty,Data on nonhydrolyzable reside of protein-sugar mixture and a ^15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis.     

Chemical characteristics and microbial degradation of humate

Abstract

Humates are often used in agriculture as a source of organic matter. This study was conducted to characterize a commercial humate and to evaluate its chemical and decomposition characteristics. Characterization methods included fractionization of humic and fulvic acids of the humate, based on their alkali/acid insolubility; elemental analysis; acidic functional group analysis; and E₄/E₆ ratio determinations. The humate consisted of the following: 58% organic matter, 32% ash, and 10% moisture. Humic fraction was mostly humic acid (76%), with some fulvic acid (18%). Organic elemental composition [59% carbon (C), 5% hydrogen (H), and 36% oxygen (O)] also suggests a humic‐acid nature. Inorganic elemental content of this humate, which was primarily aluminum (Al) [4.9%] and iron (Fe) [0.46%], reflects its spodic origin. Much of the Al present, however, results from the flocculant (alum) used at the mining site to precipitate the humate. The relatively low total acidity of this humate (250 cmol/kg) suggests the blockage of some of its functional groups by Al, Fe, and associated clay minerals. After purification, total acidity increased to 510 cmol/kg and acidity associated with carboxyl groups increased to 280 cmol/kg. Results of E₄/E₆ determinations for the humate (2.5) and the humic‐acid fraction (4.8) also suggested that the organic fraction was predominately humic acid. Decomposition of the humate was estimated by measuring the quantity of carbon dioxide (CO₂) evolved during a four‐week incubation. Results suggested a relative resistance to microbial degradation. However, results also suggested the presence of some readily decomposable C compounds associated with humate. Agricultural use of this humate reguires some modifications to produce a more reactive material. This may include a change of flocculant and a lowering of its ash content.     

Use of alkaline soil extracts for 13C n.m.r. characterization of humic substances

Previous solution ¹³C n.m.r. studies of soil organic matter have been confined to isolated humic or fulvic acid fractions. A study of 10 crude alkaline extracts from five New Zealand topsoils has now shown that such purification is unnecessary. Spectra were not noticeably broadened by co-extracted iron in concentrations up to 2 mg cm^?3. Optimized pulse parameters were similar to those reported for a solution of a purified humic acid. Relaxation results support a generalized model for humic material, in which aromatic structures, carbohydrates, amino acids and polymethylene chains are linked together to form flexible macromolecules. Relative contributions from each component varied from soil to soil.     

Formation of Aldehydes and Carboxylic Acids in Humic Acid Ozonation

The purpose of this study was to determine the different kinds and concentrations of intermediates, and investigate on the effects of contact time and ozone (O₃) doses on the removal of humic acid (HA), which is served as the main disinfection by-product (DBP) precursor. Based on that, the knowledge gap of DBPs generated was made up. The results showed that HA was the major precursor material for aldehydes and carboxylic acids. The concentrations of aldehydes increased as contact time and O₃ doses, and reached up maximum at 2~10 min but approached a plateau at the higher O₃ doses. The concentrations of formic and acetic acids increased as contact time and O₃ doses. However, aromatic acids, including protocatechuic, 3-hydroxybenzoic, and benzoic acids, declined rapidly at longer reaction time and higher O₃ doses. It was worth mentioning that aromatic acids had been rarely reported. Besides, a possible formation pathway was proposed: (a) HA was degraded into fulvic acid (FA)-like compounds; (b) FA-like compounds were further converted into aromatic acids; (c) aromatic acids were transformed into low-molecular-weight organic matters; (d) chlorine reacted with aldehydes and/or carboxylic acids by addition, hydrolysis, and decarbonylation reactions, leading to DBP formation. Furthermore, not only HA were the main DBPs precursors, but also the oxidation intermediates of HA could be the DBPs precursors, and they gave a certain amount of DBPs. Consequently, aldehydes and carboxylic acids should be under control in drinking water treatment plants.     

Chemical composition of the organic matter in forest soils: The humus layer

Decomposition and humification were studied within three types of forest humus (mull, moder, and mor) by means of CPMAS ¹³C NMR spectroscopy combined with degradative methods. The NMR data show that O-alkyl carbon decreases in all soils, and alkyl as well as carboxyl carbon increase as depth and decomposition increase; the percentage of aromatic carbon remains constant at about 25%. With increasing depth the amount of carbon that can be identified as belonging to specific compound classes by wet chemical methods decreases from 60% to 40%. Microbial polysaccharides and the proportion of non polysaccharide O-alkyl carbon increase with depth. A selective preservation of recalcitrant, condensed lignin structural units is also observed. In order to relate the spectroscopic and chemical data from investigations of whole soils with studies of humification, samples were fractionated into fulvic acid, humic acid, and humin fractions. The fulvic acid fraction contains large concentrations of carbohydrates irrespective of the soil horizon. The humic acid fraction contains less polysaccharides, but high amounts of alkyl carbon and aromatic structures. The percentage of aromatic carbon existing in the humic acid fraction increases with depth, probably reflecting the amount and degree of oxidative decomposition of lignin. A loss of methoxyl and phenolic groups is evident in the ¹³C NMR spectra of the humic acid fraction. The humin fraction resembles relatively unchanged plant-derived materials as evident from the lignin parameters and carbohydrate contents. All the observed data seem to indicate that humic acids originate form oxidative degradation of humin or plant litter.     

Removal of Natural Organic Matter from River Water Using Potassium Ferrate(VI)

In this research, we have investigated the removal efficiency of natural organic matter (NOM) from river and stream water using potassium ferrate(VI). For the study, ferrate was added in 100-ml water sample mixed either with humic acid or with fulvic acid. The removal efficiency at the ferrate dose of 2–46 mg/l (as Fe) was 21–74% for 10 mg/l humic acid and 48–78% for 10 mg/l fulvic acid. NOM was more effectively removed either at lower pH or at higher temperature. The removal performance by ferrate was comparable to that by traditional coagulants (i.e., alum, FeSO₄·7H₂O, and FeO(OH)). In addition, the removal rate of humic acid using traditional coagulants was improved by pretreatment with a very small dose of ferrate. The reaction between ferrate and humic acid was completed within 60 s, while showing first-order kinetic, and then reached a steady state.     

土壤中钙结合和铁铝结合腐殖质的组成及结构特征

Calcium-bound and iron- and aluminium-bound humus extracted from different soils collected from north to south of China were characterized by chemical and spectroscopic methods. Meaningful differences in the composition and structure between them were revealed by ¹³C NMR, visible spectroscopy and elemental analysis. Results showed that the contents of carbon, hydrogen and nitrogen were higher in iron- and aluminium-bound humus than in calcium-bound humus while oxygen content in calcium-bound humus was shown to be higher. The calcium-bound humus had higher C/N and O/C ratios than iron- and aluminium-bound humus. The calcium-bound humic acid (HA1) showed higher E₄/E₆ ratios than iron- and aluminum-bound humic acid (HA2) while iron- and aluminum-bound fulvic acid (FA2) showed higher E₄/E₆ ratios than calcium-bound fulvic acid (FA1). An inverse relationship between E₄/E₆ ratios and aromaticity as determined by ¹³C NMR spectra was observed for HA and FA from black soil. The ¹³C NMR spectroscopy revealed that HA2 was more aromatic than HA1. On the other hand, FA1 exhibited a higher aromaticity than FA2.     

The origin of oxygen in soil humic substances

The ¹⁸O/¹⁶O ratios of a number of soil humic and fulvic acids were measured and compared with those of lignin and cellulose samples originating from the same area. The average enrichments above ground water were: cellulose 32%₀ humic and fulvic acid 29%₀ and lignin 14%₀, suggesting that the oxygen in humic and fulvic acid originates pricipally from cellulose or other plant carbohydrates and not lignin as has been suggested.