Permanganate oxidation of methylated and non-methylated aquatic humus in Norway

The chemical composition of aquatic humus was investigated by permanganate oxidation. Both methylated and non-methylated samples were investigated and the results compared with those of different soil humic fractions investigated earlier.The total amount of oxidation products identified from the methylated sample was 2%, and from the non-methylated sample 0.9%. The composition of the oxidation products from methylated aquatic humus was 42% benzenecarboxylic acid methyl esters (8 different compounds), 43% methoxy-benzenecarboxylic acid methyl esters (12 compounds), 10% dimethoxy-benzenecarboxylic acid methyl esters (4 compounds), and 5% of 1, 2, 3-propanetricarboxylic acid trimethyl ester. The unmethylated aquatic humus yielded 84% benzenecarboxylic acid methyl ester (7 compounds), 7% methoxy-benzenecarboxylic acid methyl esters (2 compounds), and 9% of 1, 2, 3-propanetricarboxylic acid trimethyl ester. Three diazines isolated from methylated material were believed to be artefacts from diazomethane treatment. Two of the diazines have earlier been found by oxidation of methylated soil samples, the third, C₁₀H₁₂N₂O₆, is an oxidation product of methylated aquatic humus only.Oxidation of aquatic humus yielded more benzenecarboxylic acids and methoxy-benzenecarboxylic acids than soil humic fractions, and less dimethoxy-benzenecarboxylic acids. No aliphatic dicarboxylic acids were detected among the oxidation products of the aquatic humus.The compounds identified are mainly the same as those found by oxidation of different soil humic fractions, although their yields clearly demonstrated that the aquatic humus differed in composition from the soil fractions.     

Susceptibility of humic acid towards sodium amalgam

Three humic acids (HA-I) of different degrees of humification were treated with HCl (1:1). The hydrolyzed humic acids (HA-II) were subsequently degraded with Na-amalgam. The reduction products were divided into the following fractions: humic acid residues (HA-III), fulvic acid (FA), and ether-extractable lubstances (Et),

The humic acids used in this study were extracted from the following three soils; Inogashira (Volcanic ash soil), Kuragari (Drown forest soil, B_D type), and Higashiyama (Brown forest soil, rB_B type).

The experimental results are summarized as follows:

1. The RF values of HA-II, in the case of Inogashira and Kuragari, were higher, and the △log K values were lower than those of HA-I. The carbon and oxygen contents of HA-II were higher while the hydrogen, and nitrogen contents were lower than those of HA-I.

2. The total amount of carbon in HA-III. FA and Et added up to about 90% of the carbon present in HA-II. The carbon of HA-III found in HA-III after reduction tended to increase in the order: Inogashira>Kuragari>Higashiyama. In FA and Et, the opposite trend was followed.

In the case of Inogashira about 60% of the carbon of HA-II was found in HA-III.

3. The dark coloration of humic acid largely disappeared during the reductive treatment. As for the amorphous carbon-like structure detected in Inogashira, it was not found in the HA-III after reduction.

Therefore, it was presumed that the structures destroyed or saturated during the reductive treatment were the ones responsible for the essential properties of humic acid.     

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 DEGRADATION OF HUMIC AND FULVIC ACIDS EXTRACTED FROM MEDITERRANEAN SOILS

Humic and fulvic acids were extracted from two Israeli and tour Italian soils and oxidized with alkaline permanganate solution after methylation. Following oxidation, the degradation products were separated by solvent extraction and chromatographic methods and identified by gas chromatography-mass spectrometry. Major oxidation products were aliphatic, phenolic and benzenecarboxylic acids. In toto, 33 oxidation products were identified. These were essentially the same compounds as those produced by the permanganate oxidation of methylated humic and fulvic acids extracted from soils formed under widely differing climatic and geologic conditions, except that yields of phenolic acids from Mediterranean humic and fulvic acids were lower than those produced under similar conditions from humic materials extracted from other soils. The information provided by chemical degradation suggests that humic and fulvic acids from widely differing soils have similar chemical structures.     

Further investigations on the chemistry of fungal “humic acids”

In view of the considerable interest in laboratory-prepared fungal “humic acids” as possible precursors or incorporated structural components of soil humic substances, we degraded four fungal “humic acids” by the relatively mild alkaline cupric oxide oxidation. The oxidation products were extracted into organic solvents, methylated, separated by thin-layer chromatography and identified on a gas chromatographic-mass spectrometric-computer system.Average yields of major degradation products were: (a) aliphatic compounds, 38 per cent; (b) benzene-carboxylic compounds, 25 per cent; and (c) phenolic compounds, 21 per cent. The remaining 16 per cent consisted of a number of dialkyl phthalates. Our data agree with those that we reported earlier when we degraded a number of fungal “humic acids” by the more drastic alkaline permanganate oxidation and show that fungal “humic acids” are enormously complex organic materials containing aliphatic and aromatic structures, (some of which contain N), but only a relatively small proportion of which is phenolic. Most of the aliphatics isolated consisted of alkanes and fatty acids, which are known to persist in soils over long periods of time and are frequently firmly retained by soil humic substances.     

The alkaline hydrolysis of humic substances

A humic and a fulvic acid were subjected to four successive hydrolyses with 2NNaOH solution at 170°C for 3 h. Following each hydrolysis, the degradation products were extracted into ethyl acetate, methylated, separated by chromatographic techniques and identified by mass spectrometry and micro-IR spectrophotometry.One g of humic acid yielded 113.5 mg of aliphatic compounds (mainly n-C₁₆ and n-C₁₅) fatty acids), 72.1 mg of phenolics (principally guaiacyl and syringyl derivative) 17.1 mg of benzenepolycarboxylic acid esters and 30.4 mg of N-containing compounds (mainly secondary aromatic amides). Repeated attacks by the alkali on 1.0 g of fulvic acid released 103.8 mg of aliphatics, 133.8 mg of phenolics, 27.0 mg of benzenecarboxylic but 181.8 mg of N-containing compounds. Most of the latter appeared to have been formed during the second, third and fourth hydrolysis which produced reactive compounds that could abstract N from diazomethane which was used as methylating reagent. While 25.0% of the initial humic acid resisted repeated attacks by the alkali, practically all of the fulvic acid was converted into ethyl acetate-soluble products. The alkali-resistant humic acid residue produced high yields of benzenepolycarboxylic acids on alkaline permanganate oxidation.Alkaline hydrolysis, which is known to cleave CO bonds, was found to be relatively specific, although not very efficient, for the degradation of structural phenolic humic and fulvic acid components and for the concomitant liberation of adsorbed aliphatics and N-containing compounds, but was relatively ineffective for degrading aromatic structures linked by CC bonds.     

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.     

Pyrolysis methylation—mass spectrometry of whole soils

In-source pyrolysis field ionization mass spectrometry (Py-FIMS) and Curie–point pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) have been applied to the characterization of whole soils methylated off–line and on–line by two methylation reagents. Samples of a gleysolic Ap–horizon and a podzolic Bh horizon (C_org concentrations 2–3%) were investigated by conventional on–line and developed off–line methylation with tetramethylammonium hydroxide (TMAH) and by off–line methylation with diazomethane. For the first method, the soils were dried, milled and pretreated with TMAH for 10 min at 250°C at ambient pressure outside the pyrolyzers. For the second method, the dried and milled soils were methylated with an ether solution of diazomethane for 12 h at room temperature (～20°C). Pyrolysis methylation with TMAH enabled aliphatic C₂–C39 monocarboxylic acid methyl esters, C4–C₃₀ dicarboxylic acid dimethyl esters and benzenecarboxylic acid methyl esters to be detected. Methoxybenzenes from phenols, benzenediols and benzenetriols, methoxybenzenecarboxylic acid methyl esters from phenolic acids and furancarboxylic acid methyl esters from carbohydrates were also identified. Nitrogen–containing compounds in soil organic matter were obtained as N,N–dimethylamides. Using diazomethane as methylation reagent, distinct Py-FIMS signals were observed for aliphatic C₂–C₃₂ monocarboxylic acid methyl esters and C₃–C₂4 dicarboxylic acid dimethyl esters. Additionally, methoxybenzenes originating from lignins, methoxybenzenecarboxylic acid methyl esters from phenolic acids and N,N–dimethylamides from amides were detected. The more acid podzolic Bh horizon showed higher relative intensities for dicarboxylic acid dimethyl esters and methylated phenolic acids compared to the gleysolic Ap horizon. Similarly, benzenecarboxylic acids are connected mainly by ester linkages to the macromolecular network of soil organic matter. Both methylation procedures support conventional Py-FIMS and Py-GC/MS and give valuable additional information on the occurrence of aliphatic and aromatic carboxylic acids, substituted phenols, benzenediols, benzenetriols, phenolic acids and amides in soil organic matter.     

Comparisons of soil organic matter and its fractions by pyrolysis mass-spectrometry

Pyrolysis mass-spectra from a sample of the A₁-horizon of a soil from southern Spain showed predominant peaks related to furan derivatives similar to those observed from complex polysaccharides in which not only hexoses but also pentoses and deoxyhexoses were constituent units. Smaller peaks, typical for protein materials and phenolic units, were also observed. On the other hand, typical peaks for the methoxyphenols of lignins were very small and indicated only limited amounts of undecomposed lignin residues in this soil sample. Peaks related to benzene or toluene were also very small.Humic acid samples from this soil showed much more prominent signals related to protein materials, benzene and phenolic derivatives and weaker polysaccharide-related signals than did the entire sample. Typical lignin related peaks were small or insignificant. Spectra from the grey or brown humidic acid fractions were much like those of the parent humic acid. Brown humic acid, however, showed stronger signals for nitrogen and sulphur compounds, indicating a higher content of protein-like materials in this fraction. Preparations of humic acid hydrolyzed by 6 N HCl showed in their pyrolysis products a marked increase in phenols and methoxyphenols.In its pyrogram, humin resembled humic acid, but signals for complex polysaccharides were more evident. Lignin-like materials seem not to be higher in this fraction. Hymatomelanic acid showed prominent signals related to polysaccharides and lignin. Pyrograms from the soil polysaccharides showed the characteristic pattern of a complex polysaccharide with the presence of fragments from polymers of amino acids or amino sugars. Fulvic acid spectra showed obvious dissimilarities to those from humic acid in that signals for protein, as well as those related to phenols, were low. Depending upon the isolation method, the fulvic acid preparations showed differing signals related to polysaccharide or phenolic materials.     

Alkaline cupric oxide oxidation of a methylated fulvic acid

Fulvic acid, (FA), extracted from the Bh horizon of a Podzol soil, was methylated and then oxidized with alkaline cupric oxide. The oxidation products were extracted into organic solvents, remethylated and separated by column-, thin layer-, and preparative gas chromatography into relatively pure components, which were identified by matching their mass and i.r. spectra and gas Chromatographic retention times with those of authentic specimens.The degradation products isolated and identified accounted for approximately 18 per cent of the weight of the initial methylated FA. Major oxidation products were: (a) methylated phenolic aldehydes and esters (66.9 per cent): (b) benzenecarboxylic acid methyl esters (14.6 per cent): (c) aliphatic dicarboxylic acid methyl esters (2.7 per cent): and (d) adsorbed materials such as n-alkanes (0.3 per cent), n-fatty acid methyl esters (0.3 per cent) and dioetyl adipate (15.2 per cent). The oxidalive degradation of methylated FA indicates the presence of two types of basic structural units: (1) those yielding phenolic aldehydes and esters, and (2) those producing benzenecarboxylic acids. Alkaline cupric oxide oxidation of methylated FA is relatively selective for the isolation of the phenolic components and appears to be a promising technique for structural investigations on humic substances.     

Pyrolysis of a soil humic acid and of their hydrolyzed and methylated products

Pyrolysis of soil humic acid yields a variety of products arising from heterogeneous materials associated to the humic structure and from this self. After acid hydrolysis most of the compounds related to proteins, polysaccharides and lignin dissappear. Adsorbed compounds such as fatty and dicarboxylic acids are released after methylation and subsequent pyrolysis. In addition pyrolysis produces aromatic and substituted aromatic hydrocarbons. All the identified pyrolysis products have also been isolated by different complex and time-consuming chemical degradations and solvent extraction procedures. Pyrolysis provide some evidence of the humic acid structure.     

Aromatic constituents of humic acids released by na-amalgam reductive cleavage,koh fusion and zinc dust fusion

Eight humic acids showing different degree of humification were treated with HCI (1:1). The hydrolyzed humic acids were subjected to reductive cleavage with Na-amalgam, KOH fusion and zinc dust fusion. The yields of degradation products were determined by colorimetry gas chromatography.

The perimental results Were summarized as follows:

l. The amounts of ether-soluble substances obtained by reductive cleavage with Naamlagan ranged from 21.6% for Kuragari (A type) to 7.8% for Kisokoma B₂ (Rp type). The yields of phenolic substances expressed in terms of vanillic acid content ranged from 3.0% for Kuragari (A type) to 1.8% for Kisokoma B₂ (Rp type). Resorcinol. p.hydroxybenzoic acid, vanillic acid, protocatechuic acid and syringic acid were detected in the gas chromatograms of the ethe-soluble substances and their total yield comprised less than 0.6% of the Kisokoma F (Rp type).

2. The KOH fusion of humic acid yielded a larger amount of degradation products as compared to reductive cleavage. The amount of ether-soluble substances ranged from 42.7% for Kisokoma F (Rp type) to 12.6% for Sochiken 1 (A type). The yields of phenolic substances, expressed in terms of amount of protocatechuic acid, ranged from 10.6% for Kisokoma F (Rp type) to 4.6% for Inogashira (A type). Exept for syringic acid, the same compounds released after ramged from 2.1% for Sochiken 2 (B type) to 0.4% for Sochiken 1 (A type).

3. The amounts of benzene-soluble substances and hydrocarbons obtained from Goshikigahara (P type) by zinc dust fusion were 20.9% and 5.2%, respectively. The yields of the hydrocarbons tended to increase in the order; P type > Rp type ≥ B type. Perylene and 2-methylanthracene were detected in the gas chromatograms of the hydrocarbons fractions and, in the case of Goshikigahara (P type), their yields were 0.031% and 0.010%, respectively.     

Sodium amalgam reduction of humic acid—II. application of the method

The nature and distribution of the phenolic compounds found in humic acid on sodium amalgam reduction resemble those reported to be found in microbial cultures grown on lignifiedplanttissue.lt has also been shown that the more humified and decayed fractions of soil organic matter yield humic acids that bear less resemblance to lignin than do the humic acids from less decayed plant remains. The aromatic portion of humic acid would seem to consist of biologically modified and transformed lignin, together with phenolic units synthesized by soil microbes. Sodium amalgam reduction can be employed to estimate the degree of transformation, but cannot, however, be used to “finger print” humic acids.     

Chemical studies on soil humic acids

Seventeen samples of soil humic acids, two fractions of soil fulvic acid sample, and several related compounds such as lignin, tannin, flavonoid and artificial humic substances were decomposed in conc. KOH solution at 180°C. Succinic acid, glutaric acid, phloroglucin, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, 3,4-dihydroxy-5-methoxybenzoic acid, and gallic acid were detected in the degradation products of humic acids. The amounts of these degradation products were discussed in relation to the degree of humification or the sources of the humic acid samples. Succinic acid also resulted from glucose, polymaleic acid, and the humic acid and humin prepared from glucose, but glutaric acid resulted only from glucose humic acid and glucose humin but not from glucose and polymaleic acid. Succinic acid and glutaric acid were supposed to result from the same structural portions in humic acids because of the very significant positive linear correlation between their amounts. p-Hydroxybenzoic, vanillic, protocatechuic, and 3,4-dihydroxy-S-methoxybenzoic acids were presumed to result mainly from lignin structure in humic acids. Soil humic acids yielded small amounts of gallic acid although the yields by hydrolysable tannins were in large amounts. The yields of above-mentioned degradation products from humic acids decreased with increasing degree of humification. Phloroglucin resulting from ftavonoids including condensed tannins were also found in the degradation products of humic substances. Its yield showed no linear correlation with RF value of humic acid, and is presumed to be rather related to the vegetation at the sites of soil sampling.     

The chemistry of soil organic nitrogen: a review

1. From the data presented herein it is possible to deduce the following distribution of total N in humic substances and soils: proteinaceous materials (proteins, peptides, and amino acids) – ca. 40%; amino sugars – 5–6%; heterocyclic N compounds (including purines and pyrimidines) – ca. 35%; NH₃–19%; approximately 1/4 of the NH₃ is fixed NH₄ ⁺. Thus, proteinaceous materials and heterocyclics appear to be major soil N components. 2. Natural ¹⁵N abundance levels in soils and humic materials are so low that direct analysis by ¹⁵N NMR is very difficult or impossible. To overcome this difficulty, the soil or humic material is incubated with ¹⁵N-enriched fertilizer. Even incubation in the laboratory for up to 630 days does not produce the same types of ¹⁵N compounds that are formed in soils and humic materials over hundreds or thousands of years. For example, very few ¹⁵N-labelled heterocyclics are detected by ¹⁵N NMR. Does this mean that heterocyclics are not present? Or are the heterocyclics that are present not labelled under these experimental conditions and therefore not detected by the ¹⁵N NMR spectrometer ? Another possibility is that a large number of N heterocyclics occur in soils, but each type occurs in very low concentrations. Until the sensitivity is improved, ¹⁵N NMR will not provide results that can be compared with data obtained from the same soil and humic material samples by chemical methods and mass spectroscopy. 3. What is most important with respect to agricultural is that all major N forms in soils are available to organisms and are sources of NH₃ or NH₄ ⁺ for plant roots and microbes. Naturally, some of the NH₃ will enter the N cycle. 4. From chemical and pyrolysis-mass spectrometric analyses it appears that N heterocylics are significant components of the SOM, rather than degradation products of other molecules due to pyrolysis. The arguments in favor of N heterocyclics as genuine SOM components are the following: a) Some N-heterocyclics originate from biological precursors of SOM, such as proteinaceous materials, carbohydrates, chlorophyll, nucleic acids, and alkaloids, which enter the soil system as plant residues or remains of animals. b) In aquatic humic substances and dissolved organic matter (DOM) at considerably lower pyrolysis temperatures (200 to 300°C), free and substituted N-heterocyclics such as pyrroles, pyrrolidines, pyridines, pyranes, and pyrazoles, have been identified by analytical pyrolysis (Schulten et al 1997b). c) Their presence in humic substances and soils was also detected without pyrolysis by gel chromatography – GC/MS after reductive acetylation (Schnitzer and Spiteller 1986), by X-ray photoelectron spectroscopy (Patience et al. 1992), and also by spectroscopic, chromatographic, chemical, and isotopic methods (Ikan et al. 1992). 5. While we can see light at the end of the tunnel as far as soil-N is concerned, further research is needed to identify additional N-containing compounds such as N- heterocyclics, to determine whether these are present in the soil or humic materials in the form in which they were identified or whether they originate from more complex structures. If the latter is correct, then we need to isolate these complex N-molecules and attempt to identify them.     

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.     

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.     

Quantification of long‐chain fatty acids in dissolved organic matter and soils

The objective was to develop and adapt a versatile analytical method for the quantification of solvent extractable, saturated long‐chain fatty acids in aquatic and terrestrial environments. Fulvic (FA) and humic (HA) acids, dissolved organic matter (DOM) in water, as well as organic matter in whole soils (SOM) of different horizons were investigated. The proposed methodology comprised extraction by dichloromethane/acetone and derivatization with tetramethylammonium hydroxide (TMAH) followed by gas chromatography/mass spectrometry (GC/MS) and library searches. The C_10:0 to C_34:0 methyl esters of n‐alkyl fatty acids were used as external standards for calibration. The total concentrations of C_14:0 to C_28:0 n‐alkyl fatty acids were determined in DOM obtained by reverse‐osmosis of Suwannee river water (309.3 μg g^—1), in freeze‐dried brown lake water (180.6 μg g^—1), its DOM concentrate (93.0 μg g^—1), humic acid (43.1 μg g^—1), and fulvic acid (42.5 μg g^—1). The concentrations of the methylated fatty acids (n‐C_16:0 to n‐C_28:0) were significantly (r² = 0.9999) correlated with the proportions of marker signals (% total ion intensity (TII), m/z 256 to m/z 508) in the corresponding pyrolysis‐field ionization (FI) mass spectra. The concentrations of terrestrial C_10:0 to C_34:0 n‐alkyl fatty acids from four soil samples ranged from 0.02 μg g^—1 to 11 μg g^—1. The total concentrations of the extractable fatty acids were quantified from a Podzol Bh horizon (26.2 μg g^—1), Phaeozem Ap unfertilized (48.1 μg g^—1), Phaeozem Ap fertilized (57.7 μg g^—1), and Gleysol Ap (66.7 μg g^—1). Our results demonstrate that the method is well suited to investigate the role of long‐chain fatty acids in humic fractions, whole soils and their particle‐size fractions and can be serve for the differentiation of plant growth and soil management.     

The distribution of nitrogen in some highly organic tropical volcanic soils

The qualitative and quantitative distribution of N-compounds in 10 tropical soils, and in a number of humic materials extracted from representative samples thereof, was determined after 6 N HCl hydrolysis.Eighty to 98% of the total N in the soils and humic materials was hydrolysable by 6n HCl. Slightly less than one half the hydrolysable N in the soils and humic fractions consisted of amino acids. Well-drained soils and fulvic acids extracted from them contained unusually high concentrations of the acidic amino acids, aspartic and glutamic acids. Between 80 and 95% of the amino acids in the soils was accounted for in the humic materials + NaOH-insoluble organic residues. NH⁺₄-N released by acid hydrolysis was generally higher for the soil samples than for the humic materials. Amino sugar-N constituted relatively small proportions of the total N in the soils and humic fractions.Our data suggest that large quantities of amorphous allophanic materials coupled with relatively high enzymic activity are responsible for the observed accumulation of acidic amino acids in the well-drained tropical volcanic soils.     

Land use effects on the composition of organic matter in soil particle size separates. III. Analytical pyrolysis

Soil samples from the A horizon of an Eutrochrept under spruce forest and permanent grass were fractionated into clay-, silt- and sand-size separates. Humic acids extracted from each fraction were analysed by pyrolysis-gas chromatography-mass spectrometry. Protection of functional groups by simultaneous pyrolysis and methylation yielded pyrolysates in which methyl esters of fatty acids, aliphatic dicarboxylic acids, abietic acids, phenolic acids and benzenecarboxylic acids were represented. However, methylation was not complete, and unmethylated compounds were also present. Spectra showed differences in humic acid composition between size separates as well as across land use regimes. The abundance of lignin-derived pyrolysis products increased with decreasing particle size, and was greater in soil under spruce than in soil under grass. Also, the lipid components differed, with hexadecanoic and docosanoic acid methyl esters being the dominant compounds in humic acids from soil under spruce and hexadecanoic and octadecanoic acid methyl esters in the humic acids from grassland. A good correlation was found between previous ¹³CNMR and wet chemical data and pyrolysis data, indicating that pyrolysis-methylation can be used for fast detailed chemical characterization of humic acids extracted from size separates.