Humus composition of soils under forest, coffee and arable cultivation in hilly areas of south Sumatra, Indonesia

To understand the effect of land use changes on the composition of humus in tropical soils, samples from land under primary forest, secondary forest, coffee plantation, and arable crops were investigated at three sites in south Sumatra, Indonesia. Total carbon and total nitrogen contents were 1.7 to 4.3 times and 1.1 to 2.8 times greater in the topsoil under primary forest than under the other types of land use. Following change from primary forest to other uses, the proportion of humic acids in the organic matter of the topsoils decreased while that of the fulvic acid fraction increased. Within the range of land uses, differences in the yields of humic acids and fulvic acid fractions were, respectively, larger and smaller than those in total carbon content. The humic acids were classified into the low and middle classes in the degree of humification. Absorption due to the green fraction of humic acids, Pg, was detected in the UV‐visible spectra of almost all the humic acids. No relation was observed between the degree of humification of humic acids or the strength of Pg absorption in their spectra and land use change. The fulvic acid fractions were fractionated on insoluble polyvinylpyrrolidone (PVP) into the adsorbed fractions consisting of humic substances and the non‐adsorbed fractions consisting of non‐humic substances. A positive correlation between the amount of the fulvic acid fraction and the percentage of the PVP‐adsorbed fraction within it indicated that the variation in the amount of the fulvic acid fraction was attributable to acid‐soluble humic substances. The ionization difference spectra of solutions between pH 12 and pH 7 suggested that the chemical structures of the PVP‐adsorbed fulvic acids have been altered by land use change.     

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.     

Dissolved organic matter in lysimetric water of mountain forest soils in the southern Sikhote Alin

The fractional composition of dissolved organic matter and the chemical nature of humic and fulvic acids were studied in lysimetric waters from forest soils of different altitudinal zones in the Sikhote Alin Range. The elemental composition, infrared absorption spectra, concentrations of acid functional groups, and pK spectra of humic and fulvic acids were determined. Fulvic acids predominated in the upper soil horizons, and fraction of nonspecific dissolved organic substances predominated in the lower mineral horizons. The portion of humic acids in the humus horizons markedly decreased from the low-mountain soils to the high-mountain soils; the nitrogen content of humic and fulvic acids decreased in the same direction. Three classes of carboxyl and phenolic groups were determined in pK-spectra of humic and fulvic acids. The soils of high-mountain zones had stronger acidic properties of humic and fulvic acids in comparison with the soils of low-mountain zones. The determined characteristics of the composition of dissolved organic matter and the trends of their changes contribute to our knowledge of pedogenetic processes in the altitudinal sequence of forest landscapes of the Sikhote Alin Range.     

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.     

The humus status of brown forest soils and its changes upon intensive tea growing in the subtropical zone of Russia

Changes in the humus status of acid brown forest soils used for tea growing have been studied in a long-term stationary experiment after 20 years of the application of mineral fertilizers in increasing doses. It is shown that long-term tea growing has resulted in a reliable increase in the humus content within the upper cultivated horizon (Ap, 0–40 cm) at the expense of the nonhydrolyzable fraction of humus (humin) and the first fractions of humic and fulvic acids. The fractional composition of humus has changed against the background of a stable fulvate type of humus (Cha/Cfa < 0.5). The portion of the first fraction of humic and fulvic acids in the total amount of humus has increased, as well as the portion of the first fraction of humic acids in the total amount of humic acids. These changes are due to the enhanced humification of plant residues with a parallel decrease in the contents of the second (Ca-bound) and third (bound with clay and stable sesquioxides) fractions of humic substances.     

Multivariate analysis of CPMAS 13C-NMR spectra of soils and humic matter as a tool to evaluate organic carbon quality in natural systems

A series of humic and fulvic acids isolated from different sources, size‐fractions separated from a humic acid, and three soils of different origin were subjected to CPMAS ¹³C‐NMR spectroscopy to obtain the distribution of their carbon contents. The relative areas of chemical shift regions in NMR spectra were used to apply a principal component analysis (PCA) to the three sets of samples. The multivariate analysis was successful in efficiently differentiating samples on the basis of the quality of their organic carbon content. The PC biplots based on two principal components distinguished objectively among samples as accurately as it was possible to do by subjective qualitative evaluation of the original spectra. In the case of the soils, a discriminant analysis (DA) was applied to build a classification model that allowed the validation of the three soils according to their origin. Percentage of validation in the classification model is expected to increase when a large number of NMR spectra are accumulated and/or the concentration of organic carbon in samples is enhanced. The multivariate analyses described are likely to become a useful tool to increase the importance of CPMAS ¹³C‐NMR spectra in the appraisal of natural organic matter variations in heterogeneous natural systems.     

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.     

Ein Vergleich der Huminstoffsysteme einer Parabraunerde aus der Kölner Bucht und einer österreichischen Schwarzerde

A comparison of the humic systems from a Luvisol from the area of Köln and from an Austrian Chernozem Grey humic acids, brown humic acids and fulvic acids have been extracted from a Luvisol after removal of the “light fraction”. The humic fractions were investigated chromatographically using controlled pore glass with a pore diameter of 17,7 nm. Concentration of both coloured material and carbon were simultaneously recorded in the chromatograms. Specific extinctions at 400 nm were calculated and maximal values were taken as constants specific for “pure” humic substances. These were 349,6; 155,8 and 39,4 for “pure” grey humic acids, brown humic acids and fulvic acids, respectively, and were in part considerably below those determined earlier for an Austrian Chernozem. Using these constants “pure” humic substances could be distinguished numerically from accompanying non-humic substances. The ratio of “pure” humic to non-humic substances was approximately 2:1 for both soils. Within the “pure” humic substances Chernozem humus was dominated by grey humic acids amounting up to 52% whereas in the Luvisol brown humic acids had the same 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.     

New methodology to assess the quantity and quality of humic substances in organic materials and commercial products for agriculture

Purpose

The traditional method to determine humic content (humic and fulvic acids) in commercial fertilizers, biostimulants, and organic materials is based on the oxidation of the organic carbon contained in the basic-soluble but acid-insoluble fraction (humic acids) and the basic-acid soluble fraction (fulvic acids) of their alkaline water extracts. This methodology, merely operational, makes it impossible to distinguish if the quantified carbon corresponds to substances with “humic” chemical nature or to non-humic organic matter but with similar solubility properties to those of humic matter. The aim of this work is to develop a new methodology that not only quantifies the humic content in commercial products (and raw materials) but also assesses the humic quality of the quantified organic matter.

Materials and methods

To this end, humic and fulvic (-like) fractions have been isolated/purified from several humic and non-humic materials and characterized by means of elemental analysis and UV-visible, fluorescence, and infrared spectroscopies, and these data have been used to perform a discriminant analysis (DA).

Results and discussion

The model obtained from the DA is able to discriminate humic and fulvic fractions from apparently humic or fulvic ones and provides discriminant classification functions that have proven to successfully predict the “humic quality” of the fractions isolated from commercial products, after their elemental and spectroscopic characterization.

Conclusions

Therefore, the combination of the fractionation, characterization, and evaluation by the DA is proposed as an effective methodology for quantifying and assessing the quality of the humic content claimed in the labels of commercial products.

     

腐殖酸对汞的络合稳定特性及其环境学意义

对3种腐殖酸与Hg的络合稳定特性研究结果表明,腐殖酸与Hg的结合存在松结态与紧结态2种形态,其中富里酸主要以松结态为主,灰色胡敏酸与棕色胡敏酸则以紧结态占绝对优势。3种腐殖酸中富里酸对Hg的络合容量最高,但络合强度最低,其络合汞的环境活性将较高;灰色胡敏酸对Hg的络合容量最低,但络合稳定性最高,故所结合Hg的环境活性最弱。但受容量因素制约,灰色胡敏酸对Hg的络合稳定性将因Hg/灰色胡敏酸相对比例的升高而急剧下降。棕色胡敏酸对Hg络合特性介于富里酸与灰色胡敏酸之间。     

The distribution of the stable carbon isotope (13C/12C) in fractions of soil organic matter

The carbon-isotopic composition of fulvic and humic acid from the A horizons of eight soil types, developed under a wide variety of climatological conditions, was measured. The fulvic acid is always enriched in ¹³C as compared with the humic acid from the same soil by a rather constant factor of 0.9?. The fulvic acids are isotopically closer to the plant source of the organic matter and thus represent an intermediate stage in the formation of humic substances. Depth sections of peat soil showed that carbon isotopes can be used to evaluate the dynamic nature of the fulvic-acid fraction. With depth, a transfer of carbon groups from polysaccharides to fulvic acid is seen. Based on isotopic evidence it is shown that in addition to formation of β-humus, part of the fulvic acid is condensed with depth to a stable humic fraction — humin.     

A COMPARISON OF THE POLYCARBOXYLIC ACIDS EXTRACTED BY WATER FROM AN AGRICULTURAL TOP SOIL WITH THOSE EXTRACTED BY ALKALI

Humic and fulvic acids were isolated from an agricultural soil by conventional means. The same soil was extracted with water and the organic matter freed of inorganic and low molecular weight substances. The usual chemical differences between humic acid and fulvic acid were confirmed and the water extract was shown to resemble fulvic acid quite closely. Further fractionation of the fulvic acid and water extract showed that the elemental composition, carboxyl and acidic hydroxyl contents, molecular weights, and infrared spectra of the purified polycarboxylic acids were virtually identical. Both promoted the same growth response in cultured isolated tomato roots. It is suggested that the qualitative similarity of fulvic acid to the polycarboxylic acid extracted by water justifies the use of the more easily isolated fulvic acid in physiological experiments on the direct effects on plants of soil organic matter.     

Characterization of water soluble organic matter in soils by size exclusion chromatography and fractionation with polyvinylpyrrolidone

Water extracts were obtained from four types of soils (Brown Lowland soil, Yellow soil with manure application for 6 years, non-allophanic Andosol, and allophanic Andosol), and the organic matter in the water extracts was fractionated according to the solubility in acid and adsorption onto polyvinylpyrrolidone (PVP). For the water extracts and their fractions, the amounts of organic C, total N, and anthrone-reactive C (ARC) were analyzed, and high performance size exclusion chromatography (HPSEC) was carried out. The PVP-non-adsorbed fulvic acid (FA) fraction accounted for the largest proportion of the total water-soluble organic C, ranging from 52% for the Yellow soil to 96% for the allophanic Amdosol, followed by the PVP-adsorbed FA and humic acid (HA) fractions. The water extract of the allophanic Andosol was characterized by the lack of HA fraction and a small proportion of PVP-adsorbed FA fraction. For all the water extract samples, more than 90% of the ARC was recovered in the PVP-non-adsorbed FA fraction. The proportion of ARC in the total organic C in the fraction was also highest in the PVP-non-adsorbed FA fraction. The molecular weight (MW) of the humic substances (HS) at peak maximum was estimated at 1,300 Da for the water extracts and their fractions from the Brown Lowland soil and non-allophanic Andosol samples by HPSEC using polyethylene glycols as MW standards. Manure application increased the MW of HS in the HA and PVP-adsorbed FA fractions. On the other hand, only a small amount of HS was found in the water extract of the allophanic Andosol by HPSEC.     

The humus state of the soils of locally hydromorphic landscapes in the lower reaches of the don river

The humus state of rainfed chernozems affected by local waterlogging was studied. The total humus content in the hydromorphic chernozems increases, as well as the content of fulvic acids, whereas the content of nonhydrolyzable residue (humin) decreases. A significant increase in the portions of the third fractions of humic and fulvic acids is observed. The role of the fine silt and clay fractions in the binding of humic substances increases in the lower horizons of locally hydromorphic soils. The increase in the content of fulvic acids (fulvatization) is mainly due to their predominance in the clay fraction. The latter is specified by the significant narrowing of the C_ha-to-C_fa ratio, the lower content of the nonhydrolyzable residue, and the increased content of the clay-bound (3rd fraction) fulvic and humic acids. The composition of the humus in the fine silt fraction of the studied soils is characterized by an increased amount of humic acids of the second fraction with a decrease in the relative content of fulvic acids.     

Role of inorganic anions in the structural transformation of molecules of humic substances in soil

It was shown that inorganic anions of exogenic compounds affected the structure of humic and fulvic acids in gray forest soil, as well as the yield of humic acids and their contents of carbon and metals. Humic substances in arable soil more readily interacted with the anions of extractants and fertilizers compared to virgin soil. Changes were revealed in the energy state of the electronic system of P- and N-modified fragments of humic acids from the arable soil. New ligand groups and chelate nodes were found in modified fragments using differential electronic spectra.     

Incorporation of nitrogen from urea fertilizer into soil organic matter in rice paddy and cassava upland fields in Indonesia

Incorporation of newly-immobilized N into major soil organic matter fractions during a cropping period under paddy and upland cropping systems in the tropics was investigated in Jawa paddy fields with and without fish cultivation and a Sumatra cassava field in Indonesia. ¹⁵N-labelled urea (¹⁵N urea) was applied as basal fertilizer, and the soil samples were collected after harvest. The percentage of distribution of the residual N in soil from ¹⁵N urea into the humic acids, fulvic acid fraction, and humin were 13.1–13.9, 19.0–20.5, and 53.4–54.3%, respectively, for the Jawa paddy soils, and 14.9, 27.4, and 52.4%, respectively, for the Sumatra cassava soil. These values were comparable to the reported ones for other climatic zones. The percentage of distribution of ¹⁵N urea-derived N into humic acids was larger than that of total N into the same fraction in all the soils. The distribution into the fulvic acid fraction was also larger for ¹⁵N urea-derived N than for total N in the Jawa soils. Humic and non-humic substances in the fulvic acid fraction were separated using insoluble polyvinylpyrrolidone (PVP) into the adsorbed and non-adsorbed fractions, respectively. Less than 5% of the ¹⁵N urea-derived N in fulvic acid fraction was detected in the PVP-adsorbed fraction (generic fulvic acids). The proportion of non-hydrolyzable N remained after boiling with 6 M HCl in the ¹⁵N urea-derived N was 9.4–13.5%, 17.3–26.7%, and 8.4–16.6% for the humic acids, generic fulvic acids, and humin, respectively. The significantly low resistance to acid hydrolysis suggested that the ¹⁵N urea-derived N was less stable than the total N in soil regardless of the fractions of humus.     

In vitro assessment of the inhibition of humic substances on the growth of two strains of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis>

The effects of four humic substance (HS) samples, a soil humic acid and two humic acids and one fulvic acid isolated from a composting substrate, were evaluated on the mycelial growth of Fusarium oxysporum f. sp. melonis (FOM) and F. oxysporum f. sp. lycopersici (FOL). In general, any HS treatment reduced significantly the radial growth of the FOM mycelium either in normal [potato dextrose agar (PDA) medium] or sub-optimal (water–agar medium) nutritional conditions. Differently, the FOL growth, which was tested only on PDA, was either inhibited or stimulated on dependence of the HS treatment used. The HS fractions isolated from the composting substrate were the most effective inhibitors of mycelial growth of both fungi. Furthermore, any HS treatment was also able to alter the germination process of FOL in aqueous medium, not only by reducing significantly the number of viable germinating conidia but also by generally decreasing the rate of conidial germ-tube elongation. Apparently, the extent of the inhibitory action was related to some chemical and functional properties of HS, such as the COOH group content and elemental composition.     

用凝胶层析法和示踪技术评估腐植酸分子量分级组成及其与Cd、Zn的络合特性

通过凝胶层析法对土壤腐植酸进行了分组提取,并对其各分子量分级组成及其与Cd、Zn的络合特性进行了研究.结果表明:土壤胡敏酸通过G-50可以分成3个较集中的组分,分子量分别为M=78180、M=48339及M=22863;通过G-100可以得到2个组分,分子量分别为M=63343和M=19870.富里酸通过G-50、G-100层析,则从总体上成为单一的宽带,分子量约为M=2300.腐植酸对Cd、Zn络合量的测定显示:胡敏酸对Cd、Zn的络合量呈2个明显的峰值,而富里酸只有1个峰值.两者对Cd、Zn络合量随洗脱体积的变化曲线与其吸光值随洗脱体积的变化曲线相一致.65Zn示踪技术研究65Zn与胡敏酸、富里酸络合的结论与常规方法一致.     

Molecular composition of humic substances in tundra soils (13C-NMR spectroscopic study)

Functional groups and molecular fragments of humic substances (HSs) from cryohydromorphic peat gley tundra and surface-gley tundra soils have been identified by ¹³C-NMR spectroscopy. The analysis of HS preparations has shown that the molecules of humic acids (HAs) are enriched with aromatic fragments compared to fulvic acids (FAs). Aliphatic chains, carbohydrate- and amino acid-type structures prevail in the carbon skeleton of the FAs. An integrated parameter of the HS hydrophobicity has been proposed. The parameter represents the total portion of unoxidized carbon atoms and allows indirectly assessing the amphiphilic properties of HSs.