THE HUMIC ACIDS EXTRACTED BY VARIOUS REAGENTS FROM A SOIL

The infra-red, visible, and ultra-violet absorption spectra of humic acids extracted from a red-brown earth by various reagents, are described. The variations in the intensity of various absorption bands in the infra-red spectra are related to the method of extraction, yield, and titration data. For example, the humic acids extracted by milder reagents give rise to spectra which show relatively weak aliphatic C-H absorption whilst the intensity of the bands arising from oxygen-containing groups (carboxyl and ketone carbonyl) is relatively strong. The opposite behaviour is shown by the corresponding bands in the spectra of humic acids extracted by stronger reagents. The intensities of other infra-red bands are also considered. The optical density of the C═O band at 1720 cm^?1 in the humic-acid spectra and of the carboxylate ion band at 1380 cm^?1 in the spectra of the K salt is linearly related to the exchange capacity. The presence of carboxyl groups ionizing above pH 7 and extending to as high as pH 11, is demonstrated.     

Amino sugars in fungal melanins and soil humic acids

Humic acids from six Brazilian topsoils (three Latosols and three Podzols) and five soil fungal melanins were hydrolysed and the released amino sugars qualitatively and quantitatively determined by capillary gas-liquid chromatography. Melanins were obtained from liquid culture media, synthesized with nitrate or asparagine as a source of N, of Stachybotrys atra, Aspergillus glaucus, Eurotium echinulatum and Hendersonula toruloidea. Glucosamine (48–60%), galactosamine (39–52%), and traces of mannosamine were detected in all humic acids. The total amino sugar content ranged from 1351 to 2287 mg kg^?1. In the fungal melanins analysed, mostly glucosamine (80–99%) and trace to small amounts of galactosamine and mannosamine (<10%) were found in amounts ranging from 192 to 635 mg kg^?1. The Occurrence of mannosamine in fungal melanins and fungal polysaccharides had not previously been found. The present study gives additional data to the theory that fungal melanins may play a role, as precursors, in the formation of soil organic matter.     

A preliminary study of fungal melanin by infrared spectroscopy

Infrared spectra of melanin and methylated melanin have been interpreted to show the existence of carboxyl groups in two different environments in the melanin structure. In one, there are a small number of carboxyl groups with an absorption band at about 1700 cm^?1; these are relatively free and are capable of interaction with alkali to produce carboxylate in the normal way. In the other environment, the carboxyl groups, absorbing at 1615 cm^?1, are conjugated and strongly hydrogen bonded to presumably phenolic hydroxyl groups, and cannot be neutralized with alkali. They do, however, react with diazomethane, as do the free carboxyls, to produce methyl ester absorbing at 1728 cm^?1.The significance of these conclusions for the survival of melanin in soil and its reactions therein, is briefly discussed.     

Soil Organic Matter Quality and Zinc and Lead Sorption as Affected by a Sewage Sludge Or a Sewage Sludge Compost Application

Sewage sludge (SS) or sewage sludge compost (SSC) were applied to soil under controlled conditions, at rates of 0 or 200 Mg ha^?1, to investigate changes in dissolved organic matter (DOM), humic acids (HA), and Pb and Zn sorption in the soil. Infrared spectroscopy, visible spectrophotometry, and sorption isotherms (mono-metal and competitive sorption systems) methods were used to assess the changer. The E₄/E₆ ratio (λ at 465 / λ at 665 nm) and the infrared spectra of DOM and HA showed aromatic behaviour in compost-soil (SSC-S); in contrast sewage sludge-soil (SS-S) showed an aliphatic behaviour. Application of either SS or SSC increased the Pb and Zn sorption capacity of soil. The Pb and Zn sorption increased in soil and soil mixtures with a competitive metal system. The metal affinity sequence for soil, SS-S, and SSC-S was compared with the predicted affinity sequences obtained from metal properties. Poor correspondence was observed between the metal affinity sequence and the metal affinity sequence predicted by ionic potential, indicating that metals bonding to soils were not predominantly electrostatic. An affinity sequence based on Pearson's theory agreed with the metal affinity sequences for soils. A statistical analysis showed that the bands assigned to esters (1080 cm^?1) of DOM, phenolic OH (1420 cm^?1), amide I (1650 cm^?1), carboxyl and carbonyl C=O stretches of different nature, C=O stretch of aromatic esters, aliphatic cetone, aldehyde (1720 cm^?1), ethers and esters (1230 cm^?1), aliphatic alcohols (1125 cm^?1), and lignin (1380 cm^?1) of HA were correlated with Zn constants of Langmuir adsorption isotherm (P < 0.05).     

Elemental,functional infrared and free radical characterization of humic acid-type fungal polymers (melanins)

Summary Humic acid-type polymers (melanins) synthesized in culture media by the fungi Aspergillus glaucus, Eurotium echinulatum, Hendersonula toruloidea, Stachybotrys atra and Aspergillus sydowi were analysed for elemental composition, functional group content, infrared (IR) and electron spin resonance (ESR) properties. Results were discussed in comparison with range values referred for soil humic acids. The fungal polymers showed significant differences in carboxyl and nitrogen content and C/H atomic ratios, reflecting a different degree of condensation (aromaticity) among the various samples. IR analysis gave evidence of: (a) the predominant aromatic character of melanins from A. glaucus, E. echinulatum and H. toruloidea; (b) the high content of aliphatic and olefinic components of S. atra melanin; (c) the typical presence of amide bonds in the nitrogen-richest melanins from A. sydowi and H. toruloidea; and (d) the generally low amount of free carboxyl groups, which often appeared involved in hydrogen bonds. ESR spectra showed that all the melanins studied contained appreciable concentrations of organic free radicals of prevailing semiquinonic nature and of the same order of magnitude commonly measured in humic acids from soil and other sources. The free electron concentration was shown to be directly related to the C/H atomic ratio and to the degree of aromaticity shown by IR analysis. This indicated that the highest free radical content in the melanins from E. echinulatum and A. glaucus was associated with the highest presence of condensed aromatic structures. Humic acid-type polymers synthesized by soil fungi may, therefore, contribute to the total free radical content of soil humic substances and play important roles in all reactions involving free radicals in soils and related environments.     

Diffuse-Reflectance Mid-infrared Spectral Properties of Soils under Alternative Crop Rotations in a Semi-arid Climate

We carried out mid-infrared (mid-IR) spectral interpretation of soils 0–5 and 5–15 cm deep in selected alternative crop rotations (ACR) treatments and an adjacent native prairie soil. Ashing and spectral subtraction shows that absorbance at 3700–2850 and 1700–1550 cm^?1 indicates organic absorbance. Prairie soils, with their greater carbon (C) content, have different spectral properties from the cropped soils. Prairie soils have greater absorbance at the 2950–2870 cm^?1 and the 1230 cm^?1 CH bands. The soils from the different depths had different spectral properties, with the soils 0–5 cm deep having stronger absorbance at the 1055 cm^?1 carbohydrate band, at 1270–1460 cm^?1, and at the 1730 cm^?1 ester band. The soils 5–15 cm deep are characterized by greater absorbance at the clay band. Soil C and nitrogen (N) correlated negatively with the 3700 cm^?1 clay band and the 1830 cm^?1 quartz band and correlated positively with the 2920 cm^?1 because of aliphatic CH absorbance.     

Complex formation between humic acid and clays as revealed by gel filtration and infrared spectroscopy

Complex formation between pure silicate clay minerals and humic acid (HA) extracted from a Eustis loamy sand (Psammentic Paleudult) was investigated by i.r. spectroscopy and Sephadex G50 and G25 gel filtration. Gel filtration of humic acid after treatment with clay resulted in the separation of normal amounts of high m.w., but reduced concentrations of low m.w. HA. This observation suggested that only the low m.w. fraction of HA was adsorbed by silicate clays. As compared to i.r. spectrograms of original HA, humic acid remaining in solution after interaction with clay exhibited i.r. curves with new bands at 940 and 840 cm^?1 for O-Al-OH vibrations and increased absorption in the 1050, 1400 and 1620 cm^?1 regions for Si-O and COO^? stretching vibrations, respectively. The absorption band for Si-O was retained by the i.r. spectrum of the high m.w. fraction of HA, and the O-Al-OH absorption by that of low m.w. HA. The latter showed in addition the strong band for COO^? stretching vibrations.     

Decomposition of 14C-labeled lignins,model humic acid polymers,and fungal melanins in allophanic soils

During 1 yr, CO₂-C losses from 7 agricultural soils containing 0.5–1.5% organic C ranged from 70 to 243 mg 100 g ^{? 1} while losses from three allophanic soils containing 4.9–8.9% organic C varied from 92 to 191 mg. Losses as ¹⁴CO₂ from ring-labeled model and cornstalk lignins averaged about 30% from the agricultural soils compared to about 11% for the allophanic soils. Losses of 2-side chain lignin carbons were about the same as for the ring carbons. Carbon losses from 1-side chain and methoxyl C varied from 42 to 59% in the normal soils while losses from the allophanic soils were a third to a half these values. From 6 to 9% of protein, cysteine, lysine, and glucosamine carbons linked into model humic acid polymers were lost during 1 yr in the allophanic soils compared with 13–24% from the normal soils. Comparable losses from two fungal melanins were 7–15% for the normal soils and 2–4% for the allophanic soils.     

The infrared identification of a humo‐polysaccharide ester in soil humic acid

Abstract

Studies involving methylation, dissolution, infrared spectroscopy and gas‐liquid chromatography were conducted with humic compounds extracted from a Greenville loam and a Cecil sandy loam.

The results indicated that methylated humic acid and non‐methylated hymatomelanic acid have similar infrared characteristics, with intense C‐H absorption at 2980 ‐ 2920 cm^‐1, and strong C=0 stretching but with very weak C00^‐ stretching at 1720 and 1650 cm^‐1 respectively. Gas‐liquid chromatography yielded chromatograms, having the same number of components, appearing at similar retention times. Dissolution separated hymatomelanic acid into fraction A, with humic acid characteristics; and fraction B, a polysaccharide. This separation released the infrared carboxyl peak at 1650 cm^‐1 in fraction A.

It was concluded that hymatomelanic acid was a naturally occurring ester compound, composed of humic material in ester linkages with polysaccharide.     

PORE SIZE DISTRIBUTION IN CRITICAL POINT AND FREEZE DRIED AGGREGATES FROM CLAY SUBSOILS

Using aggregates from 2 clay soils over a range of water contents from pF 1 to oven dry, shrinkage and water release curves were measured and pore size distributions found by mercury porosimetry after critical point and after freeze drying. Freeze drying caused less shrinkage, the maximum being 6 cm³ 100 g^?1 from pF 1, but gave a large increase, up to 10 cm³ 100 g^?1, of pores in the 0.1–10 μm size range. Critical point drying produced more shrinkage from pF 1, more than half of which was attributed to loss of interlamellar water and the rest to the collapse of pores larger than 10 μm. In these clays the volume of pores of over 3 μm diameter was very small (<3 cm³ 100 g^?1) and most of the plant available water was released by collapse of narrower pores and not by pore emptying.     

Interactions of ferricyanide with humic soils and charred straw

The iron‐cyanide complexes ferricyanide, [Fe^III(CN)₆]^3?, and ferrocyanide, [Fe^II(CN)₆]^4?, are anthropogenic contaminants in soil. We studied the interactions of ferricyanide with humic soils and charred straw (maize and rye, both charred at 300, 400 and 500°C) by batch experiments and Fourier transform infrared (FTIR) spectroscopy. All soil samples sorbed ferricyanide (up to 8.4 g kg^?1). Precipitation of a manganese ferrocyanide after reduction of ferricyanide in the moderately acidic to neutral soils was deduced from both FTIR spectroscopy (CN absorption bands at 2069–2065 cm^?1) and geochemical modelling. Ferricyanide was also adsorbed onto the charred straw. The amounts of iron‐cyanide complexes adsorbed increased with increasing charring temperature, with a maximum of 1.71 g kg^?1. An absorption band at 2083 cm^?1 indicated weakly adsorbed intermediates of the reduction of ferricyanide to ferrocyanide. This band disappeared in the samples charred at higher temperature, whereas a band at 2026 cm^?1 was present in all spectra and became intensified in the high‐temperature straw. We attribute this band to ferrocyanide forming inner‐sphere complexes, presumably with quinone species of the organic matter. The band at 2026 cm^?1 was also present in the spectra of the soils, indicating that soil organic matter also adsorbs ferrocyanide. However, in humic soils the main processes of ferricyanide interaction include reduction to ferrocyanide and precipitation as manganese ferrocyanide. Quantitatively, adsorption on highly aromatic substances plays only a less important role as compared with precipitation.     

Assessment of Fulvic Acid-Like Fractions during Tannery Waste Composting

Changes in the structural composition of fulvic acids were followed during composting of tannery solid waste after neutralization of its acidity by ammonium or by lime. Different techniques (elemental analysis, Fourier transform infrared (FTIR), ¹³C-NMR spectroscopy) were applied. During both trials of composting, a decrease of carbon and increase of oxygen occurred, which originated from strong microbial oxidation and preservation of some structures during composting. In fact, Nuclear Magnetic Resonance (NMR) spectra showed the preservation of anomeric or tannin structures around 105 ppm. The infrared (IR) spectral data showed a decrease in the intensity of COO^? group bands (1623 and 1399.5 cm^?1); this is correlated with a decrease of fulvic acid levels. The variations observed in NMR spectra could be explained by the involvement of COO^? groups of certain structures in polycondensing to form humic acids. The fulvic acids remain composed of less polycondensed structures with a –COOH extremity, as supported by a decrease of the C/H ratio. In contrast, in the trial with addition of ammonia a slight increase in N content occurred, a decrease in absorbance in the 1730–1000 cm^?1 regions compared to the absorbance around 3400 cm^?1, and a strong decrease of carboxyl carbon in the ¹³C-NMR spectra.     

Decomposition of 14C-labelled melanoid fungal residues in a marginally sodic soil

Three melanoid fungi, namely Alternaria alternata, Curvularia lunata and Drechslera australiensis were grown on ¹⁴C-glucose and then fractionated into cell wall, cytoplasm and melanin. The decomposition of these fractions and their contribution to the stable organic matter fraction was studied in a marginally sodic soil. The rate of decomposition of fungal melanins was less than that of the cell wall or cytoplasm which had the highest rate of decomposition. However, the contribution of these fractions to the humic acid fraction was very low. Most of the ¹⁴C-activity was recovered in the humin fraction.     

AVAILABILITY OF POTASSIUM TO RYEGRASS FROM SCOTTISH SOILS II. UPTAKE OF INITIALLY NON-EXCHANGEABLE POTASSIUM

The stable desorption parts of soil Quantity/Intensity isotherms were used to determine the contributions of initially exchangeable and non-exchangeable potassium to plant uptake from ten soils. The activity ratio, AR^K= a_K/√^aC_a, Mg at which K was first taken up from non-exchangeable sources varied from 3 × 10^?3 to 8 × 10^?3 M^1/2 depending on the soil. Uptake rates of two categories of initially non-exchangeable K were linearly related to √times;. The first category appeared to be close to equilibrium with the initially exchangeable K, and gave effective diffusion coefficients of 10^?7 cm² s^?1 for four soils. The second category gave diffusion coefficients from 10^?20 to 10^?22 cm² s^?1, probably came from internal surfaces of micaceous clays, and began to be released at activity ratios below 3 × 10^?4 to 6 × 10^?4 M^1/2 depending on soil type. The soils fell into three groups, broadly consistent with soil series, on their ability to release the second category of potassium.     

Impact of ski pistes on soil properties: a case study from a mountainous area in the Mediterranean region

In this study, soils on 17 ski pistes in the Sierra Nevada, Spain, were investigated to identify changes induced by ski management practices and also to determine the effectiveness of grass seeding in restoring soil quality. When compared with unaffected reference soils, those of ski runs had substantial loss of organic carbon (?34%, ?11.9 ± 3.6 t ha^?1) and micropore volume and size (?33%, ?0.07 ± 0.01 cm³ cm^?3 and ?48%, ?1.62 ± 0.28 μm). Microstructure showed a dramatic reduction in organic cements and fungal hyphae. The organic content of soil seeded with grass significantly improved compared with soil not seeded or seeded unsuccessfully (P < 0.05), especially where the topsoil was reinstated. Organic C content, microporosity and soil respiration increased by 200% (+21 ± 5 t ha^?1), 70% (+0.07 ± 0.03 cm³ cm^?3) and 140% (+0.10 ± 0.04 mg CO₂ g^?1 day^?1), respectively. Average micropore size in aggregates which in undisturbed soils was 3.40 ± 0.28 μm reverted to 3.52 ± 0.36 μm. However, the microstructure of the revegetated soils did not attain the levels of organic cements and fungal hyphae in the natural soils. Dolomite and salts were added to the soil to aid slope stabilization, fertility and de‐icing of access tracks. As a consequence, there were increases in pH, exchangeable sodium percentage (ESP), electrical conductivity, calcium carbonate equivalent and base saturation. The influence of management on soil properties was found to be greater than that of environmental factors.     

Dynamics of Atmospheric Aerosol Number Size Distributions in the Eastern Mediterranean During the ��SUB-AERO�� Project

Measurements of number size distributions of submicron aerosols have been performed at the Eastern part of Mediterranean as part of an extensive measurement campaign to study photo-oxidants and aerosols (SUB-AERO Project). The measurements were made at the Finokalia station on the island of Crete (Greece) and onboard the research vessel ??Aegaeon??. Two campaigns were performed during July 2000 and January 2001 using two scanning mobility particle sizers. The particle distributions measured in the range between 7.8 < d _p < 327 nm during the summer measurements and between 7.5 < d _p < 316 nm during the winter measurements, where d _p is the mobility particle diameter. The concentration of ultrafine particles (7.5 < d _p < 30 nm) was higher during the winter period and varied mainly between 5 × 10¹ and 2 × 10³?cm^?3 with concentration peak values for this mode exceeding 1 × 10⁴?cm^?3. During the summer campaign, an average number concentration of 1 × 10²?cm^?3 at Finokalia and about 5 × 10¹?cm^?3 aboard the ??Aegaeon?? vessel was measured. An average concentration of 1 × 10³?cm^?3 was measured for the particles in the size range between 30 and 100 nm, whereas in the size range 100?C300 nm, the measured concentration ranged between 1 × 10² and 5 × 10³?cm^?3. Diurnal patterns in number concentrations were observed in connection with the transport of air masses and local sources. During the winter period, three nucleation events were observed in connection with the appearance of a particle mode at 20 nm.     

Low boiling-point compounds produced by pyrolysis of fungal melanins and model phenolic polymers

Pyrolysis-gas chromatography-mass spectrometry was used to characterize fungal melanins and model phenolic polymers. Samples were pyrolysed at 700°C for 10 s and the low boiling-point compounds were separated on a Chromosorb 102 column. Low boiling-point compounds identified with a mass spectrometer coupled to the gas Chromatograph were very similar for peptone, a model autoxidative phenolic polymer incorporating peptone, and some fungal melanins. The major low boiling-point components from fungal melanins were related to proteins and to polysaccharides. A nitrogen-free phenolic polymer yielded very small amounts of low boiling-point pyrolysis fragments. The compounds identified appeared to be derived largely from the peptide, carbohydrate, and possibly small amounts of other aliphatic materials in the polymer structures.     

Infrarotspektren der mikrobiellen Biomasse und der Huminsäure im Podsolboden

IR-Spectra of Microbial Biomass and Humic Acid from Podzol IR-examination of soil samples from podzol with or without different pretreatments was carried out in order to check the possibility of humic acid and microbial biomass detection. Pure humic acid and microbial biomass, both isolated or enriched from the soil under controle, showed distinct absorption bands or shoulders at 1730cm^?1, 1620cm^?1 and 1380cm^?1. Only weak absorption bands at the respective wave numbers were detected in the untreated soil sample.     

Adsorption sur les argiles de deux lipopolysaccharides rhizosphériques

The adsorption with time has been measured of two well characterized lipopolysaccharides onto aqueous suspensions of a montmorillonite, a kaolinite and an illite at one fixed polymer-clay ratio. The clays were prepared in the Fe⁺⁺⁺ or Ca⁺⁺ forms by washing with FeCl₃ or CaCl₂ followed with water. The competitive sorption of the two polymers was measured also in the presence of an equal concentration of a protein or a basic amino-acid. Sorption of the polymers by themselves was approximately proportional to the external areas of the three clays and independent of the exchangeable cation. The presence of the protein inhibited completely the adsorption of both polymers onto the Ca⁺⁺ clays, but usually enhanced sorption onto the Fe⁺⁺⁺ clays. Sorption in the presence of the amino-acid differed both for each polymer and according to the form of the clay. Possible reasons for the various sorption patterns are discussed.