Evaluation of the possibilities of using humic acids obtained from lignite in the production of commercial fertilizers

Purpose

Technological progress and high market demand contributed to a significant interest in the production of fertilizers based on humic acids. The aim of this study was to evaluate the possibilities of using humic acids obtained from lignite in the production of new commercial products. For this purpose, it is necessary to determine the quality standard requirements for such material. Properties of humic acids depend on source of origin as well as method of its extraction.

Materials and methods

The humic acids were extracted from polish deposit of lignite–Sieniawa Lubuska by alkaline extraction using for this purpose six kinds of extractants: 0.1 M NaOH and 0.25 M NaOH, 0.1 M KOH and 0.25 M KOH, and 0.1 M Na₄P₂O₇ and 0.25 M Na₄P₂O₇. The humic samples were used in solid powder form and characterized by UV-Vis spectroscopy, ¹³C NMR spectroscopy, fluorescence spectroscopy, and thermal analysis.

Results and discussion

The determining factor influencing a degree of humic acids extraction from lignite and their structure is type of extractant. The largest efficiency of extraction (about 50%) was obtained with the use of NaOH solutions. All examined humic acids were generally characterized by simple and heterogeneous molecularly structure with low molecular weight and low aromatic polycondensation. Therefore, it can be concluded that humic acids extracted with NaOH and KOH solutions are less condensed than those extracted with Na₄P₂O₇ solutions. It can suggest that humic acids obtained from lignite using solutions of Na₄P₂O₇ are characterized by a low transformation degree and greater amount of carboxyl groups.

Conclusions

Low rank coal can be successfully used in agriculture as a rich source of humic acids. Reagent used in their extraction, apart from high efficiency should have a neutral impact on their structure. Studies on the physicochemical properties of humic acids can be helpful in predicting behaviors of such fertilizer components in the environment and in inventing new products taking the principles of sustainable development into consideration.

     

Activity and stability of jack bean urease in the presence of peat humic acids obtained using different extractants

 The effects of two humic acid extractants, 0.1 M Na₄P₂O₇ plus 0.1 M NaOH (NaPP) and 0.1 M NaOH (NaOH), on the activity and stability of a humic-urease complex were studied. The two humic acids isolated (HA_NaPP and HA_NaOH) exhibited different elemental compositions, metal concentrations and structural modifications in the FT-IR spectra. Depending on the pH, HA_NaPP and HA_NaOH influenced both the urease activity and urease kinetic parameters (V _max and K _m) in the same way. They inhibited urease activity between pH 6 and 7 and reduced the V _max of the reaction at pH 6 and 7. The presence of humic acids improved the affinity of the enzyme for the substrate (K _m). The stability of the urease with time, and in the presence of pronase, was improved by HA_NaPP and HA_NaOH with respect to free enzyme. These results confirm the importance of the interaction of urease with humic acids as a fundamental gateway for extracellular urease stabilisation. Since no difference in the extent of urease inhibition and urease stabilisation was observed for the two humic acids, it may be concluded that neither urease activity nor stability are influenced by the humic acid extractant used. Received: 5 November 1999     

FTIR‐spectroscopic characterization of humic acids and humin fractions obtained by advanced NaOH,Na4P2O7, and Na2CO3 extraction procedures

Aim of our study was the development of the methodological basis for the characterization of humic fractions of a long‐term field experiment. Humic acids (HAs) were extracted from three layers of a nontilled soil using three different extractants (1 M NaOH, 0.1 M Na₄P₂O₇, 1 M Na₂CO₃), and the humin fraction was enriched. NaOH as extractant for FTIR analysis of humic substances yields higher resolved IR spectra, especially in the important regions of stretching vibrations including aromatic and aliphatic groups and in the fingerprint area including amides, aliphats, and aromats than the other extractants. The NaOH extraction has lower extraction yields as compared to Na₄P₂O₇ and Na₂CO₃ and represents a different part of the soil organic matter (SOM). This is reflected by lower C : N ratios and higher E₄ : E₆ and fulvic acid–to–humic acid ratios as compared to the other extractants. The FTIR band areas of HA fraction obtained by NaOH showed an increase of the aromatic and carbonyl groups and a decrease of amide groups with increasing soil depth. Aliphatic groups showed contradicting results: The bands of the stretching vibrations increased, and the band of the bending vibrations decreased. We assume that band interactions in the bending vibrations were responsible for that phenomenon under the assumption of an increase of aliphatic groups with increasing soil depth. The IR bands of the enriched humin fraction showed a decreasing trend in case of both aliphatic bands deriving from stretching vibrations and an increase of aromatic characteristics with depth. Our study led to the conclusion that HA fractions obtained by 1 M NaOH represent a small and dynamic fraction indicated by the measured yields in combination with values of N_t, C : N, E₄ : E₆ ratios, and ratios of fulvic acids (FA) to HA. The humin fraction has a high contribution to the total organic C and represents a more stabilized fraction of SOM which still shows changes in its aromatic and aliphatic characteristics with soil depth.     

鸡粪腐解过程腐殖质结合态铜变化及其与铜淋失的关系

采用H2O、NaOH以及NaOH-Na4P2O7混合液3种浸提剂对不同腐解期鸡粪中的腐殖质结合态铜（HS-Cu）进行提取,在研究腐殖质碳和铜变化的基础上,通过粪肥淋溶试验,研究了铜淋失量变化以及与腐殖质结合态铜的关系。结果显示,鸡粪中以NaOH-Na4P2O7提取的HS-Cu最高,平均占粪肥全铜量的46.8%;其次是NaOH提取的HS-Cu,平均占全铜量的34.5%,H2O提取的HS-Cu最少,仅占全铜量的6%左右。随腐解进行,NaOH-Na4P2O7提取的HS-Cu逐渐增加,而NaOH提取的HS-Cu在腐解50d以前呈增加趋势,而50d以后变化不大;H2O提取的HS-Cu在腐解21d前明显增加,21d后则下降。NaOH-Na4P2O7提取的HS-Cu以胡敏酸结合态（HA-Cu）为主,H2O提取的HS-Cu则以富里酸结合态(FA-Cu)为主;NaOH提取的HS-Cu在腐解50d以前以FA-Cu为主,50d以后则以HA-Cu 为主。粪肥铜淋失量在腐解35d以前随腐解进行逐渐增加,35d以后有所降低;淋失量平均占全铜量的20%左右。铜淋失量与H2O、NaOH提取的HS-Cu或腐殖质碳呈显著正相关,而与NaOH-Na4P2O7提取的HS-Cu无相关。     

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.     

RADIOCARBON DATING OF PALEOSOLS USING SOIL ORGANIC MATTER COMPONENTS

Soil organic matter components of classical humic acid and humic fractions were extracted from two paleosols using 0.1 M Na₄ P₃ O₂:0.1 M NaOH. These fractions were subjected to chemical treatment with 6 M HC1 or 70 per cent HNO, before radiocarbon assay, and their radiocarbon dates were compared with those of similar but untreated fractions, untreated buried soils, and previously published charcoal dates. Hydrolysis of humic acid and humin fractions with mineral acids, particularly 70 per cent HNO₃ led to older radiocarbon dates, comparable to, though slightly older than, those of charcoal derived from the same buried layers. In contrast, the dates of soils and their humic acid and humin fractions before acid hydrolysis were younger and therefore less reliable. The application of this procedure to studies of paleosols in New Zealand is discussed.     

THE HUMIC ACIDS EXTRACTED BY VARIOUS REAGENTS FROM A SOIL

Solutions of o.5N NaOH, o.1M pyrophosphate (pH 7), and o.5N Na(CO^2?₃/HCO^?₃) [2:1] extract humic acid and organic matter from a soil with decreasing effectiveness. Pre-treating the soil with o.1N HC1 increased the yield of humic acid obtained with the alkaline extractants. An additional pre-treatment with a mixture, which was normal with respect to HC1 and HF, gave a slight reduction in yield. Increasing the temperature of extraction increased the yield of humic acid. The total C extracted was usually in excess of the humic acid recovered. The difference was obtained as ‘humins’. The sum of the Fe₂O₃, SiO₂, and A1₂O₃ contents of the humic acids was always less than 2 per cent. Where the extraction was carried out at room temperatures the SiO₂/Al₂O₃ ratio suggested that they might be present as clay mineral. When extraction was carried out at an elevated temperature this ratio was altered. Humic acids of low ash content (0.1–0.5 per cent) could be obtained by the use of hot reagents. Of all the extractants used at room temperature, pyrophosphate produced the humic acid of lowest ash content (～ 0.2 per cent). The Fe₂O₃ content of the humic acids was not correlated with their SiO₂ or A1₂O₃ content. The N-content of the humic acids was substantially independent of the method of extraction. The cation-exchange capacities (C.E.C.), average pK values and range of pK values, have been determined from the titration curves of the humic acids. These quantities vary with the method of extraction. There are good correlations between cation exchange capacity and both average pK values and the range of pK values. The within-molecule variation of pK values appears to be greater than the between-molecule variation. No correlation exists between C.E.C. and Fe, Al, Si, and N content of the humic acids.     

Origin and properties of humus in the subsoil of irrigated rice paddies

Stability of humus in the plow layer soil is considered to affect the quantity and quality of dissolved organic matter leached from the plow layer soil. Therefore, a model experiment was conducted to analyze the effect of soil reduction under submerged conditions on the stability of humus in the plow layer soil. The changes in the stability of humus in the plow layer soil during submerged incubations with and without rice straw application were evaluated based on the changes in the binding type of humus. Binding type of humus in the plow layer soil was analyzed by successive extractions of organic matter with water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and 0.1 M Na₄P₂O₇ (pH 10.5) with NaBH₄. Amounts of Fe, Mn, and Mg in each fraction were also determined to estimate the relationships between humus and metals.

The successive extraction of humus indicated that the amount of organic carbon which was extractable with the (NaBH₄ +0.1 M Na₄P₂O₇) solution decreased while that of the 0.1 M Na₄P₂O₇ (pH 7.0}-extractable organic carbon increased during submerged incubation with rice straw application. The origin of the increase in the amount of organic carbon in the Na₄P₂O₇ (pH 7.0)-extractable fraction during submerged incubation was investigated further by another incubation experiment using ¹³C-glucose as a reducing agent. Atom- 13C% analysis showed that the contribution of organic carbon derived from compounds other than glucose to the increase in the contents of humic acids and fulvic acids in the Na₄P₂O₇ (pH 7.0)-extractable fractions was ca. 80%. Therefore, it was concluded that the binding type of humus changed from (NaBH₄ + Na₄P₂O₇)-extractable to Na₄P₂O₇ (pH 7.0)-extractable humus under reducing conditions. Since the amounts of organic carbon and Fe increased in the Na₄P₂O₇ (pH 7.0)-extractable fraction and decreased in the (NaBH₄ +0.1 M Na₄P₂O₇)-extractable fraction simultaneously, iron reduction was presumably associated with the change in the binding type of humus in submerged paddy soil.     

CHANGES IN MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER DURING SOIL DEVELOPMENT

Ten different topsoils representing members of three soil chronosequences were pre-treated with 0.1 M HC1 and extracted with neutral 0.1 M Na₄P₂O₇ followed by 0.5 M NaOH. Extracts were purified and fractionated into five different nominal molecular weight fractions using gel filtration. With increasing soil development, the proportion of large molecules (>200 000) in the organic matter decreased with an increase in the proportion of intermediate size molecules (200 000 – 10 000). This effect was more evident in the mild Na₄P₂O₇ extracts than in the subsequent NaOH extracts, and in soils of the Manawatu chronosequence than in those of the other two chronosequences and are attributed to changes in the nature and humification of soil organic matter during soil development.     

Cation-exchange properties of soil organic matter

The CEC was determined for humic acid preparations by changing the conditions for the CEC procedure and the CEC values obtained were compared with those of clay minerals. Humic acid was extracted from Kodonbaru and Kuriyagawa surface soils, Iwanuma peat, and straw with 0.1 M Na₄P₂O₇-0.l M NaOH. The CEC was measured by a method which eliminates washing for the removal of excess saturating salt.

The CEC of humic acid became larger as humification progressed, and increased in the order: Straw<Iwanuma<Kuriyagawa<Kodonbaru. An equilibrium of cation exchange for the humic acid preparations was attained in a short time in contrast with that for allophane. No effect of salt concentration on the CEC of the humic acid preparations was recognized. The CEC of humic acid was also determine using the procedure in which tbe excess salt was removed by washing with water. Practically no decrease of CEC with decreasing salt concentration was found. When the pH of the salt solution WBB reduced, the em: of the humic acid decreased, though the extent of the decrease was smaller than that of allophane. The CEC of halloysite and montmorillonite did not decrease through reduction of the pH of the salt solution. It was considered that humic acid is a stronger acid than allophane and a weaker acid than halloysite and montmorillonite. The difference between the CEC of humic add measured with Ca²⁺ and Ba²⁺ was small. Little temperature effect was observed for humic acid.     

MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER AS AFFECTED BY ACID PRE-TREATMENT AND FRACTIONATION INTO HUMIC AND FULVIC ACIDS

Effects of acid pre-treatment and fractionation on the molecular weight distribution of OIM Na₄P₂O₇ organic matter extracts were investigated in a chronosequence of weakly weathered soils developed on aeolian sand in New Zealand. Acid pre-treatment of soils with OIM HCl followed by OIM HCI:03M HF was found to enhance the polydispersion in the nominal molecular weights of the extracts. The same treatment resulted in significant increases in yield and reduction in ash content. However, prolonged standing of extracts in the acids led to acid-induced polymerization, resulting in a predominance of organic matter in the higher nominal molecular weight ranges. Fractionation of organic matter extracts by acid precipitation into humic and fulvic acids did not separate them according to molecular weight as commonly believed. Instead, fulvic acids from most soils were found to have similar nominal molecular weight distributions to those of their humic acid counterparts. A large proportion of soil fulvic acid compounds was in the > 100 000 nominal molecular weight range.     

Effect of long‐term combined nitrogen and phosphorus fertilizer application on 13C CPMAS NMR spectra of humin in a Typic Hapludoll of northeast China

Because of its insolubility, heterogeneity and structural complexity, humin is the least understood among the three fractions of soil humic substances. This research aimed to evaluate the long‐term effect of combined nitrogen and phosphorus (NP) fertilizer addition on the chemical structure of humin under maize (Zea mays L.) monoculture in a Typic Hapludoll of northeast China. Soil samples were collected 12 and 25 years after the initiation of the fertilizer treatment. Soil humin was isolated using NaOH‐Na₄P₂O₇ extraction to remove humic and fulvic acids, which was followed by HF‐HCl treatment to remove most of the inorganic minerals. Solid‐state ¹³C cross‐polarization magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR) spectroscopy was used to characterize the chemical structure of the humin isolates. Results showed that the organic carbon (C) content of humin increased after NP fertilizer addition, compared with a no‐fertilizer (CK) treatment. ¹³C CPMAS NMR indicated that O‐alkyl C and aromatic C of humin decreased, while alkyl C and the ratios of alkyl C/O‐alkyl C, aliphatic C/aromatic C and hydrophobic C/hydrophilic C all increased in the NP fertilizer treatment. The long‐term application of NP fertilizer changed the molecular structure of soil humin to be more alkyl and hydrophobic, and was thus beneficial to the sequestration and stability of organic C in soil.     

Effects of extractants on analytical characteristics and pyrolysis gas chromatography of podzol fulvic acids

Fulvic acids extracted from the B_h horizon of a Podzol with three reagents: NaOH, HCl and the mixture Na₄P₂O₇/NaOH, show no significant differences by physical and chemical analysis with the exception of the N-content of the NaOH extract and the E₄/E₆ ratios of those extracted with HCl and Na₄P₂O₇/NaOH, indicating that these fulvic acids have very few condensed aromatic nuclei structures.Pyrolysis gas chromatography of the three fulvic-acid specimens produces the same low-boiling-point compounds, but in different amounts. Various alkanes and olefins as well as other compounds have been identified. By pyrolysis of the methylated fulvic acids, it has been shown that part of the resulting compounds are produced by reactions of component radicals. The main pyrolysis reaction appears to be dehydration. The pyrolysis patterns of the three fulvic-acid specimens provide evidence that there are some differences in structure not evident from conventional physical and chemical analysis.     

Transformations of chemically fixed liquid anhydrous ammonia by soil microorganisms

Summary The application of liquid anhydrous NH₃ to soil leads to chemical fixation of NH₃ by organic matter and of NH _inf4 ^sup+ by clay minerals. A laboratory study was conducted to ascertain the biological transformations of newly fixed liquid anhydrous ¹⁵NH₃ in a Drummer silty clay loam by incubation of the ¹⁵N-labelled soil with glucose for 0, 7, 30, and 90 days and by sequential extraction of organic-matter-fixed ¹⁵NH₃ with 0.15 M Na₄P₂O₇, 0.15 M KOH, 0.1 M NaOH, and acidified dimethyl sulfoxide. About 16% of the ¹⁵NH₃ injected was fixed, of which 52% was accounted for by clay fixation. The various humic fractions (fulvic acid, humic acid, and humin) were obtained, and the distribution patterns of the fixed ¹⁵NH₃-N in these fractions were compared. The potential availability of the fixed ¹⁵NH₃-N was also estimated. The percentage of the ¹⁵NH₃ recovered as organic-matter-fixed ¹⁵NH₃ decreased as the length of incubation increased (to 28% after 90 days); the decrease was attributed in part to an increase in the amount recovered as clay-fixed NH _inf4 ^sup+ (from 52 to 64%). Changes in the distribution of the organic-matter-fixed ¹⁵NH₃-N in the humic fractions included: (1) an increase in the relative amount of the fixed ¹⁵NH₃ as humic acid in both the Na₄P₂O₇ and KOH extracts, (2) an increase in the percentage of organic-matter-fixed ¹⁵NH₃-N in the fulvic acid fractions as high-molecular-weight components (determined by dialysis) or as generic fulvic acid (determined by sorption-desorption from XAD-8 resin), and (3) an increase in the percentage of the organic-matter-fixed ¹⁵NH₃ as humin. The potential availability of the organic-matter-fixed ¹⁵NH₃-N decreased as the length of the incubation increased, from 22 to 4% over the 90-day incubation period, and was correlated significantly (0.05 level) with Na₄P₂O₇-extractable N. These results suggest that organic-matter-fixed liquid anhydrous NH₃ is initially more labile than the native soil N but becomes less labile with time.     

Humus composition and humification degree of humic acids of alpine meadow soils in the northeastern part of the Qinghai–Tibet Plateau

The characteristics of humus composition are important for understanding the mechanism of carbon storage in the Qinghai–Tibet Plateau. The aim of this study was to characterize the quality of soil organic matter (SOM) in this region. Soil samples from four soil profiles in fenced study sites in the alpine grassland were collected at altitudes of 4200, 4000, 3800, and 3400 m, along the southwest facing slope in the Qilian Mountains. The humus composition and humification degree of the humic acid (HA) were determined by two methods: (1) extraction with 0.5% sodium hydroxide (NaOH) followed by 0.1 M sodium pyrophosphate (Na₄P₂O₇) (OH-PP method); and (2) treating once with 0.1 M hydrochloric acid (HCl) followed by extracting with 0.5% NaOH (Cl-OH method). Physico-chemical analysis revealed higher exchangeable cation content and higher base saturation ratios could be related to slightly acidic to neutral soils, which could be regarded as calcium (Ca)-rich soils. The amounts of combined-form HAs obtained by HCl pretreatment (HA_Cl – HA_OH; ?HA_Cl) were remarkably higher than those extracted with Na₄P₂O₇ (HA_PP), indicating that the combined form of HAs is mainly Ca. In addition, the proportion of HA_PP in the total HAs extracted with both NaOH and Na₄P₂O₇ (HA_OH + HA_PP) obtained in the OH-PP method increased with soil depth and decreasing elevation, indicating that HAs associated with aluminum (Al) and iron (Fe) were distinguished in the subsoils of lower elevation. Therefore, the formation of the organo-mineral complex may contribute to stabilizing SOM in the Qinghai–Tibet Plateau. Moreover, Type A-HA with the highest degree of humification was obtained from the deeper horizons with the Cl-OH method and almost all horizons by extraction with Na₄P₂O₇ in the OH-PP method. Further studies using various spectroscopic analyses are necessary to elucidate the chemical properties of SOM in this region.     

Comparison of carbon skeletal structures in black humic acids from different soil origins

Andosols are characterized by an abundance of black humic acids (HAs) belonging to Type A with a high content of aromatic carbon (C) in particular condensed aromatic C. Black HAs are also observed in other soils, such as Chernozems and the subsoil of paddy field, and extracted after washing with an acid or using chelating agent such as sodium pyrophosphate (Na₄P₂O₇). However, contribution of condensed aromatic structures to those soil HAs are unknown. To obtain the information about C skeletal structures of black HAs in soils other than Andosols, HAs were obtained from 2 Chinese Chernozem samples, 2 subsoil samples from Japanese paddy fields (Fulvisols), and a Rendzina-like soil (Cambisols) as well as an Andosol sample (reference) by successive extraction with 0.1 M NaOH (HAs₁) and 0.1 M Na₄P₂O₇ (HAs₂), and ¹³C nuclear magnetic resonance and X-ray diffraction 11-band profile analyses were applied. In the black HAs₂ from the non-Andosol samples, the proportion of C present as aromatic C, size of C layer planes, and relative C layer plane content ranged from 52 to 59%, 0.48 to 1.92 nm (mean size, 0.76–0.91 nm), and 58 to 100 AU (arbitrary unit) mg^?1, respectively, with a positive correlation between total C layer plane content and the degree of humification. Those ranges were similar to the distribution ranges of Andosols HAs₁ reported by our previous study.     

Acid pyrophosphate extraction of soil fulvic acids

A simple three step method is described for isolation of soil fulvic acids in high yield. The complexing agent H₂P₂O₇^2? (at pH 2) is used to release soil-bound fulvic acids. Extraction of humic acids is minimal. Selective separation of the protonated fulvic acids from the ionic extractant is achieved on a non-ionic polyacrylate resin (Amberlite XAD-7); after washing the resin, fulvic acids were retrieved in >98% yield by adjusting the pH to 6.5. Two problems associated with the classical alkali extraction method are avoided: possible alkaline oxidation of phenolic components, and their oxidation by Fe³⁺ under the acidic conditions employed to precipitate humic acids. The product typically has an ash weight of <0.6% after one XAD treatment. The method has been applied to three soils and one IHSS peat sample.     

Comparison of water,DTPA, and nitric acid as extractants to assess the availability of copper in peat substrates

Abstract

An experiment was conducted to assess the suitability of three extractants, water (H₂O), 0.005M DTPA, and 0.4M nitric acid (HNO₃) for determining plant available copper (Cu) in peat substrates. Cucumber was used as a test crop. Four levels of Cu were compared in two peat substrates, each at two pH levels. There was good correlation between Cu extractable in H₂O, DTPA, and HN0₃ and the Cu content of cucumber leaves, the correlations being 0.88, 0.87, and 0.89, respectively. These correlation coefficients did not differ significantly. It was concluded that all three extractants are suitable for estimating Cu availability in peat substrates.     

SIZE FRACTIONATION, DISSOLUTION ANALYSIS, AND INFRA-RED SPECTROSCOPY OF HUMUS COMPLEXES IN ANDO SOILS

Eight samples of Ando soil A₁ and buried A₁ horizons of different ages were fractionated into clay-, silt-, and sand-size separates, and the yields and carbon contents of these separates were determined. The clay-size separates were subjected to two series of successive extractions, 1) 0.1 M Na₄ P₂ O₇/2% Na₂ CO₃/0.5 M NaOH and 2) dithionite-citrate/2% Na₂ CO₃/0.5 M NaOH; and to difference infra-red spectroscopy for identification of the extracted constituents. The result indicated that humus evolves from forms with a very low complexing ability for Al and Fe into forms that complex Al and Fe in the A₁ horizon, and that humus further interacts with allophane-like constituents, allophane and imogolite in the buried A₁ horizon. These reactions between humus and inorganic constituents result in formation of silt- and sand-size aggregates which are stable to sonic wave treatment, but are broken down into finer particles upon boiling with H₂ O₂.     

Electrofocusing: A new method for characterization of soil humic matter

Electrofocusing in polyacrylamide gel was carried out on humic substances extracted by 0.1 n NaOH, 0.1m Na₄P₂O₇, and by the method of Burns, El Sayed and McLaren (1972) from the upper and lower organic horizons of an alpine podsol. The electrophoretic patterns were characteristic of both humus origin and extractions procedure. The best resolution of the isoelectric bands for the humus were obtained by the Burns-McLaren procedure. The ionic component does not have much influence on the distribution of humus constituents within the electrophoretic pattern, but the presence of phosphate appears to be essential to obtain good separations.