ETHER-SOLUBLE HYDROLYSIS PRODUCTS IN HUMIC AND FULVIC ACIDS

The major ether-soluble products from the hydrolysis of humic and fulvic acids include levulinic, succinic and fumaric acids, accompanied by more variable amounts of 4-hydroxy-, 3-methoxy-4-hydroxy-, and 3,4-dihydroxybenzoic acid. 3,5-Dihydroxy-benzoic acid was not detected in the hydrolysates examined.     

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.     

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.     

THE OCCURRENCE OF COPPER-PORPHYRIN COMPLEXES IN SOIL HUMIC ACIDS

Electron paramagnetic resonance (e.p.r.) spectroscopy has been used to show that humic acids, which were isolated from a range of soils and from which most of the iron was removed by boiling with hydrochloric acid, contain copper in the form of porphyrin complexes. The amounts of porphyrin-bound copper in the acid-boiled humic acids were estimated to be ≤ 20 mg/kg (equivalent to 0.05-0.9 mg/kg in the soils). The acid-boiled humic acids from cultivated mineral soils showed no great capacity for further uptake of copper as copper porphyrin when treated with CuSO₄, most of this additional copper being held by groups not involving N-donor groups. In contrast, copper treatment of the acid-boiled humic acid from a raised bog peat produced a large increase in copper-porphyrin signal strength, indicating that in the peat there are considerable amounts of porphyrin by which added copper could be complexed. It is suggested that porphyrin groups may be involved in the fixation of copper by organic matter in soils.     

ELECTRON-SPIN RESONANCE OF HUMIC ACIDS FROM CULTIVATED SOILS

An examination has been made of the electron-spin resonance spectra of humic acids from (i) two groups of cultivated soils from the north-east of Scotland, and the related natural soils from which the cultivated soils are considered to be derived, and (ii) some Rothamsted soils. With the Scottish soils the humic acids from the more acid natural soils (pH <4.6) show e.s.r. spectra with a four-peak structure (class I), and those of the less acid soils (pH >4.6) almost structureless spectra (class II). The cultivated soils contain humic acids with the same class of spectrum as that of the soils from which they are derived, even though they are now much less acid (_PH 5.9 –6.5). Humic acids from Rothamsted soils, sampled recently, were compared with those from the same site sampled 80 years previously. Where the soil has been allowed to revert towards a natural state but still contains free calcium carbonate the pH remained high (7.8–7.9) and the spectrum of the humic acid remains class II. Where the soil contained no free calcium carbonate the pH has fallen from 7.1 to 4.5 on reversion and the spectrum class of the humic acid has changed from II to I. The results support the hypothesis that the class of spectrum of the humic acid depends on the pH at which it is formed.     

THE EFFECT OF pH ON THE INCORPORATION OF AMINO ACIDS INTO HUMIC ACID EXTRACTED FROM SOIL

The effect of pH on the incorporation of six ¹⁴C-labelled amino acids and a dipeptide into humic acid extracted from a podzolic soil was examined. Maximum incorporation was found to occur at a pH which coincided with the apparent dissociation constants of their α-amino groups. Incorporation took place, into forms which were both acid-hydrolysable and non-hydrolysable, the latter accounting for between ten and twenty per cent of the total.     

不同施肥处理土壤胡敏酸及其级分与蒙脱石的吸附特征 Ⅱ. 蒙脱石对胡敏酸不同级分的吸附

采用酒精沉淀法，反不同施肥处理土壤胡敏酸分7个级分，研究了胡敏酸不同级分与钙饱和蒙脱石的吸附特征。结果表明，蒙脱石对胡敏酸各级分的吸附可用单表面Langmuir、双表面Langmuir和Freundlich方程来描述。各级分的吸附量和吸附强度不是随级分数变化单一递增或递减，在7个级分中，级分4、3的吸附量和吸附强度较大，是吸附最佳级分。说明级分4、3具有与蒙脱石胶体最佳的成键吸附状态，是吸附最佳分子状态，有机肥处理，吸附最佳级分的吸附性状（吸附量和吸附强度）优于化肥、无肥处理。     

不同施肥条件土壤胡敏酸级分变异及性质的研究

以１７年长期定位试验土壤为材料,在研究土壤有机质氧化稳定性基础上,采用酒精沉淀分级方法,对不同施肥处理土壤胡敏酸的级分及光学性质进行了研究,并对胡敏酸及其级分的类型进行了划分。结果表明长期施用有机（堆肥及秸秆）土壤有机质含量明显增加,有机质的氧化稳定系数降低,土壤胡敏酸组成分布中心向高浓度酒精析出的级分偏移,颗粒小的级分比例增大,土壤胡敏酸的Ｅ４,Ｅ６值减小Ｅ４／Ｅ６增大,而单施化肥则有相反趋势。     

GEL CHROMATOGRAPHY OF HUMIC ACID

Gel-solute interactions have been reported in the application of gel chromatography to humic acid. The origins and nature of these interactions are discussed with particular reference to the behaviour of ‘Sephadex’ with compounds which are aromatic, heterocyclic, phenolic, or charged. Such structural units are known to be present in humic acid and could account for its observed interactions with ‘Sephadex’gel. The behaviour of humic acid on ‘Sephadex’and a number of other gel materials in a variety of eluants is examined. The observed deviations of these systems from that of an ideal gel chromatography system are explained in terms of charge and adsorption effects. The results indicate that a fractionation based solely on molecular weight differences can be achieved by using an alkaline buffer containing a large ammo cation as eluant together with ‘Bio-gel’, ‘Sephadex’ or an agar based gel. Systems in which gel-solute interactions occur should not be used for molecular weight fractionations.     

不同施肥条件土壤胡敏酸能态的初步研究

地球的腐殖质层是太阳能的巨大贮存库,在陆地的生物能量贮存中,约有50%含于腐殖质中。因此土壤中的有机质转化是最有意义的能量转化过程之一。此外,土壤肥力水平除与腐殖质的数量有关外,腐殖物质的组成、特性也是重要的影响因素。能态是腐殖物质的一种重要特性,腐殖物质能态的研究有助于加深对腐殖物质特性的认识。因此研究土壤腐殖质形成过程的能量转化,以及不同条件下土壤腐殖物质的能态特征具有重要的意义。     

腐殖酸对耕地棕壤固钾与释钾作用的影响研究

通过室内等温培养试验,研究了施用富里酸和胡敏酸对耕地棕壤钾素释放和固定作用的影响。结果表明,施用腐殖酸可以促进土壤钾素的释放,并有随腐殖酸用量提高而增高的趋势。其中,施用富里酸4%,在25℃条件下培养21d,土壤的钾素释放量增加了6.25%,而在相同条件下,施用胡敏酸土壤钾素的释放量仅增加了2.26%;施用腐殖酸可以降低土壤对外源钾的固定量,在施用外源钾400mgkg-1土条件下,与对照比较各处理的固钾量差异均达到了极显著水平。外源钾施用方式对腐殖酸降低土壤固钾作用的影响不同,腐殖酸与土壤恒温培养7d以后施用钾素的固钾量低于钾素与腐殖酸同时施用处理的。腐殖酸对土壤钾素释放和固定的影响是通过对含钾矿物的溶解和层间堵塞以及对钾素的吸附作用实现的。     

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.     

土壤中水溶性有机质的结构特征及其与富里酸、胡敏酸的比较

采用元素分析、1HNMR和FTIR研究了黄泥土中水溶性有机质组成及结构特征,并与富里酸、胡敏酸进行比较。结果表明:胡敏酸含有大量的芳香族不饱和物质,烷基链烃多,支链长;富里酸以含有大量的羧基为主要结构特征;水溶性有机质主要由碳水化合物组成,含有大量的羟基,芳香族不饱和物质少。     

土壤胡敏酸与铜离子络合反应及吸附过程热力学特征的研究

供试三中不同土壤溶解态胡敏酸（ＨＡ）与Ｃｕ＾２＋络合的稳定常数ｌｏｇＫ大小呈：黑垆土ＨＡ＞娄土ＨＡ＞黄绵土ＨＡ，ｌｏｇＫ的大小与ｐＨ、温度（Ｔ）及离了程度（１）有关；络合反应的热和学函数变化：标准自由能变ΔｒＧｍ＾θ＜０，标准焓变ΔｒＨｍ＾θ＜０，标准熵变ΔｒＳｍθ＜０，表明络合是自发的放热反应，体系有序性增大。ΔｒＨｍ＾θ负值大小于ｌｏｇＫ呈相同次序，称为ＨＡ络合Ｃｕ＾２＋过程中ＨＡ分子变形及络     

FRACTIONATION OF HUMIC ACID BY GEL PERMEATION CHROMATOGRAPHY

Humic acids from the L layer and B_2hhorizons of a humus-iron podzol were fractionated by gel permeation chromatography. Elution of the gel column with distilled water adjusted to pH 7.5 gave a fractionation based on both gel permeation and adsorption chromatography. This procedure gave filtered products containing most of the organic nitrogen, and an absorbed fraction. The latter contained most of the components which gave benzene carboxylic acids on oxidation of the humic acid with dilute nitric acid.     

STUDIES OF SOIL ORGANO-MINERAL FRACTIONS

Sand-, silt-, and clay-size organo-mineral fractions were isolated in bulk from surface horizons of five soils following ultrasonic dispersion in water. Good clay separation was achieved for all except one highly organic, calcareous clay soil. Organic-N and -C were concentrated in the clay and silt fractions but for each soil the organic C : N ratio decreased in the order sand > silt > whole soil > clay. Acid hydrolysis of the silt and clay fractions revealed a slight concentration of amino acid-N and NH₄-N in the clays but only small differences in the distribution of individual amino acids were observed. The results suggest that both silt and clay fractions may be important in the stabilization of soil organic matter.     

腐殖酸的数均分子量测定

腐殖酸是广泛存在于土壤、污泥、泥炭、煤和水域中的天然大分子电解质,它对土壤肥力、植物生长、环境中元素的迁移和富集有重要作用,近廿年来日益为人们所重视,但其化学结构和分子量的确切范围目前尚不甚清楚。迄今为止,尚没有一种测定各种腐殖酸分子量的良好方法^[11]。     

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.     

腐殖物质的某些物理化学性质

土壤腐殖物质的形状,与土壤物理性质和物理化学性质有密切关系.已经知道,线型分子对土壤颗粒的团聚化有着特别良好的作用^[1].腐殖物质是土壤中主要的有机物质.