Studies on the association of humic acid in soils

Introduction

The purpose of this study was to find the form of association of humic acid in volcanic ash soils, in which humus was accumulated more than 10%. Some consideration was taken, on the other hand, on the reason of this accumulation.     

Exogenous application of humic acid and salicylic acid to alleviate seedling drought stress in two corn (Zea mays L.) hybrids

Efficacy of 1?mM humic (HA) and salicylic (SC) acids on SC 260 and SC 705 corn seedlings to alleviate drought stress via polyethylene glycol was studied via hydroponics at Shiraz University, Iran in a factorial, randomized design, with four replicates each. Under stress, SC 260 had higher electrolyte leakage compared to SC 705, and exogenous application of HA combined with SA decreased SC 705 electrolyte leakage. As a general trend, photosynthetic pigment content, relative water content, root and shoot length, mean number and diameter of central and peripheral root metaxylem, and K⁺ accumulation were higher in SC 705 treated with HA and SA compared to SC 260. Application of HA with SA could be an effective and low cost approach to ensure seedling establishment and plant growth in fields affected by soil drought in the early season, especially for the SC 705 corn hybrid in semi-arid regions.     

Chemical characteristics of humic acids from five soils in Kenya

Humic acids (HAs) isolated from five soils (Luvisols, with 460–600 mm rainfall, Nitosols and Ferralsol, with 1060–1950 mm rainfall) from different ecological regions of Kenya were characterized by ¹³C NMR and IR spectroscopy, elemental analyses and optical measurements. The data suggest that excessive rainfall in sub-humid regions may lower the molecular weights of the HAs as well as their aromaticities. Concentrations of aliphatic components, including aminoacids and carbohydrates, in the HAs from the sub-humid regions were higher (40–42 wt/wt %) than those in the HAs isolated from soils of the semi-arid regions (29–32 wt/wt %). Chemical characteristics of the soils from the sub-humid regions of Kenya resembled those of the HAs from temperate regions but differed from those of HAs originating from arid regions. Annual rainfall and vegetation appeared to affect the composition of HAs but effects of elevation and temperature were less clear.     

褐煤腐殖酸对不同土壤上小麦生长的影响

Humic acid(HA),a fairly stable product of decomposed organic matter that consequently accumulates in ecological systems,enhances plant growth by chelating unavailable nutrients and buffering pH.We examined the effect of HA derived from lignite on growth and macronutrient uptake of wheat(Triticum aestivum L.) grown in earthen pots under greenhouse conditions.The soils used in the pot experiment were a calcareous Haplustalf and a non-calcareous Haplustalf collected from Raisalpur and Guliana,respectively,in Punjab Province,Pakistan.The experiment consisted of four treatments with HA levels of 0(control without HA),30,60,and 90 mg kg -1 soil designated as HA 0,HA 1,HA 2,and HA 3,respectively.In the treatment without HA(HA 0),nitrogen(N),phosphorus(P),and potassium(K) were applied at 200,100,and 125 mg kg -1 soil,respectively.Significant differences among HA levels were recorded for wheat growth(plant height and shoot weight) and N uptake.On an average of both soils,the largest increases in plant height and shoot fresh and dry weights were found with HA 2(60 mg kg -1 soil),being 10%,25%,and 18%,respectively,as compared to the control without HA(HA 0).Both soils responded positively towards HA application.The wheat growth and N uptake in the non-calcareous soil were higher than those of the calcareous soil.The HA application significantly improved K concentration of the non-calcareous soil and P and NO 3-N of the calcareous soil.The highest rate of HA(90 mg kg -1 soil) had a negative effect on growth and nutrient uptake of wheat as well as nutrient accumulation in soil,whereas the medium dose of HA(60 mg kg -1 soil) was more efficient in promoting wheat growth.     

Effects of different chemical modifications on peat humic acid and their bearing on some agrobiological characteristics of soils

Abstract

Twelve preparations from peat humic acid were obtained through laboratory treatments modifying its structural parameters, oxygen (O)‐containing functional groups and nitrogen (N) content. The treatments included acetylation, amidation, ammonia fixation, methylation, nitration, oximation, sulphonation, and selective degradations. The transformed humic products were characterized by routine laboratory analyses. Then, plant yield and different properties of two soils treated with the corresponding potassium (K)‐humates were determined in greenhouse experiments. The main effects and interactions between parameters affecting the response of soil and plant to humic acid application were analyzed through factorial designs. Whereas the application rate (2 to 4 Mg/ha) had no great bearing on plant yield (accounting for between 84 to 176% of the untreated soils), the opposite occurred with aggregate stability and cation exchange capacity. Among the parameters examined in the humic acids, the hydrogen/carbon (H/C) atomic ratio showed the most significant correlation with plant yield (inverse correlations with the optical density and relative fluorescence intensity were found), whereas the amounts of O or N were in general unrelated to the agrobiological properties of the amended soils. It is postulated that the differences observed in the edaphic role of the humic preparations were not due to a great straightforward influence of the chemical transformations applied, but mainly reflected their indirect effects on the polymer arrangement of the humic acid through changes in the surface properties of the whole macromolecular system.     

Adsorption and desorption of Cd on humic acid fraction of soils

The adsorption of ionic Cd has been investigated on three humic acids isolated from podzol, rendzina and brown Mediterranean soils of Tuscany. The adsorption isotherms have been determined at 5 and 25°C. Cadmium adsorption was described by the Langmuir adsorption equation. Langmuir parameters were related to the functional groups content of humic acids and decreased in the following order: rendzina>brown Mediterranean soil>podzol. Adsorption was independent on temperature and increased with pH. Desorption experiments with 0.1 N NH₄OAc and 0.25 M Cu (OAc)₂ proved that Cd is adsorbed on humic acid about 50% in an exchangeable form and 50% in coordination complexes.     

Determination of DTNB-reactive sulphhydryl groups in soil humic acids: their enrichment in humic acids from volcanic acid soils

Thirteen acid soils were collected from typical volcanic regions in Japan (S content: 0.9–4.1, mean = 2.2g kg^?1; pH (H₂O): 2.81–3.93, mean = 3.33), as well as nine reference soils (S: 0.6–1.7, mean= 1.1 gkg^?1; pH(H₂O): 4.10–4.74, mean = 4.47). Humic acids were extracted from the soils separately with 0.1 M NaOH and precipitated by acidification (pH = 2, HCl). After purification, the humic acids were subjected to colorimetric analysis using a DTNB reagent [5,5′-dithiobis(2–nitrobenzoic acid] for the active -SH group. Since humic acids have significant absorption at 4I2 nm, the coloured compound (5–mercapto-2–nitrobenzoic acid) was separated from the humic acids by ultrafiltration or solvent extraction prior to the colorimetric measurement. Humic acids also caused discoloration of the coloured compound when they coexisted in the reaction solutions. Thus, the reproducible determination of -SH was accomplished by employing a standard addition technique (-SH standard: cysteine). Although -SH contents obtained by the ultrafiltration method were considerably higher than those by the solvent-extraction method, probably due to the denaturation of humic acids by the higher buffer concentration used in the ultrafiltration method, they correlated well with each other. The humic acids from acid soils contained apparently higher concentrations of -SH (120–510, mean = 270mg S kg^?1 by the ultrafiltration method; 8–110, mean = 38mg S kg^?1 by the solvent-extraction method) compared to those from reference soils [20–260, mean = 90mg S kg^?1 by the former; not detectable (<5)-34, mean = 11 mg S kg^?1 by the latter]. This -SH enrichment in the humic acids from acid soils may result from the degradation and subsequent humification of S-rich debris of plants and micro-organisms and/or direct incorporation of volcanic acid gas (H₂S) into the humic acids.     

Molecular characteristics related to the biodegradability of humic acid preparations

The resistance of soil humic material in soil seems to depend on its molecular characteristics. We have studied 12 chemically modified humic samples in mineral soil to identify molecular characteristics connected with their resistance to biodegradation. The treatments, used to introduce changes in the composition, reactivity and N content of the original humic acid (HA), consisted of acetylation, amidation, methylation, nitration, oximation, sulfonation, acid and alkaline hydrolysis, hydrogen peroxide oxidation and fixation of ammonia and of stearic acid. The relations between respirometric data (total mineralization coefficient and mineralization rates at different stages of the 85-day mineralization curve) and a series of HA characteristics (wet chemical analyses, spectroscopic data and relative yields of different pyrolysis products) were examined by correlation and by multiple regression models. The structural characters of HA most directly related to the susceptibility to biodegradation were the concentration of O–alkyl structures and oxygen content mainly in phenolic structures. The aliphatic/aromatic ratio showed no significant correlation with the resistance of organic matter. The fact that the yields of lignin-derived pyrolysis compounds were directly related to carbon mineralization suggested that the structural contribution of domains consisting of preserved biomacromolecules is more important than the neat aromaticity of the HA. The multiple regression models suggested that molecular size of the HA had the greatest influence in the early mineralization stages, whereas the characteristics of the C backbone (concentration of O–alkyl and alkyl carbons) had a greater influence in the advanced transformation stages in the soil. The lack of significant correlations with N concentration indicated that native N forms as well as N-containing groups introduced in peat HA did not have a measurable trophic effect on the biodegradation. The disordered macromolecular structure of the HAs seems to play a greater role in their resistance to biodegradation than the relative amounts of their major structural constituents.     

干旱胁迫对乌头部分生理指标的影响

 运用模糊隶属法,以北乌头、高乌头、山西乌头、牛扁和华北乌头的移栽苗为试材,研究中度(T1)和严重(T2)干旱胁迫对乌头生理特性的影响,为抗旱性植物的选取提供方法和依据。结果表明：1)细胞膜透性：北乌头在T1和T2处理下分别显著低于和高于对照（CK）,高乌头和华北乌头在T2处理下才显著增高,而山西乌头和牛扁在T1和T2处理下都显著增高; 2)丙二醛质量分数：高乌头、牛扁、华北乌头在T1、T2处理下均显著升高,山西乌头只在T2处理下显著升高,北乌头则在T1处理下显著升高; 3)叶绿素质量分数：在干旱胁迫下除牛扁的叶绿素a质量分数上升外,其余乌头均显著低于对照,而干旱胁迫下5种乌头的叶绿素b质量分数增减差异较大;4)净光合速率：北乌头和高乌头在T1和T2处理下均显著下降,但T1、T2处理间无显著差异,山西乌头只有在T2处理下显著降低,牛扁在干旱处理下反而上升,华北乌头无显著反应;5)根据抗旱隶属值,5种乌头的抗旱性由大到小的顺序为北乌头、高乌头、山西乌头、华北乌头、牛扁。     

Humic substances in acid organic soils: modelling their release to the soil solution in terms of humic charge

Batch titration experiments were carried out with organic soil samples in order to investigate the release to the solution phase of humic substances (HS). Measurements were made of pH, dissolved organic carbon (DOC) concentration, and the concentration of mono-meric (inorganic + organic) aluminium, as functions of added acid or base. DOC was taken to be entirely due to HS. The results can be interpreted in terms of a model in which the soil is considered to contain two types of HS–mobile or potentially mobile (HSM), and immobile (HSI). The binding of inorganic ions by the HS is calculated using humic ion-binding model IV, previously developed in this laboratory. Model IV allows the charges on the HS (Z_HSM, Z_HST) to be calculated; these are determined mainly by the binding of H+ and A13+. Concentrations of HS in solution, [HS_aq], are given by the equation: where |Z_HSM| is the modulus of Z_HSM, n_HSM is the carboxyl group content of HSM, c_HSM is the soil content of HSM, β is a fitting parameter, and square brackets, [ ], indicate concentrations. For most of the soils a value for β of 3 gives acceptable agreements between measured and calculated values of [HS_aq], indicating a major influence of charge on release. The optimized value of c_HSM differs considerably among soils, whereas c_HIS varies by only a factor of about two. Total humic contents (c_HSM+ c_HSI estimated by model optimization are in approximate agreement with values estimated by extraction of the soils with NaOH.     

Effect of ph on precipitation of humic acid from peat and mineral soils on the distribution of phosphorus forms in humic and fulvic acid fractions

Abstract

Humic and fulvic acid fractions were isolated from a mineral soil and a peat by adjusting the pH of the alkali extracts to a range of values from 0.2 to 2.5. Total inorganic and organic forms of phosphorus (P) in the acids were measured by chemical analysis and by ³¹P NMR spectroscopy. As the pH of precipitation of the mineral soil humic acid increased, there was an increase in the total P of the humic acid which related to the inorganic P component. In contrast with the peat, the increases observed in the pH range 0.2 to 1.5 were the result of changes in organic P. Using ³¹P nuclear magnetic resonance spectroscopy, the ratio of inorganic to organic P as mono‐ and di‐esters in the peat humic acid was found to increase from 1:4.8 at pH 2 to 1:19 at pH 2.5. In contrast with mineral soil humic acid, the ratio decreased from 1:6.1 at pH 0.2 to 1:1.3 at pH 2.5. The mono‐ester to di‐ester ratio was about 3 in the peat and 10 in the mineral soil and varied little with pH of precipitation. Phosphonates were detected only in the peat humic acid precipitated in the pH range 1.0 to 2.0     

Resistance and resilience of the soil microbial biomass to severe drought in semiarid soils: The importance of organic amendments

Changes in mean global air temperature and precipitation patterns, leading to longer drought periods and more extremely dry years, are predicted. The objective of this work was to assess whether a long period of severe drought can affect the growth and activity of the microbiota of a semiarid soil, as well as the effect of organic amendments on soil resistance and resilience to this severe drought. A soil incubation experiment was carried out over 60 days, under controlled conditions (25 °C and 60/80% day/night relative humidity), with two treatments: unamended (US) and amended (AS) with manure compost (100 t ha⁻¹). Two levels of irrigation were imposed: (1) well-watered (MUS and MAS), the soil being maintained at 60% of its water-holding capacity (WHC), and (2) dry, without irrigation (DUS and DAS). Then, a single level of irrigation was established for 37 days, dry soils being irrigated under the same conditions than well-watered soils, to assess soil resilience to this period of drought. Under well-watered conditions, the soil water-soluble nitrogen contents were 73 and 88% higher, the microbial biomass carbon 63 and 48% higher, alkaline phosphomonoesterase activity 46 and 32% higher, β-glucosidase activity 16 and 25% higher and urease activity 30 and 19% higher for the US and AS treatments, respectively, compared with the dry conditions at the end of the experimental period. Furthermore, the organic amendment helped the soil to retain moisture and encouraged the growth and activity of soil microbial populations. However, a 2-month drought seems insufficient to destroy the native microbial biomass in the arid soil used in this study, indicating that it is well adapted to adverse climate conditions. Thus, microbiological and biochemical parameters experienced a rapid recovery after soil rewetting, DUS and DAS showing values similar to MUS and MAS, after rewetting, highlighting the resilience of this type of soil against drought stress.     

Effect of organic amendment on amount and chemical characteristics of humic acids in upland field soils

To assess the effect of continuous organic material (OM) application on soil humic acids, the amount and chemical characteristics of humic acids in various types of soils (n = 10) were compared between plots treated with farmyard manure (FYM) or rice straw compost (RSC) plus chemical fertilizer (CF) and plots treated with CF alone. The degree of humification (degree of darkening), molecular size distribution and ¹³C cross polarization/magic angle spinning nuclear magnetic resonance spectra of humic acids from CF‐treated soils showed wide variation among the soils. Humic acid content was generally larger in OM + CF soils than in corresponding CF soils, and the stable C isotopic ratio suggested partial replacement of indigenous humic acids with OM‐derived ones even where no apparent increase in humic acid content was observed. The rate of OM application and the indigenous humic acid content were related positively and negatively, respectively, to the apparent accumulation rate of humic acids among soils. The degree of humification of humic acids was generally smaller in OM + CF soils than in CF soils. Humic acids extracted from FYM and RSC exhibited chemical characteristics typical of humic acids having a smaller degree of humification, which suggested the contribution of OM‐derived humic acids to the differences between OM + CF and CF soil humic acids, such as larger average molecular sizes and smaller and larger proportions of aromatic C and O‐alkyl C, respectively, relative to total C in the OM + CF soil humic acids. Little change was observed in the chemical characteristics of humic acids when the degree of humification of indigenous humic acids was small. The effect of OM application on the chemical characteristics of humic acids was most conspicuous in soils containing humic acids having an intermediate degree of humification, possibly resulting from the combination of accelerated degradation of indigenous humic acids and the accumulation of OM‐derived humic acids.     

Influence of land use on the characteristics of humic substances in some tropical soils of Nigeria

In highly weathered tropical conditions, soil organic matter is important for soil quality and productivity. We evaluated the effects of deforestation and subsequent arable cropping on the qualitative and quantitative transformation of the humic pool of the soil at three locations in Nigeria. Cultivation reduced the humic pool in the order: acetone‐soluble hydrophobic fraction (HE) > humic acid (HA) > humin (HU) > fulvic acid (FA), but not to the same degree at all three sites. The C and N contents, as well as the C/N ratios of humic extracts, were large and not substantially influenced by land use. The δ¹³C values of the humic extracts were invariably more negative in forested soils thereby showing a dilution of δ¹³C signature with cultivation from C3 to C4 plants. The δ¹³C values of apolar HE fractions were generally more negative, indicating a reduced sensitivity compared with other humic fractions to turnover of crop residues. The contents of hydrophobic constituents (alkyl and aromatic C), as revealed by cross‐polarization magic angle spinning (CPMAS) ¹³C‐NMR spectroscopy, in HA, FA and HU were generally < 50%, with the exception of larger hydrophobicity in HU in the forested soil at Nsukka and HA in that at Umudike. The HE fraction contained significantly more apolar constituents, and consequently had a larger intrinsic hydrophobicity than the other humic fractions. The larger reduction of apolar humic constituents than of the less hydrophobic humic fractions, when these soils were deforested for cultivation, indicates that at those sites the stability of accumulated organic matter is to be ascribed mainly to the selective preservation of hydrophobic compounds.     

不同气候带水稻土有机碳δ13C及胡敏酸结构特征变化

选取位于吉林龙井、河南封丘、浙江慈溪和江西进贤的4种水稻土剖面,分析比较了不同气候带水稻土剖面和各粒级复合体的有机碳及其δ13C值的分布特征,探讨了不同水稻土胡敏酸结构和功能基团构成的差异,旨在为深入研究水稻土有机碳动态变化和运转机理提供参考依据。结果表明:不同气候带水稻土剖面中,有机碳δ13C值均随着土层深度的增加逐渐升高;样点位置愈往北,水稻土表层有机碳δ13C值愈高。各样点水稻土表层有机碳主要集中在<10μm复合体部分,其有机碳分配系数均大于50%。水稻土不同粒级复合体δ13C值随着粒级的减小不断升高,高δ13C的老碳在细粒中富集;水稻土表层<10μm复合体中有机碳的降解程度为:封丘>慈溪>进贤>龙井。各样点水稻土胡敏酸结构大致相似,封丘和龙井的水稻土胡敏酸含有较多CO基团,氧化程度较高,另外,其胡敏酸的芳化度和聚合程度也高于慈溪和进贤的水稻土。     

Effect of humic acid on growth and crop nutrient status of wheat on two different soils

The effect of plant-derived humic acid (PDHA) and coal-derived humic acid (CDHA) on wheat growth was tested on two alkaline calcareous soils in pots. Humic acid derived from plant and coal materials was applied at the rate 0 (control), 50 and 100 kg/ha to wheat in pots carrying two soils viz. clayey loam soil and sandy loam soil separately. Data was collected on plant growth parameters such as spike weight, grain and straw weight, and plant nutrients (macronutrients and micronutrients). Results showed that spike weight increased by 19%, 15%, and 26%, and 11% with application of PDHA at the rate of 50 and 100 mg/kg in clayey loam and sandy loam soil, respectively. Grain yield show an increase of 21% and 11% over control with application of PDHA and CDHA at the rate of 50 mg/kg on both soils, respectively, and 10% and 22% with application of PDHA and CDHA at the rate of 100 mg/kg on both soils.     

腐植酸对土壤氮素转化及氨挥发损失的影响

采用培养试验方法研究腐植酸添加量(0、5%、10%、25%、50%、75%HA)对土壤氮素转化及其损失的影响。结果表明:与CK对比,1)腐植酸可显著降低氨挥发量,各处理平均降低12.08%,且随着腐植酸添加量的增加对氨挥发的抑制作用增大;2)培养前期,5%~50%添加量范围内腐植酸能提高土壤脲酶活性,至5 d时平均提高了35.13%,75%腐植酸添加量的土壤脲酶活性降低了13.23%,但培养后期(14 d后)腐植酸处理均能提高土壤脲酶活性;3)添加腐植酸使土壤铵态氮含量增加,且随着腐植酸添加量的增大,土壤铵态氮含量呈增加趋势,至培养112 d时,腐植酸处理的土壤铵态氮含量平均增加了39.63%;4)在整个培养期间,腐植酸处理的土壤表观硝化率平均降低了17.20%,且腐植酸的添加量越大,土壤表观硝化率越低。这些结果充分表明腐植酸能够调控土壤氮素去向、减少氮素损失,对提高氮肥利用率具有重要意义。     

硝酸处理对褐煤中可提取性腐殖酸含量及其吸附特性的影响

采用硝酸氧化及一次平衡法,研究了硝酸处理对褐煤中的可提取性腐殖酸含量、CEC（阳离子交换量）、E₄/E₆及其对各种养分离子吸附规律变化的影响。结果表明:一定强度的HNO₃能使褐煤中可提取性腐殖酸含量增加45.8%以上,使其阳离子交换能力提高;随硝酸处理时间的不断延长,褐煤中可提取性腐殖酸含量和CEC均呈先增加后减小的趋势,但CEC达到最大值所需时间相对较长;硝酸处理后的褐煤腐殖酸光学性质也发生了很大的变化。经硝酸处理褐煤腐殖酸样品对铵、钾吸附能力分别可提高58.73%和41.53%,其等温吸附式分别符合Freundlich和Langmuir方程。而对磷的吸附能力降低,一定条件下其吸附量仅为处理前的5.33%,其等温吸附式用Langmuir方程描述最佳。上述结果表明,经硝酸处理后,褐煤腐殖酸更适宜作为缓效肥料基质使用。     

矿物源腐植酸肥料中可溶性腐植酸快速检测方法研究

采用分光光度法检测矿物源腐植酸肥料中可溶性腐植酸含量,讨论在检测过程中样品的称取质量、离心条件、重铬酸钾浓度以及氧化时间对检测结果的影响.进行了方法验证,计算出方法检出限为4.27％,相对标准偏差为2.1％～11.6％,加标回收率为95％～106％.     

Humus composition of mountain soils in Central Japan with special reference to the distribution of P type humic acid

The central districts of Japan are mountainous areas rising to 3,000 metres which are predominantly covered with forest vegetation. A comprehensive and systematic classification of the soils in this region has not yet been made, but the following soil types have been reported to occur: - 1. 1. Brown forest soils, podzolic soils, black soils and red soils. [Described by OHMASA (14)]

2. 2. Alpine grassland soils and alpine meadow soils. [Described by KUMADA et al. (9)]

3. 3. A series of randzina-like soils with a very restricted distribution. These are derived mainly from limestone and show various degrees of maturity. [Described by KUMADA et al. (8)]

4. 4. Red-yellow soils. These sometimes show a close resemblance to OHMASA's red soils and are found on diluvial plateaux and hills. [Described by KANNO (1)]

5. 5. Paddy soils.