Physico-chemical investigations of interaction mechanisms between s-triazine herbicides and soil humic acids

Multiple binding mechanisms that may occur upon interactions between three soil humic acids of different origins and four s-triazine herbicides, differing in chemical structure and properties, have been investigated.Results of elemental, thermal, infrared and electron spin resonance analyses of the products of interactions demonstrate that different processes are involved and that they are controlled mainly by the content of the acidic functional groups and hydrogen binding capacity of humic acid and by the basicity of s-triazines.Experimental and theoretical evidence is given on the occurrence of electron donor—acceptor processes involving free rardical intermediates and leading to stable charge-transfer complexes between the adsorbant and the adsorbate. Parallels are suggested between the biological and chemical behaviour of s-triazines towards quinone-like structures in electron donor—acceptor systems.The feasible formation of covalent bonds, which leads to interaction products of enhanced molecular complexity, capable of stabilizing free radical intermediates, is discussed.Analysis of our data suggests that the higher the capacity of humic acids to form ionic and hydrogen bonds with s-triazines, the lower their effectiveness in forming electron-transfer complexes, as related to the lower ability to generate free radicals.Finally, our results show that the basicity of s-triazines, and hence their tendency to form ionic bonds, is not the main factor governing adsorption. Indeed the most basic prometone is not the most adsorbed; nevertheless, it appears to be the most efficient among s-triazines in giving rise to electron donor—acceptor processes with humic acids.     

The nature of humic acid‐apatite interaction products and their availability to plant growth

Abstract

An investigation was conducted to determine the nature of decomposition products resulting from the interaction between humic acid and apatite and assess their availability to plant growth. Interaction analyses were performed by shaking 200 mg apatite with 0 to 800 mg/L HA or FA solutions at pH 5 or 7 for 0 to 12 hr. Phosphorus concentrations were determined in the supernatants by spectrophotometry. The nature of P‐humic acid complexes was determined by ³¹P NMR analysis. Availability of these dissolution products was studied by growing corn plants in aerated hydroponics to which 200 mg apatite and 0 to 800 mg/L HA were added at pH 5 or 7. The results indicated that the rate of dissolution of apatite was parabolic in regression with time, and increased by increasing the amounts of HA or FA applied from 100 to 800 mg/L The dissolution reaction was influenced by pH, because larger amounts of PO₄ ³‐ions were detected at pH 5 than at pH 7. ³¹P NMR spectroscopy indicated the presence of P‐humic acid complexes, previously believed to be humophosphate esters. The PO₄ ^3‐ ion was complexed by HA at pH 7 or above, but PO₄ ^3‐ appeared to be released again as adsorbed and free ions at pH <5.0. Plant performance corresponded with increased PO₄ ^3‐concentrations at pH 5.0. No significant improvement over the control was observed in the growth of corn plants by apatite + HA treatments at pH 7. However, plant growth was increased significantly over the control by apatite + HA treatments at pH 5.0. Better growth performance of corn plants were noticed by apatite + HA than by KH₂PO₄ treatments at pH 5.0.     

Pyrolysis of a soil humic acid and of their hydrolyzed and methylated products

Pyrolysis of soil humic acid yields a variety of products arising from heterogeneous materials associated to the humic structure and from this self. After acid hydrolysis most of the compounds related to proteins, polysaccharides and lignin dissappear. Adsorbed compounds such as fatty and dicarboxylic acids are released after methylation and subsequent pyrolysis. In addition pyrolysis produces aromatic and substituted aromatic hydrocarbons. All the identified pyrolysis products have also been isolated by different complex and time-consuming chemical degradations and solvent extraction procedures. Pyrolysis provide some evidence of the humic acid structure.     

Sorption of cadmium by complexes of kaolinite with humic acid

Abstract

Levels of cadmium (Cd) in New Zealand pastoral soils have increased due to Cd impurities in applied fertilisers. As there is little information on the interaction of Cd with soil mineral‐organic matter complexes, the sorption of Cd by complexes of kaolinite with humic acid has been investigated. Sorption was measured at pH and ionic strength values typically found for solutions of pastoral soils in New Zealand. Sorption increased with the content of humic acid in the complex, and as the pH of the medium was raised from 4.2 to 6.3. Sorption was also influenced by the ionic strength of the ambient solution, notably by the nature of the cation in the added electrolyte. The experimental data were interpreted in terms of the effect of solution pH and ionic composition on the charge characteristics of kaolinite and humic acid. These factors, in turn, influence clay particle association as well as the clay‐humic and metal‐humic interaction.     

EPR spectra of humic acids and their metal complexes

On the basis of ESR spectra, humic substances are believed to be hydroquinone type polymer radicals with considerable cation exchange and redox capacity. All 3d-transition metal humates appear to be ionic high spin complexes. Manganese (II) ions doped in raw peats and peat humic acids are coordinated octahedrally with six oxygen-containing functional groups, e.g., carboxylate, phenolic, hydroxyl, carbonyl ligands, whereas copper (II) ions are in square planar arrangement with two carboxylate and two aliphatic nitrogen ligands. Doping with vanadyl(II) ions results in a square pyramidal arrangement with four oxygen-containing ligands. Diamagnetic manganese(VII), chromium(VI), molybdenum (VI) and vanadium(V) oxoanions in acidic solution are reduced by humic acids into paramagnetic manganese(II), chromium(III), molybdenum(V) and vanadium(IV) ions. Diamagnetic copper(I) ions, on the other hand, are oxidized by humic acids into paramagnetic copper(II) ions.In contrast to polyronic acid gels with outer-sphere structure, 3d-transition metal ions are generally bound to humic acids as inner-sphere chelate complexes.     

Effect of residual vanadyl ions on the spectroscopic analysis of humic acids: a multivariate approach

In a study of the vanadyl (VO²⁺)‐humic acids system, the residual vanadyl ion suppressed fluorescence and specific electron paramagnetic resonance (EPR) and NMR signals. In the case of NMR, the proton rotating frame relaxation times (T_1ρH) indicate that this suppression is due to an inefficient H‐C cross polarization, which is a consequence of a shortening of T_1ρH. Principal components analysis (PCA) facilitated the isolation of the effect of the VO²⁺ ion and indicated that the organic free radical signal was due to at least two paramagnetic centres and that the VO²⁺ ion preferentially suppressed the species whose electronic density is delocalized over O atoms (greater g‐factor). Additionally, the newly obtained variables (principal components – PC) indicated that, as the result of the more intense tillage a relative increase occurred in the accumulation of: (i) recalcitrant structures; (ii) lignin and long‐chain alkyl structures; and (iii) organic free radicals with smaller g‐factors.     

Free radicals in electron donor-acceptor reactions between a soil humic acid and photosynthesis inhibitor herbicides

Products obtained by interaction of a soil humic acid with a number of s-triazines and substituted ureas, well known to act as photosynthesis inhibitor herbicides, were studied by infrared (IR) and electron spin resonance (ESR) spectrometries. Analysis of spectroscopic results showed that single-electron transfer processes take place reasonably between ring or chain donor groups of the herbicide molecule and acceptor quinone units of the humic acid, thus producing additional unpairing of electrons in the resulting charge-transfer complexes. Experimental and theoretical considerations suggested the hypothesis that the investigated herbicides may react chemically with humic compounds by simulating analogous processes that take place on biological scale in chloroplasts, on the basis of similar electron donor-acceptor reactions involving free radicals.     

Infrared spectroscopic investigations of humic substances and their metal complexes

A study has been made on the infrared spectra of lowland peats and purified humic, hymatomelanic and fulvic acids, as well as their acetylated derivatives and metal complexes. Extraction and purification may modify humic acids of untreated peats only to a small extent. Acetylation of fulvic and humic acids with acetic acid anhydride resulted mainly in the reaction of phenolic hydroxyl and quinone groups. Similarities of the spectra of the individual humic substances point to similar structures, differing only in the number of functional groups and the degree of aggregation. Metals are bound by humic substances mainly in metalcarboxylate bonds. The degree to which these bonds are ionic or covalent can be determined by the antisymmetric carboxylate stretching frequencies.     

一种水溶性腐植酸有机肥的制备及产物性质研究

为提高矿源水溶性腐植酸的提取率及产品品质，以云南褐煤及辣椒为试材，研究纳米氧化锌催化H2O₂     

The interaction of hydrazine hydrate with humic acid preparations at pH 4

Sorption isotherms were obtained by a continuous-flow method for the interaction of hydrazine hydrate with freeze-dried hydrogen-, aluminium- and calcium-exchanged humic acid preparations in aqueous suspensions at pH 4. The application of the continuous-flow method is outlined and the fit of the isotherms to three sorption equations is examined. Microcalorimetry was used to measure directly the differential enthalpies of reaction as functions of sorptive concentrations. Exchange by hydrazinium ions of the exchangeable cations on the humates, chemisorption by interaction of hydrazine with humate carbonyl groups, and non-specific sorption involving weakly- and strongly-held hydrazinium ions and hydrazine molecules are shown to be the major sorption processes in these systems. The relative importance of each of these processes for the different hydrazine/humate systems is discussed, and the influence of the exchangeable cation on humate reactivity is considered.     

硫酸铵与腐植酸及改性腐植酸配施对氨挥发的影响

通过室内连续培养试验,研究了石灰性褐土中硫酸铵与不同用量及改性腐植酸（HA）配施对氨挥发及氮素形态转化的影响。试验设置6个腐植酸用量处理,分别为CKⅠ、ASNⅠ（硫酸铵Ⅰ）、ASNⅠ+5%HA、ASNⅠ+10%HA、ASNⅠ+15%HA、ASNⅠ+20%HA(5%、10%、15%、20%为腐植酸占硫酸铵施用量的百分比)和6个改性腐植酸处理,分别为CKⅡ、ASNⅡ（硫酸铵Ⅱ）、ASNⅡ+W0、ASNⅡ+W400、ASNⅡ+W600、ASNⅡ+OHA(W0、W400、W600分别为含水量0%、400%、600%的改性腐植酸,OHA为干燥+过氧化氢氧化处理的改性腐植酸)。结果表明：培养32 d后,与单施硫酸铵处理（ASNⅠ）相比,ASNⅠ+10%HA～ASNⅠ+20%HA处理可以抑制氨挥发,其中ASNⅠ+20%HA处理抑制效果最佳,日平均氨挥发速率降幅为5.07%。腐植酸经不同改性处理后,按硫酸铵用量的20%与硫酸铵配施培养32 d后,与单施硫酸铵处理（ASNⅡ）相比,ASNⅡ+W400与ASNⅡ+W600处理加剧了土壤氨挥发,土壤氨挥发总量分别增加了50.69%和57.64%;ASNⅡ+O...     

Effects of humic acids and herbicides,and their combinations on the growth of tomato seedlings in hydroponics

The morphology and length of roots and shoots of tomato (Lycopersicon esculentum Mill.) seedlings grown on a nutrient medium for fourteen days in a controlled environment chamber were apparently not affected, whereas the dry matter content of roots was significantly enhanced when 200 mg L^?1 of humic acid (HA) isolated from either a non-amended soil or a sewage-sludge-amended soil was present in the nutrient medium. In contrast, the HA-like fraction isolated directly from the sewage sludge caused, under the same conditions, extensive alterations of tomato morphology and a significant reduction of the length and dry weight of both shoots and roots. The presence in the nutrient medium of the herbicides alachlor or imazethapyr at concentrations of 1 and 0.01 mg L^?1, respectively, caused a marked decrease of tomato root and shoot length and dry weight. Differently, the herbicide rimsulfuron at a concentration of 0.01 mg L^?1 produced a slight decrease in shoot and root length and a slight increase in their dry weight. A combination of 200 mg L^?1 soil HA and each of the herbicides alachlor, rimsulfuron and imazethapyr at concentrations of 1, 0.01 and 0.01 mg L^?1, respectively, in the nutrient medium attenuated the growth depression of tomato shoots and roots observed in the presence of the herbicide alone. However, the simultaneous presence of sewage sludge HA and any herbicide in the nutrient solution caused negative synergistic effects on tomato growth. The volume of nutrient solution and the amount of electrolytes taken up by tomato plants during the growth experiments correlated highly significantly with the total plant dry weight. Tomato seedlings induced a pH decrease in the nutrient medium in all treatments except in those where sludge-HA was present, either alone or in combination with any herbicide.     

Fluorescence intensity of organic matter molecular-weight fractions and their managanese complexes

Five fractions differing in their molecular-weight parameters, sorption properties, and infrared spectra were separated using systematic gel chromatography. The principle of the method was described, as well as the procedure of calculating the spectral-luminescence parameters of molecular-weight fractions of organic matter from the relative values of their fluorescence intensities. It was shown that complexation involves fluorophore groups of organic matter and is accompanied by a decrease in the fluorescence intensity with increasing content of bound manganese. The study of the fluorescence spectra at different wavelengths provides more information on the fluorescence properties of different organic compounds in natural materials and opens the possibilities for studying the interaction of humus substances with metal ions and determining the composition and properties of organomineral compounds.     

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.     

Quantitative and qualitative characterisation of humic products with spectral parameters

Purpose

The application of different humic products for the treatment of soils and plants has increased in recent years. The characteristics of humic products, such as the content and composition of organic carbon and the maturity, provide valuable information which is essential for an adequate application. Such information is crucial for manufacturers, business consultants and users involved in the production, distribution and implementation of humic products. This article presents the correlation between the quantitative indicators of commercial humic products and their spectral characteristics via measurements in the ultraviolet spectrum at 300 nm, in the visible area at 445 and 665 nm and in the near-infrared spectrum at 850 nm.

Materials and methods

We evaluated humic products (liquid and solid) of different origins. Via wet combustion, the content of total organic carbon in humic products can be determined. The precipitation of humic acids from the starting solution determines the composition of the humic products in terms of humic acids (HAs) and fulvic acids (FAs). The dissolution of HAs determines their concentration by titration, while the specific extinction can be assessed via spectrophotometry via measuring the absorption of HAs spectra at the following wavelengths: 300, 465, 665 and 850 nm. The degree of aromaticity and condensation of humic products determines the optical density of the HAs via the E₄/E₆ ratio.

Results and discussion

The content of total organic carbon varied widely from 0.55 to 37.5% across all groups. The content of carbon in HAs, as a percentage of the total carbon in fulvic-type humic products, ranged from 1.29 to 16.00%, while in humic-type products, it ranged from 51.43 to 91.92%. The minimum value of the E₄/E₆ ratio was 2.97, while the maximum value was 6.35. We observed a direct relationship between the dominant type of acids in humic products and the E₄/E₆ ratio.

Conclusions

The optical density of HAs indicates their quality characteristics. The presented optical characteristics for humic products show that there is a direct relationship, especially between HAs/FAs and E₄/E₆ ratios. Measurement at 300 nm (E₃₀₀) in the near-ultraviolet area and at 850 nm (E₈₅₀) in the near-infrared area can increase the range of the spectral study.

     

Interactions of allophane with humic acid and cations

Allophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl₂ or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl₂ than in NaCl of the same ionic strength. Apparently Ca²⁺ ions were more effective than Na⁺ ions in screening the negative charge on HA. In CaCl₂ the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl₂ sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co‐sorption of extraneous cations (Ca²⁺ or Na⁺) for charge balance. The Ca²⁺ co‐sorbed can attract more HA to the complex possibly by a cation‐bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca²⁺ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.     

胡敏酸对铵钾在粘土矿物上交互作用的影响

Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+4 and K+have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+4 and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+4 on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.     

Rehabilitation of saline soil with biogas digestate,humic acid,calcium humate and their amalgamations

ABSTRACT

Amelioration of saline soil is a requisite in order to increase crop productivity. A soil incubation study was performed for 60 days using digestate, humic acid, calcium humate and their combinations to investigate the influence on physical, chemical, microbial and enzyme activities of saline soil. Overall, digestate combined with calcium humate followed by humic acid treatments have shown their potency in decreasing the soil pH, electrical conductivity (EC), and sodium ion (Na⁺) concentration, and increase in potassium ion (K ⁺), calcium ion (Ca ²⁺), magnesium ion (Mg ²⁺), mean weight diameter (MWD), soil enzyme activities, microbial biomass carbon (MBC), MBC: microbial biomass nitrogen (MBN) and soil respiration than control. The digestate, humic acid individually and their amalgamation evidenced greater MBN among all the treatments. The digestate alone efficiently improved the soil properties than humic acid and calcium humate individual groups except for the MWD where it is pronounced more in the latter groups. The greater metabolic quotient (qCO₂) was observed in control than organic matter amended treatments indicating the stress conditions. The increase in water-extractable organic matter (WEOM) with minimal aromaticity (specific ultraviolet absorbance at 254 nm-Suva ₂₅₄) in integrated amendments comprising groups, laid the ground reason to improve the properties of saline soil. Therefore, this study concludes that the fusion of fresh and humified substrates could facilitate reclamation.