Nine K‐rich soils belonging to three Orders often found in Southern Italy (Inceptisol, Alfisol, Vertisol) were extracted with H2O, CaCl2, NH4OAc, HCl, Mehlich, HNO3 reagents for K and the results were compared to the EUF method. Significant correlations between the reagent extracted K and EUF K were found. The results allowed us to distinguish three basic K fractions: (i) actually available, (ii) quickly released reserve and (iii) slowly released reserve. The EUF provided both quantitative and qualitative data, suitable for a “dynamic” diagnosis of K soil fertility saving time and reagents. The EUF curves showed an unexpected strong K affinity for Inceptisol, the soil which was richest in K.

Products from reaction of four humic acids of different origin and nature (synthetic, coal, peat, compost) and four s-triazine and six substituted urea herbicides were studied. Elemental composition and infrared and electron spin resonance spectra were measured on original humic acids, pure herbicides and the reaction products. Elemental analysis data indicated that stable complexes were formed between humic acids and herbicides. Infrared analysis results showed the formation of ionic and hydrogen bonds between interacting molecules and suggested the possible occurrence of charge-transfer complexes. Electron spin resonance parameters and in particular the increases concentrations of paramagnetic centres in interaction products gave evidence that electron donor-acceptor processes involving free radical intermediates were among the most important binding mechanisms occurring. Structural and chemical properties of both humic acids and herbicides influenced the prevailing type(s) of interaction mechanism(s) which occurred.

Product of interaction obtained in aoueous medium between 3 humic acids of synthetic, peat and coal origin and 9 chlorophenoxyalkanoic acids and esters of different chemical structure and and properties (type of alkanoic chain and number of chlorine ring-atoms) were investigated by electron spin resonance and infrared spectrometries and chlorine analysis in order to obtain information on the occurring interaction mechanisms and type of bonding. The increased chlorine content and decreased free radical concentration generally measured in the interaction products, in comparison with values of the original humic acids, confirmed the already suggested incorporation of xenobiotic units by stable covalent bonds into humic polymers, through cross-coupling, homolytic reactions between indigenous humic free radicals and chtorophenoxy-radical intermediates generated by a previous chemical, photochemical and/or enzymatic degradation of the original xenobiotic molecule. For comparative purposes, the study was also extended to the products obtained by interaction of the same chlorophenoxy compounds with 7 more humic acids of different sources, including soil and compost. The various humic acids considered showed a definite, different interacting power in coupling with the xenobiotics, in the order: synthetic > peat> soil> coal>compost. The reactivity of humic acids was found to be indirectly correlated with their carboxyl content and carboxyl/phenolic hydroxyl ratio. The different molecular structure of chlorophenoxyalkanoic compounds did not apparently influence their reactivity towards humic acids. An approximate trend was shown as a function of the number of chlorine ring-atoms, which appeared to affect the reactivity according to the order: monochlorinated > dichlorinated > trichlorinated.

Theoretical aspects of the possible occurrence of electron donor-acceptor processes involving free radical intermediates and leading to stable charge-transfer complexes between electron donor herbicides and acceptor quinone-like units of humic acids have been discussed on the basis of similar mechanisms occurring on biological scale in the chloroplasts. Experimental evidence of the former hypotheses was given by the analyses of infrared and electron spin resonance data obtained from interaction complexes of a number of s-triazines and substituted ureas (photosynthesis inhibitor herbicides) with soil humic acids. In the case of s-triazines it was shown that with decrease of the capacity of humic molecules to form ionic and hydrogen bonds, the tendency to act as electron acceptor increased, as shown by the higher free radical generation observed after the interaction process. The existence of correlations between the bioactivity of substituted ureas - expressed as inhibitory potency in the Hill reaction (pI50 indexes) - and free radical concentrations in the humic acid - herbicide complexes was also demonstrated.

AbstractProducts of the interaction between soil humic acids and substituted‐urea herbicides were prepared in the laboratory and subjected to elemental, functional group, differential thermal, infrared spectroscopic and electron‐spin resonance analysis, in order to examine the various chemical mechanisms that may take place upon adsorption. The results indicate that, besides the involvement of hydrogen bonding, a prominent role is played by electron donor‐acceptor processes involving organic free radicals, which leads to the possible formation of charge‐transfer complexes. The phytotoxicity of the urea herbicides, expressed as the inhibition potency towards the Hill reaction (pl50 values), appeared to be correlated with their capacity to interact with soil humic components, and it is suggested that these two processes depend upon the same molecular parameters.

Infrared and proton resonance spectra have been used to characterize fraction extracted sequentially from humic and fulvic acids by diethylether, acetone, dioxane, tetrahydrofuran, pyridine and dimethylformamide. The results showed that the same solvents extracted structurally similar components from both humic and fulvic acids. On the other hand, the spectra showed solvent-dependent differences, some being characteristic for a preponderance of aliphatic structures, others for aromatic structures.

SummarySoil organic matter fractions were isolated from three soils by the application of a sequential extraction procedure employing a series of 10 mild organic solvents of different polarity.The isolated organic materials were characterized by elemental, infrared and electron spin resonance analyses. They showed different chemical and structural properties which varied according to the progression of the solvent series, with some similarities between two successive extracts. The corresponding fractions extracted from the three soils were substantially similar to each other in chemical character. Along each series of extracts aliphaticity appeared to decrease, whilst aromaticity, polar oxygenated and nitrogenated functional groups, transition metal ion content and organic free radical concentrations increased. ESR spectra were structured and were put in four different classes, according to their characteristic resonances.Although the yields of extracted organic material were not high, the fractions could be considered representative of the soil organic matter composition and furnish new chemical information on its nature and properties.

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.

Experiments were carried out on the effects of some phenoxyacilic acids, used as herbicides, on the glutamic-dehydrogenase (GLDH) activity.

Soil organic fractions extracted in sequence with ethyl ether, acetone, benzene and dioxane have been investigated with 13 C NMR spectroscopy. The spectra of ethyl ether and acetone fractions are identical and show the presence of signals assigned to normal long chain ( C 23±2 ) fatty acids. A very similar spectral pattern is displayed by the benzene fraction which appears to consist of a mixture (50 ± 10)% of normal fatty acids and normal alkanes ( C 21±3 ). A comparison with data in the literature indicates that the well developed signals at 14, 23, 30 (very intense) and 32 ppm are a common feature of the lipid fraction extracted from different soils. A completely different spectrum has been obtained from the dioxane fraction. Most signals appearing in the range 55–75 ppm can be attributed to oxygen bonded sp 3 carbon atoms. The lack of aromatic signals seems to exclude the possibility that this fraction was derived from lignin residues. The comparison with 1 H NMR spectra and the occurrence of distinct and sharp signals indicate that 13 C NMR is a valuable tool in the study of soil organic fractions extracted with organic solvents.

We studied the adsorption of two s-triazine and two substituted urea herbicides by three different soil humic acids, using elementary analyses and infrared spectroscopy. Obtained data show that adsorption occurs in all cases, involving such mechanisms as ionic bonds, only for the s-triazines; H-bonding; van der Waals forces; and possibly charge transfer in both s-triazine-HA and substituted urea-HA complexes. The extent of adsorption is higher for s-triazines than for substituted ureas, in the order: prometone > methoprotryne > monuron > fenuron.

The IR and 1H-NMR spectra of fulvic acids (FA) are discussed. The FA, extracted by traditional methods, were fractionated on the basis of molecular weight (m.w.). Three fractions were obtained labelled FA I (m.w. > ∼ 2000), FA II (m.w. > ∼ 12000) and FA III (∼2000 < m.w. < ∼ 12000). Fraction FA II was methylated with CH3I-Ag2O. The 1H-NMR spectra of unmethylated FA fractions show some signals common to all three fractions and some differences in the 3–5 ppm range due to the resonances of OCH3 and O-CH2 groups. The proton spectrum of the methylated fraction shows absorption areas for OCH3 groups of phenols and carboxyls. The results confirm that NMR spectroscopy is a convenient technique which can contribute to defining the chemical structure of humic substances.

Summary In 24 soils the CEC of untreated samples, of samples treated with hydrogen peroxide, and of samples treated with dimethyl sulphate, was determined at pH 3, S and 8. The CEC of clay and organic matter was calculated from multiple regression equations and compared with values after treatment with peroxide and after methylation. At pH 3 and pH 5 the CECs of clay by the three methods were similar, whereas at pH 8 they were significantly lower on untreated samples. The results are interpreted in relation to the formation of organo-mineral complexes and to the interaction of the acid functions of the clay and organic matter.

A study has been made using i.r. and n.m.r. spectroscopic techniques to investigate ten different organic fractions extracted in a series of mild organic solvents from a brown soil from Sardinia. The experimental results gave useful information about the nature of the extracted samples, which differ considerably from one another. Some of the extracts are characterized by a preponderance of aliphatic structures; others, by the presence of quinone-hydroquinone units or polymeric chains; and others, by particular chemical skeletons, probably based upon hydrolylated naphtho- or anthraquinone frameworks.