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Iron extractibility from iron-humate complexes by a siderophore and a mixture of organic acids
No full textTwo well-characterized humic acids (HA), extracted from a volcanic soil and a leonhardite, were used to synthesize insoluble Fe complexes. The complexes were treated at different concentrations and contact times with a siderophore (deferoxamine mesylate) and a mixture of simple organic acids (citric, oxalic, tartaric, and ketoglutaric acids) naturally occurring in root exudates in order to evaluate the capacity of the extracting solutions to desorb Fe from the humic complexes. Results showed that iron can be extracted from the complexes according to the concentrations and pH of the extractants. The mixture of organic acids was generally a better extractant than the siderophore at the high concentration because of lower solution pH. Despite constant differences in solution pH, the extracting capacity of the two extractants was similar at lower concentrations. However, the extent of desorption varied with HA characteristics. Iron appeared to be more easily released from complexes with HA rich in aliphatic carbons than from those with HA rich in aromatic carbons. These findings were attributed to the stereochemical complexity of highly aromatic humic substances that prevents natural chelators to easily reach the Fe complexing sites. Key words: Humic substances, iron, siderophores, organic acids, plant chlorosi
Intercalation between a well-characterized andisol fulvic acid and montmorillonite (1996).
No full textEffects of fractions of coal derived humic substances on seed germination and growth of seedlings (Lactuca sativa and Lycopersicon esculentum)
No full textLettuce and tomato seeds were treated in Petri dishes with a humic acid derived from an oxidized coal and with fractions of the same humic acid obtained by ultrafiltration through membranes of known molecular cutoff and by extracting with buffers set at pH 4 and pH 5. The unfractionated humic acid was applied at 40, 100, 1000, and 5000 mg l-1 whereas the humic fractions were applied at 40, 100, and 200 mg l-1. Germination parameters such as the number of total germinated seeds, the velocity of seed germination, the fresh weight and dry weight of total seedlings were measured and related to the chemical and physicochemical properties of the humic material. No increase in the germination percentage or the germination rate was observed for either lettuce or tomato seeds. The fresh weight of total seedlings and per seedling increased in treatments with unfractionated humic acid with increasing concentrations for both lettuce and tomato plants without showing signs of growth inhibition up to 5000 mg l-1. This was attributed to cell elongation and more efficient water uptake. For the lettuce, the fresh weight both of total seedlings and per seedling was enhanced by treating the seeds with fractions of low molecular weight and high content of acidic functions, whereas the dry weight both of total seedlings and per seedling did not change with the humic fraction used. For the tomato seeds in contrast, the dry weight both of total seedlings and per seedling was increased by the use of unfractionated humic acid and by some of the humic fractions. An uptake of humic material by growing tomato seedlings was inferred
"Iron extractability from iron-humate complexes by a siderophore and a mixture of organic acids".
No full text"Effects of fractions of coal derived humic substances on seed germination and seedling growth".
No full textReduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal.
No full textAdsorption of herbicide Glyphosate on metal-humic substances complexes
No full textThe interactionof glyphosate with a pure iron-humic acid (Fe-HA) complex was studied by constructing adsorption isotherms at different shaking times. The Freundlich equation better fitted the experimental data than the Langmuir equation. The maximum adsorption values (kf) showed that glyphosate is adsorbed on Fe-HA complex to an extent that is similar to that found for whole soils and even higher than that shown by other soil minerals. This suggests that HA complexes with polyvalent cations may represent a main binding substrate for glyphosate in soils. The S-type adsorption isotherms found through the application of the Freundlich equation, indicate that at low concentration glyphosate is adsorbed by a ligand exchange mechanism involving the phosphono group and the iron hydration sphere in the HA complex, whereas at higher concentration, more glyphosate may continue to be bound by a hydrogen bonding mechanism, to already sorbed molecules. The high strength of the glyphosate interaction with the Fe-HA complex is demonstrated by the lack of any appreciable desorption for any concentration and any time of contact applied. A rapid increase of the slope of the Freundlich adsorption isotherms at shaking times higher than 48 h is suggestive of some microbial degradation
Effects of coal derived humic substances on water retention and structural stability of Mediterranean soils
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