Fulvic acids, soils

So-called "dissolved" iron(III) consists mainly of colloidal Fe(III) oxides stabilized by humic or fulvic acids Soil Colloids... 

Sposito, G., Holtzclaw, K. M., and Baham, J. (1976). Analytical properties of the soluble, metal-complexing fractions in sludge-soil mixtures II. Comparative structural chemistry of fulvic acid. Soil Sci. Soc. Am. J. 40, 691-697. 

Tan, K.H., 1975. The catalytic decomposition of clay minerals by complex reaction with humic and fulvic acid. Soil Sci., 120 188—194. 

Humic and fulvic acids are presumed to arise by two classical natural processes. Terrestrial humates are found in the following pathway plants soil humates peat — coal. Aquatic humates start with soil leachates or marine phytoplankton and go through a sequence sediments kerogen petroleum. There are conditions which mix the two processes as well. As a result, there are a host of names and symbols applied to these compounds, such as peat humic acid, coal fulvic acid, soil humic acid, and so on. Depending on their oxidation state, they may be heavily bound to metal ions. Within each class of humic acid, there are subclassifications, such as Podzol Bj, humic acid, lignite fulvic acid. Other types are classified by geological age, depth in a sediment, and type of aquatic environment. The following discussion will attempt to relate elemental composition to these broad classes of humates. 

Sears, P. G., Wolford, R. K., and Dawson, L. R. (1956). Conductances of some acids, bromides, and picrates in dimethylformamide at 25°C. J. Electrochem. Soc. 103, 633-636. Senesi, N. (1981). Free radicals in electron donor-acceptor reactions between a soil humic acid and photosynthesis inhibitor herbicides. Z. Pflanzenernahr Dung. Bodenkd. 144, 580-586. Senesi, N., Chen, Y., and Schnitzer, M. (1977a). Hyperfine splitting in electron spin resonance spectra of fulvic acid. Soil Biol. Biochem. 9, 371-372. 

Senesi, N. and Schnitzer, M. (1977). Effects of pH, reaction time, chemical reduction, and J C irradiation on ESR spectra of fulvic acid. Soil Sci. 123, 224-234. 

SOI Soil, fractions, inorganic and organic components, microbes, biota, humic/fulvic acids, soil and pore water, amendments, fertilizers. 

MATO M.C., GONZ EZ-ALONSO L.M. and MENDEZ J. 1972. Inhibition of enzymatic indoleacetic acid oxidation by fulvic acids. Soil Biology and Biochemistry, 4, 475-478. 

SENESI N., CHEN Y. and SCHNITZER M. 1977. The role of free radicals in the oxidation and reduction of fulvic acid. Soil Biology and Biochemistry, 9, 397-403. 

In this work a novel five-step leaching scheme for HM has been developed addressing exchangeable, acid soluble (carbonate), easily reducible (bound to Mn oxides), easily oxidizable (bound to humic and fulvic acids), and moderately reducible (bound to amorphous Ee oxides) fractions extractable by 0.05 M Ca(N03), 0.43 M CH3COOH, 0.1 M NH,OH-HCl (non-acidified), 0.1 M K/,03 (pH 11), and 0.1 M (NH4),C,04 (pH 3), respectively. The sequence of extractants was chosen according to recent studies on the selectivity of leachants toward dissolved phases of soils. 

Soil extracts are usually very complex. In water samples, humic and fulvic acids make analysis difficult, especially when polar substances are to be determined. Multidimensional chromatography can also make a significant contribution here to this type of analysis. 

Humic substances in sediments and soils have commonly been, defined as heteropolycondensates of decomposing plant and animal detritus 46. For lack of a better structural definition, these macromolecular substances have been divided into three categories fulvic acids and humic acid and humin. Fulvic acids and humic acids are soluble in dilute alkaline solutions, whereas humin is insoluble. 

Acidolysis is a similar weathering reaction to hydrolysis in that is used to weather minerals, but in this case the source of is not water but organic or inorganic acids. Humic and fulvic acids (discussed in Section 8.3.2), carbonic acid, nitric or sulfuric acid, and low-molecular-weight organic acids such as oxalic acid can all provide H to weather minerals. All of these acids occur naturally in soils in addition nitric and sulfuric acid can be added to soil by acid pollution. The organic acids are prevalent in the... 

Metabolites may also play a role in the association of the substrate with humic and fulvic acid components. Two illustrations are given (a) naphth-l-ol, an established fungal metabolite of naphthalene, may play a role in the association of naphthalene with humic material (Burgos et al. 1996) and (b) it has been shown that C-labeled metabolites of [9- C]-anthracene including 2-hydroxyanthracene-3-carboxylate and phthalate were not extractable from soil with acetone or dichloromethane, and required alkaline hydrolysis for their recovery (Richnow et al. 1998). 

Table 1 Range of Di.stribution of Oxygen-Containing Functional Groups in Humic and Fulvic Acids Isolated from Soils of Widely Different Climatic Zones (in mEq/lOO g)...

S. B. Pandeya, A. K. Singh, and P. Dhar, Influence of fulvic acid on transport of iron in soils and uptake by paddy seedlings. Plant Soil I98 17 (1998). 

B. S. Rauthan and M. Schnitzer, Effects of a. soil fulvic acid on the growth and nutrient content of cucumber (Cucumis sativus) plants. Plant Soil (53 491 (1981). 

ATPase and specific modification of root cell membrane permeability directly mediated by low-molecular-weight (<5000 Da) fulvic acid-like compounds deriving from native soil organic matter (54-56) (see also Chap. 5). 

Soils Trichoderma viride, extracts of soil humic fulvic acids stim d plant growth nodule mass dec d nodule no. 120... 

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

Another compartmental partitioning issue of major consequence for pesticides is the dissolved versus adsorbed fraction in an aqueous environment. Carter and Suffet (16) present measurements of binding of pesticides to dissolved fulvic acids that-will provide inputs to compartment models. Data from laboratory measurements used in compartment models can often bypass costly field experiments in the screening stage. Thomas, Spillner and Takahashi (1 7) have related the soil mobility of alachlor, butylate and metachlor to physicochemical properties of these compounds. 

---