Organic humic substances

Dissolved mineral matter in soil is largely present as ions. Prominent among the cations are Ca, Mg, K, Na, and usually very low levels of Fe, Mn, and Al. The last three cations may be present in partially hydrolized form, such as FeOH, or complexed by organic humic substance ligands. Anions that may be present are HCO3, COj, HSO, SO, Cl, and F. In addition to being bound to... 

In the removal of contaminating ions such as (PO or Fe " a precipitate such as Ca2(P0 2 Fe(OH)2, after oxidizing ferrous ion to ferric, is formed and the soHd is removed. The addition of surfactants is usually not essential (nor desirable) since most waters contain natural surfactants that would render the soflds sufficiently hydrophobic for flotation to occur. Such surfactants derive from the degradation of organic matter, and humic substances abundantly available in nature (30). 

Biogeochemical compartment. The biogeochemical compartment consists of the O, A, E, and B horizons of soils, in which substantial organic matter can be an integral component of the soil. The load of the water leaving the soil from the biogeochemical compartment consists mainly of soluble compounds because the matrix of the soil acts as a filter that retains particulate matter. In some cases, however, clay and particulate humic substances are also car-... 

A. Albuzio, and G. Ferrari. Modulation of the molecular size of humic substances by organic acids of the root exudates. Plant Soil 773 237 (1989). 

D. Vaughan and R. E. Malcolm, Influence of humic substances on growth and physiological processes. Soil Organic Matter and Biological Activity (D. Vaughan and... 

M. Schnitzer, Recent findings on the characterization of humic substances extracted from soils from widely differing climatic zones. Proceedings of Symposium on Soil Organic Matter Studies, Braun.schweig, RFG, 1977, pp. 117-131. 

J. Gerke, Aluminium and iron (III) species in the soil solution including organic complexes with citrate and humic substances. Z. Pflanzenemarhr. Bodenk. 160 421 (1997). 

Y. Chen, Organic matter reactions involving micronutrients in soils and their effect on plants. Humic Substances in Terrestrial Ecosystems (A. Piccolo, ed.), Elsevier Sciences B. V., Amsterdam, 1996, p. 507. 

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