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Title: Influence of Soil Solution Salinity on Molybdenum Adsorption by Soils

item Goldberg, Sabine

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2008
Publication Date: 1/1/2009
Citation: Goldberg, S.R. 2009. Influence of Soil Solution Salinity on Molybdenum Adsorption by Soils. Soil Science. 174(1):9-13.

Interpretive Summary: Molybdenum is a specifically adsorbing anion that can be detrimental to animals at elevated levels. Detrimental levels can occur from ingestion of forage plants grown on soils irrigated with waters containing high concentrations of molybdenum. A better understanding of the adsorption behavior of molybdenum is necessary. Adsorption of molybdenum by five soils was evaluated as a function of equilibrium solution molybdenum concentration, solution pH, and electrolyte concentration and predicted using a chemical model and easily measured soil chemical characteristics. Our results will benefit scientists who are developing models of molybdenum movement in arid zone soils. The results can be used to improve predictions of molybdenum behavior in soils and thus aid action and regulatory agencies in the management of soils and waters which contain elevated concentrations of molybdenum.

Technical Abstract: Molybdenum (Mo) adsorption on five arid-zone soils from California was investigated as a function of equilibrium solution Mo concentration (0-30 mg L-1), solution pH (4-8), and electrical conductivity (EC = 0.3 or 8 dS m-1). Molybdenum adsorption decreased with increasing pH. An adsorption maximum was found near pH 4. Molybdenum adsorption as a function of solution pH was independent of solution salinity from pH 4 to 8. Molybdenum adsorption for five soils as a function of solution Mo concentration conformed to the Langmuir adsorption isotherm equation. The Mo adsorption maxima obtained with the Langmuir equation for both ECs were not statistically significantly different at the 95% level of confidence, with the exception of one soil. The constant capacitance model, a surface complexation model, was able to describe Mo adsorption as a function of solution Mo concentration and solution pH. Molybdenum adsorption was predicted using the soil chemical properties: cation exchange capacity, organic carbon content, inorganic carbon content, and iron oxide content. Our results are advantageous, as they indicate that under agricultural conditions (pH 4-8), Mo adsorption can usually be described without consideration of changes in soil solution salinity.